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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.
Hydrogen has about 142 MJ per kg, about 3X that of diesel and gasoline. Which themselves are about 25X that of LiPo batteries (the best, mass-producible rechargeable batteries out there). Making hydrogen about 75X the energy density of the best battery packs. Batteries are terrible for aerospace uses, and even for vehicles where hydrogen could be recharged in a matter of a few minutes, requires a LOT less mass for motion (meaning more efficient and easier on the roads), and simpler to build (as you can use a fuel cell and then drive electric motors). Why would you want to carry around 800 kg of batteries when you could do 12 kg of hydrogen? The weight savings in terms of wear-and-tear on roads and tires is massive.
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Nope. You get about 9.7MJ/L for compressed hydrogen, and about 40% of that (4.3 MJ/L) for LiPo batteries. Hydrogen is much more efficient by weight and volume.
And if you need 700+ kg of tank to store your hydrogen - you're doing it wrong. Here's a massive 850L tank that would be equivalent energy storage to about 4800 kg of batteries - and it weighs 215 kg. Not even close.
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
1. For every turbine erected, cut down a tree, so the total wind blockage remains constant. Ban the planting of new trees.
Even if your comment wasn't completely absurd in the first place, the Earth loses 18.7 million acres of forests per year .
So yeah, there's already plenty of "wind changing" going on, more so than we could ever erect enough windmills to counteract.
Multiple-assertion citations required.
Current best processes for water electrolysis (PEM or alkaline electrolysis) have an effective electrical efficiency of 70–80%. Hydrogen fuel cells have an efficiency of 70-80%. So best case is 0.8*0.8 = 64%. Plus you need copious energy to compress or liquify the hydrogen for storage, which lowers the effective efficiency even more.
Vanadium-redox has a RTE of 65-75%.
Pumped storage has an RTE of 70-80%.
In practice, compressed air has an RTE of about 70%.