The Case for a Significantly Undersized System with Time-of-Use Billing

[SolarFuture]

I am in my second year on my system, closing in on the second year of my relevant period. We leased an EV back in May 2015 so this is the first full year with an EV (although we charge about 60% at work, at 40% at home).

I have West-facing panels on SCE TOU A. I've done some spreadsheet calculations using PVWatts and although you may take a roughly 17% hit in annual energy production as compared to South-facing, the annual monetary hit is closer to just 5% if you're on a TOU rate that with a "late" peak period, such as SCE TOU A (peak is 2pm - 8pm). In short, payback period for West-facing can be very, very close to South-facing.

In any case, our system is very small. 8x 315W panels, 2,520W (LG NeON 2). We charge the EV at super off-peak times only (effectively 4 cents / kWh after taking into account the baseline credit), while we generate at close to 40 cents / kWh. That's a 10:1 ratio for on-peak credits to super-off-peak debits. For every 1 kWh we generate in the day time, we can charge the EV 10 kWh and be a net zero.

To summarize how effective this is, I've attached our true up at month 11 of 12 of the relevant period.

Screen Shot 2018-01-25 at 11.43.25 AM.png

I think it speaks for itself, but I'll summarize anyway

Our panels generated approximately 3,840 kWh of energy in the last year. We used up an extra 2,288 kWh from SCE (net consumer of energy). Our balance is a credit $60, and I expect to get a refund of approximately $40 due to the Climate Credits counting as "real money". (If want to get technical and you don't count the Climate Credits, we are paying approximately $45 for 2,288 kWh of energy, or less than 2 cents / kWh.)


[Side note: last year, we didn't have an EV for the full relevant period and ended up at with a credit of $330 for 180 kWh of net consumption. Again, this huge discrepancy is due to TOU and energy shifting. Obviously we didn't get the full amount back because we are not a net generator, but we did get a $75 refund for Climate Credits and Nest Rewards].

In short:

1. Don't size your system too large. We intentionally sized our system production at approximately 60% of our anticipated annual usage.
2. Switch to TOU as energy shifting can get you very close to net zero $ even with significantly "undersized" production.
3. Don't be afraid of West-facing panels as it can be nearly as productive as South-facing panels from a monetary point-of-view depending on when your peak period is.

[organic farmer]

Well done

[bcroe]

Thanks for detailing out your particular situation. Bruce Roe

[FFE]

We did the same thing in 2015. My wife was certain that she would never be comfortable only having EVs. Then started driving my EV more than her car. Then we switched to all EVs. Our first true up netted us money. The second was a different story but much less than we spent on gasoline the year prior. The EV, SCE TOU A with solar is a great combination. Congratulations on executing a great plan.

[J.P.M.]

Thank you for the information. A breath of common sense and head's up planning. Particularly the point you make about not oversizing an array.

Looks like your use pattern(s) and a T.O.U. tariff really worked to your benefit. Also looks like low usage helped more.

I'd agree, as you've found and shown, that west facing panels, mostly because of the way most T.O.U. tariffs and time schedules are put together, can be less cost ineffective than simple production estimates may suggest.

However, I'd add and perhaps highlight your comment that west facing is, for you, even with a time shifted T.O.U schedule, still 5% less cost effective than a south facing array. Don't know what your roof real estate orientations/directions/availability are, but for those in similar situations and locations, looks like if south and west are both available, all other things being equal (and I appreciate that they seldom are), and contrary to what may be commonly and incorrectly believed, even with a time shifted T.O.U. schedule, most of the time, south will be a better orientation in terms annual cost effectiveness than west facing orientations. West is not necessarily bad, but it is not automatically, and in reality, seldom better than, south facing orientations.

Provided shading is of a minor of no consideration, the optimum cost effective orientation for CA T.O.U. tariffs throughout most of the state is probably something like a 30 deg. or so tilt, and an azimuth of something like 195 to 205 deg. +/- some.

Since few roofs have that orientation, and fewer still are moveable, the choice of the more southerly roof will probably result in a larger electric bill offset. At least if/until T.O.U. times get readjusted to send a different set of time signals/incentives to users to modify their use patterns and so help smooth out the spikes in usage.

[ImInPhxAZ]

Well done, looks like your power company has some favorable payout schedules. Excess power in our territory is never paid out at retail rates. Best the old grandfathered plans do is offset peak 1:1, and buyback at wholesale. Newest plans buy back at 12.9c, about half the peak retail.

All about knowing your power company plan options, knowing your consumption, and planning accordingly. Looks like you struck the perfect balance.

[J.P.M.]

Well done, looks like your power company has some favorable payout schedules. Excess power in our territory is never paid out at retail rates. Best the old grandfathered plans do is offset peak 1:1, and buyback at wholesale. Newest plans buy back at 12.9c, about half the peak retail.

All about knowing your power company plan options, knowing your consumption, and planning accordingly. Looks like you struck the perfect balance.

While SolarFuture has done well, compared to what they SCE charges, they do not pay favorably for excess generation. Current (Jan. 2018) Net Surplus Compensation Rate (NSCR) = $0.02797/kWh. Excess generating capacity is simply not cost effective and becoming less cost effective as rates and tariffs continue to evolve.

[SolarFuture]

Thank you for the information. A breath of common sense and head's up planning. Particularly the point you make about not oversizing an array.

Looks like your use pattern(s) and a T.O.U. tariff really worked to your benefit. Also looks like low usage helped more.

I'd agree, as you've found and shown, that west facing panels, mostly because of the way most T.O.U. tariffs and time schedules are put together, can be less cost ineffective than simple production estimates may suggest.

However, I'd add and perhaps highlight your comment that west facing is, for you, even with a time shifted T.O.U schedule, still 5% less cost effective than a south facing array. Don't know what your roof real estate orientations/directions/availability are, but for those in similar situations and locations, looks like if south and west are both available, all other things being equal (and I appreciate that they seldom are), and contrary to what may be commonly and incorrectly believed, even with a time shifted T.O.U. schedule, most of the time, south will be a better orientation in terms annual cost effectiveness than west facing orientations. West is not necessarily bad, but it is not automatically, and in reality, seldom better than, south facing orientations.

Provided shading is of a minor of no consideration, the optimum cost effective orientation for CA T.O.U. tariffs throughout most of the state is probably something like a 30 deg. or so tilt, and an azimuth of something like 195 to 205 deg. +/- some.

Since few roofs have that orientation, and fewer still are moveable, the choice of the more southerly roof will probably result in a larger electric bill offset. At least if/until T.O.U. times get readjusted to send a different set of time signals/incentives to users to modify their use patterns and so help smooth out the spikes in usage.

I agree 100%. South-facing will nearly always be the best choice from a production and economic perspective, but West-facing comes really close (economically with certain TOU rates). Interestingly, federal/state/local incentives may push West-facing systems over the edge, but as I understand it, they are currently only available to new home builders.

[SolarFuture]

Well done, looks like your power company has some favorable payout schedules. Excess power in our territory is never paid out at retail rates. Best the old grandfathered plans do is offset peak 1:1, and buyback at wholesale. Newest plans buy back at 12.9c, about half the peak retail.

All about knowing your power company plan options, knowing your consumption, and planning accordingly. Looks like you struck the perfect balance.

While SolarFuture has done well, compared to what they SCE charges, they do not pay favorably for excess generation. Current (Jan. 2018) Net Surplus Compensation Rate (NSCR) = $0.02797/kWh. Excess generating capacity is simply not cost effective and becoming less cost effective as rates and tariffs continue to evolve.

Excess generation is rarely a good way to ensure a shorter payback period and SCE has horrific NSCR rates. This is just emphasizing the benefit of undersizing your system and utilizing TOU rates to your benefit.

Our relevant period just ended and we got a $35.45 refund check. Since I am a net consumer of energy, I am not eligible for credits via the NSCR program and this refund has nothing to do with it. It is simply the Climate Credits and Nest Rewards being counted as "real money".

Quick summary for our true-up:

• Your cumulative energy charge Year-to-Date: -$36.46 *
• Your cumulative kWh Year-to-Date: 2,557 kWh

If I had adjusted my usage absolutely perfectly, I would have received a refund check for up to $81. Climate credit of $62 and $19 for Nest Rewards, all of which is considered "real money", but is counted into your "cumulative energy charge" until true-up, at which point you receive a refund if a credit remains on your account.

Counting all basic charges, minimum charges, climate credits, and Nest Rewards over the past relevant period, my net payment to SCE for the entire year was $3.12 for 2,557 kWh of net consumption.

[J.P.M.]

but as I understand it, they are currently only available to new home builders.

Correct. I'm pretty sure that's correct.

[Guest]

Hi all,

I'm new here and trying to make some decisions about a new system. We live in San Diego and are planning to install at 6.5 kw system on our west-facing slope. We'd hoped to get it turned on prior to March 30th because after that SDGE will no longer give us the choice between tiered rates and [COLOR=#222222][FONT=arial]DR-SES. We'll be forced on to TOU with peak hours between 4pm and 9pm.

Our house, which we

[J.P.M.]

but as I understand it, they are currently only available to new home builders.

Correct. I'm pretty sure that's correct.

[Guest]

Hi all,

I'm new here and trying to make some decisions about a new system. We live in San Diego and are planning to install at 6.5 kw system on our west-facing slope. We'd hoped to get it turned on prior to March 30th because after that SDGE will no longer give us the choice between tiered rates and DR-SES. We'll be forced on to TOU with peak hours between 4pm and 9pm.

Our house, which we

[jflorey2]

I agree 100%. South-facing will nearly always be the best choice from a production and economic perspective, but West-facing comes really close (economically with certain TOU rates).

I would point out here that in some locales (coastal Socal) west facing or southwest facing have an additional benefit - you pick up late generation and do not lose much early generation, since for the best solar months (May-September) morning clouds are very common. They almost always clear by noon.

[FFE]

Welcome Lxm, this Forum does not work well with apostrophes.