In China, solar energy lags behind wind energy in installed capacity, but the country's solar energy potential is massive and untapped. Solar power converts sunlight into thermal or electricity energy. It is already producing electricity and heating homes around the world, and it is truly a power source of almost unlimited potential. Properly exploited, it could meet the world's energy demands many times over.
2007 August - A solar energy farm, in Qianwei village, on Chongming Island,near Shanghai.
In the past, solar had a reputation for being uneconomic and impractical, but this is no longer the case. Rapid advances in manufacturing techniques mean that solar is now a mature technology. Solar can be used to directly produce electricity or for heating and even for cooling. Future potential of solar is mostly limited by our willingness to seize the opportunity.
Types of Solar Power
Three main types of solar power are in regular use today: photovoltaic, solar thermal, and concentrated solar plants.
Concentrated Solar Plants
The most exciting recent developments have been in concentrated solar plants, which have been described as "the technology that will save humanity".
A form of solar thermal power generation, a CSP uses massed banks of parabolic mirrors to focus the sun's energy on a single point and generate intense heat. This is used to super-heat water, creating hot, pressurized steam, which in turn drives a turbine and generates electricity. Importantly, CSPs don’t only work when the sun shines – once built, they can operate well into the night.
Concentrated solar plants are rapidly growing in popularity. Because the energy density (or amount of power generated) per square mile of land for solar plants is low, at the moment they are still best suited to desert regions where land is cheap and the sun is strong. But the potential is enormous.
This is what many people think of when they think of solar power. Photovoltaic power uses semi-conductor cells – usually made of silicon – to convert sunlight directly into electricity. Photovoltaic cells (PVs) are most commonly used as roof tiles to take advantage of the light coming from the sun. This is trapped by the cell and turned into electricity.
Solar panels can either operate as a stand-alone or feed energy to a grid. They work best when in direct sunlight, but they continue to produce electricity on cloudy days. Due to the reflection of sunlight from clouds, days with a few clouds can even result in higher energy yields than completely sunny days.
Small devices, like calculators are often powered by very small solar cells. PV is also used to provide electricity in areas with no power grid. Greenpeace has developed a refrigerator, called Solar Chill, which can run on solar energy. After testing, it will be used by humanitarian organizations to help supply vaccines in areas without electricity.
Architects are also using photovoltaic cells increasingly as a design feature. For instance, solar roof tiles or slates can replace conventional roofing materials. Flexible thin film modules can even be integrated into vaulted roofs, while semi-transparent modules allow for an interesting mixture of shading and daylight. PV can also be used to supply peak power to the building on hot summer days when air-conditioning systems need the most energy, thus helping to reduce the maximum electricity load.
Solar Thermal (Heating)
Solar thermal uses the heat of the sun directly. A solar thermal collector on your roof can provide hot water for you home and help heat your house.
This system is based on the ancient principle that water in a dark container will warm up when the sun shines on it.
Solar thermal technologies on the market now are efficient and highly reliable and have a range of applications, such as domestic hot water heating, space heating in residential and commercial buildings, swimming pool heating, solar-assisted cooling, industrial process heat and desalination of drinking water.
Domestic hot water production is the most common application for solar thermal today. It has many advantages, especially in China, where they are many families’ first water heater in the home. Not only do solar water heaters emit no CO2 and reduce the consumption of fossil fuels, they also help lower utility bills – sunlight is free after all. In China, solar-powered water heaters are only slightly more expensive than conventional systems, and pay for themselves in five years or less through savings on electricity or natural gas bills.
There are two main types of solar thermal technology:
Vacuum tubes: Sunlight is absorbed by vacuum tubes to heat up the fluid inside. Additional heat is picked up by the reflector behind the tubes. Whatever the sun's angle, the round shape of the vacuum tube allows the sun to be absorbed directly. Even on a cloudy day, when the light is coming from many angles at once, the vacuum tube collector can still be very effective.
Flat panel solar collector: This is basically a box with a glass cover that sits on the roof like a skylight. Inside the box is a series of copper tubes with copper fins attached. The entire structure is coated in a black substance designed to capture the sun's rays. These rays heat up a mixture of water and anti-freeze that circulates from the collector down to the water heater.
Solar chillers use thermal energy to produce cold and/or dehumidify the air in a similar way to a refrigerator or conventional air-conditioning. This application is well suited to solar thermal energy, as the demand for cooling is often greatest when there is the most sunshine. Solar cooling has been successfully demonstrated. Large-scale use can be expected in the future, as the cost of the technology is reduced, especially for small-scale systems.
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