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Green Heat 3

Community-based energy technology was very much a 1970s thing, but is now back on the agenda. An ESRC backed ‘Sustainability Transitions’ seminar series included a one day conference in Manchester in April which explored the ‘lessons of the 1970s’ for the current low-carbon transition. Organised by SURF (Salford Universities Centre for Urban and Regional Futures) and SPRU (Sussex Universities Science Policy Research Unit), the conference included a look- back at some of the pioneering work of the Centre for Alternative Technology, like. the 1976 Wates super-insulated house. Now PassivHaus projects are spreading everywhere.

CAT also pioneered inter-seasonal solar heat stores, with, in 1976, a 100 sq. m solar array feeding into a 100 cu. m heat store tank; see right. Others followed, like the 1980 Swedish 10,000 cu. m heat store – linked to 55 houses. See www.jenni.ch/

Now there are many, and some are quite surprising. For example solar heating might seem an odd choice for Canada, but the Drake Landing scheme in Alberta, with 52 houses, has 2,300 sq m of solar mounted on garages and an underground Inter-seasonal heat store:144 x 35m deep boreholes spaced 2.2m apart. There are many other interseasonal heat store systems around the world, the largest so far being the 13.5 MW Marstal project in Denmark.

In terms of efficient community-scale green heating, solar district heating backed up by interseasonal heat stores is arguably at the top end of the range in environmental terms, with almost zero emissions, but it’s still expensive. District heating fed from other currently cheaper sources (chiefly gas) is much more widespread in continental Europe. Again, this was very much a 1970s thing, But now many of these projects are being converted to run on green energy sources e. g. biomass, often in Combined Heat and Power (CHP) plants. CHP coupled with district heating (DH) is seen as efficient way to deliver heat on a community scale. By contrast, individual domestic micro-CHP units and heat pumps are usually much less efficient.

There are also some large community DH schemes using very novel sources. For example, in a long-standing major project in Sweden, about 60% of the total energy input for Stockholms Central Network is provided by the Ropsten district heating plant. This uses the sea as a heat source, harvested by series of 6 large 180MW (e) heat pumps with a total heat supply capacity of 420MWth. They are used for base load production, along with biofuel-fired plants (total heat capacity 200MW). Oil-fired plants are used in times of high energy demand only. The complete plant has the capacity to operate autonomously (i.e. just on ambient energy) during spring, summer and early autumn, when large amounts of seawater are used as heat source. Warm surface water is taken during summer. In winter, the water inlet is in 15m depth where the temperature is at constant +3°C.. The plant can also provide district cooling, with a with a 60 MW cooling plant adjacent to the heat pump. See: www.friotherm.com/downloads/vaertan_e008_uk.pdf and
www.iea-dhc.org/download/city.pdf

There’s a similar system for district heating and cooling with heat in Helsinki in Finland, where a large heat pump plant produces district heating with capacity of 90 MW, as well as cooling with an output of 60 MW. The plant is in a rock cave excavated under a park. In the winter, the heat energy is taken from purified wastewater led into the sea from the central wastewater treatment plant. Then the heat pumps are used only for district heat – the energy for district cooling is obtained In summer, heat is taken from the return water in district cooling, when the heat pumps supply both district heat and cooling. CO2 emissions from the heat pump plant are said to be over 80% less than from using heavy fuel oil or individual cooling compressors in each house.

Over 93% of Helsinki’s heat is supplied by district heating systems and over 90% of annual district heating energy is produced efficiently via CHP. Overall there’s 1150 MWe and 3600MWth of CHP/ DH in Helsinki, with one plant linked to the city network via a 30km pipe in a tunnel.

That makes the point that, although we don’t all have easy access to the sea as a resource, and we may not want to have large CHP plants inside cities, heat can be transmitted over surprisingly long distances without significant energy losses. For example, in Denmark there’s a 17km link from a CHP plant to the city of Aarhus, and in Norway, district heating is provided around Oslo via a 12.3 km pipe from a waste burning plant in the city outskirts But the daddy of them all is in the in the Czech Republic, with a 60km pipe link from the Melnik plant to Prague.

CHP/DH does have it’s problems- installing the pipes is disruptive and expensive. But once you have established the infrastructure it can be fed with whatever energy source is currently the best. It is sometimes argued that if you have very low energy using houses, built to Passivhaus standards, then you will not need much energy input, so district heating schemes wont be needed. But an Austrian study disputes this ‘especially in blocks of flats, where a lot of m2 are put on top of each other’ where ‘it is a good idea to supply with district heating, what the building cannot generate by itself.’

Moreover in some situations it is actually cheaper to pipe in heat than to rehab buildings with extra insulation. For example, a study by Orchard Partners for the UK Technology Strategy Board ‘Retrofit for Future’, comparing Combined Heat (CHP) and Power /District Heating with domestic insulation concludes that, for a typical late 1960s/early 1970s London houses in a terrace of five houses, connection to district heating gives a lower capital cost per tonne of CO2 displaced than alternative insulation measures. www.orchardpartners.co.uk/

CHP/DH is at long last being taken seriously in the UK, being mentioned as a key option in the new DECC Heat strategy and also in the new Bioenergy strategy. See my last Blog. But we have a long way to go the catch up.

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