Geothermal energy.

Using the heat under your feet!

Geothermal energy is the natural heat of the earth. This energy source is exploited in the U.S. and Northern Europe. In the U.S tens of thousands of homes use this technology for heating or cooling systems. These systems offer a significant cost saving over conventional technologies. Geothermal pumps use the earth as a heat source/sink. The plant itself has few moving parts and doesn't clag up in use as when burning fuel so is generally much lower maintenance and longer life than conventional systems Another type of geothermal energy is caried out with large scale heat and power plant, drilling down to hot rock and circulating water which is superheated by the rock, turbines can then be driven by this water and electricity is generated.

Energy from Waste

Municipal and agri waste can be incinerated or biologically digested to produce energy; biogas, electricity and heat. This is a viable alternative to landfill. Local community opposition in the case of incinerators (which produce electricity.) is common as people rightly fear lax regulation of emission controls resulting in yet more pollution, this however is not necessarily the case. The burning of plastics in such plant can actually result in a better burn and consequently lower CO and SO2 emissions. The production of biogas from landfill waste is a commercial reality. Energy from Biomass. The burning of waste agricultural materials (straw, cow slurry, etc.) to produce electricity and the growing of fuel crops (oil seed rape, willow, etc.) are examples of Biomass.

Solar thermal

This info is a little out of date but as an introduction to the subject it's not a bad read. Here's a couple of interesting developments, in the large scale solar thermal electric field. At the Australian National University there stands an experimental solar thermal dish, the largest of it's type in the world, it has an area of 400m2. The dish works by concentrating solar energy onto a water pipe in the centre, which heats up to make steam and drive a turbine, the efficiency of the design is said to be capable of outperforming photovoltaics for large scale electrical generation, and those involved should now have built an experimental power station at Tennant Creek Farm, in the Northern Territories. There is also an Israeli/Belgian company, Solel, who make a similar solar thermal trough array system, they have experience in developing large scale solar thermal plant in California (in the hundreds of megawatts total.) and are planning to provide plant for the Sydney Olympics 2000. These systems supply half of all global solar capacity. The system design consists of an array of troughs each about 100m in length, which rotate to follow the suns course, the troughs are parabolic mirrors which reflect onto an oil filled pipe, the oil contained within the pipe is heated to 390c, and converts through a heat exchanger to superheated steam which drives a turbine. Efficiency gains are sought by replacing the oil with water and it's reckoned that pretty soon now this plant will compete directly with coal fired plant. The performance is poor in winter and suited best to hot, dry (places where people don't live.) areas. More gains are to be made by orienting the troughs in different ways and improving the composition and shape of the heat tube. The big dish is reckoned to be a cheaper proposition, as it heats up more effectively and doesn't need a hybrid (gas) complement to get the steam hot enough for a turbine. It can also tilt in two directions making for better tracking.