by Dave Elliott
By their nature, wind and solar energy are variable and there is likely to be excess electricity generated from using these resources at times, and shortages at other times. It is hard to store electricity directly, but the energy can be converted into more easily storable forms.
One of the big hopes for the future is the ‘wind to gas’ idea- using excess wind-derived electricity to produce hydrogen gas by electrolysis for storage and then use, when there is a lull in the wind and high demand, to generate power in a fuel cell or gas turbine. Alternatively, the hydrogen, or methane derived from it (and from captured CO2), can be fed into the gas grid to replace fossil gas. For once the label ‘game changer’ might even be right- perhaps the key to a balanced energy future, compensating for variable inputs from renewables. It seems like an idea whose time has come: www.aspo2012.at/wp-content/uploads/2012/06/Pengg_aspo2012.pdf
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”. www.theguardian.com/business/2013/aug/25/anger-fracking-cant-manage-without-gas
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%. http://k.lenz.name/LB/?p=6525. Longer term, dozens of studies claim that renewables could supply 100% of the worlds electricity in many countries by around 2050. http://www.mng.org.uk/gh/scenarios.htm. 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.
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): www.natta-renew.org