18-3 Using Renewable Energy to Provide Heat and Electricity

What Are the Main Types of Renewable Energy? Solar Capital

One of the four keys to sustainability based on learning from nature is to rely mostly on renewable solar energy. We can get renewable solar energy directly from the sun or indirectly from moving water, wind, and biomass. Two other forms of renewable energy are geothermal energy from the Earth’s interior and using renewable energy to produce hydrogen fuel from water.

One reason that renewable energy provides only 16% of the world’s energy is that renewable energy resources have received and generally continue to receive much lower government tax breaks, subsidies, and research and development (R & D) funding than fossil fuels and nuclear power have received for decades.

The other reason is that the prices we pay for fossil fuels and nuclear power do not include their full costs, such as harm to human health and the environment in the case of fossil fuels, and hidden costs of decommissioning in the case of nuclear energy.

A key advantage of renewable energy, aside from low environmental impact, is that it allows energy problems to be solved in so many versatile ways depending on the combination of renewable energy sources (such as solar, wind, hydro, microhydro, geothermal, biomass, and efficiency) that are available locally. Renewable energy installations can be large or small, and can allow communities and individuals to be more directly involved with their energy options.

How Can We Use Direct Solar Energy to Heat Houses and Water? Face the Sun and Store Its Heat

Buildings and water can be heated by direct solar energy using two methods: passive and active:

  • A passive solar heating system absorbs and stores heat from the sun directly within a structure. In today’s passively heated buildings, energy- efficient windows and attached greenhouses face the sun to collect solar energy by direct gain. Walls and floors of concrete, adobe, brick, stone, salt-treated timber, and water in metal or plastic containers store much of the collected solar energy as heat and release it slowly throughout the day and night. A small backup heating system such as a vented natural gas or propane heater may be used but is not necessary in many climates

  • An active solar heating system absorbs energy from the sun by pumping a heat-absorbing fluid (such as water or antifreeze solution) through special solar collectors usually mounted on a roof or on special racks to face the sun. A typical active collector has a flat black surface, a coil through which the heat-absorbing medium such as water is pumped, and a cover consisting of two or three layers of glass

How Can We Cool Houses Naturally? Insulate and Work with Nature

Here are some ways to have a cooler house. Use superinsulation and superinsulating windows, open windows to take advantage of breezes, and use fans to keep air moving. Block the high summer sun with deciduous trees and window overhangs, or awnings.

Another option is to place plastic earth tubes underground where the earth is cool year-round. In this geothermal cooling system, a tiny fan can pipe cool and partially dehumidified air into an energy- efficient house. In warm climates you can also use high-efficiency heat pumps for air conditioning.

How Can We Use Solar Energy to Generate High-Temperature Heat and Electricity? Desert Power

Several solar thermal systems can collect and transform radiant energy from the sun into high-temperature thermal energy (heat), which can be used directly or converted to electricity. These systems are used mostly in desert areas with ample sunlight:

  • One method uses a central receiver system, called a power tower. Huge arrays of computer-controlled mirrors called heliostats track the sun and focus sunlight on a central heat collection tower

  • Another approach is a solar thermal plant in which sunlight is collected and focused on arrays of oil-filled pipes running through the middle of a large area of curved solar collectors

  • On an individual scale, inexpensive solar cookers can focus and concentrate sunlight and cook food, especially in rural villages in sunny developing countries. They can be made by fitting an insulated box big enough to hold three or four pots with a transparent, removable top. Solar cookers reduce deforestation for fuelwood and the time and labour needed to collect firewood. They also reduce indoor air pollution from smoky fires.

How Can We Produce Electricity with Solar Cells? Use Your Roof or Windows as a Power Plant

Solar energy can be converted directly into electrical energy by photovoltaic (PV) cells, commonly called solar cells. A typical solar cell is a transparent wafer containing a semiconductor mate- rial with a thickness ranging from less than that of a human hair to a sheet of paper. Sunlight energizes and causes electrons in the semiconductor to flow, creating an electrical current.

The semiconductor material used in solar cells can be made into lightweight paper-thin rigid or flexible sheets and incorporated into traditional-looking roofing materials. Glass walls and windows of buildings can also have built-in solar cells. In 2004, energy giant British Petroleum (BP) began building the world’s largest factory to produce windows and siding and roofing materials that will incorporate BP’s power-producing solar cells.