Output of solar panels depending on slope and azimut

[Adriaan Kragten]

Recently I found a very interesting website of PVGIS Europe. On this website you can find the output of solar panels depending on the country, the total peak power, the slope and the azimuth for every month of the year. I have written the small Dutch note: "Opbrengst van zonnepanelen in december afhankelijk van de dakhoek (slope) en de stand t.o.v. het zuiden (azimuth). This note can be copied from my website: www.kdwindturbines.nl at the menu KD-reports at the bottom of the list with reports. Figure 1 out of this note gives a direct impression of the effect of the slope and the azimuth for December. Although the note is in Dutch, this figure can be understood by everyone (dakhoek = slope). The figure gives the reduction factor for the output if the solar panel is compared to a panel with a slope of 75° and an azimuth of 0° in The Netherlands. December is the most difficult month for solar power at the northern hemisphere and therefore this month is chosen. But a similar figure can be made for every other month and every other country in Europe using the website of PVGIS Europe. For America, you have to chose a point on the map of Europe with the same latitude.

[bigrockcandymountain]

susdesign.com has some great tools for North America on the same topic. I used their tools for slope planning on my rooftop solar.  I also used their overhang calculator to visualize how my overhangs would work on my south facing windows.  They worked out almost perfect.

My slope is 65 degrees in winter and 20 degrees in summer.  The winter should be steeper for good snow shedding.  Otherwise it works out well. 

The new panels on the shop are vertical (90 degrees) and do great in the middle of winter.  They wont make much power in june, but we usually have lots that time of year. 

[taylorp035]

I use the NREL website for this.  It can output the monthly totals and is fairly customizable from just about every input you can think of.

https://pvwatts.nrel.gov/index.php

[XeonPony]

susdesign.com has some great tools for North America on the same topic. I used their tools for slope planning on my rooftop solar.  I also used their overhang calculator to visualize how my overhangs would work on my south facing windows.  They worked out almost perfect.

My slope is 65 degrees in winter and 20 degrees in summer.  The winter should be steeper for good snow shedding.  Otherwise it works out well. 

The new panels on the shop are vertical (90 degrees) and do great in the middle of winter.  They wont make much power in june, but we usually have lots that time of year.

If you have a smart phone a great app is Sunontrack, it is a paid app, but has reality augmentation so gives virtual overlay of the sun at various seasons real time.

Used it a fiew times and is pretty accurate, and based on reviews around the globe

[Adriaan Kragten]

I have written a similar note but now about the output in June which can be found at the same place on my website. The curves given in figure 1 of both notes are completely different. With both notes it is now easy to compare the output in December and June. In the second note, I have compared two systems. System 1 has 12, 400 W peak panels in the direction of east and 12 panels in the direction of west at a slope of 15°. System 2 has 24 panels in the direction of south at a slope of 60°. It appears that the gain in December because of the larger slope and the orientation to the south is more than the loss in June.

If the energy is supplied to the grid, energy supplied in the winter is much more valuable than energy supplied in the summer. So the finananciel output for a certain investment in solar panels and inverters is much higher for system 2 than for system 1. A disadvantage of system 2 is that you need a rather large distance in between the rows of panels to prevent that panels come in each others shadow. But if the ground is cheap, system 2 is still a better choice. System 2 also has as advantage that the ratio in between the energy supplied in December and the energy supplied in June is about a factor three higher than for system 1 and so system 2 creates less imbalance in the grid. System 2 also has as advantage that melting snow, leaves and dust are easier removed and so the panels of system 2 need less cleaning. The panels of system 1 are normally laid very close to each other and the ground below the panels will get almost no light and almost nothing will grow there. For system 2, a certain crop can grow in between the panels and so nature is more lively.

[Adriaan Kragten]

The calculations of the output have been reviewed because I took a too high peak power of a solar panel size 1 * 1.65 m. The peak power is reduced from 400 W up to 300 W.

[brandnewb]

The calculations of the output have been reviewed because I took a too high peak power of a solar panel size 1 * 1.65 m. The peak power is reduced from 400 W up to 300 W.

Dear Adriaan,

So in general; if one has far too much power generated by the solar panels oriented in a east-west back to back setup in summer times. with as goal generating as much as possible during winter times.
even after you have refined your study a bit based on the new peak values.

Would you still conclude that an optimal south facing orientation of the panels, even though now needing more spacing between rows, will benefit the power generation during winter times?

If that is the case then I need to find some new and inventive ways to reposition more than 22 panels as my roof is already maxed out (I now have 44 panels in a east-west back to back configuration)

One thing I have been considering is to have floating arrays of panels. But especially during winter time the sun is rather low so I will need to have them float outside of my property to have full sun. But I guess no one minds as then we have little to no boating activity during those times anyway. But then that damned freezing that could happen. Now I have to think of a raft type that can deal with that.

{1}reason I ask is because I am trying to transition away from grid connected as even though netmetering has been extended for some time by our government again. electrical utility providers are actively trying to circumvent the loss of revenue by employing really nasty tricks like for people with smart meters. Some if not most of them are now being taken from behind by now netmetering will be done on a monthly basis rather than annually.

I am ecstatic I have always resisted the installation of a smart meter. And please believe me they tried! hard!!{/1}

[MattM]

Besides the original devices being rolled out via a discrete Chinese partnership, it sure seems odd the incessant push for these smart meters as they literally made zero impact on the grid.  Your solar panels facing east-west are probably only superior under dynamic loads like net metering, where you would be softening price gouges at peak draws.  But if you are overproducing during the day with a storage system, to cover your night usage, it would seem south facing would be a wise choice.  Regardless, without adjustments for slope the choice is pretty much permanently made at installation.  Moving panels without reroofing is adding holes to the boat.

[Mary B]

Besides the original devices being rolled out via a discrete Chinese partnership, it sure seems odd the incessant push for these smart meters as they literally made zero impact on the grid.  Your solar panels facing east-west are probably only superior under dynamic loads like net metering, where you would be softening price gouges at peak draws.  But if you are overproducing during the day with a storage system, to cover your night usage, it would seem south facing would be a wise choice.  Regardless, without adjustments for slope the choice is pretty much permanently made at installation.  Moving panels without reroofing is adding holes to the boat.

Smart meters made revenue jump/bills jump because they can measure the power factor all the switch mode supplies put on the grid, old analog meters didn't.

[brandnewb]

Regardless, without adjustments for slope the choice is pretty much permanently made at installation.  Moving panels without reroofing is adding holes to the boat.

Nah, I designed and build my home. So in this case restructuring the panels has nothing to do with the structure of roof the (that is in fact not a roof in terms of structure but just another floor) they are situated on. Other than of course the dimensions they allow for panels to be placed on.

But in general terms you might well be correct. And I did ask for an in general response.

[bigrockcandymountain]

For off grid, as Adriaan pointed out, south facing makes the most sense.  You will never be short on power in June (at our location 50 deg North) but you will be quite short in december, when east and west facing panels make the least amount of power. 

For a fixed array, the old rule of thumb is south facing with angle matching your latitude.  That gets you set not bad.

 I find it better to have a 2 position tilt. 65 deg winter 20 deg summer. 

Net metered grid tie is a whole different deal, and then the summer output maximising setups might work out better. 

[Adriaan Kragten]

The calculations of the output have been reviewed because I took a too high peak power of a solar panel size 1 * 1.65 m. The peak power is reduced from 400 W up to 300 W.

Dear Adriaan,

So in general; if one has far too much power generated by the solar panels oriented in a east-west back to back setup in summer times. with as goal generating as much as possible during winter times.
even after you have refined your study a bit based on the new peak values.

Would you still conclude that an optimal south facing orientation of the panels, even though now needing more spacing between rows, will benefit the power generation during winter times?

If that is the case then I need to find some new and inventive ways to reposition more than 22 panels as my roof is already maxed out (I now have 44 panels in a east-west back to back configuration)

One thing I have been considering is to have floating arrays of panels. But especially during winter time the sun is rather low so I will need to have them float outside of my property to have full sun. But I guess no one minds as then we have little to no boating activity during those times anyway. But then that damned freezing that could happen. Now I have to think of a raft type that can deal with that.

{1}reason I ask is because I am trying to transition away from grid connected as even though netmetering has been extended for some time by our government again. electrical utility providers are actively trying to circumvent the loss of revenue by employing really nasty tricks like for people with smart meters. Some if not most of them are now being taken from behind by now netmetering will be done on a monthly basis rather than annually.

I am ecstatic I have always resisted the installation of a smart meter. And please believe me they tried! hard!!{/1}

If you want to put solar panels on an existing house you have little choise about the slope and the azimuth. But for as new house or a new solar park, I think it is best if you optimise the positioning for the month December. If the solar panels are grid connected, the fee which you recieve for one kWh is much higher in december than in June. Maximising the output in December means orientation to the south and a large slope of about 60°. My calculations show that then the loss of energy in summer because of the large slope is less than the gain in winter.

Recently a new solar park was made in my town with east west orientation and a slope of 15°. I have calculted that the output in December is only about 10% of the output in June. If all solar panels would be orientated south at a slope of 60°, the output in December is about 1/3 of the output in June and so the grid imbalance is much lower. Another disadvantage of a small slope is the sensibility of damage by hail. Today I read a story that thouthends of solar panels were damaged is Texas by golf ball large pieces of hail. This was not only caused by the small slope but also because of the too small thickness of the panels ralated to the other dimensions.

[MattM]

High slope angle also lengthens the life of roof materials.