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Renew your energy: October 2011 Archives


Although its days are now numbered, following the Electricity Market Reform proposals, the Renewables Obligation is still set to take in new projects and run with them, and existing RO projects, until 2017, offering ROCs- Renewable Obligation Certificates- for each MWh produced. After 2017, the new Contracts for a Difference system will be the main support mechanism. Indeed, if the CfD offers more, some existing and new projects may chose to go for that before then, as soon as it's in place- in 2013/14?

Meanwhile DECC has released new proposals for RO tariff levels and technology banding- for consultation. Chris Huhne, Secretary of State for Energy and Climate Change, said: 'We have studied how much subsidy different technologies need. Where new technologies desperately need help to reach the market, such as wave and tidal, we're increasing support. But where market costs have come down or will come down, we're reducing the subsidy.'

So there are winners and losers. In the proposals wave and tidal stream have both been boosted from 2 to 5 ROCs/MWh, for projects below 30 MW. Offshore wind also has a boost, with one more year at 2 ROCs, but on-land wind falls back to 0.9 ROCs. Solar PV gets two more years at 2 ROCs, then tails off. The same for geothermal and microgen. Hydro gets demoted to 0.5ROCs, while, more understandably, low cost/low new resource potential landfill gas is finally written out, but sewage gas stays unchanged at 0.5ROCs. There is some serious tinkering with various biomass and co-firing definitions and arrangements, with some old bands removed/combined and new ones proposed, and some ROC cuts later on. A lot to debate there.

Crucially DECC say 'These proposals are expected to cost between £0.4bn and £1.3bn less than retaining current bandings', but they claim that we will get 'more from less'- the new tariffs will 'drive a higher level of deployment than leaving bandings as they are'. In addition 'the proposals also provide industry with the certainty needed to make investment decisions and will overall mean a lower impact on consumer bills, without reducing our level of ambition'.

The main saving (about £372m p.a.) would seem to be from the revised support pattern for biomass/wastes, but there's also a £60-80m p.a cut for onshore wind. On the plus side, wave/tidal get £13m p.a. extra, while offshore wind gets £130m-190m p.a. more. The DECC report is backed by a new study of costs from consultants ARUP. Amongst other comments, it says that PV solar is a technology 'with very significant deployment potential of 16.6 GW by 2030 (medium forecast), but with very high capex' (capital cost). So it's surprising, especially given the recent 72% cut in the Feed In Tariff cut for PV projects over 50kW, that DECC leaves it at 2 ROCs and falling later- expect major complaints!

DECC's overall rationale for the new RO tariff levels reflects a concern for cost effectiveness. It comments 'Any support above 2 ROCs, marks a significant change for the RO in England & Wales, and moves us away from supporting only the most marginal technology needed to meet our 2020 renewables target'.

It sees offshore wind as the high bench mark: 'offshore wind is considered to be the most expensive technology required on a large scale to meet our 2020 renewables target. Therefore, in the context of meeting the 2020 renewables target, it would not be value for money to provide a higher level of support to any other technology for the purposes of meeting that target.'

But it says, with the UK a world leader in the emergent wave and tidal current area, there may be 'other reasons for setting a higher level of support', such as 'the desirability of securing the long term growth, and economic viability, of the industries associated with this technology' (e.g. UK jobs and export potential) and as a 'hedge' against 'underperformance of other forms of generation out to 2050.' (i.e. insurance). So they get 5ROC/MWh- quite a breakthrough.

This RO consultation applies to England and Wales only. There will be separate banding consultations on proposals in Scotland and Northern Ireland. DECC consultation/Arup report: www.decc.gov.uk/en/content/cms/consultations/consroreview/consroreview.aspx

*What next? *

There will be some haggling over the details, but the winners will be keen to push ahead. Offshore wind in particular. They will be helped long-term by funding from the Energy Technologies Institute (ETI), which is to invest up to £25m in a floating offshore wind system demonstration project It is to be installed by 2016 at a relatively near shore site with high wind speeds up to about 10 metres per second in water between 60 and 100 metres deep. The main aim is to help bring generation costs down.

Floating wind turbines offer a way to go into deep water, where it is very hard and expensive to provide sea-bed mounting, and have often been seen as the way ahead for projects further out in the North Sea than the current rounds of projects. But floating system are not cheap and the cost of undersea grid links back to shore are very high.

The ETI seem to have adopted a different interim tack - to open up near shore sites off the West coast. Dr David Clarke, ETI Chief Executive said: 'Our studies have shown that access to high wind areas which are close to shore should be an attractive investment compared to some existing UK sites which are further from the coast in areas of lower wind. We also expect there is likely to be a considerable global market for floating wind turbines which can be developed in the UK'.

The ETI backed Nova vertical axis turbine project, which led to the 10MW Aerogenerator X design, would seem likely to be one candidate for support. But there are several others, including their Deepwater design and Norwegian Sway, a prototype of which is already under test. ETI has invited proposals for projects in the 5MW to 7MW range. Of course there will also be opportunities, under Round 3, for location further out to sea off the east coast, where there are shallow areas e.g. the Dogger Bank, without having to use floating devices. Although the cost of installing undersea grid links will be high, that may be offset by having the option of delivering power to mainland Europe - a much bigger market- with the project being part of an emerging North Sea supergrid. For example see: www.forewind.co.uk/dogger-bank/overview.html

When and if that is established then it may become economically viable to infill in the deeper water with floating devices.

Meanwhile, wave and tidal project will also be moving ahead, nearer to shore, with around 2GW expected to be operating by around 2020, mainly off Scotland, Wales and Cornwall.

Whether PV solar will also boom now seems to depend on the results of the current DECC review of the Feed In Tariff system, which covers project under 5MW. But signs are that there will be further cuts - of perhaps 50% for some tariffs.

Contested nuclear views

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After the Fukushima accident, Japanese Prime Minister Kan, said 'Through my experience of the March 11 accident, I came to realize the risk of nuclear energy is too high. It involves technology that cannot be controlled according to our conventional concept of safety.'

His view that 'Japan should aim for building a society that is not dependent on nuclear power' now seems widely shared. In a national poll in September, 60% of those surveyed said the number of nuclear reactors should be reduced gradually, while 20% said the nuclear reactors should continue to operate, but no more built. 12% wanted all reactors stopped as soon as possible, while 6% said the existing reactors should be operated and new reactors should be built. The survey showed that overall 70% wanted an end to the country's reliance on nuclear power generation. Interestingly 65% would accept a cut in electricity use, even if living standards dropped.

Japan plans to formulate a full new energy policy for 2030 by 'early 2013,' with the emphasis on renewable energy- it has already introduced extra support for PV solar. When stepping down as Prime Minister, Kan said he would devote himself to renewables, and has called on Japan to do 'everything we can to make renewable energy our base form of power, overcoming hurdles of technology and cost.'

A similar position has been adopted in Germany, where Angela Merkel has said 'Germany can become an international pioneer, the first nation to manage to move away from traditional energy sources to renewables.' It now gets over 20% of its electricity from renewable sources, which will be expanded to around 35% by 2020, by which time most of the country nuclear plants will be closed- the last ones are scheduled to close in 2022.

Italy is in the perhaps enviable position of having no nuclear plants to close, and following the national post-Fukushima referendum, when 94% opposed the governments plans for new nuclear build, it is also now focusing heavily on renewables. Interestingly, it now has more wind power capacity installed than the UK.

Switzerland has decided not to replace its existing nuclear plants, and several other countries around the world have also backed off from planned nuclear programmes , including Thailand, Malaysia and the Philippines.

The situation in the UK is very different- we still have plans for eight new plants. The nuclear lobby takes some comfort from opinion polls, some of which suggest that, although support in the UK had fallen after Fukushima, it still outweighed opposition. For example, according to an Ipsos-MORI Poll in August carried out for the Nuclear Industry Association (NIA), when asked 'how favourable are you to the nuclear energy industry', 28% said favourable, 24% unfavorable. When asked 'do you support or oppose building new nuclear power stations to replace the existing fleet', 36% supported, 28% opposed. However, the results are not consistent across all polls: a poll for the British Science Association found that opposition was still in the majority: it said 37% of the UK population support the use of nuclear power for producing energy in the UK, but opposition was at 47%. www.britishscienceassociation.org/web/ News/FestivalNews/nuclearpoll.htm

Moreover the responses depend a lot on the questions asked. An earlier Ipsos MORI poll, in May, part of a global survey, found that, in the UK, 74% disagreed with the idea of 'modernization' of electricity production via nuclear, while a massive 80% felt that 'nuclear was not a viable long term option.' www.ipsos-mori.com/Assets/Docs/Polls/ipsos- global-advisor-nuclear-power-june-2011.pdf

Given this ferbile context, it is perhaps unfortunate that the BBC has seen fit to produce a series of what many critics have seen as unbalanced, very pro-nuclear TV programmes- notably a Horizon documentary, and an edition of its popular science show, 'Bang Goes the Theory', both ostensibly focusing on nuclear safety. The main message from them was that the science was clear- there were relatively few deaths at Chernobyl and none could be expected from radiation at Fukushima. This is not the place for a rehearsal of the data and its analysis, but it was not made clear in the BBC programmes that there are divergencies of scientific opinion, over for example the potential negative long-term impacts of low level radiation contamination and the significance of absorbed 'internal emitters'. This is a contested area, and one you might think worthy of proper coverage. For example, for an exemplary exercise in exploring some of the different views, see: www.safegrounds.com/radiation_risk.htm

Many groups have reacted angrily to the alleged lack of balance in these BBC programmes: for example see: www.sgr.org.uk/resources/sgr-supports-joint-complaint-bbc-over-fukushima-documentary And http://www.nuclearconsult.com/information.php (which includes responses from the BBC)

The critics view is that the programmes basically adopted the arguably rather limited view that what mattered was the hard, confirmed, data, on deaths, rather than speculation. So Bang Goes the Theory claimed that they were just 122 from Chernobyl and zero, from radiation, from Fukushima. A report on Chernobyl from the UN Scientific Committee on the Effects of Atomic Radiation, published in February, adopted a similar approach. While earlier IAEA/WHO studies had talked of possibly around 4000 subsequent early deaths in the region amongst some classifications of those exposed, and studies covering a wider area put the full figure for total eventual deaths very much higher (ranging up to 60,000), the new report decided not to speculate about future deaths 'because of unacceptable uncertainties in the predictions'.

Even higher death rate projections have been put forward by some critics. See for example www.wagingpeace.org/articles/dbarticle.php?articleid=141 and http://fukushima.greenaction-japan.org/ 2011/06/01/analysis-the-health-outcome -of-the-fukushima- catastrophe/

They, and the other dissenting critics, may be wrong, but it is arguably evasive to just ignore the debate or the issues. But you can see why it might be an attractive approach for those keen to promote nuclear power.

Nuclear safety and risks are very emotionally charged issues, with any uncertainty clearly being likely to lead to public concern. But limited and simplified analysis may not be sufficient to calm fears. Dr Mike Weightmans new NII report on UK plant safety gives the UK nuclear industry a clean bill of health, but, given what its critics see as a relatively narrow terms of reference, it may not convince those opposed to nuclear power, who in any case put forward many other reasons for their opposition. While the nuclear industry and the government many wish the debate over nuclear to be closed down, economic, security, and other wider strategic issues, as well as the ongoing debate over risks, seem likely to continually open it up. In that context, and with Japan, German, Italy and others backing off from nuclear, what we need from the media is coverage that is better balanced.

Energy storage - Part 2

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As more renewables come on the grid, it is helpful to have more energy storage capacity. However, as I said in my previous Blog, storing electricity is not easy or cheap and there are other ways to balance grids. http://environmentalresearchweb.org/blog/2011/10/energy-storage---part-1.html

For countries like the UK, where the renewable contribution is still relatively small, it's easier and cheaper just to providing balancing power from the already existing gas turbines. But in countries with larger renewable inputs and access to large hydro projects, hydro reservoirs provide an opportunity for pumped storage, and there are some interesting new developments underway, making use if hydro facilities that already exist.

For example in the Voralberg area in Austria a set of relatively small reservoirs at different levels in the Alps have been linked up, with several being modified so that surplus power from the nearby Bavarian wind turbines can be used at off-peak periods to pump water back up to higher reservoirs, so that it can be used to generate power when needed. www.univie.ac.at/crm/ew06/Schmoeller.ppt

Also, in the Harz Mountains in Germany, old mine workings are being looked at as possible sites for new underground pumped storage facilities. That's not a new idea: Dinorwig in Wales already does this- storing off peak excess power.

For a good global overview of pumped storage, see www.renewableenergyworld.com/rea/news/article/2011/08/balancing-the-grid-with-pumped-storage?cmpid=WNL-Friday-August12-2011

You don't have to have large mountain ranges, and it can be done on a relatively small scale. For example, El Hierro, the smallest of the Canary islands (278 sq km) is to generate power for its 10,700 residents and its many tourists from a five turbine 11.5MW wind farm. Some of the electricity will go into the mains network, some will be used for desalination, and any excess will be used to pump water from a 150,000 cubic metre reservoir near the harbour up to a much larger reservoir (550,000 cu metres) at an elevation of 700 metres, housed in a volcanic caldera. 3 km of pipes will connect the two reservoirs. If the wind drops, water is released at the top to drive six hydraulic turbines (11.3MW).

Reporting on this project, the Guardian noted that there was nothing very revolutionary about pumped-storage hydro of this type. Morocco has already built one facility and is about to launch another project near Agadir. The Grand Maison dam in the French Alps, operates along similar lines. But El Hierro is the first big scheme not to use conventional power.

The idea is spreading and developing. Copenhagen-based architect firm Gottlieb Paludan has proposed an innovative Green Power Island idea using seawater pumped into a lagoon-like reservoir built into an artificial island. When demand is low, pumps driven by wind turbines empty the reservoir. At peak demand periods, water is allowed to flow back into the reservoir, via turbines generating electricity to meet the demand.

Green Power Islands have been proposed for Copenhagen, Bahrain, Jiangsu, and Tampa, Florida. Although primarily using wind , the islands can also include PV and concentrated solar, and even biomass. The developers says that Some could also have recreation trails, beaches, harbours, and even residential and business units. www.greenpowerisland.dk/

However the hunt is also on for other forms of storage not reliant of geographical features. Some look to various types of advanced flow batteries, others to compressed air storage or flywheels. Another choice is to convert electricity produced by wind turbines or PV arrays to hydrogen , which can be stored as a compressed gas or a cryogenic liquid and then used to generate power when needed, either by direct combustion in an engine or turbine, or in a fuel cell.

There are several projects around the UK testing this out, including the Hydrogen Office in Fife, Scotland, using surplus energy from a 750 KW wind turbine stored as hydrogen for use in a fuel cell, which can generate power when needed. www.hydrogenoffice.com/

The system was developed by the Pure Energy Centre who have pioneered this approach. www.pure.shetland.co.uk/

Some cleaver new ideas are also emerging for new types of hydrogen storage media. I mentioned the Highview cryogenic storage system in my previous Blog. But another, perhaps more advanced option was outlined on the Clean Tech Blog recently, in an interesting article on hydrogen storage of wind energy by David Anthony and Ken Brown, based on Safe Hydrogens system with which they are involved. As normal, they suggest using the electrolysis of water to produce hydrogen, noting that with an 80% efficient electrolysis unit, it takes about 50 kWh of electricity to create 1 kg of hydrogen. But then they say that 'To avoid the high cost of compressing hydrogen or of cooling and liquefying hydrogen, a good alternative is to store the gas in a metal hydride slurry'.

Basically, hydrogen is chemi-absorbed as metal hydride in a molten mix, which can then be made to release it's hydrogen, when required, in a managed reaction with water, producing hydrogen and heat. That process converts the metal hydride to a metal hydroxide, which can be recycled back to a metal hydride.

The article explain that 'Safe Hydrogen uses magnesium as the metal and mineral oil as the liquefying agent. With the use of small particles and a suitable dispersant, the particles will stay in suspension almost indefinitely. Using a hydriding reactor, hydrogen is absorbed by the Magnesium Slurry with suitable pressure and temperature that ensures rapid reaction. The Magnesium Hydride Slurry that is created in this reactor then can be stored in large quantities at ambient conditions. The hydriding reaction to create the magnesium hydride slurry creates heat. This heat is about 30% of the heating value of the hydrogen gas. About 10 percentage points of this heat, or one-third of the heat, can be used to perform useful work such as generating more electricity. The rest of the heat can be used for space heating or to produce hot water. Thus the hydriding step in the process can be from 110-130% efficient'.

The hydrogen can be used to power a gas turbine-generator, so the wind farm owner can either sell power either directly or at later stage- and the hydrogen slurry can thus be used as a store to compensate for the variabilty of the wind power. The article says 'typically, only 15% of a wind farm's output can be counted on as reliable capacity-likely to be available in any given time period'. e.g. 7MW out of a 50MW wind farm. But with storage, this can be doubled. Clever stuff. See: www.safehydrogen.com

Energy storage - Part 1

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Energy storage is often seen as a key to grid balancing- matching variable renewable inputs to variable energy demands.

So far pumped hydro storage is the only significant form of storage, except of course for stored fuels like coal, gas, oil or biomass. At present though, energy storage is still very expensive. So far it's only been done- at least in the UK- when there is thought to be a serious need. For example, the giant Dinorwic underground pumped hydro project, located in a vast cavern in Wales, which at the time of its construction, was Europe's largest infrastructure project. It was it seems initially conceived, financed and built in part to provide backup in case the Sizewell B nuclear plant went off line. It could go from zero to full generation within around 20 seconds and therefore could compensate for sudden loss of power on the grid, but also for sudden increases in demands for energy. Dinorwic could of course only hold the fort for a short while- 1-2 GW for perhaps 2 hours, while other backup came on line. And it was very expensive, so much so that when, following UK electricity privatisation, a lot of cheap and flexible Combined Cycle Gas turbines came on the grid, it became less attractive and has evidently had a harder time making money in the new market.

However, some see it as the sort of thing that will be needed in addition to more conventional pumped hydro projects, as we move to have more wind and other variable renewables on the grid. An EU wide supergrid link could also help, not least by linking into pumped hydro storage capacity around the EU - for example there is a lot in Norway. See www.theoildrum.com/node/7404

There are of course also other electricity storage options, including, for the short term, capacitors, flywheels, utility scale batteries, and flow cells; for the medium term, compressed air systems; and, for longer term storage, the conversion of electricity to hydrogen for storage and then for use in fuel cells or combustion engines to produce electricity again when needed. In parallel there's the option of conversion to heat, which can be stored in molten salt stores.

These options all have their pros and cons- high capital costs and low energy conversion efficiency being key problems. On this basis, the hydrogen lobby has had a few years in the doldrums e.g. electrolysis is seen as inefficient and storing hydrogen as a cryogenic liquid is expensive, and there are energy losses when it's cooled and then regassified. But recently it's been reinvigorated by new production possibilities including a new 'Green Hydrogen' production cold-plasma technology, which could tilt the balance more in favour. www.gasplas.com/w3

There are also some novel storage ideas emerging, with.claims about the viability of large scale underground hydrogen gas storage in salt caverns. See: www.whec2010.com/fileadmin/html/78-4.html

On a smaller scale, Highview Power Storage has demonstrated a novel 300kW prototype cyrogenic storage system which stores excess energy at times of low demand by using it to cool air to around -190 °C. via refrigerators, with the resulting liquid air, or cryogen, then being stored in a tank at ambient pressure (1 bar). When electricity is needed, the cryogen is subjected to a pressure of 70 bars and warmed in a heat exchanger. This produces a high-pressure gas that drives a turbine to generate electricity. The cold air emerging from the turbine is captured and reused to make more cryogen. If waste heat from a nearby industrial or power plant is used to re-heat the cryogen, it's claimed the efficiency rises to ~70%. http://www.highview-power.com

Do we really need storage?

However storage, by whatever means, is still going to be expensive. Fortunately there are alternative ways to deal with variable supplies . For example, working on the demand side of the equation, we can develop dynamic demand management techniques - delaying load peaks by a few hours or switching off some loads when wind power is low, using smart meter links. Though we don't need it yet. At present, and for some way ahead, the variable inputs from wind generation can be easily balanced by running conventional gas fired plant up and down from full power. They already have to do this to balance the daily demand cycles, with more wind on the grid they just have to do this a few times more often, adding a small extra cost and undermining to carbon saving role of wind very slightly. As we have to accommodate more inputs from variable renewables, we may have to install more balancing capacity, but its relatively cheap and can increasingly be fuelled with biomass or geothermal heat-or perhaps even some solar heat, backed up by heat stores. As I pointed out in an earlier Blog, that could be linked to a system with Combined Heat and Power Plants feeding district heating networks and heat stores.

Moreover when wave and tidal energy are also being to fed into the grid, they can help balance varying wind (and solar) to a degree, since waves are in effect stored wind, and tidal cycles are unrelated to the weather.

Couldn't nuclear plants also be used to balance the variable outputs from renewables like wind? The short answer is no- at least not much. Nuclear plants are usually run 24/7 to recoup their large capital costs and there are operational and safety reasons why they can't be run up and down from high to low power regularly and rapidly. It's not just thermal stresses in PWRs, but also the excess production of contaminating isoptopes which can interfere with proper and safe operation. Even so, it seems an EPR could ramp-up from 25% to 100% capacity, at 5% per minute, of its maximum output (i.e 80 MW per minute) e.g. from 400 to 1,600 MW in 15 minutes, but only100 times per year e.g. once every three days. Not much use for balancing regular wind variations, but maybe OK for long lulls in wind, if the nuclear operators will accept running at lower power (and loosing money) when there is wind available. Note also that nuclear plants, like all power plants, have to be backed up: for example a 300 MW light oil fired gas turbine plant is being built in Finland to back up the new, much delayed, Olkiluoto nuclear power plant.

The simple message though is that, basically inflexible nuclear is not very suited to balancing variable renewables. Moreover, if we try to have a lot of both on the grid there will be conflicts when demand for power is low- which then do you switch off? Storage might help reduce this conflict, but at extra cost. Really we don't want to have large amounts of both nuclear and renewables on the grid system.

For more on nuclear balancing here's an audio file : www.nuclearinst-ygn.com/ Docs/Vol5Iss6Track%202.mp3 And for a good overview: www.claverton -energy.com/is-nuclear-power-flexible-does-it-have-load-following-capability.html

It could be argued that, to some extent, we only need large amounts of storage if we are having problems with balancing the grid system more directly-and, if for example, we have a large inflexible nuclear component on the grid. But, even if that not an issue, it is true that if we could come up with a cheap storage system that would help grid balancing, and the hunt is on for new ideas. I will be looking at some in my next Blog.

For more ideas, there was an energy storage session at this years All-Energy Aberdeen conference: www.all-energy.co.uk/Powerstorage-theholy_grail.html


We've got used to the idea that solar heat collectors can be viable in the UK, despite its often poor weather, and when it comes into operation for the domestic sector next year, the Renewables Heat Incentive may lead to a lot more roof top panels being installed on houses. Typically they can halve annual heating bills- depending on location and what heating fuel is usually used .

There are a few larger schemes used for swimming pools or in hotels, but what is less familiar in the UK is large-scale solar, feeding heat to community-scaled district heating networks.

There are some significant advantages to operating at larger scale. For example, then you can have large efficient heat stores; the ratio of their outer surface area to the contained volume decreases with size, and so therefore does heat loss. In addition, instead of having to match the heat demand patterns of an individual household, a large store can serve many houses, so that the individual demand patterns are averaged out.

This approach is sometimes called 'grouped solar', with individual housing blocks or terraces sharing a large solar array and large heat store. But to do this on a larger scale you have to have district heating pipe network , and that adds to the capital cost. Although once installed the running is low - and if its solar fed, the heat is free. There are few conventional district heating projects in the UK, but many elsewhere in northern Europe. For example, district heating (DH) networks supply 60% of Denmarks heat at present, much of this from fossil sources, although some from straw burning.

What about using solar? Well there are already some impressive projects, 85MW(th) in all in Denmark, some with solar heat stores. For example see the 5.6MW Braedstrup project and also the 13MW Marstal project - which is shortly to be doubled in size: www.solarmarstal.dk

And Denmark has some ambitious Solar DH targets: 2015: 1 TWh, 3 % of the DK district heating demand 2030: 2.7 TWh / 10 % of the DK district heating demand 2050: 7 TWh / 40 % of the DK district heating demand

For more: www.solar-district-heating.eu

Austria is also moving ahead in the solar DH field. For example, there is a large district heating network in Graz, with 6.5 MW(th) of solar input . Germany has installed nine research and demonstration solar arrays linked to district heating networks since 1996, including some with inter-seasonal heat stores. Depending on their size, they can meet 40-70% of the annual heating needs of a building.

In most case though, with large DH networks, the solar input is a small to medium additional input alongside other sources, for example gas or biomass fired combustion plants, some of them being 'co-gen' Combined Heat and Power (CHP) plants, generating electricity as well as heat. But the proportion of solar seems likely to grow, with some novel ideas emerging. For example, in Copenhagen, a new 280kW demonstration solar plant is being developed to deliver solar heat to its district heating system, with 90 square meter of solar panels, a heat store and a heat pump. The heat pump raises the temperature of the water from the solar panels or the storage tank, before the heat is delivered to the district heating network. www.copenhagenenergysummit.org/applications/Copenhagen,%20Denmark-District%20Energy%20Climate%20Award.pdf

The 'Heat Plan Denmark' a study financed by the Danish District Heating Association, claims that district heating combined with CHP and renewable energy is more cost effective than individual solutions based on more investments in the building envelope and/or investments in individual renewable energy solutions. So it argues for the expansion of district heating and energy storage, fed increasingly from large scale solar arrays, biomass and biogas fired CHP, and geothermal sources. More at www.danskfjernvarme.dk

Whatever the fuel used, one off the big pluses with CHP/DH systems, especially when coupled to large heat stores, is that it can be used to balance the variable energy inputs from wind turbines. When there is excess wind generated electricity, it can be used to produce extra heat, either for storing or for direct use via the DH network, the CHP plants then throttling back on heat production, or feeding it to the stores. When there is not enough wind, they can increase the proportion of electricity they produce.

A new IEA report on Co-gen/CHP and renewables backs this idea, noting that 'storing heat is simple but storing electricity is still difficult and expensive.' www.iea.org/index_ info.asp?id=1941

Interseasonal heat stores of course open up even more options- storing energy from winter wind, or summer solar heat, for use at other times.

What is tragic is that the UK does not seem to be taking CHP/DH seriously, much less solar DH. A recent report for the governments Committee on Climate Change produced by consultant Matt MacDonald simply says more work needed to see if it 'could complement or substitute heat decarbonisation in buildings from heat pumps or resistive electric heating'.

It seems the emphasis is still mainly on electricity, even for heating, given the focus on offshore wind and nuclear. But if nothing else, CHP/DH with heat stores might help match their outputs (24/7 from nuclear, variable from wind) to varying demand. A recent paper from the AECOM Technology Corporation, claims that Combined Heat and Power/ District Heating is the most cost effective solution for grid balancing in terms of carbon saved for a given additional lifecycle cost (Paper C92-EIC_029 to Energy in the City Conference, London South Bank University, June 24th) . And solar heat, along with biomass, could help top up the system.