From Greenhouse to Green House

The threats of climate change
CO2 emissions and savings


This page reviews renewable forms of energy and conservation of energy in relation to various categories of sources and uses, and provides an assessment of potential in each area (with sources of information and figures where they are available). Much of the available information relates to electricity rather than total energy demands but there is some discussion in sections below about energy supply and conservation in areas such as transport and space heating where electricity is not currently the main form of energy. Further information may be found in Energy UK.

It is becoming increasingly clear that renewable forms of energy, with conservation of energy, can meet current and anticipated future needs without undue cost and that we don't need nuclear power with all its many headaches. A growing number of reports show how it is feasible to make deep cuts in CO2 emissions without nuclear power. For example, the 'TRANS-CSP' report, commissioned by the German government, shows in detail, country by country, how Europe (including the UK) can meet all its needs for electricity, make deep cuts in CO2 emissions, and phase out nuclear power at the same time. A study from Pöyry Energy (Oxford) Ltd (PDF, 734 KB, August 2008) shows that the planned growth in renewable electricity in the UK, with energy conservation, can ensure adequate generating capacity in the UK until at least the mid 2020s.

On this website, a spreadsheet summarises the sources and savings described on this page and shows clearly that current UK demands for electricity can be met very easily, with plenty left over. Even allowing for the electrification of road transport (see Appendix 8 in Energy UK) and the use of electricity to power heat pumps for space heating, there is more than enough potential in renewable sources of power. For example, less than 0.3% of the area of the Sahara desert could meet all of the EU's electricity needs (see below) although any such source of power should be developed in conjunction with other renewable sources of power.

Given that estimates vary, the figures that have been used in the spreadsheet are marked on this page with the symbol: . Generally speaking, the more cautious figures have been chosen, except where there is evidence that a given figure may be over-cautious.

While it is true that "the wind does not blow all the time", it is also true that all sources of electricity are intermittent, including conventional sources, and that demands for electricity are highly variable. There are techniques and technologies for managing this variability in supply and demand and good reasons to suppose that it is much less of a problem than sometimes suggested.


Concentrating solar power (CSP) (click the title to read more)

This is the big one, quite capable by itself of meeting all the world's energy needs. Using CSP, less than 0.3% of the area of the Sahara desert could meet all of the EU's electricity needs.

Every year, each square kilometre of sunny desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of deserts world-wide, this is several hundred times the entire current energy consumption of the world. Using the proven technology of CSP, less than 1% of the world's deserts could generate as much electricity as the world is now using. Contrary to what is commonly supposed, it is feasible and cost-effective to transport solar electricity over long distances. Modern, highly-efficient HVDC transmission lines provide the key.

How much?

The TRANS-CSP report suggests that 15% of Europe's electricity could be supplied by imports of CSP electricity by 2050. This figure reflects caution about the planning and construction of CSP plants and the proposed trans-Mediterranean HVDC transmission grid. But we should not forget that Britain's railway network was built almost entirely in the 20 years between 1830 and 1850 using little more than picks and shovels. With the right political and financial impetus, the system proposed in the TRANS-CSP report can certainly be put in place. Given the huge amounts of solar energy falling on desert regions, and the well-established technologies for capturing it as electricity and distributing it, the UK could in principle obtain 100% or more of its electricity from this source.

Wind power

Wind turbines are a well-developed technology and the potential is huge. The UK has been estimated to have over 33% of the total European potential offshore wind resource - enough to meet the UK's electricity needs three times over (BWEA - offshore wind). There is similar potential in many other parts of the world.

A common objection to wind power is that the wind does not blow all the time. But a conventional power station is often shut down for routine maintenance or because of unscheduled breakdowns. And the demand for electricity varies from minute to minute.

Although the wind does not blow all the time at any one place, it is rare for the wind to stop blowing everywhere across an area the size of Europe—so that widely-distributed wind farms with grid connections give a much more stable output than any one wind farm. Airtricity has proposed a Europe-wide 'Supergrid' of highly-efficient HVDC transmission lines (see electricity transmission grids) to reduce the effect of intermittency in wind power. Wind farms deliver more power in the winter, just when it is most needed.

A fascinating idea is that 'Plug-in Hybrid Electric Vehicles' (PHEVs), which appear to be the hot favourite with motor manufacturers for greening the road transport system, will provide a means of ironing out peaks and troughs of supply and demand in the electricity distribution grid. This is explained in the section on PHEVs.It is sometimes argued that the gains from wind farms are cancelled by the need to provide 'spinning reserve' in conventional power stations to cope with the intermittency of wind power. This argument is false: what matters is that there should be a mixture of 'base load', 'intermittent' and 'peaking' power so that the whole combination can cope with variability in the system, both in supply and in demand. This is well explained in the TRANS-CSP report (on page 10 and elsewhere).

Although the wind does not blow all the time, wind power could, in principle, provide us with a high proportion of the electricity we use. How is this possible? When there is more wind power than we need, the surplus electricity may be used to generate hydrogen which is stored. When the wind drops, the stored hydrogen may be used as fuel for an engine that drives an electricity generator. It is true that energy is lost as heat in this process but, using CHP, much of this 'waste' heat may be used for space heating. For further information, see wind and hydrogen and energy transformation and transportation, below.

Another common objection to wind power is that "several thousand wind turbines would be needed to produce the same energy as a conventional power station". But the London Array wind farm that has been proposed for the Thames Estuary will have 271 turbines and these will produce up to 1000 MW of electricity—approximately the output of a small-to-medium-sized conventional power station.

How much?

It is generally accepted that 20% of the UK's electricity may be met from wind power without the need for any significant provision for the fact that the wind does not blow all the time (see BWEA myths about wind power). In principle, 100% or more of the UK's electricity could be met from wind power but there would need to be greater provision of techniques and technologies for managing the variability in supply and demand. A report from the European Environment Agency (Europe's onshore and offshore wind energy potential, PDF, 3.5 MB) calculates that the "economically competitive potential" of wind power in Europe comfortably exceeds projected demands. Another report, from the US National Academy of Sciences (Global potential for wind-generated electricity, PDF, 1.9 MB) calculates that wind power could supply more than 40 times current worldwide consumption of electricity and more than 5 times total global use of energy in all forms.

Links: floating wind farms




Wave power

The disastrous effect of the Asian tsunami demonstrated in a tragic way the enormous amount of energy that can be carried by waves. From at least as far back as Stephen Salter's 'ducks', prototype systems have been developed for capturing the energy of waves. One of the most promising at present is the Pelamis 'sea snake' comprising a jointed tubular structure designed to float on the sea, flex with the waves and capture the wave energy by means of hydraulic rams, turbines and generators. Each single 750-kilowatt Pelamis could generate the same amount of power as a land-based wind turbine and a 'wave farm' covering a square kilometre of ocean would provide enough electricity for 20,000 homes.

How much?

Ocean Power Delivery say that "There is sufficient energy breaking on the UK shoreline to power the country three times over.  However, it is not practical to recover all of this energy. The economically recoverable resource for the UK alone has been estimated to be 87TWh per year, or ~25% of current UK demand." (see The Resource). Erring on the side of caution, we have assumed in our calculations that up to 20% of UK demand could be met by wave power.


Tidal currents

Technologies have now been developed for generating electricity from the energy in tidal currents (see links below).

How much?

From information in a report from Black & Veatch, the Carbon Trust (The UK tidal stream resource and tidal stream technology) say that "The UK technically extractable tidal stream resource is ~18 TWh/year ± 30 %, which is roughly 5% of current UK electricity demand." However, they add that the "economically extractable UK resource" is about 3% of current UK electricity demand. More optimistically, the Carbon Trust estimates that tidal streams could generate as much as 20% of the UK's electricity demand (see "The rise of British sea power", below).


Tidal lagoons

An attractive idea is to build lagoons in shallow sea water that generate electricity from turbines powered by the flow of water into the lagoons as the tide rises and out again when it falls.One attraction of this kind of system is that the energy is totally predictable. With three or more lagoons grouped together, it is possible to manage the flows of water using computers in such a way that peaks and troughs in supply are reduced.Another fascinating aspect of tidal lagoons is that they can be used as pumped-storage devices: water is pumped into the lagoons when there is more electricity available than is needed and then it can be used to generate electricity when demand is higher or when supplies from other sources are lower.

Neil Crumpton of Friends of the Earth argues that tidal lagoons in combination with tidal reefs could produce more electricity than the proposed Severn barrage and they would be more friendly to wildlife (see A Severn barrage or tidal lagoons?, January 2004; see also The Severn barrage, September 2007 and Severn reef plan is 'more green' (BBC News, 2008-11-26)).

How much?

Peter Ullman, Chairman and CEO of Tidal Electric, estimates (personal communication) that 8% of the UK's electricity could be met from tidal lagoons.

How much from marine sources in general?

In its report Future Marine Energy the Carbon Trust estimates that "Between 15% and 20% of current UK electricity demand could be met by wave and tidal stream energy". Judging by the figures quoted above, that estimate is probably too low.

'Micro' generation

There is a growing realisation that much of the electricity we use could be generated domestically by photovoltaics, small-scale wind turbines, combined heat and power, and fuel cells. Some of the possibilities are described on web pages under the 'Links' heading.


Although PV panels have been expensive, there are improvements in the technology and costs are falling (see SunPowerH-Alpha Solar and Flexcell). We may be approaching the point where it is feasible and affordable to install PV panels on any surface that receives sunlight.

How much?

A report from the Tyndall Centre ("Renewable Energy and Combined Heat and Power Resources in the UK", 2002) says: "ETSU [Energy & Environment Research Programme, now Future Energy Solutions] estimates the practicable resource to be 266 TWh in 2025 (calculated as electricity generated by the application of PV to all surfaces of available domestic and non-domestic buildings, allowing for 10% non-suitable surfaces and 25% shading, ETSU 2000 p.141)." Since current UK demand for electricity is about 400 TWh, this estimate means that about 66% of the UK's electricity could be generated by photovoltaics.

At that level, it would of course be necessary to make provision for the fact that the sun does not shine at night. However, as with wind power (above), it seems likely that up to 20% of the UK's electricity could be generated by photovoltaics without the need for special provision.


Micro-wind power

The EST report, "Potential for Microgeneration", estimates that as much as 6% of the UK's electricity could be generated by micro-wind turbines by 2050.

CHP and fuel cells

If CHP and fuel cells are run on bio-fuels they are a source of electricity that does not release fossil carbon into the atmosphere. But even if they are run on fossil fuels, their use can mean substantial savings in CO2 emissions compared with current systems—so they may be regarded as a partially-renewable source of electricity.

Erring on the side of caution, figures from "Potential for Microgeneration" suggest that as much as 16% of the UK's electricity could be supplied from these sources.


In a report published in March 2010, the UK Environment Agency estimates that hydropower in England and Wales could generate approximately 1900GWh to 3660GWh, or approximately 1% of the UK’s projected electricity demand in 2020.


Enhance Geothermal Systems (EGS)

Enhanced geothermal systems—which should not be confused with ground-source heat pumps—means drilling to depths up to 10 km to tap into the energy in hot rocks below the surface. Water which is pumped down the bore hole returns hot enough to drive electricity generating equipment.

A report about EGS from MIT says (in Section 1-4):

By evaluating an extensive database of bottom-hole temperature and regional geologic data (rock types, stress levels, surface temperatures, etc.), we have estimated the total EGS resource base [in the US] to be more than 13 million exajoules (EJ). Using reasonable assumptions regarding how heat would be mined from stimulated EGS reservoirs, we also estimated the extractable portion to exceed 200,000 EJ or about 2,000 times the annual consumption of primary energy in the United States in 2005. With technology improvements, the economically extractable amount of useful energy could increase by a factor of 10 or more, thus making EGS sustainable for centuries.

Not only is the resource very large but, like CSP, geothermal power has the attraction that it can deliver electricity that is dispatchable.

It appears that there may be similar large potential for EGS in many other parts of the world, including the UK. EGS Energy estimates that there is potential in the UK (mainly in Cornwall) to produce over 35TWh per annum, or almost 10% of the UK’s electricity demand, for about 200 years.


Geothermal and hydro-electric power from Iceland

Iceland generates 100% of its electricity from hydro-electric and geothermal sources and all of its space heating is geothermal.

There appears to be considerable potential for export of clean energy, either directly via HVDC submarine cables or indirectly by the siting in Iceland of energy-intensive applications such as computer data centres.


Electricity conservation

The Friends of the Earth (UK) electricity sector model for 2030 (A Bright Future, March 2006) says "Around one large power station, or two medium-sized ones in the UK have to be kept running in order to provide power for appliances not in use and on standby mode. Replacing ordinary light-bulbs with energy-efficient light-bulbs could reduce electricity consumption by at least 2 per cent (equivalent to one nuclear power station) by 2020. The potential is much higher if we implement a programme to replace inefficient street lighting and lighting in the commercial sector." (pp 11-12). Although they do not give a percentage saving for eliminating standby, the amount of energy that could be saved appears to be similar to the 2% figure quoted for switching to low-energy light bulbs.

In A Bright Future, FoE says "Studies for the European Commission, and supported by industry groups, have identified the potential to make significant cuts in electricity-use and considerable financial savings by ensuring that industry uses correctly-sized and super-efficient motor devices. These studies show a potential to reduce electricity consumption by around 6 per cent in the UK within a few years simply by encouraging a switch to more efficient motor drives."


Other ideas

  • Energy Island. Ocean Thermal Energy Conversion (OTEC) on floating islands in tropical parts of the world.

Carbon capture and storage (CCS)

The German Aerospace Centre (DLR) has done an interesting study of CCS. Here are the main links for the project:

The main conclusions are that CCS is unlikely to capture more than about 80% of emissions, there will be losses in efficiency, the technology will not be available for some time, and it is liable to be expensive.


Road and rail transport


Railways can be, and often are, powered by electricity and, if that is 'green' electricity, rail transport would also be green.

For road transport, electric vehicles and plug-in electric hybrid vehicles (PHEVs) are coming on to the market (see EVUK). As with rail transport, this can mean that emissions of fossil CO2 from road transport may be completely eliminated or substantially reduced.

What is not clear at present is how much electricity would be needed to power the railways and all road vehicles. However, the fairly cautious figures that have been quoted on this page and summarised in the accompanying spreadsheet suggest that there is considerable scope for powering road and rail transport by green electricity.



Biofuels can be made from crops that are grown for the purpose but there is a potential worry that this will divert agriculture away from food production and it may lead to the destruction of rainforests or other wild ecosystems to make way for oil-palm plantations or the production of soya beans.

A much more attractive idea is to make biofuels from things that may otherwise be wasted, like waste cooking oil, forestry or agricultural waste, old packing cases, and so on.

In a public lecture at Bangor University on the 26th of June 2006, Richard Parry-Jones, Ford Motor Company's global head of product development, quoted research suggesting that, without destruction of rainforest, 20% of road fuels could come from plants, assuming that food production was given priority over the production of biofuels.



Air travel is a large and rapidly growing source of CO2 without much sign of an acceptable carbon-free technology to solve the problem. Sir Richard Branson of Virgin Atlantic Airlines is said to be interested in the possibility of powering planes with biofuels but, as mentioned above, this could become a headache in its own right. There have been experiments in running planes on hydrogen but we don't hear much about that now.


In principle, all shipping could be powered by the wind, as it traditionally was. Some of the modern options are referenced under the Links heading.


The Internet

In principle, a lot of business travel can be eliminated by the use of video conferencing via the internet. No doubt the internet will have to improve before this kind of communication can be as good as face-to-face meetings but even now there is clear potential for reducing CO2 emissions from business travel, especially if there are incentives via carbon taxes and carbon rationing.


In cold climates, a lot of CO2 is emitted by burning coal, oil or gas to keep us warm. Much of this can be eliminated by using levels of insulation that are much higher than have been traditional in the UK but are not unusual in countries like Sweden or Canada (see also Zero-carbon eco-renovation and Domestic heating).

Residual heating needs may be met by the use of technologies such as passive solar heating, ground-source heat pumps, bio-fuels, inter-seasonal heat stores, and more.

Solar water heaters can save a lot of the CO2 emissions currently produced by using fossil fuels for heating water (about 4% of UK CO2 emissions).



The smelting of aluminium requires large amounts of electricity. For example, the power consumption of Anglesey Aluminium is 250 MW. Although this is large, it can in principle be supplied entirely from renewable sources. For example, with backup from the grid, the projected offshore Gwynt y Mor wind farm in Liverpool Bay, with a peak output of 750 MW and a load factor of about 33%, would provide all the power needed by Anglesey Aluminium. Marine Current Turbines estimate that there is 150 MW of exploitable power from marine currents near Anglesey and that would cover a large part of what is needed by Anglesey Aluminium.

It seems likely that the needs of other power-hungry industries can also be accommodated. Given the enormous quantities of solar energy available in hot deserts, there may be a case for moving some of those industries to the areas where they can get the power that they need.


The potential of renewable forms of energy generation, coupled with energy saving, is huge. There is no need to return to nuclear power with all its problems.

The spreadsheet on another page summarises the figures for electricity marked with '' on this page.

The main unsolved problem at present is how to power air transport without the use of fossil fuels.

STOP PRESS: New report shows how Europe can make deep cuts in CO2 emissions and phase out nuclear power at the same time