Renewable Energy - Out of the shadows06 December 2004

Green energy is high on the UK agenda. Announcements are spawned on a seemingly daily basis about the government's commitment to renewable energy - and the Prime Minister has said that he will try to use Britain's forthcoming pole positions as head of the G8 and presidency of the European Union to push the environmental arguments still further.

One source of renewable energy is solar power, which is generated in three main ways: passive power, where design ensures a building's form and fabric captures the sun's energy, so reducing the need for artificial light and heating; active solar water heating, which converts solar radiation into heat which can then be used or stored; and photovoltaics (PV), which converts sunlight into electricity.

Certain materials, semiconductors, can be adapted to release electrons and so generate electricity when they are exposed to light. One of the most common of these materials is silicon, which is the main material in 98% of solar PV cells.

All PV cells have at least two layers of such semiconductors: one that is positively charged and one that is negatively charged. When light shines on the semiconductor, the electric field across the junction between these two layers causes electricity to flow - the greater the intensity of the light, the greater the flow of electricity.

There are four main types of PV system:

- Grid connected
The most popular type of solar PV system for homes and businesses. The solar system is connected to the local electricity network allowing any excess solar electricity produced to be sold to the utility. Electricity is taken back from the network outside daylight hours. An inverter is used to convert the DC power produced by the solar system to AC power needed to run normal electrical equipment.

- Grid support
The solar system is connected to the local electricity network and a back-up battery. Any excess solar electricity produced after the battery has been charged is then sold to the network. A grid support system of this kind is ideal for buildings in rural areas where the conventional power supply is unreliable.

- Off-grid
Completely independent of the grid, the solar system is directly connected to a battery which stores the electricity generated and acts as the main power supply. An inverter can be used to provide AC power, enabling the use of normal appliances without mains power.
- Hybrid system
A solar system can be combined with another source of power - a biomass generator, a wind turbine or diesel generator - to ensure a consistent supply of electricity. A hybrid system can be grid connected, standalone or grid support.

Leading lights

BP Solar has manufactured around 75% of all the solar power systems installed in the UK: it has been involved in such projects as a 97kWp (kilowattpeak) PV rooflight installation on assemblies at Ford's Factory for the Future, in Bridgend, which provides over 75,000kWh of electricity per annum, as well as many other projects for universities and businesses.

Another leading company in the field of PV is London-based solarcentury, which designs and manages projects but does not manufacture its own PV product - it distributes PV systems for manufacturers such as Sharp and Sanyo. Jeremy Leggett, solarcentury's CEO, says: "Solar photovoltaic roofs and façades on buildings give you high-value insurance against rising future energy prices at increasingly low cost, right where you need the energy. We can power much of the country and do so much faster than most people realise. Together with our sister low-carbon technologies, we are capable of powering the entire country without the need for greenhouse gas emissions or oil and gas imports. All we need is the collective will and imagination to make the change."

Where there's the will, as they say. But in today's world, the will is not enough without the financial viability. The cost of applying PV cladding is from a minimum of around £500/m2 up to £900/m2 - it may seem expensive but, as solarcentury points out, the bronze façade on the Westminster Parliament office complex cost more than £7,000/m2. The PV option would not only have been cheaper to install, but would have provided clean, free power.

But of course most buildings are not clad in bronze, so cost of PV remains an important factor. Enter the major demonstration programme (MDP) for photovoltaics, a government scheme launched in 2002 by Secretary of State Patricia Hewitt to give £20m of grant aid for the installation of solar PV systems. Earlier this year, a further £5m funding was announced - then, in September, Minister for Energy Mike O'Brien extended this through to the summer of 2005 with an additional £6m. After this time, it is expected that the government will start a new low-carbon buildings programme to replace the MDP.

Jeremy Leggett applauds the latest £6m announcement, saying that it will help more companies and individuals to experience what he calls the 'seeing is believing' effect of PV on roofs and façades. "We have every confidence that the new funding is just a step towards building PV into a key role in what the Prime Minister called the coming green industrial revolution and that further substantive market-building initiatives by government lie ahead," he adds.

Until then, however, the MDP is managed for the government by the Energy Saving Trust. Grants of up to 50% of the installed cost for small systems are awarded through a fairly straightforward, continual approval process. Larger projects, up to 100kW, are subject to a competitive process on a quarterly cycle, and grants of up to 55% are awarded to these installations.

There are three types of grant:
- Small-scale applications (0.5-5kWp)
These offer 50% funding for owners of domestic buildings, for public bodies and for organisations with less than 250 employees and an annual turnover of less than £25m. Approval is on a rolling basis and grants are fairly automatic, provided applications meet certain criteria. Applicants have six months from grant approval to finish the work, and once the installation is complete and the required paperwork completed, the grant is paid over.

- Large and medium-scale applications for social housing groups and larger-scale public authority building projects (5-100kWp)
Grants for up to 60% of the total installation costs. Applications are made on a quarterly competitive call basis. An independent panel considers the applications and if approved, applicants have 12 months to complete the installation. The grants are paid in two stages: up to 70% at approval and 30% on completion.

- Large and medium-scale applications for commercial organisations (5-100kWp)
For commercial organisations the funding is up to 40%. Applications are organised and considered, and grants are made, in the same way as for the category above.

Of course, making funding applications - successfully - isn't always straightforward, but solarcentury, for instance, will work with companies throughout the process. All works, up to and including help with the preparation of the funding application, will be provided free of charge on the condition that prior to submission of the funding application, or the issuing of tender documents, it is formally agreed that solarcentury will be the specialist contractor for the project.

PV systems can be incorporated into buildings in various ways. Sloping rooftops are an ideal site, where modules can simply be mounted using frames. Photovoltaic systems can also be incorporated into the actual building fabric; for example, PV roof tiles are now available which can be fitted as would standard tiles. In addition, PV can also be incorporated as building façades, canopies and skylights among many other applications. This is a rapidly growing market in the UK and throughout Europe and it is mainly this type of system for which the MDP provides funding.

The main types of PV cell are:

- Monocrystalline silicon: made from cells which are cut from a single cylindrical crystal of silicon, this is the most efficient PV technology. The main advantage of these cells is their high efficiency (around 15%), but the complex process required to make them means they are usually more expensive than other options.

- Multicrystalline (also referred to as polycrystalline) silicon: made from cells cut from an ingot of melted and recrystallised silicon. Molten silicon is cast into ingots of polycrystalline silicon: the ingots are then cut into very thin wafers and assembled into complete cells. The process is simpler than that for monocrystalline cells, but the typical efficiency rating is slightly lower at 12%.

- Thick-film silicon: the silicon is deposited in a continuous process onto a base material. This results in a fine-grained, sparked appearance.

- Amorphous silicon: cells contain silicon atoms in a thin homogenous layer, rather than a crystal structure. This type of silicon absorbs light more effectively, so the cells can be thinner, hence cells of this type are usually termed thin film. Efficiency is markedly lower, at around 6%, but amorphous silicon cells are easier and cheaper to manufacture.

Other materials such as cadmium telluride and copper indium diselenide, also known as thin film, are starting to be used for PV modules. And solarcentury also offers what it terms a 'hybrid' PV system, where monocrystalline and thin-film silicon are used to produce cells with the best features of both technologies.

Applications that solarcentury has fulfilled to date include the High Performance Centre at the Alexander Stadium for Birmingham City Council. The firm worked with the City Council to design a solution which demonstrates how PV can be costeffectively integrated into low energy buildings. The large flat roof of the centre meant thin-film modules were the best solution and a 54Wp amorphous silicon square module was fitted over an area of 1,500m2. The PV system has a life expectancy of more than 20 years and it's anticipated that the Centre will generate 80 MWh per year - more electricity than it uses - so the excess electricity will be directed to power other buildings on the site.

Another project involved the University of Ulster - solarcentury installed its Sanyo hybrid modules, which combine amorphous and monocrystalline technologies, at the energy and nanoengineering research facility. Covering 76m2 on a wall, rather than a roof, the system generates 6.1MWh per year and cuts CO2 emissions by 2.6 tonnes.

These are just two examples: the fact that all businesses will need to move to cleaner, greener energy over time is indisputable. A PV system never needs refuelling, has no moving parts, emits no pollution and requires minimal maintenance. And, although as with any new technology, the cost is offputting for many firms, the government's supporting financial position makes this a renewable energy source worth investigating.

SOE

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