Renewable energy derives from natural resources such as sunlight, wind, rain, tides and geothermal heat, which are naturally replenished. These sources are directly or indirectly powered by the sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation, the resulting level of energy within the Earth-Atmosphere system 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 energy flows involve natural phenomena such as sunlight, wind, tides and geothermal heat, as the International Energy Agency 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."
Each of these sources has unique characteristics which influence how and where they are used.

Renewable Energy Technologies are technologies that have the capacity to exploit renewable energy resources-such as wind, solar, geothermal, biomass etc. - that are constantly replenished and never run out, and turn them to power, thermal or mechanical energy.

Energy Efficiency Technologies are technologies aiming to increase the efficiency in energy use, i.e. increase energy savings and decrease environmental pollution and CO2 emissions. The spectrum of application of these technologies is rather enhanced. They include building fabrics, engine technologies, transmission technologies, heating and cooling, lighting as well as integrated energy management approaches, i.e. plant maintenance, energy use monitoring, staff awareness-suggestions and competitions, etc.

Within the scope of the FINA-RET project, as small-scale RET and EE technologies application are considered renewables energy technologies and energy efficiency technologies, which have an application in individual households, farms and SMEs (including industrial applications) or even small cities and villages, where the energy produced is mainly consumed locally within the confines of the generating facility (i.e. within the farm, enterprise, household or the vicinity of the small town or village).