Renewable energy comes from sources that are essentially inexhaustible, using modern technology to harness that energy, such as wind turbines, hydro-electric, offshore wind and wave power, solar energy or photovoltaics, geothermal technology, fast growing trees and other 'energy crops', animal waste to produce methane and the burning of biomass (wood) to produce energy.
Today renewable energy accounts for less than 4% of the UK's energy sources. The majority coming from burning fossil fuels (for example coal, oil and gas) and nuclear energy. However, fossil fuels form so slowly in comparison with the rate of energy use, that they are considered finite or limited resources. Moreover, the burning of fossil fuels produces greenhouse gasses and other pollutants linked to changes in the Earth's climate.
Renewable energy, on the other hand, generally produces few or no greenhouse gases and reduces our dependence on non-replenishable resources.

On the Trail... 
Solar hot water systems - The Environment Centre, St John's Church and the Blackpill Wildlife Centre all have hot water heated by the sun. You can try the outdoor shower at the Blackpill Wildlife Centre, next to Blackpill Lido in the summer months. 

Photo Voltaics (PV) - The Environment Centre uses PV panels to generate electricity to power the ventilation system for the whole eco-annexe building. You can see the panels by visiting the turf roof at the Centre.

Biomass - Biomass is organic matter of recent origin. It doesn't include fossil fuels, which have taken millions of years to evolve. The CO2 released when energy is generated from biomass is balanced by that absorbed during the fuel's production. We call this a carbon neutral process. Singleton Botanic Gardens uses wood chip to burn to generate heat which keeps the tender plants in the greenhouses at the right temperature.
As the pressure to find alternatives to fossil fuels increases, more and more resources are being put into researching alternatives such as tidal and wave power.