Help Reviewing Energy Audit & System Sizing Calculator


New Member
I just completed my first energy audit and am trying to figure out the proper system size. Here is a screenshot of the calculations:

Screen Shot 2021-09-11 at 10.19.32 PM.png

I have three primary goals: (1) to offset grid cost (2) to slowly become more self-reliant and (3) to create a backup solar generator in the event of a power outage.

The items that I've chosen in the energy audit above represent the most important items to keep running in the event of a power outage.

What I'm hoping is that someone might be able to help let me know if I've done this correctly. I was quite surprised by the cost as well as the number of years it will take to break even. I fully admit that I may have missed something in all these calculations.

I chose the insolation # of 2.29 because that's the absolute worst for my area (of NE Ohio). If I am going to run the heater in the winter, I need it to work during the worst time for solar. Even so, 32 panels at 440 watts each seems a little excessive to me for just a couple of appliances.

I have a smart thermostat that tracks heater usage. The coldest month last year (February) averaged almost 10 hours per day. I cheated on this number just a bit and bumped it down to 7 hours per day. I figured I could use grid power if absolutely necessary. Otherwise, in a power outage, I can justify keeping it a bit colder in the house.

Power in my town is $0.10 per kWh. I know that's cheap, and that this affects the payback period. Even so...44 years seems incredibly unreasonable. Even if I paid twice that amount it's still 22 years. By that time batteries may need to be replaced anyway, so I don't see any scenario where this is going to be a wise decision from an economic standpoint.

I am still willing to move forward if I can't accomplish my first goal of offsetting grid cost. Even if it doesn't pay for itself, I still accomplish the goal of achieving more self-reliance and having backup power. That's valuable to me.

But I still think this should be cheaper than it's looking like it will be. Did I make an error in my calculations? What variables should I change or sacrifice to get the cost down?



Participation Medalist
Even so, 32 panels at 440 watts each seems a little excessive to me for just a couple of appliances.
Heating and air conditioning are huge energy users. Its easier to find alternatives to electricity for heating than A/C.

Its pretty hard to save money with solar. You can offset big electricity bills but the upfront cost and the number of years to break even makes it hard to be financially a sound investment. You get tax credits (30%?) and can buy big cheap panels on craigslist and Santan Solar and other places that have great prices but its still a big cost up front.

Power in my town is $0.10 per kWh
I am not familiar with the exact numbers but solar in general and in sunny areas is usually much more expensive than this.
In California it about triple that. We have lots of blackouts from our power company and politicians so aside from cost, self sufficiency is a major factor.

And great job with taking the time and effort to do the energy audit. You are miles ahead of most who show up here with that alone.