Introduction

The current energy level of the Earth, evolving through billions of years, has resulted in a very sensitive equilibrium. In the beginning this equilibrium was only exposed to the power of nature, like volcano eruptions or meteor crashes, already proving that the equilibrium is quite fragile and easy to spoil. At that time the Earth was not much affected by human existence, as people satisfied their heat and energy demands by burning wood and other materials of plant origin, by harnessing natural forces like water, or deploying human and animal power. Forming an integral part of Nature, this equilibrium was preserved and sustained up until the Industrial Revolution.

Industrial Revolution brought a new era of dynamic development, endangering the Earth’s fragile energy equilibrium. The turning point was the increased use of fossil fuels i.e. burning coal, oil and gas. Fossils burnt to generate heat produce noxious by-products, which are released to the atmosphere. One of the most dangerous substances, threatening the balance of Earth, is CO₂. The multiplication of CO₂ emission retains more heat from the Sun in the atmosphere, producing similar effects to a greenhouse. More and more measurement data proves that global warming, caused by greenhouse gases, is a real danger that cannot be neglected. Due to the greenhouse effect, the kinetic energy of the atmosphere and that of the oceans have started to grow, which causes recurrent and devastating hurricanes, thunderstorms and floods. Also recent investigations claim global warming to be responsible for climate change, which tends to be a serious burden to human existence.

If our energy thirst, our constantly increasing demand for heating and cooling and the ever-growing number of automobiles continue to be satisfied with fossil fuels at the current rate, it will cause major difficulties in the future. The use of fossil energy poses two major concerns:

the finiteness of reserves, which has often been declared in the recent past, and

the CO₂ load of the atmosphere that has been neglected for quite a long time.

In the past, the main concern was the exhaustion of reserves, but even today new oil and gas reserves are being discovered, and we have plenty of coal supplies. Practically speaking, it is not the use of fossils, but the emission of greenhouse gases that most threatens human life and well-being.

In order to reduce the emission of greenhouse gases there is a more and more pressing demand to increase the share of renewable energy sources, particularly in those countries which are dependent on large scale import to fulfil their often squandering energy use.

Renewables have recently started to gain importance. In the European Union the total energy consumption of all Member States being derived from renewables is currently 6%. The Member States – in accordance with the Kyoto Protocol - set as a common goal to increase the share of renewables to 12% and to achieve a 15% reduction in greenhouse gas emission by 2010.

If we try to describe the present situation of renewable resources objectively, we find ourselves faced with several difficulties. First of all the term renewable is not universally defined and is often used as a synonym for alternative. While alternative simply means not nuclear or fossil, enabling incineration for instance to be considered an alternative energy, renewable means that a source can be replenished. As terms are generally interchanged, such resources as hydroelectric power and biomass incineration are also frequently taken as renewables. However, not only do the definition of renewables and the resulting approaches vary substantially, but also the statistics, which tend to paint an uncertain picture of the renewable energy situation. In the present discussion alternative will refer to those renewable sources that are considered to be either developing or emerging technologies, not yet widely accepted, or for some reasons under-utilised.