Tips on solar cells by Greg Gayheart
LARGER-SCALE AND UTILITY-SIZED PV SYSTEMS
As well as being fitted to the roofs of domestic houses, PV arrays can also be mounted on or integrated into the roofs and walls of commercial, industrial, school, community and public sector buildings. The additional capital costs of the PV system can, partially at least, be offset by savings in roof and cladding material that would otherwise have been incurred. Commercial, industrial, school and public sector buildings are mostly occupied during the daylight hours, which is when the highest levels of solar radiation are available and when electricity demand is highest. The electricity generated by a PV system will offset the electricity supplied from the local energy company, thereby reducing costs.
The output from PV systems during daylight hours can be highly variable, changing dramatically over short timescales with variations in cloud cover. The output over a longer period, however, is largely predictable and this would be of benefit to electricity grid operators. The array is 340kWp and generates about 250,000kWh a year. As well as testing the output and electrical characteristics of panels, the installation demonstrates how the array integrates into the surrounding environment and has permitted the German utility to gain good large-scale PV operating experience.
A large-scale 100MW utility-sized installation has been proposed for a former nuclear test site in the Nevada desert.
Monocrystalline and Polycrystalline Silicon Cells
Cells produced using the Czochralski process have a distinctive circular or squared-off shape, which makes them physically larger per kW output with non-productive areas between cells.
Polycrystalline silicon consists of small, randomly aligned grains of monocrystalline silicon. Polycrystalline silicon cells have the appearance of chopped-up bits of silicon in suspension. Polycrystalline solar cells are cheaper and easier to make than monocrystalline cells, but they have a lower efficiency. Careful orientation of the grains during manufacture can reduce the efficiency loss.
The loss in efficiency has been minimal and simpler manufacturing processes have been employed.
LARGER-SCALE AND UTILITY-SIZED PV SYSTEMS
As well as being fitted to the roofs of domestic houses, PV arrays can also be mounted on or integrated into the roofs and walls of commercial, industrial, school, community and public sector buildings. Commercial, industrial, school and public sector buildings are mostly occupied during the daylight hours, which is when the highest levels of solar radiation are available and when electricity demand is highest. A working demonstration of this is at Northumbria University in Newcastle, which installed a 40kWp system on the front of a refurbished computer centre building in 1995, making it Britains first building with PV cladding.
The output over a longer period, however, is largely predictable and this would be of benefit to electricity grid operators. In Europe there are growing numbers of utility-sized grid-connected PV installations. One of the most significant is the RWE Kobern-Gondorf array on the banks of the Mosel River, close to the city of Koblenz. The array is 340kWp and generates about 250,000kWh a year. As well as testing the output and electrical characteristics of panels, the installation demonstrates how the array integrates into the surrounding environment and has permitted the German utility to gain good large-scale PV operating experience.
A consortium including RWE has constructed a I MW PV plant near Toledo in Spain. High-efficiency BP Solar, monocrystalline panels make up half the array and the plant is operated in association with a hydroelectric scheme. A large-scale 100MW utility-sized installation has been proposed for a former nuclear test site in the Nevada desert.
THE ECONOMICS OF SMALL-SCALE PV SYSTEMS
Depending on the application, there may also be a cost for connecting to the grid, or upgradingthe existing connection, or for batteries in stand-alone systems with their associated chargers, housings, fans and irrigation systems.
Most systems will have an associated display unit that can indicate, in real time, the PV systems output in kilowatts. These displays are a central, though not essential, part of the PV system, since they give a highly visible, real-time, indication of the output from the cells. PV systems that have concentrators or tracking will also have the associated costs of these devices.
Grants for PV Systems
In England, Wales and Northern Ireland the uptake PV systems for domestic, community and other buildi has been encouraged through a number of capital grant support programmes. Due to the difficulty in estimating uptake in these schemes, the duration and level of available grant funding is subject to change at any time. (For contact details for these schemes, their accredited products and approved installers, see article 1.)
Somebody on squidoo told us about this blog site on solar energy.
About the Author
How PV cells work. Tips on pv cells.
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