Free Hot Water often receives questions from people just starting to enter the solar business. One question that comes up is the correct way to measure insolation.

What’s insolation? It’s basically a measurement of the amount of sun that’s expected to hit your solar site over the course of the year. An important part of that calculation is what’s not going to hit your solar collectors. In other words, shading.

A proper shade analysis is especially important in the solar PV (electric) world due to the complications of the inverter. However, a shade analysis is equally important for solar hot water—and by important, we mean monetarily, as well as technically.

In both solar electric and solar water heating installations, your insolation and shade analysis play important roles in calculating most state rebates. If the city inspects your system post-installation and finds you’ve guestimated these figures or performed and submitted a faulty site survey, your client (and you) may receive a lower state rebate unless fixed.

Of course, performing another survey and resubmitting your plans may also cost you fees and time, frustrating yourself and your client. Consequently, a bad insolation/shading survey costs money and time, and it also reflects poorly on your solar installation skills.

The good news is that there are several accurate insolation measurement tools on the market today. Some are low tech, like the Solar Pathfinder. With this tool, you’ll still have to do some manual calculations and have a few more steps to integrate with your site plans, but it does work, so long as you follow their directions. It’s also a bit bulky.

A more compact and automatic option is the Sun Eye 210. It’s the only site evaluation tool we carry at Free Hot Water. The reason? It’s simple, it’s largely automatic, it’s accurate, and it works.

The Sun Eye is a handheld electronic solar tool that includes an electronic inclinometer, so it recognizes and can record your exact height when you’re on that roof. There’s also an electronic compass, automatically revealing your orientation and accounting for magnetic North.

Perhaps the most convenient feature is the Sun Eye’s digital camera with a fish eye lens that snaps a digital photo of your entire solar site, including all of that important shading data. And if you really want to make it ultra-simple, there’s also an optional integrated GPS, saving you the hassle of looking up your site’s exact longitude and latitude, as well other relevant location data.

Of course, all of this sunny data is transferable to Sun Eye’s included companion PC software, which can edit and export into great looking professional reports.

What ever tool you use, we urge you to read the instructions and practice before using the data for a genuine site survey that you submit with your permitting plans.  The city and your customers will thank you.