Mark's Blog

GASTEC at CRE (GaC)

Hydrogen as green energy vector

My blog is based around Chapter 26 Page 201 of the excellent book Sustainable energy Without Hot Air by David MacKay. Ref http://www.inference.phy.cam.ac.uk/withouthotair/c26/page_201.shtml

This page identifies but does not solve the conundrum of the very seasonal nature of our annual heat demand and thus carbon emissions.

The chapter shows the modest increase in electricity demand from typical summers day to winter day (about 13 to 18kWh/p/day) and similarly for gas (about 35 to 70kWh/p/day), BUT the latter in particular is heavily distorted by gas used for power production, which in future will have to come from wind power, wave/tidal power or nuclear. The range of gas used for heating is typically 1 to 7 (or more) from summer (4kWh/p/day for DHW) to winter >40kWh/p/day. The problems of seasonal storage are acknowledged and the reader is pointed in the direction of air source heat pumps, with a brief consideration of the use of hot rocks or aquifers.

The trouble is that seasonality is a huge problem. Heat pumps are really only suitable for continuous heating with low temperature emitters eg underfloor heating and thus have non of the inherent savings (usually >20%) associated with bimodal heating ( 07:00 -09:00 and 16:00 -23:00). Bimodal or in commercial buildings (eg schools) heating is best carried out with high output energy emitters that provide heat on demand; this can most effectively be provided by either very high output electric heaters (typically resistive) or a flammable gas such as hydrogen. The high COP’s spoken of the book tend to apply to good quality ground source installations rather than air source, and very large electrical infrastructure as required to met such peak loads from resistive use is expensive to both build and operate. There is a good rule of thumb that the relative costs of nat. gas: electricity: hot water as energy transport vectors are 1:7:49 cost units/kWh/km.

This would again tend to point to hydrogen as a useful green vector. Why:-

  • It can be produced from renewable or nuclear electricity at a proven efficiency of>85% or from the Sahara via long distance pipelines . Conversion loss is comparable with and probably less than HVDC.
  • It is probably no more dangerous than nat gas. It was 50% v/v of Towns Gas.
  • It can be conveniently compressed and stored underground in huge quantities.
  • It avoids the instantaneous supply problems of electricity (no power cuts!)
  • Transmission is likely to be significantly cheaper than electricity
  • It solves the summer/winter problem and can be used to drive heat pumps, via simple hydrogen fuel cells, in contrast to methane (nat gas) based cells.
  • It can address the transport issue simultaneously to the static emission problem.
  • Hydrogen production is easily matched with carbon capture and storage if using pre-combustion(gasification) technology (ref studies by British Gas in the early 1980’s)

Surely the UK should start investigating hydrogen today.