x Abu Dhabi, UAESunday 23 July 2017

How to put solar cells on the Gulf's buildings

Buildings use two-thirds of the region's energy. And as cities grow, the need to limit that is ever more pressing.

Buildings account for about two-thirds of the Gulf's energy consumption. As the region's cities grow, the need to reduce this figure is ever more pressing.

One answer is to integrate solar cells into buildings. This is particularly advantageous for the UAE, where many people live in areas where it is not economically feasible to provide electricity through the national grid.

Building-integrated photovoltaics not only generate energy but also contribute to buildings' architecture, as roofs, façades, skylights and glass cladding. If you use a solar panel for your roof, you may not need to spend so much on the roof itself.

So why is it still rare in the Gulf? One reason is that the atmospheric conditions here are quite different from other regions - the air, for one thing, is much dustier. This means many of the lessons learnt and technologies fine-tuned elsewhere are not wholly transferable.

So we need to look at different solar panel technologies. For each, we need to assess cost, efficiency, climate, flexibility, use of diffuse sunlight, long-term stability, sensitivity to the angle of inclination, transparency, aesthetics and long-term operation costs.

Cost has long been the biggest barrier to large-scale use of solar cell technologies. We need to work out how to make them more cheaply, and put in place a system of feed-in tariffs to make the pay-off of installing them worth it. In a solar plant out in the desert, efficiency is less important - you can happily have thousands upon thousands of low-yield cells that sprawl over many square kilometres and add up to a large total production. But in cities, space is limited, so the technology has to be compact and collect as much energy available as possible.

This is where climate - namely temperature - becomes a problem. Some photovoltaic technologies work dramatically less well when it is hot, making them unsuitable for the Gulf. We need to look at technologies that do not suffer this temperature drop-off.

Flexibility is important, too. Buildings can be nearly any shape, making a flexible photovoltaic module more useful than a rigid one.

Even square buildings are an awkward shape for solar panels. They are often tall, with lots of vertical but few horizontal surfaces. And they are of course immobile, so the amount of power received by any one panel changes as the sun moves.

So they need to be as tolerant as possible to various angles of inclination, giving a similar power output when installed on either the facade or the roof.

And they need to be able to efficiently harvest energy both from full direct sunlight and more diffuse light - perhaps reflected from another surface.

Transparency is useful - a transparent cell can be used as a window, dramatically increasing the area on which it can be used. And if not transparent, they at least need to look good, or architects are unlikely to want to use them.

They need to last, too. If incorporated into buildings, solar cells need to last as long as possible without losing power over time.

While operation and maintenance costs for photovoltaics tend not to be high, they still contribute to overall cost. Their maintenance requirements must be manageable for the Gulf market.

All these parameters need to be assessed together to meet the local needs. To this end the solar energy materials and devices laboratory, which I head at the Masdar Institute, has received funding from abroad to test flexible solar cell technologies in the built environment within our campus and under the real outdoor conditions.

This joint project is allowing us to investigate the performance and other key features of these flexible solar cells for integration into the built environment.

Abu Dhabi is a very good model for a coastal Gulf city, so our results could be used as reference for applications throughout this region, as well as feeding into the Abu Dhabi solar rooftop plan, which aims to install 500 megawatts of photovoltaic panels on the emirate's buildings over the next 20 years.

 

Dr Mahieddine Emziane is associate professor of materials science and engineering at the Masdar Institute of Science and Technology.