Thoughts on Solar

We occasionally encounter potential clients who have been given wildly optimistic proposals that promise amazing performance and use every square inch of the roof, regardless of the major shade issues of the site.  We recently drove by a house that suffered from this exact problem.

White picket fence, solar, and SHADE!

What you see here is a west-facing roof with an almost permanently shaded roof section. There are two large trees that completely shade the solar panels for about half of the day. And, since the panels are facing west, they are not going to produce very much energy in the morning when the sun is in the east.  As much as we love microinverters, they cannot save the day here!

After some research (gotta love online permit databases!), we determined that this is a 9.54 kW system consisting of 36 265 Watt panels. We analyzed the system’s potential performance assuming that the installer used the best products on the market (i.e., LG solar panels and Enphase microinverters).  Based on the satellite image of this property, we see that most of the roof is in full sun. The overall system has 5 panels south facing, 6 east, 10 on a flat roof, 6 west in full sun, and our suspect 9 panels on the west roof in almost full shade.

For our analysis, we used a 50% solar access value for those 9 panels (a very generous assumption). The rest of the system was assumed to have minimal shading.  Based on those assumptions, this system is likely to produce 217,875 kWh over the next 20 years. Of that, only 30,726 kWh will be produced by those 9 west-facing panels. What that means is that  25% of the system (9 panels of 36) is only going to produce 14% of the system’s energy, and that is based on a very generous assumption about how much sun actually reaches those panels.

Put another way, over the life of the system, at best, those 9 shaded panels provide half as much value to the homeowner as the rest of the array. 

What you see in that picture is the result of an installer who failed to provide their customer with enough information to make an informed decision. Instead, the customer was sold the biggest system possible to maximize the installer’s profit, not the customer’s benefit.  If you are comparing solar bids, and one company is proposing a much larger system than the others, you might want to ask, who will those extra panels benefit the most?