Putting Clean into Practice

27 July 2010 (Last Updated July 27th, 2010 18:30)

Whether it is warming in the sun or blowing in the wind, new ways to create power are helping the shift towards clean energy sources. Mitch Beedie reports.

Putting Clean into Practice

The urgency placed on projects dealing with the turn from fossil fuels to renewable energy means that adding power stations ad-hoc is no longer enough – a structured and timetabled plan is now required to meet rising demand. Regardless of this, the mix of technologies has to provide secure baseload power at the lowest possible costs.

To date, a number of exotic renewable technologies have been proposed to help the energy industry switch, but the important ones over the next decades will be those that relate to the lowest cost.

The US Department of Energy (DoE) publishes average building and operating costs over the lifetime needed to pay for the different power technologies. The latest figures – for January 2010 – show that renewable sources are already broadly competitive with fossil fuels and nuclear. In US$ cents per kWh, prices for non-renewable technologies are: eight and 14 for natural gas (combined cycle and combustion turbine), 10 and 13 for coal (conventional and advanced with carbon sequestration), and 12 for nuclear. The comparable figures for renewables are: 11 for geothermal and biomass, 12 for hydro, 12 to 19 (onshore and offshore) for wind, and 26 for solar thermal.

Like all comparisons, the figures depend on the assumptions being made. Unfortunately, the DoE's last figure is actually, unintentionally, grossly misleading because it deals with average costs of power already installed. Solar thermal, particularly concentrating solar power (CSP), is actually the most promising and potentially lowest cost large-scale renewable technology.

"Capturing less than a third of a percent of the light falling on the Sahara and Middle Eastern deserts would meet all Europe's energy needs."

CSP uses large mirrors to concentrate sunlight onto water running through pipes. The water boils and drives a steam turbine in much the same way as in coal, gas and oil power plants, but using free energy. Plants have been generating reliably in California for 20 years and can generate reliable baseload power. Most solar energy is generated around the equator, though, which is not where most energy is consumed. Hence a co-ordinated effort and low-loss high-voltage DC (HVDC) lines to transport it are required for projects using CSP.

The German Aerospace Centre (DLR) calculates that CSP plants are today already competitive with fuel oil at $50/barrel, and heading for competitiveness with natural gas and coal. It estimates prices of solar thermal imports could be from 5.5 to 6.5 €c/kWh by 2020.

Offshore wind and wave power from the UK, hydro from Norway, geothermal from Iceland and solar power from Germany could hang from the European HVDC backbone. A similar solar backbone would work for the Americas and the East, topped up again – depending on local availability and in general order of profitability – by wind, geothermal, biomass and hydro. These are the technologies that should be getting the huge subsidies fossil fuels and nuclear power attract.

Solar thermal supplying the bulk

Capturing less than a third of a percent of the light falling on the Sahara and Middle Eastern deserts would meet all Europe's energy needs. By using heat storage tanks to run through steam circuits, supply can pretty well follow the times of major demand and can be extended into the night time (or production can be increased at peak hours). CSP plants in North Africa and the Middle East could be producing up to 470GWe by 2050.

"With nearly 1 TWe worldwide, hydroelectricity supplies around 20% of world electricity."

The Desertec project aims to generate the power in the deserts of the Middle East and North Africa and transmit it throughout Europe via an HVDC network. The project aims to provide at least 15% of Europe's electricity by 2050, and is supported by major companies including Siemens, E.On and Deutsche Bank. European energy commissioner Günther Oettinger has recently suggested that Europe could be importing hundreds of megawatts within
five years.

Electricity from CSP farms could also help power the equatorial region, provide heat for industrial processes and desalinate sea water to irrigate the deserts themselves (the land under the mirrors can be used for agriculture). On a larger scale, it could help power electric cars, which will actually increase CO2 production without renewable supplies and so go some way to solving our transport problems, too.

Objectors to Desertec say it would limit European countries to only a few sources for energy. Now, though, each new non-renewable power station commits the operator to a lifetime's worth of uncertain fuel prices for gas, oil, coal or uranium (which brings its own dangers and disposal problems). Backed up with other renewable sources, Desertec could actually improve security of supply by having many solar plants and medium-capacity lines.

Topped up by mainstream renewables

Wind is actually one of the cheapest power technologies – both renewable and non-renewable. The US Department of Energy admits that best wind costs are lower than its levelised figures, with wind projects in the most fruitful areas actually costing around 9 US$c/kWh. Wind generation is growing quickly globally, too. The US has highest installed capacity in the world, followed by Germany, China, Spain and India, and together, they account for around two-thirds of the world's 160GWe supply, with around half of that figure generated in Europe. Offshore wind farms should also be part of the mix – although they have higher construction costs they have higher load factors and unlimited capacities.

"Potentially the largest and lowest-cost 'renewable resource' is actually energy efficiency."

Geothermal resources are mainly spread along the edges of tectonic plates. Major belts roughly stretch down the western Americas coast, across the Mediterranean and down eastern Africa, and off the eastern coast of the Far Eastern countries. The International Geothermal Association (IGA) reports 10GWe of geothermal power worldwide. Most plants are in the US, which has just over 3GWe, and much of those are in California. There is another 50GW of geothermal heating around the world. Recent developments such as binary cycle power plants have greatly increased the recoverable resources, so geothermal is no longer limited to around the tectonic plates.

There is about 50GWe of biomass power production worldwide but whether this is sustainable depends on how the biofuel was produced, and how cleanly it is burned. With sensitive and effective forest/crop management and efficient stoves, biomass could fill much of the world's energy requirements. Modern biomass sources include pulping liquor, municipal waste, manufacturing waste and landfill gas.

With nearly 1 TWe worldwide, hydroelectricity supplies around 20% of world electricity. The major environmental and social impacts of large projects means the trend is towards small-scale projects (up to about 10 MWe) with small reservoirs.

Energy efficiency – the ignored resource

Alongside those mainstream renewable supplies, photovoltaic and wave power cost more but have their own unique advantages. Although initial capital costs are higher, running costs are again virtually zero. And other ways of viewing the financing tilt the balance further in renewable sources’ favour. With typical power plants still generating at well below 50% efficiency, each kWh produced from renewable sources equals more than 2 kWh of electricity from fossil fuels.

Although photovoltaic now generates only around 10GWe worldwide, it is the fastest growing energy source. Incorporating panels at the point of electricity demand reduces transmission losses, which somewhat offsets the high 40 $USc/kW costs. Efficiencies are increasing and prices are dropping, and this figure is changing rapidly.

With nearly three-quarters of the earth's surface covered by water, wave power is surprisingly poorly developed. Generation is less than 0.5GWe worldwide, but there are several promising technologies. The Limpet, for example, now being trialled on the island of Islay off the west coast of Scotland, is a shoreline wave energy converter using an inclined oscillating water column driving a turbine. Developers Voith Hydro Wavegen points to potential use in breakwaters, coastal defences, port walls and similar. An offshore generator from Pelamis, meanwhile, takes advantage of tides and fast-moving tidal streams.

Potentially the largest and lowest-cost 'renewable resource' is actually energy efficiency. Much of the world's energy is used for space and water heating, and much of this is inefficiently supplied by electricity. Demand can be reduced by a range of low-cost measures such as better insulation and more efficient boilers, better use of waste heat in industry, and use of low-energy equipment such as LED lighting. Reducing energy demand – often called the 'fifth fuel' alongside petroleum, coal, nuclear and renewable energy – cuts the price of the whole generating system.