How not to generate low carbon innovation: DECC's flawed choices for energy storage.

Terrajoule (Simon Daniel of Mioxa - one of the winners of the DECC competition and a company whose understanding of USB technologies I have always much admired  - sent me some notes and has kindly allowed me to use them as a comment at the end of this article).

(Second update: John Samuel of REDT, the owner winner, has also contributed comments below the article. See the post at 10.44 on Monday 11th November)

Storing low carbon energy is the most difficult technical challenge we face. Fossil fuel power stations can cheaply vary their output as demand changes. Neither nuclear power nor renewables have the same flexibility. Nuclear plants are so expensive that it makes no sense at all not to run them all day and every day. Renewable technologies generally either suffer from unpredictable variability (wind, solar in high latitudes) or from predictable variations (tidal range and tidal stream). Matching supply with demand is increasingly difficult. Unless we solve the storage problem, we’re facing a future of unplanned power shortages and gluts.

The British government’s response to the storage challenge was to launch a competition to reward promising technologies. We need huge innovations, imaginative leaps and investment in new ideas. What we got from DECC this week was unexpectedly small amounts of money dribbled to two battery companies with standard technologies. There’s nothing particularly wrong with the winning projects: it’s just that they are very small scale and the batteries can never hope to address the huge need for long term storage of energy.

This is so disappointing. When will government understand that handing relatively small amounts of cash to companies – however competently run -  that offer marginal improvements on existing technologies actually damages the rate of progress by diverting intellectual energy away from genuine innovation?

Rather than just rail about DECC’s short-sightedness, I thought I’d also briefly write about another company that has just obtained a new round of venture finance. This may be a good way of demonstrating just how mindlessly conventional the UK has been. Contrast Terrajoule in California, with its potentially cheap, resilient and quite low-tech solution that offers local storage using pressurised steam, and the two UK companies sponsored by DECC.

The DECC competition


DECC said it had £17m available for innovative storage projects. In the end it seems to have given away about £5m of this fund. The majority of the money has gone to the provision of a 1.2 MWh battery on the small Hebridean island of Gigha.

Gigha is a fascinating place; entirely community owned and with its own three turbine wind farm (about 600 kW in total). The total annual production from the wind farm is about 2.1 GWh and most of this is exported. (As far as I can tell, the island has about 100 people living on it and they probably would probably us less than 10% the output of the turbines). Expanding wind generation is difficult because of what is called the ‘ageing’ cable taking power to the mainland a few miles away.


Eventually places like Gigha will want to be almost separate from the wider electricity grid, generating their own power and selling it to the local population. This requires storage of the electricity generated by the high winds coming off the Atlantic. The DECC award is for a 1.26 MWh vanadium redox battery, storing approximately 0.06% of the island’s annual wind production. (1.26 MWh is approximately a third of one household’s annual electricity use).

Of course these numbers aren’t really fair. The advantage of a battery is that is can cycle from flat to full many times in one year. Most batteries deteriorate a little every time this cycle happens but vanadium redox is capable, its proponents claim, of almost indefinite use. But when it blows hard on Gigha, it can blow for several days and the battery will be full almost all of the time during winter. It’s unclear to me quite how useful this will be. Clearly the most interesting application of the battery its potential for replacing grid electricity in the event of a malfunction of the cable but it’s not clear from the press releases whether it will actually operate as an emergency power supply.

The cost is high. £3.6m for 1.2 MWh of storage is £3,000 a kilowatt hour, over three times the price of the equivalent cost of a new battery for an electric car. It may not be an appropriate comparison but Gigha is also planning a fourth wind turbine at a cost of about £3,000 a kilowatt. This turbine will probably produce 1,200 kWh per kilowatt per year and the battery will only ever be able to store four hours of the peak output of this extra turbine. The disparity between storage costs and generation costs is dispiriting.


The second project is smaller. The battery company Moixa is being given about a million and a half pounds to install domestic electricity stores in about 750 homes. The idea is that rooftop PV power is usually exported from the home in the middle of the day and it makes sense to store it for use at night. And, second, that electricity will eventually be much cheaper for all customers in the middle of the night than in the early evening when power demand is highest. So the battery can also be charged during the night and the electricity used at other times. The battery will produce DC power and the homeowner will install a second circuit to deliver electricity to such things as low voltage LED lights or rechargeable home devices including tablets and mobile phones.


The Moixa product, which already in test, stores 1 kWh. The Maslow is priced at around £1,250, or about 40% of the cost of the Gigha vanadium redox battery per unit of storage. 1 kWh is 10% of the average home’s daily electricity use. A home with a 3 kW PV installation on the roof will (very roughly) generate about 15 kilowatt hours a day during the high summer and 3 kWh during the winter. The Moixa battery will therefore store a relatively small fraction of total electricity generation.

The second problem is slightly complicated to explain. During the summer, the stored DC power will probably not be used. The householder probably won’t need the LED lights (because the sun is above the horizon in the UK for sixteen hours) and an iPad will only take about 50 watt hours (one twentieth of 1 kWh) to charge. A  phone is less. So the battery will never use its full charge during the summer. In winter, the problem is different. If your 3 kW set of PV panels is generating 300 watts, as it might be on a sunny day in November, much of that electricity will be used already by the background household power needs. There won’t be much spare to recharge the Moixa battery.

Perhaps I am being too cynical but I think a third point may also be crucial. Today, many new domestic PV installations come with a device that diverts surplus power to the hot water tank immersion heater. Power that is not being used in the house is not exported but goes to heat water. (In the UK FIT regime, this doesn’t affect the householder’s payments because for most homes 50% of power production is deemed to be exported, whatever the actual use in the house). The average home needs about 10 kWh a day for heating hot water, implying that there will generally be few days on which all the surplus power generated by the PV panels is not productively used to heat water. And these hot water diversion devices only cost about £450 installed in a new system. Put bluntly, this form of storage is about thirty times as cost effective as a Moixa system. Even adjusting for the cheaper price of the gas typically used to heat water, the difference is still ten to one against the Moixa battery.


California recently mandated that electricity suppliers would have to add some storage to any new power plant connecting to the grid. This will produce a huge surge in investment in electricity storage technologies. (If my research is correct, several 5 MWh batteries have already been connected to regional grids in the US).

If its technology is robust, Terrajoule will benefit from the Californian law and its sophisticated investors have just put in a further $11m. Its technology is appealing because it is relatively simple technology and works well at a small scale. As electricity generation moves remorselessly from centralised plants to smaller local units, storage must be made to work economically in quite small units. Terrajoule links a concentrating solar power plant producing high temperature steam to a storage unit that holds the steam (as very hot liquid) at high pressure.

Steam engine

These high pressure tanks are nothing more than cheap domestic LPG cylinders, as seen in off gas grid homes around the UK. When electricity is needed during the night, the steam is released to a standard steam engine with pistons that convert to a rotary motion generating electricity through an alternator. (The company is at pains to point out that this is not a steam turbine, think more of a 1930’s steam locomotive).

Terrajoule’s claim is that it can turn a simple concentrating solar plant into a generator of 24 hour electricity, particularly in desert regions where the sun is almost guaranteed. The use of standard, fifty  year old technologies for storage and generation means the costs are low and maintenance simple, which will be important in remote locations.

In theory I think the Terrajoule system might also work for wind. The turbine would use surplus power to heat water into steam. This would stored in Terrajoule’s cylinders and then used to drive a piston steam engine when the wind drops.

I don’t know whether Terrajoule will work, or much about its costs, but I’m certain that the UK would get better value from investing in genuinely innovative technologies like this rather than giving rather small cheques to companies enhancing existing and well understood battery technologies. One news report suggests that Terrajoule could take storage costs down to $100 a kilowatt hour, one fifthieth of the Gigha project. I know where I would put my money.

The purpose of government support is to take very risky (and hence unfinanceable) but potentially game-changing ideas to the point where they can be commercially developed. DECC's selection of two well established companies for its support from the tens of more challenging projects that entered its competition suggests it has lost any sense of purpose.


Simon Daniel, CEO of Mioxa sent me the comments below and has given permission for their use here. He also wants to stress the importance of domestic batteries reducing the peak of UK electricity use between 5 and 6pm. As the UK runs close to not having enough electricity generation capacity at this time of day in winter, using batteries to reduce home use of electricity makes good sense.


Hi Chris, couple of notes 

- were reusing existing light circuit in home during retrofit, and converting fittings to DC led 

- typical avg uk lighting is 2kwh per day which reduces with cfl but on a DC led circuit is assured to <400wh a day. Then on battery circuit can be shifted off peak to lower carbon night or day solar

- peak domestic in UK drives national peak as industrial demand inventory less then. Hence any shift or assured reduction during peak is useful 

- DC demand not easy to shift by price behavioural change otherwise 

- DC demand growth significant and expected to dominate with ict / IOT. Currently is about 1kwh avg ict a day, 2kwh audiovisual/ electronics etc

- DC taking over a lot of things

- our USB DC sockets can lower DC-DC up to 35v/100w so laptops, led monitors etc without an ac/DC

- inverter, ac:DC typically wasted around 30%+ and IOT will see tenfold increase in DC devices by 2020. These will further increase peak domestic issue

- USB power delivery now making this a standard so that all ac/DC could disappear and opportunity to power all this from time shift renewables . See article researched in economist

- also provides resilience over lighting.elecrronics. Storm st Jude say 1/40 uk lose power

- our Maslow aggregates all distributed batteries to use as bulk storage, eg excess wind or balancing local voltage issues caused by otherwise peak solar

- by enabling local DC PV to battery, we could deploy zero cost/carbon use lighting, or PV powered ict Into urban households. Though if our system is seen not to be innovative and served ok by usual then we might not get enough support to try offering low price systems to mass market / urban or elderly

- website prices are high:indicative though if pilots go ok showing that storage is helpful for grid challenges then systems could be almost free to end users and help fuel poverty and particularly dramatically reduce (average halve peak period cumulative consumption) even with small batteries and assured co installed efficiency measures 

- it's a shame the short decc announcement did give company details of why projects deemed to be innovative from the 50+ options considered. But is perhaps difficult In short summaries to explain the myriad technical points the different projects are exploring