The Many Applications Of PV

It is a cliché to say that applications of solar power are limited only by the imagination of the user. Sure, PV is uniquely scalable amongst generating technologies – and the input source is almost ubiquitous. But in practice the actual market for solar cells has been defined by the evolution of technology and cost as described in my previous articles.

The key technological advantage that PV has over other power generation technologies is that it is solid state. Traditional generating sets employ rotating machinery; they need maintenance and are subject to failure. Secondly, PV's fuel source – photons of light – is available around the globe, and comes with free delivery! These two characteristics enabled the early PV industry to find its initial markets at a time when solar cell costs were orders of magnitude higher than established electricity sources.

Spacecraft need highly reliable power supplies and cannot practically be refuelled. At first, the only available electricity sources were primary batteries, whose weight was a serious handicap. Under these circumstances, the high cost of solar cells could be tolerated, and so the space industry proved the first commercial market, when PV technology emerged in the late 1950s.

It was the OPEC oil crisis of 1973 that sparked interest in potential terrestrial deploy­ment of PV. Two of the three specialist solar companies established at this time were founded by pioneers from the space industry – Bill Yerkes from Spectrolab, and Joseph Lindmayer and Peter Varadi from Comsat.

In due course battery-powered consumer products also turned to PV, and a host of solar-powered watches, lights, fans and garden products emerged.

The first practical uses on earth again focused on high reliability applications, where cheap electricity was unavailable. Solar systems started to supplement or replace batteries where dependable power commands a premium, notably for navigational aids and telecommunications equipment. Because the size – and therefore price – of a solar system is proportional to its output, low power applications are most cost-effective. In the telecommunications sector, in particular, this meant that manufacturers of the most energy efficient equipment found that they had a competitive advantage.

In the early years, the lion's share of PV systems were used for off-grid applications, replacing batteries and fuel-powered generator sets. As costs reductions continued into the 1990s, grid-connected uses started to emerge, with solar at last displacing traditional mains electricity. Before photovoltaics was cost competitive with fossil and nuclear energy, subsidies – such as feed in tariffs – were needed to bridge the price gap. Rooftop systems were the most prevalent initially, with residential and industrial solar roofs becoming widely deployed. As costs declined, solar systems became viable for progressively larger power requirements. They started to replace diesel generators, particularly in the telecommunications, transport and oil and gas sectors. Communities in remote islands, villages and health centres also turned to solar systems to replace diesel and kerosene.

The production volumes stimulated by these applications led to accelerated cost reduction and the trend towards grid parity, as previously described. This in turn makes utility scale solar power generation attractive. This has led in recent years to explosive growth in the deployment of 'free field' solar generating stations, the largest of which are now at the gigawatt scale.

The content is based on Philip Wolfe's book on the first quarter century of the terrestrial PV sector 'The Solar Generation: Childhood and adolescence of terrestrial photovoltaics', which was published by Wiley and IEEE last summer.