Renewable energy has been around for centuries but what forms are there? and how have they changed over the years?
Types of renewable energy
Solar panels are used to convert the light energy from the sun into electrical energy. When the solar panel is hit by the light energy from the sun, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the silicon to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect. Currently, solar panels are able to convert most of the visible light spectrum and about half of the ultraviolet and infrared light spectrum to usable solar energy.
Solar energy can be used:
- To heat water, making it hot.
- Produce electricity directly from the sun.
We have been using wind energy for hundreds of years. From using windmills for pumping water and grinding grain to wind turbines which are used for generating today’s modern electricity.
Wind turbines are mounted on a tower to capture the most energy. The is place more than or even to 100 feet above ground, they can take advantage of the faster and less turbulent wind. Turbines catch the wind’s energy with their propeller-like blades. Usually, two or three blades are mounted on a shaft to form a rotor enabling it to rotate and generate electricity.
A blade acts much like an aeroplane wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called the lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity.
Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system. For utility-scale sources of wind energy, a large number of wind turbines are usually built close together to form a wind plant. Many electricity providers today use wind plants to supply power to their customers.
Stand-alone wind turbines are typically used for water pumping or communications. However, homeowners, farmers, and ranchers in windy areas can also use wind turbines as a way to cut their electric bills.
Small wind systems also have potential as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.
Geothermal energy is the heat from the Earth. Like all of the other forms of renewable energy, it’s clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.
A geothermal heat pump system consists of a heat pump, an air delivery system, and a heat exchanger. A system of pipes is buried in the shallow ground near a building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.
biomass energy or bioenergy is the energy from organic matter. This has been used for thousands of years, ever since people started burning wood to cook food or to keep warm.
today, wood is still our largest biomass energy resource. But many other sources of biomass can now be used, including plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills can be used as a biomass energy source.
The use of biomass energy has the potential to greatly reduce our greenhouse gas emissions. Biomass generates about the same amount of carbon dioxide as fossil fuels, but every time a new plant grows, carbon dioxide is actually removed from the atmosphere.
Hydropower generates around 18% of the UK’s energy. The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, causing it to rotate, which in turn activates a generator to produce electricity. But hydroelectric power doesn’t necessarily require a large dam. Some hydroelectric power plants just use a small canal to channel the river water through a turbine.
Another type of hydroelectric power plant – called a pumped storage plant – can even store power. The power is sent from a power grid into the electric generators. The generators then spin the turbines backwards, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored. To use the power, the water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbines forward, activating the generators to produce electricity. But this is rather pointless as the only extra energy gained from it would have been from the rainwater as electrical energy is being used to pump the water into the reservoir.
The ocean can produce two types of energy:
- Thermal energy – from the sun’s heat.
- Mechanical energy – from the tides and waves.
Oceans cover more than 70% of Earth’s surface, making them the world’s largest solar collectors. The sun’s heat warms the surface of the water more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.
Ocean thermal energy is used for many applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean’s warm surface water to vapourise a working fluid, which has a low-boiling point, such as ammonia. The vapour expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. And hybrid systems combine both closed-cycle and open-cycle systems.
Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.
A barrage, or dam, is typically used to convert tidal energy into electricity by forcing the water through turbines, pushing a generator.
Hydrogen and Fuel Cells
An atom of hydrogen consists of only one proton and one electron. It’s also the most plentiful element in the universe. Despite its simplicity and abundance, hydrogen doesn’t occur naturally as a gas on the Earth – it’s always combined with other elements. Water, for example, is a combination of hydrogen and oxygen (H2O).
Hydrogen is also found in many organic compounds, notably the hydrocarbons that make up many of our fuels, such as gasoline, natural gas, methanol, and propane. Hydrogen can be separated from hydrocarbons through the application of heat – a process known as reforming. Currently, most hydrogen is made this way from natural gas. An electrical current can also be used to separate water into its components of oxygen and hydrogen. This process is known as electrolysis. Some algae and bacteria, using sunlight as their energy source, even give off hydrogen under certain conditions.
Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. NASA has used liquid hydrogen since the 1970s to propel the space shuttle and other rockets into orbit. Hydrogen fuel cells power the shuttle’s electrical systems, producing a clean byproduct – pure water, which the crew drinks.
A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water. Fuel cells are often compared to batteries. Both convert the energy produced by a chemical reaction into usable electric power. However, the fuel cell will produce electricity as long as fuel (hydrogen) is supplied, never losing its charge.
Fuel cells are a promising technology for use as a source of heat and electricity for buildings and as an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure hydrogen. But fuels like natural gas, methanol, or even gasoline can be reformed to produce the hydrogen required for fuel cells. Some fuel cells even can be fueled directly with methanol, without using a reformer.
In the future, hydrogen could also join electricity as an important energy carrier. An energy carrier moves and delivers energy in a usable form to consumers. Renewable energy sources, like the sun and wind, can’t produce energy all the time. But they could, for example, produce electric energy and hydrogen, which can be stored until it’s needed. Hydrogen can also be transported (like electricity) to locations where it is needed.
Green power is electricity that is generated from resources such as solar, the wind, geothermal, biomass, and low-impact hydro facilities. Conventional electricity generation, based on the combustion of fossil fuels, is the nation’s single largest industrial source of air pollution. The increasing availability of green power enables electricity customers to accelerate installation of renewable energy technologies. As more green power sources are developed – displacing conventional generation – the overall environmental impacts associated with electricity generation will be significantly reduced.