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Powerful partners: sun, wind and natural gas
Generating power from the wind or sun is clean, but costly, and the flow varies with the weather or time of day. Fossil fuels are reliable. Now some companies are making the most of both by creating hybrid plants that combine renewable energies with traditional fuels such as natural gas.
Solar power is clean and steady – until the sun goes down, or clouds roll in. Wind turbines stop spinning when the breeze dies. To provide reliable electricity, renewable energy sources need back-up. This is fuelling a new generation of hybrid power plants in which solar or wind installations are supported by natural gas.
Just as hybrid cars marry the efficiency of electric propulsion with the flexibility of liquid fuel, these hybrid power plants combine emission-free renewables with the reliability of traditional fuels.
Hybrid plants could help drive the growth of renewable energy from its current global share of less than 5% of power production to 15% by 2035. They allow wind or solar energy to operate on the back of fossil fuel systems and feed into established transmission lines.
Heat from solar operations combines with exhaust from gas combustion to power steam turbines, while wind power is transformed directly into electricity. Adding wind or solar to a gas-powered plant and sharing steam turbines can be significantly cheaper than building a stand-alone renewable facility.
Natural gas is the most effective fossil fuel to partner with renewables. It’s cleaner than other hydrocarbons, producing half as much carbon dioxide and far less local pollution than coal when used to generate electricity. It’s also more flexible.
Gas provides heat almost instantly, and can be switched off quickly. Coal, by contrast, takes time to generate optimum power and cannot be turned off as quickly. And nuclear power is far less flexible.
Most of the power in hybrid plants – more than 80% – comes from the traditional fuels, with the rest from solar and wind. As renewable energy technologies improve, they can pick up more of the load.
More new hybrid plants are under construction in northern Africa, Europe and the USA, with the help of government subsidies for the development of renewable energy projects.
In some cases, a hybrid plant is simply the result of adding alternative energy to an existing natural-gas plant.
In the USA, for example, Florida Power & Light operates a 3,722-megawatt natural gas facility in Martin County, the biggest fossil fuel plant in the country.
In 2011, the company added a 75-megawatt solar plant to the operation. The plant already recycled heat from its systems to help generate steam for producing power. Now the concentrated solar system of parabolic mirrors also contributes heat to make steam.
As renewable technologies develop, the efficiency of wind and solar energy is expected to improve. In the meantime, the hybrid model helps to give renewable energy vital room to grow.