How To Compare Solar Quotes: Site Surveys and Design Factors

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.

Solar companies use a number known as a ‘design factor’ to calculate kWh/year output. A design factor can be calculated during a site survey, or estimated from a satellite image.

During a site survey, a solar designer will go onto the roof and use a tool such as a ‘Pathfinder’ or ‘Suneye’ to measure the distribution of sun to shade on the roof, roof tilt and building orientation. From that data, the design factor, or percent efficiency, of the proposed solar system is calculated, and an accurate annual kWh/year output is obtained. The designer will also take roof measurements and note any obstacles such as vent pipes and skylights. The number of solar panels are determined from those measurements and the system panel wattage and kWh output are calculated.

Some solar companies will perform a ‘site survey’ but not go on the roof. Other solar companies will generate a quote using a satellite image and an estimated design factor of 95% or greater to calculate kWh/year output. A high kWh/year output will make the financial return on investment appear to be very attractive.
However, a design factor of over 95% means that the house roof is at a close to perfect north/south orientation, and there is no shading on the solar panels during the hours of 9 am – 3 pm (solar window) throughout the year. An estimated design factor should always be verified by a site survey with actual measurements to determine a realistic annual production.

Using Energysage, for example, a homeowner can request an initial quote from a satellite image. After receiving this, the homeowner can follow up with the installer to come out for a site visit. After the visit, the installer can upload a new, more accurate quote. It’s important to remember that the satellite images are not always accurate, and may not reflect new constructions, tree removals, or other changes made to a property.

A site survey is used to collect information for an accurate quote.
A homeowner should never sign a purchase agreement until a site survey with measurements is conducted to verify annual solar production given in a quote.

The next blog will focus on production ratio, another piece of data that homeowners can use to compare solar quotes.

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