Slashdot Mirror
How Orkney Leads the Way For Sustainable Energy (theguardian.com)
An anonymous reader shares a report: It seems the stuff of fantasy. Giant ships sail the seas burning fuel that has been extracted from water using energy provided by the winds, waves and tides. A dramatic but implausible notion, surely. Yet this grand green vision could soon be realised thanks to a remarkable technological transformation that is now under way in Orkney. Perched 10 miles beyond the northern edge of the British mainland, this archipelago of around 20 populated islands -- as well as a smattering of uninhabited reefs and islets -- has become the centre of a revolution in the way electricity is generated.
Orkney was once utterly dependent on power that was produced by burning coal and gas on the Scottish mainland and then transmitted through an undersea cable. Today the islands are so festooned with wind turbines, they cannot find enough uses for the emission-free power they create on their own. Community-owned wind turbines generate power for local villages; islanders drive nonpolluting cars that run on electricity; devices that can turn the energy of the waves and the tides into electricity are being tested in the islands' waters and seabed; and -- in the near future -- car and passenger ferries here will be fuelled not by diesel but by hydrogen, created from water that has been electrolysed using power from Orkney's wind, wave and tide generators.
Orkney was once utterly dependent on power that was produced by burning coal and gas on the Scottish mainland and then transmitted through an undersea cable. Today the islands are so festooned with wind turbines, they cannot find enough uses for the emission-free power they create on their own. Community-owned wind turbines generate power for local villages; islanders drive nonpolluting cars that run on electricity; devices that can turn the energy of the waves and the tides into electricity are being tested in the islands' waters and seabed; and -- in the near future -- car and passenger ferries here will be fuelled not by diesel but by hydrogen, created from water that has been electrolysed using power from Orkney's wind, wave and tide generators.
Lithium batteries have a round-trip efficiency of about 95%.
For hydrogen, it is about 60%.
So lithium wins for most applications.
Hydrogen wins when weight is a really big concern. So it may make sense for aviation.
Hydrogen also scales well, since big tanks have a better volume-to-area ratio. So it may make sense for ships.
For static applications like grid-storage, sodium-ion or vanadium-redox may be better than either lithium or hydrogen.
But for cars or smaller, lithium batteries are the way to go. You will never see a hydrogen fuel cell in a cell phone.
Hydrogen wins when you need to store store truly massively amounts of excess energy which is something you cannot currently do with batteries. That is the one big thing what still makes Hydrogen interesting despite the low conversion efficiency. If you are producing huge amounts of excess energy and can't store it in battery arrays, storing it as Hydrogen at 50% round trip efficiency is still better than letting all that energy go to waste assuming you can do the hydrogen conversion cost effectively. The currently most sensible thing to do with this hydrogen is use it to power always on gas power plants to supplement solar and wind power and then use the energy to charge cars or whatever else it is you need the energy for. This, again, assumes that you can do the round trip conversion of electric energy into hydrogen cost effectively.