Off-Shore Electricity from Wind, Solar and Hydrogen Power

Off-shore wind-turbines generate electricity, as we all know. Now I’ll explain how off-shore solar and hydrogen can power our electricity too.

Solar at sea is easy. Simply mount photovoltaic panels on platforms isolated on their own or in the wide-open spaces between the off-shore wind turbines. Mount PV-panels high and dry but be sure to mount them below the height of the rotors of the wind turbines so as not to interfere with the wind flow.

Deep Sea Hydrogen Storage

Floating platforms can generate electricity from wind, sun or hydrogen gas, which can be stored in inflatable gas bags in deep sea water.
Floating platforms can generate electricity from wind, sun or hydrogen gas, which can be stored in inflatable gas bags in deep sea water.

The diagram shows how hydrogen gas can be used to store energy from renewable-energy platforms floating at sea by sending any surplus wind and solar electrical power down a sub-sea cable to power underwater high-pressure electrolysis to make compressed hydrogen to store in underwater inflatable gas-bags.

Later, when there is a lull in the wind or when it is dark, the hydrogen can be piped from the gas-bag up to the platform on the surface to fuel gas-fired turbine generators or hydrogen fuel cells to generate electricity on-demand in all weather conditions.


Air lifting bags for use in diving and salvage work, are available up to a volume of 50 metres-cubed.

Seaflex 50 tonne Air Lifting Bag

It should be possible to make much bigger gas-bags and anyway it is possible to rig multiple gas-bags together – for example, as shown in this diagram to rig 3 gas-bags together.

Three Gas Bag Rigging

Density of hydrogen gas with sea depth

Deeper seas are better because the water pressure is proportional to the depth allowing the hydrogen to be compressed more densely, so that more hydrogen and more energy can be stored in an inflatable gas-bag.

Density of hydrogen with sea depth

Click to view a larger image

Consider how many 50 m3 gas-bags we’d need to store the energy required to provide 1 MW of electrical power for 1 day – a useful amount of back-up energy to store to serve one floating platform.

1 MW for 1 day = 1 MJ/s x 60 x 60 x 24 = 86.4 GJ of electrical energy which can be generated from 86.4/e GJ of hydrogen energy of combustion where “e” is the efficiency of the hydrogen-to-power generator and can vary from 30% to 60% depending on the complexity and expense of the generator.

The combustion energy from 1 gram of hydrogen is 143 kJ.

So the mass of hydrogen with 86.4/e GJ of energy is
mass = 86.4 x 109 J / (143 x 103 J/gram x e)
mass = 604/e Kg of hydrogen to provide 1 MW of power for 1 day

Consider three scenarios – 50 m3 gas-bags floating on the surface, at 200 metres depth and at 2000 metres depth.

Surface density of hydrogen 0.1g/L
Volume = 604,000g / (0.1g/L x e) = 6,040,000/e L = 6040/e m3
= 121/e x 50 m3 gas-bags
for efficiency of 30% that’s 121/0.3 = 403 x 50m3 gas-bags – far too many gas-bags!

200m density of hydrogen 1.8g/L
Volume = 604,000g / (1.8g/L x e) – 335/e m3 = 6.7/e x 50 m3 gas-bags
for efficiency of 30% that’s 6.7/0.3 = 23 x 50m3 gas-bags – inconveniently many gas-bags.

2000m density of hydrogen 16 g/L
V = 604,000g / (16 g/L x e ) = 37.75/e m3 = 0.755/e x 50 m3 gas-bags
for efficiency of 30% that’s only 0.755/0.3 = 3 x 50 m3 gas-bags – a practical number of gas-bags.

So the advantage of depth in reducing the volume and therefore the number of gas-bags required to store a given mass and energy content of hydrogen is clear.

High-pressure electrolysis

I’m not sure if it is worth collecting the oxygen from the undersea electrolysis situation. I had in mind the option of just letting the oxygen gas bubble away.

One reason to store the oxygen would be to increase the efficiency and reduce the nitrogen oxide combustion by-products of hydrogen-fired generators. Whether that advantage is worth the cost of collecting the oxygen, I’m not sure.

Be aware that for undersea electrolysis in order to produce oxygen as the anode gas, a custom electrolyte solution will have to be used. If you try electrolysing sea water directly you get chlorine gas off at the anode, which is not so easy to dispose of and can be poisonous.

So the technique will be to separate the custom more-concentrated electrolyte solution from the sea water by a semi-permeable membrane and allow pure water to pass through it by osmosis from the relatively dilute sea water.

It’s worth pointing out that whereas we might describe this process as undersea “high-pressure” electrolysis, it is only so, “high-pressure”, because of the ambient high-pressure resulting from being under water at depth.

So there’s no high-pressure-vessel containment required for the electrolyte solution – as is required for high-pressure electrolysis which operates on the surface – and so undersea, a semi-permeable membrane is all that is required to keep the electrolyte solution contained.

Where is best for off-shore solar and hydrogen?

This “Atlas of Solar Power From Photo-Voltaic Panels” shows where on land and sea the most solar energy can be generated from a PV panel.

Atlas of Solar Power from Photo-Voltaic Panels

Click to view a larger image

So for example, the area of sea off the west coast of north Africa, between the Canary Islands and the Cape Verde Islands, coloured orange in the Atlas of Solar Power and scoring 1,600 – 1,800 looks like the highest scoring area for off-shore solar power which is not too far from western Europe.

Even closer to Western Europe, there are plenty of areas of sea, coloured yellow in the atlas of solar power, around Spain and in the Mediterranean and scoring not quite so high at 1,400 – 1,600, but which are closer to Western Europe and so would mean shorter and cheaper connection cables.

Deeper seas, which are better for storing hydrogen in, can be found from an atlas of the oceans, such as this one.

Atlantic Ocean

Click to view a larger image

Looking at a close-up of the map for the area of sea closest to Scotland, Britain and Western Europe –

Sea depths near Europe

Click to view a larger image

– this shows that deep sea water most suitable for hydrogen storage is not to be found around the coast of the British Isles but depths greater than 4,000 metres can be found in vast areas of the Atlantic beginning a few hundred miles to the south-west in the Bay of Biscay.

So one area of sea which looks suitable for both solar and hydrogen powered electricity generation appears to be just to the west and south-west of the Canary Islands and to the north of the Cape Verde Islands. Whether this area is near enough to western Europe to be the best choice to supply western Europe considering the additional costs of longer interconnection cables remains to be estimated.



52 thoughts on “Off-Shore Electricity from Wind, Solar and Hydrogen Power”

  1. It would seem that solar at sea would require too much expense for support structures. Figure, say a sq km, generating 180 MW (with no access space) at the usual 20% capacity factor for an average of 36 MW. Will that justify the expense of whatever structure and processes required to keep salt water off of the panels?
    Perhaps the turbines are cheaper at sea because they would seem to have a much smaller structural footprint.
    As for storage, batteries would be best from the efficiency POV, but not yet from costs POV.
    Now you got me wondering about the possible solar support structures – because a sea of solar would solve all the problems! Keep them away from shoreline waves with strong anchors, air filed flotation tanks and cheapest possible spaceframe scaffolding.
    If used to store H2 (at lower pressures) the whole thing could probably be as a power barge, to use wind from oncoming storms to move it around (and delete costs of deep sea anchors).
    At about $35/MW, about $11 million dollars could be earned per year minus the expense for the 1 sq km floating space frame of panels. Definitely would require a virtically integrated company! (Now i have to figure how much a square meter of PV panel costs). At $0.5/watt, it should cost $90/sq meter.
    Sadly, after all this, the PV part of it alone (without support) would cost $90 million (how does solar get so low electricity prices)? Are they less than 50 cents per watt (I’m not a banker)?
    I looked up Scottish money and learned that the British pound is = to $1.22.
    Anyhow, i hope your idea works because even though not as efficient, would seem to be far cheaper than batteries. If we worked out storage to be the other 80% (from the inverse of the capacity factor of solar minus 1 for non stored use) then we would need to store up to 180 minus 36 MW for 4/5 ths of 24 hours. At the hopes of $100/kWh for advanced, long lasting batteries, that amount of storage would cost 144 * $100,000/MWh * about 20 hours – or almost 150 million dollars!


    1. Wrong math (because i didn’t use calculator).
      144 MW * 20 hours * $100,000/MWhour of battery storage = whopping $288 million.
      Of course, all the renewable energy advocates seem to have ideas around the necessity for that much storage (I’d say build a global power line grid system).


  2. Hello 🙂
    one day i was reading a magazine and read about the underwater compressed energy storage, later that day during taking a shower (ehre most ideas are born 😀 ) i though…why not anchoring these big balloons and storing hydrogen instead in a balloon with a foil lining for H2 not to escape…then taking the produced hydrogen to the top with the same pressure to drive a turbine, (no H2O icing like air storage….and better thermal performance) or even put the electrolizer underwater, then using the Hydrogen weather in Fuel cells or mixing the allowed amount with natural gas if there is a nearby grid link……I grabbed a piece of paper and assumed 35% efficiency for electrolysis and supposed that we need some energy to distill the water through RO….I thought of course someone has thought the same…it is straight forward and cheap option, so i stumbled by your blog of course 😀
    of course the round trip efficiency is still not good, but it is still a good cheap approach…so i was very impressed by your page 🙂
    more surprisingly, I live in Egypt and I kept making calculations also for my county !! I kept calculating the initial investment approximations for big PVs and Wind turbines, we have a long shore with one of the world best spots for consistent wind speeds along the red sea, and also a perfect locations for solar projects !! more than 7 peak sun hours average per year, with no extreme weather or sand conditions.

    also we have top of a mountain natural lake-like terrains more than square KM wide in many places along the Red sea which are in locations few kilometers of the HV network lines and more than 800m high and less than 1KM away from the red sea water, a pumped storage couldn’t be more affordable !!!….yet there is only 1GW of installed wind parks and PVs are few MWs, meanwhile, Egypt contracted with Russia for constructing a 4 GW Nuclear station with 30Bn USD loan !!! while we are almost defaulting on our external debits….+ extra 14GW of Combined cycle GT plants….featuring the world’s largest CCGT plant with 4.8 GW capacity…..

    these 30bn$ for the nuclear station could have been used to construct 10GW PVs and huge storage plants…
    anyways i though it maybe interesting for you 🙂


  3. WIRED: This boat will make its own fuel on a round-the-world voyage

    “We will produce hydrogen onboard from the ocean, we will clean and purify the water and then we will electrolyse it and then compress it in tank storage.”
    The Energy Observer, which sets sail from Paris in May 2017, is an ex-racing catamaran that can generate hydrogen from 130 square metres of solar panels, two wind turbines, a traction kite and two reversible electric motors.

    ENERGY OBSERVER – The first hydrogen vessel around the world

    I LOVE IT! 😀


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