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Need 13,000 kWh annually; does that mean I should get 8.39 kW in panels?
- Thread starter Grayson73
- Start date
Like many things "it depends" -
We have an 8.88 kw (dc) system that will output AC at 7.3 kw (inverter limited).
In New England we did 12,200 KW last year. On an annual basis, our monthly average is just over 1000kwh.
Our state has 100% net metering, but at the end of the month any surplus KWH are credited at the current electric rate. (to be used for future bills, can't cash it out).
That catch is when we are in inflationary times the $ value buys less electricity at that later date.
Your cost per KWH and how the utility handles your situation will dictate the best solution as far as cost/payback.
That said, more is usually better.
We have an 8.88 kw (dc) system that will output AC at 7.3 kw (inverter limited).
In New England we did 12,200 KW last year. On an annual basis, our monthly average is just over 1000kwh.
Our state has 100% net metering, but at the end of the month any surplus KWH are credited at the current electric rate. (to be used for future bills, can't cash it out).
That catch is when we are in inflationary times the $ value buys less electricity at that later date.
Your cost per KWH and how the utility handles your situation will dictate the best solution as far as cost/payback.
That said, more is usually better.
Matt-FL
Member
My suggestion is to get the most you can comfortably afford and can fit on your roof or property. While you may look back and say "I wish I had gotten more", you'll never look back and say "I wish I had gotten less".
At least in Calif, my attitude has always been get as much as your roof will support, and your utility will approve, which gives you max tax credit. Going back and adding more later is just about impossible!!!
+1 on erring on a larger system. They wear out and get dirty over time. What works this year may not a few years from now.
Also, the 8.39 kW rating is not very meaningful alone. It depends on your location and how they are configured. If they pointed them all north for example.
I have a slightly bigger 10.125 kW that was guaranteed for 14,000 kW in the 1st year and made closer to 15,000 kW in sunny California. But I also had a weird roof shape and south facing panels didn’t meet the Wife Approval Factor.
I’m adding more panels get squeak under the NEM 3.0 deadline and regretted not getting the largest setup possible. My wife is ok with southern panels, but the wiring gauge cannot handle it, so I’m SOL on that part. So, the new panels will go in other places where a new cable run is more feasible.
Also, the 8.39 kW rating is not very meaningful alone. It depends on your location and how they are configured. If they pointed them all north for example.
I have a slightly bigger 10.125 kW that was guaranteed for 14,000 kW in the 1st year and made closer to 15,000 kW in sunny California. But I also had a weird roof shape and south facing panels didn’t meet the Wife Approval Factor.
I’m adding more panels get squeak under the NEM 3.0 deadline and regretted not getting the largest setup possible. My wife is ok with southern panels, but the wiring gauge cannot handle it, so I’m SOL on that part. So, the new panels will go in other places where a new cable run is more feasible.
For an analogy, I see this question like this:
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A young couple , early 20s, newly married, is house hunting. They see a house that meets their needs, but its 2 bedroom / 1 bath. They say to each other... "Well, there is only 2 of us. We alternate working from home, but we have a bedroom for us, and a spare bedroom we can use for an office, so its exactly what we need. I know we have talked about Kids and dogs and cats, but we dont have those right now, so this is fine."
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Adding on solar is not that different from Adding on a bedroom (and / or a bathroom) to the above fictitious 2 Bedroom 1 Bath house. If the above couple asked for advice, they would probably be told "have you talked about kids? Pets? Does anyone ever come to stay with you to visit, ever? Since you are purchasing, if you can afford it, you might look for a home that meets your needs with more space than that".
Most people wouldnt advise going "house poor" for the above couple, to get more space, but if they could afford it, then they should probably plan for extra usage / expansion.
Same deal here. Its not really a good idea to try to "hit the number of current production". With housing, of course, in general terms its an appreciating asset, so you can trade up by selling your current one and buying new. Solar doesnt work that way, so its better to get as much as allowed, at least until we get penalized with taxes on production, etc.
Probably depends a lot on your electricity costs, doesn't it? Also depends on what your goals are. Some want to be able to go completely off grid ... others are just looking to maximize return on investment. Isn't the cost of solar and battery backup decreasing over time as well?
bradtem
Robocar consultant
Depends on local utility and metering rules. Many locations also have a minimum interconnect charge that may charge you for a certain amount of electricity even if you don't use it. In this case, you may want to modestly underprovision, so that you net out at least as much as what you will pay for whether you use it or not. However, the problem is that demand varies, and some times you will use more and sometimes less.
Generally, don't get a lot more than you will need unless the power company will pay you super well for that excess. Most don't want to and rules are changing so they don't have to.
The reason? Panels will get cheaper with time. If you increase your load in future, get more panels at the lower future price. Indeed, the lower future price is also with future dollars rather than present dollars. Your spreadsheet (and you need one) will tell you how much. You may want to leave upgrade capacity in your inverter, which may not be that expensive, but you can also upgrade with micro-inverters if your wiring is set for that.
Don't get extra if you don't have a good south or southwest sloped roof to put it on.
Generally, don't get a lot more than you will need unless the power company will pay you super well for that excess. Most don't want to and rules are changing so they don't have to.
The reason? Panels will get cheaper with time. If you increase your load in future, get more panels at the lower future price. Indeed, the lower future price is also with future dollars rather than present dollars. Your spreadsheet (and you need one) will tell you how much. You may want to leave upgrade capacity in your inverter, which may not be that expensive, but you can also upgrade with micro-inverters if your wiring is set for that.
Don't get extra if you don't have a good south or southwest sloped roof to put it on.
That sounds great... if you could just "add panels" but you cant. No one is simply adding panels onto an existing install, they are installing all new systems, with the prerequisite costs. If you are DIYing it, thats great advice. Otherwise, recommending someone can just "add panels" later does not match the experience anyone has had. No company is adding onto another companies existing install, and in fact even the company that did it does not want to do that, as more than 10% requires all new permits, etc.
bradtem
Robocar consultant
It is much harder than it should be. It's easier with microinverter systems which in theory you should just be able to mount and connect if the wiring is adequate. And the permitting system definitely creates more pains than it should. Which is why today people write as they do above, because the panels are now a minority portion of the cost of a solar system. You could design a system so that all that's needed is to mount and plug in new panels, and do that if you felt you might expand your system in future.
One problem with people getting systems that are too large is the utilities complain they were not designed to receive this much power from customers. Ideally this is all going to get easier in the future. Panels will get cheaper. Inverters will get cheaper. Grid intertie will improve (at least in some areas.) Permits and inspecitions, we can dream, will get streamlined.
In Europe, they allow plug-in solar panels. In the USA that's not allowed. The reason is that you can set it up so that more current can flow on wires than they can handle, but not through the breaker (because it flows from the panel to a load on the same circuit.) In the future, we could see smarter designs for such systems so they can't overload, and that could make it a lot easier to add capacity as needed.
Thanks for the replies. What I've read agrees with what you are saying; order as much as I can afford now (panels and powerwalls) because it costs more to add them later.
Or even at all at any price, code changes, installers change
CrazyRabbit
Active Member
PVWatts
Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations
I would probably add 10% to that for aging and probably more for expected usage changes.
My project in south bay area just finished the initial design phase. It's 8.1kW, 11,254kWh/year, 30.8kWh/day, 3.8 peak hours/day. The panels are 10 south-southeast facing, 2 east-northeast facing, 8 north-northwest facing. I think the facing makes my peak hours even lower. The size is smaller than I expected, but the shape of my roof just doesn't allow more solar panels. It has too many small faces and structures.
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TomServo
Active Member
My experience in southern IL was every proposal I was presented after the initial interview was for a system scaled to cover about 85% of my annual consumption of 11,600 kWh. I had to keep pushing. I finally wound up with 31 405-watt panels rated under STC to produce 12.5 kWh or about 15,000 kWh/hear - 8 East and 23 West. I oversized to accommodate adding batteries next year and to account for system degradation and bad weather here in Illinois. After 7 days I’m on tract to meet the 15K estimate. But winter is approaching and will probably see a 30% to 40% reduction in generation. So it will take a year to see net results.
So my advice would be to install as much as you can afford and fit. Good luck.
So my advice would be to install as much as you can afford and fit. Good luck.
Puma2020
Member
From my experience in southern NH, I would agree with the recommendations of getting what you can afford. Things change and you don't know what your future power needs will be. For myself, I got an EV (Y), several years after I got solar. However the EV actually doesn't dramatically increase you energy consumption based on my "average" usage. I did dramatically add to the house load by switching to a heat pump last year. Didn't plan for that, but the resulting drop in the fossil fuel furnace use (and resulting pollution) saved me money over the year. It also meant I sold less back to the grid, which I am fine with that trade off.
As I have a 8.16 kWh solar system and I have been collecting the data for about 6 years now, I thought I would provide it to help you with your decision.
Solar is very variable. Your latitude, the pitch of the panels, weather, clouds, smoke from wildfires thousands of miles away, length of the day, dust and temperature all will factor into how much energy the panels produce. For example, my best day ever (after 6 years) was May 13, 2020 with 67.34 kWh produced. My worst day(s) was 0.00 kWh due to snow storms. If it snows at night, and the next day is sunny, usually the panels will avalanche about 10 AM. That is another thing to think about, when the snow falls off, it's an avalanche and you don't want a car or pet to be underneath of that. It will NOT be next to the house but about 3 or 4 feet from the roof edge. If it snows enough during the day that the panels stay covered, that is when I might get zero. I have also never washed my panels nor snow cleared my panels. The amount of money the tools would cost to do a decent job is higher than the slight increase in energy I would produce.
Here is my monthly values so far
You'll notice that June, 2023 was the worst June ever as we had only 8 days without rain, but May (almost no rain) was the best!
July 2021, was also a highly unusual rainy month (top 3).
It's solar, it's variable and be happy
May 2023 looked like this (what a great month looks like)
June (with the longest days) showed:
By comparison, an "average" December (shortest days) looks like
With apologies to John Denver, I will occasionally sing
Sunshine on my panels makes me happy
Sunshine behind the clouds can make me cry
Sunshine on my panels looks so lovely...
As I have a 8.16 kWh solar system and I have been collecting the data for about 6 years now, I thought I would provide it to help you with your decision.
Solar is very variable. Your latitude, the pitch of the panels, weather, clouds, smoke from wildfires thousands of miles away, length of the day, dust and temperature all will factor into how much energy the panels produce. For example, my best day ever (after 6 years) was May 13, 2020 with 67.34 kWh produced. My worst day(s) was 0.00 kWh due to snow storms. If it snows at night, and the next day is sunny, usually the panels will avalanche about 10 AM. That is another thing to think about, when the snow falls off, it's an avalanche and you don't want a car or pet to be underneath of that. It will NOT be next to the house but about 3 or 4 feet from the roof edge. If it snows enough during the day that the panels stay covered, that is when I might get zero. I have also never washed my panels nor snow cleared my panels. The amount of money the tools would cost to do a decent job is higher than the slight increase in energy I would produce.
Here is my monthly values so far
You'll notice that June, 2023 was the worst June ever as we had only 8 days without rain, but May (almost no rain) was the best!
July 2021, was also a highly unusual rainy month (top 3).
It's solar, it's variable and be happy
May 2023 looked like this (what a great month looks like)
June (with the longest days) showed:
By comparison, an "average" December (shortest days) looks like
With apologies to John Denver, I will occasionally sing
Sunshine on my panels makes me happy
Sunshine behind the clouds can make me cry
Sunshine on my panels looks so lovely...
