So how does it work?
Water is circulated between the solar
collector on the roof to heat your hot water cylinder (usually in the airing
cupboard). Once installed, it's fully automatic and its performance can be
monitored with the controller display.
The vacuum
tube solar collector concentrates
sun's energy to the manifold at the top of the collector. The
controller
continuously compares the temperature in the manifold against that in the hot
water cylinder. When the water temperature in the manifold is hotter than the
water in the cylinder, a pump circulates water through the manifold, down well
insulated pipe-work and through a second heat-exchange coil in your hot water
cylinder (referred to as a solar cylinder or twin-coil cylinder). The
water + antifreeze flowing around the solar system is used to heat the water in
the cylinder indirectly. This means that no water in the Solar Heating system
will come into contact with water in your hot water cylinder. The heat is
transferred, not the water.
The slightly cooled water then returns back
to the solar panel. As long as the water in the hot water cylinder is at the
required temperature, your existing boiler will not switch on.
Will I need planning
permission?
From April 6 2008, homeowners have been able
to install solar panels, without needing to get planning permission, as long
as there is no impact on others. Size limitations have been set to reduce
impact on neighbours. Solar panels attached to the building must not protrude
more than 200 millimetres from the roof slope. The only exception is if your
property is a listed building or is in a conservation area, in which case you
will need to consult with your council planning department.
Will I still need my fossil
fuel boiler?
A solar system will provide typically between
50-70% of your hot water annually. This ranges from 95% in summer to 10-20% in
winter. Your existing boiler will provide the rest. Solar systems can be
used effectively with gas or oil boilers, Agas, Rayburns, solid fuel boilers,
and many combi-boilers.
Do I need to replace my
existing hot water cylinder?
Replacing your existing cylinder with an
efficient purpose-built, twin-coil solar cylinder will result in the most
efficient system, so this is recommended. However a lower-cost option is to
use a "retro-fit" solar coil, which can be fitted in place of the immersion
heater in your existing cylinder. This will reduce the initial outlay, and if
required the system can be upgraded by replacing the cylinder some time
later. Another option is the use of an external heat exchanger (Willis
Solasyphon). This can be used with pressurized and unpressurized tanks.
Do I need a larger cylinder?
In many cases, it is recommended to increase
the size of the hot water cylinder by ~25% due to the higher position of the
boiler coil in a solar cylinder. Since in winter, when the solar contribution
is less, some water below the boiler coil will not always be heated.
How can I connect solar panels
to my existing combi-boiler ?
Any solar hot water system requires a tank
somewhere in the system to store the large quantities of heat generated. When
connecting to a combi boiler, a tank (referred to as a "Thermal Store") is
situated upstream of the combi-boiler, so that the water going into the combi
is pre-heated. For all but the most recent "solar-ready" combis, it is
necessary to install a mixer valve to limit the temperature of the water on
the inlet to the combi to about 40-45 degrees. This prevents the combi from
cycling. For most of the summer the combi can be switched off completely and
the mixer valve temperature can be increased to ~60 degrees.
I am getting a new boiler now
and would like to add solar later, what
do you recommend?
I would recommend the following: get a conventional condensing boiler
(not a combi) and a solar twin coil water cylinder. A twin coil
cylinder has one heating coil that is connected to your boiler and the
other (the lower one) connects to the solar panel. Check out the prices
here for our vented and unvented twin coil cylinders.
Unvented (mains pressure) cylinders give better water pressure for
showers etc, but the cylinders are more expensive since they have to
withstand high pressure. If you already have a vented cylinder (with a
header tank) you may want to simply replace this with a
vented twin coil
cylinder. A solar twin coil cylinder is not much more expensive than a single coil
cylinder and it gives you the option of adding the solar panel very
easily at a later stage. So since you plan to add solar at a later stage you should definitely ensure that you get the right cylinder
now. The cost of your solar kit will of course be less when you come to
buy it, since you will already have a suitable cylinder.
Does the solar water heating
system contribute to the central heating?
In most installations the system is designed
for water heating. This reduces the load on the central heating boiler and the
improved insulation of the new cylinder makes the conventional water heating
system more efficient. Towel rails can be added to system, however winter
space heating is not a recommended application.
If a company tells you
otherwise, seek a second opinion. (The
reason for this is that when the energy demand is at its peak (e.g. cold long
winter evenings) the supply of solar energy is at a minimum.)
Can I install this myself?
For a successful installation, a solar hot
water system requires plumbing, roofing and to a lesser degree, electrical
skills. Some solar training is recommended, but many competent DIY enthusiasts have
successfully installed their own systems. What is most important is an
appreciation of the high temperatures that these solar collectors can achieve.
We offer training, and advice on installation, and can provide assisted on-the-job
training (one of our experienced installers will guide you through your first
installation).
Where will I place the solar
collector?
On a roof or wall, ideally facing South, or
anywhere between South-East and South-West for best performance. If your roof
ridge is oriented north-south, you can install two smaller panels, one on each
side of the roof (a dual-aspect installation). This works well since the east facing panel will take
advantage of the morning sun and the west facing panel the afternoon sun. The
controller can be programmed to take account of dual panel installations such
as this.
What is the ideal angle to
mount the panel?
Usually when mounting on a roof
just use the roof angle. Angles between 25-90 degrees (i.e. wall mounted) are
fine. If you are not constrained by a roof angle (such as with a flat-roof
installation) then the simple answer, is to use the latitude. Using a south
facing panel in Southern England as the example (latitude 51 degrees North).
At the spring/autumn equinox the ideal angle for the panel is 51 degrees to
the horizontal. The earth's axis is tilted 23 degrees, so at the height of
summer the ideal angle would be (51-23)=28 degrees, and in mid winter
(51+23)=74 degrees. Some people prefer to set the optimum angle for winter
(~60 degrees) since there is a surplus of energy in the summer. If you
specify larger panel size but use a winter-optimized panel angle, this is one
way of flattening the supply/demand curve, and giving more contribution out of
season.
How does a thermosyphon system
work?
As water is heated, it expands and becomes less dense, so hot water rises. If
the solar panel is positioned below the hot water tank, this natural
convection effect will automatically circulate the working fluid around the
system. The top of the panel should be at least one metre below the hot water
tank, and it is best if it is positioned close, but 2-3 metres below. A
thermosyphon is simple and elegant since it does not require a pump, or
electronic controller.
I have a
swimming pool, will I benefit from this system?
Swimming pools are a
very good application for solar heating. Our collectors can be roof-mounted or
pool-side. Its possible to design a system that will provide hot water for
your home as well as your pool. Heating a pool using conventional fuels is an
expensive business. Solar will make significant energy savings and enable you
to maximize the season.
