Are north facing panels worth it?

american.patriot · Wednesday at 6:39 AM

Roof is quite steep, but given our roof design, we are trying to max out panels, which would mean 12 panels being north facing, per design below. I expect some drop in efficiency compared to south-facing panels, but is it typically a ~50% dip like I see online?

BentleyJ · Wednesday at 6:51 AM

You can model expected output of the PV array on each area of the roof with this. Using your address, azimuth, tilt and STC rating of the array.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

gotbeans · Wednesday at 6:53 AM

american.patriot said:
but is it typically a ~50% dip like I see online?

I get a 50% dip in power just by laying them flat vs being tilted. On the north side I'd expect more like 80-90%.. for that reason I'll never do it on the north side of my roof

american.patriot · Wednesday at 7:25 AM

BentleyJ said:
You can model expected output of the PV array on each area of the roof with this. Using your address, azimuth, tilt and STC rating of the array.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Thanks. Dumb question, but what's the best way to find my azimuth?

gotbeans · Wednesday at 7:29 AM

american.patriot said:
Thanks. Dumb question, but what's the best way to find my azimuth?

http://www.solarelectricityhandbook.com/ this site has all of them calculators

Solar Guppy · Wednesday at 7:31 AM

luckielab · Wednesday at 7:31 AM

I'm in SE Virginia. The front of my house faces almost due south (azimuth 4'), roof pitch is 33' (8:12).

For my system, here's the annual estimated production per 400W panel:
573 kWh: south-facing
308 kWh: north-facing
Actual production was close to estimates last year (my first year with the system).

The only reason I went with north-facing panels was because they produce during the summer when we're most likely to lose power. All other roof space is in use (i.e. I couldn't add any more south, east or west facing panels).

american.patriot said:
Thanks. Dumb question, but what's the best way to find my azimuth?

That looks like Tesla. My advisor was able to share detailed plans that include that info (below, top-right).

Redflyer · Wednesday at 7:32 AM

Azimuth is the direction of the panel, per the compass.

7 years ago, I installed 32 panels facing south on a separate building. 5 facing south on the house, and one on the house facing east.

I used the NREL pv watts calculator for every array (individually). It came back with 19,500 per year. The numbers I've actually recorded are within 1% of that. It's almost scary accurate.

I don't think north facing panels will pay for themselves in the long run. I would only do it if.....it's not about your return on investment, but about just making 'some' power.

Redflyer · Wednesday at 7:35 AM

Roof pitch and azimuth are two different things. Both have to be inputted in the calculator for a result.

1. Location
2. Panel output (size of your system in watts)
3. Roof tilt
4. Azimuth

Those four things will give you a very accurate output per year.

Cmy · Wednesday at 8:45 AM

I am south of Dallas and get north side sun starting early June. Breakfast area faces east and we note the rising sun's march from south to north and back south to its winter home. I miss my north side shade washing the cars in the Texas summer sun.

Getting on in the summer but check your north side roof. Panels are more affordable and north side may be a benefit. Got an MPPT that can take another string? Check your neighborhood on google maps, others using north side panels?

If you haven't tried suncalc.org it would be interesting to see shading on different days. Address and date upper left and zoom in.

american.patriot · Wednesday at 9:11 AM

Redflyer said:
Azimuth is the direction of the panel, per the compass.

7 years ago, I installed 32 panels facing south on a separate building. 5 facing south on the house, and one on the house facing east.

I used the NREL pv watts calculator for every array (individually). It came back with 19,500 per year. The numbers I've actually recorded are within 1% of that. It's almost scary accurate.

I don't think north facing panels will pay for themselves in the long run. I would only do it if.....it's not about your return on investment, but about just making 'some' power.

ROI is less important. I just want to get the most production I can for >100% offset. Per PV watts, the 12 north facing panels will produce about 4200kWh/yr

solarsimon · Wednesday at 9:29 AM

If you're trying to increase your yield on a dull winter day, north facing won't be much worse than south facing. If it's too dull to see where the sun is, the panels can't tell either...

Cmy · Thursday at 7:29 AM

Or, put the north install money toward higher watt panels on the other exposures. Cost for mounting and wiring doesn't vary much with panel watts and is in your planning.

Are north facing panels worth it?

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