Residential PV test site reports results

By J.P.R. Tansley

Bsc DipSurv

Photovoltaic (PV) systems convert sunlight directly into electricity. The PV effect was first observed in 1839 and significant influences on the evolution of PV technology have included the use of PV cells to power US space satellites since 1957.

PV is a proven technology that is being used increasingly in Europe, the US and Japan. Applications include consumer products, such as watches and calculators; remote power systems; grid-connected electricity generation; and building-integrated electricity generation, such as the project described below. The latter can be fitted with reversible meters which automatically subtract electricity exports from imports, so the customer is charged only for net imports.

Northumberland

The UK`s largest PV demonstration scheme was unveiled at the University of Northumbria, Newcastle-upon-Tyne in January 1995. The project comprises the rainscreen overcladding of the Northumberland building, a five-story 1960s concrete building, which like many of its era, was in need of restoration.

However, this refurbishment differs from others since the cladding contains m2 of PV modules on the south face. These are designed to contribute a peak electrical output of 40 kW and generate 30,000 kWh annually for use within the host building. Any excess power is sold back to the regional electricity company, Northern Electric.

The (US)$2.3 million project, of which (US)$549,000 paid for a PV system, is one of the largest PV facades in Europe and was partially funded by the European Community, 40 percent, and the Department of Trade and Industry (DTI), 9 percent. Other investors included Northern Electric, Greenpeace and the Newcastle Building Society.

The project aims to clarify technical issues concerning weather-related performance and grid connection, to identify future research requirements and to demonstrate that building-integrated PVs are a practical energy option, even at northern latitudes. By the middle of the next century, up to 20 percent of the UK`s electricity could be provided by PVs, helping redress the energy imbalance in the north of England, where electricity consumption exceeds generation.

Results

Monitoring of the Northumberland building was initially commissioned for one year, with results due in early 1996. The system generally peaks at between 30 kW and 35 kW, depending on sunlight levels and module temperatures. A high of 39 kW was reached during the spring when the sun is perpendicular to the angled PV panels, thereby maximizing solar collection as the PV cells are operating at more efficient, cooler temperatures, aided by the ventilation gap behind the modules.

The results are expected to show that the system provided approximately 25,000 kWh of electricity during its first year (approximately 87 kWh/m2 of PV facade), less than the original estimate of 30,000 kWh, and would have been nearer 35,000 kWh (approximately 122 kWh/m2) if the building had been completely unshaded. Consequently, approximately one-third of the building`s annual electricity demands were met. However, the building is somewhat atypical in that it houses an unusually high number of computers which have high energy demands. If these were discounted, the PV system would provide one-half the electricity demand.

Costs

It is difficult to quantify the cost of PV electricity because of the number and complexity of issues involved, many of which are site and/or design specific. Factors such as the variability of supply; conversion efficiency; design and monitoring costs; price of electricity sold to the grid and others, suggest a high cost which does not reflect other important but largely unquantifiable factors, such as the environmental benefits; low maintenance costs; aesthetics and reduced transmission losses.

The cost of the PV electricity generated by the Northumberland building is estimated to be between 46 cents/kWh and 69 cents/kWh; but it would be at the lower end of the range if the system was unshaded, the design and monitoring costs were discounted and there was an avoided cost.

Context

The principal rationale for supporting renewable energy sources, such as PVs, is the concept of sustainable development and the recognition that their use can be a major antidote in the foreseeable future to issues such as the greenhouse effect, acid rain, the depletion of finite fossil fuels and the potential hazards associated with nuclear power generation.

The built environment accounts for approximately one-half of the UK`s primary energy consumption and the same proportion of the UK`s total emissions of CO2. Hence, there is a significant potential market for PVs, particularly since they can be integrated into both new and refurbished buildings–the only renewable that can be deployed in an urban environment.

PV technology generates electricity without noise or the emission of the environmental pollutants associated with fossil-fuel-based energy production. Additionally, building-integrated PV systems generate electricity without land use, visual blight, transmission losses or the distribution of electricity via unsightly overhead pylons.

Other advantages of building-integrated PVs include: modular construction, permitting flexible design and on-site building; low operation and maintenance costs, due to solid state electrical components with no moving parts; no land or support structure costs; and an avoided cost of the roof or cladding material being replaced.

Conclusion

The DTI recognizes that PV technology is one of the most attractive renewable energy sources in terms of a large, accessible resource, potential for cost reduction, simplicity of operation, flexibility of deployment and small environmental impact. Building-integrated systems on commercial buildings, such as the Northumberland building, have been identified as the most likely applications to become economically viable in the UK–primarily because there is a good match between the buildings, energy demand and the PV electricity supply. Also the avoided costs are generally higher.