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Vehicle to grid balancing

By Dave Elliott

The vehicle to grid (V2G) debate continues, offering a way to balance variable renewables and also demand peaks, by using the batteries of electric vehicles, linked to the grid when parked at home, to store excess power during low demand periods, ready to export when demand is high and renewables low. It sounds a clever idea but in addition to economic issues (e.g. the extra costs of the home-based power uploading system) it opens up some interesting logistical issues. (more…)

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Grid battles

‘Battle of the Grids’, a new Greenpeace report, says that we are fast reaching a showdown between ‘green’ and ‘dirty’ energy. ‘Thousands of wind turbines delivering near free energy were turned off in 2010 to allow polluting and heavily subsidised nuclear and coal plants to carry on business as usual. It is estimated Spain had to ditch around 200GWh of energy last year. The buzz on the lips of industry specialists, lobbyists and in boardrooms is about system clash and the costs of building and running what is increasingly becoming a dual system’.

It is certainly true that there is a conflict looming as we plan the expand both nuclear and renewables. What happens when there is a lot of wind power available but energy demand is low, as at night in summer. Do we then switch it off or switch off inflexible baseload nuclear plants?

The Greenpeace report demonstrates the problem on a European scale, and offers suggestions for how it can be resolved. Together with Greenpeace’s 2010 Energy [R]evolution report, it builds on its earlier Renewables 24/7 study, exploring a new system for the EU which it says can deliver 68% renewable energy by 2030 and nearly 100% by 2050, with the use of gas, coal and nuclear then phased out. That’s in line with several other recent ‘100% renewables by 2050’ studies; see my earlier blog.

But this report goes a further and looks in more detail at how to balance variable renewables and variable demand across the EU

It’s based on modeling work by Energynautics, covering electricity consumption and production patterns for every hour 365 days a year at 224 nodes of electricity interconnections across all 27 EU countries, plus Norway, Switzerland and the non-EU Balkan states.

The report calls for the development of a smarter, more efficient EU-wide grid linking up variable renewables and energy storage facilities, which it claims could ‘guarantee supply despite extreme weather conditions, delivering green energy around Europe via efficient, largely below ground DC cables’. High Voltage Direct Current supergrids are much more efficient over long distances than conventional AC grids (with energy losses of perhaps 2% over 1000km compared to up to 10% for AC grids) and it’s claimed that it is easier and cheaper to put DC cables underground.

In the proposed optimal approach to balanced energy supply, natural gas is phased out by 2030 as are most coal and nuclear plants, and by 2050 it’s almost 100% renewable with wind and solar dominating: ‘even if technical adaptations could enable coal and nuclear plants to become more flexible and ‘fit in’ the renewable mix, they would be needed for only 46% of the year by 2030 and further decreasing afterwards.’

A key element in their approach is demand side management via an EU-wide interactive smart grid system, which allows loads to be shifted in time to avoid peaks, and can balance inputs from variable renewable across a much wider geographical area – thus avoiding the need for curtailment of excess wind or back ups when there isn’t enough wind locally or regionally.

That is pretty ambitious. At present wind is usually seen as only having a small capacity credit (i.e. only perhaps 10–15% of the installed capacity can be relied on statistically to meet peak demands, due to natural wind variability). So it’s seen as mainly just a fuel saver, replacing the output of some fossil plants some of the time – these fossil plants then returning to full load when there is no wind. So they are the back-up – they are mostly gas-fired plants that we already have, so there is no extra capital cost. Indeed they are already used to balance the twice daily peaks in demand and to deal with variable supply e.g. when a conventional or nuclear plant goes off line suddenly. Balancing the slower variation in wind (with improved wind forecasting helping to reduce the uncertainty) means that they have to ramp up and down to and from full power a few more times.

However, that involves operational and economic penalties – these plants are less efficient when running part loaded. That is even more the case with nuclear plants, which are run 24/7 to recoup their large capital costs and can’t ramp up and down quickly or repeatedly. So that is why we are seeing excess wind being dumped and hearing talk of having to build more back-up plants to balance wind. Greenpeace suggests that similar inflexibility problems would also emerge with coal plants fitted with Carbon Capture and storage.

In the Greenpeace scenario all this is avoided by using a mix of demand side measures (e.g. switching off some loads than can be easy interrupted without problems for a few hours, such as freezer units) and importing green power from other regions via the EU wide supergrid. In addition, their system has inputs from biomass-fired plants and geothermal plants, that can be varied, and from pumped hydro storage, topped up when there is excess wind or other green power somewhere on the system.

It’s a much more interactive system, with no formal ‘always on’ baseload, although the biomass, geothermal and hydro plants can perform that function.

What would it cost? They claim that it’s much more expensive to waste valuable wind and other variable renewables than to build balancing supergrid networks. They put losses from curtailing wind at €32bn/p.a. but offer a version of their proposed grid system which they say would cost €74bn between 2030 and 2050.

This ‘Low Grid’ pathway would seek to produce as much renewable energy close to areas with high electricity demand as possible (i.e. within central EU, e.g. with PV solar). They say: ‘Security of supply relies less on the electricity grid and long distance transmission. Instead the gas pipelines are used more intensively to transfer gasified biomass from one region to the other, thereby optimising the use of biomass as a balancing source’, with former gas plants converted from natural gas to biogas.

By contrast their ‘High Grid’ approach would install ‘a maximum of renewable-energy sources in areas with the highest output, especially solar power in the south of Europe and interconnections between Europe with North Africa.’ This would minimize generation costs but increase interconnection costs to €581bn between 2030 and 2050. It would give strong security of supply, 24/7, since they say the supergrid capacity exceeds demand. It also balances solar production in the south and wind production in the north of Europe.

It’s challenging stuff, with some very large capacities being installed, for example, by 2050, in the EU27, PV is at 888–974GW, wind 497–667GW, bioenergy 224–336GW, depending on the scenario, while Hydro is at 163GW, CSP 99, Geothermal 96, and Ocean energy 66GW.

See www.greenpeace.org/international/Global/international/publications/climate/2011/battle of the grids.pdf.

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