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Plenty of renewables – and they can be balanced

By Dave Elliott

Is there enough renewable energy to meet global needs and can the use of variable sources be effectively balanced?  Recent reports say yes on both counts. In terms of the total resource, a GIS-based study of land/sea use/availability has put the total 2070 global potential for renewable electricity at up to 3,810 EJ, led by solar PV, with about a third of the PV being on buildings. The total estimated resource was roughly in line with most other global renewable studies, like that from the IPCC, and well above likely total global electricity demand, put at around 400 EJ: www.sciencedirect.com/science/article/pii/S0959378015000072

The global renewable resource was not evenly spread, with in some regions, the scale, and access to it, being more constrained, but overall there was plenty available for growth. And that seems likely to happen, as the costs of its exploitation fall. According to a new report from Bloomberg New Energy Finance, the average cost of developing wind projects will fall by 32% and the cost of solar PV projects will fall by 48% by 2040. Within a decade, wind will become ‘the least-cost option almost universally.’ And by 2030, solar will become the cheapest resource. As a result, wind and PV uptake will continue to accelerate, across the world, up from 370 GW and 180 GW respectively now, with renewables overall representing just under 60% of the 9,786 GW of new generating capacity by 2040: www.bloomberg.com/news/articles/2015-06-23/the-way-humans-get-electricity-is-about-to-change-forever and http://fs-unep-centre.org/publications/global-trends-renewable-energy-investment-2015

A new study by the Fraunhofer Institute for Wind Energy and Energy System Technology commissioned by Agora Energiewende looked at the situation in the EU. The study assumed that, by 2030, around 50% of electricity in the EU would come from renewables, wind and PV mainly. That of course would lead to integration and grid balancing problems, since these sources are variable. However the study found that greater grid and market integration of Central Western European (CWE region) power systems could significantly help cut costs in balancing weather-related electricity fluctuations, while reducing losses due to the need to curtail excess output.

It concluded that ‘regional European power system integration mitigates flexibility needs from increasing shares of wind and solar. Different weather patterns across Europe will decorrelate single power generation peaks, yielding geographical smoothing effects. Wind and solar output is generally much less volatile at an aggregated level and extremely high and low values disappear. For example, in France the maximum hourly ramp resulting from wind fluctuation in 2030 is 21% of installed wind capacity, while the Europe-wide maximum is only at 10% of installed capacity.’

It added ‘Cross-border exchange minimises surplus renewables generation. When no trading options exist, hours with high domestic wind and solar generation require that generation from renewables be stored or curtailed in part. With market integration, decorrelated production peaks across countries enable exports to regions where the load is not covered. By contrast, a hypothetical national autarchy case has storage or curtailment requirements that are ten times as high.’ http://www.agora-energiewende.de/en/press/agoranews/news-detail/news/europa-50-prozent-erneuerbare-energien-bis-2030-sind-bei-staerkerer-integration-gut-darstellbar/News/detail/ For a summary: www.nanowerk.com/news2/green/newsid=40581.php

The central message was that differences in weather across Europe to some extent cancel each other out. The study simulated hourly and weekly power production from renewables over a full weather-year, taking into account the expected number of solar and wind facilities that will be available by 2030. The results show that more closely networking power systems in France, Switzerland, Austria, the Benelux countries and Germany would reduce demands for flexibility commonly associated with swings in wind and solar power production. Closer integration of power networks would make it possible to balance regional weather differences and thus the differences in wind power production on a large scale. Indeed, the effect was so strong that the fluctuation in wind power production across the entire CWE region amounted to only half of all fluctuation in individual countries. Greater integration also allowed the system to take advantage of national time zone and peak demand differences, and as noted earlier, prevented losses due to the need for curtailment of renewable output on very windy or sunny days, since surpluses in one region can offset shortfalls of supply in others. Compared to power systems that are not integrated, such power plant cut-offs could be avoided in 90% of all cases. That raises the monetary value of power from renewables.

Overall then, this study flies in the face of the contrarian view that cross-EU balancing via supergrid links can’t help much since the wind is often low everywhere: e.g. a study for the Adam Smith Institute claimed that integrating wind operation across the northern European plain, covering Belgium, Holland, Denmark and Germany, and also Ireland, ‘does little or nothing to mitigate the intermittency of these wind fleets.’ www.adamsmith.org/wp-content/uploads/2014/10/Assessment7.pdf   Similar claims have been made about even wider integration than considered in the new study e.g. see http://euanmearns.com/wind-blowing-nowhere/. The reality seem to be that substantial balancing can be achieved, as the Agora report’s hourly and weekly balancing charts show.

However closer integration of the power system does not entirely reduce the need for other types of system flexibility: for example, the Agora report says ‘avoiding curtailment altogether would be difficult to achieve just by increasing transfer capacities, as highly correlated feed-in situations can still occur’. So the report notes that flexible power plants (pumped storage, gas plants) and power storage facilities will still be needed to back up and balance fluctuations, although less-flexible power plants that run continuously will only be needed to a very limited extent. Though backup will still be needed, since occasionally ‘situations can occur in which conventional power plants and imports must cover almost the entire load’, regardless of the capacity share of variable renewables. Even so, ‘base load capacities will decrease relative to those of today, while peak load and mid-merit capacities will increase’. All of which means a very different approach to system design and management, and ‘renewables, conventional generation, grids, the demand side and storage technologies must all become more responsive to provide flexibility’.

The focus in this analysis was on wind and PV derived electricity, but of course that’s only part of the story. There are also renewable heat sources and some of these can help with overall energy balancing, for example with solar heat being fed to large heat stores to meet demand when there is less solar (or wind) input. The new annual review from the International Renewable Energy Agency notes that there is now over 400GW (thermal) of solar heat capacity in use globally: http://www.irena.org/menu/index.aspx?mnu=Subcat&PriMenuID=36&CatID=141&SubcatID=604

That’s actually more than wind. Much of it is in China, but there are also large solar-fed interseasonal heat stores in use in Northern Europe, with 60 projects in Denmark, many more planned, and the expectation that up to 18% of its district heating demand can be met from solar by 2030: http://www.solar-district-heating.eu/NewsEvents/SDHConference2015.aspx

Surplus power from wind/PV can also be stored as heat, using immersion heaters in water tanks- or heat can be produced directly by wind: www.sciencedirect.com/science/article/pii/S0960148115003079

One way or another, it looks like solar and wind can be used extensively across the world without major balancing and curtailment problems and with supergrid links helping out. Although, as I will report in my next post, gas grids and (green) gas storage may also have a role to play.

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