Am I oversizing my system?

[jplee3]

Hey guys,

EDIT: I realize the title doesn't make much sense lol - I don't see a way to change it, so what I really should have titled it was "Am I oversizing my system by too much?"

I'm in contract with a local company to install solar on our roof here in Southern CA (under SDGE). They initially sized me out with a 15 panel 6kw (generating 9017kwh/yr) system. I was thinking it might make sense just to maximize the install on that side of the roof and after the site survey they were saying I *could* install 19 panels on this roof section - that would increase the size to 7.6kw (generating 12,000+kwh/yr).

Our current usage estimate (we haven't lived here a full year) is in the 7500kwh/yr ballpark. But I was thinking upsizing might be good as far as "future proofing" our needs (like if we get an EV/charger or two, moving towards more electric appliances, adding a minisplit or two possibly). We are planning to have our new HVAC system installed (our furnace is dead) in October and this system I think is roughly twice as efficient (4ton/15-16seer) as our current (4ton/probably 7-8seer) so I'm pretty sure our kwh usage will actually go down once that system is in place.

Do you guys think I'm grossly oversizing the system and that I should just stick with the 6kw proposal? SDGE charges the highest rates in the nation as well. In terms of adding more panels later, t seems like it's a bit of a pain to go through all that as it involves permitting and is then subject to any new NEM changes etc. I was also considering a battery but may hold off on that (btw: would battery additions to a solar system cause you to lose your "grandfathered" NEM status?)

[organic farmer]

I would get the biggest system possible. There are many possible reasons that might cause you five or ten years in the future to need a larger system. But I have never heard of anyone who later decided that they wanted a smaller system.

Also get the battery option NOW. Normally grid-tied or net-metering systems are required to shut down every time the grid goes down. So when the grid goes down you are dark also. The ability to 'island' or isolate yourself from the grid is important. So when the grid goes down, there is still a possibility that you can have power during their outages.

[jplee3]

I would get the biggest system possible. There are many possible reasons that might cause you five or ten years in the future to need a larger system. But I have never heard of anyone who later decided that they wanted a smaller system.

Also get the battery option NOW. Normally grid-tied or net-metering systems are required to shut down every time the grid goes down. So when the grid goes down you are dark also. The ability to 'island' or isolate yourself from the grid is important. So when the grid goes down, there is still a possibility that you can have power during their outages.

My initial thought was to just maximize the entire roof space on one side. It would be a huge pill to swallow to complete max out our entire roof though lol...

For battery, I'm on the fence - I've heard as technology improves the cost of batteries *should* go down. I would think a major deciding factor is how many black/brown-outs we normally have around here too - we don't experience all that many but it would be nice to have that cut-over option. The battery they are selling is an Enphase Encharge 3 3.6w system and it would cost $7k. Adding the smart switch adds another $3500 so it would cost $10,500 to add that on (this is before the incentive I believe)

[organic farmer]

Solar is expensive. After spending so much money on solar, it would be humiliating to sit in the dark during the next power outage.

I live in Maine, a state that is NOT particularly known for power outages, but living here we document grid down outages at least once every month for the past 15 years. What we see on the national news makes it sound like California is notorious for their power outages.

[RichardCullip]

Bigger is better if SDG&E lets you over size by that much. You will be living with the solar system for many years to come and over sizing now will be great future proofing.

Not sure about the battery in SDG&E territory as we, here in Poway, haven't had any disruptive power outages in the 3 1/2 years I have solar. My system is over-sized right now and has allowed me to add an EV (Rav4 Prime plug-in hybrid) which I can charge at virtually no cost with the excess solar. So far in the three months I've had it my projected SDG&E bill at true-up will still be a small credit carried over into next year. Granted the credit will be a bit smaller than it would be without charging the Rav4 but I have enough solar capacity that I'm only paying for the additional NBCs from drawing from the grid during charging. I will still be a net producer of electricity come true-up time which still gives me some future flexibility.

[jplee3]

Solar is expensive. After spending so much money on solar, it would be humiliating to sit in the dark during the next power outage.

I live in Maine, a state that is NOT particularly known for power outages, but living here we document grid down outages at least once every month for the past 15 years. What we see on the national news makes it sound like California is notorious for their power outages.

Yea, I see your point. I think adding a battery on even if we were to do that next year would be reasonable though - I think the only thing we might save on doing it now is the permitting process. But this isn't one of those critical urgency types of deals either it seems. I've heard of outages being a lot more common in Northern CA. Down here, I think we've had a total of 2-3 in the past 10 months living in this house. Even before that, power outages in my general area (Orange County) were infrequent. This isn't to say they won't become more frequent in years to come...

Bigger is better if SDG&E lets you over size by that much. You will be living with the solar system for many years to come and over sizing now will be great future proofing.

Not sure about the battery in SDG&E territory as we, here in Poway, haven't had any disruptive power outages in the 3 1/2 years I have solar. My system is over-sized right now and has allowed me to add an EV (Rav4 Prime plug-in hybrid) which I can charge at virtually no cost with the excess solar. So far in the three months I've had it my projected SDG&E bill at true-up will still be a small credit carried over into next year. Granted the credit will be a bit smaller than it would be without charging the Rav4 but I have enough solar capacity that I'm only paying for the additional NBCs from drawing from the grid during charging. I will still be a net producer of electricity come true-up time which still gives me some future flexibility.

I have neighbors who have 20+ panels on their roofs. But I think some of them have pools and possibly hot tubs too. Not sure what else they'd be running that consumes so much electricity but maybe they all oversized with the same thoughts.

What is your total system size(# of panels/kw/total kwh generated) and your monthy usage, if you don't mind me asking? Just trying to get a gauge of how much over I might want to consider oversizing. I just don't want to get too carried away to the "point of diminishing returns' with this whole thing.

[peakbagger]

If you have a EV in your future go for larger system. They do slurp up the juice when recharging.

[jplee3]

If you have a EV in your future go for larger system. They do slurp up the juice when recharging.

Yep, this is what I was factoring in when upsizing from the original 6kw.


So I think we'll stick with the 19 panel plan then on the front side of the house. At this point. I think that should be pretty sufficient even long term... we have no plans to be adding a pool or hot tub which I know would be a huge source of consumption.

[RichardCullip]

...What is your total system size(# of panels/kw/total kwh generated) and your monthly usage, if you don't mind me asking? Just trying to get a gauge of how much over I might want to consider oversizing. I just don't want to get too carried away to the "point of diminishing returns' with this whole thing.

I have a modest system and modest electrical usage. My 4kW system has averaged ~7,700kWh per year and our usage has averaged 5,500kWh per year. This leaves use with a 2,200kWh per year buffer for future use. Now that I've added a Rav4 Prime I've been averaging 100kWh of charging each month. We don't drive much, less than 5,000miles per year. So far the 42mile range on a full charge in the Rav4 has covered about 90% of my driving. In the 3.5 months I've owned it I driven 1,150 miles and used a quarter of a tank of gas (say 3.5 gals). I've used 370kWh for charging. I'm happy with the results.so far.

[jplee3]

I have a modest system and modest electrical usage. My 4kW system has averaged ~7,700kWh per year and our usage has averaged 5,500kWh per year. This leaves use with a 2,200kWh per year buffer for future use. Now that I've added a Rav4 Prime I've been averaging 100kWh of charging each month. We don't drive much, less than 5,000miles per year. So far the 42mile range on a full charge in the Rav4 has covered about 90% of my driving. In the 3.5 months I've owned it I driven 1,150 miles and used a quarter of a tank of gas (say 3.5 gals). I've used 370kWh for charging. I'm happy with the results.so far.

Thanks Richard. What is your sq footage? I'm just wondering how much of a correlation there is in that sense, if any. Also, are you running your HVAC pretty regularly and if so what size HVAC system do you have??

I was just googling the "average" # of kwhs an electric oven/stove, heat pump water heater and electric dryer all end up using on an annual basis. Between the three of those it all adds up to around 2500kwh annually. If we got say a Tesla, and we put 5000miles on it (which is what we put on our Rav4) per year, I believe that translates to somewhere between 2500-3000kwh annually. So in total, we're looking at probably 5000-5500kwh of annual load usage that could be [gradually] added if/when/as we convert to electric appliances and a single EV. Right now we're at 7500kwh annually but when we get the new heat pump in that number will probably drop a good amount. Let's say it drops to 6500kwh, another 5500kwh puts us at 12000kwh. The 7.6kw system is slated to generate just over 12000kwh. So I think we may be roughly 'on target' here...

[jplee3]

I have a modest system and modest electrical usage. My 4kW system has averaged ~7,700kWh per year and our usage has averaged 5,500kWh per year. This leaves use with a 2,200kWh per year buffer for future use. Now that I've added a Rav4 Prime I've been averaging 100kWh of charging each month. We don't drive much, less than 5,000miles per year. So far the 42mile range on a full charge in the Rav4 has covered about 90% of my driving. In the 3.5 months I've owned it I driven 1,150 miles and used a quarter of a tank of gas (say 3.5 gals). I've used 370kWh for charging. I'm happy with the results.so far.

Hey Richard one other question I forgot to ask but what do you get paid per KWH that goes back onto the grid? Per the current NEM it seems to indicate 2-3 cents per KWH?

"Net Surplus Compensation and Renewable Energy Credits (RECs)


At the end of a customer's 12-month billing period, any balance of surplus electricity is trued-up at a separate fair market value, known as net surplus compensation (NSC). The NSC rate is based on a 12-month rolling average of the market rate for energy. That rate is currently approximately $0.02 to $0.03 per kWh (for up-to-date NSC data, follow these links: PG&E, SCE, SDG&E). This rate structure was established in Commission Decision (D).11-06-016 pursuant to Assembly Bill (AB) 920 (Huffman, 2009). More information on the Commission's implementation of AB 920 can be found here.

Customer-generators may also receive compensation for the renewable energy credits (RECs) associated with this excess generation. To receive compensation, a customer-generator must register their generation facility with the Western Renewable Energy Generation Information System (WREGIS) and follow the eligibility guidelines contained in the latest version of the Overall Renewable Energy Program Guidebook from the California Energy Commission."


Unless you got into an earlier NEM?

[peakbagger]

I also have a plug in Rav 4 Prime. It takes about 16KW to fully charge. I have a 2300 Kw array with a battery pack that takes about a sunny day to recharge.after charging the Prime overnight.

[jplee3]

I also have a plug in Rav 4 Prime. It takes about 16KW to fully charge. I have a 2300 Kw array with a battery pack that takes about a sunny day to recharge.after charging the Prime overnight.

Thanks. How big is your battery pack btw?

[RichardCullip]

Hey Richard one other question I forgot to ask but what do you get paid per KWH that goes back onto the grid? Per the current NEM it seems to indicate 2-3 cents per KWH?

Yes, SDG&E pays a small pittance for excess kWh at true-up. I was paid $0.4365/kWh for a grand total of $99.04 which rolled over as a credit . The price paid varies each month and is based on the true-up month. I'm on NEM2.0 as my system was install in early 2019.

[ktran1]

currently NEM2.0 in CA, peak time will be 4pm-9pm where solar does not generate enough power. If you have EV, need about 3500KWH to drive 12000 miles. You should oversize it, otherwise you will pay big time at true up, especially if you use AC during peak hours, the cost about 1.5 time off peak