Knowledge: Solar thermal
Domestic bliss
With biomass dominating the early dRHI installation figures, Richard Hiblen, MD
of Green Square, reasserts the case for solar thermal
ecently OFGEM released a report
on the first 10,000 domestic RHI
installations which publicised
that biomass technology has had
the largest uptake. But not many people are
aware that the second is solar thermal, and
with good reason, especially when mixing
with other renewable technologies.
Solar thermal is a simple system, and
although it is often confused or looped
together with solar PV, not only operates in
a totally different way, but delivers a totally
different kind of energy. Where PV panels are
generally around 15 percent efficient, solar
thermal is over 80 percent efficient – which
means significantly less panels for the same
amount of energy (as measured in kilowatts).
Another positive for solar thermal against
PV is the storing of energy. PV needs to be
used at point of generation (i.e. when the
sun is out) whereas solar thermal can store
R
Hidden gem: Although often overlooked in
favour of other renewable technologies, solar
thermal offers high efficiencies and simple
installation, says Richard Hiblen, MD at Green
Square
34 | www.renewableenergyinstaller.co.uk
its energy for later use via a thermal store
ensuring the homeowner maximises on the
free energy it produces.
Therefore, for a like-for-like sized system
(in kW output terms) they should both
produce approximately the same amount of
annual energy, however with solar thermal
you would generally use 100 percent of the
free energy produced whereas PV depends
on home occupancy at the time and what
appliances are being used at the time. Add
to this the capital cost difference – solar
thermal is typically half the cost of PV – and it
becomes clear why solar thermal is becoming
increasingly popular.
Furthermore, if you mix solar thermal with
another renewable technology the financial
benefits from the RHI increase further.
On a domestic installation, the RHI
currently pays 19.2p per kWh produced. If
we assumed annual generation of 2500 kWh
p.a. then the repayment would be £480 per
year. In addition you would obviously save
on your primary fuel bill as the main boiler
wouldn’t be required. This is especially
relevant in the summer as not only do solar
thermal panels produce around 80 percent
of the domestic hot water requirement, but
during the summer season traditional boilers
are also quite inefficient. High efficiency gas
boilers in a traditional system typically run
at around 57 percent efficiency during the
summer.
In addition, if you were to use a biomass
boiler as your primary heat source, not only
would this barely be used during the summer
months, but the RHI financial payments on
the biomass boiler is deemed as if it were. In
effect, you receive double payments on this
element of the energy requirement. This
was introduced as an extra incentive to
homeowners to increase the take up of more
than one renewable technology. And when
you consider the work required to replace a
traditional heating system, adding in solar
thermal at this stage is much lower cost
compared to a stand-alone solar thermal
retrofit installation as a singular piece of
renewable technology.
So once the financial incentive has been
established and the decision to install solar
thermal has been decided, you now have to
choose the best system and design for the
property and its owners. With solar thermal
still in its relative infancy in the UK, opinions
and examples vary from installer to installer,
but we are personally fans of the flat plate,
pressurised, glycol filled system. It works
every time, the capital cost is generally better
and there is very little to go wrong.