メモ「ドイツの冬は再生可能エネルギーのアキレス腱を示す」by Reuters

[Gerard Wynn: "German winter shows Achilles heel of renewables: Wynn" (2012/10/16) by Reuters]

The extreme variability of wind and solar power in Germany is laid bare by 2012 data that also illustrates a particular vulnerability when power demand surges on cold winter days - they are often both weak at the same time.


Intermittent renewable energy requires grid balancing services, primarily from stand-by baseload fossil fuel capacity or battery and pumped storage, but also via interconnectors bringing power from other countries and regions.

The cost of that balancing need is still unclear, as European countries ramp up wind and solar capacity with an eye to meeting 2020 targets, with ambitious goals including Britain's aim to meet 15 percent of its primary energy demand from renewables, compared with less than 4 percent now.

Germany provides a good litmus test, given its large economy and rapid shift to renewable energy in the past five years.

Data from Germany's Fraunhofer Institute provide a detailed picture for the first 40 weeks of the year, from January 1 to October 7, and indicates the scale of grid balancing already needed.

For example, while the renewable energy lobby cheered a solar power peak at 22.4 gigawatts (GW) (or about a third of total lunchtime demand) on Friday, May 25, perhaps more relevant was a slump in combined wind and solar power during a surge in demand in an early February cold spell.



大規模な経済と過去5年の再生可能エネルギーへの急速なシフトにより、ドイツは良い判断材料を提供している。ドイツFraunhofer Instituteのデータは、2012年の1月1日から10月7日までの40週間分のデータは、既に必要となっているグリッドバランシングの規模を示している。例えば、再生可能エネルギーのロビーたちは5月25日に、ランチタイムの需要の1/3に相当する22.4GWを太陽光発電が記録したことを喜んだだろう。しかし、2月早朝の寒い需要増大時に、風力発電や太陽光発電の同時の落ち込んでいる。


Superficially, wind and solar in Europe complement each other seasonally, with summer peaks for solar power coinciding with a lull in wind power and the reverse holding true.

For example, aggregate solar power generation in the first week of January was only 7 percent of peak production in the final week of May, while for wind power generation the same week saw eight times the level in the first week of July, the minimum for the year so far.

However, that only applies when considering aggregate weekly or monthly data. In fact the two do not average out.

At a more refined hourly and daily level, wind power is seen to be equally unpredictable at any time of the year, recording minimum generation of 1 percent or less of installed capacity in each of the first nine months of the year.

Lulls in wind power in winter especially coincide with anticyclones bringing clear skies and cold weather when power demand is also high, revealing an Achilles heel for renewables, when sunlight is still relatively weak and the wind drops.

A northwest European cold snap which hit a nadir in the week starting February 6 is illustrative.

The week recorded the second lowest combined German wind and solar power generation of the 40 weeks in 2012 to date, at 0.77 terawatt hours (TWh) compared with a weekly average of 1.48 TWh, Fraunhofer Institute data show.

In the same week, French power demand hit at an all-time record of 102 GW, on the evening of February 8, which affected Germany as it is a major exporter to France in February.

French power demand is especially high in winter because of a reliance on electric over gas heating.

Following this combination of factors, German conventional power production (fossil fuels and nuclear) also hit a 2012 high on the evening of February 8, at 65.9 gigawatts.

Natural gas in particular supplied the gap left by renewable energy, with peak production of 22.4 GW, very close to total gas-fired capacity of 24 GW.

While the grid survived, the risk of blackouts is clearly elevated without substantial fossil-fuelled back-up capacity.

And the narrowness of the margin suggests the confidence of the European Commission, in its "Quarterly report on European electricity markets", for the first quarter this year, may be misplaced:

"Despite harsh winter conditions, there was not a single serious disturbance in the European electricity system. This underlines the strength of the European internal electricity market and the effectiveness of related European policies."




2月6日から始まる週に北西ヨーロッパを襲った寒波は、その例である。その週は、ドイツの風力発電と太陽光発電の合計出力が2012年最小の0.77TWhとなった。Fraunhofer Instituteのデータによれば、平均1.48TWhである。



電力グリッドは生き延びたが、火力発電のバックアップ容量の増大がなければ、停電のリスクは明確に上昇している。予備力の減少は、欧州委員会の第1四半期の "欧州電力市場に関する四半期報告書"が表記するグリッド信頼性が見当違いなものであることを示している。
Despite harsh winter conditions, there was not a single serious disturbance in the European electricity system. This underlines the strength of the European internal electricity market and the effectiveness of related European policies.



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