North facing Panels

[solarix]

OMG, North facing array! might as well point them at the moon.... Our utility here used to check on array orientation as art of their red-tape process and dock your rebates depending on how far from South the array was. Then they killed the rebates and the orientation check. One of their people told me that they don't care how you mount them as long as they are right side up! This is the kind of thing that gives solar installers a bad rep.

[TurkeyBob]

The moon?
After 15 years of work in the RV solar world I have say something. I have had people tell me they were getting charging under a full moon. The foot candles on the ground from full sun is over 20,000. A full moon on a clear night can do about 2/10 of a fc. You do the math, but people have argued. The same thing was said about parking an RV with solar panels on the roof under a parking lot light at Wallyworld. People are generally pretty gullible and will believe the things they hear if repeated a few times.

When I told professionals in this business that I could run my house on a 2KW array I was told that is impossible. How else can they sell big systems? I am doing exactly that, but figuring out which of the solar charge controller manufacturers had a clue was key. Many of the people on this forum have drunk the Koolaid and bought the wrong things, but I won't go into the details here because they won't believe me. I use Morningstar now with Crown batteries.

[J.P.M.]

OMG, One of their people told me that they don't care how you mount them as long as they are right side up! This is the kind of thing that gives solar installers a bad rep.

Kind of like making sure turf installers aren't color blind ? (As in:"Remember guys - green side up !")

[compchat]

Turns out when it is cloudy the north facing panels generate about 50% of the south facing panels (usually in the morning in S.Calif). So it does add something. Obviously if I had a larger South Facing roof more Southern facing panels would have been better.

[littleharbor]

If the north facing array could be tilted up to something like level you would at least get some benefit from the summer season. Not too aesthetically pleasing and would require manual cleaning regimen.

[SunEagle]

Turns out when it is cloudy the north facing panels generate about 50% of the south facing panels (usually in the morning in S.Calif). So it does add something. Obviously if I had a larger South Facing roof more Southern facing panels would have been better.

When it is cloudy I would expect the South facing would not produce much of anything.

So if the North is 50% of the South then IMO 1/2 of "a little bit" is next to nothing and might not have been worth the extra expense for those North panels.

[J.P.M.]

When it is cloudy I would expect the South facing would not produce much of anything.

So if the North is 50% of the South then IMO 1/2 of "a little bit" is next to nothing and might not have been worth the extra expense for those North panels.

That depends to a large degree on the nature of the cloudiness. Solid, heavy overcast will produce what is mostly isotropic GHI at a flux rate that might be ~ 5-10+ % or so of a clear sky value (say a GHI value of ~ 50 - 100 W/m^2 or so). If the cloud cover is not quite as solid, say with a GHI of ~ 200 W/m^2 or so, the area of the sky around the sun may, depending on the atmospheric conditions, be the source of more of the irradiance. In those situations, often in the morning before the A.M. haze burns off, but other times as well, equator facing arrays may see increased output that could be measurably higher than output from arrays facing away from the equator, particularly if the panels have somewhat better low irradiance performance - some of which BTW and sort of off topic, will be the result of lower operating temps due to lower irradiance.

[SunEagle]

That depends to a large degree on the nature of the cloudiness. Solid, heavy overcast will produce what is mostly isotropic GHI at a flux rate that might be ~ 5-10+ % or so of a clear sky value (say a GHI value of ~ 50 - 100 W/m^2 or so). If the cloud cover is not quite as solid, say with a GHI of ~ 200 W/m^2 or so, the area of the sky around the sun may, depending on the atmospheric conditions, be the source of more of the irradiance. In those situations, often in the morning before the A.M. haze burns off, but other times as well, equator facing arrays may see increased output that could be measurably higher than output from arrays facing away from the equator, particularly if the panels have somewhat better low irradiance performance - some of which BTW and sort of off topic, will be the result of lower operating temps due to lower irradiance.

Good point. I just related "clouds" as being a heavy overcast and not something that will allow any significant light through.

[J.P.M.]

Good point. I just related "clouds" as being a heavy overcast and not something that will allow any significant light through.

Adjuncts to Murphy's law, particularly with research or reality: Constants aren't, variables won't and absolutes never happen.

[JFinch57]

I would have a Suneye analysis done to find out which has the least shading, east or west. No matter how perfect it looks one will be better. The north panels should be moved ASAP!

[compchat]

Sun out all day in S. Calif. You can see te peak is about 6.8 around 1 pm. This is with one south facing 6 KW system and one north facing 5 KW system. About 5 KW system is from the southern facing panels and 2 KW from the north facing panels.

Based on today's output at this time of year what might I expect in June?

[compchat]

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Picture should go with prior message.

[J.P.M.]

Sun out all day in S. Calif. You can see te peak is about 6.8 around 1 pm. This is with one south facing 6 KW system and one north facing 5 KW system. About 5 KW system is from the southern facing panels and 2 KW from the north facing panels.

Based on today's output at this time of year what might I expect in June?

Run PVWatts with the hourly output option and 10 % system losses. Look for a high output symmetric clear day around this date. You'll get a reasonable SWAG.

[john phillips]

There are a lot of good things said so far but I have a little different feeling about this.
Given that ROI on PV is kind of low at best when you degrade the output ROI goes way up.
Ask your self if the North facing panels were your only project would you do it.
If you have tiered billing the South array will really cut into your bill and should keep you in the cheep electric rates.

To pay for the North array after your bill is lowered by your South array seems like a real looser.

On the other hand is this a PPA?
If the north array does not produce any electricity what happens to your billing?
Unless your condition is artificially enhanced by the contract I would make them take the North array out of the deal.
They may not even want to come back, remove the array and redo your roof. Get the contract rewritten for just the South array and see how that looks.
Then you may consider a West array but you should evaluate it on its own merritt.

What is the panel name plate rating. You are only getting about 150 watts / panel Something seem really wrong even for your best array. Your inverter seems way over sized.
Seems like you have 260 watt panels producing 150 with great sun. What is you slope? Latitude? Is it getting any better with sun angel change?
What happens if you buy a 11KW system and it works like a 4 KW system?

[J.P.M.]

There are a lot of good things said so far but I have a little different feeling about this.
Given that ROI on PV is kind of low at best when you degrade the output ROI goes way up.
Ask your self if the North facing panels were your only project would you do it.
If you have tiered billing the South array will really cut into your bill and should keep you in the cheep electric rates.

To pay for the North array after your bill is lowered by your South array seems like a real looser.

On the other hand is this a PPA?
If the north array does not produce any electricity what happens to your billing?
Unless your condition is artificially enhanced by the contract I would make them take the North array out of the deal.
They may not even want to come back, remove the array and redo your roof. Get the contract rewritten for just the South array and see how that looks.
Then you may consider a West array but you should evaluate it on its own merritt.

What is the panel name plate rating. You are only getting about 150 watts / panel Something seem really wrong even for your best array. Your inverter seems way over sized.
Seems like you have 260 watt panels producing 150 with great sun. What is you slope? Latitude? Is it getting any better with sun angel change?
What happens if you buy a 11KW system and it works like a 4 KW system?

While folks who peddle PPA's may use people's solar ignorance to make money, I doubt their all so stupid as to get themselves in a situation where their property - the array - would produce poor revenue by peddling an array to a homeowner with a lousy orientation. Double/accelerated depreciation and other tax breaks homeowners don't get are nice but there are other suckers with better orientations for their equipment that will produce more revenue for the array owners. If the PPA needs a higher price/kWh to make up for a poor orientation, that will decrease the competitiveness of the product.