Are Solar Chimneys a Viable Alternative to PV Cells?

Friday, May 8th, 2015
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While solar power is most commonly associated in the public mind with photovoltaic cells, there exist other promising alternatives for the conversion of the sun’s radiation into usable energy.

One such alternative is solar updraft technology, which is highly suited to hot and arid climates and overcomes some of the limitations that hamper the usage of conventional solar cells.

The approach entails the construction of extremely tall solar “chimneys” which uses air heated by the sun to generate energy, as opposed to direct solar radiation.

Solar updraft technology works by first using sunlight to heat the air contained by an immense transparent canopy positioned between two and 20 metres above the ground.

At the centre of the canopy stands the solar updraft tower itself – a tall, hollow conduit, through which the air heated from the sun’s radiation is channeled. As this warm air rises through the chimney, it powers turbines at the base of the chimney that generate electricity.

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The technology is easy to adapt to many parts of the world, given that all it requires is flat expanses of land and ample sunlight.

While the solar chimney may strike many as an innovative alternative to the common photovoltaic cell, the technology was actually first proposed over a century ago in Spain by army colonel Isidoro Cabanyes, and has already been deployed in various parts of the world, including Germany, Spain, China and Chile.

The technology possesses a critical advantage compared to the solar PV cells in that it is capable of overcoming the intermittency issues that hamper the operation of climate-reliant forms of renewable energy.

The solar chimney isn’t dependent upon direct sunlight to generate electricity, and can operate as long as the air in the canopy remains at a sufficient temperature.

Operation can be maintained long after sunset given that the solar radiation absorbed by the surrounding land mass will continue to provide warmth well into the night.

The ability of the adjacent land to trap and release heat can also be further improved by means of simple, cost-effective measures, such as the addition of a layer of gravel on the ground surface.

A further advantage is that the solar chimneys are not significantly affected by the presence of dust or grit in the atmosphere – a major problem in the types of desert environments that often considered the most suitable sites for photovoltaic cells, since the accumulation of opaque matter on panel surfaces impedes their efficiency.

Despite these advantages, the solar chimney remains a comparatively obscure technology within the field of renewable energy, chiefly as a result of their exorbitant initial capital costs.

Solar chimneys need to be built on an immense scale because of their low efficiency rate – estimated at between one and two per cent, as compared to eight to 15 per cent efficiency for photovoltaic cells, in order to be economical.

A classic example is the 200-megawatt solar plant currently proposed for a tin mine in Western Australia.

The project, which is being developed by German engineering firm Schlaich Bergermann and Partner (SBP) in collaboration with Hyperion Energy, will entail the construction of a one-kilometre high cement and steel chimney, propped upon a canopy measuring a staggering 10 kilometres in diameter.

The estimated cost of building such an immense infrastructure is approximately US$1.67 bilion.

If these initial funding costs can be overcome at the outset, however, solar chimneys still make sense from an economic perspective, given that they are capable of generating electricity at costs that are roughly in alignment with standard forms of solar power when built to adequate scale.

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