Renewable energy resources that are commonly used for construction applications include solar, wind, geothermal and biomass energy. Strictly speaking, energy storage systems are not a renewable source. However, the ability to store electricity for later use is very useful in many applications. This common type of renewable energy is typically produced by photovoltaic cells that capture sunlight and convert it into electricity.
Solar energy is also used to heat buildings and to obtain hot water, as well as for cooking and lighting. Solar energy has become affordable enough to be used for domestic purposes, including garden lighting, although it is also used on a larger scale to supply energy to entire neighborhoods. Currently, wind farms are considered to be the most efficient source of green energy, since they require less refining and processing than the production of, for example, solar panels. The prevalence of green buildings is increasing around the world, something that both customer demand and government policies encourage and often even demand.
The use of a building shape and housing to accept, store and distribute energy from renewable sources appropriate to buildings is commonly defined as passive solar design. Shading, reflection of solar heat, insulation of the building element, floor cooling, wind cooling, water cooling, evaporative cooling, dehumidification, night radiant cooling, nighttime cooling of the thermal mass of buildings, exotic methods of passive cooling and seasonal cold storage. Other factors also favor green energy, such as the ability to produce relatively cheap localized energy solutions, such as solar farms. Among all renewable sources, solar energy is the least demanding in terms of site conditions, making it the most viable option for most buildings.
With design applications for passive solar systems, solar heat gains from solar energy can be increased during the winter months. Green energy solutions are used in buildings that range from large office blocks to people's homes. The fundamental concept of using solar energy for heating is to design the elements that shape the exterior of the building for this purpose (the roof, walls and floor are insulated at a high level) and allowing the maximum possible use of solar radiation. By converting solar radiation into thermal energy with collectors, solar heating systems can heat water, air, etc.
Active solar systems are distinguished from passive systems, which use the structure of the building, in terms of collecting solar energy, storing accumulated heat and distributing heat to spaces. As an energy source, green energy often comes from renewable energy technologies such as solar energy, wind energy, geothermal energy, biomass, and hydropower.