Supergrids

Renewable energy sources are not always located conveniently where we want them, so it is fortunate that efficient high-voltage direct current ‘supergrid’ power transmission has emerged. HVDC can cut energy transmission losses to 2%/1,000 km, compared to maybe 10% for conventional HVAC transmission and distribution. 

HVDC supergrid links can be used to enhance power trading between those countries with excess renewable supply at any particular point in time and those with shortfalls.  In particular, they can help deal with the local variability of some renewables. Linking up sources over a wider geographical area increases the probability that there will be surplus power available for trading: the wider the geographical spread, the better the balancing potential. 

However, there may be issues with supergrid power trading, depending on the location. For example, in the context of using solar arrays in North Africa to provide power for Europe, there is the risk of ‘land grabs’ and exploitative relationships between rich EU countries and poor African communities. In theory, it could be a mutually beneficial trade, with money from the North invested in projects in the South, and in grid links to them, leading to local energy, economic and employment gains. But its net impact would depend on the terms of the trade and ownership rights in relation to the resource and the systems.

That is not just an issue for North Africa and the EU or, for that matter, European green power imports from what could become a solar-rich Middle East. The proposals emerging for supergrid links across Asia also illustrate some of the likely regional geopolitical issues there, as for example with the proposal to link major solar and wind projects in Mongolia and the Gobi desert with energy demand centres in China, South Korea and even Japan. China should be able to meet most of its energy needs from its own vast renewable sources and perhaps also export surpluses at times, although there could be benefits from imports from outside for balancing. However, the situation in South Korea and Japan is very different. They have major space constraints, Japan especially, with high population densities and fewer areas available for solar, onshore wind or biomass projects. So they would likely be net consumers of green power, imported via supergrids, which would also help with balancing. There may be times when local demand and the availability of local supply from elsewhere are not well matched, but, given a wide spread link up, there could be major, and lucrative, power trading of surpluses to meet shortfalls.

Geopolitics

However, the geopolitics could become quite difficult. For example, in the Golden Ring north-east Asia-wide concept, linking China, Japan and possibly India, it would make geographic sense for west to east supergrid lines to cross North Korea on the way to Japan. Links have also been proposed westwards from China to Russia (linking up to the latter’s hydro resource), with obvious political implications and, perhaps equally contentious, there have been proposals for links between Asia and Europe. In the latter case, an EC Joint Research Centre study looked at possible HVDC grid routes west to the EU, linking the major wind resources in north-west China and Mongolia, and also large resources on the way across. The ‘high’ route, via Russia and Ukraine, was seen as politically problematic, the middle route, across the Near East, avoided Russia but would involve some costly undersea/lake cables, while the lower route crosses some tough terrain, and also Iran and Afghanistan. Plenty of geopolitical issues there.

Similarly, the idea of linking the EU up to Russia’s extensive renewable resources is contentious. Russia has yet to develop this large resource significantly, hydro apart, but longer term, if it did and supergrid links can be made, it could become a major exporter of green power, for example from wind projects in the vast windswept steppes of Siberia. Kazakhstan also has a huge wind resource and could become another major player. 

Links from Europe to North America are also technically possible and open up another set of geopolitical issues. One route would be between the United Kingdom and Canada via Greenland. The United States might find that hegemonically challenging, and so might the EU with, post Brexit, the United Kingdom being outside the EU. The North American link could of course be routed to Ireland. Indeed, that might be the most direct route. Interestingly, in that context, although the United Kingdom already has undersea links to the European mainland and plans more, including to Ireland, Ireland has recently been planning its own direct links south to mainland Europe. 

What next?  

Will any of this happen? The early plan for EU-linked  ‘desertec’ projects in North Africa have faded away, but as the use of renewables spread, so will the need for new grid links, not least for balancing. China is building a huge 90,000 km national HVDV network internally and new links are also being planned in Germany, from North to South. So new supergrids are beginning to spread. 

However, there are problems of public opposition to grids of all sorts. Buying cables underground is one option for avoiding that, but it is very expensive. A key problem is that the energy loss with grid cable transmission means that the cables get hot and have to be cooled. With cables on towers the heat is dissipated in the air, whereas cooling is much harder if they are underground. But the lower heat loss with HVDC links reduces the problem, and makes it less costly to bury HVDC links under- ground. Burying the wires would not only reduce objections to the visual intrusion of power lines and towers in sensitive areas but might also help reduce the risk of accidental wildfires, which are sometimes caused by (tree) contact with, or failure of, overhead cables. So we may see buried HVDC spread on that account. 

That said, buried HVDC, and HVDC generally, is unlikely ever to make much sense for short transmission distances and multiple load servicing: HVAC comes into own for that, since, with AC, relatively cheap transformers can be used to change voltages easily, stepping up and down whenever needed along the line. With HVDC, the stepping up and down is more complicated, so you only want to have the expensive bit of kit to do this at the far ends of a long transmission link. Then it starts making sense-although, so may bulk local energy storage - if that gets cheaper. And some see local storage as more reliable than getting power from somewhere else Then again, large scale storage facilities, such as pumped hydro reservoirs or underground green gas cavern stores, are likely to be in geographically remote locations, so you may need long distance grid links to give wider access to them. HVDC supergrids look like a winner there too. 

However, given the worsening global geopolitics, some of the more ambitious supergrid ideas and especially the idea of a global grid, look increasingly unlikely to be followed up for a while.  That’s a shame since it would hold out the intriguing possibility of using solar power captured on the day time side of the planet on the night side!