I have solar panels(5KW) on my roof in Redwood City(they cut my electric bill from $4000/y to $800/year). Solar is not cost effective if you currently use less than $250/m($3000/y) for electrical only(not including gas). The min. PGE charge is $.11/kwh for the first 300kwh/month. Their charges for the higher tier usage go up to $.55/kwh( and are increasing at 8%/year). People that use lots of power(mainly homes over 2500sf) will use a lot of juice at the higher rates and will save the most money. I recommend REC solar, but get at least 3 bids. I hear a 5kw system now costs $16,000 after all the incentives and tax credits. If you donâ€™t want to buy you can "lease" a system and give most of the savings to the solar generating company.
Solar only works cost effectively for a few houses. The most efficient house will have a SSW orientation of at least 400 sf of available roof. The ideal roof pitch is 4:12. The Solar people will give you the estimated efficiency of your system in their computer generated bids. My roof is almost ideal and gets about 95% of the power of a perfect orientation. If your layout ends up with only a 50% efficiency then obviously youâ€™ll have to pay double to get the same power as a perfect roof orientation. If you have a flat roof the panels can be put on frames in the right orientation. Donâ€™t install solar over a tile roofâ€“it will leak. Donâ€™t put solar on any roof more than 5 years old(you want the roof to last longer than the solar panels-25 years or more). Solar roof shingles are an attractive alternate to panels but cost more and are less efficient.
The big problem in SF is fog. When the clouds come over my house, whether it if fog, high overcast or rain clouds. My system will go from generating 3900 watts down to less than 1200 watts. Basically fog will knock down the power generation by 75%. Also in the winter youâ€™ll get about one half the daily power output as in the summer(figure16 of sun hrs vs 8.)
A 5kw system like mine only puts out about 4kw of actual usable power(because of line loss, panel inefficiency, inverter conversion loss) for a perfect roof orientation at the perfect time of day(10-2pm). The best my system ever yields is 3.9KW.
If you really want solar buy the right house orientation, or one with a flat roof, have REC solar give you an estimate on performance rating during due diligence and get an accurate estimate of number of foggy, rainy or overcast days(the Solar companies estimates may be wrong because SF micro-climates are hard to figure.)