Exploiting the potential of PHOTOVOLTAICS.

Efficiently harnessing the sun's power through photovoltaics remains a tantalizing ideal for all those concerned with sustainable development. Duncan Price looks at how the technology is evolving and its future potential.

INTEGRATING PHOTOVOLTAIC CELLS into buildings is a satisfying idea: the building produces electricity as well as using it, so saving running costs and contributing to a reduction in greenhouse gas emissions. At some point, improved cell performance and economies of scale will solve lengthy payback problems, manufacturers will have engaged fully with the needs of the building industry, and electricity companies will have become enthusiastic about buying as well as selling electricity. All new buildings will then either integrate panels or be designed so that they can be fitted at a later date.

First, PV systems need to become more efficient. The PV industry must continue to investigate concentration technologies and develop standards for mechanical stability, building integration details, watertightness and durability. Cost is arguably the greatest barrier to investment in PVs at present, but volume production will bring about reductions.

The effect of PVs on architectural imagination will be minimal unless people start to think differently about risk and the use of PV systems. Concerns about panel reliability linger. Other risk perceptions are a lack of sufficient sun (changing), safety problems with live panels and the safe disposal of panels when they reach the end of their working life.

A big problem seems to be reluctance of some electricity companies to buy back surplus electricity at an economic price. Without this, the PV revolution will not happen. At present, small-scale individual producers have no power to negotiate. Bulk contracts for neighbourhood developments or major buildings could establish incentive. Or developers might choose to rent wall or roof space to electricity companies. Power generation would become a significant incentive in design.

Governments should encourage PV use and actively favour green development through tax systems. Grants for experimental PV installations are not enough. Developers could be given tax breaks to include PVs as part of a low energy building strategy and, in the interests of consistency, should be penalized if the running costs of new buildings exceed an agreed level. Absurdly, running costs can be offset against tax but a green specification cannot.

Low energy design should be seen as coordination of many factors. Development of building concept and environmental strategy ought to be part of the same process. The object is to produce a building in which orientation, zoning and structure -- including thermal mass and facades -- work with environmental systems to achieve optimum efficiency and comfort. PVs have the potential to be a key aspect of low energy designs.

As architects explore new ways of using the technology, it will be increasingly important for engineers to gain experience and technical capability in PV system design. This is one of the objectives of a building-integrated PV design study that engineers Whitby & Bird have recently completed on behalf of The Energy Technology Support Unit for the Department of Trade and Industry under the UK Solar Programme. The focus of the study has been a mixed use development for the Peabody Trust on a brownfield site in Kensal Green, West London (architects CZWG in succession to Cartwright Pickard). The project is a demonstration of the use of renewable energy in an urban setting and will include one of the largest uses of PV panels in Europe.

Both residential and commercial buildings will incorporate PV panels where possible, replacing 1500[m.sup.2] of conventional cladding material on roofs and facades. On sunniest days, the system will generate 200kW, meeting all electrical requirements of the site. A site-wide energy management system will move power between buildings to meet local demand. Annually, 15 per cent of the development's total electricity needs will be panel-generated, which will have the added benefit of reducing carbon dioxide emissions by 200 tonnes.

Whitby & Bird's remit was to address issues of module integration and examine energy generation and use. They have also considered the distribution of energy over the 10 acre site. The objective is an autonomous community (on sunny days at least), which is more worth while than autonomy for individual buildings. This project concerns itself with issues of replication -- it is not a theoretical study.

As cell efficiency increases, unit size will decrease and greater variety and subtlety emerge. The future should therefore show designers not having to make such obvious trade-offs between how buildings perform and how they look. PVs, as highly efficient bespoke glass laminates, will be part of the vocabulary of energy efficient design without dominating it. Facades and roofs will become increasingly viewed as sites on which to hang units, although there is already competition for space between PVs and glazing or shading elements. Combination of structural shading and PVs into a single system can be particularly elegant. In future, will transparent PVs be integrated into glazing?

There are major challenges for architects and engineers in the next few years. First, to keep up to date with the technology. Second, to encourage the use of PVs so that the technology becomes increasingly demand led. Third, to ensure that new buildings are PV-friendly wherever possible, by routinely assessing possibilities for appropriate orientation, panel siting and structural integration of fixings. Fourth, to work with the manufacturers of PV modules, curtain walling and glazing systems to drive the production of the integrated systems of the future.

Duncan Price is a physicist working in the Building Physics group at Whitby Bird & Partners developing low energy concepts and analysing building environmental performance.