DEBRIS.COMgood for a laugh, or possibly an aneurysm

Our photovoltaic array has five racks of solar panels. Due to the presence of nearby trees, the chimney and exhaust fans on the roof, and even more importantly to the fact that the most open roof space faces east rather than southwest, the panels were difficult to fit, given the design goal of maximizing exposure to the south/southwest sun.

There’s a problem: production is below projections. I think the core problem is that the projections are incorrect, but I’m eager to increase production if possible. The more power we generate, the sooner my PV system pays for itself. (This is a purely virtual goal — my out-of-pocket costs for energy are going to be very low for the next 30 years, regardless of when we cross the breakeven point.)

We had the panels inspected. They passed; the technician found no evidence that any of the panels were failing. Kudos to our installer for providing this check-up for free.

But a more sinister problem apparently exists: by mid- to late afternoon, our panels are creating their own shade. We knew we’d lose some afternoon sun due to tree cover, but this picture shows a much worse problem — really, a design flaw.

Photovoltaic arrays in California should be designed to maximize production during peak periods: 12:00PM - 6:00PM. The picture here was taken shortly after 5:00PM, indicating that we’re losing generation capacity during peak hours. Of course the amount of shadow depends on the height of the sun in the sky; still, any shadow during peak hours is a bad thing.

Research indicates that even a small shadow can cause a huge drop in generation performance:

Even partial shading of crystalline solar panels will result in dramatic reduction of solar panel output. One completely shaded cell can reduce a solar panel’s output by as much as 75%. Three cells shaded can decrease 93% of the panel’s output.

I think there’s a relatively easy way to move the last rack of panels out of shadow, by raising its standoffs. But the larger rack in the foreground of the picture will be harder to reposition. I’m hoping my installer has some suggestions.

What’s surprising about all this is that our PV installer ran numerous “shade studies” to illustrate the shadow of the chimney and the other panels throughout the year. They designed the racks to prevent exactly this problem.