Select Committee on Science and Technology Appendices to the Minutes of Evidence


APPENDIX 42

Memorandum submitted by Mr Paul Spare

1.  INTRODUCTION

  The UK is an advanced industrial economy wherein a reliable electricity supply is as fundamental to prosperity and social welfare as are food or water. Electricity is currently supplied with about 99.97% reliability,which is the level of service that society and industry expect to continue. Similarly, the supplies of oil and gas are extremely reliable. For any novel technology to supplant these existing systems by normal commercial means, it must achieve the same performance more economically, or provide better performance for the same cost. If these criteria are not met, statutory measures will almost certainly be required to change behaviour, especially at the start, when the economics of replacement system are most unfavourable. The remainder of this paper examines the problems associated with "non-carbon" replacements for existing energy supplies.

2.  THE OPTIONS

  There appear to be only two main options for the non-carbon (ie no coal, gas or oil) fuel economy:

    (1)  Use electricity generated from sources contributing little or no CO2 in conjunction with hydrogen. (The hydrogen can be either burned to generate heat or used in fuel cells to generate electricity.)

    (2)  Use electricity generated from sources contributing little or no CO2 + battery storage devices.

  This analysis is concerned only with Option 1.

3.  CURRENT ENERGY CONSUMPTION

  There are two stages to reviewing the implications of the "non-carbon" (hydrogen) economy. Firstly, identifying the power supplies that would have to become hydrogen-based and secondly identifying/providing the resources and structures to accomplish the change. This latter point is introduced at an early stage, as it is demonstrated below that hydrogen-based economies will require a massive increase in electricity generation, over present levels. The scale of the problem may not be apparent when the use of hydrogen is viewed in sweeping "policy" terms.

  Various current carbon-intensive technologies could be replaced in whole or in part. The table below shows some energy consumption data in the UK from recent DTI statistics. The fuels are used for many purposes and the thermo-mechanical efficiency achieved varies over a wide range, eg transport 25%, heating 75% and electricity production 40%.


Energy source/Fuel
Annual Consumption
Consumption in Mtoe

Natural gas1,100TWh
95
Oil76 million tons
76
Coal64.5 million tons
55
Nuclear electricityApprox 83 TWh
23
Nuclear Imports11 TWh
3
Hydro + others12 TWh
3.5
Total
255


  Consider the replacement of half of the three most important fuels, shown above, by hydrogen. In round terms, energy equivalent to 100 mtoe would be needed annually. If the same thermo-mechanical efficiency is achieved then, allowing for the higher calorific value of hydrogen compared with hydrocarbons (2.5:1), as much as 40 million tons of hydrogen would be required each year. This implies many thousand times the current annual rate of production. This illustrates the scale of the challenge. The capital investment, planning, construction and environmental issues involved may not be apparent when considering broad political gestures. Changes of such an order generally take several decades to accomplish, even when driven by favourable economics; ie steam replacing sail or the internal combustion engine replacing the steam engine. For the conversion to the low-carbon society, the economic pointers may not be favourable for 10 or 20 years.

4.  POTENTIAL FOR LIGHT-VEHICLE DISPLACEMENT IN 2020

  Consider replacing the fuel supply for certain vehicle users. This transition would involve four elements.

    —  Production of the hydrogen.

    —  Delivery to point of use.

    —  Storage (not considered here).

    —  Utilisation.

  The same technical approach can be taken to other fuel supplies. This analysis follows a well-understood methodology. I am indebted to the Alistair Miller and Romney Duffey of Atomic Energy of Canada Ltd (AECL) for the calculations for vehicle fuel.

5.  PRODUCTION

  By the terms of an EU agreement with car manufacturers, new cars are expected to emit 140 g CO2/km by 2008 and so it would be reasonable to use this as representative for the UK fleet by 2020. This is equivalent to 6.2 L/100 km. Or -27% fuel efficiency. The full energy content of motor spirit is estimated as 9.1 kWh/L; so 2.45 kWh/L would be delivered energy. The alternative of water electrolysis (70% efficient as compressed hydrogen energy) followed by a fuel cell (50% efficient in net output) has an overall efficiency of 35%. To deliver 2.45 kWh of drive energy by this electrolysis/fuel cell route will require 7.0 kWh of electricity to the electrolysis cell. This is equivalent of one litre of motor spirit in terms of delivered, propulsive energy.

  The DTI report projects motor spirit consumption only to 2010 but the proportion is reasonably steady at about 38-39% within a rising total that is projected to reach around 65 Mtoe in 2010 and would, by simple projection, be around 75 Mtoe by 2020. Hence motor spirit consumption of about 29 Mtoe is projected for 2020. Taking the density of sweet crude as 0.85, 29 Mtoe become 34 x 106 m3. Assume that about 95% of this by volume is converted into product, including motor spirit. So estimated total consumption in 2020 would be 32 x 109 L.

  Based on fuel-cell powered vehicles in significant numbers emerging about 2010 and a turnover of the light vehicle fleet of around 5%/a, it appears reasonable to project that about 20% of the light vehicle fleet (ie vehicles fuelled by motor spirit) will be using fuel cells by 2020. Then 5.6 x 109 litres of motor spirit (5.1 Mtoe of oil) could be displaced by electricity. If generated by nuclear or other power source with negligible CO2 emissions, emissions would be reduced by 4.3 MtC. Electricity for this displacement would be 43 TWh/a, the output of 5.5 GW of electric capacity operating at 90% efficiency. This is slightly less than the output of five Sizewell B reactors, or eight 700-MW Advance CANDU (ACR) reactors.

  There are two options for distribution:

    —  Produce the hydrogen in a small number of regional electrolysis plants and distribute to users.

    —  Distribute electricity to the local communities for electrolysis plants to make hydrogen locally.

  The former may appear at first site to be the more expensive, since an entirely new distribution system will be needed. However, the second would need substantial investment in the electricity distribution network. The present system will not be capable everywhere of carrying the extra energy supplies on top of the existing demand. It will require substantial reinforcement with commensurate investments.

6.  REPLACEMENT OF NATURAL GAS

  Gas is used in a ratio of about 70:30 for direct heating/electricity generation. Consider the replacement of the 70% component used for direct home heating/cooking, industrial heating and commercial operations.

  One option would be for the heating function of gas to be replaced by nuclear generated electricity, amounting to 700 TWh. The distribution of electricity and its use for heating should have an efficiency of 90%, compared with 75% for direct combustion of gas. About 600 TWh of electricity would therefore be needed. That can be achieved by about 75 GW of nuclear plant operating at 90% availability. This implies about 50 new nuclear plants such as Sizewell. Again however, the HV super grid and distribution network would have to be strengthened—doubled or trebled in power handling capacity—to provide power to consumers.

  The second option is to replace natural gas by hydrogen +fuel cells, with hydrogen distributed via the (otherwise redundant) gas pipe work infrastructure rather than direct power through the electricity supply grid. In this case, more electricity would be required to compensate for the lower efficiency of hydrogen production/fuel cells, compared with heating directly by electricity. As quoted above this efficiency may be only about 35%. In which case the generation of electricity would have to be increased by 90:35 is about a factor of 2.5 times. However, the change would necessitate over 100 new reactors. An increase of this magnitude is probably not feasible, because of one or more of the following restraints:

    —  beyond the capacity of the available coastal and estuarial sites;

    —  beyond the output capacity of fuel manufacturing plants; and

    —  beyond the capacity of the construction contractors.

  Such obstacles almost certainly rule out this option. They also serve to illustrate in the clearest possible terms the importance of rationing the remaining stocks of natural gas. Proposals (which I supported) to debar the use of natural gas for electricity generation were not successful. The consequences of that decision will be visited upon us in the next few years, if the supplies planned to be imported from eastern Europe, do not materialise. Nuclear plants would have to be constructed to replace CCGT plants, but it could still prove impossible to meet energy demands.

  Utilising the gas transmission network should be technically feasible, being akin to reversing the conversion from Towns Gas to Natural Gas that was accomplished about 30 years ago. It would also avoid the need to triple or quadruple the power handling capacity of the typical domestic electric supply system that would be needed if home heating is supplied by electricity rather than gas.

7.  POWER SOURCES

  Nuclear-generated electricity is a particularly attractive source for any hydrogen production, since the reactors can meet the peaks of daytime electric demand and produce hydrogen in the broad periods of reduced demand. A small contribution from renewable sources would not be excluded, but the scale of increased energy demand is probably two orders of magnitude beyond their most optimistic potential.

14 October 2002



 
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