Can renewables meet the need?

A recent tweet celebrated the supposed fact that at peak, recently, Germany derived 25% of its power from solar. The source given was data published by the Fraunhofer ISE at https://www.energy-charts.de/power_de.htm.  But is the claim true?

Actually no. The highest proportion in recent weeks was reached during August 2nd when a combination of low demand, low winds and strong sun produced about 56% of Germany's electric power from solar pv. A very good result - though obviously excluding fuels used for space heating, travel, etc.

But it's a power number - a measurement over a short time - specifically the middle of the day. There is no solar power at night and not much in the early morning and evening. A bit of rough analysis for a more representative day, 27 July in fact, shows that solar produced 22% of the power at peak but 10% of the day's energy. Extra investment in solar PV could increase the peak as much as you like - even to 100% - but that would still need over 50% of the energy to come from somewhere else (possibly wind or a storage system).

And this is mid summer.

A similar analysis for January shows a solar PV power peak of c8% but providing only c2% of the day's electricity. And the average over that week is much worse.

Is wind the answer? Sort of. Germany gets more energy from wind than from solar PV and it's available at night and in winter. But it's even less predictable than solar. At midnight on January 5th it provided just 3% of the needed electrical power.

Moreover periods of low wind can last for days - there was almost no wind for the whole seven days starting January 17th.

There are partial low-carbon solutions - nuclear, tidal, hydro, import of power from very large new solar farms in north Africa and various kinds of storage - but they all have their own problems.
Any responsible plan for our energy future must show how it would cope with periods like 17 to 14 January - and at what cost.

Wind farms perform better than we feared

Some commentators have claimed that the performance of wind farms will decline catastrophically with age. For instance, a report by Prof Gordon Hughes for the Renewable Energy Foundation claimed that the “normalised load factor for UK onshore wind farms declines from a peak of about 24% at age 1 to 15% at age 10 and 11% at age 15”. That implies an annual worsening of about 5% and would presumably be due to mechanical wear. 

It would greatly reduce the long-term value of wind farms both economically and as sources of low-carbon electricity.

Fortunately a more recent study, Staffel and Green, 20 13, suggests that it isn’t true. This is an extremely detailed study which draws on very large quantities of data about both weather and wind farms. The authors show that, though wind farm performance varies considerably:

•  The initial load factor is 28.5% not 25%.
•  The annual performance loss is about 1.6% not 5%.

This is good news for investors in wind farms and for the climate.

References

Hughes, Gordon, 2011: The Performance of Wind Farms in the United Kingdom and Denmark. 2012, London: Renewable Energy Foundation. URL: http://tinyurl.com/cn5qnqg.

Staffell, Iain, and Green, Richard, 2013: How does wind farm performance decline with age? Renewable Energy. Volume 66, June 2014, Pages 775–786. URL: DOI: 10.1016/j.renene.2013.10.041.

Blowing Away The Warming Pause Mystery

Let's be honest. The 14 year pause in global warming has been been an embarrassment to climate modelers and a joy to climate change deniers. Until now. But now modellers at several research centres in Australia and the US have explained the pause as the effect of strong winds.

No-one who's been watching the UK news this year will be unaware of the persistent extreme weather - winds, rain, storms and floods - that has afflicted the UK. These extremes were predicted by climate models and will become more severe for decades to come whatever we now do.

Now these researchers noticed that the Pacific Trade Winds have been much stronger than forecast by the climate models. When they fed the actual wind speeds into a suitable model it showed that the winds made ocean currents stronger and that these currents drove more mixing between warm surface and cool deep waters. Result - lower surface temperatures and thus lower air temperatures. Thus the pause.

The study does not tell us whether the pause will continue since that depends on the degree to which future wind speeds exceed those in the climate change models.

There are lessons in humility here for all concerned!

Summary: New Scientist, 15/2/14, p 14.

Original paper: Nature Climate Change, 9 FEBRUARY 2014 | DOI: 10.1038/NCLIMATE2106