Solar Net Metering Payout

DavidM
DavidM Registered Users Posts: 4
The following is probably a little geeky, but that is the nature of this subforum:

I have been seriously considering adding about 3.7 kW of grid tied solar to my house. The only place for it is on a SE facing garage roof that is shaded in the morning and is blocked by a neighbor's roof in the late afternoon. I think I can get a good 6 hours of strong sun, but off a bit as it faces SE not due south, and the roof angle is 30 degrees whereas optimum is 42 degrees.

S-E priced up a 3.7 kW system consisting of ten 365 watt panels and ten Enphase Microinverers plus mounts, combiner and disconnect switch which was $8600. Call it $9,000 with cable and misc hardware That is kind of a neat system because all ten pairs (panel and microinverter) are independent and if one is shaded or fails, the others should still work. You tie the 220V L1 and L2 output to an available double pole breaker on your main house panel and the power flows, but.....

Connecticut where I live and Eversource our utility have sensible but not liberal rules for how excess power is handled. Since all of my power will be generated in the middle of the day and it should be several kW on a sunny, summers day, that is more than our home uses. We rarely use the A/C in the summer which would be a potential high power hog but not for us. So all of the excess between what we produce and what we use is "banked" to use Eversource's term. At the end of the year that banked power is paid back to us at some low rate. The terminology is weird but I am guessing it is the cost of Eversource buying or producing power and does not include the higher cost of distributing it. Today the supply is about 9 cents per kW and the distribution is about 11 cents per kW giving a total variable cost for power of $0.20 per kW.

I am not sure that if we use more than we make, such as would be the case when the sun goes down, if we can then draw on that banked power. I suspect not. It would significantly improve the economics if we could.

I ran our situation through NREL's PVWatts calculator which is rather comprehensive and it calculated that we would produce a total of 5,200 kWhrs in a year. If we assume that 1/3 of that is produced when we are using that much and the other 2/3 is banked, then we would save 1733 * $.20 = $347 plus get paid 3467 * $.09 = $312 or an annual total of $659. FWIW our total annual power bill before the solar system is about $1,500.

Presumably I will get a 26% tax credit on the system leaving a net cost of $6,600 since I will DIY the installation. So I get a ten percent return. Not great but not horrible. My installation is difficult because of the direction it faces and the morning shading. There is no other potential location at my house due to tree shading.

It makes me wonder how a perfect installation site would work in our area. Panels would face due south and be oriented 42 degrees (my latitude) not the 30 degrees of my roof, with no shading. Power would probably go up 50% and my return would be a nice 15%. But it makes me wonder how solar installers make out when they get paid by power savings. I bet it would cost $3-5,000 to professionally install such a system. Maybe I would get10% and the solar installer would get paid out in ten years or so. Doesn't sound too lucrative here in CT though.

Our local high school just put in a large, maybe 100 kW system and I understand it is underperforming. No doubt someone was looking through rose colored glasses when they bought into it.

Thoughts?

David




Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    Hi David,

    It sounds like you have a good understanding of the system. But to make an "economic argument"--You need to understand the rate/billing plan in detail.

    I guess you are around middle of Connecticut:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Hartford
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 48° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.13
     
    3.85
     
    4.39
     
    4.42
     
    4.61
     
    4.82
     
    JulAugSepOctNovDec
    4.76
     
    4.67
     
    4.49
     
    3.96
     
    3.05
     
    2.85
     

    Add all the numbers together for 49 hours / 12 months = 4.08 hours of sun per day average
    • 3.7 kWH array * 4.08 hours ave sun per day * 365 days a year * 0.77 GT Solar eff = 4,243 kWH per year average
    So, I get about 20% less harvest--But guessing your location and PV Watts (assuming used correctly) should be more accurate.

    Regarding billing... Things have been changing over time... From very good for GT Solar customers (lots of subsidies from utility/other utility customers--But excess production lost at end of billing year) to now less payments, higher charges that tend towards darkness (peak power to 8 or 9pm... Not much solar on my roof at those times). But better payments for "banked energy". Still "over production" is not a huge "income" for a residential customers. And California PUC + Utility are reducing the advanta
    ges for GT solar. In our case, they would only guarantee our original rate plan for 10 years--After that, the can change plans every year.

    With a 2 story home SE facing home and some trees... Not a lot of room for arrays, and not great afternoon generation (partial peak and peak summer pricing). But as long as we do not use much power (fairly efficient home and too wasteful)--It works well.

    For our home, we paid up front (plus state+federal tax/payments for initial install costs). And we harvested what we harvested.

    If you have an installer with solar leasing/payment plans/renting your roof space/etc... There can be plans where the installer "guarantees" the solar harvest. Or will sell you subsidies GT energy for your home.

    From ~2010, here are a couple of contracts from a major solar leasing company. Part of a relatively long discussion:

    https://forum.solar-electric.com/discussion/comment/119744#Comment_119744

    That is 12 years go.. .I am sure things have changed--But you can see some of the issues/questions if you take part of a leasing/renting solar option.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset