We get this question a lot, and there’s no easy answer. How much energy your home or business consumes has to do with several factors, including:
- How many people live in your home and how often are they there?
- Do you have children living in the home (they’re MASSIVE energy suckers).
- How comfortable to you like to keep your home? Do you run the AC at 72 at night, or 75? 76 during the day or 82?
- Do you and/or your spouse work from home?
- How energy efficient is your home?
- How old is your HVAC system and what is the SEER rating of your air conditioning condenser unit? Do you have more than one?
Do two houses of the same size use the same amount of energy?
We have seen instances where we bid on two homes with the exact same floor plan in the same neighborhood with a 5,000 kWh/yr. delta between the two family’s energy consumption. There’s no way to guess and get it right. And until we have an accurate idea of how much energy you are trying to produce in order to eliminate your electric bill, we can’t really provide much info about how big of a system you need.
What we are concerned with is collecting your usage data from your last year of utility bills, as well as other factors like future changes to your family (kids going off to college, mother-in-law moving in, planning on adding a pool, etc). We then build out a system designed to offset as much of your consumption as we can.
How do we model solar production on a project?
Once we have your consumption defined, it’s actually pretty simple. The National Renewable Energy Labs (NREL) is a national laboratory of the U.S. Department of Energy, and they maintain (via the Alliance for Sustainable Energy, LLC) a tool called the PVWatts Calculator. Once we calculate how many solar panels you need on each roof plane of your home or business, we simply input your location, the total wattage of all those solar panels, along with the tilt they will be installed at, and the azimuth angle (a numerical representation of which direction the panels will be facing). PVWatts does the rest. It knows based on 25 years of historical data what the average sun hours are for where you live and then models how much energy the proposed array will produce.
We run these projections for each tilt/azimuth/wattage combination and add them together and voila! We now know how much solar potential your home has. Most solar proposal software products on the market today have a PVWatts calculator built into them.