Thermal energy storage could make offshore wind dispatchable for an additional cost of only €17 ($19) per MWh within five years, according to wind-power pioneer Henrik Stiesdal.
The Danish inventor and former chief technology officer of Siemens Wind Power tells Recharge that a North Sea offshore wind farm, backed up by a 24-hour thermal storage unit from his Stiesdal Storage Technologies company, could sell round-the-clock power for a levelised cost of energy (LCOE) of €82 ($92) per MWh.
For his calculations, Stiesdal looked at a 500MW project operating at a 50% capacity factor, with an LCOE of €65/MWh for its variable output — the same price Orsted will receive at its 1.4GW Hornsea 2 project.
Such a price would make dispatchable offshore wind cheaper than new coal-fired power plants in many parts of the world, when including the cost of carbon emissions. According to consultant Lazard, new coal plants built today would operate at an LCOE of $60-143/MWh, while every MWh produced would emit 0.92 tonnes of carbon. In the EU, for example, that would add a cost of about €23 ($25.35) per MWh, according to current carbon market prices.
Stiesdal Storage Technologies is currently testing its hot-rock thermal storage technology at a small pilot project in Denmark, being run by the Danish University of Technology (DTU), and is due to build and begin operation of a 1MW/24MWh commercial pilot next year, with a view to commercialising the system within the next two years.
Stiesdal’s technology uses renewable energy to heat crushed volcanic rocks to 600°C, with the rock staying hot for days or weeks simply by being well insulated. Then when energy is required, the heat is converted back into electricity via a power-generating turbine.
The commercial pilot is expected to be built in 2020 at a Welcon steel-making facility in Give, Denmark, which will utilise some of the waste heat from the project.
Stiesdal expects an LCOE at the Give pilot of “well below €100/MWh, assuming that we have to buy electricity at €20/MWh”.
Stiesdal is wary of making cost predictions, citing the unpredicted cost reductions seen in both wind and PV over the past decade — largely due to high volumes, bigger products and economies of scale.
“Therefore, when it comes to storage and where prices will go, the real game changer is to get volumes on,” Stiesdal tells Recharge. “That's why I focus a lot on doing modular things that can be made in big volumes, because I know from experience that that is the key to cost reductions.”
Stiesdal says the potential for cost reduction in his hot-rock storage system is very substantial because his technology is highly modular — it can be built to any size by simply adding more or bigger components — and largely uses existing off-the-shelf equipment.
He tells Recharge that his technology could be used in several ways.
“One of the totally obvious use cases is solar farms, because even in very decent areas with high insolation, they have a really terrible use of their electrical infrastructure for the simple reason that for half the day, on average over the year, there's no power going through their transmission lines.
“If you placed these types of storage systems decentrally, behind the meter at solar farms you could have three or four times the PV capacity on a given transmission network and supply 24-hour solar PV. This would not only solve the problem of variability, but would also help reduce your investment in grid capacity."
He adds: “The variability in solar PV is so predictable, the sun comes up every day. For wind, it’s somewhat different, because winds can be calm for several days at a time. And it is a little more difficult to solve that completely with storage — you'd need much more than one-day [of storage] capacity for wind. Still, one full day of storage goes a long way towards mitigating the challenges of variability.”
Another potential use case is to place storage capacity on selected nodes on the transmission network to enable grid operators to smooth the output from nearby solar panels (rooftop or utility-scale) and wind turbines. This could reduce the need for new transmission lines to be built.
Alternatively, cost-effective storage technologies could be used to enable islands or isolated communities to supply all their power from renewable energy.
“I’m convinced that new storage technologies will be needed, besides conventional battery technologies. The thermal energy storage system that we are developing could be one, but... I'm not saying at all that this is the only solution, and I'm not saying it's by default the best solution. If somebody outsmarts us and can do it even cheaper, they will be our friend, because we need storage, the more cost-effective, the better. So all I'm saying here is that we are about to build something that could create a kind of, 'well, at least we can do it at this cost level'. And then if it turns out that it's smarter to do it with some other technology, perfect.”
Stiesdal’s companies are more interested in providing affordable climate solutions than making profits (see panel), so he welcomes competition in energy storage.
For instance, he says he follows Highview Power “with interest and admiration”, and describes Siemens Gamesa’s work on thermal storage as “wonderful” and “fantastic”.
“[Siemens Gamesa’s system] is geared slightly differently than what I'm presently working on, in the sense that they are very good at larger projects and my field is more in the industrialized, commoditised thinking. But Siemens can do anything and it may well be that their system will ultimately have lower cost than mine. And that would just be great.”
Henrik Stiesdal has been responsible for some of the most important inventions in the wind power industry over a 40-year career, building his first turbine by hand on his parents’ farm in 1978.
His turbine design — comprising upwind rotors, automatic yawing and two-speed generators — was later sold to Vestas, then a manufacturer of farm wagons and truck cranes, helping the company become the world’s leading turbine maker.
Stiesdal was responsible for the world’s first offshore wind farm, Vindeby, in Denmark in 1991, and the marinisation of wind turbines to enable them to survive at sea. Later, as chief technology officer (CTO) at OEM Bonus Energy, he designed the first one-piece turbine blade and then the first variable-speed turbine. Then as CTO of Siemens Wind Power, which purchased Bonus in 2004, he was in charge of the direct-drive technology that eliminated the then-unreliable gearbox that had become the Achilles heel of the wind sector.
He retired from Siemens in 2014, and has since formed his own eponymous innovation company Stiesdal A/S, which aims to provide cost-effective climate-fighting solutions to the energy and transport sectors.
The company is split into four subsidiaries: Stiesdal Offshore Technologies, which has developed the low-cost TetraSpar floating turbine foundation; Stiesdal Storage Technologies, which is developing a hot-rock thermal energy storage technology called GridScale that can enable 24-hour wind and solar power; Stiesdal Fuel Technologies, which is developing SkyClean, the carbon-negative jet fuel; and Stiesdal PtX Technologies, which is developing a low-cost electrolyser called HydroGen.