Record temperatures put the heat on solar in Europe

Renewables International

According to preliminary data, Spanish solar power production was 27.7 percent below its maximum despite excellent sunshine during the recent heat wave. As temperatures rise, the efficiency of photovoltaics drops. A new solar power production record in Germany may have also been set on a relatively cool day.

As I recently explained with reference to solar in Dubai, the efficiency of photovoltaics drops by up to 0.5 percent per degree Celsius above the laboratory testing temperature of 25 degrees Celsius. The result, by the time you hit 45 degrees Celsius, is a 20 percent reduction in peak output. Note that what matters is not the ambient temperature, but the panel temperature; at an ambient temperature of 40 degrees Celsius, the panels could easily reach 60 degrees Celsius. Likewise, at temperatures below 25 degrees Celsius, efficiency increases. So in cold, sunny areas, like Colorado or mountainous Chile, PV is likely to be more efficient than its rating.

Now, my colleague Ralf Streck, who covers Spain for German website Telepolis (where my career started), writes that the heat wave in Spain raised power consumption to a near all-time high, and PV was not able to keep up. The official data from Spanish grid operator REE (table in Spanish) for Monday do not quite reveal what he reports; we only see the number of GWh generated that day for each technology, not a comparison with the potential. But according to REE’s analysis, solar power production was 27.7 percent lower than would otherwise be expected. The official data will apparently be published on August 5.

On Monday, Spanish power demand also reached 39.3 GW at 1:31 PM, close to the most recent record for the summer of 40.1 GW from 28 June 2011 (website in Spanish). Note that power demand generally peaks for the year as a whole in the winter in Spain as well; in 2013, the maximum demand was reached at 39.963 GW on February 27 between 8 and 9 PM (see page 11 of this PDF). In comparison, summer peak demand last year reached 37.4 GW. The all-time high in Spain is 45.4 GW from the winter of 2007 (report in Spanish). (That report also estimates the recent efficiency losses from heat at around 25 percent but also cites other sources putting the figure at between 10 and 12 percent.)

Spanish peak power demand is thus relatively balanced compared to northern Europe; the difference is less than 10 percent in Spain and generally more than 10 percent north of the Alps. In countries with higher peaks for demand in the summer, more photovoltaics can be integrated without curtailment or storage because electricity demand and solar power production coincide – especially when, as in Spain, those summer peaks come around noon time.

On Sunday, Germany posted its all-time high temperature of 40.3 degrees Celsius, so I took a look at German solar power production data. That day, solar power production peaked at 21.4 GW, compared to 26 GW on June 1 – a difference of around 15 percent.

 

Sundayrecord

 

Cloud cover needs to be taken into account; unfortunately, I do not know of any website that provides insolation data for Germany on specific days (please use the comment box below if you do). The weather forecast for that Wednesday (in German), however, shows less cloud cover than on Sunday (in German), but also lower temperatures – around 10 degrees, it seems.

On 21 April 2015, Germany posted a new record for solar power production, originally reported at just below 25 GW so the level of 26 GW on July 1 would be a new record (strangely, I have not seen it reported as such – the record from April was widely celebrated immediately). However, Fraunhofer ISE adjusted that figure from April upwards to 27.3 GW in its recent overview (PDF in German). Note that Agora reports only 23.15 GW of solar power on July 1 and 25.8 GW for 21 April 2015.

A spokesperson for German grid operator Tennet told a German newspaper that the high temperatures over the past week also led to haze, which partly reduced solar power production along with the temperatures. A PV expert is also quoted in the paper saying that the “maximum power production from all PV arrays in Germany is around five percent under such extreme conditions.” At Telepolis, Streck quotes the Spanish photovoltaics association Unef, saying that a 20-25 percent reduction in efficiency due to heat is “normal.”

The heat wave led to significant power outages in France, where up to 800,000 people were temporarily without electricity as transformer stations failed. Germany also experienced similar transformer failures, but the damage remained smaller. On July 6, a 43-year-old Swiss nuclear plant had to shut down because of the heat (report in German), shortly after it had to reduce its power production because the temperature of the river water it uses for cooling approached the limit (report in German). Otherwise, nuclear plants in Europe seem to have performed well during the heat wave. Coal plants also occasionally have to reduce power production for similar reasons, but I have seen no reports on recent failures.

Source: Renewables International. Reproduced with permission.

Comments

One response to “Record temperatures put the heat on solar in Europe”

  1. Ray Miller Avatar
    Ray Miller

    This is all a surprise! Well to some maybe, but all this information needs to be seen as a system, and a some what unstable system at that. The fundamental problem is the temperature coefficients of all the components (minus the occasional exception) in our physiological, biological and energy systems are made worst by increasing temperature. If we truly understood the physics and engineering of increasing temperatures our society be would be solving a different problem. What is 2 or more likely 3 degrees of warming going to look like if all this happens at less than one?

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