Andreas Späth

A rooftop solar revolution

2015-08-31 10:11

Andreas Wilson-Späth

Next time you get the chance to look at your home town from an elevated position, the top of a hill or a tall building, for example, take a moment to consider how much unused space there is available on the roofs of the houses – perfect real estate for acres of photovoltaic solar panel arrays that could pump out cheap, clean electricity every sun-drenched day. So why aren’t we using this untapped urban resource?

Granted, with the price of solar panels dropping continually around the world, we are starting to see them glistening on more and more roofs, even here in South Africa, but there is still a lot of unutilised potential out there. Luckily, new tools promise to make it easier for the owners of buildings to assess whether they should be investing in their own rooftop solar power installation.

In the United States, a Boston-based start-up company called Mapdwell is using aerial and satellite imagery in conjunction with sophisticated software to evaluate the solar potential of roofs in cities.

After creating a high-resolution three dimensional model of urban areas, their system takes into account various parameters, including the shape, size and orientation of a building’s roof along with the relative position of the sun through the year, the potential shading effect of nearby structures and trees, as well as historical sky conditions such as cloud patterns.

It then allows homeowners to assess how they can best use their roof to farm sunlight, providing them with a detailed cost-benefit analysis and information about how much they can expect to pay, the potential carbon offsets they can achieve and how long the payback period for their initial investment will be.

Apparently Mapdwell’s system, which was developed at MIT, is capable of predicting solar potential to within 4 to 10% of actual real-world observations. Currently their maps are only available for a selection of cities in the USA and two in Chile, but they have plans to expand their coverage.

In a 2013 pilot project, the company showed that the 17 000 roofs of the city of Cambridge, Massachusetts, where MIT is located, could provide as much as a third of the municipality’s electricity requirements if they were used to install solar panel arrays costing a total of US$2.8bn.

More recently, they’ve used their system to estimate the solar potential of the million odd roofs in New York City’s five boroughs. The result? A combined total capacity of about 11 gigawatts, generating over 13 million megawatt hours of electricity per year.

Producing that much renewable energy using sunlight instead of fossil fuels would represent a carbon offset equivalent to planting 185 million trees. Not a bad way to use a lot of otherwise empty space.

Earlier this month, Google entered the fray with its Project Sunroof which currently allows people in selected parts of the USA to evaluate the solar potential of individual buildings. There are plans to increase coverage to the rest of the country and, knowing Google, probably the remainder of the planet in the due course of time.

Perhaps we should take the South African decision-makers who are so intent on spending a trillion rand on a fleet of new nuclear power stations on a sightseeing trip – to the top of Jozi’s Carton Centre or Signal Hill in Cape Town, say – to show them what they appear to be missing: the space to generate plenty of climate-friendly electricity quickly and affordably.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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Sweet day for justice

2018-03-18 06:03

Sweet day for justice

2018-03-18 06:03

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