Solar Power
Solar energy can be captured by solar panels, which absorb the energy from the sun and transfer it to heat water. Solar Power water heating systems are the most popular form of solar energy used, and can provide over half of a household's hot water requirements over the year. Flat plate and evacuated tubes are the two types of solar water heating collector.

More information can be found here and here.

Wind Power - Wind Turbines
Wind Power has been used for centuries to produce mechanical power for milling and pumping water. In recent years wind turbine technology harnesses wind to produce electricity. Wind power is one of the safest and cleanest methods of generating electricity, and can be found in both offshore and onshore wind farms. More information can be found here and here.

Location of Wind farms in Ireland - from SEI.

Geothermal - Ground Source Heat Pumps
When the sun shines on the ground, heat energy is absorbed. Ground source heat pumps extract this energy to use for space heating. The energy source that is used for ground source heat pumps is the sun and not the heat from the earth, though it is absorbed from the earth.

More information can be found here.

Hydropower - Water Wheels
The energy potential of moving water has been harnessed for thousands of years, originally using water wheels to drive mills and machinery. While most hydro power comes from large projects, smaller implementations are possible. Currently, 6% of Ireland's power comes from hydro power plants. Further information can be found here and here.

Small Scale Hydro Power - from SEI.

Biofuel and Biomass - Wood fuel/pellets burning stoves/boilers
Biofuel and biomass include pupre plant oil, biodiesel, and bioethanol, as well as logs, wood chip and wood pellets.

Biomass is part of the carbon cycle. Carbon from the atmosphere is converted into biological matter by photosynthesis. On death or combustion the carbon goes back into the atmosphere as carbon dioxide (CO2). This happens over a relatively short timescale and plant matter used as a fuel can be constantly replaced by planting for new growth. Therefore a reasonably stable level of atmospheric carbon results from its use as a fuel. It is accepted that the amount of carbon stored in dry wood is approximately 50% by weight.

For more information on biomass and biofuels, SEI has a number of documents available for download. This Wikipedia article also has a lot of useful information and links.