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CA Solar Use Falling Because of Economics
mdsolar writes "The LA Time reports that California is seeing a big drop off in rebate applications for solar power systems. It seems that to get a rebate you have to also switch to a time of use rate with your utility. The math is not working out, especially for smaller systems that don't fully cover use during peak hours. The result: homeowners are reluctant to go with solar energy. 'The difference between peak and off-peak rates is particularly large in the 11 counties of Central, coastal and Southern California, where Edison provides electricity service to 13 million customers. Edison charges summer time-of-use rates that range from 29.7 to 35.9 cents per kilowatt-hour between 10 a.m. and 6 p.m. on weekdays. It drops to a range of 16.3 to 18.6 cents per kilowatt-hour from 10 p.m. to 6 a.m. weekdays and all weekend days and holidays, according to documents filed with the PUC.' There is likely an optimal system size that reduces consumer costs, but with things in flux you'd want some flexibility in your system."
Off-peak here is 11 hours per day, so I'd need to sustain something like 1kW (at a guess) 13 hours - let's call it 15 for a bit of slack. No, sod it, let's go for a full 24-hour supply at an average of 1kW (I don't have a lot of heavy electrical appliances that run during the day). So that's 24kW/h - and I suspect I'm guessing high there.
Right, let's consider our power delivery system. Forget 12v, to reduce the current draw I'm going to use 24v electrics. This page has a range of 24v to 240v inverters. They run at around 90% efficiency (inverters are very good these days). Lets assume a full load draw of 50A - that's 1200Ah. LED lighting tends to be easier to get in 12V form, with GX53-type replacements being cheap and easy to get. They put out about the same light as a halogen lamp (maybe a little less) for an input power of less than 2W. At most they're going to pull down maybe 15A for a houseful. Let's for argument's sake say it's 10W, because that gives us a total load on the batteries of 60A. We'll split the lights across the batteries to even the load.
Still with me? Good. We have a total power requirement of 60A at 24v, for 24 hours. This is 1440Ah (it's also 1440kW/h, but that's just co-incidence. 24 volts, 24 hours). Let's go look at batteries.
A quick Google suggests the Elecsol 125 batteries might be the way to go - they're relatively cheap, small enough to be handled by one man (28kg - they're not light!) and not too expensive (a little below the £1/Ah price point). With 125Ah capacity, we'll need 24 to cover our day's requirements.
These are 34x17x24cm, and this is where my crappy arithmetic and geometry fails me. I could arrange them on a special stand about 102x68x80cm, or very roughly the size of a small chest freezer. You'd need a bit more room for the services board, and some switchgear, the inverter and the regulator. You'd still easily fit it in your garage, though.