 Environmental pollution is a serious issue and it is important to take steps on an individual level to reduce it. But now, since it is becoming an international issue, it is time to take environment protection to higher level  Renewable energy is fundamental in stopping environmental pollution and in providing an alternative to conventional energy resources that are each day less. As long as fossil fuels remain dominant sources of energy we will not be able to stop the ever-growing pollution that is happening almost everywhere in our planet.

 The solar resource is enormous compared to our energy needs. It can be captured and transformed into heat or electricity. It varies in quantity and quality in places but also in time, in ways that are not entirely predictable. Its main components are direct and diffuse irradiance.  It takes the sun one hour and 25 minutes to send us the amount of energy we currently consume in a year, or a little more than 4.5 hours to send the same amount of energy only on land.  While proven fossil reserves represent 46 years (oil), 58 years (natural gas) and almost 150 years (coal) of consumption at current rates the energy received by the sun in one single year, if entirely captured and stored, would represent more than years of total energy consumption.

 Photovoltaic (PV) cells are semiconductor devices that enable photons to “knock” electrons out of a molecular lattice, leaving a freed electron and “hole” pair which diffuse in an electric field to separate contacts, generating direct current (DC) electricity.  Photovoltaic cells are interconnected to form PV modules with a power capacity of up to several hundred watts. Photovoltaic modules are then combined to form PV systems.

 Crystalline silicon technologies– single- crystalline (sc-Si) or multicrystalline (mc-Si) – currently dominate the market with an 85% share.  Crystalline silicon (c-Si) solar cells are currently the most common solar cells in use mainly because c-Si is stable, it delivers efficiencies in the range of 15% to 25%, it relies on established process technologies with an enormous database, and, in general, it has proven to be reliable.

 Thin films are made from semi-conductors deposited in thin layers on a low-cost backing.  There are four main thin-film categories: amorphous (a-Si) with efficiencies from 4% to 8%; multi-junction thin silicon films (a-Si/ μc-Si), made of an a-Si cell with additional layers of a-Si and micro-crystalline silicon (μc-Si) with efficiencies up to 10%; cadmium-telluride (CdTe) with efficiency of 11%; and copper-indium-(di)selenide (CIS) and copper- indium-gallium-(di)selenide (CIGS), with efficiencies from 7% to 12%.

 To maximise the energy efficiency per surface area of receiving panels, manufacturers now offer hybrid systems, which collect electricity from the PV effect and heat simultaneously thereby adding the efficiency of PV to that of heat collectors, reaching a cogeneration efficiency of 80% or more.

 Organic solar cells are either full organic cells (OPV) or hybrid dye-sensitised solar cells (DSSC). They have lower efficiencies and shorter life-times, but can be made using roll-to-roll and usual printing technologies, which could lead to very low manufacturing costs.

Full organic cells (OPV) Dye-sensitised solar cells (DSSC)

 Using mirrors or lenses or a combination of both, concentrating PV (CPV) focuses the solar radiation on small, high-efficiency cells usually made of several layers (often called “tandem” or “sandwich”) each capturing a specific wavelength of the solar light spectrum.

Light-emitting diodes (LED)

 LEDs create light by electroluminescence in a semiconductor material. Electroluminescence is the phenomenon of a material emitting light when electric current or an electric field is passed through it - this happens when electrons are sent through the material and fill electron holes. An electron hole exists where an atom lacks electrons (negatively charged) and therefore has a positive charge.  Semiconductor materials like germanium or silicon can be "doped" to create and control the number of electron holes. Doping is the adding of other elements to the semiconductor material to change its properties. By doping a semiconductor you can make two separate types of semiconductors in the same crystal. The boundary between the two types is called a p-n junction. The junction only allows current to pass through it one way, this is why they are used as diodes. LEDs are made using p-n junctions. As electrons pass through one crystal to the other they fill electron holes. They emit photons (light).

LED LIGHTING TECHNOLOGY TRADITIONAL LIGHTING TECHNOLOGY  Innovation driven lighting systems  Flexible applications  Energy saving fixtures  Environmentally friendly tech  Long life span  Maintenance free  High quality of the light  Integrated control systems  Medium class costs  Shorter life span  Maintenance needed  Pollution generators  IR and UV radiations emitters  No flexibility in the applications  Lower chromatic rendering resulting in lower quality of the light

 The sun offers mankind virtually unlimited energy potential. Only wind power comes close, only biomass is equally versatile. Solar energy can be tapped in many ways, which should be combined to best fulfill the energy needs of the global population and economy. Because it is available all over the planet, it can provide faster access to modern energy services for the disadvantaged communities in rural areas with low population densities.  The benefits of LEDs are their long lifetime, color- mixing possibilities, spectrum, design flexibility and small size, easy control, and dimming. For LEDs huge technological development is expected to continue.