According to multiple news sources, PV arrays should face west or both east and west, rather than to the south, as is the standard.

These largely misleading reports were generally ignored by the industry. But then last year, Europe’s largest solar farm — the 300MW Cestas plant in southwest France — was built with its panels oriented towards the east and west.

The developer, Neoen, announced that this allowed the project to generate three to four times more energy per square metre than if it was facing south.

So were the alarmist headlines actually correct? Is it better for solar panels to look east and west? In some cases, yes, although not for the reasons you might expect.

The sensationalist news reports mainly stemmed from two studies, one in 2013 from Texas-based Pecan Street Research Institute, and one in 2014 from the UK’s Loughborough University, which both pointed out that panels facing west, or east and west, provided more electricity at times of high demand than south-pointing modules with their noon peaks.

This is entirely true and perhaps highly important for the future of the industry. It is partly why there is a growing trend for east-west panels on residential rooftops in markets such as Germany — yet nothing to do with why the Cestas plant was built that way or why there is an increasing number of east-west commercial rooftop projects.


“[East-west panels] looked like a strange idea,” Neoen chief operations officer Paul-François Croisille tells Recharge.

“We had seen it up in Germany in the various trade magazines, so it was something we tried out.

“When we identify a plot of land for a plant, we consider trackers, different distances between the rows [of modules] and different inclinations to find the best layout for those plants. The numbers [for Cestas] showed that the east-west solution was the best.”

It meant that Cestas would generate 15% less total energy than a south-facing plant of the same capacity. “But in terms of LCoE [levelised cost of energy], it turned out to be more interesting because of the high fixed costs,” Croisille says.

When Neoen was tasked with developing the site near Bordeaux, its initial plan was for a 150MW south-facing installation. The French company knew that would require a relatively costly connection to a 400kV transmission line (rather than the standard distribution grid) and an expensive high-voltage substation.

The size and complexity of the project would also mean high development costs for permitting, legal and regulatory issues, not to mention the complex financing arrangements, which eventually involved eight shareholders. These costs would largely stay the same, regardless of the final capacity of the project.

By comparison, the per-MW installation costs — panels, substructures, cabling and other hardware — would also remain largely the same, so a higher capacity would mean a lower LCoE.

But as the site could not be expanded beyond its 265 hectares, Neoen could only increase the capacity by squeezing more panels into the same space. South-facing panels, which generally operate optimally at a 25-30° tilt, have to be kept far enough apart so that shadows do not fall on neighbouring panels and hinder output.

But by alternately aligning panels east and west at shallow angles of 5-10°, they can be installed more closely together, eliminating the shading issue and allowing a lot more panels to be erected per square metre.

“We found out during our calculations that it was more interesting to pack more power into this site to divide the fixed costs over a larger number of megawatts,” says Croisille. “It’s truly a numbers-based analysis.”

So if the LCoE of a site can be lowered by packing in east-west panels, will Neoen continue to build solar parks in this way?

Croisille does not rule it out but says that the company has yet to find another site where such an arrangement makes commercial sense.“It was really very specific to that particular plant with very constrained land and very high fixed costs,” he says.

Some have argued that utility-scale east-west solar farms, with their flatter power curves, will become more commonplace to help grid operators balance supply and demand.

Others say this is unlikely.“There’s a small technical argument for east-west oriented modules [on flat roofs or open land] in that the daily curve of production is a bit more rectangular,” says Christian Reise, senior scientist at the Fraunhofer Institute for Solar Energy Systems in Germany.

“But it’s not a big difference.“If you do east-west on typical residential houses with 45⁰ tilted roofs, then it does have an effect — you have the morning peak and the afternoon peak. If you just do it with 5-10⁰ tilt, then there’s no real double peak, there’s only a noon peak, which is slightly flatter than the standard one.

“So it’s used as an argument, but it’s not the best argument.”


Yet the growing trend for east-west rooftop arrays in countries such as Germany has nothing to do with helping grid operators balance their loads. It is purely due to the growth of self-consumption — a result of falling feed-in tariffs (FITs) and rising electricity prices.

“We [in Germany] pay somewhere between €0.25 and €0.30 [$0.27-0.33] per kWh [for electricity from the grid], and you get power from your rooftop panels for something like €0.15,” says Reise. “So of course it’s better to use your own electricity during the day than to buy it from the grid.”

And with Germany’s FIT for standard residential arrays at only €0.127/kWh, it makes little economic sense to sell your solar energy to the grid, only to buy back the same amount of electricity for double the price.

So it is clearly better for consumers to use the energy that they generate. As people generally leave home in the morning and come back in the afternoon or early evening, it is logical for them to have PV panels that provide more electricity at these times, rather than at midday when so many properties are empty.

Of course, you cannot install east-west-facing solar panels on your roof if it does not already slant in those directions.

“If you look back to systems that were built a few years ago, you would typically find them facing south,” says David Wedepohl, director of communications and markets at the German solar industry association, BSW.

“And now you would typically see new systems on different parts of the roof that in the past you wouldn’t have used. One of the reasons is module prices have come down so significantly that even if you have a lower yield [per kW] it’s still worthwhile doing, particularly if you use the electricity yourself.”

Commercial (flat roofs)

The east-west orientation is also a growing trend on flat commercial and industrial (C&I) rooftops in Germany.

It allows warehouses, factories and offices to cram more panels onto their roofs, while the modules still generate a power curve that closely matches the buildings’ energy needs (as workplaces are usually busiest during the middle of the day), leading to more money-saving self-consumption.

“You can pack more kW of solar modules on a given roof area if you do it in very flat tilt angles; then you can use more or less the whole of the roof area for a PV installation,” says Reise.

“Nowadays, modules are quite cheap and you want to put as many as possible on a given roof because of the other costs for preparation on the roof — for connection, for cabling, this all is fixed — so if you put more modules on, you can save [on the LCoE].”

There are also other advantages for C&I east-west panels. South-facing panels tilted at 30° need heavy concrete ballasts to prevent winds blowing the modules over, or off the roof (fixing directly to the roof is rare as this usually causes waterproofing damage).

Tightly packed, shallow-tilted panels do not require such heavy ballasting, thereby lightening the load on the roof and cutting the per-kW costs.

And despite the extra weight due to the increase in the number of panels, east-west arrays may consequently be lighter than smaller south-facing ones. With C&I roofs generally not built to withstand heavy loads, the east-west orientation could make projects feasible that otherwise wouldn’t be.

Also, in Germany, businesses have to pay a capacity fee for their grid connection, priced according to their peak demand. A high amount of self-consumption will also reduce these costs.

“So if you take it all together — cheaper mounting, better use of area, lighter weight on the roof, there are many factors which may be in favour of east-west systems,” says Reise.

“Up to five years ago, the sector was more oriented around module prices and revenues, and today it’s more about space on the roof. You put all the modules you can on your roof and then look at what you can do with the electricity.”