Frequently Asked Questions v1.0 alpha

(Under Modification)

On this Page:

• What is a solar water heater?
• How does it work?
• What can I expect from my solar water heater?
• What should I do (and not do) to maintatin my solar water heater?
• Trouble-shooting guide

What is a solar water heater?

A solar water heating system consists of a collector, an insulated storage tank and connecting pipelines. The solar panel of the solar water heater collects the sun's energy with a black absorber, facing the sun to catch as much solar radiation as possible. The heat collected by the absorber is transferred to the water flowing through the absorber and is stored in the storage tank. The storage tank is insulated so the water stays hot and can be used later in the day or even the following day. Solar water heaters are available in various sizes. An electrical backup for the water heater is also installed to provide hot water during periods when the sun does not shine.

How does it work?

The solar water heater works like a miniature greenhouse. Heat is trapped under the transparent glass cover. The absorber is made out of copper sheets covered with a special black coating that is designed to absorb as much solar radiation as possible. To prevent the loss of heat to the surroundings, the absorber unit is insulated at the back and around the sides. At the back of the copper sheets are copper pipes filled with water. When the sun shines on the absorber, the metal warms up, and the heat is transferred to the water. A cold water storage tank is positioned above the collector. One insulated pipe runs from the bottom of the storage tank to the bottom of the collector. Because the density of the cold water in the storage tank is higher than that of warm water, cold water flows down to the collector. The water that has heated up in the absorber will then be pushed upwards into the storage tank. This circulation will start automatically when the sun's radiation is strong enough, and will continue as long as the water in the tank is colder than the water in the absorber. This system does not require an electric pump, which is why it is called a natural circulation or thermosyphon system. Because of this peculiar system design, the hot water is always at the top of the storage tank. The hot water is therefore tapped from the top of the tank, and fresh, cold water flows in at the bottom. To maintain the undisturbed functioning of the system a constant supply of cold water should be available.

What can I expect from my solar water heater?

Obviously the output of a solar water heater system will depend on the amount of solar radiation available. On a good sunny day (i.e. solar insolation level @ 1000 WM2) the absorber will collect enough solar energy to heat 100 litres of water up to 60~C. One person uses about 25 litres of hot water per day, so the capacity of the system should be sufficient to provide hot water for a small household of three or four people. For larger households, or if more hot water is required, the size of the system should be increased accordingly. On partly cloudy days the solar water heater will still be able to heat water. Only when the sun is not shining at all will water need to be heated using the electrical backup system. But even then electricity is saved because the sun will have at least partially heated the water. The electrical backup will provide hot water within minutes after switching it on. The electric element will switch itself off when the set temperature of the thermostat is reached. It is not advisable to set the temperature higher than 60C. Water hotter than this is not usually needed, and a lot of electricity can be saved by limiting the temperature. Don't forget to switch off the electric element! Otherwise the sun won't have the opportunity to heat the water and a lot of electricity will be wasted. An average urban household uses approximately 30% to 40% of its electricity to heat water, about 85% of which could be saved with a solar water heater. Assuming that the average use is 100 litres of hot water per day at 60C, approximately 1000 units of electricity can be saved annually by using a solar water heater (also assuming that the sun provides enough energy for nine months of the year). In the remaining three months the electrical backup system can be used. These are very conservative estimates; in practice, the savings can be higher or lower depending on the use of the solar heating system.

What should I do (and not do) to maintatin my solar water heater?

Do's

Solar water heaters require little or no maintenance. Because of the thermosyphon principle there are no moving parts and no control units that can malfunction. Tile system will work automatically but there are some procedures you can carry out to improve the functioning of the solar water heater and thus increase electricity savings:

1. Clean the glass cover regularly. Dust and dirt that is allowed to settle on the glass cover will block the sun's rays and will reduce the output of the system. Depending on the surroundings (close to a road, dusty environment, etc.) it is advisable to clean the glass cover from twice every week to several times a year.
2. ' Prevent any shade on the collector. Trim back the branches of trees around the collector to allow as much sunshine to reach it as possible.
3. Be economical with the use of hot water. Try to minimize the frequency of hot water use. Only a small amount of energy may be lost, but if the pipes are long and you use hot water frequently, it will mount up.
4. Run the hot water slowly; this will avoid the mixing of hot and cold water in the storage tank.
5. Set the thermostat of the electrical backup as low as is comfortable. A temperature of 60C is usually sufficient. A higher setting will increase your electricity bills.
6. Ensure that there is always a cold water supply to the solar waler heater. Always leave the valve on the cold waler inlet open and ensure that the cold water tank is a/ways filled with water.
7. Once a year, flush out the complete system to remove any floating and settled dirt. If the water in your area is hard, use a water softener to prevent blockages in the collector pipes.
8. Once a year, inspect the cladding of the storage tank, the collector and the pipes between tank and collector. Make sure that the cladding is not damaged, and repair it if necessary. This will ensure that no rainwater runs into the insulation of collector, tank and pipes. This will improve the functioning of your system and increase its working lifetime

Dont's

Although a solar water heater is a relatively simple system and there is little that can go wrong, there are some things you should not do:

1. Do not close or block the vent pipe. It is essential that this vent pipe is open to the atmosphere and is higher than the cold water storage tank.
2. Do not place obstacles in front of the collector that will shade it.
3. Do not use coarse materials when cleaning the glass cover.
4. Do not leave the electrical backup switched on when it is not necessary.
5. Do not close the valve on the cold water inlet to ensure constant supply of cold water to the solar water heater.

Trouble-shooting guide

Here are some common problems with solar water heaters, and their solutions.

If, after using this trouble-shooting guide, you still cannot solve the problem, please contact us or any skilled solar water heater installer.

• No water is coming from the hot water taps:
  • Check the cold water supply: the valve on the cold water inlet should be open, and the cold water storage tank should be full.
• The system is only delivering cold water:
  • This is normal on heavily overcast days. A solar water heater can only heat water when the sun is shining or when there is light cloud. For an immediate supply of hot water, use the electrical backup. · If you have used more water that day, the solar water heater will need time to warm up the water again. For an immediate supply of hot water, use the electrical backup. · If neither of the above is relevant, check that there are no obstructions in the collector circuit. The thermosyphon force that circulates the water is rather weak, and it can be stopped by small air bubbles in the collector or by bends in the pipes between the tank and the collector. Check the circulation by feeling the temperatures of the inlet and outlet pipes close to the collector. When the sun is shining the outlet temperature should be much higher than the inlet temperature. Be careful: the outlet, pipe can be very hot! If you cannot detect the thermosyphon circulation (and there are no bends in the pipes), it is likely that there are air locks in the system. Drain the water out of the collector unit and then refill it. If this does not work, contact us.
• There is a large drop in water temperature overnight (more than 100C):
  • · Check the insulation around the storage tank. The warm walls of the storage tank and the pipes close to the tank should not be exposed to the cold night air. Ensure that the insulation is dry. If it is wet due to rain leaking through the cladding, or due to a leak in the tank, then it will not keep the water in the system warm. Ensure that the storage tank is positioned at least 1 foot (30 cm) higher than the collector. The thermosyphon circulation flow may reverse on cold nights if there is too small a difference in height between the storage tank and the collector.
• The system delivers only lukewarm water :
  • Ensure that the glass cover on the collector is clean. If it is dirty it will reduce the efficiency of the solar water heater. If necessary clean the glass. Ensure that obstacles are not shading the collector. If possible remove them. Ensure that a non-return valve has been installed. If a NRV is not installed, and there are mixing taps (for a shower) in your system, cold water can flow into the storage tank because the pressure in the cold.water line is always higher than that in the hot water line. If a non-return valve has not been installed, cold water can mix with hot water, thereby lowering the temperature in the storage tank. The solution is to install a non-return valve or have separate lines and taps for hot and cold water. Contact a skilled installer or plumber. Check the insulation around the water tank, collector and pipes. If the insulation around the tank is dainaged or wet, a lot of heat can be lost. Repair small holes in the cladding or insulation, or contact a skilled installer.
• There is condensation on the inside of the collector glass cover:
  • If this occurs only on cold mornings there is no problem. The air in the collector box always contains some moisture and this can condense onto the glass cover if it is cold. As soon as the sun shines on the cover the condensation should disappear. · If the condensation does not disappear when the sun comes out there is probably a leak in either the glass cover seal or the absorber. You can repair a visible leak in the glass cover seal yourself using a weather-resistant repair kit. For other leakages contact a skilled installer.
• The solar water heater is leaking water fry to determine the source of the water:
  • If it is not rainwater, try to locate and repair the leak or ask a skilled plumber to do it.
• There is no hot water supply even with the electric heater switched on:
  • Turn on the electrical backup. If there is no hot water after 30 minutes check that the thermostat has been set at the right temperature. For comfortable bathing 40C is sufficient, and for washing around 60C is required. If the thermostat has been properly set, check whether a fuse has blown (replace it), or there has been a power cut (in which case wait until the power comes back on). Check that the electrical backup system is firmly plugged in. If the backup still does not work, contact an electrician or your installer.