Is My Roof Right?

Determining whether solar makes sense…

Revisiting our Real-World Example

Let’s take another look at my own solar decision. I bought my home in December 2003. It was a fixer-upper, to say the least — the house came came with buckets inside, to catch water from the different leaks.

For a half-year, a large blue tarp was the solution to the leaks. But I knew that I would need new roofs, and I started thinking about solar.

The obvious roof to consider was the roof furthest from the hillside – since it was highest compared to the trees.

It also had two nice strips of open space, just waiting for solar.

Since this is a flat roof, tilt racks made sense. Aesthetics plus efficient use of the available space meant that the mounting racks would run parallel to the edge of the roof, so a proper south orientation wasn’t possible – my panels would actually face southwest.

And I elected to reduce the tilt a bit to improve aesthetics – and reduce my concerns about the impact of large wind gusts we sometimes get here on the hill during winter storms.

So my system’s calculations:

0° (South) 0.89 0.97 1.00 0.97 0.89 0.58
23° (SSE, SSW) 0.89 0.97 0.99 0.96 0.88 0.59
45° (SE, SW) 0.89 0.95 0.96 0.93 0.85 0.60
68° (SE, WSW) 0.89 0.92 0.91 0.87 0.79 0.57
90° (E, W) 0.89 0.88 0.84 0.78 0.70 0.52

My tilt of roughly 18°, coupled with my southwest orientation means that my panels are capturing 95% of what they could have caught if they were oriented exactly south, with a slope of 30°.

Shade-wise, my panels do fine, except in the middle of winter, when shadows are hitting the rack closest to the hillside much of the afternoon.

I have not paid a PG&E utility bill since January 2005.


Learn more. Email me (at and I’ll send you two other reports: PG&E and Solar, and Solar As an Investment.

PG&E and Solar explains how PG&E pricing actually encourages you to purchase solar.

Solar As an Investment starts with a simple “years til payback” model, then adds layers of real-world complications, including utility rate increases, inverter replacements, panel degradation, and even the interest you might be earning elsewhere, if you didn’t invest in solar.

By reading and understanding these two papers, you will be a smarter shopper when shopping for solar for your home.

Bill Fridl
Solar Advocate

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