Hot rocks, carbon capture and tidal turbines: alternate power sources for a greener future

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Not just solar and wind, there are other green technologies competing for a slice of the renewable energy pie.

Renewable energy sources accounted for just under 13.5 per cent of Australia's electricity generationi and almost 23 per cent of the world's electricity generation in 2014. Of that global renewable energy pool, wind, solar and the more traditional hydroelectricity power plants contributed more than 93 per centii.

However experts say it is a more diverse group of technologies that will power cities of the futureiii.

New developments in renewable energy technologies provide alternatives to wind and solar as countries wean off fossil fuels.

By 2030, Bloomberg expects renewables to account for 37 per cent of global electricity generation in a mix of technologies that will allow power companies to balance capacity and "hedge against volatility in gas and coal prices, security threats, natural disasters and changes in environmental regulation"iv.

So what are the new sources of renewable energy to look out for? The current forerunners include a new spin on geothermal power, reducing the carbon output in biofuel use and harnessing the energy of the sea.

Geothermal hot rocks

Geothermal power plants use heat stored beneath the Earth's surface and have been used to generate electricity commercially since 1913v. The US generates the greatest amount of geothermal powerii, while Iceland is best known for using geothermal energy to heat about 90 per cent of all homesvi.

Energy is traditionally extracted from seismically active "hot spots", where temperatures are highest and water naturally flows through the area, but emerging Enhanced Geothermal System (EGS) technology could allow energy to be extracted from a new, more abundant source: hot, dry rocks deeper undergroundvii.

EGS technology has been tested in Koreaviii, Franceix, the UK, US and Australia. In the US, it could allow at least 20 times more geothermal energy to be extracted and provide "100 Gigawatt (GW) of new capacity by 2050"x.

In Australia, Geodynamics began testing EGS technology in South Australia's Cooper Basin in 2010xi, but abandoned an EGS project in the Hunter Valley this year amid tough market conditionsxii.

According to global renewable energy policy body REN21, growth in geothermal energy generation has been "slow but steady", with cost and project development risk constraining investmentii.

Carbon-negative biopower

For millennia now, people have been burning biomass - grasses, wood, manure, and organic material - for energy, but the process can be environmentally damaging. Burning releases carbon dioxide into the atmosphere and energy crops take time and resources to replace, making them a less sustainable optionxiii.

New bioenergy with carbon capture and sequestration (BECCS) technology could improve the environment by removing carbon from the atmospherexiv.

BECCS does this in two ways: crops naturally consume carbon dioxide until they are harvested for fuel, while power plants capture carbon dioxide from the burning process and store it underground, or in the oceanxv,xiv.

There were 16 BECCS projects worldwide as of June 2012xiv. Researchers say the technology could cut carbon emissions by 145 per cent in western USxv, and remove 65 million tonnes of carbon dioxide from Australia in 2050xvi.

Gasification technology, used by groups like Californian start-up All Power Labs, takes the concept of carbon capture and storage a step further: carbon is "stored" in a nutrient-rich byproduct that can also be used as fertiliser. All Power Labs' $27,000 machines generate cheap, clean energy and have been popular in countries like Ecuador, Haiti, Thailand and Nicaraguaxvii.

Meanwhile, Finnish power company Vaskiluodon Voima Oy has operated a large-scale biomass gasification plant alongside its pre-existing coal-fired power plant since 2013xviii. The project was granted €10 million from the Finnish government and expected to cut Vaskiluodon Voima's coal use by up to 40 per centxix.

Ocean energy

Ocean energy refers to harvesting energy from changes in ocean temperatures, salt content, waves and tides. The technology is still in its infancy, but could yield up to 80,000TWh of electricity, meeting more than four times the world's electricity demandxx.

According to the CSIRO, wave energy could supply up to 10 percent of Australia's electricity needs by 2050. Source xxiv.

There are only about 530MW of ocean energy generators in operation worldwide. Most are tidal barrages, of which the largest are a 254MW facility in South Korea and a 240MW station in Francexxi.

Tidal barrages operate like dams, and are built across narrow passages with at least a 16-foot (approximately 4.9m) difference between high and low tides. Emerging technologies like tidal fences and turbines and offshore ocean float systems could allow more energy to be harvested elsewherexxii.

The CETO unit in Australia's Carnegie Wave Energy project is a float system that can generate 20MW of electricity - enough to power 1400 households - from three hectares of seabed . A unit was installed on Perth's Garden Island last November and is expected to begin producing power this yearxxiv.

According to the CSIRO, wave energy could supply up to 10 percent of Australia's electricity needs by 2050xxv.

iClean Energy Council 2014, Clean Energy Australia report 2014, viewed 21 August 2015,

iiREN21 2015, Renewables 2015 Global Status Report, viewed 20 August 2015,

iiiThe Wall Street Journal 2013, The experts: what renewable energy source has the most promise?, 17 April, viewed 20 August 2015,

iv McCrone A 2013, Energy forecasts for 2030 and beyond – why they differ so much, 30 May, viewed 21 August 2015,

vEncyclopedia Britannica Online, Geothermal energy, viewed 20 August 2015,

viPhillips A 2014, In Iceland, magma used to create geothermal power for the first time, 4 February, viewed 21 August 2015,

vii AUS Department of Energy 2012, What is an Enhanced Geothermal System?, September, viewed 20 August 2015,

viiiSong Y et al 2015, Background and progress of the Korean EGS pilot program, April, viewed 21 August 2015,

ixGenter A et al 2010, Current status of the EGS Soultz geothermal project, April, viewed 21 August 2015,

xTester, JW et al 2006, The future of geothermal energy: Impact of EGS on the United States in the 21st century, viewed 20 August 2015,

xiAustralian Renewable Energy Agency, Cooper Basin Enhanced Geothermal Systems Heat and Power Development, viewed 20 August 2015,

xiiABC News 2015, Plans scrapped for Upper Hunter hot rocks renewable energy, 16 June, viewed 21 August 2015,

xiiiGreenpeace 2011, Fuelling a BioMess: Why burning trees for energy will harm people, the climate and forests, October, viewed 23 August 2015,

xivMilne J L, Field C B 2012, Assessment report from the GCEP workshop on energy supply with negative carbon emissions, viewed 23 August 2015,

xvSanders R 2015, Electricity from biomass with carbon capture could make western US carbon-negative, 9 February, viewed 23 February 2015,

xviThe Climate Institute 2014, Moving beyond zero: understanding bioenergy with carbon capture and storage, 9 April, viewed 23 August 2015,

xviiNguyen T C 2013, Carbon-negative energy is here! This device makes clean energy and fertilizer, 1 November, viewed 23 August 2015,

xviiiGibson L 2011, Huge biomass gasifaction plant in Finland largest of its kind, 8 June, viewed 23 August 2015,

xixEuropean Commission 2015, State aid: Commission approves support package for gasification plant in Finland, 24 June, viewed 23 August 2015,

xxInternational Energy Agency, Ocean: Pilots, projects and potentials, viewed 23 August 2015,

xxiEY 2013, Rising tide global trends in the emerging ocean energy market, viewed 3 September 2015,$FILE/EY-Ocean-energy-Rising-tide-2013.pdf#page=4

xxiiRenewable Northwest, Wave & tidal energy technology, viewed 23 August 2015,

xxiiiThe University of Western Australia 2013, Fact sheet: Water wave energy, viewed 23 August 2015,

xxivCarnegie Wave Energy, Perth project, viewed 23 August 2015,

xxvHayward J, Knight C 2013, Explainer: what is ocean energy?, 21 May, viewed 23 August 2015,