energy


ONE PLANET — the environmental documentary radio programme of BBC World Service — last month broadcast (and podcast) a documentary which explored whether a future solution to Europe‚Äôs electricity supply problems might come from giant solar-thermal generating stations in the Sahara Desert, feeding hundreds of megawatts into the European grid through undersea cables while also bringing ‘an industrial revolution to the Southern Mediterranean,’ to quote one of the scheme’s supporters, Prince Hassan of Jordan.

What the programme didn’t mention is that the idea is at least five years old and is championed by TREC, the Trans-Mediterranean Renewable Energy Co-operation project, an initiative of the German association for the Club of Rome, together with the Hamburg Climate Protection Foundation. But what Miriam O’Reilly’s inverview with Professor Galal Osman revealed is that there are people in Egypt who see the construction of the pioneering solar-thermal power plant at El Kureimat on the Nile as possibly the first step towards realising that dream.

El Kureimat, a few kilometres south of Minya, is the site of a power generation centre that already has two gas-powered generators installed. Now under construction is a ‘Concentrated Solar Power’ (CSP) solar-thermal plant which will generate 20 megawatts of power, rising to 50 MW. Similar in principle to solar-thermal plants operating in the deserts of south west USA, the plant will feature an array of mirrored fifty-metre parabolic reflectors covering 100,000m2. These will focus the sun’s rays onto a vacuum-insulated heat collector tube running down the centre of each reflector, through which water pumped under pressure will carry the heat to a central facility where steam is generated and electrical power is produced using turbines.

Sun, water and salt

Photovoltaics, using for example silicon cells, is a completely ‘dry’ process, witness its efficacy in outer space and the surface of Mars. But CSP solar-thermal plants are the affordable technology when scaling production up to tens and hundreds of megawatts. One factor that might be seen as a hitch to implementing ‘desert power’, then, could be shortage of water; but there are plenty of zones around the desert edge where water is to hand, though it may be sea-water.

One vision for an integrated system to harvest the desert and make it blossom involves using CSP plants not only to make electricity, but also to desalinate marine and brackish water, for human consumpion and for agriculture. It has also been pointed out that if the solar arrays are constructed so that the ground beneath them is accessible, those shaded spaces could be ideal for agricultural and horticultural use.

Apart from cost, solar-thermal has another advantage over photovoltaics, in situations where a reliable constant energy supply is desired. Electricity is expensive to store — but harvested heat can be stored cheaply for use in overnight power generation. The 50 MW solar-thermal plant which Spain commissioned at Solucar near Seville a couple of years ago uses underground vats of molten salt to store up to seven hours’ worth of power-generating heat.

High tension

In the programme, Professor Osman, fancifully invoking a memory of Ancient Egyptian worship of the sun, also imaginatively sketched a vision of ten thousand square kilometres of desert covered with CSP mirrors, generating potentially much of Europe’s electricity needs. How would this be brought across the Mediterranean? The TREC plan calls for three High Voltage Direct Current (HVDC) cables under the sea: one from Libya to Sicily, a second from Tunisia to Sardinia, and a third across the Straits of Gibraltar from Morocco to Spain.

In the early 20th century, in the competition between rival electricity transmission techniques, it was Alternating Current that won out. AC, which reverses polarity fifty or sixty times a second depending on the design of the system, can be stepped up to very high voltages with cheap transformer technology — and high voltage is important, as this vastly reduces the amount of power lost to electrical resistance in the transmission cables.

However, developments in semiconductor technology never stand still. In recent decades the advent of high-energy solid state static inverter circuits has made it simple to ramp voltages up and down for direct current, too. And this has real advantages: less electrical power is lost per thousand kilometres in DC cables, and the cables are cheapoer to make and lay. The problem is that DC static inverter stations are still much more expensive to build than AC transformer stations; but where energy must be moved long distances, especially underwater, HVDC is the sensible choice. (The longest current HVDC power circuit is overland, however — it’s the 1,700-km line that runs from Congo’s Inga Dam hydropower scheme to the copper mines at Shaba.)

HVDC has another benefit where international sales of electricity are contemplated. AC grids can exchange power only if synchronised in frequency and in phase. When AC circuits go out of step, they can bring the system crashing down, with wide-area power outages. DC power flows constantly in one direction and can easily be distributed to AC local circuits through an inverter regardless of local phase and frequency. Indeed, sometimes HVDC links are incorporated into power grids just for the stability they bring.

Energy and security

In the BBC programme, Prince Hassan spoke about the benefits which widespread adoption of solar-thermal power could bring to the Middle East and North Africa, especially in terms of prosperity and development, industry and agriculture — and flowing from this, greater social and political stability.

However, a gloomy note was stuck by Open University֦s Professor Dave Elliot, co-Director of the Energy and Environment Research Unit. He pointed out that almost insurmountable obstacles have arisen in negotiations between European nations about cross-border sharing of power; how much more difficult would it be to negotiate prices and access for power from another continent?

European policymakers are also understandably nervous about energy security; the way Russia plays politics with its gas pipelines illustrate the dangers of dependence. It is said that one of former Congolese president Mobutu Sese Seko’s motivations for supplying the Shaba copper mines with electricity from 1,700 km away, rather than develop allegedly cheaper local hydropower sources, was the advantage to him of having his hand on a big switch to render Katanga province powerless should it rebel. How stable is North Africa?

‘We’ve got to get the balance right in the future,’ concluded UK Energy Minister Malcolm Wickes, ‘between the energy we’ll have to import — mainly oil and gas and coal at the moment, maybe one day solar — and the energy we can produce here in Britain and just offshore. Energy security will become an increasingly important component of a nation’s security, given the huge global demand, the global grab for energy in the 21st century, and all the difficult geopolitics around that.’

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AS COMPUTER CHIPS get more compact and run faster, they also run hotter. Attaching radiator fins to their surface and blowing air over them are the usual solutions. But what happens when chips are stacked on top of each other to improve the flow of data between them in parallel processing? The heat-producing volume increases, while the heat-shedding surface gains very little.

The Economist Technology Quarterly, bound into the September 6th edition of the magazine, reports on IBM’s experiments in water-cooling such stacks of chips. Thomas Brunschwiler of IBM’s Zurich laboratory points out that processors stacked in this way generate heat at about two kilowatts per cubic centimetre, a greater density than in a nuclear reactor. Therefore the IBM team has developed a stacked processor through which water is pumped in channels, as thin as a human hair, etched in the process of silicon-chip fabrication. Nor need this heat be wasted: in compact multiple installations such as data centres, the heat can be exploited to warm community housing or other buildings.

Water cooling can also be applied to silicon-based solar cells. Another IBM researcher, Supratik Guha, has increased the efficiency of solar power by using mirrors to concentrate 2,300 times the normal intensity of sunlight onto a solar cell. Without water-cooling, the cell could reach 1,500 degrees Celcius and melt. The cooling system means that the cell is maintained at a safe temperature of 85 degrees C, and generates a record output of 70 watts per square centimetre: a very promising technology for economical electricity generation even in high-latitude countries.