Tests of solar panel systems show that the UAE's harsh desert environment may limit the technology's affectiveness.
Cloudy skies for Masdar's solar project
On a dusty fenced lot near the planned site of Masdar City, the Abu Dhabi Future Energy Company has assembled 41 solar panel systems from 33 firms and has been testing them against one another for 10 months in the harsh desert climate. It is the first time anyone has undertaken a test on this scale, according to Sameer Abu-Zaid, the infrastructure manager for power and distribution for Masdar City.
Most panel manufacturers test their product in climate-controlled labs under perfect conditions, Dr Abu-Zaid said, but at the test site haze and humidity partially block sunlight, and swirls of dust coat the panels nearly every day. On the hottest days of summer, the surfaces of some panels were 75 to 80 degrees Celsius, which reduced the efficiency of silicon photovoltaic (PV) cells markedly, he said. "It's not optimal conditions," he added, noting that the panels had not achieved the output levels claimed by their manufacturers.
The test is not simply a science experiment for the company also known as Masdar, which is weighing a purchase of 230 megawatts of solar panels to provide 80 per cent of the power for zero-carbon Masdar City - a contract potentially worth billions of dirhams. Dr Abu-Zaid said solar panels would cover every roof and available surface in the city of 50,000, and it was crucial to see how each product would actually perform in the field.
"We decided to do our homework up front," he said. "The difference between this manufacturer and that manufacturer - it's never been tested." A quick detour to the control room demonstrated the potential payoff of the research. Across a wall, 41 electrical inverters displayed the amount of electricity produced by each unit. In the late afternoon sun on Tuesday, the best unit was producing above 400 watts - the worst, less than 200w. Each was advertised by the manufacturer as producing 1,000w under peak conditions, which usually occur between 10am and 3pm.
Testing will continue for at least eight more months and Masdar plans to release a report on the results. The winner, presumably, will be the firm picked to supply the panels for Masdar City. Dr Abu-Zaid was careful to not divulge details of which company was performing the best so far, but he said the test had offered some important lessons about the use of solar panels in desert conditions. The foremost challenge is the dust that settles on the glass coating, blocking the solar exposure of the cells.
"Dust has an impact, certainly," he said, adding that the panels were cleaned at least every other day. At one point, researchers left the panels untouched for a month, leading to "significant degradation" of performance. Masdar is now looking at developing automated systems to clean the panels in the field. The diversity of panel shapes and sizes demonstrated the array of technologies competing against each other. Some of the panels were blue, diamond-shaped cells under glass that looked just like the traditional photovoltaic panels common on rooftops around the world.
These silicon-based crystalline panels are expensive, but have achieved the highest rates of efficiency ever recorded for photovoltaic technology. Other panels in the field were enormous - at least three metres across - and looked more like black tar paper squeezed under glass. Called "thin-film" photovoltaics, the panels are viewed by many as the future of the industry because they can be made from inexpensive materials and are thin enough to coat the façades of buildings.
The trade-off, however, comes in lower efficiency. The thin-film panels need to be much larger to generate as much power as their silicon counterparts, leaving the designers of Masdar City with a tough choice. "If you've got a limited rooftop space, you don't want to go for thin film," Dr Abu-Zaid said. Even before it makes a final decision on which panel to buy, Masdar is moving forward with a 10-megawatt panel array that will provide power for the institute and initial buildings starting in March next year. The clean power will also feed into the national grid and offset emissions from construction vehicles, Dr Abu-Zaid said. Half of the panels would be silicon-based and half would be thin-film.
Masdar is also planning a second solar competition involving up to eight concentrated photovoltaic (CPV) systems next year. CPV systems use mirrors to concentrate sunlight up to 1,000 times on a small solar cell. Unlike standard solar panels, they adjust to follow the sun throughout the course of the day and can be much more efficient. Moving parts, however, are even more vulnerable to the heat and dust, and a field test of CPV technology was crucial, as well, Dr Abu-Zaid said.
Whatever technology the company ends up using, he said the tests had demonstrated that solar power works in the UAE, and is increasingly able to compete with more traditional forms of power generation. "In many part of the world PV, within five years, will be at grid-parity," he said. "All the manufacturers are forecasting price reductions year after year." Masdar is taking steps to make sure that when solar panels do enter the mainstream market, they will have already been vetted by their harshest challenger: the Arabian Desert.