Its expensive. I could use some help on my estimates. I have a 1400 sqft house. Currently I have a 7kw solar system built in 2014 and my power bill last year was $1040 for the whole year current usage estimate of around 4000kw + my solar loan of $250 a month ($4040). I am NEM1 California so I am grandfathered in for another 16 years to stick with the tiered plan which means whatever power I produce I either use or get a 1:1 credit for. Tier 1 is $.27 per kw Tier2 is $.47 summer $.23 / .40 winter. Baseline limit is pretty low but the idea is that I want to stay in tier 1. This year I added a chevy volt at the end of march. It gets me roughly 40 miles a day on electric off it's 10kw battery (it's actually 16.5 kWh lithium-ion but I believe only 10.4 or so is usable?). My Commute is 82 miles. Efficiencies aside I would need twice that much power to get to work and back in all electric. So I am estimating 25kw of power a day for my commute. Or using tesla math 70kw/310 = x/82 = 18.5 kw to commute to work and back assuming I'm not using heater or AC driving 50 or what have you. I think 25kw is a better number to use. So thats 261 days a year. = 6525kw for cummuting. + 104 Weekends and I will assume I drive 1/2 as much (I probably really drive more but whatever). so 13kw*104 = 1352kw Total estimated usage is (7877kw) per year. Round this up to 8000kw. Solar company is suggesting I add 4.6kw system which for me should produce around 5,756kw (seems lower than I need so I will follow up with them). Current electric bill cost is estimated to be $80 a month and cost after adding the system will be $11 but cost of adding the system will be $93 $93-11 = $82 for the loan, which includes my tax credit paid into the loan. So it's more expensive to add more solar than to just pay my electric bill. However once I add in the model 3, that will be another 8000kw per year in power, most of which will be at a tier 2 rate. Or the cost of $.40 (using winter rate since some will still be in tier 1) = $3200 per year say $3000 for estimation purposes + the $1040 I already pay so $4040 a year for power for the tesla (yes this is more than gas). Where as if I add the system it will compensate for the car. So my cost would be around the same as now maybe $1200 per year for power (it will go up a bit) and $1116 for the loan. or $2316. I'd save around $1700 - $1800 per year if I add solar? Now there's TONS of estimation and rounding here but the whole situation is VERY hard to be accurate about. WAY too many variables. This is assuming I put more panels up without permits to stay in NEM1. If I go to NEM2 and have to pay TOU, my system would be undersized and I would end up paying more money. I don't even know how to calculate switching to TOU as it just introduces a gazillion more variables.