Saving Energy All Year Round with Solar Thermal Systems
One of the great energy saving revolutions of the last 20 years has been the steady move towards renewable energy systems that are powered by sources other than oil, gas, coal and other fossil fuels. Solar thermal hot water is perhaps the most visible and widely embraced of all renewable energy technologies and pipe insulation has a major role to play in ensuring a more efficient system.
The solar thermal family
Solar thermal is focused on generating hot water (solar photovoltaic or "solar PV" may look superficially similar but is a completely different technology that generates electricity - not hot water). For consumers "solar hot water" can seem like a monolithic technology it is actually a collection of different technologies that all do the same thing (heat water using the power of the sun!) in quite different ways.
"Direct" solar thermal
The simplest solar hot water systems are “direct” systems. In these systems water from the storage cylinder is pumped up to the solar panels, directly heated by the light of the sun and then returned to what then becomes a hot water cylinder. The water that ultimately comes out of your taps might have been pumped through your solar panels many times.
“Direct” systems are inherently simple but they have a number of disadvantages. The most obvious, and most critical, is that systems of this type are very vulnerable to pipe freezing. Because of this direct systems are only ever used in climates where the temperature is never expected to drop below freezing.
"Indirect" solar thermal
“Indirect” systems are slightly more complicated. Instead of heating water directly the solar panels heat a glycol-water mixture that never comes into direct contact with the drinking water. The glycol-water mixture circulates in a closed system, up to the solar panels, through them and then back down to the storage cylinder. Inside the cylinder the glycol-water mixture stays inside a looped pipe that effectively acts as the heating element of the system.
Because glycol has a much lower freezing point than water these systems aren't prone to freezing during the Winter. Other advantages are more subtle but just as important. Having a separate, closed, system running up to the solar panels means that the feed & return from the panels can be easily run at a different pressure level and temperature to that being maintained in the rest of the hot water system.
So which pipes need insulating anyway?
With complexity often comes confusion. Some of the pipes associated with a solar hot water system are located outdoors, others are indoors, some are operating at temperatures of 50-60°C whilst others might experience temperature well in excess of 100°C. How to correctly insulate such a system is one of the questions we're asked here at Kaimann on a very regular basis.
The short answer is that you can save energy and make the overall system more efficient by insulating any pipe that operates above ambient temperatures but the longer answer is that not all insulation materials are appropriate for use throughout a solar thermal system and you may need to install a bigger thickness in areas where the energy saving potential is higher. This is something that we'll explore in more detail in a future blog entry.