Solar Install Do’s, Don’ts, or Tips?

General Sense Discussion
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Hi all, I know at least a handful of Sense users here have solar. My wife and I are getting proposals from multiple companies, and have already learned a lot, beyond what I learned on my own and from this forum. Such as, making sure our homeowners insurance will cover it.

What are some do’s and don’ts you learned before, during, and after your install? Any additional tips to share? Thanks!

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If applicable, make sure you (and possibly the installer) know your utility’s rules around net metering.

My experience follows. NOTE: your utility may have different rules.

When I had solar installed, the utility looked back at my last 12 months’ worth of usage to determine the maximum size system (kW) I could have eligible for net metering (I could have a larger system, but they would do some calculation to determine what my net metering “bank deposit” was each month). As it was, because inverter sizes aren’t infinitely variable, I was oversized by 1% (details on the calculation below). My electrification plans started with solar, so my GSHP and future HPWH and electric car(s) wouldn’t change my net metering calculation until I had them installed and running for 12 months (and I can apply to have my net metering calculation redone once every 12 months, and with this fall being one year with my GSHP, I’ll do it then).

How the calculation works (for my utility) in practice:
My inverter is 3.8kW, which was oversized by 1% according to the utility’s determination of what is eligible for net metering banking.
Every month, the utility calculates consumption (from grid) vs. production (to grid). Self-consumption doesn’t enter into this at all.

  • If my consumption equaled or exceeded production, for consumption-production, I withdraw from the net metering bank and pay retail rates for anything beyond what I had in the bank.
  • Otherwise (production exceeded consumption), the utility pays wholesale rate for 1% of production-consumption and I bank the remaining 99%. If I had a positive bank balance at the end of the year, I would get paid for that amount (I don’t recall what that rate would be; it has never happened, and I don’t see it ever happening). If I had oversized the system by more, the percentage that the utility paid wholesale rate for would increase accordingly.

The reason for this rule is to prevent people from installing huge systems and making the utility pay retail rates for all of that electricity (when they could otherwise buy it for wholesale prices on the market).

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Here’s something that falls into the “don’t” category…

Avoid excessive over-paneling… There is an epidemic of over-paneling, and it really only lines the pockets of the solar companies, and results in a LOT of wasted money…

To give you a sense of how egregiously poor the financials are for over panelling, I have 10 panels that cost me roughly $1,000/panel installed (including smoothing out the fixed costs of the inverter and other infrastructure & labor costs across the total number of panels)… My entire system generates an annual 5.6mWh, that means each panel is (on average) produces 560kWhs… So for every unnecessary extra panel, it will cost me $1,000 and the excess energy will be bought back by PG&E for 3¢/kWh (or $16.80). If you keep generating energy you never use, and sell it back to PG&E for $16.80 in revenue, it’ll take you nearly 60 years to recoup the cost of that panel!!!

Everyone worries about not having enough panels… But honestly, you are better off (from a financial perspective) having slightly less paneling and using every bit of what you produce… I personally did end up slightly over-panelling… I keep meticulous records of my energy consumption and here is my annual consumption over the last 5 years:

  • 2016: 5.222mWh
  • 2017: 5.600mWh
  • 2018: 4.670mWh
  • 2019: 4.355mWh
  • 2020: 4.642mWh

Based on my 2020 consumption, I over produced by almost a full 1.0mWh… But much of the under consumption was driven by the fact that my AC broke at the beginning of the cooling season and we sweated it out this summer (and I think I used my AC lightly in 2018 and 2019)… My capacity planning took into account more generous use of my cooling system, as well as the potential of adding a low mileage EV to putt around town with. I’d also like to consider moving to an electric heat pump for winter heating. I know nothing about the consumption profile of a heat pump, so I might need to add panels if I wanted to move to electric heating… But at the end of the day, I might just stay with natural gas…

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A few things in the “do” category:

  • Watch the installers and be sure they are positioning the panels correctly (if aesthetics are important to you)… My panels are landscape oriented, and it actually does make a difference if they aren’t consistently positioning all of the panels the same way… It won’t matter functionally, but from the street the white grid lines of my panels were about a quarter inch staggered because some panels were installed with the correct orientation, but not consistently in the same direction. Because I was watching the installation, I was able to request that they reposition panels that were not installed in the same direction. This was super important to us because our panels are street facing…
  • Again, if aesthetics are important to you, be sure that you pay attention and make adjustments to your panel placement on your rooftop. These guys are NOT the homeowner, and they don’t have a homeowner’s perspective when they configure your panel placement. For the most part, they are solar guys trying to eek out the best placement based on performance alone (and good for them…that’s what they should be doing). My initial panel configuration looked like someone played Tetris on my rooftop. When I asked them what the solar production difference was if I moved a few panels to make the visual street-facing rooftop look nicer, they told me that the difference was negligible… But math wise, it was better to have the Tetris configuration… I opted for the negligible loss in production in favor of maintaining curb appeal… Obviously, this step needs to be done well ahead of the installation…
  • Think about how you want your conduit run across your rooftop… My installers gave me the option of running the conduit either on the top of the roof, or in the attic… We had a lot of brand new blown-in insulation in the attic, and we decided we didn’t want them to disrupt the insulation uniformity, nor did we want any more unnecessary holes in our roof to risk compromising water-tightness… We ran it on top of the roof, and we instructed them to run it directly to the back of the roof as quickly as possible, and then they could navigate the majority of the conduit from the back of the house, where it was not visible from the street. Again, aesthetics were important to us.
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Thank you @qrnef and @MikeekiM !! We had a meeting and a follow-up meeting with a large, but locally-based solar installer. We like them and their plan was cheaper than a National installer and much better than a large National installer. Our system would meet 95% of our current usage. If our usage were slightly more, about 100kWh, we could add another panel and get up to 99%, but as it is right now, our utility wouldn’t let us add another panel. As such, our system would be 21 Sunpower panels with micro inverters. Our utility banks our excess production instead of buying and selling it, so we don’t need to worry about retails vs wholesale rates, just the balance of kWh.

We are trying to decide placement of the panels. 16 of the panels can face south on a pitched roof. 2 will face west on a pitched roof. Those will all be hidden from the street. The last three are being proposed for a front south facing elevation. We’re not the keenest on that because our house is 101 years old and we want to keep that look. The other location is a northern, flat, roof. The would take additional supports, and cost, but most importantly would result in 65w less generation per panel. I have no idea how that math would add up, but 195w per day? month? seems like it would equal a lot over 25 years. Conduit and it’s look is also important to us. The installer even mentioned it’s so important to them that if we don’t like how the conduit needs to be run, that’s grounds for terminating the agreement.

A new issue is I have dedicated circuit monitoring setup, so I’d need to ditch that for solar and will also need to run my solar CTs somewhere.

Thanks again all, this is just the beginning to a new process for me.

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I also sized my system based on the last 5 years of usage. It was around the time when I changed most bulbs to LED. Just after I installed the system, I had the replace the AC the following year. The new AC was 25% more efficient. My recommendation is to make sure you’ve save all you can before sizing your system. Also with the acceleration of EV cars, you may want to make sure your inverter can handle future upgrades. I believe I can add an additional 4 panels.

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Thanks for the feedback. Did you not want to size your system based on current usage so you would have extra capacity? It seems like with the LEDs and new AC, you could’ve saved significant dollars by scaling down your system size. Our proposed system uses micro inverters, so inverter size for an EV isn’t an issue, I don’t believe. Our salesman has had a Model 3 for three years and said 4,000kWh (or was it just Kw?) gets him about 10,000 miles a year. At 450w per panel on our primers panel location, he said that same 4,000kWh would be 8-10 additional panels. Obviously we’re not adding those right now.

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No, you got it right the first time… It’s kWh…

As an analogy, think of kW as similar to a speedometer… and think of kWh as similar to an odometer…

kW is energy produced at a point in time… kWh is stored/consumed energy… The “W” is capitalized because it is the formal last name of a person (James Watt).

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