Solar installations need not always be an eyesore.
Scientists at the Nanyang Technological University (NTU) have found a way for them to look good too.
The researchers have come up with solar cells made of perovskite, a man-made substance.
The cells can be translucent and come in an array of colours, making it possible for them to be pasted on windows where they can convert sunlight into electricity, and beautify the place at the same time.
The effect is much like sunlight streaming through a stained glass window.
Like silicon, the material used in most solar cells today, perovskite can convert sunlight into electricity.
However, unlike brittle silicon, perovskite is processed from solutions and can be printed onto plastic sheets, making flexible solar panels a possibility.
Last week, scientists from NTU and the Singapore-Berkeley Research Initiative for Sustainable Energy showed The Straits Times a prototype of what such a flexible panel could look like, by printing perovskite on a 30cm by 30cm plastic sheet.
First, the researchers mixed various liquid chemicals, including the perovskite, together.
The solution is then poured into a screen printer, such as those used in T-shirt printing businesses, and printed onto sheets of plastic.
The scientists demonstrated that perovskite could also be printed on glass sheets of the same size. In 2013, the researchers said they could only produce glass panels measuring barely 1cm by 1cm.
A challenge in scaling up the panels was ensuring that efficiency was not compromised, as larger panels are usually less efficient than smaller ones, due to factors such as increased electrical resistance.
The researchers' first glass panels with perovskite covered areas of 0.75 sq cm and had an efficiency of less than 2 per cent. But the 70 sq cm one unveiled last week had an efficiency of about 14 per cent, compared with the 17 to 18 per cent of conventional silicon solar panels found on rooftops.
However, silicon panels are not ideal for use on building facades or windows as they are opaque and would block out light, pointed out Professor Subodh Mhaisalkar, executive director of NTU's Energy Research Institute.
But perovskite-printed cells are still more efficient when compared to other thin-film solar cells suitable for use on facades that are available in the market.
For example, dye-sensitised solar cells, made of carbon-containing organic material, have efficiencies in the range of 10 per cent.
Assistant Professor Nripan Mathews from NTU's School of Materials Science and Engineering said: "Perovskite solar cells have many attractive properties for commercial use. They can be made semi-translucent, to be used as a tint for windows... and they can also be thin and flexible, conforming to different surfaces and objects."