Multi Angled Ground Mounted Array Configurations

mtautoken

I have a ground mounted array that I installed that is two panels high, portrait mounted. The panels side frame faces approx. SE and the length of the array stretches length wise down a 4 to 1 Slope to approx. a SW Direction.

Now I was taught that a PV Module sees the sun as it sits perpendicular to level. Or in other words, if you were to pour water on the panel, the direction it falls will be your azimuth. However I use a level and a square to determine this. The Panel tilt is set at 30 while referencing this direction as well.

My Customer has a contractor friend that has taken some solar classes and believes that the side frame of the module should be used to determine the azimuth regardless of it being mounted on multiple angles.

I would like to get some confirmation from a few that have more experience than my self and possibly an article to reference.

While I am talking about this system. The Customer also believes that because he is on a "Time of Use" metering with his Peak hours between 1:00pm & 7:00pm, he believes the array should face for to the SW to take more advantage of the better payback. I have explained that there may be an advantage to moving it a small amount in that direction, but he will also be loosing an optimum azimuth for his peak sun hours.

If I was correct in setting my azimuth, because the Array is on a 4 to 1 slope, if I tilt the panels to a lesser degree, they will begin to face more to the SW and I will loose some tilt, but I'm quite sure that the azimuth is more of a factor than the tilt.

I use the Clean Power Finance tool and I was going to play with the azimuth numbers to see how the payback would change by moving the array more to the SW.

Does anyone else have any other ideas or is there a website that I can load this data into that might be a better fit?

Thank you in advance for anyone that can help me with this issue.

BB.

Re: Multi Angled Ground Mounted Array Configurations

PV Watts has an Hour by Hour output that can be loaded into a spread sheet... A bit messy, but should work for you as a brute force solution.

PV Watts is based on typical day 20 year averages--so should take afternoon clouds and morning sun for your local climate conditions into account.

In my case, Peak Summer rates (Mon-Fri, Noon to 6pm) are as much as 3x my off peak rates. My winter rates are much closer ($0.12 vs $0.09 per kWH) so not so much difference.

-Bill

Peter_V

Re: Multi Angled Ground Mounted Array Configurations

mtautoken wrote: »

Now I was taught that a PV Module sees the sun as it sits perpendicular to level. Or in other words, if you were to pour water on the panel, the direction it falls will be your azimuth. However I use a level and a square to determine this. The Panel tilt is set at 30 while referencing this direction as well.

I think I understand what you are asking, but a clearer way of stating it might be:
"Place a marble on the highest point on the panel and let it roll down the panel. The line the marble rolls along is where you take your azimuth."
Is that what you're asking? If so then the answer is yes.
That is the line to measure both the azimuth and the tilt on.

The panel is effectively rotated around it's center while facing the same direction, this rotation does not effect power output.

mtautoken wrote: »

While I am talking about this system. The Customer also believes that because he is on a "Time of Use" metering with his Peak hours between 1:00pm & 7:00pm, he believes the array should face for to the SW to take more advantage of the better payback. I have explained that there may be an advantage to moving it a small amount in that direction, but he will also be loosing an optimum azimuth for his peak sun hours.

That's going to depend on a variety of factors. You might want to check with his power company to find out EXACTLY how they handle TOU and Netmetering.

For example, with TOU meters my power company only allows On-peak power generation to offset On-peak power consumption. Since night time is mostly off-peak, any power I generate during on-peak daylight hours (most of them) won't help me offset night time energy use.
At the end of the year, any surplus peak and/or off-peak power gets paid back at the same rate, the utility companies avoided rate (just under 4 cents/kwh)
Because of this, I'm not on their TOU program.

IF (!!) the power company will pay more for on-peak generation, then you'll want to model how much energy he will generate during peak and off-peak and see which works out more profitably.
You can do this using PVwatts, but it's going to be VERY labor intensive. If you're not getting paid extra for this additional labor, then I'd probably just do what the customer wants.

solarix

Re: Multi Angled Ground Mounted Array Configurations

You are correct in your azimuth understanding and he is correct that a more SW orientation will produce more savings on a TOU rate. Without knowing the rate details in your case, I can say that with a 3:1 on-peak to off-peak ratio, an orientation of about 45deg west of south is optimum. Even though less power is produced, it will have greater savings. (Difficult to compute though. PVwatts will do it) Kind of bad that this encourages inefficiency, but the goal is to reduce peak usage and thus reduce the need for additional conventional generation - reducing additional coal plants etc. Actually, in our area, the peak load occurs around 6pm typically - well past when solar PV can make much of a difference. The utilities here are scaling back the solar PV incentives as past a relatively low level of maybe 10% of total capacity, added PV will not reduce the peak load significantly. Lifestyle changes or some sort of "grid battery" (solar thermal) will be needed beyond that point. We have a new utility rate here called Super-Peak where the on peak rate during the 3 summer months between 3 and 6pm is a whopping 48 cents/kwh! The rest of the time is way low though so would be very rewarding to those who can shift off-peak and to us that can generate during that time. Sort of makes that siesta idea make cents.