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Don’t let them install solar panels on a north-facing roof. A cautionary tale.

Avatar for Ben Zientara
Published on 02/04/2020 in
Updated 02/04/2020
Solar panels on a north-facing roof in Houston, TX

Check out that picture above. It was spotted by a smart solar-loving Reddit user who calls themselves “theworldsworstphotog.” It’s been a while since we saw something that looked so much like a solar panel scam, and we figured we’d better point out the problems so nobody else has to suffer like this.

What you see above is a house near Houston, Texas, with a large solar array placed on a north-facing roof with a pretty dramatic pitch. The reason this looks like a scam is because in the northern hemisphere—which contains the entirety of North America—the sun shines out of the southern sky, even at the summer solstice. That means north-facing roofs like the one above receive no direct sun. Ever.

That’s not to say the solar panels in the picture will make no energy at all; in fact, they’ll produce quite a bit over 25 years. And given that the Redditor added the fact that the south-facing roof is covered in shade, maybe this was the only option. But was it a good option? How much more or less energy would be made by the same system on an unshaded south-facing roof?

Let’s look at some estimates to show you how it all works.

Our guess at system components and size

Without actually looking at the contract the homeowner received, we can’t tell you exactly what the installation company used. But by some careful sleuthing, we can determine the likely components used in the system.

To us, this looks like a 5.5-kW system made of 20 REC TwinPeak 2 modules, probably the 275-watt version (REC275TP), laid out in landscape orientation. These panels get some very good reviews, and were very popular between 2015 and 2017, when this system was likely installed.

The panels are installed on a north facing roof with a pitch that looks like about 9/12 (37° angle up from the ground). There are long runs of external conduit that join strings together, which is a big problem in its own right. Would you want to buy a house with solar that looks all disjointed and ugly like that?

Anyway, forget about the looks for now. Let’s see if it’s worth the money! From the thread on Reddit, we hear the homeowner is paying $120 per month for this lease. If we’re right and this is a 5.5-kW system pointed northward on a 37° angle, here’s what we found:

South-facing solar vs. north-facing

Solar panels work best when they’re pointed directly at the sun. You’ve probably seen those solar tracking devices where the panel turns from side-to-side and up and down as the sun travels across the sky during the day. That tracking requires two measurements: azimuth and tilt.

Azimuth is the one that has to do with north/south/east/west. Like we said above, in the northern hemisphere, the sun shines on us from the southern sky. Solar panels on trackers in the northern hemisphere turn from the southeast to the southwest to point toward the sun, but solar panels on roofs are stuck in one place, so true south is the best way for panels to be pointed in the USA.

Here’s an image showing azimuth for south-facing roofs (180° is true south):

A view of a roof with azimuth arc overlaid

The difference azimuth makes

Looking at the panels above, if we assume that the roof is pointed due north and the panels are angled at 37°, PVWatts tells us that the 5.5-kW system will produce an estimated 4,483 kilowatt-hours (kWh) during a whole year. That month-by month-calculations look like this:

PVWatts results for a 5.5-kW solar system on a north-facing roof in Houston TX

If those panels were mounted at the same angle on a south-facing roof instead, they’d make an estimated 7,667 kWh/year. That’s an increase of 71% over the north-facing panels.

PVWatts results for a 5.5-kW solar system on a south-facing roof in Houston TX

How roof pitch affects solar production

Roof pitch has to do with how many inches a roof rises for every 12 inches of horizontal length, expressed as X” in 12″, or more commonly “X/12.” Here’s a chart that shows pitch values from 1/12 to 12/12 and their corresponding angles:

roof pitch in degrees

As we mentioned above, the house in the image looks like it has a pretty steep pitch. Maybe 9/12 or more. If it had a shallower pitch, around 3/12, those solar panels would actually produce more electricity than they can at the current angle, and this north-facing install might not seem so scammy.

What roof pitch has to do with solar panel production

As the earth travels on its orbit every 365.25 days, the sun shines from higher in the northern hemisphere sky between the spring and fall equinoxes and lower in the sky during the rest of the year, based on the angle of earth’s tilted axis as it faces the sun. It never shines out of the northern sky, but even Northern roofs that are flatter can collect a bit more energy than those angled up.

The proper tilt of solar panels in the Northern hemisphere can be determined based on a pretty simple formula (your latitude times 0.76, plus 3.1 degrees). For most of the USA, it’s between 25° and 38°, south to north. For Houston, the ideal tilt for solar panels on a south-facing roof is about 25.7°.

That optimal tilt will make you an estimated 7,732 kWh in a year from 5.5 kW of solar panels. On a north facing roof at 25.7°, that would be 5,362°. But on a north-facing roof with a shallow pitch, say 3-in-12 or 14°, production would be 6,234 kWh/year, or 16% higher though still nearly 25% less than the ideal tilt on a south-facing roof).

The bottom line: why this looks like a scam

The way solar panels save you money is by offsetting your electricity bill. Remember, the homeowner in question was paying $120/month or $1,440 per year for the solar lease on the system in question. Given a production estimate of 4,483 kWh/year, that works out to $.32/kWh. There is no place in the United States (much less Texas) where electricity costs that much.

According to the U.S. Energy Information Administration, the average home in Texas uses about 14,500 kWh per year and spends $1,801 for that energy. That’s about $.12/kWh. So the homeowner in our example here is replacing a little less than 1/3 of their annual energy usage with solar power, but spending 2.7 times more money on the energy they replaced.

That sounds like a scam to us, folks. Do not let the installation company put panels on the north side of your house, unless you fully understand what you’re getting. Is it worth an extra $900 per year (net) to replace a little of your energy needs with solar? probably not.

At least on a north-facing roof, you don’t have to worry about shade from that giant chimney in front of the panels.

Last modified: February 4, 2020

2 thoughts on “Don’t let them install solar panels on a north-facing roof. A cautionary tale.

  1. Avatar for CA dude CA dude says:

    Dude, electricity costs 38 cents/kwh in PG&Es ETOU-B program, which is mandatory for PV customers.

    1. Avatar for Ben Zientara Ben Zientara says:

      Dude, I know. California electricity prices are super high. Luckily having solar panels means you can eliminate those high TOU prices, especially if you have west-facing panels or a battery.

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