An increasing number of countries are investing in solar power to produce electricity locally and reduce greenhouse gas emissions. Germany and Japan, the two leading countries in this field, have rolled out massive programs to equip households and companies with "solar roofs". In the case of households, these are just small installations, but when installed on an industrial building or in a field, they become genuine solar power plants.
As a solar power plant requires a large inital investment, and does not yet provide enough kWh to compete with thermal power production (nuclear, oil, coal etc., power sources which do not integrate external costs such as CO 2 and the industrial risks in their pricing), the authorities in various countries are offering incentives to help develop this new industry:
- subsidies on equipment purchases
- low rate bank loans
- high prices for kWh sold back to the grid
How it works
Power is generated by photovoltaic modules on the roofs of industrial buildings, supplying some of the user's power needs. When there is little or no sun, a connection to the main grid provides a top-up.
It is also possible to feed all power generated back into the main grid. The set-ups can then be referred to as photovoltaic power plants, just like the thermal power plants run by national producers.
In some countries, Germany in particular, power plants with thousands of m² of photovoltaic modules have been set up in the countryside to produce large quantities of electricity.
High power solar power plants:
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 The above images show examples of installations in Dollern, Germany; installed on the roof of Photowatt's buildings, France; and in Spain. |
These installations are becoming increasingly widespread on the roofs of private companies and public buildings (schools, town halls etc.). Depending on the clients and contractors' requirements, photovoltaic modules can be integrated into the external walls, glass roofs or sunshades of buildings. The criterion here is the best compromise between performance and architectural integration.
Examples below show three types of integrated photovoltaic power plants (glass roof, sunshade, curtain wall):
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 A 100 kWp (800 m 2 ) south-facing power plant, at an angle between 20 and 40°, optimal conditions in Europe, can generate between 80,000 and 140,000 kWh per year depending on its geographical location (Northern to Southern Europe). |
Power Plant Connected to the Grid (system architecture)
A photovoltaic power plant is made up of the same components as a small individual household's solar roof: solar panels, a bracket to attach them to the roof and an uninterruptible power supply (UPS) which converts the power supplied by the panels into a form suitable for the grid, alternating current of 50 Hz synchronized with the grid with a voltage of 230 V. The power is directly fed back into the low voltage three-phase network.
Several small single-phase UPS’s can be installed and connected in parallel to feed the entirety of the power plant's production into the three network phases in equilibrium. Alternatively, a single centralized UPS can be installed directly producing 50 Hz three phase.
The power plant is "sun dependent", i.e. power is produced in proportion to the amount of contact from the sun. Main voltage and frequency must be monitored in order to be automatically disconnected in the event of problems. Depending on the UPS used, it may be able to carry out this monitoring; otherwise, an external protective system may be required.
Energy production and performance data from the installation can be measured and recorded, fed into a PC and then displayed in real-time on a large display (1 m²) in a public place (e.g. reception or foyer area).