-- Conventional: these are the fossil fuels of Coal, oil and natural gas some may consider nuclear "conventional".
-- Alternative: these are everything other than fossil fuels. Nuclear is likely an alternative fuel.
-- Renewable: These are sources that are alternative but also can be renewed in a reasonable time-frame. Nuclear would not be considered a renewable fuel. Within the idea of renewable is some suggestion of "natural" or "biological" or "recurring." Bio-gas, sunlight, wind, wood and dung are likely renewable while peat which takes hundreds of years is likely not a renewable sources of fuel. Wood found in a desert from an ancient forest is not a renewable fuel.
While tides and waves are likely renewable, geothermal energy stretches our understanding. Most geothermal sources are slowly getting cooler. They don't "renew" but can be expected to last for a very long time. Solar energy is similar but lasts for an even much longer time.
-- Sustainable: Considers more than simply the the fuel is renewable. Wood is renewable. A wood lot as a fuel source would be sustainable for a family but not for a city. Sustainable takes into consideration usage.
There is another term: "Green" which would be the most restrictive and implies that the product or fuel does not harm to humans or the environment. A wood fire inside a house that filled the home with smoke would probably not be considered "green," but neither would an electric stove that resulted from a polluting manufacturing and transportation process. "Green" takes into consideration the manufacture of products.
"Green" and to a more limited extent "sustainable" are the only terms that begin to consider the harm from externalities of pollution. These are not exact, scientific terms and they tend to not be used in an exact or perfectly consistent way. What is probably more important than the terms is the different considerations we can have for fuels.
The first thing that comes to my mind is solar energy or sunlight. I've always felt enough is not being done here. We have to come together collectively to figure how to use this renewable source of energy for the good of mankind. Sunlight can be used for electricity, for heating, for cooling and I'm sure a whole host of other things that I'm not familiar with.
Sea water is another renewable source of energy or at least oceans with their constant and powerful waves can help in generating electricity.
Natural wind is another potential source of renewable energy. But I'd have to really understand a lot more here.
Renewable resource of energy is the natural resource which can refill through the passage of time. The examples for renewable resources are sun, wind, water, etc. and the non renewable resources are fossil fuels. The energy generated from the sun is called solar energy. The hydel is the energy is derived from the water. And the energy of the wind also used to generate electricity. Energy from ocean waves and tides can be harnessed to generate electricity. These are some of the renewable energy resources.
Renewable sources of energy are those energy which do not get exhausted and can be found in the nature and surroundings such as solar energy from sunlight, tides, waves, wind, rain, etc.
Renewable energy is energy that comes from resources which are continually replenished such as sunlight, wind, rain, tides, waves and geothermal heat
