Technology and technique

Photovoltaic solar panels are about  17% efficient at the moment but direct hydrogen generation by solar radiation is in the low 20% range. Wind turbine generators have a complex efficiency measure. They are generally rated in the 30% range, mostly due to the undeterministic nature of the wind. However they are generally much higher in their efficiency at converting wind energy into electricity (50-60%) and are improving.

Electrolysers of greater than 85% efficiency are common in industrial capacities of 100kW or above. This means that the majority of the electricity is converted into energy stored in the hydrogen.

If the de-coupling of the wind turbine generators from the grid would not result in at least a 15% saving in efficiency of power generation (or whatever the combined value of electrolyser + fuel-cell efficiencies is), then a parallel arrangement could be configured where both the fuel-cell and turbine generators can feed the grid but the generators can feed the electrolyser instead or as well. This has the advantage that the grid could feed the electrolyser in the event of low-wind, low-demand and excess generation.

For example, tidal flow can be captured in unused dockland areas. Incoming tides are held back by dock gates and at high tide valves are released and water can flow through turbine generators into the dock. Once full, the valves are closed and at low tide the dock is emptied though the turbines once more, ready for the next high tide. Those generators, connected to electroylsers, can create hydrogen for storage and controlled release to generate on-demand electricity, via fuel-cells, for the local area.

Capturing the energy of waves is appealing in that waves carry massive amounts of energy and cause coastal erosion. However, not only do they tend to destroy man-made objects put amongst them but they help oxygenate the sea and the long-shore drift they cause is often essential for coastal life. Nevertheless, some areas of coastline should be suitable and the highly variable nature of the wave induced energy is quite acceptable to electrolysers and the subsequent generation of hydrogen. A corollary of this process is that the oxygen by-product of electrolysis could be pumped back through the sea if the negative consequences (algal blooms, etc.) are mitigated.

Tall buildings are designed to withstand the substantial force of the wind. It would be possible to design ducted turbines into such structures to take advantage of this wind force. However, the unpredictable nature of the captured energy, even at these elevated locations, means they are difficult to integrate with a building's electrics in a manner that saves money, which is generally the only reason they would be fitted. However, once again, by buffering through hydrogen, not only is the generated electricity more controllable, reducing the demand for peak-rate mains electricity no matter what the wind conditions for example, but the system continues t work all day and night. Therefore, in principle, low power consumption overnight could offer the opportunity to buffer significant amounts of hydrogen for daytime use. For businesses, such a capability also offers a degree of resilience to mains supply failure.

One feature of adopting hydrogen as the core energy carrier is that the natural boil-off of LH2 could be used by the vehicle transporting the fuel so that none is wasted. Boil-off can be routed to the LH2 expansion tank, where the vehicle's own LH2 is evaporated into gaseous form for consumption by the fuel-cell.

Having LH2 on board a vehicle may assist air-conditioning. The LH2 is very cold and heat is transferred to it  between being pumped out of the LH2 storage tank to return it to the gaseous state before it enters the fuel-cell. The fuel-cell generates (but may also need) heat so some heat could come from that. For air cooling, cabin air could be circulated near the LH2 expansion area. Heating could either come from an exothermic fuel-cell or have to be created.

These technologies are an opportunity to enhance existing designs but also to bring in designs more optimised for the technological possibilities. It has been shown that for cars, existing designs do not fit well with LH2, fuel-cell and motors. However, the required optimisations can be accomplished and still fit the existing expectations and limits for car design.