Hello, I'm remodeling a home and have received two proposals for a rooftop pv system. Having never lived in the home, and likewise having rented for the last ten years with my utilities covered by the landlord, I don't have a good reference point to provide for my normal usage of electricity. Both estimators assured me they could estimate based on the information provided below: The house is 1300 sq-ft, with a 300 sq-ft attached woodshop (which will be used 4-5 days a week). There is no AC system or hot tub. The house is being rewired entirely and the lighting will be LED. The domestic hot water and radiant heat boiler system will be supplied with gas, as will the stove. The dryer is electric, but there is access to gas should a replacement be needed. Only two people will be living in the house for now, both of us fairly conscientious of usage. Given that info we received two fairly different estimates for usage: one design is for a 2.78kw system providing 4,600kwh of annual production. This is Sunpower (with all panels having microinverters). The second design is for 4.3kw system providing 7,700kwh of annual production. This would be with LG 360w panels and an SMA inverter. The Sunpower system is less $, given that it's smaller. What I wonder is if it will be enough. I'm tempted to go somewhere in the middle by asking Sunpower to add a few more panels, bringing it to 3.5kw or so...which I think would raise the price up somewhere close to the other, still-larger system. Overall it seems like the LG panels might be more efficient in terms of production? But the warranty is better for Sunpower, esp. when taking the lack of inverter into account. And (according to Sunpower) their panels have a lower rate of failure and don't lose as much production power each year as their competitors. The system will be grid-tied to PNM, and the arrangement with the utility is that all excess generated power is banked indefinitely, meaning if we got an electric car in a few years we could draw on anything built up now. All thoughts much appreciated!!!

Unless you don't drive very much a single EV would use ALL of the annual output of the smaller array. You should probably be looking at something like a 6-8kw array (assuming it even fits on the house) if there's an electric car in your future that you plan to charge up mostly at home.

Maybe this might help bound things a bit. I have a system a little shy of 6.0 kW. There are just two of us in a 2,100 sf house. We are conscientious about consumption but do need to run AC in the summer months (we are in Boise, ID); heating is gas.

The system has provided all of our energy and has provided us with 3,800 KW/h in the Idaho Power "bank". This is over the course of 18 months. I would suspect that running a wood shop would consume a good deal of your total power depending on how many hours you use it and the size of your equipment. My best suggestion is to live in the house for a few months and look at your consumption. That would give you a bit of a baseline that you could tweak for months that would typically be more/less based on weather/sun exposure etc. You might also ask the previous owner to supply you with their yearly consumption records.

We also hope to have an all electric auto some day and purposely oversized our array by 10% of the suppliers estimate. Hope this helps.