The future is solar
The majority of renewable energy technologies are powered by the sun. The earth-atmosphere system is in such a balance that heat radiation into space is equal to incoming solar radiation; the resulting level of energy within the earths atmosphere can roughly be described as the earth’s climate. The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress. Solar energy is also responsible for the distribution of precipitation which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels.
Renewable and solar thermal energy
Renewable energy flow involves natural phenomena such as sunlight, wind, tides and geothermal heat, as the International Energy Agency (IEA) explains:
“Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources”.
In this context, solar energy refers to energy that is collected from sunlight and can be applied in many ways, including:
- Generate electricity
- Heat and cool air
- Heat buildings
- Heat foodstuffs
- Heat water or air for hot water
Solar water heating or solar hot water is water heated by the use of solar energy. Solar heating systems are generally composed of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage. The system may use electricity for pumping the fluid, and has a reservoir or tank for heat storage and subsequent use. The systems may be used to heat water for a wide variety of uses, including home, business and industrial usage.
In many climates, a solar heating system can provide up to 85% of domestic hot water energy. This can include domestic non-electric concentrating solar thermal systems. In many northern European countries, combined hot water and space heating systems (solar combi systems) are used to provide 15 to 25% of home heating energy.
Residential solar thermal installations can be subdivided into two kinds of systems: compact and pumped systems. Both include an auxiliary energy source (electric heating element or connection to a gas or fuel oil central heating system) that is active to heat the water in the tank when it drops below a certain temperature setting. Hence, hot water is always available. The combination of solar water heating and using the back-up heat from a wood stove chimney to heat water can enable a hot water system to work all year round in cooler climates, without the supplemental heat requirement of a solar water heating system being met with fossil fuels or electricity.
Directives & grants
As fossil fuels become more scarce and environmental issues are daily discussed, globally and within the European Union several environmental and sustainability plans are being created with European leaders committed to increase the share of renewable energy. By 2020 renewable energy should account for 20% of the energy consumption.
Each country has created their own energy policy based on this European agreement combined with their national preferences. The three main objectives in these plans should be, according to the IEA:
- Sustainability: developing competitive renewable sources of energy and other low carbon energy sources and carriers, curbing energy demand within Europe and leading global efforts to stop climate change and improve air quality.
- Competitiveness: ensuring that energy market opening brings benefits to customers and to the economy as a whole, while stimulating investment in clean energy production and energy efficiency.
- Security of supply: tackling the EU’s rising dependence on imported energy through an integrated approach.
These objectives are taken into account in the measures taken in the United Kingdom. The UK Government states: “Although renewable energies are an integral part of our fight against climate change, they also contribute to economic growth, job creation and increase our energy security”. The UK key issues are a green certificate system with an obligation to suppliers to purchase a certain percentage of electricity from renewable energy sources and several incentive programmes. These measures are taken throughout the complete range of renewable energy sources; from electricity production to biofuels and from the production of heat or cold to biomass possibilities. For the production of heat or cold by renewable energy sources several incentive schemes are available.
The awareness is growing amongst everyone. People want to contribute to a cleaner and greener world. Thanks to the efforts of the government renewable solutions are within reach for everyone. In the solar thermal market several suppliers have created systems for various applications and the development of solar thermal products continues.
Currently the solar thermal installations include an auxiliary energy source that is constantly active. Because of the lack in communication in these systems the auxiliary source is the method to ensure the requested water temperature.
A.O. Smith Water Products Company created an energy efficient intelligent controller. This controller regulates the use of the auxiliary energy source. The auxiliary source is only switched on if absolutely necessary. Therefore the gas contribution is minimised and the solar contribution is used very efficiently.
We developed two different solar thermal installations. The SGS is a high efficiency solar gas water heater that should be installed with an indirect tank with integrated heat exchanger. This installation is very suitable for large applications. The SGS is deliverable in capacities varying from 28 to 120 kW combined with an IT indirect tank with a storage capacity of 300 to 3000 litre with integrated heat exchanger. The heat exchanger in the IT transfers the solar energy from the collectors to the water. The intelligent controller mixes the water from the SGS and the IT to create the requested draw off temperature. In this system the extra solar contribution can be as high as 40% compared to standard solar systems.
The SGE is a high efficiency solar gas water heater with integrated heat exchanger for medium sized commercial applications. This installation is available in capacities of 40 to 60 kW and a 370 litre volume. The heat exchanger is situated at the bottom of the SGE and transfers the solar heat to the water. If the sun heats the collector to a temperature exceeding the water in the tank, the exchanger will transfer the heat.
This integrated system solution is a compact installation. The available solar energy is used very efficiently and because of the direct connection via the heat exchanger little energy is wasted.