SOLAR ENERGY

Photoelectricity was discovered by Hallwachs [16] in 1888, and its quantum mechanical analysis was provided by Einstein in 1905. However, the necessary research toward viable electrical power units actually began in 1954 with transistor development by Bell System Laboratories NJ. Solar cells for this purpose are now [17] series — connected arrays of p-n junctions in ribbon polycrystalline silicon which have a quoted life expectancy of 30 years.[2] Though mono­crystalline devices offer a somewhat greater conversion efficiency of sunlight into electrical energy, ribbon technology is cheaper with a theoretical maximum conversion efficiency [17] of 29%. By manu­facturing ever-thinner devices charge carrier recombination during diffusion has been reduced so as to achieve efficiencies of around 18%. Conversion losses also occur as a result of atmospheric or bird deposits and in the thyristor inverters between domestic and Grid networks. Because solar radiation has no cost, a low conversion efficiency principally aggravates capital investment and environmen­tal impact.

During the four winter months Table 1.2 and Figure 1.1 show that the average of 1-2 sunshine hours around mid-day are well outside the UK’s national peak demands between 1600 and 2100h. Though solar cells provide some twilight output the 17% capacity factor for UK solar arrays from Table 1.2 suggests an inadequate annual return on capital for commercial plants. However, Spain and the United States lead the

Table 1.2

Average Sunshine Hours Per Day [18] in the United Kingdom and Spain

Month

J

F

M

A

M

J

J

A

S

O

N

D

London

1

2

4

5

6

7

6

6

5

3

2

1

Madrid

5

6

6

8

9

11

12

11

9

6

5

5

world in the use of solar energy [19]. Spain has a currently installed capacity of 432 MW with plans for a total 900 MW, and the United States has presently 457 MW with a large 968 MW unit under con­struction in Riverside County, California. As well as Capacity Factors twice that of a UK plant, their solar output conveniently peaks with that of summer noon-time electricity demand for air conditioning. By avoiding the synchronization of low merit order[3] fossil-fired stations, Spanish and US solar units further enhance their economics and reduce carbon emissions. Moreover, these countries have large arid or other­wise unusable areas of land whose purchase offers no impediment to commercially sized developments. For example in the United States, a Boston plant [1] of 1.3 MW was recently built on the contaminated land of a derelict gas works with a utilization of 1.9 hactares per installed MW. On the other hand high land prices, climate and incompatibility with the national electricity demand further militate against solar generation in the United Kingdom. Indeed the United Kingdom reduced its subsidy for commercial generation [30] (>50kW) in February 2011, and later in February 2012 attempted to cut the feed-in tariff for domestic roof-top units of a few kW.

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