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Supergrid (2) – could it work?

By Dave Elliott

In my previous post I looked at the potential and problems of supergrids. The basic idea is that, since, in various parts of the EU, there will be times when there is excess electricity generated from wind etc. over and above local demand, this excess can be shunted to regions which are short and have high demand, using low-loss HVDC supergrids. Would it work on a large scale?

Actually it is already done. For example Denmark exports excess (from wind) to Norway who may either feed it directly to their consumers, or use it to pump water into their hydro reservoirs, for later generation when demand is high. Denmark then imports electricity back, when there is no wind and/or high demand there. So in effect the Norwegian pumped storage/hydro reservoir system acts as a wind energy store.

There are some problems with this, which give us some idea of the problems that might face a large supergrid system. Firstly, in the spring and early summer, Norway’s hydro reservoirs may actually be full from snow melt, so they may not be able to pump any more water up. And in the summer, Norway may not need (imported) extra power, or indeed extra generation from it later on, since energy demand will be lower than in winter. The result is that Norway charges more for any power exported than it pays for what it imports – its value is low for them. That means an extra surcharge for Danish wind balancing.  And perhaps no exports available from Norway in winter, if its demand is high and reservoir water levels low. Germany has been eying Norway’s hydro storage as an option for balancing their much larger wind excesses, so these problems will only get worse. There will be increased competition for Norway’s storage capacity.

What about a wider system, not just for storage, but for balancing supply and demand peaks and troughs in real time?  Winds are often westerly from the Atlantic, so the UK and Ireland gets them first, central Europe some hours later. That means there is an initial opportunity for the West to export to the East for a while, the different clock time also helping.  At other times, usually in winter, there are strong easterly winds from the Arctic (as last winter). Although the North may have an initial advantage, energy demand will be high everywhere, and there may not be much spare.  And at other times there will be little wind anywhere. That’s when you need the stored hydro! Or stored hydrogen produced from excess wind derived electricity. As well as demand management to shift/delay demand peaks. But it could be tight. In 2011, National Grid modeled 2030 scenarios (PDF) assuming zero input to the UK from interconnectors at peak times (in two if not all three scenarios) presumably since it was felt that there would be little surplus available from continental Europe during peak demand times.

However demand peak timings do vary with location (and clock time)  around the EU, as does wind, so this assumption may be too sweeping.  Moreover, this has all been just about wind, and hydro storage. But there are also other renewables.  In last winter’s cold spell, at some points during daytime, when skies were relatively clear (as they can be in winter), Germany’s 30 GW of solar capacity was offering the grid nearly12 GW, while wind was offering under 20 GW, out of its 30 GW capacity.  For comparison, in the UK, in late March last year, wind offered over 5 GW, out of its installed 7 GW, but solar more or less zero (out of its 2 GW), since panels were mostly covered by snow and it was cloudy. If the UK had wave and tidal power capacity, that would have added a useful input.  So would geothermal and biomass. Depending on how much wind, wave and tidal etc. capacity the UK had, it could have probably exported some power; it did actually export power to Ireland in the March cold spell, although it imported much more from the continent, using the existing 3 GW or so of undersea links.

These interconnector electricity imports were partly due to depletion of UK gas stocks and reserves and the failure of a gas grid import link from the continent, something that would be avoided if there was stored hydrogen (or methane) from (earlier) excess wind.  And if the UK had a large offshore wind capacity, then it would often have had enough to export. The Pugwash High Renewables study found that over the year the UK could export over £15 bn worth!

However we come back to the basic question I looked at in the previous post, of whether there would be demand for it all.  If not, at any particular point, then it could be turned into hydrogen/methane, and that might be a better idea anyway, giving the UK an indigenous stored reserve.  To some extent it depends on the economics.  Hydrogen electrolysis and storage is expensive. It might be more lucrative to sell the excess electricity abroad and import any when needed – if it’s available.  Possibly using power from pumped hydro storage in places where there is sufficient – the UK is never going to have as much as Norway.

Despite these uncertainties, it seems inevitable that some elements of an EU super-grid will emerge, especially as offshore wind farms spread across the North Sea. They will initially just be linked back to shore, to the UK or to the continent, but as they are installed further and further out, links right across to North Sea will be made, with power sent to wherever it commands the highest prices. This may happen piecemeal and possibly be a mess, or we can plan it coherently to create an effective balancing system.  That’s even more important if links are extended to the large solar potential in the South and in Africa. That needs to be thought about, since a northern-only supergrid relying mostly on wind could occasionally be becalmed, although even then it would still give access to energy stores elsewhere and help to balance loads. However a full-scale supergrid must surely be the long-term aim. It may take time. But as I argued in my previous post, given the role it could play in balancing the EU’s variable renewables, it seems unlikely that the potential for importing energy derived from huge solar resources of north Africa will be ignored indefinitely.

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