A minute's worth of sunshine apparently provides enough energy to power the earth's needs for a year. Just walk outside on a sunny day and you can't fail to notice that the sun provides heat and light. These simply observations illustrate two of the main types of solar energy systems in use today, solar thermal and photovoltaics (PV).

Solar thermal

There is a very simple principle behind solar thermal systems. Wearing white or light coloured clothes in the summer is not only fashionable, it's cool. On the other hand, darker coloured materials absorb more light and consequently heat. Solar thermal system use black coloured plates which heat up under the influence of the suns rays. These system fall into two basic category's: either a passive or active.

The simplest example of passive solar heating is drawing open the curtains to let the sun in and heat the room. Slightly more complicated are solar water heating systems, for swimming pools, or domestic water etc. that consist of a collector which transfers the suns heat to water passing thought it.

There are some situations when passive water heating systems require the use of pumps to move the water through the collector, these are known as active systems. Others include collectors (mirrors or parabolic dishes) that move and track the sun.

Some of the active systems can reach temperatures hot enough to smelt iron. Other produce steam that can be used to generate electricity, however the more usual method to do this is with photovoltaics.

Solar heating systems can save money by reducing the costs usually associated with heating. More importantly, they are also environmentally friendly, avoiding the harmful emissions and problems associated with non renewable energy sources.

Photovoltaics (PV)

The term photovoltaics (PV) comes from photo or photons, particles of light, and voltage, a measure of electricity. Quite simply, photovoltaics is generating electricity directly from light. There are several different technologies currently being used to do this. The most common is based on crystals of silicon. Efficiency (the ratio of sunlight converted to electricity) has been steadily increasing with improvements in technology. Typical figures are around 15% and figures of 30% or more are possible but not yet in commercial products.

Other forms of solar energy

With all the technology associated with solar power it's worth remembering that nature utilises solar power, quite literally, every day. The sun is pretty much the source of all forms of renewable energy including wind and hydro. The suns energy is also used by all living things and enables them to grow. The biomass created, such as wood used as a fuel, can therefore be considered a stored form of solar energy. Biomass still constitutes about 15% of the energy used by humans - and that doesn't include the energy gained from eating food etc.

At Steward Wood

Our community utilises solar power in a number of forms: solar thermal, photovoltaics and as biomass. Our dwellings are designed to take advantage of passive solar heating with south facing windows. We also have a number of flat plate solar collectors that we plan to incorporate into our water heating system for the bath house. Additionally we have a small number of PV panels which provide us will a maximum of 40 watts during sunny days. Since our hydro power system does not operate during the dry summer months, the contribution from the solar panels is very welcome. However, it must be said that we are generally not fans of photovoltaics. They appear to us to be an elitist and high technology solution that can not be built or repaired by the likes of us. We are also dubious about he amount of energy used to create them compared to the amount they will produce during their useful lifetime.