To be able to install a solar thermal water heating panel system you need a store of water in your property. I am often asked…
Can I keep my existing Hot Water Storage Cylinder/Tank?
Many companies offer customers the option of keeping their existing hot water storage tank. This reduces the cost of installation significantly. However, is this the right thing to do?
To determine whether this is a good idea we should look at why the cylinder is normally replaced. For this article I will use the word tank and cylinder interchangeably.
Normal hot water tanks only have a single heating coil that comes from a boiler. This heating coil enables the boiler to heat up the tank. A new tank is normally required so that the tank has a second heating coil. This coil can be connected to the solar panels.
Hot water rises so in a normal tank the hot water is at the top and the cold (inlet) is at the bottom. This means that it is best to position the second heating coil at the bottom of the cylinder. This enable the solar panels to heat up the coolest part of the tank. It is not uncommon for the top of the tank to be very hot but the bottom to be at the mains water inlet temperature of about 10 degrees. If configured in this way, on a cloudy day, when the panels are only at about 25 degrees they can still make a significant impact on your heating bills. This is because the 25 degree water can be used to heat the 10 degree bottom of the tank to 25 degrees. The final heating can then be done by your boiler.
Systems that utilise the existing tank normally operate in one of two ways. Take a look at the diagrams below.
Immersion Heater Solar Coil
This device screws into the hole in your cylinder usually dedicated to an immersion heater. This consists of a small pipe that is coiled. Apart from being a poor design for a heating coil (due to the restriction of the immersion hole), Sadly most immersion fittings are at the top of a water tank (usually designed to boost the top of the cylinder). So if the top of the tank is at 50 degrees the solar panels will need to be significantly higher than this before the system will operate.
This heavily compromised configuration mean that the output from the panels is enormously reduced. This reduction in performance would certainly outweigh the cost of replacing the water cylinder for the twin coil variety.
Direct Solar Water Heating
The other method of retaining the original cylinder is to pump the actual water you use through the solar panel. This type of system pumps water from the bottom of the cylinder through the solar panel and then back into the top of the cylinder. This method completely upsets the natural way in which the hot water rises to the top of the cylinder. This type of system would not operate if the top of the tank is hotter than the panel. Unless the tank is cold or the the sun is shining brightly the system will remain switched off.
These types of system give the user the sense of having a solar heating system without many of the benefits. This is no good for either the environment or your bank balance.
As a result Intelligent Energy Solutions only fit twin coil systems for this type of application. We always make sure that what we are fitting will give you highest performance and the best return.
