It is believed that by the middle of this century the sun could provide 10% of the UK’s energy needs. Over the course of a year, the sun emits between 900 and 1200 kWh per square meter – hard to believe on a wet and windy winter’s day – and can be used to generate electricity via photovoltaic (PV) panels or hot water with Thermal solar energy. panels
Photovoltaic panels
Photovoltaic panels generate energy from the sun. Without getting too technical, photons of light transfer their energy to electrons in a silicon crystal and generate a direct current with a voltage equivalent to 12V. It is then run through an inverter to make it suitable for 240V circuits.
The panels are ideal for buildings that use a lot of electricity during the day, such as offices, but they should never be viewed in isolation, because the electricity they generate requires expensive batteries to store.
The average photovoltaic panel has an output potential of 1.5 to 2kWp. This is enough to provide around one-fifth of the average household’s annual electricity requirements. However, power production varies seasonally and has an impact on the costs of electrical accessories. In the height of summer, full production may be able to meet all the needs of a building.
There are three types of system available:
Monocrystalline panels are the most effective as they collect around 15% of the total energy potential; the rest is lost in the conversion process; Polycrystalline panels are less efficient, collecting 13% of potential energy; and Only 7% thin film amorphous silicon panels, only really viable in buildings with a large roof span.
As long as the panel is placed on the same slope as the roof and does not protrude too far from the roof profile, planning permission must be granted. However, it is worth checking a local authority’s record on these issues.
Once installed, barring occasional cleaning, there are no operating or maintenance costs and the panels should last 30+ years.
Until now, the acceptance of photovoltaic panels has been low. This is largely because the payback period can be very long, anywhere from 60 to 120 years, as the UK power industry pays a very low rate for power sold to the grid.
Elsewhere in Europe, some countries require electricity to be purchased at triple the rate paid for it, significantly reducing payback times and increasing panel adoption.
Thermal Solar Panels
In Europe, the solar heating market grew by 18% in 2005. By 2010, the UK is expected to have 25,000 new domestic solar water heating installations, rising to 75,000 by 2020.
Solar water heating systems collect the energy radiated by the sun and convert it into useful heat in the form of hot water. Since hot water requirements are minimal in offices, its main use is in domestic developments where it can provide almost all of a property’s hot water during the summer months and around 50% throughout the year, according to the Energy Saving Trust. . It can also reduce CO2 emissions by between 0.4 and 0.75 tons per year, depending on the fuel replaced.
There are two types of systems available. Flat plates are the most economical and least efficient option. These glazed panels, usually rectangular in shape, work best on hot days and use a metal absorber plate, which is in contact with the water pipes.
Vacuum tubes are more efficient and therefore more expensive. Its energy is derived from light, which enters a ‘vacuum flask’ type of glass tube and is converted to heat in the water through contact with an absorbent such as black paint.
Both systems pump the heated water (mixed with antifreeze) through heat exchangers that are connected to hot water tanks.
The panels vary in size from 0.7 m² to 8 m²; vacuum tubes typically take up less space. Most manufacturers will typically suggest that one panel will provide a home with two-thirds of its annual hot water needs.
Flat plate panels are expected to last 10-25 years and vacuum tubes 20-35 years. Payback is normally about 10 years.
