Outlined below is an extensive guide on how solar energy works. see also How solar panels work

Available sunlight, Radiation

The rays from the sun (both direct and diffuse) supply the earth with an enormous amount of energy. On average, some 1700 kWh per square metre are beamed to earth each year.

Solar cells convert the sun’s energy into electricity. Aiming the cells directly at the sun means they receive maximum solar radiation. The efficiency of a PV system depends on this orientation and the angle at which the cell is set. Radiation is usually expressed as a percentage of the maximum feasible radiation that can be achieved when the system is unhindered, orientation is optimal and the cells are adjusted to the best possible angle. In the Netherlands, for example, the optimum orientation is south, at a tilt angle of 36° to the horizontal.

Obstructions and shadows

In order to generate maximum results from a PV installation it is important that obstructions and shadows be reduced as much as possible. Depending on the situation and the electrical coupling, a limited solar cell obstruction can cause an entire series of solar cells to be switched off. One cell in the shadow can block the total throughput of electrons. As well as efficiency losses, shadowing can also lead to damage, e.g. a thermal break. It is important to remember that all objects in the surrounding areas, even if their shadows do not fall on the PV system, can still block out the diffuse components of daylight.

Solar Panels and town-planning

The town-planning proposals must therefore meet a number of irradiation conditions. The irradiation loss as a result of non-optimised orientation and tilt angle should be less than 5%. Given a maximum permitted irradiation loss of 5% (in an otherwise optimally oriented system) and a tilt angle of 36°, then it is easy to calculate that the obstruction angle must be less than 12°. With a roof angle of 30° and an obstruction angle of 30°, the loss is 12%. for more information on UK Government initiatives on solar panels and solar power click on the link.

At a maximum annual irradiation of 90-100% in Europe the orientation of a PV roof can vary, with few problems, between southwest and southeast. Within this bandwidth the roof angles may vary between 30° and 50°. If roofs are oriented east or west then the irradiation is reduced to 80-90% and the roof angles are restricted to angles of between 10° and 30°. With steeper angled roofs (slanting facades) ranging between 50° and 90° the orientation is limited to a deviation of plus/minus 30° from the southerly line.

The bandwidth within which the urban planning conditions are determined should be calculated on the basis of the irradiation and efficiency levels. Pollution is also a kind of shadowing, as it stops the light from reaching the solar cells. However, an angle of more than 20° should ensure that, depending on the climate, most solar cells are washed clean by the rain. Only particular types of dirt (e.g. soot particles) need to be cleaned in another way. This is why it is important that cells can be easily reached.

Europe Ahead of the UK in solar power

In the Netherlands, for example, similar types of constructions, at the same height and standard block distances of 16-18 metres, generally do not create any interconnecting obstructions. However, many urban situations concern a mixture of one, two and three-storey residences, which increases the risk of interconnecting obstructions.

Shadowing through vegetation should be prevented, where possible, i.e. plant trees on the north wide, or smaller trees, or trim everything back.
Ensure that the application of PV does not conflict with the use of passive solar energy (such as solar heating). Prevent problems caused by the sun flickering on other objects.

Many of the aforementioned points generally come down to the fact that urban profiles must be suitable for using PV. NB: these profiles are often chosen according to reference photos and desired imaging, without studying the effects of PV integration.
Relationship between efficiency and surface area.

Energy saving (Dutch example): Approximately 800 kWh generated per installed kWp (1 kWp = around 10 m2). With a surface area of 20-25 m2 an energy-efficient family can generate all the energy they need on an annual basis.

Enviko Commitment - Free online home survey