Harnessing the power of the Sun
By Dr TieJun Zhang
Sunlight is free, plentiful and a ready source of energy to harvest.
But while a number of technologies exist today to provide solar energy for a range of needs, other technologies have yet to be fully developed.
One that has good potential for the UAE is high-concentrating photovoltaics (HCPV) – producing electricity by using mirrors and lenses to concentrate light from the sun on to super-efficient cells.
HCPV takes up far less land space than standard photovoltaic arrays and panel fields, and can be far more efficient.
This is because it usually uses advanced multi-junction PV (photovoltaic) cells.
Each junction absorbs part of the solar spectrum, and multiple junctions can between them absorb a broad spectrum.
For instance, Boeing Spectrolab has made HCPVs that are a centimetre squares, 1,000th the size of other cells and yet able, because the energy is concentrated, to produce the same amount of power.
These cells can capture up to 43 per cent of solar energy, more than twice as much as commercial silicon PV cells.
In addition, HCPV is much less sensitive to temperature than common silicon cells, a great advantage in hot countries such as in UAE.
HCPV has a price advantage, too, as it uses only small PV panels (which are expensive), and relatively cheap concentrating optics.
Now the challenge for scientists at the Masdar Institute is to make use of the remaining 57 per cent of energy that current HCPV arrays do not capture, which is currently wasted as heat.
Working with researchers at the Massachusetts Institute of Technology, our aim is to use that thermal energy directly for power generation, cooling, desalination or other crucial functions.
We intend to do this by using tiny heat exchangers to collect the energy, and then an expander and pump to turn it into electricity.
Because HCPV takes up less space, it can be used in places where there isn’t much – such as the UAE’s many islands in the Arabian Gulf, remote stations or even on "urban islands", which are buildings and facilities that may be kept off the electrical grid within a city.
And with HCPV arrays being as small as a tree, they can also be mobile, providing energy like a portable generator.
We are looking into whether one could power car air conditioners or even an in-car refrigerator.
Additionally, the waste heat can be used to drive mechanical systems within the array, for desalinating water through reverse osmosis, or providing cooling with vapour-compression refrigeration. That would give us a more holistic product – one that not only provides power, but potentially water, cooling and other functions.
One aim now is to further improve the reliability and efficiency of these systems, using cutting-edge automation technology.
We want to produce arrays that can operate smoothly and without management from technicians, making them easier and more attractive for potential customers.
They need to handle the natural variation in solar energy, getting the maximum power output whatever the time of day or season with minimal effort from array owners.
It is our hope that this research will yield for Abu Dhabi a useful part of the overall sustainability puzzle that will contribute to the emirate’s goal of getting 7 per cent of its energy from renewable sources by 2030.
And with the global HCPV market expected to reach US$1.6 billion (Dh5.87bn) by 2017, we also hope to provide the UAE with a revenue stream through the intellectual property and potential exports of this unique technology, which will surely find applications around the world.
– Dr TieJun Zhang is an assistant professor of mechanical engineering at the Masdar Institute of Science and Technology.