You can't really power anything with one panel, you can't even generally use one panel in terms of a residential scale. Your typical grid-tied inverter will run anywhere from $1500-$3000 and there's string sizing the you must abide by. Also the smaller the system, the higher the cost is per watt(solar is priced per watt the same as gas is priced per gallon, note that watt is a physical measure...ie....panel is 230 watts, but will produce more kilowatt hours than 230). Realistically, unless you're in an area like in California were electricity is priced on tiers and going from one tier to another can result in much higher cost of electricity...for example Tier A charges you $0.012 for the first 1000 kilowatt hours, Tier B charges you $0.018 for the next 1000 and Tier C charges you $0.035 for the 1000 after that(in which case it makes a hell of a lot of sense to avoid Tier C, where a small system can really help), then I wouldn't go any lower than a 4-5 kilowatt system.
If you buy the system, you can expand on it later and add more panels down the road assuming that the inverter will handle the additional panels(or if you have micro-inverters, adding one for every panel). If you go through a lease, you can't expand on the system but you will typically pay less for a prepaid lease with some additional benefits.
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