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Tag Archives: green heat

Solar heating shines again

By Dave Elliott

The UK may be doing reasonably well on green power, but it is not making much progress on green heat. What about solar heating? The familiar roof-top solar heat collector, with a flat glass plate on top of a box with pipework for cooling water, has been upgraded over the years to more efficient evacuated tube and focused solar and hybrid PV/Thermal variants. These systems can offer cost-effective no/low carbon heating in some locations and are mostly scalable, suitable for a range of small or large-scale applications. And you can store solar heat for use later and also use it to drive cooling systems. All in all, it’s an energy source with multiple attractions.

The UK Solar Trade Association (STA) says: It’s time to look again at solar thermal. The strategic importance of this mature, proven technology is growing as our homes become more thermally efficient and require less space heating – we will continue to need hot water. The UK also needs to do much more to decarbonise heat, where we lag badly behind in Europe.’


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Green heat in the UK

by Dave Elliott

‘Heat is very difficult to decarbonise and no consensus is yet reached on the mix needed for the long term and you will have seen that from the various different reports on the subject.’  So said the then UK Minister of State for Energy, Baroness Neville-Rolfe, at the Heat Summit last December, with the next phase of the Renewable Heat Incentive (RHI) central to the agenda. There certainly are some competing options, including community-wide heat networks, green gas supply networks, biomass and solar home heating and domestic heat pumps powered by electricity.


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What sort of green grid system?

By Dave Elliott

It’s clear that we will need energy transmission grids and networks to help balance variable renewables and link up locations where there is excess to areas where there are temporary lulls, but what sort of energy is best for transmission? And for storage? Both are important and can interact: in some cases storage may be better as a local option than long distance transmission, while in other cases, long distance transmission may allow access to areas where storage (e.g. pumped hydro reservoirs) is easier.  However, electricity isn’t necessarily always the best option for either: for example, gas can be transmitted long distances with low losses and, once installed, gas pipelines are less invasive than power grid tower links. Gas can also be stored in bulk in underground caverns and the gas grid itself is a store. So as we move to a new energy system, we need to think about all the possible energy vectors – and that also includes heat.


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ETI on energy saving in buildings

By Dave Elliott

The UK Energy Technologies Institute’s report by Jeff Douglas on Decarbonising Heat for UK Homes notes that ~20% of CO2 emissions are from domestic heating, but says insulation/upgrades won’t cut that enough: ‘the scope for cost effectively reducing the energy demand of existing buildings to the great extent required to meet emissions targets is limited as comprehensive insulation and improvement measures are expensive and intrusive. A several hundred billion pound investment in demand reduction for the entire building stock might deliver less than half of the emissions abatement needed. The most cost effective solutions therefore involve the decarbonisation of the energy supply combined with efficiency improvements that are selectively rather than universally applied, as part of a composite package’.


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Green heat: not all going to plan

By Dave Elliott

A new report ‘Policy for Heat: Transforming the System’, from Carbon Connect, follows a cross-party inquiry chaired by Shadow Energy Minister, Jonathan Reynolds MP, and Conservative MP Rebecca Pow. It argues for the better development and greater integration of policy on low carbon heat, energy efficiency and new-build homes. It notes some big problems with current programmes, not helped by the scrapping of the Green Deal and the Zero Carbon Homes policy. (more…)

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Water source and gas fired heat pumps

By Dave Elliott

Heat pumps are seen as a clever way to get an energy upgrade, with the input energy driving a compression cycle, pumping heat collected from outside a building into radiators inside, like a fridge working in reverse. Most systems use heat from the air or from the ground, but there are also some water-source systems. For example there are large water-source heat pump schemes in Scandinavia, feeding heat to district heating networks. About 60% of the total energy input for Stockholm’s Central Network is provided by a district heating plant with six large heat pumps using the sea as a heat source. Warm surface water is taken during summer, while in winter, the water inlet is in 15m depth where the temperature is at constant +3°C. Helsinki in Finland also has large heat pump plant producing district heating with capacity of 90 MW, as well as cooling, with capacity of 60 MW, using heat from the sea and from wastewater led into the sea from a central wastewater treatment plant.

These are large projects, but a medium-scale system is being developed in the UK, using Mitsubishi’s Ecodan pump, which was voted the best new product or technology at the 2014 Climate Week Awards. It’s the first application of a system of its kind in the UK, and is backed Mike Spenser-Morris, a local developer and director of the Zero Carbon Partnership. The heat pump will use the Thames to provide hot water for radiators, showers and taps in nearly 150 homes and a 140-room hotel and conference centre at Kingston Heights in Richmond Park, cutting heating bills, it’s claimed, by up to 20%. It’s based on using water drawn from two metres below the surface of the Thames, where the ambient temperature, sustained by ambient heat from the sun, stays at around 8C to 10C all year round. A system of heat exchangers, pumps and condensers boost that to 45C. The electricity used to power the system is supplied by Ecotricity, which makes it zero carbon. According to a report in the Independent on Sunday, the system is thought to have cost about £2.5m, though this is for a ‘first of a kind’ project. The cost of future systems should be lower, and the Renewable Heat Incentive can offset supply costs.

Energy Secretary Ed Davey told the Independent on Sunday: ‘This is at a really early stage, but it is showing what is possible. You never have to buy any gas- there are upfront costs but relatively low running costs. I think this exemplifies that there are technological answers which will mean our reliance on gas in future decades can be reduced. Here you have over 100 homes, you have a hotel with nearly 200 bedrooms and a conference centre that won’t be using gas. It will be using renewable heat from the nearby River Thames. This is a fantastic development. My department is exploring the potential for this sort of water-source heat pump across the UK, so we’re going to map the whole of the UK for the potential’:

As the Independent noted, in theory, any body of water, including tidal rivers as well as standing water such as reservoirs and lakes, can be used as long as they are in the open and heated by the sun. The Government has a target of 4.5 million heat pumps across the UK, though most will be using heat from air or ground and will be small domestic units. Prof. David MacKay, until recently DECC’s chief scientific adviser, has described a combination of heat pumps and low carbon electricity as the future of building heating. However, as I’ve noted before, there are limits to the viability of small domestic systems: they make most sense in off gas-grid areas. Larger units, feeding district heating networks, are more efficient, and make more sense in urban areas, where there are large heat loads. Operation at the larger scale also make it easier to provide an effective maintenance regime, important for heat pumps, which need careful adjustment and servicing to maintain optimal performance. Otherwise the coefficient of performance (CoP), usually expected to be around 3, can fall dramatically. For example, in winter in damp cold countries like the UK, the external heat absorption pipes of air source heat pumps can develop a film of frost, reducing the heat flow. Without regular de-icing, the pump then has to work harder, potentially, in the extreme, reducing the CoP to perhaps 1 or less- making it less efficient than a simple one bar electric fire.

Moreover, large or small, the current type of heat pump run on electricity, and it’s been argued that the idea of shifting to heat pumps instead of gas for home heating on a national scale may be suboptimal, since using heat pumps run on mains electricity generated in large gas fired-plants, may be no more efficient than using gas direct in a domestic scale condensing boiler. It’s also argued that the wide-scale use of electric heat pumps is impractical, since the electricity network could not supply the large amount of power needed – the gas grid carries 4 time more energy than the power grid. It’s perhaps worth noting in this context that in the 1950’s, Southbank’s Festival Hall was heated by a large 7.5MW gas fired heat pump using the Thames as a heat source, although it seems it was taken out mainly as it produced too much heat: it was oversized

There is now renewed interest in gas-fired absorption cycle heat pumps. They are less efficient than the electric motor driven compression-cycle variant, but gas is cheaper/kWh than electricity, much of which, after all, is made inefficiently by burning gas (and coal), so a 50% net fuel saving is claimed. At the World Renewable Energy Congress in London in August, Prof. Bob Critoph from the University of Warwick noted that there were now three domestic gas-fired systems on or very near to market (Robur, Vaillant, and Viessmann) with others under development. He proposed a mixed heating solution with both gas-fired and electric heat pumps, and also the use of hybrid electric heat pump-gas boiler systems, e.g. for older properties. He felt that the proposed mix, whilst not being the minimal emission route, was an affordable and pragmatic solution to domestic heating. There are of course other novel ideas, for example solar thermal fired absorption cycle heat pumps, which may have relevance even in the UK, with the combined air source/solar Solaris system claimed to be 25% more efficient than standard air-source electricity-powered units depending on location: and

Whatever the heat and power source, are heat pumps the way ahead? Some say that large community scaled gas-fired combined heat and power (CHP) plants, with CoP equivalents of up to 20, are better in energy efficiency and carbon emission terms than heat pumps of any scale or type. That may be true at present, but, longer term, if electric heat pumps use green electricity, or gas fired heat pumps use green gas (biogas or stored gas produced using surplus wind/solar-derived power), then net emissions would be near zero. Although the same would be true for green gas fired CHP.

In the final analysis, given its high CoP, CHP seems to have the edge for the moment, but, in economic terms, the optimal systems choice may depend on the location and the size of the load. One of the largest gas-fired heat pump systems so far is the 140kW unit at Open University:;Ener-G_teams_up_boreholes_with_absorption_heat_pumps_.html

In some locations, large water sourced units may make sense, but large gas-fired units might have even wider applications. But then so may CHP, linked to district heating networks. However, to complicate matters further, it may not be a straight choice between CHP and heat pumps: e.g. a heat pump can be run using electricity from a CHP plant, while using the heat from the CHP plant as its heat source, thereby upgrading the heat output. Plenty of room for innovation!

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Green energy in the UK

By Dave Elliott

UK renewable electricity generation grew by over 56% in the second quarter of 2013, with its share of total electricity generation up to a record 15% from the 10% share in the second quarter of 2012. Projections from the Department of Energy and Climate Change (DECC) for the future suggest continued growth is possible, with in one scenario offshore wind reaching 39 GW by 2030, up from 3.6 GW now, and in another scenario, PV solar reaching 10GW and perhaps even 20 GW by 2020, up from 2.6 GW now.  and (more…)

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Renewables: observing the future

by Dave Elliott

In its business leader column on August 25th The Observer, said “If there is a body of opinion that states that wind farms and energy efficiency can fill the looming energy gap, then it is small and deeply unrepresentative”.

Germany is aiming to get at least 80% of its electricity from renewables by 2050, with overall energy demand cut by 50%, so the Observer seems to have it wildly wrong, certainly long term.  And in fact, far from being marginal, around 50 countries are already getting more than 60% of their electricity from renewables in the form of hydro, some of them near 100%. Longer term, dozens of studies claim that renewables could supply 100% of the worlds electricity in many countries by around 2050. That is what Denmark and New Zealand are aiming for and many others see renewable as their main future energy option- with China leading the way.


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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

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: and

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.

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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Renewable heat

Detailed proposals for the governments Renewable Heat Incentive (RHI) have emerged, after a long delay. Heating accounts for 47% of total UK final energy consumption and 46% of carbon emissions, so it’s not a marginal issue. The RHI cover biomass, ground source and water source heat pumps, solar thermal and bio-methane, and participants will receive quarterly payments for 20 years from the date they enter the scheme.

It will be introduced in two phases. The first phase is expected to start after the regulations have been processed by Parliament in July. It will offer long-term tariff support for non-domestic projects, i.e. for the big heat users – the industrial, business and public sector – which contribute 38% of the UK’s carbon emissions. But under this phase there will also be grant support of around £15m for households through an interim ‘Renewable Heat Premium Payment,’ for ‘well-developed’ projects, essentially as a ‘test drive’ for the more diffuse domestic sector.

The second phase of the scheme will see households also able to apply for long-term tariff support, this transition being timed to align with the ‘Green Deal’ loan system, which is intended to be introduced in October 2012.

Unlike the feed-in tariffs for renewable forms of electricity, which are paid for through higher energy bills, the renewable heat incentive will be paid for from taxes – in all, £860m government funding has been allocated. The proposed tariffs (still subject to consultation) range from 1.9 pence / kWh for small biomass projects, to 8.5p/kWh for solar thermal, but these prices will be degressed’ (i.e. reduced) in stages over time to match the development of the market and avoid a boom-and-bust situation. Details of that are promised soon.

The RHI only meets the extra costs above that for installing conventional systems, not the total costs. Even so, it should yield a rate of return on outlay of about 12%. So it could be quite popular- if participants have the upfront capital available. However, DECC says that ‘We do not intend to allow agents, such as installers, suppliers or other third parties, to apply for support from the scheme on an applicant’s behalf.’ So you are on your own!

And there are some other limits. DECC says ‘by domestic installations, we mean installations where a renewable heating installation serves a single private residential dwelling only. This does not include multiple residential dwellings served by one renewable heating installation (e.g. district heating) nor residential dwellings which have been significantly adapted for non-residential use’.

Rural areas won’t get special treatment, despite DECC accepting that ‘a higher proportion of rural than urban areas tend to lack access to the gas grid and organisations not connected to the gas grid, for example small rural businesses, tend to have higher heating costs due the use of more expensive fuels’. It simply says that ‘those off the gas grid will have the potential to benefit most from the RHI’ and ‘those in rural off-gas grid areas may have better access to biomass in particular and not face the same installation and biomass fuel supply barriers as those in urban areas.’

The RHI will operate via Ofgem, who will provide accreditation and will carry out equipment inspections. In that context there some interesting technical conditions/requirements e.g. heat pumps must have a COP of 2.9 or above (but air sourced units will not be supported initially) and biomass sources must meet eco-eligibility criteria. As a condition of receiving support, participants will also be required to maintain their equipment to ensure it is working effectively: Ofgem may check this periodically.

All biomass, ground and water source heat pumps and solar thermal plants of 45kWth capacity or less will need to be certified under the Microgeneration Certification Scheme (MCS) or equivalent schemes. The MSC , not too popular in some circles. will be upgraded.

The RHI will only support ‘useful heat’, with Ofgem determining eligibility according to RHI regulations. In outline, acceptable heat uses are said to be ‘space, water and process heating where the heat is used in fully enclosed structures’. The heat must be supplied to meet an ‘economically justifiable heating requirement i.e. a heat load that would otherwise be met by an alternative form of heating e.g. a gas boiler’. This should be an ‘existing or new heating requirement i.e. not created artificially, purely to claim the RHI’. The only exception is for bio-methane injection into the gas grid, with no specifications on how it is then used

Heat used for cooling counts towards the renewables targets under the EU Renewable Energy Directive and therefore, provided it meets all other eligibility criteria, it will be eligible for RHI support, but not passive solar or exhaust air heat pumps.

Renewable heating systems that replace an existing renewable heating system will be eligible for the RHI support, despite the risk that some people may therefore scrap old but viable systems to get the RHI. More commonly, renewable heating capacity is likely to be expanded, and the extensions are eligible for the RHI up to the (joint old/new) total capacity threshold.

And finally, the RHI is not intended as a mechanism to support ‘innovative technologies in development or early deployment’- but happily, deep geothermal is allowed.

The delay until Oct 2012 for the domestic sector scheme raised some eyebrows and some saw the solar tariffs as too low, but otherwise the RHI was generally welcomed.

It could involve some quite big schemes. Public sector and not-for-profit organisations, such as schools, hospitals and charities, can use the RHI, and DECC says ‘the support provided by the RHI will also enable communities to come together to find local solutions tailored to local energy needs. The opportunities are many, from setting up anaerobic digestion plants using local waste to establishing community- owned biomass co-operatives sourcing fuel from sustainable local woodlands’

It adds ‘In some situations, district and community renewable heating, whether as a central boiler for an apartment building, or as a network of pipes delivering heat from a central installation to a number of local households or businesses, can be a cost-effective alternative to installing individual heating systems in properties. By supporting this sort of application, the RHI will encourage investment and give developers confidence to install centralised plant’.

So we could be seeing some local district heating networks like those elsewhere in Europe, powered using renewable sources. But the RHI won’t pay for the pipes!

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