Utilizing websites such as Energysage is a great way to get multiple estimates on a solar project. However, all the information can be overwhelming, and make it difficult to choose an installer. Luckily for homeowners, there are some key pieces of data to look for to make it easier to compare quotes. Our series of blog posts, “How To Compare Solar Quotes” will explain each piece of data so you can feel more confident as you look at different solar proposals.
Production ratio is another piece of date that can be looked at when comparing solar quotes.
The production ratio is simply the estimated amount of kWh/year a solar array will produce, divided by the total wattage of the solar array. A higher production ratio usually indicates a higher percent efficiency.
Solar installers can calculate kWh/year using Powerclerk, as explained in last week’s post. The total wattage is calculated by taking the number of panels in the proposed array and multiplying by the watts/panel. The manufacturer’s model number usually indicates the wattage under standard test conditions (STC) – for example, an LG280N1C panel will produce 280 watts.
The chart below gives a comparison of two companies with different production ratios. Both companies quoted the same cost per watt. Company A calculated a 1.29 production ratio with a satellite image. Company B went to the same site and took measurements in person, and got a lower, but more accurate, production ratio and design factor.
While a satellite image can get you a preliminary estimate and help you determine if your property is viable for solar, having someone come out and do a complete evaluation will get the most accurate numbers.
In the next blog, we will discuss what actually goes into the cost per watt of a system.