Breaking with solar traditions since 2008

Radically new solar plant designs: best inclination angle – how low should I go?

Solar plants are changing. From one-size-fits-all towards well-adapted systems that give better technical answers to the most common (cost) problems. With these posts I’d like to contribute with new solar technologies that I’ve developed over the last couple of years.

In my previous I’ve shown several variations of the X-panel solar technology where the solar modules are neither installed in a portrait nor in a landscape orientation, but in a position “in between”. These arrangements all help the solar panels to stay clean due to better evacuation of (dirty) water.

Typical soiling due to a backwater effect.

The reason is: Most of today’s solar panels are embedded in aluminum frames. At low slope angles the lower frame rail of the panel builds a horizontal raised rib at the lower edge of the module. This rib causes a back-water effect. The filthy water is not correctly run off resulting in the accumulation of dirt on the glass alongside the lower frame rail (see picture). This often results in significant loss in yield.

Rotating the panel is a simple yet cery effective way to ensure proper runoff of the rainwater.

Leading solar project developers like ENERPARC declared that as far as the module angle, 20° was the “magic number”. They didn’t go flatter to avoid soiling losses. Now they do because with the new X-panel arrangement the horizontal corrugation disappears. The lower frame rails now both show slopes ensuring proper runoff of rainwater (see pictures). Thus the panel will remain clean, even at slope angles of only a couple of degrees.

After reading my articles, people sent messages like “Ok, I understand that now I can go much lower with the same modules than before. But why should I?” The answer is: For most solar parks in this world, you can use slope angles of 20+ degrees (or trackers), and you’ll have a very economic solar plant. However, there are at least three situations where you can lower your electricity cost (LCOE, levelized cost of electricity generation) by going flatter with your panels. This article tries explains these main reasons.

reason one: You’re close to the equator.

If your plant is quite close to the equator (e.g. within the 15th degrees of latitude), a reduction of slope angle below 20 degrees will boost energy yield. If this boost comes without additional cost due to soiling, your LCOE will drop.

reason two: You’re threatened by tropical thunderstorms.

If your solar plant is going to be installed in a region where excessive wind loads are common, you have to go as low as possible with your slope angles, first and foremost to protect the modules. The same wind will apply a lot less forces on the panels of a 10 degrees system then it will apply on the very same panels installed at 20 degrees. Solar aerodynamics Guru Dr. Thorsten Kray regularly comments on this point. More protection, less LCOE.

reason three: You’re in Germany. Or in the Netherlands. Or anywhere else where land is expensive.

ENERPARC’s 7.7 MWp solar park near Parsberg, Germany. Picture: ENERPARC

ENERPARC’s X45 solar park (7.7 Megawatt peak, picture: ENERPARC) is a perfect example to explain this point. This solar park is located in southern Germany. The location is unsuspicious of being close to the equator or being regularly at the mercy of thunderstorms. Nevertheless, ENERPARC switched from their 20 degrees south-facing standard system to a 12 degrees X45 design. The reason to lower the slope lies in the cost structure of current solar parks. Panel prices (and other variable costs) have declined considerably over the last years while fix cost (and most of all the cost for land) have not (or not to this extent).

X-panel allows to reduce the distance between the tables significantly without adding any additional shading.

This shift in the cost structure from “variable” towards “fix” cost has made EPCs to start changing their perspective on LCOE especially in countries where land is expensive. Now they try to get more and more panels on a given ground, because: A larger number of panels per hectare reduces the cost per kWp. The variable cost per kWp still remain constant, but fix cost are allocated to a larger number of modules, hence the total price per kWp drops. At the same time there’s this 20-degrees-limit to avoid soiling. There are some south-facing solar parks in Germany by now with an extremely high ground coverage ratio of close to 0.8. If you combine a “dense” solar park where 80 percent of the ground is covered with solar panels at a slope angle of 20 degrees, the self-shading losses become very important: With this layout, the lowest line of modules on the tables is shaded even at noon for five months a year. That means significant yield losses.

X45 system, inclination angle is 12 degrees. Picture: ENERPARC

The X45 system (picture: ENERPARC) allowed ENERPARC engineers to lower the slope angle by 8 degrees. They did not change the ground coverage ratio, they only went down from 20 to 12. The result was: On the one hand the (theoretical) irradiation in the module’s plane decreased by three percent, since the panels had been “turned away from the sun” to a certain degree. At the same time the shading losses decreased by six percent due to the now significantly flatter module tables. The net gain was three percent more yield per year, nota bene with the same number of panels as before and on the same ground (see PV magazine, issue March 2017). Or, if you want it that way, an additional 700.000 kWh per Megawatt peak over the next 25 years, compared to the previous system.

Summary: Most of today’s solar parks work very good with slope angles of 20 or more degrees, so they wouldn’t benefit much from a switch to X-panel (or other low-slope technologies). However, if the plant is close to the equator or wind loads are a major issue, X-panel arrangements might be helpful. The third reason is high land cost. The higher the fix cost portion of a solar project (Capex and Opex), the more it pays off to place more panels on a given ground. Cost for land is often the most important fix cost part. So if the land is expensive, it may be very economical to use panel arrangements (e.g. X-panel) that allow for much lower slope angles than today’s standard systems. If land is expensive, then fill it up with modules. It pays off, it lowers LCOE.

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