Concentrating Solar Power

 

There are two kinds of solar energy: solar photovoltaic and solar thermal energy.

Solar photovoltaics converts solar energy directly into electricity. Solar panels on placed on rooftops and generate on-site power for localised use.

Solar thermal converts sunlight into heat. The best known form of solar thermal energy is solar hot water. But there's also concentrating solar thermal power (usually called concentrating solar power, or CSP).

Concentrating solar power reflects and concentrates sunlight to create high-temperature heat, usually to create steam to drive traditional turbines. This power source is best harnessed through large, centralised power plants located in desert regions with high direct normal radiation. Direct normal radiation is strong sun in desert areas with little cloud cover or atmospheric moisture.

The graphic below shows how concentrating solar power works in the case of parabolic troughs, the most developed form of the technology. With parabolic troughs, concentrated sunshine is focused onto a central receiver pipe to heat a liquid to 400-1,000C. The heat is then used to create steam to drive a traditional steam turbine.

Other forms of concentrating solar power are solar towers (lower left), solar dishes (lower middle) and and linear fresnel reflectors (lower right). Solar towers and dishes reach the highest efficiencies (ie highest temperatures), but also have highest manufacturing and construction costs. Fresnel reflectors have the lowest efficiencies in creating heat but this is offset by lower manufacturing and construction costs.

Parabolic troughs: most tested., medium efficiency, medium cost
Solar Towers: high efficiency but expensive	Solar Dishes:high efficiency but expensive	Fresnel Reflectors: lower efficiency, less expensive
Source: US National Renewable Energy Laboratory

Concentrating Solar Power is Here, Now and Proven

Parabolic trough concentrating solar power plants have been generating electricity for the California grid since the 1980s. Concentrating solar power is proven. In the Mojave Desert, 350 megawatts of capacity (roughly enough to power one third of Canberra) has been operating for the past 25 years. Half of all solar electricity ever generated has come from concentrating solar power.

California parabolic troughs	Parabolic troughs in California have been providing a constant, reliable stream of solar energy now for more than 20 years.	California parabolic troughs
	Source: Schott Solar

Concentrating solar power is an enormous energy resource.The entire world's electricity demand could be satisfied by a hypothetical concentrating solar power mirror field in Outback Australia 432 kilometres on a side. Global primary energy demand (ie all energy usage ranging from electricity to transport fuels on down to energy sources such as biomass wood fires used by the world's poor) could be satisfied through a solar field 1,230 kilometres on a side located in central Outback Australia -- a region with few other uses.

In the graphic below, the sizes of various hypothetical mirror fields needed to satisfy electricity needs ranging from Australia to the world are overlaid on the Australian continent.

Looking at the graphic below, Australia's electricity needs could be met by a mirror field 50 kilometres on a side represented by the tiny square in the northwest corner of New South Wales. Above that, a mirror field 164 kilometres square could power China. Above that, a mirror field 223 kilometres square could power the US and a mirror field 432 kilometres square could power the world's electricity needs.

Concentrating solar plants in California have been operating for more than 20 years
Source: US Renewable Energy Laboratory

Molten Salt, the 'battery'

Concentrating solar power can be made more commercially attractive by its ability to temporarily "store" energy.

To do so, salt (or other medium such as graphite blocks) is heated through the solar thermal process to 400-1,000C. It is then held in insulated storage tanks from which it can be drawn upon later. This means excess solar thermal energy generated during hot, sunny afternoons can be saved and used to 'double up' power generation during the afternoon peak period, or to extend the electricity generation day until well after sunset.

"Molten" salt technology is advancing rapidly. One Australian company in California -- Ausra -- believes it can soon extend 'storage' of solar energy to 24-hours through molten salt technologies. if it succeeds, it will open the door to round-the-clock generation of 'solar' energy.

Today, 24-hour baseload power can be generated by combining concentrating solar power plants with natural gas turbines. Under this configuration, the natural gas turbines can produce power at night, while solar supplies power during the day. Such 'hybrid' solutions (such as Acquasol's and Wizard Power's) create low-cost, low-greenhouse gas emission baseload power.

Concentrating solar power now generates electricity, without molten salt storage, for about US12c/kwh and falling rapidly. Coupled with molten salt and natural gas backup, a hybrid solar-gas-molten salt power plant can today generate electricity for about 8c/kwh. This is roughly the price new coal-fired power plant equipped with carbon capture and storage might achieve in 2015.

Furthermore, hybrid concentrating solar power/natural gas plants offer electricity supply flexibility coal-fired power cannot. For instance, during a very hot weather afternoon in summer, a solar plant with storage and natural gas backup can 'triple up' electricity generation by running the natural gas turbine and the solar field at the same time as drawing down on stored heat to deal with grid demand spikes. This makes the overall electricity system more efficient because less 'spinning capacity' is needed on the grid to prevent blackouts. This, in turn, lower electricity costs to consumers.

Concentrating Solar Power Prices Are Falling Rapidly

During the first wave of investment in concentrating solar power (between 1983 and 1989), concentrating solar power prices fell by half in just seven years (from US25c/kwh to 12c/kwh). In the 1990s, low oil prices prevented new capacity from being built. But today, with oil prices well over $100, money and brains are flowing back into CSP. Prices are rapidly falling again. Experts expect current concentrating solar prices of about 12c/kwh (without molten storage) will halve again by 2015, probably sooner. That will put CSP on a price par with existing natural gas and coal-fired power generation even before carbon penalties are added to gas and coal.

Concentrating solar power prices fell by half in the 1980s. Prices are set to fall again by half in coming years as more CSP projects come on line globally.

Source: US National Renewable Energy Laboratory

The compound effects of ongoing innovation are rapidly bringing these technologies to price competitiveness with fossil fuels. The 'crossover' should occur around 2015. Carbon capture and storage has no similar potential. It is unproven, has limited price reduction potential and isn't infinitely scalable like solar.

Indeed, if 3.2c worth of carbon costs (derived by taking $40 per tonne carbon prices and multiplying them by coal-fired power emissions of .8 kg/kwh) are added to coal's current 3c/kwh generation costs and another 1.5c/kwh is added for upstream carbon emissions of mining and delivering coal to power stations, concentrating solar power with solar thermal storage and natural gas backup is already price competitive with coal-fired power since both now cost about 8c/kwh, all costs included.

Renewable energy, led by high-volume concentrating solar power, geothermal and wind, offers the prospect of low-cost, clean, abundant energy in coming years

Sources: ABARE, IEA, IPCC, DESERTEC

CSP Worldwide

Investment markets are sensing the dynamics in the concentrating solar power market. Money is flowing rapidly into the industry. Global capacity is expanding. In 2007, the first new concentrating solar power plant since 1987 went online: the 64MW "Nevada Solar One" project outside Las Vegas, Nevada. In Spain, 50MW of parabolic trough capacity named "Andasol 1" is also now online. Its capacity will be tripled to 150MW in coming years.

Natural gas rich Abu Dhabi also is investing in concentrating solar power to provide electricity for its MASDAR 'green city.' In California, proposals for nearly 3,000MW of new CSP capacity are now before permitting authorities, and 7,000MW of new capacity is planned worldwide.

Given that CSP plants take much less time to construct than nuclear or coal, much of this new CSP could be online by 2012. This will spur a virtuous circle of deployment and innovation that will lower costs. Planned capacity expansions worldwide are expected to swell the industry 15 times over in the next five years, providing a firm commercial platform for future growth.

Huge capacity expansions are planned for concentrating solar power in coming years

Parabolic troughs Solar dish Solar tower Photos: US National Renewable Energy Laboratory (NREL)