Utility Week

20 | 16TH - 22ND FEBRUARY 2018 | UTILITY WEEK Policy & Regulation Market view U K coal mines, which have contributed so greatly to climate change issues, are now being seen by some pioneers as a source of clean energy. Certainly, that is the thesis being put forward by the Coal Authority, an executive non- departmental public body which manages around £3 billion-worth of coal mining issues. While previously considered a histori- cal liability, the UK's mining legacy is now viewed by the Coal Authority as an asset of strategic importance. For more than 200 years, UK coal was intensively mined, with more than 100 billion miner and machine hours employed in its extraction. This vast industrial undertaking has le behind an extensive network of tunnels, roadways and fractured ground. As mines are abandoned, pumps switched off and mines flooded, geothermal heat, transmit- ted from the Earth's centre, warms the mine water to temperatures of typically 20-40C. Calculations suggest the flooded mine work- ings are now a source of heat producing an estimated 2.2 million gigawatt-hours of harvestable heat a year. That is enough to heat five times the number of homes in the UK, and with more than one-quarter of UK homes being in the coalfields, the opportu- nity is enormous. Mine heat is low grade, which means it is unsuitable for generating electricity as steam but ideal for cost-effectively heating homes, warehouses, leisure centres and offices. With approximately 45 per cent of energy in England and Wales used for heating, and 55 per cent in Scotland, this is a significant proportion of UK energy demand. To harvest the heat requires the use of heat exchangers and pumps. These work the same as refrigerators do at home. They use electricity to remove heat and cool the heat source. This is a highly efficient pro- cess, for every 1KW of electricity, 5-10KW of heat equivalent are produced (depending on source temperature). This represents a cost and carbon advantage over public supply gas. If the electricity used in the heat pumps is supplied from renewables, the mine heat would be virtually carbon free. Mine water heat would not be subject to external fac- tors that cause energy price fluctuations; this could provide commercial advantages to horticultural growers and in attracting new industries to the coalfields. Another opportunity is redistributing money from local heating into the local economy, as at the Heerlen Mine Water Heat Scheme in the Netherlands. This means the communities built on the coalfields, once disadvantaged by their closure, have an asset beneath their feet that can tackle fuel poverty, energy resilience, price instability, climate change and be a catalyst to create new jobs. There is something quite poetic about this. Energy storage UK mines come in all shapes and sizes. Some are ideal as a continuously recharging source of geothermal energy. Others could see a reduction in temperature if the rate of withdrawal exceeds natural recharge. This is where storing of energy in the mine comes into its own as a means of holding signifi- cant quantities of energy across-seasons for later use. Thus it can be used as a means of assisting the balancing of the electricity grid, not only across seasons but also through daily peaks. Sources of energy for storage could come from energy-from-waste plants, sewage, industry, renewables, and spare grid capac- ity. The Coal Authority is particularly inter- ested in promoting a district heating scheme using thermal panels on residents' roofs as a source of heat for long-term storage. Ther- mal panels are 95 per cent efficient and can produce up to 60 per cent of a home's heat requirement a year. The difficulty is that they produce high temperature hot water mostly during the summer and most efficiently between peak usages. If this heat was stored in mines, residents would benefit from being able to draw their heat back when they most need it. There are more than 134,000 known mine shas in the UK. Many have been backfilled, but where they have not, they have potential to be converted into large heat storage flasks. The Coal Authority is currently working with Midlothian Council, Scotland, on the use of an abandoned mine sha as a heat storage vessel of some 12,000 cubic metres, charged from surplus heat from an energy-from-waste plant under construction. Stored heat will feed into a district heating scheme, provid- ing operational and energy savings to the scheme and plant operator. The future? The Coal Authority is keen to see the build- ing of commercial scale pilot schemes to kick-start an industry. One of the first will be the Bridgend Council, Wales, Caerau dis- trict heating scheme in which pilot boreholes have found 20.5C in a roadway at just 220m below ground level. Jeremy Crooks, innovation manager, the Coal Authority Coal mine energy storage The UK is littered with flooded abandoned mines, which can be tapped as a source of geothermal energy. The commercial possibilities are mouth-watering, says Jeremy Crooks. 100C 40C USE OF COAL MINES FOR GEOTHERMAL AND HEAT STORAGE Cool return Heat/cooling users Short-term storage in mine shafts with volumes up to 12,000 million cubic metres Source: The Coal Authority 11-21C Mine workings Up to 40C Annual geothermal heat in UK mines 2.2 million GWh Heat sources for cross-seasonal storage in mines • Energy from waste • Renewables • Sewage • Industry Heat exchanges/pumps S H A F T S

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