This credit, only for the prescriptive pathway (it is modeled in the performance pathway), awards up to ten points for generating electricity on-site through renewable energy sources. It is important to note that passive solar designs must be modeled and can take credit using the EA1 performance path, and solar hot water heating systems–a completely different type of solar collection system than photovoltaic solar panels–are rewarded in EA 7.3. Ground source heat pumps are not considered renewable energy.
Since a small residential wind system is not really an option for us right now (I’m sure we would need a variance, and we are not in a prime windy location), nor is a hydro system or biomass a realistic possibility, we designed our house to put solar panels on the roof of my office above the garage. Just this past week we had them installed, although they are not yet operational. (See postings under Going Solar.)
What is interesting is how points are rewarded: we could receive one point for every 3% of the annual reference electrical load met by the system. The annual reference electric load is defined as the amount of electricity that a typical home would consume in a typical year — not what our home consumes in a typical year. I care much more about the percentage of total electricity our system will generate, and since we have lived here for over one year, I can figure that out. But for this credit, I need the denominator to be a typical home’s electric load (also referred to the HERS Reference Home).
Starting with the numerator, our solar photovoltaic system is estimated to produce about 4,400 kilowatt hours per year. (One kilowatt hour is one 100-watt light bulb turned on for ten hours, or one 2000-watt hair-dryer turned on for 30 minutes.) There’s a great on-line calculator that helps estimate the output given your physical location (which estimates the solar radiation for that area), the angle of the panels toward the sun, and the panel watt rating, at www.pvwatt.org.
On to the denominator: I can’t find it. I’ll update this post if / when our Green Rater gets back to me to tell me the typical HERS Referency Home electrical consumption. For now, I’ll assume its 20,000 kilowatt hours/year (more than average, but our house is larger than average). In that case, our solar system will provide 22% of our total consumption. We get 1 point for every 3 percentage points, so that equates to seven points. On the other hand, our Green Rater did update our HERS Index rating for our solar panels, and the index went from 46 to 39, giving us another 2.5 points (see comment on EA1 post). So, I guess I’ll have to go with that. If we do the math the other way, 2.5 points equates to 7.5% of total electrical consumption being provided by solar.
EA Prescriptive Path points so far: 20.5