I keep seeing posts on the NextDoor site about how one should go solar and “eliminate your electric bill” and while I realize that claim is complete BS based on our history with having panels on our RV…but I wanted to get a post up on the web so that I can refer anyone that asks to actual numbers. I based this post on some calculations Neil did…and in the interests of giving solar the greatest amount of benefit of the doubt he really was fairly generous his assumptions.

And granted…he’s a mechanical and not electrical engineer…but they learn electrical stuff as well…and in addition, all of this pretty simple math anyway, While we don’t and won’t have solar at home…we did have it in the RV days and you can make it work but it’s clearly not the same as being able to flip the switch to on for whatever you want whenever you want it.

So…let’s dive in.

For purposes of this…I’m using 200 watt rated solar panels which cost about 220 each from Amazon and they’re 56×26 inches in size or about 10 square feet each. Our neighbor has this type of panel on their roof and there are 14 of them if he counted correctly…but I went ahead and assumed an installation size of 30 panels or 300 square feet.

So…a 200 watt panel doesn’t actually produce 200 watts except under specific conditions…the biggest two are at a temperature of about 75 degrees and perpendicular to the sun rays…and since panels on your roof don’t move and are rarely at 75 even in winter in FL…at best you get about 60% of rated output or 120 watts. And in Florida you only get about 6 hours per day of maximum 120 watt output and perhaps another 5 at half output so each panel ends up providing about 1000 watt hour or 1 KWH per day…so with 30 panels you produce 30KWH/day.

Our house only uses A/C bout 5 months per year and the other 7 we are mostly open window people…and in 2023 we used about 13,000 KWH or 36 KWH per day at an average monthly cost of $160. So…even with the generous 30 panels you aren’t producing enough to cover the 36KWH per day needed and realistically most houses run the A/C unit a lot more down here than we do.

Can you run an A/C unit on solar with no grid? Well…your panels produce about 3,600 watts peak in the summer time…and by the time you factor in losses in the wiring from the panels to the inverter and the efficiency of the inverter you get about 3,200 watts AC or about 26 amps. Your typical 5 ton A/C unit takes 9KW to start (75 amps) and 6KW running (50 amps)…so no, you can’t run A/C on 30 solar panels even ignoring the other loads in your house (water heater, stove, lights, computers, etc). And realistically most houses down here have more than a 5 ton A/C unit   

Those 30 panels cost about 6,600 plus the inverter, wiring, and installation. I don’t have any quotes for installation but based on our cost of about $5,500 back in 2013 to put 8 panels on our RV (which is essentially the same as putting them on the roof and we already had the inverter and wiring from the roof and the inverter from the RV build), it would cost about 5 times as much and that’s around $33,000 in 2013 dollars and I’m sure it costs more now. A quick loan amortization calculation for 20 years on 33,000 loan at 6.25% which is what it is in January 2024 puts the payment at about $241 a month which you’ll note is more than the $162 our household electrical bill is. And that doesn’t include the fact that your 30 panels barely cover the total annual usage, the lower rate the power company pays you for power fed back to the grid vs the power flowing to your house…and the fact that you’re still going to be pulling power from the grid all day long in the summer to run the A/C anyway.

He even went so far as to give you another 25% of actual power output over his already pretty reasonable assumptions above and it’s still cheaper net to pay the electrical bill…and you’re not really off grid anyway.

In fairness though…if you don’t need A/C at all…and if you’re careful about managing power and all that……and if you have mostly 12 volt lighting for efficiency…and if you have a bunch of expensive, heavy batteries…you can produce enough to live off grid…it is doable but it isn’t easy and there are certainly drawbacks to trying to do so, especially with a house that was not built with an electrical system designed to subsist on solar alone.

So…that’s it. As we used to say in the RV days…solar is a lifestyle thing, not a fiscally responsible thing. In an RV it allows you to park off grid in the plains or desert and mostly subsist on solar with some generator usage…but again an RV is designed to run with a generator and unless you have a whole house generator and a bunch of expensive switchgear that most houses don’t have then adding in generator power at home isn’t all that simple either. 

Cyas.