Researchers at Ulster University’s Centre for Sustainable Technologies have recently tested their prototype SolaCatcher device that heats water and stores it at night.
Commercially available domestic solar thermal systems can provide about 60 per cent of total hot water at a capital cost of around £4,000. For more than 10 years, Dr Mervyn Smyth and Dominic McLarnon of Ulster University have been developing simple, low-cost alternatives for the UK market.
‘The existing distributed systems work fine — I have it in my own house — but you’ve got piping arrangements, control systems and pumps, which all add in additional cost, whether that be components or bringing specialist labour in, and you’ve got major disruption to your existing systems as well,’ said Smyth.
The team claims that SolaCatcher — a passive device — has an installation cost of around £500 and will produce between 15 and 20 per cent of domestic hot water over the same period.
The device is a black, vertically positioned cylinder made from three concentric tubes — the outer tube forming the aperture and casing. The two inner tubes form the collector and storage element, and are arranged to create an annular space subject to lower pressure, which contains working fluid, generally water.
‘At a very low pressure, at around 0.05 bar, it will boil off at 35°C to create vapour inside the cavity that condenses on the outer surface of the inner vessel, giving you a latent heat transfer,’ said Smyth.
The condensed vapour then runs down the tube to a reservoir at the base of the annulus to restart the cycle.
‘It continues and continues as long as you’ve got heat or solar energy falling on the outside; conversely, at night time that process stops, therefore your thermal store is insulated via the vacuum — a thermal flask in essence,’ he added.
The team has been testing a prototype device measuring 1.2m in height with a volume of 40 litres out in the field and at the university’s solar-testing facilities.
The next step will be to work with local housing authorities to bring the technology into existing premises and new stock.
McLarnon said the device could also have military applications in temporary housing for soldiers and for disaster relief, caravans and even beach showers.
‘[It could be used] anywhere where you’ve got a cold feed going into a hot water storage tank, as long as you’ve got access to that cold feed,’ he said.