The direction your roof (the one with solar panels) face is called its azimuth. You get the best performance when panels face south, but they are very effective facing east or west as well (or anywhere in between).

The tilt is the the angle of you roof off horizontal. The California Solar Initiative Rebate system is set up to favor a tilt of about 17°. This angle provides the greatest production in the summer months and helps meet the regions peak demand during hot days with a lot of air conditioners running. Coincidentally, most houses have a tilt of near 17° so panels matching this slope work very well and provide for a ore pleasing aesthetic. If you have a flat roof, the solar panels will be placed on a frame that will hold the panels at about 17°. You could place them flat on your roof and they would still work pretty well. However, you want some tilt to dust doesn’t build up and reduce their performance.

Ok this section may make you eyes glaze over a little, but to be able to compare proposals from different installers and to understand how the CSI rebate is calculated, you need to know a little about how PV systems are rated. Take a deep breath, keep calm, and read slowly. There may be a quiz afterwards.

The first rating is called DC-STC which stands for Direct Current - Standard Test Conditions. This is also referred to as the nameplate rating. This measures how many watts of direct current are generated under lab test conditions. Solar panels usually give DC-STC rating in there model number. It will be something like XYZ180, and would have a DC-STC rating of 180 watts. Multiply the panel rating times the number of panels and you get your system DC-STC Rating. This is important because DC-STC is used by the PVWatts Calculator to predict how much electricity your system will produce in a given day, month, or year.

The next rating you need to know is DC-PTC which stand for DC-PVUSA Test Conditions. This is a test by an independent lab and predicts performance in conditions closer to real life. The DC-PTC rating is always lower than the DC-STC rating. This is important because this is used to calculate the CEC -AC rating.

The CEC-AC rating starts with the DC-PTC rating, corrects this for azimuth and tilt, and multiplies this by the inverter efficiency. This gives a reasonable way to compare a PV systems capability to produce the alternating current we use in our homes. This is important because your CSI rebate is calculated based on the CEC-AC rating of your system.

Ok, this brings us to one last rating, the AC rating. In addition to inverter efficiency, there are other losses in converting the potential direct current produced by the solar panels to the alternating current we use in our homes. This includes things like wiring losses, dust on the solar panels, and manufacturing tolerances. Estimates are made of all the losses in the system to determine a DC-to-AC Derate Factor. Multiplying the DC-STC rating by the derate factor gives you the AC rating. This is important because this is what is actually used to predict how much usable electricity PV system will produce.

Ok you made it through. You did so well, we won’t have a quiz.

With the information you now know, you can go to the PVWatts calculator and calculate how much electricity your PV system will produce on a monthly bases. Simply plug in your location, the PV system DC-STC rating, the azimuth, and the tilt and it will calculate how much usable AC electricity your PV system will produce on a monthly basis. This is the standard in the industry and is used by the California Solar Initiative for its performance calculations.The UCAN PV Calculator uses PVWATTS as the basis for its performance calculations.

For SDG&E customers the California Center for Sustainable Energy (CCSE) is the program administrator for the California Solar Initiative. All the paperwork for your rebate goes through the CCSE. They also offer a number of workshops and seminars for homeowners and installers. There are other programs, including a solar water heater program, that are manages through their offices. Check out their website at www.sdenergy.com.

The California Solar Initiative (CSI), also known as the Millions Solar Roofs program, has a overall goal to help create a self sustaining solar photovoltaic market in California. The idea is to provide a rebate program to encourage consumers to by solar pv systems. This will allow the solar market to grow and as volume go up costs will go down and eventually reach a point were incentives are no longer needed. Overall the program provides $3.3 billion dollars in incentives to create 3,000 megawatts of new solar generated electricity by 2017.

The CSI rebate for homeowners can pay for close to one-third of the cost of a PV system. Not too shabby. The rebate is usually paid to homeowners in a one time payment called the Expected Performance Based Buydown (EPBB) Incentive. The current incentive is $2.20 per watt based on the CEC-AC rating. To calculate the rebate, you multiply the your PV systems CEC -AC rating in watts by the current incentive. For example if your PV systems CEC-AC rating is 2500 watts (2.5 kilowatts) at the current incentive level your rebate would be: $2.20 x 2500 = $5,500. Two things to note:

The CSI Rebate goes down over time as more systems are installed. To find out the current incentive level go to www.sgip-ca.com.

The rebates are calculated using the CSI-EPBB calculator. This is available to the public and you can use it to check the rebate you should be getting for your PV system.