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Is my solar panel system too big?

Fairly new to this. Just passed inspection and currently waiting for PTO. I was looking through my past year energy usage and looks like I used about 6,800 kwh annually. Tesla recommended a 5.78 kw system for my house and according to Tesla, this system should produce about 9,600 kwh annually. Is this too much for what I need? I’m thinking I could of gone with a smaller system and still would of been okay?
 

jboy210

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Dec 2, 2016
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Northern California
Much of the cost of the system is fixed so reducing size may not reduce the cost that much. Also, summer weather is getting hotter and longer. So the amount of electricity we use for A/C today will likely rise in the future. Additionally, power rates will continue to rise, so the less power you can consume the better.
 

Ampster

Active Member
Supporting Member
I agree with @jboy210. It also depends on the rate trends and how much of a hedge against erosion of NEM benefits you want. Are you with SCE? The economic benefit of overproducing may not be much but the ability to service future needs may be priceless. My next conservation investment will be replacing my natural gas fired furnace with a heat pump that will change my consumption patterns. The A/C portion may become more efficient but the higher winter electric for heat pump will be offset by reduced natural gas consumption.
 
I agree with @jboy210. It also depends on the rate trends and how much of a hedge against erosion of NEM benefits you want. Are you with SCE? The economic benefit of overproducing may not be much but the ability to service future needs may be priceless. My next conservation investment will be replacing my natural gas fired furnace with a heat pump that will change my consumption patterns. The A/C portion may become more efficient but the higher winter electric for heat pump will be offset by reduced natural gas consumption.

yes I am with SCE.
 
If your power company approves this oversize, take it. PG&E would not as they limit to 110% of previous usage.
And, if you have battery backup, it should las mush longer in an outage if weather conditions during outage allows, sun.:)

PG&E approves applications that exceed 110% if you say that you planning on increasing your usage.
 
Much of the cost of the system is fixed so reducing size may not reduce the cost that much. Also, summer weather is getting hotter and longer. So the amount of electricity we use for A/C today will likely rise in the future. Additionally, power rates will continue to rise, so the less power you can consume the better.
yes, this ^^^. And to add that over the years, the output from your system will gradually reduce. After 10 ten years, you might see a 8-10 % loss depending on your type and brand of modules.
 
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definitely "oversize" .. i went conservative and i'm already going to be ordering another powerwall and more panels moment PTO approved .. much more economical to get all 1st time or "oversize" .. not to mention hassle going thru inspection / another PTO (i assume ?) / possible more strict system size limits from elect utility etc etc
much rather be in your position :)
 
OP, you are on SCE, you need to produce more than you use to get not get charged too much. The reason is that the solar generation period is during the day until about 4pm and you get paid the lowest rate ($0.26 to $0.27/kWh) by SCE. When you have to use the energy after 4pm (no more solar generation), you have to pay the highest rate ($0.37 to $0.43/kWh) unless you have powerwall or battery.

So you will need to over produce by about twice the energy you needed for evening prime time usage (lights, TVs, electric oven, etc...) from 4pm to 9pm to get the lowest bill possible.

(4pm - 9pm) energy usage x 2 + (rest of the time) energy usage = your solar generation if you want the lowest bill possible.
 
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OP, you are on SCE, you need to produce more than you use to get not get charged too much. The reason is that the solar generation period is during the day until about 4pm and you get paid the lowest rate ($0.26 to $0.27/kWh) by SCE. When you have to use the energy after 4pm (no more solar generation), you have to pay the highest rate ($0.37 to $0.43/kWh) unless you have powerwall or battery.

So you will need to over produce by about twice the energy you needed for evening prime time usage (lights, TVs, electric oven, etc...) from 4pm to 9pm to get the lowest bill possible.

(4pm - 9pm) energy usage x 2 + (rest of the time) energy usage = your solar generation if you want the lowest bill possible.

I do not have battery or powerwall.

Has anyone been able to generate enough energy to cover the the electricity bill?
 
Believe that people with excess generation tend to use it. They keep the AC/Heat at more comfortable levels, leave on lights for ambience and tend to obsess less about their electric bills.

If something is "free" people tend to use more of it.
yup, we do that on occasion (more AC, but NOT more heat). Electricity isn't that expensive up here anyway.
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
7,278
4,943
Northern California
I do not have battery or powerwall.

Has anyone been able to generate enough energy to cover the the electricity bill?

Our 12.75 kW system will generate between 2-10 kW from 7AM to 6 PM in June. Our house uses approximately 1-8 kWh during those hours. In addition to the solar, we also have Powerwalls that picks up the load when the solar drops to cover the evening and overnight. Our June electric bill dropped from $500 to $50.
 

Ampster

Active Member
Supporting Member
PG&E would not as they limit to 110% of previous usage.
I installed solar on a newly purchased home so there was no history. I told the installer what size system I wanted and that I would be charging two EVs. I had already applied for the EV rate so PG&E already had that documentation. I also explained that I was replacing the existing gas fired water heater and installing an electric dryer. I got the system size I wanted but too late I realized that the the DC to AC ratio was 1.5 to 1. I don't know if that was a constraint imposed by PG&E, but the system has performed well with respect to pvwatts model and installer guaranty.
 
I do not have battery or powerwall.

Has anyone been able to generate enough energy to cover the the electricity bill?

Currently you can't generate enough to cover all your monthly charges as you have to pay about $0.02 to $0.03/kWh for non-bypassable charges. So you will probably pay about $13 to $20 a month even if you over produce. At the end of 12 months, you get a check back for over production at about $0.03/kWh.
 

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