When we talk about solar energy we can be referring to one of two systems. Concentrating solar thermal panels (CSP) use light to create heat and steam to drive turbines and solar photovoltaic (PV) power which generates electricity directly from the sunlight. During operation solar power emits no noise, greenhouse gases or other chemicals. There are no moving parts except for the systems that track the sun to concentrate the flow of sunlight.
Solar thermal power systems are most commonly used as the source of solar water systems or can run air conditioners (HVAC). Infra-red radiation is used to heat water to around 60 degrees Celsius at which point thermal efficiency drops off to avoid overheating. Standard solar panels can heat water to around 3 times the maximum temperature for the day while special titanium panels can achieve heating of up to 4 times the maximum temperature. Alternatively, solar thermal generators use reflectors to collect heat energy to make steam which drives a turbine that produces electricity.
Photovoltaics (PV) or solar cells operate by means of two layers of semiconductor. When light falls on the solar cells they create an electronic reaction by electrons getting knocked loose from the atoms in the semiconductor material. The voltage produced can drive a current with one side of the cell getting a negative charge and the other getting a positive charge. When a circuit connects the two side, an electric change is formed.
When you connect a number of solar cells electrically to each other and mount them in a frame you have what is called a photovoltaic module. These modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module.
The Case for Solar Energy
Small units can be installed in domestic homes to supply a proportion of the household electricity needs.
Solar cells, once installed do not produce any carbon emissions at all and costs nothing to run. In fact, if more electricity is produced than is required, you can sell the excess back to the power company.
The Case Against Solar Energy
Depending on who you listen to or what you read, the main problems with solar energy may either be that there is not enough solar power being produced or there is too much solar power being produced.
Not enough solar power is produced at the global level at this stage to power a high proportion of the population. While it can supply a certain level of electricity coverage it has to be subsidized by fossil-fuel produced electricity.
Some countries have reported that there is currently too much solar power being produced for their local grids to keep up. This requires an increase in the installation of electricity utilities to keep up with the increase in supply.
Intermittency is perceived as a problem. For domestically installed systems this would be true for prolonged cloudy days, forcing the house power to cut over to the grid.
The Cost of Solar Energy
A residential solar energy system typically costs around $8-$10 per Watt. Government incentives exist from country to country which will help bring these costs down even further. Solar Energy (PV) prices have been falling at around 4% per year over the past 15 years and this is expected to continue in the near future.
To put the price in terms of price per kWh, solar electricity costs around 30 cents/kWh which is around 2 – 5 times the average price of most residential tariffs.
Solar Energy Use By the Numbers
Photovoltaic solar energy still only accounts for less than 0.01% of the global energy source, although it has been increasing rapidly for the last 10 years. In 2006 PV capacity reached a record high of 1,744 megawatts (MW) which represented growth of 19% over the previous year. This is still an industry that is relative infancy when you consider that in 1985 annual solar installation demand stood at 21 MW.
Germany accounted for a 55% share of grid connected solar production with Japan maintaining a 17% share with barely any growth for the year. In 2006, the strongest growth was exhibited by Spain with over 200% increase and the US which increased by 33%.
These figures have been taken from the Solarbuzz MarketBuzz 2007 Industry Report