Every year, the sun irradiates the land masses on earth with the equivalent of 19,000 billion tons of oil equivalent (toe). Only a fraction — 9 billion toe — would satisfy the world's current energy requirements. Put differently, in 20 minutes, the amount of solar energy falling on the earth could power the planet for one year.
Solar energy comes to us as high intensity radiation (light energy). As it falls on the earth, it is transformed into heat by any surface or material — be it the atmosphere, soil, buildings, or even the furniture in front of a window. This heat also drives the world's weather systems including wind, rain and river flow. Through photosynthesis, plants also turn solar energy into new growth.
So, in fact, all energy originates with the sun except for nuclear, geothermal and tidal energy.
Capturing and Using Solar Energy
Solar energy is collected in three ways:
- Passive Solar
Measures used to trap and store solar energy inside buildings are called passive solar techniques, and have been used for centuries as a source of heat. Recent innovations include low-emissivity (low-E) energy efficient windows to trap more energy, and the strategic placement of ceramic or concrete floors, walls, etc. to store more energy.
By designing a home to maximize its use of passive solar (i.e. the sun’s free heat), the annual costs to heat a home can be reduced by up to 50%. Simply positioning homes to take advantage of southern exposures can reduce home heating costs by 5%.
Solar Heat Collectors
Solar energy can also be "collected" as heat. Solar collectors absorb the solar radiation falling on them or focus this energy onto smaller areas — thereby raising the intensity or temperature of the energy. Solar heat collectors are used for water and space heating and cooling and power production using air, water, steam or thermal fluids to transfer the heat to the location where it is used.
- Flat plate collectors consist of a series of pipes set into a flat copper or other metallic plate under a glass cover in an insulated box. The glass cover traps the heat produced when the solar radiation falls on the plate, and the heat is transferred to the fluid in the pipes.
For higher temperatures, evacuated tube are more effective. These collectors consist of a series of finned tubes encased in separate glass vacuum tubes. The vacuum prevents heat loss and allows more heat to be transferred to the circulating fluid. For even higher temperatures, reflectors are used to focus the solar radiation onto the tubes.
Solar water heating systems are the oldest application of solar energy and first appeared during the early 1900s. Year-round operation in colder countries like Canada is achieved by circulating an antifreeze fluid through the collectors and transferring the heat to hot water using a heat exchanger. Solar water heating systems are now common in many countries including China, Australia, Kenya, Egypt, Barbados, Germany and Spain.
China is the largest solar market in the world with over 10,000 solar manufacturers. Canada, in comparison, has only four solar manufacturers. In Austria, one out of every seven homeowners now uses solar to heat their hot water. The village of Gleusdorf in southern Austria — population 35,000 — has a greater installed capacity for solar heating than all of Canada. Canada did have a thriving solar water heater industry in the 1980s, and environmental concerns and rising conventional fuel prices are generating a renaissance of this industry.
Solar wall air heaters were developed in Canada in the 1980s and are used mainly for pre-heating ventilation air in large open buildings and warehouses. Air is drawn through holes or channels in a black metal collector where it picks up heat, and is then drawn into the building. A glass cover may be used to increase effectiveness.
Solar thermal power systems use solar heat energy concentrated using mirrors to drive steam turbines that generate electricity. This application of solar energy is relatively new but is growing rapidly in several countries, especially in desert areas where solar energy levels and land availability are high.
- Solar cooling systems use high temperature heat from evacuated tube collectors to drive an adsorption cooling system that would normally powered by natural gas.
3. Solar Photovoltaic (PV) Collectors
Solar electricity collectors use the photovoltaic principle to convert sunlight directly into direct current (DC) electricity. A solar PV collector or module consists of several individual PV cells wired together in a protective container. Modules may be linked in any numbers to provide small or large amounts of power. The most common materials used for PV cells is semi-conductor crystalline silicon or quartz. Silicon in the form of sand and quartz is one of the most common elements found on earth. Other materials used include amorphous silicon, cadmium telluride or copper indium di-selenide that are manufactured into thin films and incorporated into modules.
The PV cell industry is rapidly changing with new manufacturing techniques being introduced that will significantly decrease costs. Solar PV collectors were first developed for satellite applications. They then became the technology of choice for remote power applications such as radio towers and lighthouses, and for home lighting and other power needs in developing countries. In each of these applications, batteries are used to store power. Solar PV is now being used to supply the grid using inverters to convert the DC output to AC power. Large-scale stand alone PV power plants are now being built in several countries including the United States, Spain and Portugal, while smaller roof-mounted systems are now common place in California and many EU countries thanks to special tariffs and incentive polices. Germany — the world leader in solar electricity — installed over 600 MW last year, while Canada installed less than 2MW.
- After initial capital costs are paid, the energy from the sun is virtually free.
- The sun's energy is unlimited and available everywhere in the world.
- Solar is very flexible and modular. It can provide energy on its own, connected to a grid or jointly with other energy sources.
- Solar can meet a wide range of applications for heat and power and provides an excellent match with summer energy demands.
- Solar systems have few moving parts, are clean to use, use commonly available materials, and provide users with more control over their energy systems.
- Solar energy is not always available. Therefore, to be really effective as a continuous source of energy it needs to be stored and integrated with other renewable energy sources.
- All the costs of a solar energy system are required upfront. This means that innovative financing is needed to spread this cost over several years so that capital costs can be paid for out of the income or savings received.
- The cost of a solar energy systems generally does not reflect many of the environmental and peak saving benefits provided by solar.
- The cost of solar systems that generate electricity are coming down rapidly as new manufacturing techniques are introduced, but financial incentives from government will be required for several years to develop a competitive market.
- Some jurisdictions in Canada have not updated their policies to make it affordable for small power producers to connect to the electricity grid.
- Rapid investment in PV cell manufacturing recently outstripped the supply of metallic grade silicon in some countries. This was a temporary problem as silicon is one of the most common elements. New investment and recycling of computer grade silicon by the industry has redressed the problem.
Global Status and Potential
According to the World Watch Institutes's Renewable 2005 report, the fastest growing energy technology is grid-connected solar PV, which grew in existing capacity by 60% per year from 2000—2004. There are more than 400,000 homes in Japan, Germany and the United States that have rooftop solar PV. Global solar PV cell production is expected to climb to over 5 gigawatts per year by 2010 spurred by new initiatives in the United States, Germany, Japan and Spain.
Canadian Status and Potential
Canada ranks 14th of 20 reporting International Energy Association (IEA) countries in deployment of PV and ranks 17th of 22 reporting countries for solar thermal.
In 2001, Canada's public budget for PV was only $0.10 per capita, placing us 16th of the 17 IEA reporting nations. Our governments invest only 16% of the international average and lag significantly behind Japan and Germany, the solar leaders.
Ontario has become the first Canadian province to introduce mandatory premium prices for electricity fed into the grid from solar PV systems. This should provide a major boost to the solar industry in Canada.
Links for more information
- American Council on Renewable Energy (ACORE)
- American Solar Energy Society
- Canadian Association for Renewable Energies
- Canadian Solar Industries Association
- Solar Buildings Research Network
- Solar Energy International
- Solar Energy Society of Canada
- Canadian Renewable Energy Network: Solar
- Pollution Probe's Primer on the Technologies of Renewable Energy
- Renewable Energy World — Fundamentals of Photovoltaic Systems
- RETScreen — Solar Air Heating / Water Heating and Passive Solar Heating: pre-feasibility assessment and instructional modules
- World Energy Council: Solar