Making the most of the sun to heat buildings is nothing new. Socrates encouraged it. More recently, glazed cavity walls have maximised passive solar gain, but with the problem that the heat can’t be regulated precisely. Now, a relatively new solar thermal air-heating technology has made its biggest appearance anywhere in the world on a British building: the Marks & Spencer (M&S) distribution centre in Castle Donington, set to open this year.
The ‘transpired solar collector’ (TSC) technology is a perforated metal cladding with a 20cm air cavity between it and the building wall. On a southerly or south-easterly aspect, the metal cladding is heated by the sun while ventilation fans create negative pressure in the air cavity, drawing in the heated air through the panel perforations. This heated air rises and is ducted into the building. When no heating is needed, the warm air is vented out, and fresh, cool air is drawn into the building instead. On cloudy days, supplementary heating may have to be used. The industrial appearance of this technology, and the large scale needed for efficiencies, means that it’s more suited to commercial properties and public buildings, so far, rather than homes.
The installation at the M&S distribution centre – branded SolarWall by installers CA Group – covers an area of 4,334m2 (about 16 tennis courts) and is the largest in the world, according to the Group’s Director, Brian Watson. On a clear day it will harvest in the region of 500w of thermal energy per square metre, and is expected to reduce CO2 emissions by over 250 tonnes a year.
In the UK, a SolarWall costs £60 per square metre, and the average size of installation is 200m2. “Payback is usually less than three years”, said Watson, who credits the SolarWall on their headquarters with reducing fuel bills by 51%.
“This technology is a fantastic innovation”, says Leonie Greene of the Renewable Energy Association. “Here in the UK, we’re familiar with solar thermal for water heating but not so much for space heating. We’re far behind Europe.”
Chuck Kutscher, Principal Engineer at the National Renewable Energy Laboratory in Colorado, says that – while TSC is efficient, cost-effective, simple and reliable – the downside is that it’s limited to preheating ventilation air during the day. “This technology competes with natural gas preheat as well as heat recovery devices”, he explains, “both of which can operate when the sun isn’t shining.”
TSC was first developed in the US by Conserval Engineering in the 1980s. In 1992, the US Department of Energy said it was in “the top 2% of energy related inventions”; today, there are over a thousand examples across 25 countries. – Paul Miles
Photo credit: Marks & Spencer