SOLAR PANELS 3
THERMAL PANELS FOR HOT WATER
By John Murphy
(Republished courtesy of the Informer)
Over the last two months we have explained the Government’s new Conto Energia, designed as an
incentive to install photovoltaic (PV) solar panels, and then examined whether they would be
worthwhile for you. This month’s topic is Thermal Panels, the ones that produce hot water, not
electricity. In terms of technology, they are a good deal less sophisticated that PV panels, which
also means that they are cheaper and, for the time being at least, a lot more efficient. Given that they
don’t generate electricity, they have nothing to do with the Conto Energia and do not attract any of
the government incentives that we have been discussing in these pages. This doesn’t mean that they
don’t or won’t attract other kinds of grants (e.g. EU, regional or local government grants), but these
are for you to research at the time you decide to invest, because they can vary considerably from
area to area and from period to period.
Also worth remembering is that installing solar panels would normally be considered a house
improvement and therefore eligible for the tax deduction of 36% of the cost spread over 10 years.
The Government seems to want to extend this benefit to 2006, but it is not a permanent deductible.
The essential point about thermal panels, especially if you are in an area with a lot of sunshine, is
that you save money on the energy (generally gas, oil or electricity) that you would have used
otherwise to heat water for your house. And if you reckon that this could be your main area of
savings (as opposed to lighting or other power uses), then thermal panels could be a cheaper and
less complicated route for you to take.
What about installing both, you ask? If you heat water electrically, this would almost certainly be a
case of overkill, especially under the Conto Energia system as you need a fair amount of power
consumption to absorb the savings that you will run up with PV panels. The situation would be
different if you normally heated the house and the water supply with gas.
HOW DO THERMAL PANELS WORK?
The basic principles are fairly simple: the rays of the sun heat up the “solar liquid” (a mixture of
water and anti-freeze) in tubes running through the solar panels. Heating up, this liquid then flows
naturally through the system and transfers its heat to the water held in a tank, from which it enters
the house’s plumbing system. At this stage we have to introduce the concepts of natural and forced
circulation, because this is a choice that you will have to make if you decide to go this route.
In the case of natural circulation, the water tank is positioned horizontally at the top of the panels.
Not altogether pleasing aesthetically, but simple to install and therefore cheaper than the alternative.
The water in this tank gets heated by the sun, via the panels, prior to reaching the boiler, with the
result that less energy (if any) is needed to get the water to the desired temperature. Generally
speaking, no extra heating will be necessary if the house is in a very sunny area or the house is used
mainly during the summer. In winter or during a prolonged period of bad weather, an extra boost
will be required.
To summarise, the advantages of a thermal panel system with natural circulation is that it is
relatively cheap, fairly easy to install and highly efficient when used essentially during the summer
or in places with a high level of sunshine. Disadvantages are that the external water tank can be a bit
of an eyesore and efficiency is a lot lower in winter or in places with a low level of sunshine. Mind
you, almost anywhere in Italy gets more sunshine than Germany or Scandinavia, where these panels
are very popular. So these levels are all relative. You don’t necessarily have to be in Sicily.
A forced circulation system is more sophisticated than one with natural circulation. Out on the roof
there are only the panels (so no unsightly tank). The tank is installed inside the house and stands
vertically, rather than horizontally, which means that cold water doesn't mix with hot water, raising
its efficiency even more. When the sun heats up the solar liquid in the panels, a mechanism
measures the temperature reached. If it is higher than the temperature of the water in the tank, a
pump shifts liquid from the panel into a coil in the tank which heats up the water for use in the
house. If then additional heat is needed, say during winter or a prolonged period of bad weather, the
boiler can be called on to boost the temperature. In any case, the boiler will be used less than it was
without the solar panels and this will lead to considerable savings on your gas, oil or electricity bill.
To summarise, the advantages of a thermal panel system with forced circulation are that it is more
efficient because the water tank is vertical and it is aesthetically more pleasing. It is more suitable
for houses in places with a relatively low level of sunshine and especially when there is prolonged
winter use. The main disadvantages is a higher cost and more complex installation.
Another point worth bearing in mind is that, the roof has to bear the weight of the water tank in the
case of a natural circulation system, whereas it doesn’t with forced circulation because the tank gets
installed inside the house. Depending on the type of roof, this could be a limiting factor.
SIZE IT UP
But – you might be asking – how does this work out in terms of size and volume? Also depending
on the number of people who are likely to be using the house at any one time.
Natural circulation Panels Tank Weight on roof
No. of people Panel size No. Tot. surface Size & capacity Panels & tank
2 people 2.05 x 1.010m 1 2.1 m2 0.53 x 1.10m = 120 lt 295 kg/m2
3 people 2.05 x 1.275m 1 2.6 m2 0.57 x 1.32m = 200 lt 340 kg/m2
4-5 people 2.05 x 1.010m 2 4.2 m2 0.57 x 2.05m = 300 lt 350 kg/m2
Forced circulation Panels Tank Weight on roof
No. of people Panel size No. Tot. surface Size & capacity Panels
3-4 people 2.136x1.003m 2 4.4 m2 0.69 x 1.55m = 300 lt negligible
5-6 people 2.136x1.246m 2 5.4 m2 0.79 x 1.58m = 400 lt negligible
For further information, contact Enerpoint (www.enerpoint.it).