Solar: Solar energy is the radiant light and heat from the sun that has been harnessed by humans since ancient times utilizing a range of ever-evolving technologies. In the not-too-distant past, solar water heaters prevailed all over the United States. We all use solar energy daily. We hang our laundry under the sun, using the heat from it to dry the clothes. Using photosynthesis, green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.

There is no debate that solar energy is the most abundant energy at present. Research shows that the total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. There is more energy generated in one hour than the world uses in one year.

Applications of Solar Energy: Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight as energy. Active solar techniques use photovoltaic panels, pumps and fans to convert sunlight into useful outputs. Therefore, the use of active solar energy requires additional support from other types of technologies. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air and referencing the position of a building to the Sun. The term "passive" indicates that no additional mechanical equipment is used, other than the normal building elements (i.e. positions and designs). All solar gains are brought in through windows and minimum use is made of pumps or fans to distribute heat or effect cooling.

Architecture: Taking advantage of the sunlight to absorb heat has impacted building design since the beginning of history. It was first employed by the Chinese and Greeks, who constructed their buildings facing toward the south for maximum exposure to sunlight.

Heating & Cooling Systems: Solar heating designs collect and store thermal energy from direct sunlight. Thermal mass is any material that can be used to store heat from the sun. These materials include water, stone or cement. Thermal mass has been used in warm regions to keep buildings cool during the day by absorbing solar energy and preserving the heat to maintain warmth at night. It has also been employed in colder areas to heat the atmosphere. This way of utilizing solar energy with minimum support of additional technology is considered passive solar energy. In addition to thermal mass, passive solar heating of buildings also occurs when sunlight passes through a window, hits an object, is absorbed, and converted to heat. The most efficient window orientation for heat gain is due south. All passive techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation.
Passive cooling minimizes the effects of solar radiation through shading or generating air flows with convection ventilation, or, as mentioned above, by using thermal mass to prevent the heat from reaching the building. External solar radiation can be prevented by shading devices. These can reduce solar gains up to 90%, but still provide necessary amount of indirect sunlight. The heat can also be reduced by applying reflective wall or roof materials and appropriately adjusting the window size.