Tuesday, 10 November 2009

World’s first hybrid power plants show promise

November 5. 2009

In the urgent search for a quick fix to the world's carbon emission problems, some of the most promising technologies are those that marry new energy sources to old. Thus fuel-saving hybrid cars, powered by a combination of electricity and petrol, have found more buyers than zero-carbon vehicles, and have done more to cut overall transportation emissions. Soon, a bridging approach to solar and gas-fired electricity could reduce carbon emissions from power generation. Meet the integrated solar combined-cycle (ISCC) power plant, a hybrid design being pioneered in North Africa.

Currently there are three utility-scale ISCC plants under construction in the region, which will be the first of their kind in the world. At least two, and possibly all three, should start operating next year. Algeria's 150 MW Hassi R'Mel project, which is scheduled for completion next October, is likely to be the first. It will be closely followed by the start-up of Egypt's Kureimat power plant, another 150MW facility. Morocco's 472MW Ain Beni Mathar power project was scheduled for completion in the middle of next year, but construction delays may push start-up into 2011, according to industry sources.

Elsewhere in the MENA region, Iran is expected to invite bids within the next two months for an engineering, procurement and construction contract for a 430MW ISCC plant. Kuwait has completed a feasibility study for a hybrid plant proposed for a site south-east of its capital, but the emirate's electricity and water ministry has not yet unveiled plans to follow through on the 280MW project. The promise of hybrid gas-solar energy plants is that they would reduce the need to build separate gas plants to compensate for fluctuating power output from solar arrays, which at best generate electricity about 30 per cent of the time.

"Instead of relying upon a separate power plant miles down the road to guarantee grid reliability to generate electricity when the solar plant cools off, just one plant can be built with two sources of heat – sunlight and natural gas," said Craig Severance, a US accountant and energy expert. "This saves on construction costs because only one steam turbine is needed instead of two. Also, much of the ancillary equipment such as controls, pumps, valves, et cetera are not duplicated. Perhaps most importantly, duplicate sets of transmission lines are avoided."

Further savings can be realised on operating costs, because only one team of workers is needed to run an integrated plant. Gas costs can also be lowered by combining two heat sources. The Kuwaiti feasibility study, conducted by the Japanese firm Toyota Tsusho, found that by using solar thermal energy to supplement gas-fired steam generation, the proposed hybrid power plant could save 21.1 million cubic metres of gas per year. That should be significant to a state with insufficient gas to meet domestic demand, and which imported liquefied natural gas this summer to cover a seasonal shortage.

Mr Severance has estimated that hybrid plants could be built for about US$2,500 (Dh9,181) per kW of capacity, versus $1,100 to $1,500 per kW for gas-fired plants. The difference could be recovered over the plant's lifetime through lower operating costs. For a hybrid plant running all the time "the two choices are near parity in total generation costs, but the solar hybrid plant would have less exposure to long-term increases in fossil fuel prices and carbon penalties", Mr Severance concluded. Price tags for the Algerian, Egyptian and Moroccan ISCC projects are respectively $370 million, $310m and $472m. The proposed Iranian plant has an estimated cost of $322m.

North Africa is in many respects an ideal location for deploying the hybrid power-generation technology. It has abundant supplies of gas and sunlight, and plenty of cheap, under utilised land to accommodate solar arrays. The region is also well positioned to export electricity to Europe. But a number of other countries are also planning to develop ISCC capacity, notably the US. There, the primary interest is in retrofitting gas-fired plants with solar arrays. The $476m Martin Next Generation Solar Energy Centre, a solar array under development in Florida, will be the first in the world to be connected to an existing power plant when it is completed next year. The 75MW solar thermal facility with 180,000 mirrors will be a component of the 3,705MW Martin County power plant.

US solar energy developers also hope to add solar arrays to coal-fired plants in suitably sunny locations to reduce emissions from the most carbon-intensive form of power generation. But the scheme has been heavily criticised by environmentalists who want to see coal-fired facilities phased out as quickly as possible. Nonetheless, Abengoa Solar, which builds big solar thermal power plants in Arizona, in August announced plans to connect a solar array to a coal-fired plant in Colorado. Ausra, a solar energy company based in Melbourne, has demonstrated similar technology in Australia.