Are renewables the answer to the enegy problem? Sadly, the answer to this question is no. Juggling reliability of energy supplies, affordability and the need to deal with climate change is an incredibly complex task where no single set of technologies offer a definitive answer. Tackling these issues on several fronts will mean reducing our demand for energy, cleaning up fossil fuels and looking hard again at the nuclear option.
That said renewables could have a huge role to play. After all, in a hundred years when oil and gas resources have dwindled and we have inflicted further damage on our planet, can we imagine renewables not playing a major role in sustaining our societies?
One issue with renewable energy is that it is incredibly diverse. ‘Mechanical’ renewable technologies, such as wind or hydroelectric power are the most advanced; huge investments in hydroelectric power were made in the 1930s, 40s and 50s. Although many of these developments would not now survive environmental scrutiny, well-established hydroelectric technology plays a major role today in many countries, with continued investment in China and other parts of the developing world.
People have been extracting power from the wind for well over a thousand years. Technological advances mean that today a single wind turbine can generate up to 5,000 kW of power, equivalent to 50,000 standard light bulbs. Scores of turbines connected to a single grid point can generate power on a scale similar to conventional fossil fuel power stations. In fact, with soaring gas prices, it has been claimed that wind has been providing some of the cheapest electricity around.
Although wind is a ‘proven’ technology and has a valuable role to play in reducing harmful emissions, some people find clusters of turbines plain ugly. This places obvious limits on their siting, as do areas of best wind resource. These are often in remote areas, which may make it necessary to reinforce the electricity grid. The movement offshore – where wind resources are both greater and more reliable – poses additional grid connection issues.
There is growing interest in energy from waves and tidal streams. A bewildering variety of prototype devices bob, duck or twist in the ocean to harness power. The challenge here is to create devices that can survive some of the most hostile environments on earth while bringing costs down to an acceptable level, which is where experience from the offshore oil and gas industry is being brought to bear. As a result, prospects are more promising than they were 30 years ago.
Moving away from the ‘mechanical’ technologies - using solar energy to heat water is straightforward and well established. Photovoltaic (PV) cells for generating electricity are also becoming well established, though this remains an expensive way of generating electricity except for remote off-grid applications or when PV is integrated into building structures. Conventional silicon cells can be further improved and need continuing applied research and development. Meantime, more fundamental research into solar cells made from organic compounds holds out the promise of fundamental breakthroughs in the efficiency of light to electricity conversion.
Bio-energy includes both solid biomass, such as forest products or agricultural waste, which is already being burned to generate electricity, heat or both. Liquid bio-fuels, often from food crops, are used as transport fuels. Using bio-energy leads to carbon emissions at the point of use, but these emissions can be at least partially offset when growing crops take up carbon dioxide from the atmosphere.
Brazil already makes massive use of bio-ethanol (a petrol substitute), grown from sugar, for transport and bio-diesel is used in several countries. However, existing bio-fuels do not necessarily lead to dramatic reductions in greenhouse gas emissions over their life cycle. The big potential for carbon reduction lies with ‘second-generation’ biofuels produced from woody crops such as short rotation willow or poplar or certain tropical grasses. Selective breeding and even genomics could substantially improve the yields of biofuel crops and improve their viability.
Given the diversity of technologies, policies to encourage renewable energy need to be carefully tailored. With its low-carbon credentials, wind is close to the point where it should be able to make it on its own.
Marine energy, bioenergy and PV however, need further research and development if experience is to be built up and costs reduced. As they get closer to market, incentives in the form of guaranteed feed-in tariffs or Britain’s Renewables Obligation are needed. But each technology needs to be weaned off these subsidies over time.
An intriguing new possibility is to use very small-scale renewable energy – ‘micro-generation’ – at the household level. Small wind turbines and solar PV are among the options, though solar hot water panels are probably more cost-effective. Cost is a big challenge for micro-generation; large-scale renewables tend to be cheaper though micro-generation avoids electricity transmission and distribution losses.
As with houses, the key to renewable energy is location, location, location. Different countries need to exploit the forms of renewable energy that best suit their natural conditions. Britain, for example, has among the best wind and marine energy resources in the world, but it is not the best place for solar.
Many of the renewable technologies will deliver us energy down electric wires. But we should not forget the potential of solar and bio-energy to provide us with heat as well. And bioenergy holds out the longer-term promise of fuels which will break the iron link between oil and transport.
If that vision can be realised it may be that we can put the fossil fuel era behind us.
Professor Jim Skea is research director at the UK Energy Research Centre.