Watch the video here! Solartwin are working on a several technical innovations in 2009-10. Here is news of one. It is a revolutionary “thermal step change” thermochromic solar collector which, if successful, will change the global face of solar heating forever. Volunteers (from existing Solartwin DIY customers) are sought for field trials where two prototype collectors will replace one existing collector – for free.

Barry Johnston, Managing Director of Solar Twin Ltd, said today: “It’s still a project with some commercial and technical challenges. Right now we have a 30-40% chance of succeeding in profitably producing a commercially viable “thermal step change” solar thermal collector. But recent successful trials have boosted this chance of success from my original estimate of merely a 10% chance. This is why we are today going public with the story, one which we had previously shared mainly with with the International Energy Agency.

Past innovations

“A decade ago, Kerr MacGregor and Solartwin pioneered a simple solution to two big problems which were being faced by solar heating installers. A gloopy and bothersome chemical which we eliminated was antifreeze. This needs replacement every few years and it is six times more sticky than water. Replacing antifreeze is inherently not very green – and it needs six times more energy to pump than plain old water needs. By developing freeze-tolerant solar collectors, we were able to switch over to using 100% water as a heat transfer medium instead. The next problem we solved was that many old solar heating systems needed to be plugged into a mains electric socket in order to work at all. We simply deleted this problem and its associated 20% carbon clawback – which is attributable to this mains parasitics – by   making sure that all Solartwin’s zero carbon solar water heating systems use a solar electric (photovoltaic) pump to circulate the water which they contain.

The new challenge

“But here’s the new challenge – the solar water heating industry has a third big technical problem. It is this – that you simply can’t attach too many solar panels onto any hot water cylinder before something, somewhere, boils in summer, for example when you go away on holiday.

Boiling problems in old solar

“Boiling where collectors are oversized is a big problem, with nasty blow-offs in pressurised solar, and overheated antifreeze even coagulating and blocking some collectors. I hear anecdotally that oversizing is most acute in Ireland. The Irish solar boiling problem originates in its rather ill-thought out solar subsidy scheme. This appallingly wasteful scheme incentivises the installation of gigantic solar collectors because the subsidy is dished out only on the basis of   “per square metre of collector installed” – rather than on anything more sensible and performance-based such as (a) net energy gained or, better still, (b) net carbon saved. One hopes that the current retrenchment in my home country’s finances will result in this subsidy being better targeted in future.

How to stop boiling

“Solving boiling forever is where Solartwin’s new prototype “thermal step change” solar collectors come in. Having started off successfully with small scale “thermochromic thermal step change” collectors, we are now prototyping full size Solartwin collectors which, when they get hotter than you would want a hot water cylinder to be (ie 70-90C) they simply stop delivering any energy to it at all – by turning white.

Collector to reflector switch (and back again)

“By turning from black to white they reflect rather than absorb sunlight at high temperatures. We achieve this change by using a specially formulated, and currently rather expensive, “thermochromic” paint. Up to 70C this paint is black, and looks just like any normal solar collector’s black paint. But when it gets hotter than 70C its colour gradually starts for fade, so that when it reaches 80C the solar collector has become a solar reflector instead. This clever thermochromic effect is completely reversible. so if, after someone in the house uses some hot water, the collector finds it once again has to heat up water which is say at 20C. So it imediately turns black once more in order to heat it up.

R&D team

“We are working across Europe with a team of specialist chemists, high temperature coating developers, testing labs and a leading university in order to try to make this innovation happen. Above is a picture of two Solartwin collectors. The thermochromic one at the front is paler than the one at the back, which is a normal black Solartwin panel. This is because it is just starting to turn white at over 70C.

Loadaspanels

“This innovation, if we can get it to become commercially viable, will change the face of solar heating forever because no longer will you be limited to putting say 3 sq metres of solar panel on a normal 120 litre hot water cylinder. Instead you will be able to put up 30 sq metres instead – because nothing will ever boil. It is inherently safe. Plus some people will be able to reposition these larger collectors so that they are fixed to south facing walls in order to catch the scarce winter sunshine.

Trial volunteers needed

Besides doing lab tests, we are wanting to do actual customer field tests and so Solartwin are currently looking for an existing DIY Solartwin customer who has one Solartwin fitted to an existing hot water cylinder who is prepared to swap out their existing collector for two prototype thermochomic ones and who will give us regular performance reports. If, within five years they are not entirely satisfied, we will replace them with one normal collector. All for free – the catch is that the DIY customer supplies all the labour! Volunteers welcome…

The future

“My vision is that the south side of many buildings, new and old will be clad with afordable, freeze tolerant, non boiling thermochromic collectors – so that whenever the heat in them is needed it can simply be used.” says Barry Johnston.