Solar Energy

Solar Hot Water Panel

This solar water-heater can provide from 140-180 liters of hot-water per day at temperature of 60-75 degree Celsius depending on the weather. View of Solar Water Heater Panel (AG-I), which is manufacturing in metal factory.


Open Loop Solar System Operation
This is the most common type of solar hot water heating installation in southern California.Technically, this system is known as an "active open loop" type. It's operation is very simple.In an "active open loop" system, water from a large storage tank or tanks is heated by the sun as the water passes through solar panels. The system is called "active" because it uses a small pump to circulate the water from the storage tank through the collectors and back into the storage.

The pump is turned on automatically by an electronic differential thermostat. This device reads the temperature in the collectors and also in the storage tank. When the water temperature in the collectors is higher than the tank water, the pump is turned on. Water gets circulated through the panels and solar energy is harvested.

The system is called "open loop" because the loop of plumbing from the storage tank up to the collectors is open to city water pressure. So the whole solar system is open to the city water line. In a "closed loop" system, the solar plumbing is separated, closed off, from city water. Heat is transferred through a heat exchanger. An open loop system is more efficient. It is also simpler, and therefore more reliable.


Solar System Performance

On warm sunny days, your solar water heater will produce storage temperatures of approximately 140 degrees F.

* Note: Large amounts of heat are lost through the recirculation lines. We have reduced this loss with two devices. First, a time clock automatically turns off the recirculation pump between the hours of 12:00 a.m. and 5:30 a.m. when hot water use is minimal. Also, an Aqua stat allows the recirculation pump to come on only when the water in the line falls below 120 degrees F.

** Note: Recirculation lines are most commonly found on apartment buildings rather than single family dwellings.

The information provided in this pack is of a general nature and should not be used as a foolproof guide to carrying out solar water heating installations. The CEI takes no responsibility for any actions you may take in relation to the information given in this pack. You must make sure that you familiarize yourself with manufacturers instructions, water company regulations, planning permission if required, or any other laws or regulations in place at the time of installation and that any person carrying out an installation does so at their own risk.


What is Solar Water Heating?

Solar Water Heating (SWH) is a system for heating water using energy from the sun. Solar energy is collected by a panel, which is connected by pipes to a hot water storage device such as a hot water cylinder. Systems can be installed for domestic hot water, swimming pools, caravans and similar applications.The main focus in this pack, is on domestic water heating, but the same principles apply to all solar systems. A description of a typical domestic hot water heating system is described here.


Why install Solar Water Heating?

  • It can save you money using free energy from the sun to heat your water
  • It helps the environment by reducing greenhouse gas emissions 
  • It takes your hot water system into the 21st century 
  • It could add to the value of your house 
  • It can be a fun DIY project 
  • If installed properly, it should be virtually maintenance free


What happens in different seasons of the year?

SWH depends on radiation not direct sunlight so it works even on dull days. However, in winter, although a panel can be effective in helping warm your water, you will still need your existing hot water heater to provide most of your water heating needs. You should note that these systems are not designed to work in conjunction with your central heating radiators - they can only heat your water. 

However, in the Autumn, Spring and Summer, a solar panel can yield surprising results, often not requiring any support from your boiler. Depending upon your system and how and when you use your hot water, you could find that almost all your needs are met by a SWH panel at these times of the year.



  • You need either a southerly facing roof or two roofs facing east and west 
  • The panel usually sits on top of existing tiles/slates 
  • You can carry out a DIY installation or can use an approved contractor 
  • SWH systems start at about £1200 for a DIY installation


Disclaimer: Whilst many people have successfully fitted their own solar panels, it is important to recognize the dangers involved, especially when working on a roof. This information pack does not attempt to deal with issues surrounding health and safety for DIY installations of systems. As such, the CEI urge extreme caution if you intend to carry out the work yourself.


Technical Details
The diagram shows a typical SWH sealed system used to supplement a conventional domestic hot water system.

The collector (solar panel) should face south or close to south and lie on a pitched roof that will provide the natural angle to face the sun.

A conventional central heating pump forces water through a coiled pipe in the solar panel where it is heated by the sun. The heated water then flows down and through a second (lower) coil in your hot water cylinder, referred to in the diagram as a solar cylinder. The hot water passing through this coil heats the water in the cylinder.

The slightly cooled water is then returned back to the solar panel via the pump. The controller box continuously compares the temperature in the panel against that in the hot water cylinder (see dotted lines). It switches the pump on when the water temperature in the panel is hotter than that in the cylinder and switches it off when the reverse conditions apply. As long as the water in the hot water cylinder is at the required temperature, your existing boiler will not switch on. The water flowing around the solar system is used to heat the water in the cylinder indirectly. This means that no water in the SWH system will come into contact with water in your hot water cylinder. The heat is transferred, not the water.


This is beneficial because:

  • It keeps the total amount of water flowing in the solar system to a minimum, making the system more efficient at bringing heat down from the panel 
  • anti-freeze needs to be added to the water in the solar system circuit as it is partly outside the house and could freeze in winter. As an alternative to using anti-freeze, a drain back system can be used. In this the panel water drains back into a special bottle when the pump switches off.


An extra coil in your hot water tank

Normally the solar coil in the hot water cylinder is additional to the standard cylinder coil connected to your boiler. It is possible to fit a second solar coil into your existing cylinder, but as this can be a very tricky operation, it is generally better to purchase a new twin coil hot water cylinder. These can be purchased with an optional immersion heater socket at the top if required. However one manufacturer, Solar twin, has developed a system that uses a solar pump and your existing cylinder.

The air vent shown on the diagram is installed at the highest point and is required to prevent air locks. As this is a sealed system, an expansion vessel is also shown which allows for expansion and contraction within the system as it heats up or cools down. 

The system is filled using a one-way valve (not shown). Care must be taken to ensure that water contaminated by anti-freeze does not get into the water feed supply. As an alternative, systems may be filled up from a small water tank as in a conventional central heating system. In these systems the tank needs to be higher than the top of the panel, so that water drains back into the system. In this case an expansion vessel is not needed and the water supply will be automatically isolated.

You can also buy an electronic display board which can be mounted in a convenient inside location which gives both roof panel and cylinder water temperatures. This is fun when showing guests how marvelous it is to heat your water from the sun!



Solar panels of the type described above are called flat collectors. A flat collector is basically a piece of copper tube, bent to form a serpentine shape and then soldered to a sheet of copper. The tube and sheet are painted black and are mounted in an insulated box with a suitable glass or plastic lid.

You can even make them yourself but, if you do not wish to do so, they are available at increasingly competitive prices from various manufacturers. They are very effective and require little maintenance. An alternative is a vacuum tube collector that contains a heat sensitive liquid. Vacuum tube collectors are more expensive than flat collectors but are more effective in winter.

The table below shows suggested collector area and cylinder capacity needed for hot water provision for various sized households. This can only be a rough guide as it depends on whether residents are in or out most of the day, prefer a shower to a bath, use a washing machine regularly and so on.


Solar twin Solar water heater System
100% solar hot water from an efficient solar panel for washing and bathing

FREE HOT WATER ? in your home, all year round INFLATION FREE - TAX FREE

Solar twin ? this is the name of the unique 100% solar powered water heating system, which was invented, patented and developed at Napier University in Edinburgh and was awarded a SMART technology award by the DTI. The Solar twin solar heating design make possible an annual saving of up to 70% of the overall hot water heating bill for a house of 4 people, frees you from safety concerns about toxic antifreezes, mains voltage and smash able glass panels or tubes.