Solar (Thermo-solar)

Photovoltaic (PV) devices generate electricity directly from sunlight via an electronic process that occurs naturally in certain types of material, called semiconductors. Electrons in these materials are freed by solar energy and can be induced to travel through an electrical circuit, powering electrical devices or sending electricity to the grid.

 

Photovoltaic cells have been developed that will provide electrical power to pump drinking water from wells in remote villages. British Telecom have developed a system that can be used to power a radio telephone system. During the day the cells power the phone and also charge batteries. The batteries power the phone during the night. Often photovoltaic cells are used as a backup to conventional energy. If conventional fails the cells are used to produce electricity.

 

Hydraulic Energy is what is produced by the water which is stored in  reservoirs and lakes at a high altitude (so that it has gravitational potential energy). If at a given moment it falls to a lower level, this energy is transformed into kinetic energy and afterwards into electrical energy in the hydroelectric plant.

 

Advantages: it is a clean energy source, without waste products and is easy to store. Also the water stored in reservoirs situated at altitude permits the regulation of the flow of the river.

 

Disadvantages: the construction of hydroelectric plants is expensive and needs  large  networks of power cables. Reservoirs also mean the loss of productive soil and fauna due to the flooding of their habitat. They also cause a decrease in the  flow of the rivers and streams below the dam and alter the quality of the waters. The following animation shows how hydraulic energy is stored and exploited.

 

Geothermal Energy comes from the heat within the earth. The word "geothermal" comes from the Greek words geo, meaning earth," and therme, meaning "heat." People around the world use geothermal energy to produce electricity, to heat buildings and greenhouses, and for other purposes.

The earth's core lies almost 4,000 miles beneath the earth's surface. The double-layered core is made up of very hot molten iron surrounding a solid iron center. Estimates of the temperature of the core range from 5,000 to 11,000 degrees Fahrenheit (F). Heat is continuously produced within the earth by the slow decay of radioactive particles that is natural in all rocks.

Surrounding the earth's core is the mantle, thought to be partly rock and partly magma. The mantle is about 1,800 miles thick. The outermost layer of the earth, the insulating crust, is not one continuous sheet of rock, like the shell of an egg, but is broken into pieces called plates. These slabs of continents and ocean floor drift apart and push against each other at the rate of about one inch per year in a process called continental drift.

Magma (molten rock) may come quite close to the surface where the crust has been thinned, faulted, or fractured by plate tectonics. When this near-surface heat is transferred to water, a usable form of geother- energy is created.

Geothermal energy is called a renewable energy source because the water is replenished by rainfall, and the heat is continuously produced by the earth.

 

Biomass is biological material derived from living, or recently living organisms. In the context of biomass for energy this is often used to mean plant based material, but biomass can equally apply to both animal and vegetable derived material.

 

Chemical composition

 

Biomass is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms, including alkali, alkaline earth and heavy metals.  These metals are often found in functional molecules such as the porphyrins which include chlorophyll which contains magnesium.

 

Plant material

 

The carbon used to construct biomass is absorbed from the atmosphere as carbon dioxide (CO2) by plant life, using energy from the sun.

 

Plants may subsequently be eaten by animals and thus converted into animal biomass. However the primary absorption is performed by plants.

 

If plant material is not eaten it is generally either broken down by micro-organisms or burned:

 

If broken down it releases the carbon back to the atmosphere, mainly as either carbon dioxide (CO2) or methane (CH4), depending upon the conditions and processes involved.

If burned the carbon is returned to the atmosphere as CO2.

These processes have happened for as long as there have been plants on Earth and is part of what is known as the carbon cycle.

 

Categories of biomass materials

 

Within this definition, biomass for energy can include a wide range of materials.

 

The realities of the economics mean that high value material for which there is an alternative market, such as good quality, large timber, are very unlikely to become available for energy applications.  However there are huge resources of residues, co-products and waste that exist in the UK which could potentially become available, in quantity, at relatively low cost, or even negative cost where there is currently a requirement to pay for disposal.

 

There are five basic categories of material:

 

• Virgin wood, from forestry, arboricultural activities or from wood processing

• Energy crops: high yield crops grown specifically for energy applications

• Agricultural residues: residues from agriculture harvesting or processing

• Food waste, from food and drink manufacture, preparation and processing, and post-consumer waste

• Industrial waste and co-products from manufacturing and industrial processes.