I'm trying to figure out what I should look at in the way of a home solar system, in anticipation of my Nissan Leaf. I seem to have a choice between trying to cover the entire household use, including the car, or part thereof. We use between 15kwh and 19kwh in the house daily, depending on season, for between 400kwh and 550kwh monthly (or ~6000kwh a year). The car will need ~16kwh per work day for just under ~300kwh a month (or ~3,300kwh a year). We live in LA, so generally have sun for 9 hours a day in winter and 14 hours a day in summer, and we also have plenty of south facing roof. I have to try and offset cost against return and can't be spending ~$40k on a system, but would be willing to go ~$20k net after incentives. Kyocera has a website with a cool calculator, but I am a little confused about some of the numbers. Their biggest residential system is supposedly 5kwh. But the calculator talks about watts-dc, and indicates that I need a 7000 watt-dc system to cover me for 9900kwh of production a year. Where does this watt-dc figure come from and how does it relate to the 5kwh system they offer? Is it also sensible to try and produce too much? I'm not yet sure if my utility (SCE) allows for negative billing over the course of a year. Your input welcomed!
First try here: http:Launching the PVWatts v.2 Internet Map Server Application You can plug in your exact location and parameters and get a pretty good handle on what to expect with any given array. Next, I would read here:Grid Tie and Grid Interactive Systems - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun These guys have forgotten more about PV than most of us will know. My biggest suggestion is to get as well educated as you can, do all the conservation you can, as every dollar spent on conservation saves ~$10 in PV costs, and avoid the ready, fire, aim, syndrome. Just to answer a couple of your questions. PV systems are rated in DC watts. There is a conversion factor to allow for system loses to get AC rated numbers,, typically ~75% depending on circumstances. As for generating more than your annual loads. To some extent that will depend on your local utility and it's net metering program. Here is a simple Pv watts calc for a 4 kw system in LA. http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi 4 kw system should net ~ $734 worth of power. At todays install prices a 4 kw system might run $8/watt or $32k,,before rebates and tax credits. Good luck and keep in touch.
Icarus' reply contains some good advice and references. I just went through the process you are going through. I elected to go with a 3kw system and it will be installed next month. The size of the system is mostly dependent on what your budget is and what your power generation goal is, either in kwH or percent of power you use. An additional factor is how good your site is - orientation towards the south and presence of trees/buildings that cause shading. If not perfectly south facing, then you will either not get as many good hours per day or the arrays will not have a good angle to the sun and you will generate less than the panel's nominal wattage rating. In terms of hours per day, there is a normalized metric, called "solar hours" that is used. In other words, your description of "9 hours a day in the winter" should be more properly mapped to solar hours, to calculate your actual power generation potential. In my area, we get 4.5 solar hours per day. SoCal gets 5.5 solar hours per day. As Icarus points out, there is a loss due to the DC to AC conversion. He said 25%, my installer says 20%. This likely is dependent on the inverter you use; I am using EnPhase micro- inverters. Thus, to calculate your power generation potential, you use the following formula: (rated PV array capacity in DC watts) times (80% efficiency) times (solar hours per day) times (factor for less-than-perfect orientation/shade) So for me: 3.0 kw * 80% * 4.5 solar hours/days = 10.8 kwH/day My installer estimates I may take a 10% hit due to an imperfect roof orientation, so my likely number is closer to 10 kwH/day. [By the way, PVWatts does a more precise calculation of the above.] My goal was to retire 25% of my average daily usage. Looking at two years' data from my utility company, I determined that I use 36kwH per day, thus anything greater than 9kwH per day capacity would meet my goal. Now for the cost part of the equation... In my area, the going rate for a full installation is $6-8 per watt. That would put my 3kw PV array in the $20K range. From this one subtracts any/all of the following incentives: 1. State or Utility Company rebate ($2/watt for me). 2. Federal Government 30% tax credit, applies to balance *after* rebate. Remember though that you won't get this money until NEXT YEAR. 3. Credit for Solar Renewable Energy Credits (SRECs); a fixed amount of money, varies by state, for each MW generated. NJ residents have probably the highest SREC payment, ~$500/SREC, and they pay you there for 15 years. In my state, it is zero, but there is a proposal to pay $350 per SREC for 10 years. Note that SREC money is considered ordinary income and hence is taxable. In my case, the first two incentives cover 51% of my total capital cost.
Good information so far - some additional SoCal specific information: At a minimum with tiered pricing, you want to aim to eliminate all your over-baseline usage. This is probably anything more than 300 kWh/month or so. Depending on whether or not you get a special EV charging rate, that could mean just 150kWh - 450kWh/month as a minimum target (~2000-5000 kWh/year) - or if you are aiming to offset most of your usage, that would mean 6000-9000 kWh/year depending on your target. Based on your budget and usage, something around a 5 kW system should generate around 6500 kWh/year assuming minimal shade and a roof that is fairly close to facing south. A system like that should cost between $30-$40k before any rebates. It looks like any new applications for SCE will be in the 5th year, or $1.55 CEC-AC (not DC) watt. The CSI rebate calculator lets you plug in specific components and panel mounting to estimate yearly system output and your CSI rebate amount. It simply uses PVwatts behind the scense (which icarus) linked to earlier. I would be sure to get at least a couple quotes from a couple reputable companies. Ask them about their warranty and what it includes. Ask to see some references so you can see their work. Also, there is a solar group buy organization called 1BOG. They basically pre-negotiate pricing with a single company in exchange for finding a lot of highly interested potential customers. You should still get quotes from other companies (and they recommend you do, too) even if you use them.
