Solar And The Power Company

I Just Found Out, I'm Mad as Hell...

It's March of 2022, and a bill is set to go before the governor that will potentially upend residential solar in the state.

But what are the arguments, and what are the facts?

The local power providers in the state contend that it's "unfair" for solar customers to pay "less" than their non-solar neighbors for power.  It is said that residential solar generators are being "subsidized" by non-solar customers.  They also contend that they're not getting enough income from solar customers to offset upkeep costs.

Is it true?  Let us consider some numbers.

Based on Actual Data

I took an hourly data report from my Sense for the period of May 17 to June 16, of the year 2021, which recorded both solar production and overall energy usage.  From this I could calculate how much we sold back to our provider, and how much we would have purchased without solar.  

If anyone is interested, I can rerun this experiment with a whole year of data.  I picked this particular period somewhat at random: it had good solar production and represented a warm-to-hot time of year.  This production period is near the top - most elsewhere in the year, we will produce less energy from our system.  Anyone who complains that I cherry-picked data will receive nearly a year's worth of raw HOURLY data in reply.

At the end of the period, we had generated 3,265 kWh.  We used overall 2,392 kWh, leaving us with an energy credit of about 872 kWh.  Now, power isn't grain - unless you have huge batteries, you can't store it for long.  So what happened to all this extra power?

It Was RESOLD...

This power didn't just disappear...  Our provider resold it.  How they resold it, to whom they resold it, we do not know.  But they buy power from other providers, and they sell power to other providers, and of course they sell to us customers.  Solar customers, according to one report, represent 1% of that customer-base.

The power my system generated went to "the grid."  What does this mean?  Well, it went up and down the same power lines feeding all my neighbors, to put not too fine a point on it.  There is no way that I know of to differentiate power we generate from power the provider generates, if looking at someone else's meter box.  This is why we monitor usage at the residence, not at the provider or the substation.  Once power gets onto those two or three skinny pole-suspended wires, all trace of who produced it is lost.

So let's say there's one other neighbor on the immediate line that feeds my transformer.  They don't have solar.  Our provider is charging them at standard rates - the same rates they charge me when the sun doesn't shine or we don't generate enough to cover our usage.

Now, I'm going to simplify numbers here.  Our provider has tiered billing, but let's just consider usage costs up to 1000 kWh, which boils down to 13.266 cents per kWh of energy, fuel, and assets.

If our neighbor benefited from our solar generation, so did our provider, to the tune of at least $115 for the period in question.  That would've been our provider's income for the 872 kWh we supplied over our usage.  Our provider would have "sold" it to our neighbor, assuming our neighbor used it all (and they very likely did), and our provider charged them accordingly.  That's just income, not profit.  So what was our provider's costs?

What Does It COST?

We don't know what it costs to run a power company, but we can take a guess based on the changes presented in the legislation.  

Under the guise of making power bills more "equitable", the legislation reduces the value of kWh's supplied to power companies from 1-kWh-credit per kWh-generated down to 1/2 kWh-credit per kWh generated -- 50% of what is produced.  This means that if I generate 872 kWh over for the month, my provider will be able to say that I only produced 436 kWh for them.  They'll still get to sell 872 kWh, and charge others for 872 kWh, neither of which they produced.  I am, at worst, renting their power lines and maybe a few small transformers.

I, on the other hand, will be at a loss in both the short and long term: the energy credit I would be carrying into the darker months of the year won't be there, and my winter bills will skyrocket because I won't be "generating" enough power - by this bookkeeping - to offset my usage.  In my spreadsheet, for that period of May to June I wouldn't have "produced" enough power to even avoid "using" grid power, let alone carry a balance into next month.  Whereas I would have had 872 kWh of credit, I would have owed 171 kWh to my provider, with nothing banked for the next or any future month!

This is what we affectionately call "getting shafted."

It should be noted that after almost a year of production (my system came online in February), I was in the "negative" by the end of December - I had used up all my credits and had to pay a rather ugly power bill for my usage overages.

So, how much does our provider profit?  If they are willing to reduce the value of our production by upwards of 50%, then they must be able to produce power or buy power for around that rate.  This would mean they are charging a 100% markup on power sold (i.e. they buy for $0.05, and sell it for $0.10 - these are not actual values, just examples to be clear what I mean by the markup).

If they produced and sold 872 kWh of power (for $115), it should cost them around $57.  That gives them a $57 profit.  But they're not spending $57 in fuel, generation equipment and whatnot, when they get power from me.  My power might not even be making out to most of the equipment that they are otherwise using to transfer power from place to place.  It might be getting used by my numerous neighbors (not just the one in this example), and never touching any of the equipment located miles away.

My provider is already $57 better-off thanks to my generation.  If it actually costs them less to produce or buy power, then they are even better-off than that.  Why exactly do they deserve or need more?

Shafting the Future

Given that I had used up all my credits before the end of the year, and expect to do so again this year, I would expect that a system generating (or receiving credit for) only 50% as much power would have substantially higher power bills.  This doesn't benefit my pocketbook, to be sure, and might drive me to invest in batteries.  

I would even want to take it a step further and not even provide power back to the grid, if I could.  After all, why should they profit so pointedly at my expense?  They aren't paying for my panels, they didn't help with the install, they wouldn't be paying for battery installation and upkeep, they would basically just be getting super-cheap power and I wouldn't be able to negotiate a goddamn thing.

Free-Market Power

If we want a free market for power, we cannot live under the guidance of utilities.  They have a profit motive, as any good and successful business does.  But they have no competition - except from small-time residential solar providers.  A surefire way to dissuade people from "going solar" is to take their power and give them little-if-anything in return.

Here's a little-known fact: according to my provider's own "how to go solar" page, you can't build a system that generates more than you use on average.  I use a lot of power, so I was allowed a large system.  But most people don't, and so most people won't, even if they have the roof-space for it.  That lost real-estate in solar-generating-potential will now cost them even more.  

Do we assume our energy needs will stay the same or diminish over time?  Every time I plug in my car, I consume between 5 and 15 kWh of power.  Do that every day for a month, and suddenly my usage is through the roof.  With more people buying electric cars, using electric gizmos, and sucking power like there is no tomorrow, usage isn't going to go down.

Still, here we are with utility companies talking "equity."  Equity for whom?  Wouldn't it be more equitable to charge my neighbors less?  After all, why should they pay for fuel that the utility didn't consume?  Or maybe I should be receiving some of the profits as an incentive to keep my grid-tied system tied to the grid!  Where is my profit in all of this?  "Good Feels for the Planet" doesn't put food on the table.  But money back to customers makes cheap power available to the lowest-income groups and helps them more than charging local energy-producers over-and-above.

An Allegory

Can you imagine a gas station charging more for a fuel-efficient vehicle to fill there?  

If you drive up with a beastly, gas-guzzling and aging SUV, you pay $3 per gallon.  But if you arrive with a brand-new Toyota hybrid, the gas station charges you $6 per gallon.  

Why?  

Because your vehicle uses less fuel, which means you normally won't buy as much gasoline as the SUV, and it's not equitable to make the SUV pay more than you even though you paid a lot more money for that advanced fuel-efficient technology.  Plus, the gas station has to be able to do upkeep on their pumps, pay their attendants, and maybe occasionally paint the place.  Your more efficient vehicle, they say, costs everyone, and therefore you should pay for it.

How in the every-loving-**** does this make sense?

In Summary

To summarize: We analyzed collected data from an actual month of energy usage and solar production.  At the end of that period, we had - by original design - a surplus of 872 kWh of solar credits, to be used in the darker months of the year or whenever the sun doesn't shine.  

The legislation will eventually reduce this to 50%.  Our surplus is obliterated, and we end up owing 171 kWh to our energy provider for the month in question.  Other months, I predict based on observations, will be far worse.

Our provider profits from our 872 kWh of produced power, by reselling it to my neighbors.  They sold our generated power for $115, without incurring the estimated $57 of generation and fuel costs.  What's more, the tier structure means that if my 872 kWh reduced my neighbor's usage from above the 1000 kWh limit to below the 1000 kWh limit, my neighbors were then overcharged for fuel and energy that wasn't produced by the provider (since the provider makes no distinction on where my neighbors get their power).

As for infrastructure, power lines do not get "used up" like light bulbs, so the lines that supply their houses and mine are not likely to degrade significantly even if left hanging for 30 years.  After all, when was the last time your utility replaced YOUR power lines?  The upkeep here is minimal.

Other infrastructure does require upkeep (substations, transformers, and whatnot), and for that surely a base cost applied to everyone still applies.  There I think we can all agree, and it shouldn't matter if we're consuming the power or providing it.  Cables don't care which way the power runs.

Solar Panels and Heat

 Does Heat Impact Panel Production?

A friend asked me this question.  I felt compelled, as a result, to expound upon it here!

The short answer is: yes it does.  The more important questions:

• By how much?
• Are more efficient panels worth it?

A Tale of Two Panels

As I was doing my research, I wanted to know between the two candidates just how their panels would perform over the hypothetical long-run.  Actual production is affected by many factors:

• Overall panel efficiency
• Heat losses
• Age losses
• Soiling 
• Obstructions

Let's talk briefly about these.

Overall Panel Efficiency

The panels convert solar energy into electrical energy, but not at a 1-to-1 rate.  The photons striking the panel have to interact with electrically-complex junctions, and not all wavelengths are used evenly.  Beyond being a way to compare two panels for scientific purposes, this number is - to the consumer - little more than a curiosity.  

Most panels operate around 19% efficiency.  Some panels tout a 20% or 21% efficiency.  What does this mean to you, dear buyer?  Smaller panels, usually with a larger price tag.  A bigger 19% panel will generate just as much power as a smaller 21% panel.  Unless you're a solar farm and installing a cool million of them, those two percentage points probably won't be worth much.

Do we want more efficient panels?  Yeah, someday, when they're maybe closer to 40% or more, but only so long as they are still affordable.

Heat Losses

Panels lose efficiency as they get hot.  Conversely, they perform better as they get colder.  All panels are tested at a standard reference temperature - usually 25 C (77 F).  Most roofs during the day get hot, and that heat will belong to your panels after they're installed.  Some panels will advertise better resiliency against heat (lower losses).  Are they worth the superior price?

Age Losses

Panels also degrade over time.  This should be a no-brainer (Kansas nods slowly).  But the rate is usually guaranteed not to exceed some amount of loss over some amount of time.  A common standard is around 15% over 20 years.  The loss rate is usually given as a percentage of degradation per year, something like 0.8% per year.

Soiling and Obstructions

These two have no representation on the spec sheets, because the panels can't control where they're installed.  However, for the purposes of generating power effectively, these two factors must be borne in mind.  Panels need occasional cleaning (I'm told maybe once a year).  Obstructions, such as trees, clouds, and adjacent buildings, will affect their performance.

Evaluating

The last two losses - soiling and obstructions - we'll take as constants because no matter what panels we put on the roof, they're all going to be suffering the same fate.  In other words, there is nothing for us to calculate there.  We'll assume that all panels receive awesome, direct light, and focus on heat and age.

I punched in all the data from the data sheets, if for no other reason to see them side-by-side.  Data sheets, by their nature, do not make such a comparison otherwise easy.

The question under consideration, in my case, was "how does the SunSpark configuration compare to the REC configuration?"  We could argue fine points all day long, things like max power, overall efficiency, and annual degradation (which the REC panels all technically "won" on).  But our goal is to produce power over the long-run, and to do so affordably.

Considering Heat Losses

We're given that the SunSparks lose slightly more power (Temperature Coefficient of Pmax) for each degree C than the RECs.  How does this look for daily, monthly, and yearly production?  I present a somewhat unrealistic calculation below, since over the course of the year production varies with the sun's position and duration in the daytime sky.  I also hold constant the temperature through the "day", the "month", and the "year".

Is this a legitimate way to compare?  Well, panel temperatures are probably going to vary the same - or so we'll tell ourselves - no matter what panel we put up there.  Some might even be hotter from being placed directly on the roof shingles, but we'll assume the mounting is essentially identical.  So we can scratch hourly variation off the list.

If a panel is constructed in such a way as to not be as badly affected by the heat, that should be represented by the coefficient - and so there it is.

Second, panels are going to receive the same amount of incoming light no matter what panel is in place. The sun is the sun, clouds are clouds, and a panel can't make power out of nothing.  Even the most "efficient" panel won't convert darkness into power.  It'll just produce more in any light than a less efficient panel would.  For sake of comparison then, it seems fair to keep the incoming sun and the overall module temperature the same.

We see int he above that at evaluation temperature (25 C), our yearly production would provide 43,006 and 36,385 kWh for SunSpark and REC respectively.  Bear in mind there are two different panel populations, with two different costs and overall production targets.  But both arrays are intended to deliver 100% power replacement for my needs.

At 45 C (113 F), panel efficiency is predicted to drop by the given rates.  REC has better rates, slightly, but you can be sure a salesman will make sure you know it!  Our yearly production totals?  40,597 and 34,638 kWh, respectively.  SunSpark lost roughly 2400 kWh and REC lost 1740 kWh.

Considering Age Losses

The 5 year age loss estimate is listed in the table above, but for sake of reference here is the complete table:

At the toasty-hot temperature of 60 C (140 F), the arrays might produce 38,791 and 33,328 kWh for the year, respectively.  Our losses on the SunSpark are greater, but we're still producing quite a lot.  What's more, it hasn't dipped below the RECs, and of course it shouldn't given the specs.  But the aging effects are more considerable.

The SunSparks are expected to lose 0.8% per year, whereas the RECs should only lose 0.25% per year.  That will definitely be in the advertising slick.  But over twenty years, what are the results?  At the temperature we just considered (60 C), this comes to 32,585 and 31,662 kWh expected production for the year, SunSpark and REC respectively.

The Cost of Production

Ultimately, the question we find ourselves asking is: "Is it worth it?"  Over the course of twenty years, the slightly more-expensive array - at first glance - will still be out-producing the smaller, less-expensive array.

There are few things we could do here.  We could up-size the smaller array, albeit at a much more expensive price-point (a 22.4 kWh REC system, which is how large the SunSpark array is spec'd to be, would have cost around $69,753.60).  We could down-size the larger array (down to around $54,256.80 in case you're interested - remember these are rough estimates though).  We could even split the difference.

However, one thing to bear in mind is that panels that produce more watts are also usually larger.  Even with the slightly higher "efficiency," a 370 watt panel is going to be heftier than a 320 watt panel, which means potentially fewer panels on your roof.  Whether this is good or bad depends on your goals.  If you want to squeeze as much power as you can get out of your available space, larger panels might compromise that desire by being too large to fully utilize the available space - think having only a single row instead of a double row, or losing a few huge panels because of vent stacks, chimneys, roof joints, etc.

Another way to look at it is: are the cheaper panels a worse deal?  I think that is an easier to answer question, and the answer here is that they're not.  Yes, there are more of them.  Yes, they will degrade faster over time.  But they are not unreasonably priced and thanks to the larger overall system size, the long-term degradation is somewhat nullified.  That is to say, my overall needs will still be met, ideally, twenty years down the road.  Our goal is then to make sure we've received a good return on our investment, so as long as the system covers our power needs for the foreseeable future, that return will be solid.

Conclusion

This is obviously not a "you should buy this" article, and it wasn't meant to be.  It was only meant to explore and demonstrate some of the complexities when evaluating prospective panels and arrays, and to understand a few of the gimmicks that are used and based off of honey-colored statistics.  Overall, the simplest comparison for the price-focused consumer is simply the cost-per-watt, which is simple and direct to calculate.  If nothing else, hopefully the above shows that a panel can tout absolute awesomeness over the competition, and yes in the end it might not really amount to much.  

Maybe you're aesthetic-focused and can't bear the thought of panels on the front of your house: larger panels in the back might be superior for you.  Maybe a crazy roof is not conducing to large panels, and you need a more flexible layout.  Maybe you are driven primarily by price-point.  Maybe you want to check every efficiency box you can.  Those factors are going to drive your decisions more than the spec slicks probably will.

My First Solar Install - Notes and Experiences (Part 5)

The Ongoing Solar Install Journal 

This post is an update on how the system has been performing.

The Addition of Sense

Part of the way into March, I was talking with my solar company salesman and he mentioned whole-house power monitoring that included solar production - namely, Sense.  Since I'd been looking for a solution (and my desire to build one did not match up with my available time), I went for it.  About $400 later, we had whole-house power monitoring...again.  We used to, with the TED-5000, but it had died a few years ago after a very long and good run of monitoring.

Intense Tracking

Overall, I like it very much.  I prefer to warehouse my own data, which is the only detracting attribute of Sense: it requires a constant uplink and stores nothing locally.  Everything you do with your Sense, you tend to have to do via the webapp or the phone app.  The phone app is, however, very useful.

Aside from totals, it uses machine learning to identify device patterns and can detect when individual devices turn on and off.  With that info, it can tell you how much power a particular device uses over time.  It takes time to get a decent bunch of them found, but all in all it's pretty neat and quite functional.  But since this isn't a sales pitch for Sense (and they sure aren't paying me to talk about it), let's just focus on the graph above.  That's May's recorded usage, and for the most part (i.e. minus a couple hours one day when my firewall lost power before I woke up), it is a complete summary of our use (blue bars, green plug icon) and our daily generation (orange bars, sun icon).  

You can probably ignore the dollar figures - I do... it's based on a flat rate, so I punched in $0.12, which is in the neighborhood but doesn't account for the usage tiers my provider has.

May was, as you can probably tell, a good month.

Generated Credits

We have, so far, not had to pay for a single kWh since the February billing cycle.  We're already up to nearly a month's worth of kWh credits, or around 2,200.

I have been able to fill in a couple of months-worth of bills now, and here are the results:

Thanks to the detail that Sense captures, I can calculate what we would've paid if we hadn't had solar.  Basically, for May we saved around $80.  Once the system is paid off, that will look more like a $350 savings.

System Performance

So far the system is performing beyond expectations.  Lately the generation has been a little more spotty due to daily cloud-cover and thunderstorms, but even with those our worst day in the last seven was 52 kWh, our best 105 kWh, and the 7 and 14 day moving averages (as of today) were 81.8 and 95.7 (respectively).  The 14 day moving average for last week was around 105 kWh, and at the end of May it was 116 kWh.

I have a chart that tracks all of these figures, which of course I hand-enter daily from my inverters:

It's important to note that as long as we're generating more than we're using overall, we're in good shape.  A few bad days here and there does not break the bank, and right now we're continuing to increase our credits.

Our expected and actual power generation is tracked on the Sunny Portal (SMA's PV management site):

Note that for June, the month that we're in, obviously we're still in it and so the total yield bar is justifiably below the expectation.  Also note that January we were technically not online, and February we were turned on part-way through the month.

Comments, Considerations

The guy who came out to rebury our CATV cable had also used my solar provider, even the same salesman.  We had a good laugh and compared notes.  He managed to get his system installed during the 30% tax rebate days.

Overall, I am extremely happy and pleased with the system.  It is operating beyond my expectations and is now at the point of operating basically autonomously.  I only baby-sit it still because I'm neurotic like that.

Batteries

Would I invest in batteries?  At this time, no.  My situation unfortunately (or fortunately, given the cost of batteries) does not lend itself to such an investment.  For what it's worth, the power company is my "battery" and since I'm feeding in more to the grid than I'm using per day (most days), I really have no qualms about not running my own battery bank at the moment.

I would consider investing in them if the prices dropped dramatically, or an alternative energy storage solution (alternative to typical batteries) became readily available.  I've read about one that uses pumps and a special liquid, but the tech isn't really ready for production yet.  That said, the only time batteries would benefit me here is during a major outage.  So, let's hope we don't have one of those...

The Panels

Do I like my entire roof covered in panels?  Why yes, yes I do.  To be perfectly honest, I've never been a stickler for aesthetics, though I have developed a more critical eye in my older years.  That said, I want power...lots of power, and so I put as many panels up there as I legally could.  Given how much power we are able to produce, and the fact that we've zeroed our bill the last few months, I have no regrets.  And as long as we continue to zero our bill through to the end of the year, I will continue to have no regrets.

The Electric Car

I've had a few people now ask about our solar.  They also get excited when they see my little Focus Electric charging in the driveway.  "Oh man, and you charge this with your solar, don't you?" they ask.  No...not really.  Sorry.

The car doesn't care where it gets its power from, and my charger unit (an OpenEVSE box), runs off the mains.  The grid-tie doesn't give me the option to run separately, though I think SMA might offer some solutions to that effect.  That said, given the credit system with my energy provider, why bother?  Currently I don't drive it much, so it doesn't draw any more than what is necessary to keep the battery topped and cooled during hot days.  When I was driving it daily, I'd chew through the 22 kWh battery almost completely.  That said, it was probably more like 18 kWh, since you can't run it to zero.

18 kWh per day off our current generation totals would probably hurt a bit, but it looks like what we're generating would more than cover it.  Even if it didn't, even if we were breaking even with our usage and generation, and the car us over by 360 kWh onto the bill, that'd be only like $50 a month.  Still way cheaper than gas for doing 50 miles a day for 20 work days.

Other Solar Tech

One of the other companies I was looking into called me and wanted to know if they could close my file.  I'd already let the guy down once, but I guess he was a glutton for punishment.  And once again I filled him in on what I bought.  He let out a most annoying groan when I told him I'd gone with string inverters (his company does optimizers).

Now, here's the thing.  I've read the sales and specs sheets myself, I've studied the tech, and I've read what is apparently the only available research out there that bothered to compare these types of systems.  Obviously, the industry in general - and the solar research institutes in particular - need to do better here.  But given what I learned, and my specific situation of full sun all day long (barring clouds), I had and still have no reason to believe that optimizers or microinverters would win me much benefit.

For kicks I tried to figure out a way to perform a comparative calculation between the two proposed systems (the one I chose, and the one I didn't).  I decided that the two most sensible numbers to use were the system design watts, and the total expected production in kW.

Dividing total expected production by system design, we end up with two almost-dimensionless figures: 1.388 and 1.407 expected kW per design watt, chosen and not-chosen systems respectively.  What this basically says is that these two systems are nearly identical.  Over the course of a year, I should get almost the same kW per unit design watt.  In other words, the optimizers would have to do something very special to provide me additional benefit.

My system is the lower of the two numbers (1.388), and yet because we could afford more panels, we wound up with a better overall value.  We should generate around 4000 kW additional power over the course of the year, or about 1.6 months-worth.

Now, the problem with the above calculation is that I really don't know how well one can expected optimizers to...well...optimize panel output.  So many of the major worries that are thrown at prospective customers - such as "a single bad panel will take out a whole string" - are passe.  The better panels have bypass diodes, so that isn't a problem.  A weaker panel might slow things down a little, but the underlying question is: how much loss do you have to incur to make the optimizers worth it?

I won't go into a bunch of "what if's" here, if only to keep this readable and on-topic.  What I can say is that this is where we need more research, and unfortunately the only research I was able to find, when I made my decision, basically strongly supported the string inverter technology.  SMA also recently started advertising shade-fix boxes for individual panels, which are meant to act almost like optimizers but can be used on a panel-by-panel basis (instead of having to attach them to every panel in your array).  Do they work?  Are they worth the money?  I really can't say.

What I can say is that given the overall costs of the two candidate systems, and the expected outputs and performance to-date, I have no regrets with choosing the technology that we did.

Moving Forward

I'll update this blog again once a few more months have passed.  At this point, anyone following this should expect business to proceed as usual: the panels will keep generating power, my bill will remain practically zero, my electric car will be sitting in the driveway doing nothing much of anything.

Daydreaming

If I were to be in a position to build my own community, I would definitely do this:

• Put solar on every house and centralize the upkeep of them all - basically give the people living there nothing much to do other than enjoy the benefits.
• Work with the local energy provider to set up a local-to-the-community battery substation, sort of like what was done in Australia (though theirs was, like, state-sized).

The key benefits I'd be looking to extract from the above would be:

1. With solar on every roof, the community generation should be utterly fantastic - far more than what the community as a whole would or could use.
2. With a battery substation, we'd be in a position to offer community-wide power during outages, for as long as the batteries could hold out.
3. The battery substation could also be useful during brownouts or whenever the main energy provider needs a bit of a break on the grid, or to supplement the provider during the evenings/nights.

Of course, to achieve the above, you'd need the community to pay into it, either via HOA fees (egad, I hate HOAs), or as a community "power bill."  Without running the numbers on upkeep costs (mainly for the batteries), I couldn't say what that number would be.  But as soon as the solar was paid off, the batteries and other infrastructure would be all you'd be on the hook for - aside from the occasional re-roof job or when panels start to wear out.

My First Solar Install - Notes and Experiences (Part 4)

 ACTIVATED!

Our provider finished their musings and, much sooner than expected, an engineer showed up to swap out the uni-directional meter with a bi-directional meter.

The system was officially turned on with our meter change, which occurred three days into our last billing cycle.  This was fortuitous, since it meant we'd get most of that bill on solar.

So, was it worth it?

Real Time Use

I found a Python library that can talk to the SMA SunnyBoy inverters.  One of the downsides of a string inverter is that you don't get per-panel statistics.  But, the flip-side is that it's that fewer electrical components to deal with, which helps with cost.  We're in full-sun, with no trees nearby (except when the sun gets very low), so by and large there is no need for the extra components.  One could argue having the additional data is useful, and sure that could be a thing.  That said, is it worth $40-$60 per panel?  That's another conversation.

Anyway, the Python library, after a minor modification, gave me the data that I wanted.  After a little Curses play (console text magic, for those who don't know), I have the following little "dashboard" that updates once a second:

Obviously, I am a little obsessive about data breakdowns and aggregations.  The above values should be easily understandable: mostly watt values listed per-string, then per-side, and finally in total (that is, what we're sending to the grid if we don't use it all).  Given the theoretical panel max values, and the inverter limits, and I'm able to calculate how well we're producing.  The above image was captured just before I started typing this, and represents a rather sunny moment in March.  Today is partly cloudy, however, and moments earlier I captured this:

Cloudy versus Cloudless Comparison

On cloudless days, the total output graph of the system looks like this - at least for these shorter pre-summer days:

Partly-cloudy looks more like this:

These graphs were pulled from the SunnyPortal site, which aggregates all our data and provides centralized monitoring and reporting to both us and the installer (and, of course, SMA).  So, the graphs show the total of all three inverters for the days shown.

The sunny day was a 111 kWh day, while the partly-cloudy day rang in at 87 kWh.  Both are still more than we're consuming, but it should be noted that we're also making an effort to cut power usage where possible.  The solar isn't going to save us money if we crank the air down to 60 degrees and leave all the lights on.  Part of that power-savings came in the form of combining three different fish tanks into one system, so that only a single tank heater was necessary.  Ultimately, our goal is to zero out the power bill in the long run, and anything we pull above that is just gravy on top.

The First Bill, In Review

Our first on-solar billing statement finally closed, we are now able to assess just how well the system is doing.  Of course, bear in mind that there are many variables that will play into future performance and cost efficiency, but we're ready to track the data that is available.  Our last few bills, and our latest, are summarized here:

That $39.64 is our most recent bill, and as can be seen from the Used and Generated column, we did pretty good for missing the first three days of the cycle.  We've been averaging about 100 kWh per day of production, so if we'd been able to capture those three days, our overall bill might very well have been zero or negative kWh (which doesn't obviate the flat usage fee, but I'll take whatever I can get).

The expectation is that future bills will see the Credits column light up, and over the summer months a nice balance build there that we'll be able to feed off of as the winter months reduce our yields.

Tracking the daily inverter yields is also an activity, for the moment:

Most of the numbers on this chart are in kWh.  The provider bills based on whole kWhs, so the "month total-to-date" is configured thus.  The "Moving Average" column takes the last 7 days production totals into consideration.  I might add a 14-day moving average column as well, to give us a more stable estimate on expected yields.

Equipment Operation Review

By and large, the system has been self-sufficient.  There were some issues initially, some caused by my tendency to tinker and set things up in a "non-standard" way (such as putting the inverters on their own VLAN and then forgetting to give that VLAN internet access).  After those were ironed out, about the only thing that has cropped up has been intermittent loss of string on daily start-up.  Since the installer came back to finish the necessary setup steps, that has only happened one time.  I'm keeping a log regardless.  The issue isn't with the inverters, but with the Sunspec rapid-shutdown devices (TS4s) attached to all the panels.  These are minimalist devices that are designed to respond to data-over-power-line commands and allow energy to flow only when the inverter says it's safe to do so.

The trouble is, some were getting confused and not activating.  Like I said, this appears to be a very intermittent issue, but one right now worth tracking, as the loss of a single string would noticeably impact yields.  This might be taken as an argument for optimizers or micro-inverters, but remember that optimizers still have to aggregate and send their power to a central inverter.  Micro-inverters would be the only things unaffected, but would be significantly more complex and expensive.  Ultimately, the TS4s shouldn't be doing that anyway, so if there is an ongoing problem, it will be tracked and addressed.

Another option might be, in the future, replacing the TS4s with more advanced modules.  There are modules that would allow the array to be used as a grid-detached independent power source, which would be very useful during a major outage.  It would mean running extension cords, since in this mode the inverter does not feed the main panel, but instead feeds an outlet attached to the inverter itself.  However, between that and having no power at all, it's basically an instant-win.

At that point, will the system be much different from an optimizer system?  I think the answer is still: yes.  The TS4s only control flow of power, they do not otherwise interact with it.  In that way, there are no efficiencies or losses to be considered - optimizers do DC-to-DC power conversion at the panel, and some power is lost in doing so.  The TS4s are supposedly glorified relays, so losses should be minimized and, in theory, far below the optimizer losses.  Note that this is conjecture, though, and my working knowledge of these devices is relatively limited.  The TS4s do require some power to operate, but I do not know their actual watt consumption.  I'd hope they'd be minimal.  

By comparison, it is not uncommon for optimizers to report 97%-99% efficiencies.  One SolarEdge optimizer touts a "maximum" 99.5% efficiency - but what are their minimum and typical efficiencies?  To take the best case, however, for a 330W panel, you are guaranteed to lose 1.65W.  Across 68 panels (my array), that's 112 W if the panels are operating at their maximum.  Yes, that's still an aggregated 0.5% loss of overall yield, which doesn't seem like much; I guess the question then is would they provide additional power that I would not otherwise get, given my situation?  If not, then I'm at a total loss in both power and money.  For semi-shaded scenarios, this might play out different.  What little research that is available on the subject seems to point to the reality that with an unshaded reference array, optimizers do not help with yield.  This particular subject seems fertile for further study.

To really assess the impacts of optimizers, we would need to understand what their actual raw power requirements are, at which point we could plot them against a range of panel production values.  For instance, I have yet to see my panels max-out, but 80% production is pretty common.  If the optimizer requires a constant feed of, say, 2W to operate, taking that away from 100W per panel hurts a lot more than from 270W per panel.  We'd also need to do the same for the TS4s, for fairness.

Monitoring

Generally, monitoring has been extremely easy.  I did the Python program for fun, but the inverters have nice web interfaces, which include a "smart screen" display that gives you the current status without having to log in:

This is especially handy for pulling the daily totals down.  I took the liberty of renaming the devices according to their positions on the outside wall.  

In the long-term, I'd like to get a Modbus-enabled recording app running, and to record more details from my inverters into a central database.  I'd also like to build a little Angular front-end that will basically provide the same details as my Python console app, but in a much more visually-pleasing and network-accessible way.

More to come as we track how the system performs in the coming months!

My First Solar Install - Notes and Experiences (Part 2)

During our serious investigations and talks with potential contractors, we were introduced to PVWatts (as mentioned in my last post).  With the rough estimate, I worked out probably yearly and monthly production numbers based on the PVWatts simulation.  Now, I have a more complete and near-final layout in hand.  Time to plug in the numbers!

The Layout

Certain building codes require set-backs.  I didn't know about those when I was first playing with the idea.  You evidently also cannot saw the vent pipes shorter (not that I really expected that to be allowable).

We had to sign off on the splits in the arrays, otherwise all the panels (at least on the east face) would be together.  The split was caused by a vent pipe in an inconvenient spot.  I don't care much about aesthetics, personally - I'd rather have MORE PANELS!

Simulation Configuration

The orientations of each roof is given in red, in degrees.  The 4/12 pitch comes to about 18.4 degrees.  Surprisingly, an extra panel was able to be added to the south-facing roof.

The configuration I used for each roof in PVWatts was:

• DC System Size: 320W * number of panels / 1000 (kW)
• Module Type: Premium
• Array Type: Fixed (roof mount)
• System Losses: 14.08% (default)
• Tilt: 18.4
• Azimuth: azimuth of each roof

Numerical Results

I didn't bother with PVWatt's power cost estimates, since my utility is...a little complicated.  That said, here are the results:

This should provide about 2,600 kWh per month (average) production, 200 kWh more than my original target.  Good thing, since certain people in my household have recently taken to extra-long, extra-hot showers.

Column details:

• AC System Output (kWh): The amount of power the solar system should generate for each month.
• Expected kWh Usage: Based on my 2020 usage, with the last three months extrapolated.
• Production Over/Under: Positive numbers indicate we produced more power than we consumed.
• Credits: If we produced more than we consumed, the provider will roll our overage.
• Energy after Solar: The amount of energy we didn't cover with solar (which is the negative of our Production Over/Under, not ironically).
• Credits Accumulated: Since our provider rolls credits month-to-month, this is the "current balance" for the given month.  Cannot go below zero.
• Energy after Credits: The amount of power not covered by both solar and credits.
• Energy Costs: Cost of our energy usage after everything has been accounted for.
• Costs without Solar: What it would cost us for the power used, without solar input.

Note that the costs are at my provider's current rate schedule, and are not extrapolated beyond the anticipated inputs.  Also, for simplicity this considers a constant rate schedule, whereas my provider tends to change their rates several times during the year.

Whereas most companies will estimate how many hundreds of thousands of dollars you'll save in the future, this table tries to estimate what we might have saved or spent for just the power we used in 2020, with the system as designed.  With energy rates expected to increase at around 4% per year for our provider (YMMV), the "savings" as it were should only go up.

This table does not show how much the system will cost on a monthly basis (we're anticipating around $250/month), so the final Savings number is slightly misleading.  But, if we saved $3,806 on actual energy costs for the year, and spent $3,000 on the loan, we'd be $806 ahead.  That's over three months of payments we could make to pay down the loan quicker (or about 100 sub sandwiches a year from our favorite sandwich shop - my preferred way to calculate money saved and spent).

Heat Losses and Discussion

I had to do a little digging, but PVWatts actually considers performance degradation due to heat.  This is encoded in the Module Type parameter.  Their loss number was a little nicer than my actual panel specs:

• PVWatts power loss due to heat: -0.35% per C
• My panel's power loss due to heat: -0.37% per C

But, with such a small percent, we are not talking a considerable amount.  After all, at +30C operating temperature, we're talking a difference between 10.5% losses and 11.1% (0.6% off).  Just roughly, that amounts to 1 kWh less production for the year, if I did the math right.  Bear in mind that a lot of marketing for panels, inverters, etc, will tout efficiency improvements around 1-2%.  At the end of the day, what matters is how much power it produces, and whether or not that power is worth the cost of those percentage points.

So, let's call that "margin of error," especially since this tool is also using historical weather data from a location at least an hour away to drive its simulation.

If things go according to plan, we should see an insufficient production for the first two months, but then zero energy costs (aside from the monthly fee) through to the end of the year.  If we're able to run the house at a lower consumption rate, that will just mean a better buyback at the end of the year.  If panel performance isn't as good as we expect, we'll (at worse, hopefully) be paying upwards of $300 for energy for the year.  That amount is based on double the system losses due to heat (which I added in before realizing PVWatts already accounted for it).

Guess we'll see how it goes!

My First Solar Install - Notes and Experiences (Part 1)

We just signed up for a solar install.

O.M.G.

One horrifying power bill after another, and the looming lowering of the Solar Energy Tax Credit, and it was time to do something drastic.

Some Basics You Need To Know

Cost per Watt

It's common to compare systems in terms of cost per watt.  That's the total cost you pay for the materials and install, divided by the watts your system is rated for.  If you put 30 panels on your roof, and each panel produces 290 watts (max output), that's a 8,700 watt system (30 panels * 290 w/panel).

If that system costs you $28,275 out of pocket (i.e. before incentives, rebates, or tax credits), then your system cost you $28,275 / 8,700, or $3.25 per watt.  Using this, you can create a rough comparison of vendors and their offerings.  There are finer details to consider, but if you have two vendors offering roughly the same products, and you want the lower price (often, but not always, a good choice), you can reduce them to price per watts and go from there.

Propaganda - I mean, Sales Pitches...

Here are some things you'll hear and read:

• Over 30 years, you'll pay X dollars in utility power, and it's only getting more expensive.
• These panels offer the highest efficiency/wattage on the market.
• These inverters/optimizers are 99% efficient.
• Solar payments will be lower than your existing power bill.
• Warranties!!!!

First, yes, power is getting more expensive every year.  They usually also tell you how much you'll save by going solar.  This is a gimme.  The numbers are legit, but let's be real, this is an argument to go solar, not to go with a particular company.

The second is not untrue, but higher efficiency and higher wattage panels usually come at higher cost.  They will take up less room on your roof for the same kWs, by the numbers.  That's great if you don't have a lot of space, or have high-enough needs that you need to squeeze every watt you can out of every square-foot of roof.  But will you see a return on that investment?  For example, a 21kW system will require 65 panels at 325W per panel, and 55 panels at 385W.  At $209 and $319 (prices of a couple of comparable panels I pulled from a solar component reseller), this yields $13,585 and $17,545, respectively, for the same total kW of generation.  You need to crunch the numbers and not get blown away a mere data-point.  

The third is another data-point, and this one makes me mad because it's misleading when presented the way it is.  Optimizers and inverters condition or change the power (respectively), and to do this, they need electronics.  No electronics are 100% efficient.  So, touting this is just a comparison between one brand of optimizer with another, or one brand of microinverter with another.  For our calculations, the efficiency they report translates to how much power you're going to lose to your optimizer/inverter.  They consume power to operate.

Fourth, generally another gimme, but be careful.  Companies often show up and look at your bill, then quote you a system that is $20-$50 less per month.  But the price per watt might be through the roof (read on for examples, and no pun intended)!  What seems like a great deal, relative to your current energy costs, might not be a great deal compared with other offerings.  Even the same tech installed by a different company can yield savings.

Finally...Warranties.  OK.  These appear to be important.  But like the other points, they need to be considered in the overall picture.  Most solar tech seems to be quite robust, so offering a 25 year warranty on something that has an extremely low probability of failing is, well, almost pointless.  Not entirely, but...almost.  But everyone is doing it, and if it signs up more customers, so be it.  On the other hand, at least you have that level of assurance that your new system will reach its maturity (and then some) before it starts having costly problems.  If you opt for a more complicated system (i.e. microinverter or optimizer), those warranties will probably come in very handy.

Our Usage Needs

A 12-month moving average of our kW usage showed a recent usage trend of around 2300 kW / month.  I set our target for 2400 kW / month of generation.

We have about 5.2 sun-hours (yearly low) in my location, and luckily no trees or buildings to shade our roof.  We could expect to get a decent amount of input.  If our per-day goal is 80 kW, then we'd need a system at least 15 kW in size.  That's the layman's sizing; actual sizing is more complicated, and needs to take into consideration the fact that you won't generate that much power from your array every day, or every month (seasons, sun location in the sky, etc).

Every system we were quoted went above 17kW. Where I'm at, any system about 11.2kW is called a "type 2" system, and requires more gravy to get the train moving.

DIY Solar Options

If you are willing to forego better warranties, and you can either find someone to install it, or are willing to drill a few hundred holes in your own roof and reap that harvest during the next big rain, then you can buy kit systems online for $1.50 / W.  I'd certainly seriously consider it for a ground-based system, but not a roof system.  That said, the law may also not be on your side (and it wasn't on mine).

We need a certified installer to make the power company happy, otherwise no grid-tie for us.  Why grid-tie?  Batteries are too expensive, the ROI is just not there; and grid-tie is really the only option here.  So, we had to find a vendor.  We asked around for buy-and-install pricing, and found exactly one willing to do it, but the warranties offered on whole systems were just too appealing.  Plus, there is a ton of work and permitting that has to be done with a solar install.  

If you can do it, go do it.  If you are old and tired, and have multiple kids driving you crazy and a need to get stuff done, better to let a good installer take it on.

Finding a Vendor

After a fateful visit from a door-to-door solar salesman, I started deep-digging into vendors.

I found a list of the best local installers, who had hundreds of ratings and reviews each, plus certifications or accreditations from NABCEP (that's important): The North American Board of Certified Energy Practitioners.  I contacted four of them.  At least one was based in California.  The others were local of various size.

Spoiler Alert: a local company, and NOT the door-to-door guy, came out on top.  A good company also shouldn't hound you or pressure you.  Watch out for gimmicks like "improving your A/C system to cut down on your solar bill" - these just equate to easy money for them, and significantly higher $/W for you from your solar system.  And no, the guy who offered me that didn't have a crystal ball, but he should have for making such sweeping predictions about how great my A/C would be after that $5,200 treatment.

My takeaway: If you have already optimized your energy savings in your house, then size your system to cover your needs.  Don't under-size a system in anticipation of how much power you can maybe save after fixing your home's energy leaks. That's just putting the cart before the horse.

The System Quotes

All sorts of different systems were offered:  string-inverter, optimizer, micro-inverter, different kWs, even one A/C treatment.   Names hidden, we received the following quotes (cost per watt):

• A: $2.82 / W
• B: $3.11 / W
• C: $3.40 / W
• D: $4.02 / W

Lower is better for the wallet, but only if the other features match your needs and expectations.  We were offered systems of sizes:

• A: 22.4 kW (string-inverter)
• B: 19.24 kW (optimizer)
• C: 22.11 kW (micro-inverter)
• D: 17.985 kW (micro-inverter)

All $/W values are raw (before tax credits).

The Technology

There's a lot of information, and misinformation, on the Internet.  I'll try to sum up the realities here.

Inverter Tech

You have three major choices.  All inverters need to find the Maximum Power Point (MPP) of the panels - this the point in the panel IV curve that gives maximum Power output (where Power is Current (I) times Voltage (V)).  It's the "knee" in the IV diagrams you'll see for panels, where it stops going sideways and starts plummeting like a rock.

The MPP varies with sun, shade, soiling, etc.  There are different algorithms for finding it and keeping it optimal.  A less-intelligent inverter can get stuck in a local maxima.  Smarter ones will occasionally sweep to ensure the global maxima is actually the one it's on.

The String Inverter

Large inverters on the side of your house or garage, ideally near the meter.  No electronics on your roof, just panels.  SMA makes one of the best, and claims to compete with the newer tech.  

Overall, it's a simple, durable system with the fewest parts, and time-proven technology.  On the downside, it might not offer the overall energy generation of newer tech.  One reason for this might be it doesn't optimize as frequently as it could or should; another might be that individual panel losses add up more in a system like this.  However, take all this with a grain of salt: the research on all these claims is extremely lacking.

Optimizers

Basically DC-to-DC power conditioners.  They send ideal voltage to a central inverter, modulating the amperage accordingly all over the array.  The idea is to make the inverter work as efficiently as possible, by insuring it always has the right voltage.  An under-performing panel will be adjusted at the optimizer, along with all the related higher-performing panels, such that the total voltage is what's expected.

There are costs for this: every panel needs an optimizer.  The optimizers need power to do their job, and they are not 100% efficient at the transformation.  The sales sheets will tout 98% efficiency like it's a great thing (and compared to less efficiency, it is).  But that's 2% loss from every panel during the conversion process.  What that means in terms of actual power production, I do not know.  It could be 2% voltage loss, or 2% amperage loss, or even 2% overall power loss.

If it's a power loss, a 70 panel system at 320 W per panel would lose 462W due to the conversion loss.

Also, because every panel needs one, they are up there on the hot, hot roof, under a hot, hot panel.  So, there is a reliability concern.  You also still have a central inverter, but it might be smaller than the string inverter unit.

On the upside, if they do indeed perform better in intermittent shade scenarios, the losses during high-sun might be made up in gains during less optimal solar conditions.  You also get per-panel statistics, which is nice for diagnosing panel issues...or, I guess, bad optimizers.

Micro Inverters

These are like optimizers, but instead of doing DC-to-DC, they do DC-to-AC right at the panel.  No central AC inverter is required.  I'm not sure if they require any special junction equipment, but if you wanted ultimate efficiency with maximum shade tolerance, this is probably the way to go.

Of course, the cost here is that the micro-inverters are significantly more complicated than optimizers, and like optimizers you need one for each panel, at the panel itself.  So, complicated electronics in a harsh environment.  Again.

Like optimizers, you get per-panel info.  You also get a pretty hefty price-tag increase.

But What the Heck is a "String"?!

If you have 70 panels, you're not going to run 70 individual wires down your wall into your inverter or meter box.  You're going to group, or "string," them together, upwards of six at a time.  Usually wired serially, to kick up the voltage while keeping the amps relatively low.  Each string will run down to the inverter.  Each inverter can take in so many strings.  

For the SMA, a 70 panel system will require 3 SMA boxes (at least of the model we're getting - OOH SPOILER ALERT!): 6 panels per string, 4 strings per inverter, 3 inverters.

Panel Tech

People like to say that panels wired serially in a string will fail like Christmas tree lights.  But that is not the case for most modern panels.  For both power production and - more importantly - fire concerns, bypass diodes are pretty standard.  Most panels seem to set up groups of cells, and wire them to a bypass diode, with multiple diodes in a panel.  This means that if part of the panel is obstructed or fails, the other groups of cells can keep working.  If the whole panel is obstructed or fails, the whole panel can be bypassed.

Since bypass diodes are a thing, it begs the question of how useful optimizers are in such scenarios.  A somewhat contentious study by a university in Denmark suggests that the power costs of optimizers outweigh their benefits, except where (as stated above) intermittent shading or whole-panel issues are a thing.  You can read it here: https://www.sdu.dk/-/media/files/om_sdu/centre/cie/optimizer+for+pv+modules+ver11_final.pdf

Panel efficiency is a rather stupid number: aside from telling you how many watts per square meter you can generate, it tells you really nothing else, and ceases to be applicable very quickly during most actual operating conditions.  If you really wanted to compare apples-to-apples, and you had nothing else handy, panel efficiency will tell you the panel that will give you the most for the least space.  Is that the whole truth, though?  No.

There are two kinds of degradation you have to be aware of, at least to filter out the bull that will be handed to you by the sales guys: temperature, and standard lifetime panel degradation.

Panels perform worse when hot, and they give their stats on their spec sheets.  I studied two: a 320W and a 370W panel.  The 320W will put out 320W in optimal light conditions (read the spec sheet if you want to know what they are, and don't expect them to be numbers that match actual sun-obtained reality), at 25C.  My roof can easily get to 70C in places during a nice hot day, which should drop the 320W panel's production to 280W.

Panels degrade over time as well.  Industry standard warranty is 80% production at the 20 year mark, with the degradation being linear (meaning you should NOT see a lousy 80% production on year 3).  Below I'll talk about how linear degradation isn't quite the selling point the salespeople wish it was.

An Estimate - PVWatts

The PVWatts tool is pretty awesome: you can enter in your address, punch in some configuration details, and get a simulation on how your system will perform.  I did this for the two top systems quoted to us.  In order to get relevant results, I had to break the systems down into three estimates for the tool, since the tool doesn't handle multiple roof faces. 

Here's my yearly production estimates, after adding my roof simulations together:

• A: 22.4kW => 31,101 kWh
• B: 19.2kW => 27,071 kWh

I can only hope that PVWatts actually accounted for panel losses due to heat, but I honestly am not sure how much it did.  It's probably in the tool documentation.  One thing I could do, however, is calculate system losses over time.  Given each systems' panel specs, I calculated the amount of degradation I could expect at the 5, 10, 15, and 20 year marks.

At the 20 year mark, I had the following two numbers:

• A: 22.4kW => 26,125 kWh
• B: 19.2kW => 25,643 kWh

Even though the A panels degraded faster, the larger (yet cheaper per watt) system still produced more at the 20 year mark.

Extrapolating for Like-Kind Analysis

Is it worth it to beef up the B system and get both the better life and greater overall generation?  Let's look.

If we resized the B system to match its sizing to the A system, it should produce 31,582 kWh per year on year 1.  For that amount of array, the price tag would increase by $9,952.  An already expensive system (by comparison to A) would go up in cost by 16%.  This, to get a return of 481 kWh over the course of the year.

Other Considerations

There are other things you need to look into, when shopping solar installers.  They are just as important as the tech.

Financing versus Cash Price

Some vendors will sell you a much better cash-price, though one potential downside of that is you might not be able to claim any closing costs or origination fees for the federal tax credit.  Of course, that'll all be moot once the tax credit vanishes.

Financing Terms

Most vendors will sell 20 year financing.  25 years is probably not a good deal, and the "lower" payment might just be equal to or worse than a better 20 year system.  The internal pricing of parts and labor is completely opaque until after you've signed (and even then you might not see it).  Shopping around seems to be the only way to ensure that both your terms, and your total system costs, are optimal.

Warranties

A good vendor offers warranties.  Our select vendor offered warranties from the manufacturer (so we're told) that go beyond the standard, due to their rating with the NABCEP.

Panel warranties come in two parts: performance, and the panel itself.  The performance warranty covers that linear degradation I discussed above.  The panel warranty should cover a panel outright failing, de-laminating, or suffering some other catastrophic pre-end-of-life fault.

The roof penetration warranty is your installer saying your roof won't leak for some period of time after the install is complete.  Ideally, it's at least the life of the roof.  One vendor put a cap on top of that (albeit it was 25 years).  Our selected vendor said they'd restart the warranty following a reroof reinstall, and warranty for the life of the new roof.

The inverter needs a warranty as well, and it will often be different from the panels.

Finally, a workmanship warranty will cover a job-well-done (or maybe not so much).  The longer the better: if something goes belly-up, the vendor shouldn't be charging you to fix their mistakes.

Reroof Costs

If you need a new roof, it is not advisable to let Handy Roofer Dude take your Expensive High Voltage Solar System off your roof.  Let the solar installer do it.  It's another cost, of course, but varies widely.  Prices are sometimes listed per panel (like $50/panel or $100/panel for take-down and reinstall, plus storage fees).  Prices are also sometimes given in flat rates.  Most vendors couldn't guarantee what the panel removal and reinstallation costs in the future would be, but I settled for a "right now" cost estimate.

The Tax Credit

Get it while you can.  Once you do, you have five (5) tax seasons in which to fully recover it.  This means that if you can't claim enough taxes to get your full credit from the IRS, you can roll over the remainder to the next year.  After five years, you're out of luck, but I imagine for most people this won't be a problem.

Secondly, my thinking is that it's stupid to spend a dollar to save a quarter.  While it may be appealing to buy a larger system to get a larger tax credit, think about what you're doing here:

First, every solar loan operated with the expectation that you'd take that nice, fat tax credit and stuff it into your loan repayment by the 18 month mark, otherwise they'd re-amortize you at a higher rate.  Ironically, at least with one lender if you pay more than that by the 18 month point, you can get re-amortized to a lower monthly payment.

Second, the overall cost of the system is something you have to pay, credit or no credit.  Even after the tax credit, you're only getting a 26% discount (for 2020).  A $60,000 system is cheaper than an $80,000 system, and it will STILL be cheaper after you take that 26% off the price tag.  It seems to me the best way to overpay for your solar is to try to get your credit as large as possible.  Just Don't Do It.  Get a good system and let your actual power savings do the rest.

Additional Insurance

We have to obtain a $1 million general liability policy.  That amounts to about $19/month with our insurance provider, and is called an "umbrella policy".  Not every power company requires this, but ours does.  Lovely.  It's something to keep in mind, though, when you think about your total monthly cost.

Unused kW Credits

If I produce more power than I consume, my power company will roll those "credits" from month to month.  The idea here is that I can generate more than I use in the cooler months, and use more than I generate in the hotter months, and still come out net-zero for overall power cost.  At the end of the year, my company will supposedly "buy back" the unused credits, effectively zeroing me out to start afresh on the new year.

The buy-back isn't much - it's significantly lower than what they charge for their power.  But meh.  As for the production goals, I took a close look at the per-month report from PVWatts.  After comparing each month of simulated generation to the previous matching billing cycles, I will probably pay for some power in January and February.  The rest of the year I should be good.  I should generate enough to get a bit of a refund back.  In real numbers, I should go from spending $3900 / year on power to $133.

Remember, however, I still have a loan to deal with.  That's the trade off.  But, if the utility rates continue to increase, it will speed up my effective ROI, since that's more expensive power that I'm no longer buying.  I trade a highly variable, increasing power bill for a relatively stable and fixed solar loan.  The catch to this is generating enough to make that a reality.

In Conclusion

There are many ways to analyze the value and return of solar.

• In 10 years, I would have paid my power company enough to have bought my chosen system for cash (after tax credits).
• In about 16 years, I should see my ROI from the amount of savings I should get by going solar.  (That's my break-even point)
• After the system is paid off, it will continue to generate power, even if we move and rent out the house.  Offering a relatively fixed, low power bill to the renters will probably be very alluring.

That said, what remains to be seen is the actual system install and performance.  I will write again once I have more to say about that.  The install process should take only about 3 days, including a meter panel swap.  We're going with the string-inverter system, for simplicity and because our shading is practically non-existent.  It's hoped that however the panels are wired, they will perform optimally regardless and we should see at least what PVWatts estimated for production.

My Solar Experience - Table of Contents

My First Solar Install

Table of Contents

 For ease of reading and sharing, here is the table of contents for all my articles on My First Solar Install.  Click any of the following to head to the specifics!

• Part 1: Research and Sign-up (aka Everything You Never Wanted to Know)
• Part 2: Managing Expectations - The Estimate and Further Calculations
• Part 3: Installation Day
• Part 4: POWER UP!  System Activation
• Part 5: Dollars and Sense - Reviewing Performance and Musing Solar

Appendix:

• The Reality of Heat on Solar Energy Production