Scarcity of Fresh water
...ncern. The thermal energy required for desalination using thermally-driven distillation processes can be achieved by collection of solar energy using flat plate collectors, evacuated tube collectors or solar ponds. Such devices can achieve temperatures of 80-130 C which are quite suitable for such desalination processes. Solar energy can also be converted to electrical power using either photovoltaic panels or high-temperature concentrating collectors associated with a heat engine operating on a thermodynamic cycle. Such electrical power can then be used to operate power-driven desalination processes such as reverse osmosis or vapor compression. Conventional desalination technology is fairly well developed and some of the processes may be considered quite mature, although there is still considerable scope for improvement and innovation. Conventional desalination is energy intensive. Thus, one of the major concerns to developing water production by desalination is the cost of energy. Apart from the cost implications, there are environmental concerns with regard to the burning of fossil fuels. The coupling of renewable energy sources with desalination processes is seen by some as having the potential to offer a sustainable route for increasing the supplies of potable water. Renewable energy processes are less mature but are developing rapidly. Wind energy and photovoltaics (PV) in particular have made enormous advances over the last two decades but still have plenty of scope for improvement. The amount of energy used in the world for desalination is comparable to the total energy requirement of an industrialized country such as Sweden. This gives an idea of the amount of CO2 emitted by this industry. Global phenomena such as the greenhouse effect must receive due attention. Last but not least there are regions where a significant fraction of the total energy consumption is due to desalination and which are deficient in conventional sources. In these cases regional or national economies may benefit from a reduction of oil imports. In a finite world, the conventional wisdom tells us that we shall eventually run out of nonrenewable resources, such as crude oil, iron ore, and bauxite. And long before exhaustion actually takes place, this same wisdom informs us, the growing scarcity of these resources will limit our ability to consume. These views have led to fears of "running out of oil" and have even spawned books and movies depicting the resulting chaos. Yet according to recent research by Martin Weitzman (1999) of Harvard, the economic impact of exhausting nonrenewable resources is far less important than you might think. Indeed, it appears that by failing to explicitly account for exhausting such resources, we are overstating our welfare by one percent at most. Because the earth is finite, physical stocks of nonrenewable resources must shrink over time. Barring other developments, this reduction in supply tends to push up the prices of these resources. People respond to these higher prices by using other factors of production instead, but this means devoting more and more of other resources to coping with the disappearing nonrenewable resources. We somehow must account for this coming rise in scarcity if we are to accurately judge our current well-being. For example, when the price of oil rises, we can adjust by developing more fuel-efficient cars. But this comes at a cost, a more expensive new engine. This cost is not properly reckoned with by orthodox income measures. The cost of developing the improved engine is conventionally counted as part of income yet it represents an expense that would be unnecessary if oil were renewable. And so, the question is, by how much are we worse off because some resources are in fact nonrenewable? The answer, it turns out, is fairly easy to calculate: We need only adjust current income, measured as net domestic product, downward by the value of the nonrenewable resources exhausted in creating that income. For example, in one recent year, the world used up about ten metric tons of silver. Its market value after deducting extraction costs was $40 million per ton. Thus, to account for the nonrenewable nature of silver, $400 million should be deducted from world income figures. The logic of the Weitzman adjustment is much like what economists already do when they go from gross domestic product (GDP) to net domestic product (NDP), accounting for the depreciation of the capital stock. When output is produced, some of the capital is used up--it depreciates. If we want to continue to produce at the same rate, the capital stock will have to be replaced. Net domestic product adjusts for this; GDP does not. Weitzman has devised a way to make a similar adjustment to net domestic product to account for the exhaustion of nonrenewable resources. In effect, the income that nonrenewable resources seem...