OR GEOTHERMAL

The transition from petroleum, coal and gas to cleaner, renewable energy sources has been many decades in the making. We’ve had hydroelectricity for a long time now, but its capacity is localised and limited, and according to some not all that environmentally friendly. The same could be said for other renewable energies such as aeolic (wind) energy and even solar panels distributed across the planet, but even so they belong to the alternatives that are considered preferable to either fossil fuels or the kind of nuclear power currently available to us.

Some decades ago, nuclear power appeared to be the solution of the future – and it is – but the first wave of fission plants proved potentially dangerous (see Chernobyl, Three Mile Island and Fukushima), and also produce highly toxic nuclear waste. Billions are being poured into the ITER international research centre in France, where it should only be a question of time before far more stable and waste-free fusion technology becomes a reality, but in the meantime the search for presentday alternatives is on. Wind, wave and similar sources are limited in their capacity and efficacy, so right now two of the most important options are solar and geothermal energy.

PHOTOVOLTAIC (SOLAR) ENERGY

Solar energy is perhaps the sustainable, CO2-free source that most hopes are pinned on, and it can be used for heating as well as generating electricity. The technology used for the latter revolves around the photovoltaic process by which solar rays captured on devices such as solar panels are converted into electric energy with the use of semiconductor materials such as silicon. Though the original concept dates back almost a century, the technology became feasible in the 1990s. Since then, the nature and cost of solar panels has changed favourably, with technical development and economies of scale reducing costs by up to 90% and producing far more durable and effective production methods.

The essence of solar power generation is the conversion of light into electricity, a process by which solar panels – or rather, the solar cells they are made up of – catch the sunlight that hits the earth’s surface and feed this energy into an electric grid, be it a localised one or the greater power grid. Though they operate best at an oblique angle, solar panels can be mounted on the ground, fitted to a wall or attached to a flat or sloping roof, as is often the case. The main material used as the semiconductor, silicon, is abundant and cheap to produce, though others, such as silver and polysilicon are more costly.

For all this, the hundreds of thousands of panels placed on rooftops and brownfields around the world amounts to little more than 2% of global electricity supply – a fraction of what is possible. Moreover, the panels last 10-30 years and cannot be recycled, but tests with a new semiconducting material, perovskite, point towards a potential wave of breakthroughs that could yet see solar energy realise its potential.

Solar panels have become increasingly efficient and economical forms of energy production

Geothermal Energy

As a sustainable energy source, geothermal has the capacity to produce heating and generate electricity from the heat – or thermal energy – stored under the earth’s surface. In all, the planet’s subterranean heat content is about double the present energy requirement of us humans living on the surface, but it isn’t as easy as all that, as the process is only viable in locations where the hot steam can be tapped at the surface or drilled down into.

Nature gave us the example of potential heat extraction early on, as there are many spots around the world where natural geysers spray geothermally heated water jets high into the air. Think of New Zealand, Iceland and of course ‘Old Faithful’ at the Yellowstone National Park in Wyoming, USA. About a century ago, scientists cottoned on to this potential, but geothermal energy production has only gradually evolved since the 1950s, yet now seems set for a big leap forwards. Currently, world output stands at around 17,5 gigawatts (GW), which though considerable is just a fraction of the energy required and produced every year, and also roughly onetwentieth of the potential capacity of geothermal energy.

Developing all the potential that lies under the earth’s crust will, however, require a great deal of further investment, technological development and the perfecting of extraction and storage systems around the world. Over time, different systems have been developed to extract thermal heat and convert it into electricity, and currently there are three in use: Flash Steam, Dry Steam and Binary Cycle. Geothermal is one of the cleanest energy forms, though detailed geological studies of potential sites is important, as it has caused subsidence and even earthquakes. Even at full viable production, it will extract only a relatively small amount of the earth’s thermal heat capacity, and if development and investment continue to accelerate, it can account for 3-5% of our energy needs by 2050 and reach approximate full potential at 10% by 2100.

Geothermal will never be the magical one-stop solution to humanity’s power requirements, but it is renewable, sustainable, generally safe and a big potential source in localised settings around the world. Like wind and solar energy, it will make a big contribution to present and future energy needs, but in the end it is still nuclear fusion that holds the key to a world free of fossil fuel pollution.

“We’ve come to a crossroads where the need to distance ourselves from fossil fuels and find new sources of energy has become an imperative. There is no one solution today, so we will need various sources, and both photovoltaic and geothermal energy look set to play a big role, with implications for investment.”

Roberto Gómez Calvet Professor of Economics at Madrid European University and an energy expert. Valencia, SPAIN