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
However there are issues. The multiple energy conversion processes involved mean that overall efficiency may be rather low, with for example electrolysis being typically only 60-70% efficient, but the energy conversion losses are mainly as heat, some of which can be captured and used in total energy combined heat and power systems. Moreover, since the input energy is the excess from wind or other variable renewables, which would otherwise be dumped, it is in effect free, which should make the economics reasonable. And it also opens up the option of making a range of high added value synfuels- from renewables. http://www.iwes.fraunhofer.de/de/publikationen/uebersicht/2010/towards_100_renewablesandbeyondpowerthepossibilityofwindtogenera.html
Given its large wind and PV solar programme (62GW so far), Germany is pushing ahead rapidly with this idea, sometimes called more generically ‘power to gas’ since it can also use excess solar PV output or indeed surplus outputs from any other variable renewable source.http://www.gasnaturally.eu/uploads/Modules/Publications/marcogaz_power2gas_fact_sheet.pdf
By 2013 there were over 7MW of ‘power to gas’ projects in Germany, using surplus electricity from wind plants to make hydrogen by electrolysis. Car companies were amongst the initial leaders. Audi’s product is called ‘e-gas’, designed for use in their new combustion engines.
However public energy supply is now also a major focus. ENERTRAG is using three 2 MW wind turbines to produce hydrogen, which, mixed with biogas made from local corn waste, is used in a CHP/cogen plant, so that electricity can still be fed into the grid when little or no wind is available. It is also feeding its green gas into the natural gas grid, and some of this ‘windgas’ is being bought by Greenpeace Energy to sell to households: http://www.enertrag.com/en/project-development/hybrid-power-plant.html
E.ON has a €5m wind-to-gas pilot project for gas mains injection, with support from Canada based Hydrogenics, who have now installed a $2m 2MW wind-to-gas project: www.hydrogenics.com/ In addition, Thüga Group is testing a 360kW wind-powered electrolysis plant, in Frankfurt, supplied by UK company ITM Power. Initially the hydrogen will be injected into the gas grid in a 5% mix, but later it will be reacted with CO2 from a local power plant to make synthetic methane for full-scale injection. Thüga claim that ‘the municipal natural gas network is capable of storing all future generated excess renewable energy’, and could be ‘the battery of the future’. So they are ‘building the battery charger’ http://www.itm-power.com/wp-content/uploads/2013/04/Platts-April13.pdf
In parallel, Haldor Topose has developed high temperature electrolysis/methanisation systems which can use wind-derived electricity to convert water and CO2 into hydrogen and a range of synfuels/syngases and the EU’s CO2RRECT project is working on similar lines : http://co2chem.co.uk/carbon-utilisation/co2rrect
This approach is also being explored in the UK by Airfuel, using CO2 from the air and electricity from wind to make synfuel, mainly for vehicles- ‘fuel from the air’ : see http://www.airfuelsynthesis.com and http://www.imeche.org/news/archives/12-10-15/UK_engineers_create_petrol_from_air.aspx
Meanwhile, ITM power have developed a novel electrolytic system for grid balancing, with the resultant syngas being fed to the gas grid, using their PEM electroytic cell, which can be run on varying power and deliver gas to a compressor without the need for an interim store. Graham Cooley, ITMs chief executive pointed out that ‘The UK gas grid is three times the size of the power grid in terms of energy but the main difference is that it has storage – it’s relatively easy to store gas. Every day we shift energy from the gas grid into the power grid via power generation. What we need now is a way of moving energy back from the electricity grid into the gas grid.’ He added ‘all the excess wind we’re ever going to produce on the power network can be stored in the gas grid.’ And there does seem to be some interest in deploying it in the UK: http://powertogas.eventbrite.com/
However for the moment most of the running is being made in Germany, and as noted above, ITM have a 360kW project in Germany. A great, if sadly rather rare, UK triumph- selling UK green technology overseas . For more see http://www.itm-power.com/news-item/first-sale-of-power-to-gas-plant-in-germany and www.apgtf-uk.com/files/documents/13thWorkshop2013/56JohnNewton.pdf
Readers with long memories may recall that the celebrated 1970’s Lucas Aerospace workers alternative plan included proposals for various energy and fuel cell systems, with much of the running being made by Mike Cooley, a pioneer of radical ideas about technology and trade union involvement. http://www.redpepper.org.uk/a-real-green-deal/ The political context these days may be very different, but it’s good to see his son Graham is now a leading light in the ITM wind-to-gas project mentioned above. It would be even better if this approach gets adopted in the UK.
A key linked issue is not just the storage aspect: if the hydrogen or syngas is injected into the gas mains, that offers a way to transmit wind derived energy long distances without the losses and visual disruption associated with electricity grid transmission. That’s especially important in densely populated countries like Germany and the UK, where the main wind resources are remote from centres of energy consumption. It could be that we will see pipes replacing wires in future, with green gas being the new energy transmission vector, some of it being converted to electricity, where and when needed, near the point of use.
Some of the above is taken from my new book ‘Renewables; a review of sustainable energy supply options’ now published by the Institute of Physics, which offers print and e-versions http://iopscience.iop.org/book/978-0-750-31040-6