In the previous section we considered PV’s requirements for raw materials and land – two environmental issues that surface before PV production even begins. Further important environmental questions arise during a PV system’s lifetime, which starts with extraction and purification of raw materi
als; proceeds through manufacture, installation, and many years of operation; and ends with recycling or disposal of waste products. The whole sequence is referred to as a life cycle, and it is important to appreciate its environmental consequences. Note that this form of life-cycle analysis (LCA) is not the same as the classical economic version introduced in the previous section, which deals with cash flows and financial decisions. We are now moving on to something much broader, with important implications for global energy policy and society as a whole.
In this brief introduction we will consider LCA under two main headings:
■ Environmental and societal costs. What costs, in addition to classic economic costs, are incurred or avoided?
■ Energy balance. How does the amount of electrical energy generated over a system’s lifetime compare with the energy expended in making, installing, and using it?
We start with environmental and societal costs.1 It is clear that all methods of energy production – whether based on oil, gas, coal, nuclear, or renewable sources – have impacts on the environment and society at large that are ignored by the traditional notion of ‘cost’. A narrow economic view of industrial processes assesses everything in terms of money, while ignoring other factors that common sense tells us should be taken into account in any sensible appraisal of value. For example, the ‘cost’ of generating electricity in nuclear power plants has traditionally been computed without taking any account of accident or health risks; in the case of coal-fired plants, without acknowledging their unwelcome contribution to global warming; and with wind power, without placing any value on landscape.
There are two main reasons for this apparent short-sightedness. First, aspects such as health, safety, environmental protection, and the beauty of a landscape cannot easily be quantified and assessed within a traditional accounting framework. We all know they are precious, and in many cases at least as important to us as money, but appropriate tools and methodologies for including them are only now being developed and accepted. It is surely vital to do this, because so many of our current problems are bound up with the tendency of conventional accounting ‘ – o know the price of everything and the value of nothing’.
The second reason relates to the important notion of the external costs of energy generation. These costs, most of which are environmental or societal in nature, have generally been treated as outside the energy economy and to be borne by society as a whole, either in monetary terms by taxation, or
in environmental terms by a reduction in the quality of life.1 They contrast with the internal costs of running a business – for buildings and machinery, fuel, staff wages and so on – that are paid directly by a company and affect its profits. If Planet Earth is treated as an infinite ‘source’ of raw materials and an infinite ‘sink’ for all pollution and waste products, it is rather easy to ignore external costs. For example it seems doubtful whether the 19th – century pioneers of steam locomotion ever worried much about burning huge quantities of coal; or the 20th-century designers of supersonic civil airliners about fuel efficiency and supersonic bangs. One of the remarkable changes currently taking place is a growing world view that external costs should be worked into the equation – not just the local or national equation, but increasingly the global one. In other words external costs should be internalised and laid at the door of the responsible industry or company. In modern phraseology, ‘the polluter should pay’.
Many of the external and internal costs associated with industrial production are illustrated by Figure 6.15. The external ones, representing charges or burdens on society as a whole, are split into environmental and societal categories, although there is quite a lot of overlap between them. You can probably think of some extra ones. Internal costs, borne directly by the organisation or company itself, cover a very wide range of goods and serv-
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External : Environmental
External : Societal Figure 6.15 External and internal costs. |
ices, from buildings to staff wages. The distinction between internal and external costs is somewhat clouded by the fact that many items bought in by a company, for example fuel and materials, have themselves involved substantial ‘external’ costs during production and transport. In the case of electricity generation a proper analysis of the environmental burdens should take proper account of all contributing processes and services ‘from cradle to grave’, whether conducted on – or off-site. Needless to say this is a challenging task.
One of the special difficulties facing renewable electricity generation, including PV is that so many of its advantages stem from the avoidance of external costs and are therefore hidden by conventional accounting methods. Renewables tend to produce very low carbon dioxide emissions, cause little pollution, make little noise, create few hazards to life or property, and have wide public support. PV can claim all these benefits. Yet when economists and politicians talk about PV reduction or avoidance of external costs is seldom mentioned. Fortunately, energy experts and advisers to governments are taking increasing notice of environmental life cycle analysis in their decisions, and assessing the risks and benefits of competing technologies on a more even footing.5 Certainly, the PV community must be involved in countering outdated thinking about the wider benefits of its technology.
We now move on to the much-discussed topic of energy balance. Clearly, it takes energy to produce energy. But how does the total amount of electrical energy generated by a PV module or system over its lifetime actually compare with the input energy used to manufacture, install, and use it? Closely related to the energy balance is the energy payback time, the number of years it takes for the input energy to be paid back by the system.6 We naturally expect PV to have favourable energy balances and payback times, especially in view of its claims to be clean and green.
Two initial points are worth making. First, energy payback is not the same as economic payback. The latter is concerned with repaying a system ’s capital and maintenance costs (including cost of energy consumed) by a long-term flow of income, and is essentially a financial matter; energy payback is much more about the environment. Secondly, the environmental benefits of a short payback time depend on the present energy mix of the country, or countries, concerned. If the required input energy is largely derived from coal – burning power plants, it is more damaging than if it comes from, say, hydroelectricity.
Major energy inputs to a PV system occur during the following activities:
■ extraction, refining, and purification of materials.
■ manufacture of cells, modules, and BOS components.
■ transport and installation.
Interestingly, some of the most significant energy inputs are for components such as aluminium frames and glass for modules, and concrete foundations for support structures in large PV plants. Although the energy required to refine pure silicon and make crystalline silicon solar cells is considerable, the continual trend towards thinner wafers using less semiconductor material is reducing this problem. The energy input for thin-film cells is generally very small.
The other side of the energy balance – the total electrical energy generated by a system over its lifetime – depends on a number of factors discussed in previous chapters:
■ efficiency of PV modules and other system components.
■ the amount of annual insolation.
■ alignment of the PV array, and shading (if any).
■ the life of the system.
The energy balance is most favourable for systems that are efficiently produced in state-of-the-art factories, and installed at optimal sites in sunshine countries. Things get even better if systems last for longer than their projected or guaranteed lifetimes – but of course this is hard to predict.
Some major life – cycle studies carried out in the early years of the new millennium painted a rather gloomy picture of PV ’- environmental and health impacts, due largely to the fossil-fuel energy used during cell and module manufacture. However, a more up-to-date report5 that takes proper account of external costs and recent advances in PV engineering comes to far more optimistic conclusions.
The report considers the many factors, including rising solar cell efficiencies, use of thinner semiconductor layers, larger more energy-efficient factories and processes, and improvements in BOS components that are driving down PV’s environmental impacts year by year. Energy payback times for roof-mounted systems are especially favourable because of their modest BOS requirements, including light mounting structures. If based on crystalline silicon modules and installed in southern Europe or sunshine states of the USA with typical annual insolation values of around 1700 kWh/ m2 – payback times are currently about 2 years – surely an excellent result for systems expected to last for 25 years or more. The figure is nearer 4
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Figure 6.16 Helping reduce environmental impacts: a modern solar cell factory (EPIA/Q-cells). |
years for similar systems installed in the less sunny climates of northern Germany, the Netherlands, or the UK. The situation is even better for systems based on the new generation of thin-film modules, which use extremely small quantities of active semiconductor materials. In favourable locations energy payback may soon take no longer than a single orbit of Planet Earth around the Sun – another pointer to PV’s exciting future.
