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Windows Can Power City Skyscrapers

Windows Can Power City Skyscrapers

By Kamal Alameh

City skyscrapers could soon be powered by windows that deflect infrared light passing through them to solar panels.

The world currently runs on about 16 TW of energy, and most of it is generated by burning fossil fuels. To level off the carbon dioxide concentration in air at 450 ppm – as recommended by the Intergovernmental Panel on Climate Change – there is a need to reduce the energy from fossil fuel burning to about 3 TW and produce the rest of the energy required from renewable sources. Currently around 0.5 TW comes from clean hydropower and 1 TW from clean nuclear, leaving 11.5 TW to be generated from new clean sources.

Much of the world’s increase in renewable electricity is fuelled by hydropower and wind power. Of the 4.5 trillion kWh of increased renewable generation projected for the period 2007–2035, 54% is expected to come from hydroelectric power and 26% from wind.

Apart from these two sources, most renewable generation technologies are not economically competitive with fossil fuels over the projection period, outside a limited number of niche markets.

Photovoltaic solar farms and wind turbines require extensive areas of land to generate significant amounts of power. For example, the land area needed to generate the renewable energy required to keep the carbon dioxide level at 450 ppm is about the size of Australia. Therefore, the integration of photovoltaic systems into buildings can offer a pathway to a future beyond fossil fuel dependence without needing huge land areas.

The residential and commercial building sector consumes about 20% of the world’s total energy. Since modern city buildings typically have small roof surface areas and large window areas, there are fundamental limitations on the maximum possible power output that can be generated using conventional roof-mounted solar panels.

However, substantial additional power could be generated through solar windows. Considering that solar infrared radiation carries around 50% of the total solar energy, and that strong infrared radiation exists day and night in the areas surrounding city buildings, infrared-harvesting windows could generate electric power even when the sun is behind cloud cover and even for some time after sunset.

With glass window panels covering vast areas of walls and roofs in modern buildings, significant economic benefits could be achieved if these glass surfaces were made energy-efficient. In hot climates, substantial reductions in air conditioning requirements can be achieved by integrating spectrally-selective “sunshade glazing” that reflects or otherwise redirects the infrared rays. Reducing the amount of non-visible radiation entering buildings would reduce the running costs of air-conditioning systems, thus providing substantial energy savings of up to 40%.

In addition, the energy generation for a typical 30-storey building could exceed 0.3 MWh/day – enough to power around 50 servers. As the glass could generate 50 W/m2, a 100 m2 panel facing the sun would generate 5 kW of electricity, providing more than 50% of the average energy needed by an office.

The use of energy-harvesting clear glass windows would also reduce the capital cost of the building infrastructure by up to 10%, with wider benefits including a reduced need to build new power stations.

My team at Edith Cowan University is collaborating with Tropiglas Technologies Ltd to develop and commercialise energy-generating clear glass panels capable of transmitting most of the visible spectrum of light while routing solar infrared radiation towards the panel edges for subsequent conversion to electrical energy. The glass panels significantly reduce the amount of radiation transmitted into buildings, thus achieving substantial savings in cooling-related electricity costs.

The technology is based on the integration of transparent microengineered optical structures and infrared-selective thin-film coatings to create shatterproof clear glass panels that harvest and convert ultraviolet and infrared radiation to electricity via photovoltaic cells placed within the window frames. Micro-engineered elements in conjunction with nanoparticle layers deposited between the glass panes deflect infrared light to the window edges, where it is converted to electricity by photovoltaic cells.

Our glass panels are especially designed to operate vertically. A larger angle of incidence leads to better infrared light deflection towards the glass panel edges, and hence to higher energy harvesting. Being vertically placed, a substantial reduction in land area required for panels will result, thus providing substantial growth in solar energy generation without large increases in land use.

Due to their ability to concentrate solar energy onto small areas at the edges of the glass panels, the window-integrated solar panels will require less volume of expensive semiconductor materials per Watt of energy generated compared with conventional roof-based photovoltaic modules.

Furthermore, the energy-harvesting clear glass technology directly addresses the impact of climate change by:

  1. improving the energy efficiency of commercial and residential buildings, with up to a 40% reduction in cooling energy compared with conventional glass windows;
  2. reducing the amount of artificial lighting required by transmitting a high proportion of visible light; and
  3. generating renewable power to replace fossil fuel-generated electricity.

Our energy-harvesting clear glass panels are designed in a variety of modules that can be integrated into new buildings or retrofitted into existing buildings. Examples of potential installations include glass windows, roofs, skylights and facades.

Tropiglas is also targeting the automobile and transport industries. For example, in the USA, 27 billion litres of fuel – or 10% of US imported crude oil – are currently used in automobile air-conditioning. Vehicle air-conditioning systems increase the fuel consumption of a conventional vehicle by 28%, and 100% for a hybrid electric vehicle. Tropiglas technology reduces this amount significantly and generates additional power for all types of cars.

Currently there are no commercial energy-harvesting clear glass products available that feature high optical transparency simultaneously with high energy-conversion efficiency. Our international R&D team in Australia, Korea and Russia is currently working on large-scale manufacturing processes for panel sizes exceeding 1 m2 with an energy-conversion efficiency of 5%.

Kamal Alameh is Director of the Electron Science Research Institute at Edith Cowan University.