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Renew your energy: September 2009 Archives

Underground energy

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Geothermal energy is coming back in favour in the UK as an energy option, after some years in the wilderness. A major geothermal "hot dry rock" test project in Cornwall was abandoned in the 1980s after it was assessed as not being likely to produce sufficient energy for electricity production, and although Southampton persevered with a more conventional aquifer heat-based system, geothermal was basically left to other countries.

There is now over 11 GW of installed geothermal aquifer electricity generation capacity around the world and even more heat supplying capacity, but deep "hot rock" geothermal technology has recently had a renaissance, in part due to the availability of improved drilling techniques developed in the oil industry.

Enhanced geothermal systems (EGS) as they are now called, are beginning to move towards commercialization. A 2.9 MWe plant is operating commercially in Landau, western Germany, while projects are now being developed in Australia, the US and Japan, and plans are taking shape for a 3 MWe plant in Cornwall, at the Eden Project.

In its recent Renewable Energy Strategy, the UK government said that it would "commit up to £6 m to explore the potential for deep geothermal power in the UK helping companies carry out exploratory work needed to identify viable sites".

Depths of 3,000 to 10,000 metres can now be reached, with water pumped down to be heated by the hot rocks to around 200 degrees centigrade. Feeding back to the surface, this water can then be used to drive turbines to generate electricity.

Martin Culshaw of the Geological Society's engineering group, said: "Cooling one cubic kilometre of rock by one degree provides the equivalent energy of 70,000 tonnes of coal. This has the potential of equalling the nuclear industry in providing 10–20% of Europe's energy." Geothermal systems have the big advantage over many other renewables of supplying "firm" continuous power, although they aren't strictly 100% renewable, in that heat wells exhaust the local heat resource over time. But it's topped up eventually by the heat from deeper inside the earth- derived from nuclear isotope decay. That makes it one form of nuclear power that seems benign.

However there can still be problems. Iceland has been developing geothermal electricity production on a large scale, but as Lowana Veal has reported in IPS News, there have been concerns about emissions of hydrogen sulphide gas. Moss in the area was being effected. Levels were well below what was thought have any health risks for humans, but it is being monitored. H2S can be filtered out of the steam and water vapour that is emitted by geothermal plants, or it can be reinjected back into the well in a closed loop binary system. But that all adds to the cost.

Perhaps more importantly, carbon dioxide gas is also present. To deal with this a "Carb Fix" programme is being developed.  The idea is to dissolve the CO2 in water under high pressures and then pump the solution into layers of basalt about 400–700 m underground, in the expectation that the dissolved CO2 will react with calcium in the basalt to form solid calcium carbonate. The project is a form of carbon capture and storage (CCS). But rather than filling empty oil or gas wells with CO2 gas under pressure, mineral storage offers a safer bet, since there is less chance of leakage.

There may also be a potential problem with earthquake risks from deep drilling in some locations. Drilling kilometres down and then pressurising the system can lead to release of geological stresses, lubrication of fissures and small earth tremors. There were some recorded for example with a geothermal project in Switzerland in 2006, when water was injected at high pressure into to 5 km deep borehole. A shock measuring 3.4 on the Richter scale was detected, which caused local alarm, but evidently no injuries or serious damage, although further work was halted. There was a 3.1 scale tremor subsequently. This issue has recently led to concerns about some of the new German projects.

Problems like this apart, the prospects for geothermal seem good. The USA is in the lead in terms of geothermal electricity production, and has around 4,000 MW of new capacity under development. recently put £5.4 m into enhanced "hot rock" geothermal systems , supporting three new projects in the USA, and Obama allocated $350 m to geothermal work under the new economic stimulus funding.

The resource potential is very large. The US Department of Energy has suggested that in theory the US could ultimately have at least 260,000 MW of geothermal capacity. Large resources also exist elsewhere in the world and there are many projects in operation or being developed. As already mentioned, Iceland is a leading user, but the Philippines, which generates 23% of its electricity from geothermal energy, is the world's second biggest producer after the US the United States. It aims to increase its installed geothermal capacity by 2013 by more than 60%, to 3,130 MW. Indonesia, the world's third largest producer, plans to have 6,870 MW of new geothermal capacity over the next 10 years – equal to nearly 30% of its current electricity generating capacity from all sources. Kenya has announced a plan to install 1,700 MW of new geothermal capacity within 10 years – 13 times greater than the current capacity and one-and-a-half times greater than the country's total electricity generating capacity from all sources.

Finally, the use of ground-source heat-pump technology is also expanding rapidly, with perhaps 200,000 units having been installed in domestic and commercial buildings around the world. This is also sometimes labelled as "geothermal", not really completely correctly, since at least for surface based heat pipe extraction, the heat is mostly ambient heat ultimately derived from the sun, not from deep in the earth. But some heat pumps do use deeper pipes and they can also be used to upgrade the value of geothermal heat. In addition, heat can be stored in the earth via underground piping, creating local underground heat stores.

In its recent report on geo-engineering, the Royal Society argues that "air capture" carbon dioxide absorption techniques are probably the best geo-engineering option in that we should "address the root cause of climate change by removing greenhouse gases from the atmosphere". Solar heat reflector techniques were seen as generally less attractive. It may well be true that carbon dioxide absorption is the best type of geo-engineering option,but surely, geo-engineering of whatever type in no way deals at source with the "root cause" of climate change – which is the production of carbon dioxide in power stations, gas boilers and vehicles.

The Royal Society report, like the parallel report from the Institution of Mechanical Engineers, does stress that "No geo-engineering method can provide an easy or readilyacceptable alternative solution to the problem of climate change" and that mitigation and adaptation programmes are vital. However, there is the risk that "technical fix" geo-engineering approaches may be seized on as an alternative to dealing with the problem at source, since they could seem to offer ways to allow continued use of fossil fuels. That's not to say there is no role for geo-engineering, but we need a hierarchy of options.

Mitigation via renewables would come top of my list, along with improved energy efficiency. Adaptation will inevitably have to occur – given the emissions that we have already produced, whatever we do about mitigation, or for that matter geo-engineering, we are going to be faced with some climate change. Geo-engineering, as a pretty inelegant "end of pipe", trying to clean up "after the event" approach, might be seen as an ancillary option, rather than as a last line of defence, or as "Plan B".

Tim Fox, who led the IMechE study, commented sensibly that "We're not proposing that geo-engineering should be a substitute for mitigation [but] should be implemented alongside mitigation and adaptation. We are urging government not to regard geo-engineering as a plan B but as a fully integrated part of efforts against climate change."

Even so, there are major uncertainties over costs, reliability and eco-impacts, as both reports recognised. Both proposed a £10 m pa UK research programme, which seems not unreasonable, to try to identify the best options and the risks more clearly. But let's not get too deflected from what ought to be the primary aim of avoiding carbon dioxide release in the first place.

Prof. John Shepherd, from Southampton University, who chaired the Royal Society's study, said: "It is an unpalatable truth that unless we can succeed in greatly reducing CO2 emissions, we are headed for a very uncomfortable and challenging climate future. Geo-engineering and its consequences are the price we may have to pay for failure to act on climate change."

Fair enough. But, if we really are worried about climate change, it would be better if we got seriously stuck into mitigation, and didn't have to add to our problems by launching potentially risky large-scale geo-engineering programmes.

Of course not all will be risky – though they still may not be wise. It was good to see re-afforestation mentioned by the Royal Society as an option, even if it could only realistically absorb a smallish proportion of our ever-increasing emissions. However, while the IMechE backed the idea of painting roof tops white to reflect solar heat and reduce global or least local heating, the Royal Society said: "The overall cost of a 'white roof method' covering an area of 1% of the land surface would be about $300 billion/yr, making this one of the least effective and most expensive methods." Putting solar collectors on roof-tops might be a better idea! I'm not so sure about chemical air capture though. Both reports back the "Artificial Tree" idea for carbon dioxide absorption. Submarines, and, famously, Apollo spacecraft, used sodium, hydroxide to do this. If we are thinking along the same lines now for the whole planet, we must be getting desperate. Biochar might be a better option – but not if on a very large scale, surely?

Geo-engineering may have a role, and these reports are useful, but there are still a lot of unknowns – after all its basically about tinkering further with the climate and linked ecosystems, albeit consciously rather than accidentally. Quite apart from the cost, there is the risk that, if we adopt large-scale programmes like seeding the oceans with nutrients to increase CO2 uptake, or pumping aerosols into the atmosphere to reflect sunlight, we could create major new unexpected eco problems.

Geoengineering the climate

For more discussion of renewable energy options and policies, visit Renew.

The public debate and the government consultations in 2006 and 2007 on nuclear power were framed in the context of a replacement programme for existing reactors scheduled to close. On this basis it has been suggested that there was if not a clear consensus then at least a majority in favour.

However, subsequently the government began to talk about going beyond replacement. For example, in May 2008 Prime Minister Gordon Brown commented "I think we are pretty clear that we will have to do more than simply replace existing nuclear capability in Britain" while Secretary of State John Hutton said, that, although it was up to the private sector developers, he would be "very disappointed" if the proportion of electricity generated by nuclear did not rise "significantly above the current level". In August 2009 Malcolm Wicks MP, the PM's Special Representative on International Energy, produced a report calling for a UK nuclear contribution of 35–40% "beyond 2030".

The government has also indicated that it saw a major role for exporting UK nuclear technology and expertise. Gordon Brown has indicated that he believes the world needs 1,000 extra nuclear power stations and has argued that Africa could build nuclear power plants to meet growing demands for energy. In 2009 a new UK Centre for supporting the export of nuclear technology was set up with a budget of up to £20 m.

You do not have to be anti-nuclear to feel some sense of unease over the global expansion programmes being discussed, not least since they could lead much greater long-term risks for global security in terms of the proliferation of nuclear weapons making capacity and the potential for nuclear terrorism. There are other geopolitical issue as well. For example, uranium is a finite resource and, if a major global expansion programme emerges, based on existing burner technology, then there must inevitably come a time when there will be conflicts over diminishing high-grade reserves. That is one reason why interest has been rekindled in fast breeder reactors, which can use the otherwise wasted parts of the uranium resource, and also in the use of thorium, which is more abundant than uranium. But those options are some way off. For the moment, the programmes around the world are mostly all based on upgraded versions of the standard Pressurised Water Reactor, with passive safety features to reduce the risk of major accidents, plus in some case, higher fuel burn up, so as to improve their economics – though that wlll result in higher activity wastes, which could present safety and waste management problems.

There are also other operational issues. In the UK the various contenders – EDF, E.ON etc – have "reserved" a total of 23.6 GW of grid links for new nuclear capacity with National Grid. That's about the same as the wind power capacity we are aiming to have by 2020, albeit with lower load factors. But as EDF have pointed out, there are operational and economic reasons why a major expansion of nuclear would be incompatible with a major expansion of renewable electricity generation – at periods of low demand you would not need both. So which would give way?

In addition, the renewables and nuclear will inevitably also be in direct conflict for funding. A major nuclear programme could divert money, expertise and other resources away from renewable energy and energy efficiency, which arguably are the only long term sustainable energy options.

It used to be argued that renewables were interesting but marginal. Now however, they have moved into the mainstream – with, for example, more than 120 GW of wind generation capacity in place around the world. And they are expanding. Last year solar PV generation capacity grew by 70% around the world, wind power by 29% and solar hot water increased by 15%. By 2008, renewables represented more than 50% of total added generation capacity in both the United States and Europe, i.e. more new renewables capacity was installed than new capacity for gas, coal, oil and nuclear combined. Interestingly, by 2008 China had installed as much wind capacity as it had nuclear capacity (8.9 GW) and there are plans for continued rapid expansion of wind, to 100 GW and beyond. However, there are also plans for nuclear expansion.

It is sometimes argued that you can and should have both nuclear and renewables – to ensure diversity. But, quite apart from the conflicts mentioned above, nuclear is not only one of the most expensive options, it is only just one option. By contrast, there are dozens of renewable energy technologies of various sorts, using a range of sources. It is true that they are at varying stages of development, but given proper funding, they seem likely to offer a more diverse set of options.

What's the best bet for the future? An energy source with limited resource availability and major waste and security implications? Or a range of new technologies based on natural energy flows, with no emissions, no wastes, no fuel resource limits, no fuel price rises, and no security implications, unless that is we start squabbling over the wind and solar resource around the planet.

I used some of the arguments above in a recent resignation letter to the Labour Party, as reported to the Guardian.

Chemical engineers keep coming up with clever new ideas for producing green energy from novel sources.In many, hydrogen gas plays a key role. It can be produced, as mostly at present, by high temperature steam reformation of methane (natural gas or biogas), or by electrolysis of water using electricity – which can be generated from renewable sources, or from nuclear plants. It can also be produced by very high temperature direct dissociation of water – using focused solar, or heat in, or from, nuclear plants. Or, more efficiently, by thermo-chemical processes aided by catalysis. Once produced, hydrogen can be used as a fuel for a conventional combustion engine or a gas turbine, or fed to a fuel cell, so as to generate electricity. It can also be used as a feedstock to produce synfuels.

Dr Charles Forsberg from MIT's Nuclear Fuel Cycle Study project, has proposed using nuclear plants combined with biomass gasification to provide the energy and carbon feedstock for the production of liquid synfuel using the well known Fischer–Tropsch process. The nuclear plant provides electricity for the electrolysis of water – generating hydrogen and oxygen. The oxygen is used to run a biomass gasifier the output of which is used, along with the hydrogen, as a feed stock for the production of synfuel – diesel or gasoline. He says that the use of external heat and hydrogen can double to triple the liquid fuel output per ton of biomass compared to using just biomass as the feedstock and as the process energy source.

There are various possible variations (e.g. heat or steam from the nuclear plant can be used for high temperature biomass reforming, rather than electrolysis of water). Or you can go for direct hydrogenation of biomass with nuclear-derived hydrogen. The production of ethanol from biomass using steam from nuclear plants is another option. Forsberg's claim is that approaches like this offer a way to make better use of high capital cost nuclear plants to produce a high-value storable fuel as well as electricity. He doesn't see hydrogen as being a replacement fuel across the board, but as being used for producing products like this.

Even so, there may be some options for hydrogen as a new energy vector. Advocates of the hydrogen economy argue that, one attraction of hydrogen is that, like natural gas, not only can it be transported down a pipe with relatively low losses, it can also be stored, so it has advantages over electricity as a energy vector. However it's bulky. Cryogenic storage, as a liquid, is expensive and energy inefficient. Chemi-absorption techniques exist, for trapping it in organic lattices, but are not yet widely available on any scale. Storage as a gas in pressurised tanks is the easiest option, but takes up room. Underground storage in caverns is about the cheapest bulk option.

The generation and storage of hydrogen could be one way to allow nuclear plants to be able to meet variable/ peak energy demands. Forsberg suggests using excess electricity from nuclear plants at low grid demand periods to generate hydrogen by electrolysis and then using the electrolyser in reverse to generate electricity to meet demand peaks. Evidently high-temperature electrolysis units can be operated as high-temperature fuel cells. A parallel, probably more energy efficient, approach would be to use the nuclear hydrogen and the oxygen also produced by electrolysis, to fuel an oxy-hydrogen burner unit, producing high temperature steam for a gas turbine. That could have an overall efficiency of 70% – since no boiler is required.

Solar hydrogen/synfuel

In passing, Forsberg does mention that solar thermal could be used as the heat source for some of the systems he outlines. This would make a lot of sense. The SOLASYS 'Power Tower' in Israel is already being used to steam 'reform' methane into hydrogen and carbon monoxide at around 700 °C.

Meanwhile the US Dept of Energy Energy Efficiency and Renewable Energy Web site, describes how a solar concentrator can use mirrors and a reflective or refractive lens to capture and focus sunlight to produce temperatures up to 2,000 °C. The CNRS solar heliostat/parabolic mirror system at D'Odeillo in southern France has in fact been doing that since 1970. Direct dissociation of water at temperatures like this is possible but is relatively inefficient – perhaps 1–2%. However, there are systems being developed: e.g. see Hion Solars approach:

An alternative is to use the high-temperature focused solar to drive chemical reactions that produce hydrogen, possibly aided by catalysis. For example, the US DEn EERE web sites say that in one such system 'zinc oxide powder is passed through a reactor heated by a solar concentrator operating at about 1,900 °C. At this temperature, the zinc oxide dissociates to zinc and oxygen gases. The zinc is cooled, separated, and reacted with water to form hydrogen gas and solid zinc oxide. The net result is hydrogen and oxygen, produced from water. The hydrogen can be separated and purified. The zinc oxide can be recycled and reused to create more hydrogen through this process. See:

Clearly the nuclear fission lobby is looking at how to redeem its capital intensive technology, for example by using otherwise wasted heat. Combined Heat and Power operation is one option, if there are heat loads nearby. But supporting hydrogen to synthetic fuel production, as proposed by Forsberg, is obviously another. General Atomics has developed a Sulphur–Iodine cycle for thermo-chemical water splitting, which in principle, can, it's claimed, achieve cycle efficiencies of 50% using heat at 850 °C. That's achievable by some fission plants – and possibly also, at some point in future, by fusion plants. But it's also a route that could be taken by solar, with arguably less problems- no wastes to deal with, or fuel to find.

*Forsberg spoke at the World Nuclear University in Oxford last July. For more from him, see International Journal of Hydrogen Energy 3, 4 (2009).

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