Extract from the Royal Academy of Engineering Report "An Engineering Appraisal of the Policy and Innovation Report's Energy Review"

3.6 Renewables

There are many different sources and many still unproven technologies considered
under the umbrella of Renewable Energy. At present clearly hydro, wind and waste
combustion have proven potential for making significant contributions to alternative
energy supplies in the short to medium term. Biofuels might enter the picture in the
longer term, especially in the transport sector.

For power generation, however, the picture for other technologies is unproven. Short
rotation coppicing requiring 10% of the farmed area in the UK to be planted could
ultimately support 9,000 MW, but it is unlikely that more than 1000 and 2000 MW
could be achieved during the next ten years, i.e. 6.1 - 12.2 TWh (British BioGen)
enough to satisfy only 1.5 to 3% of demand at that time. It would require the whole of
Kent to be covered with coppiced willow, for example, to replace the output of
Dungeness B power station on the Kent coast. The economic transport limitations on
the size of the area of harvested land surrounding each power station would further
restrict the size of the stations to between 40 – 70 MW (i.e. Dungeness B is equivalent
to 17 to 30 small coppice willow-fired power stations).

With the exception of biomass and to some extent hydro sources, all renewable
generation available in the UK is intermittent. This intermittency must be
compensated by output from other generating plant or from storage systems. Other
than in some hydro schemes it is not at present possible to store electricity in large
quantities. There is a possibility that novel storage systems may be developed that
would reduce somewhat the costs of stand-by, but it is likely always to be a
significant factor in the economic performance of intermittent plant. For the moment
these technologies are not available and it would be a serious risk to assume that they
will become available at low cost. The DTI has initiated a study to ascertain the
effects of high contributions from renewable energy sources to the electricity supply
system and this initiative is to be commended.

Small variations can be met from balancing plant available to the National Grid
Company (NGC) and the figures quoted in the PIU Energy Review (0.1p/kWh) refer
to the additional operating cost needed to support the short-term hourly variations for
5-10% of energy being contributed by intermittent supply on the distribution network
(Table 7.1 of the PIU Review) based for the most part on retaining existing
conventional generating plant. The UK currently has a good reserve capacity so a
certain amount of intermittency can be accommodated, but if the Review
recommendation of "…a firm target of 20% of electricity to be supplied from
renewables for 2020, i.e.… a further 39TWh" is realised then with most of this target
supplied by intermittent sources, the reserve plant fixed plus operating costs per unit
of energy supplied increase substantially.

Wind generation is singled out in the PIU Report for major expansion. For onshore
and offshore wind, the PIU recommends installation rates of 1-2 GW per year (nameplate
capacity rating) for the period 2010-2020 (i.e.3 - 6 MW per day for ten years!).
Taking into account the 7.5 GW capacity possibly constructed by 2010 the
implication is that 17-25 GW of wind power capacity will be connected to the grid by
2020, supplied by perhaps between 10,000-15,000 wind turbines (the precise figure
would depend on the size of turbines installed).

It is noted that a very considerable building programme would be required to
commission windfarms at the rate recommended in the Review and questions remain
as to whether the perceived environmental impact would be tolerated by the public or
whether the Ministry of Defence would tolerate the implications for air safety,
communications disruption and radar interference. The infrastructure necessary to
fabricate, install and commission let alone collect and transmit the power is not trivial
and much of it does not exist at this time. The costs of constructing and
commissioning a wind turbine onshore are well known, but the transition to offshore
installation introduces many additional demands and a significant increase in cost.
These are serious difficulties that need addressing. To assume that such a policy is
feasible and desirable prevents serious consideration of realistic alternative policies.

Apart from these reservations a major problem is shown up in the wind data records
covering the whole of mainland UK. Regardless of the capacity installed, there is a
sizeable probability of no or very little wind blowing across the entire country. Figure
2 illustrates the situation where a hypothetical wind power capacity of 7,300 MW
installed throughout the country is correlated with actual Met Office wind data. The
most likely power output nationally is seen to be less than 200 MW.
If, say, 22,000 MW were installed, as mooted by the PIU, then this figure would rise
to only approximately 600 MW. Perhaps as much as 75 – 85% of this wind capacity,
i.e. of the order of 16,000 – 19,000 MW, would have to be available in the form of
conventional plant capacity in order to provide back-up power when wind is light or
absent. The fixed capital costs of this partly used plant would have to be borne by the
consumer – possibly of the order of £1billion in the above case.
There are even higher probabilities of parts of the country being without wind for
several hours, e.g. England, Wales or, less frequently, the whole of Scotland. With
small levels of penetration, this would not be serious, but for large levels of wind
capacity, these extra system costs would push the additional cost of wind generation

substantially above levels quoted in the Review. High levels of wind power capacity in the
system could also cause severe stability
problems as they have in Denmark, even though Denmark has the advantage of being
stabilised by the connections to Norway, Sweden and Germany. On the assumption
that the mainland UK system continued to be "stand-alone" all such large-scale
alternative reserve balancing capacity would have to be installed in the UK and paid
for in full. The analysis is complex but should be undertaken urgently before policy
decisions relying on high levels of intermittent generators are taken. It cannot be
emphasised too strongly that for the UK system intermittent generation capacity does
not replace the need for conventional generation capacity, even though within the
limits imposed by intermittency there is a degree of replacement of electrical energy
produced.

A number of reports have suggested that using excess electricity at times of low
demand to produce clean hydrogen could mitigate the intermittent nature of wind
generation. This hydrogen could then be used directly as transport fuel or stored and
used to power fuel cells to compensate when wind generation is not available. This
scenario is theoretically attractive but will not be of any practical use until the UK has
properly developed a hydrogen economy. Hydrogen as a potential fuel is discussed
under section five on transport.

Tidal power is a technology that has been demonstrated in France for over 30 years,
but not without problems (including environmental and cost) and only recently
proposed elsewhere. It is an intermittent power source, but the power delivery of the
tides is highly predictable and a barrier type installation gives some flexibility as to
when electricity is generated within the tidal cycle. Although an expensive project,
with attendant environmental questions, the Severn Barrage Project could, if built,
contribute 17TWh of renewable electricity annually, or 6% of UK demand. A purely
commercial case has yet to be made for a large tidal barrier such as the Severn
Project, but current studies show that with a capital cost of around £9 billion, it could
generate electricity at 5.5p/kWh. As a renewable source, this would avoid
approximately 18million tonnes of CO2 emissions per annum. A number of other
smaller sites have been identified for tidal schemes such as the Humber and the
Mersey. Additionally, serious consideration should be given to incorporating tidal
electricity generation into future flood protection projects such as the replacement for
the Thames Barrage.

Although at an earlier stage of development, tidal flow generation and wave power
should not be written out of the picture.
Photovoltaics could, with encouragement, make a contribution to the UK’s renewable
energy target and the recent announcement that Government grants would be
available for up to half the cost of installation is welcome. The nature of photovoltaics
is that they are best suited to use on individual buildings and as such have an
additional benefit of reducing stress on the local electricity grid. The UK significantly
lags behind countries such as Germany on the roll out of photovoltaics but there is no
reason why Germany’s success could not be repeated here. Government support for
photovoltaics and solar water heating could be signalled by encouraging their use in
refurbishment of public buildings under Agenda 21.

Recommendations

Intermittent generation provides energy over time, but in the UK system does
not replace the need for (conventional) generation capacity. Detailed
engineering studies should be undertaken urgently before policy decisions
relying on high levels of intermittent renewable generation are taken.
The study should determine the full costs of employing high levels of
intermittent renewable energy sources (including the provision of standby
plant, energy storage, upgrading of the transmission and distribution systems)
and identify the impact on electricity prices.

It has been argued that traditional fossil fuel based electricity generators
should incorporate the costs of environmental pollution into their pricing and
that this process would make renewable generators appear more competitive.
Likewise renewable generators should incorporate into their pricing the cost
of maintaining and running reserve capacity required for grid stability and for
covering demand when intermittent generators are not available.