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Tag Archives: renewable heat

Energy storage technologies

by Dave Elliott

There are many energy storage options which can be used balance grid systems so as to compensate for the variable output from some renewables. They include existing and newly emerging electro-chemical and electro-mechanical systems (batteries, pumped storage and compressed air storage), as well as a range of thermal and hydrogen based systems 


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Green Heat 1

I have often been less than impressed by reports from the Royal Academy of Engineering (RAE) , which usually seems to take a conservative line on energy issues, but their new report on heating for buildings seems overall very well done, although with lapses. It makes the sensible point that we need to deal with the building envelop first, but also notes that most of the houses that will be lived in by 2050 have already been built, so we must look to remedial measures. It also notes that ‘Manchester isn’t Leipzig’, and looks at patterns of heating need and perceptions of comfort. It assumes we are talking about well insulated buildings, and familiar levels of comfort, and it reviews the energy supply options for supporting that.

It sets the scene by pointing out that ‘If space heating could be decoupled from water heating it would change the selection criteria for heating appliances and boilers. There would no longer be a need for the heating system (as opposed to the hot water system) to be on standby during summer months or to be capable of operating at a sufficiently high temperature to prevent Legionella developing in water systems. All domestic heating is currently thought of as low-grade heat requirement, but there is a case for distinguishing space heating as low grade and hot water as medium grade. A policy for heat should separate these two different uses’.

It looks at heat pumps as a possibility, but is not too convinced. ‘While the general reduction in carbon intensity of grid electricity makes the use of electric heating (direct or via a heat pump) more attractive, peak heat loads tend to coincide with peak electricity loads. There is, therefore, a significant likelihood of heating demand being met by high carbon electricity generation brought onto the system to meet peak loads over and above the capacity of low carbon generators’.

It goes on ‘Air source heat pumps have been rising in popularity for new build in the UK, but this is partly an effect of the way in which electrical energy is treated in the regulations that makes CO2 targets more lenient than for gas systems.’ While it admits that ‘Air source heat pumps integrate well with well insulated dwellings, if properly sized and installed,’ and it suggests that ‘micro-CHP complements and could balance some of the properties of heat pumps’, it also notes that ‘several reports discuss inadequacies of the application or system engineering in heat pump installations. It is clear that heat pumps are not forgiving if installed inappropriately.’

By contrast, it’s much happier will larger-scale communal system. ‘Communal air source heat pumps are an interesting area of development with some new configurations of systems coming to market. Central systems may be more efficient and are likely to offer much greater energy storage than do systems designed for individual household’.

It adds ‘Larger district systems, incorporating a CHP facility and providing heating are significantly more efficient than domestic level installations. This is because waste heat can be used in district heating after it has generated an element of electricity. Such district heat is therefore always of significantly lower CO2 emissions than any heat only production utilising the same fuel’. And that, it seems, includes domestic scale heat pumps.

The RAE does seem to been moving towards community- scaled system across the board. However, it is less happy with renewables. Although it sees some potential for bioenergy e.g for CHP/District Heating , it is not very impressed with solar, and overall treats renewables as problematic in terms of grid power supply, reverting to the traditional RAE line on the problems of intermittency and the delights of nuclear: ‘During the summer months, most of the night-time load could be provided by nuclear power with renewables providing additional power during the day’, while in winter ‘we would need sufficient renewables to guarantee 40GW during the evening peak. As wind, tides and the sun are intermittent, that would require significantly higher installed capacity of renewables or thermal back-up capacity, much of which would be unused for long periods in the summer’ making renewables uneconomic.

Nevertheless, it does look at smart grid /load management options which might change the situation radically, helping to deal with intermittency. A bit grudging, but at least there is now some recognition that a new interactive supply and demand system might be viable. It’s taken decades to get the community CHP/DH message across to the traditionalist engineers, so maybe it’s too early for idea of smart dynamic grids to have got through! And it may take even longer for them to give up on ‘baseload’ nuclear, which they still see as essential, rather than as getting in the way of a more interactive flexible system based on renewables ( which is the view emerging from Germany) .

However, as far as CHP/DH in concerned, the RAE is now full of praise. It says that ‘CHP plants, biomass combustion, and heat pumps are more efficient, reliable and cheaper at scales larger than a single dwelling. The costs of large scale heat pump installations per kW are a quarter of that for domestic-scale installations.’ It adds that ‘it is more efficient to use the available skills for fewer large systems than for many individual units’, and that, since energy storage will be needed ‘district heating systems have another important benefit – the mass of water in the underground pipes provides a heat store that evens out daily peaks and troughs in demand. This can be supplemented by hot water tanks to increase energy storage’. And taking it one step further, it points out that ‘well insulated hot water tanks or underground inter-seasonal thermal stores will be simpler to provide on a community basis given the small (and reducing) size of most UK homes’.

Some sense last! And DECC seem to be taking notice, in their new Heat strategy- see my next Blog.

‘Heat: degrees of comfort?’ Royal Academy of Engineering

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Survival of the FiTs – for now

The government’s spending review brought fears that the government would backtrack or water down the existing Feed-In Tariff (FiT) for electricity and also the proposed Renewable Heat Incentive (RHI). A coalition of 22 groups, including the Renewable Energy Association, the National Farmers Union and the Federation of Master Builders, warned energy secretary Chris Huhne that cutting schemes that subsidise household generation of renewable energy would jeopardize job creation, energy security and greenhouse-gas targets. An open letter to Vince Cable and Danny Alexander from 64 companies, including E.ON & British Gas, adopted a similar stance: ‘premature adjustments to the tariff would have a profoundly damaging effect on long term investor confidence in the clean tech and renewable energy sectors, and may cause investors to flee altogether’.

Energy & climate change’s minister, Charles Hendry, had said: ‘We inherited a situation where we could see who was going to benefit commercially but we couldn’t really see how it was going to be paid for and that it would create pretty substantial bills.’

Neither the existing FiT or the RHI cost the government anything directly, other than administrative effort – it’s suppliers and then consumers who pay ultimately. But if the FiT leads to a take-up boom, these costs could grow faster than the prices falls due to the FiT, and overtake the built in price degression mechanism, as arguably happened in Germany and Spain. And the government may then wish to limit the cost to consumers. The electricity FiT levels are due for reassessment in 2012, but it was feared that this might be advanced prematurely.

One of the problems with the RHI is that, whereas it’s relatively easy to identify who the suppliers are for grid electricity, and levy a FiT charge on them accordingly, heat is supplied by a range of companies in a range of forms – natural gas, propane, butane, oil, wood and other biomass and even direct heat. And the scale is much larger than just for electricity – heat is about 49% of UK energy end use. But it ought to be faced, and as the REA/NFU coalition argued: “Costs come down when the industry can plan and invest with confidence, and economies of scale are achieved- that is one of the simple aims of these policy mechanisms.”

In the event, the campaigning seems to have paid off: the electricity FIT was left untouched for now, and the RHI will go ahead, although cut back to £860 m p.a. and with a two-month delayed start, until June 2011. The government said: ‘This will drive a more-than-tenfold increase of renewable heat over the coming decade, shifting renewable heat from a fringe industry firmly into the mainstream.’ However it added that it would ‘not be taking forward the previous administration’s plans of funding this scheme through an overly complex Renewable Heat levy’.

The government also noted that the existing Feed-In Tariffs will be refocused on the most cost-effective technologies, saving £40 m in 2014–15. ‘The changes will be implemented at the first scheduled review of tariffs, unless higher than expected deployment requires an early review’, presumably because of high cost PV solar.

There may be a case for changes, but it does seem sensible to leave the FiT system to bed in first to see how it goes. Friends of the Earth had commissioned Arup to review the current Feed-in Tariff. The report Small Scale Renewable Energy Study: FIT for the Future uses financial modelling of the performance of 20 generic renewable-energy schemes, and concluded that for some technologies, it could ‘seriously damage investor confidence’ to amend the tariff levels before the end of the previously announced review period in 2013.

Arup found that, while there were some perverse scale effects for wind and also PV project, due to the structure of the FiT price bands, in some cases, the FIT could work very well (e.g. a community co-operative that buys a 1.5 MW wind turbine could earn 15.9% return on investment annually for 20 years). This would mean the scheme would pay for itself in seven years. But micro-wind only had an Internal Rate of Return (IRR) of 7%. Micro hydro was in the range 10–13% IRR.

On the heat side, heat pumps had an IRR of 7%, unless used in off-gas grid contexts, when they were 12%. Domestic scale biomass boilers had very good returns: IRR 18%, but biomass fired micro-CHP was less attractive, with solid biomass micro- CHP coming in at under 5%. Individual domestic solar heating was also very poor, with an IRR of only 3%, although grouped schemes were better. The IRRs for AD biomass were even lower.

So coming up with a viable RHI system is obviously going to be tricky. That point was made strongly in a report The Renewable Heat Initiative: Risks and Remedies produced on behalf of Calor Gas Ltd by the Renewable Energy Foundation. It said that the government should scrap the proposed Renewable Heat Incentive (RHI) scheme and start again because it would be bad for the sector by encouraging technologies that ‘are not quite ready’. RHI was ‘an expensive leap into the dark’, relying on a major deployment of technologies that are new to, and untested in, the UK context. REF also uses government data to estimate that the RHI could, in practice, consume around 2% of the annual income of the poorest households – funds that REF claims will go directly towards reducing bills of the richest households, who are able to put up the initial capital for installations and so benefit from the RHI subsidies.

Dr John Constable, REF research director, said: “It appears to be a severely regressive policy; I can’t believe the previous government anticipated this impact as it is clearly an iniquitous policy. The only winners from this are those with initial capital to install the technologies in the first place.” The same argument that has been used by some against the FiT.

Overall REF claimed that the cost of the RHI could potentially increase the average domestic gas bill by 14% p.a. by 2020. Constable commented: ‘The simplest thing to do is to stop it. It is in the public interest to cross this one off and start again. Otherwise, significant changes will need to be made to avoid the risks we have identified.’ In free market mode, he added: ‘Left to its own devices, the market will learn. The RHI on the other hand would embed and shelter bad technologies and bad implementations,’ pointing to the recent Energy Saving Trust’s report on heat pumps as an example. That had found that about 87% of heat-pump systems tested in the UK didn’t achieve a system efficiency (COP) of 3 ,which the Trust considers the level of a “well-performing” system. And 80% failed to meet 2.6. EST blamed the use of multiple contractors for fitting systems instead of a single contractor as used in Europe, wrongly sized systems, complicated controls and a lack of education for householders using them. Obviously there are some issues to be resolved before the RHI can be sorted but, although the government did say that it would scrap the RHI levy idea, it clearly did not take REF’s advice and scrap the whole thing.

The EST study:

The FoE/Arup study:

As an interesting coda to the debate on the FiT and its possible amendment, energy minister Greg Barker seems to be worried about the recent boom it has created in solar farms – large ground-mounted PV arrays. He said that the government would not act retrospectivel, but ‘large green field-based solar farms should not be allowed to distort the available funding for domestic solar technologies’. Roof-mounted PV is probably preferable aesthetically but what seems to be the issue here is a concern that the very limited FiT allocation will get used up rapidly by large commercial schemes.

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Zero-carbon heat and power

Neil Crumpton, a member of the Bath-based Claverton Energy Group of energy experts and practitioners, and also Friends of the Earth Cymru’s energy campaigner, has produced a draft zero-carbon, non-nuclear scenario to 2050 and beyond intended to initiate feedback and debate in the Claverton Energy Group. It aims to identify the low-carbon energy generating and supply infrastructure needed to build a resilient, demand-responsive UK energy system. It relies heavily on renewables, urban heat grids, possibly suburban hydrogen networks, and carbon capture and storage (CCS) during the four decades of transition.

It is very ambitious. Renewables would supply about 200TWh/y by 2020, scaling up to more than 1,100 TWh/y by 2050. Offshore windfarms, at least 10 miles from any coast occupying some 20,000 sq. km, would supply ~ 550 TWh/y, about half his estimated 2050 final energy demand. But the real innovation starts on the heat side, with much use of Combined Heat and Power plants and large heat pumps feeding industrial users and town/ city heat grids. Up to 15 GWe of industrial Combined Heat and Power (CHP) plants would supply industrial clusters, while 15 GWe or more of urban Combined Heat Pump and Power (CHP&P) schemes (typically 0.5–100 MW) would distribute reject heat from fast-response ‘aero-derivative’ gas turbines, and large heat pumps.

They would feed heat grids, with up to 5 GWe of ‘initiator’ CHP&P schemes, progressively linked up to form wider district and eventually town-wide and city-wide heat grids over the next 15–20 years. Large-scale heat pump installations would deliver renewable heat from air and ground- and from solar thermal and geothermal sources.

Even more innovatively, large thermal stores (accumulators), up to traditional gasometer-scale, would optimise the system. Peaking renewable electricity, particularly from marine technologies, would primarily be stored as heat at electricity ‘regenerator’ sites comprising a mix of technologies like molten salt stores and 10 GWe or more of steam turbines, electrolysers and hydrogen fuel cells and compressed air. Chemicals and fuel synthesis could also feature and connection to the heat grids would greatly aid conversion and regeneration efficiency and heat demand response.

Crumpton says ‘such an energy storage and electricity regeneration capability would be a significant aid to delivering the UK’s large but highly variable renewable energy resources, particularly wind energy, to consumers as and when demanded’.

Initially the energy input for the heat grids would be mostly from gas, but all the gas-fired industrial CHP and urban CHP&P capacity would be progressively converted to hydrogen, piped in from coal and biomass CCS gasifiers. There could also be a direct solar heat input to local heat stores, and possibly also some from geothermal sources. Low-pressure hydrogen might also be supplied to the 9.5 million sub-urban homes via the existing (upgraded) gas network to power 10–30 GWe of mCHP boilers (possibly fuel cell) and domestic heat pumps.

All large emitters would be fitted with Carbon Capture by 2025. CCS fitted gasifiers co-fired with 15+% biomass or imported solar synthetic fuels would then provide ‘carbon-negative’ baseload to the extent climate protection policy required. The 10 GW of CCGTs already consented would operate until about 2040, then be retained for occasional duty during prolonged winter anti-cyclones.

There would also be HVDC links to Europe, including Norwegian hydro and pumped storage schemes, which would help optimise the system to high marine renewable variability, and open the option of delivering net imports of around 10% of final energy from Saharan wind and concentrated solar power schemes.

The complete system, with molten salt heat stores at regeneration sites, would comprise some 50 GW of firm electricity generation, plus peaking plant, suburban mCHP, and inter-connectors. He says the system’s firm generation and storage capacity would be designed to supply ‘smart’ demand even during a deep winter anti-cyclone lasting days. And he says that ‘Depending on the availability of sustainable bio-sources and transport sector emissions, the UK could be net zero carbon by 2040’.

It is of course all very speculative, although the use of large heat pumps is not novel- The Hague has a 2.7 MW (ammonia) seawater community heating scheme and Stockholm has a total of 420 MW (multiple 30 MW units) of heat / cold pumps feeding its district heating / cooling grid. Crumpton says ‘The large heat pumps would harness heat from sources which 11 million urban domestic heat pumps could not do, including large solar thermal arrays and geothermal’.

Using coal still might worry some environmentalists, but there would be CCS and he says it would be used in minimal amounts by 2050. Generating and piping hydrogen is also a novel idea – but there are now some pilot schemes in the UK. And piping heat is much more common – on the continent.

Installing that, and the rest of the system, would though involve a lot of new infrastructure, but he claims that ‘strategic siting the gasifiers would combine locations with good transport access for coal and biomass (dock-sides, railheads, collieries), together with hydrogen pipeline routes to CHP schemes, and CO2 pipelines to geological storage sites under the North Sea or Liverpool Bay’. And similarly ‘regeneration schemes should be sited adjacent to industrial clusters, refineries, and existing chemical sites with hydrogen, CO2 and heat grid pipeline access’. In addition, ‘coastal locations with direct HVDC connection from marine renewables would minimise need for new cross-country transmission lines’.

So disruption would be reduced. Nevertheless, building the heat grids (polypropylene pipes) would involve some short-term local disruption to pavements and roads during the pipe/conduit laying. But he says it would ‘provide low-carbon energy infrastructure for the children of today and future generations’.

The draft scenario is outlined in more detail in the current issue of Renew (183):

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Pipe Dreams

Construction has started on the first part of the ‘Leningrad II’ nuclear plant on the existing nuclear plant site on the outskirts of what is now St Petersburgh. The first 1170 MWe pressurised water reactor is scheduled for commissioning in October 2013 and the second a year later, at a cost of $3.0-3.7 bn per pair. Leningrad II will eventually have four new reactors.They are claimed to be super safe, with passive as well as active safety features.

As well as supplying electricity to the grid, the four new Leningrad II reactors, like the existing plant there, will also provide heat to the city- 9.17 petajoules per year of district heating. In well insulated pipes, heat losses over 10-20 km are relatively low and the demand for heat in Russia is high given the climate. Nuclear Cogeneration/Combined Heat and Power (CHP) capacity in Russia will then be supplying about 12 petajoules of heat per year, and it plans to have 5 GW of small nuclear reactors for electricity generation and district heating by 2018 at Arkhangelsk, Voronezh, Chukoyka and Severodvinsk.

So will others follow the lead and install nuclear plants in or near cites- and feed the waste heat into district heating pipes? So far most nuclear plants in the West have been located in relatively remote areas- for safety reasons and to be near sources of cooling water. But there are economic attractions in being able to use the otherwise wasted heat produced by the steam turbines. As with all steam raising power plants, whatever the fuel, the losses represents nearly 70% of the heat energy produced from the fuel, more than half of which can be reclaimed by operating in CHP mode i.e. supplying heat and well as electricity.

Even if you don’t like the idea of urban nukes (and if nothing else it could have a significant impact on property values!), there are some other interesting and possibly equally controversial ideas related to CHP/district heating. We are all used to the standard argument that putting insulation on buildings is the cheapest energy option. ‘The cheapest watt is the negawatt,’ and so on. But is it always so? Studies by CHP consultants Orchard Partners London Ltd have suggested that, in terms at least of retrofit/rehab options, it may be cheaper and lead to more carbon emission savings, to provide piped heat from urban gas-fired CHP plants, than to install insulation, especially for some hard to access high rise flats. Put simply, the argument is that it’s easier and cheaper to insulate pipes than whole buildings. They have developed a clever kerb stone pipe module that they say makes urban retro-installation easy. They claim that ‘Houses, when connected to low CO2 piped heat supply would immediately achieve the highest rating for buildings without any investment in demand side measures. The disruption to residents and traffic with the new route that has been identified will be minimal compared to the disruption replacing an unsustainable gas network under the roads and minimal for residents compared to retrofitting insulation and glazing to existing premises particularly all our pre 1950s stock.’

If you also moved to biomass, or biowaste /biogas fuelled CHP plants, then you would be more or less zero carbon- and cities have a lot of biowastes, sewage biogas for example being one of the cheapest energy sources around. At present much of it is used just for electricity production, but CHP is the logical next step. With interest in renewable heat supply growing (heating accounts for about 40% of UK energy use) some fascinating new ideas are emerging about new ways of supplying consumers’ needs- using pipes. At present we transmit electricity long distances from large power plants, with up to 10% transmission loses and even more local distribution losses. But you could have a large remote biomass fired plant, perhaps using biogas from a landfill site, which transmits heat to consumers in cities. Or a large anaerobic biogas digestor on the edge of a town or city, or even miles away, using municipal waste, and feeding biogas along a pipe to an inner city CHP plant. More likely biogas will just be added into the conventional gas main – that’s actually now been agreed as an acceptable option and some projects are underway or planned. But one way or another we may be seeing a lot more pipes in future…whether running heat or gas, the attraction over electricity being that both can be stored. We may even see the return of the classic large inner city gasometer for gas storage, along with local buffer heat stores, as are used in parts of northern Europe as a part of local district heating systems

Other renewable energy sources can also be run into heat stores- solar heat for example, allowing for variable supply to be matched to variable demand. There are even some inter-seasonal solar heat stores in operation. Once again, put simply, while no one is suggesting we don’t do both where appropriate, it’s easier to insulate a heat store than a whole house. And it’s not just solar heat, or geothermal heat, we could store. Dr Mark Barrett, senior researcher at the UCL Energy Institute, has suggested that we could use our domestic hot water cylinders as a national distributed heat store, storing excess energy from wind turbines and other large but variable electricity supplying renewables, like wave and tidal power, ready for use to reduce heat demand peaks.

Plenty of new ideas then to suit all tastes, and good news for plumbers and pipelayers! And an interesting challenge to those who think in terms of an ‘all-electric’ future.

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