Many individuals, organizations and institutions are working on the development of renewable energy. Solar is one of the main renewable energy source. Till date the following developments came to light.


1. Photovoltaic:
Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material. Mainstream materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide. Due to the increased demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced considerably in recent years.
Solar photovoltaics is a sustainable energy source. In 2013, its fast-growing capacity increased by 36% to a running total of 136 GW, worldwide. This is sufficient to generate 160 TWh/year or about 0.85% of the electricity demand on the planet. China and Japan are now the fastest growing markets, while Germany remains the world?s largest producer, contributing almost 6% to its national electricity demands.


2. Thermal:
Solar thermal energy (STE) is a technology for harnessing solar energy for thermal energy (heat) requirement in industries, residential sector and commercial setup. Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use.
High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for fulfilling heat requirements up to 300 deg C / 20 bar pressure in industries, and for electric power production. However, there is a term that used for both the applications. Concentrated Solar Thermal (CST) for fulfilling heat requirements in industries and Concentrated Solar Power (CSP) when the heat collected is used for power generation. CST and CSP are not replaceable in terms of application. The 377 MW Ivanpah Solar Power Facility is the largest solar power plant in the world, located in the Mojave Desert of California. Other large solar thermal plants include the SEGS installation (354 MW), also in the Mojave, as well as the Solnova Solar Power Station (150 MW), the Andasol solar power station (150 MW), and Extresol Solar Power Station (100 MW), all in Spain.


3. Solar ponds:
One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy collectors with integral heat storage for supplying thermal energy. It can be used for various applications, such as process heating, water desalination, refrigeration, drying and power generation.
The solar pond works on a very simple principle. It is well-known that water or air is heated they become lighter and rise upward e.g. a hot air balloon. Similarly, in an ordinary pond, the sun?s rays heat the water and the heated water from within the pond rises and reaches the top but loses the heat into the atmosphere. The net result is that the pond water remains at the atmospheric temperature. The solar pond restricts this tendency by dissolving salt in the bottom layer of the pond making it too heavy to rise.


4. Hydrogen:
Photovoltaic panels convert sunlight to electricity. In this cycle, the excess electricity produced after consumption by devices connected to the system, is used to power an electrolyzer. The electrolyzer converts water into hydrogen and oxygen, which is stored. This hydrogen is used up by a fuel cell to produce electricity, which can power the devices when sunlight is unavailable.


5. OTEC:
Ocean thermal energy conversion (OTEC) uses the temperature difference between cooler deep and warmer shallow or surface ocean waters to run a heat engine and produce useful work, usually in the form of electricity. OTEC is a base load electricity generation system, i.e. 24hrs/day all year long. However, the temperature differential is small and this impacts the economic feasibility of ocean thermal energy for electricity generation.
Systems may be either closed-cycle or open-cycle. Closed-cycle engines use working fluids that are typically thought of as refrigerants such as ammonia or R-134a. These fluids have low boiling points, and are therefore suitable for powering the system?s generator to generate electricity. The most commonly used heat cycle for OTEC to date is the Rankine cycle using a low-pressure turbine. Open-cycle engines use vapor from the seawater itself as the working fluid.
OTEC can also supply quantities of cold water as a by-product. This can be used for air conditioning and refrigeration and the nutrient-rich deep ocean water can feed biological technologies. Another by-product is fresh water distilled from the sea.


6. Hydro-thermal:
Hydrothermal energy is the process of obtaining heat or energy from a large body of water. ?Heat?, in this case should not be associated with high temperature but rather a relative heat content or relative temperature difference. The abundance of this renewable energy source was testified by the eminent ocean energy scientist, Hans Krock. ?The energy flowing through the surface layer of the tropical ocean is about 10,000 times greater than the energy used by human societies. As such it is the only energy resource on Earth that is large enough to replace fossil fuel.


7. Solar-powered pump:
A solar-powered pump is a pump running on electricity generated by photovoltaic panels or the thermal energy available from collected sunlight as opposed to grid electricity or diesel run water pumps. The operation of solar powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an
internal combustion engine (ICE). Solar pumps are useful where grid electricity is unavailable and alternative sources (in particular wind) do not provide sufficient energy.