Frequently Asked Questions about Solar Water Heaters

1. Is solar water heating a viable alternative to gas or electricity?

Solar should not be considered an alternative to gas or electricity, but rather a supplement. Solar cannot completely replace the need for gas or electric heating, as there are sometimes days with little sunlight. Averaged over a year, a properly sized solar system can provide 60%–70% of a household's hot water needs. Providing more than this is not advisable, as it can lead to excessive heat production in the summer. The hot water system can easily be automated to ensure hot water regardless of sunlight levels.

2. How long will it take to recoup my investment?

Solar collectors are much cheaper than many other solar water heating systems. For a household of four, the price of a complete system may not be much more than a new electric or gas system. Depending on your location (solar levels) and your electricity usage for hot water, the annual savings on electricity or gas will vary. However, in a typical household that spends 25% of its electricity bill on hot water heating, the full purchase price can be recouped in just 4-5 years through reduced bills. You will certainly achieve significant savings over the lifespan of the solar hot water heating system.

3. Can solar collectors be used in cold weather?

Yes. Collectors can be used in temperatures as low as -50°C, although performance is significantly reduced in such extreme conditions. Good heating performance is still achieved in mild sub-zero conditions.

4. What happens if one of the solar tubes is broken?

Firstly, the tubes are very strong and not easily broken, but if the worst should happen, solar tubes can be easily replaced. They are inexpensive and readily available from your local dealer. The solar collectors can operate with several broken tubes, but efficiency will be reduced, so it is recommended to replace broken tubes immediately.

5. Will water be heated on a cloudy day?

Yes. Although the heat output of the solar collector is reduced on cloudy days, it will still be possible to heat water. If it is a very cloudy day or raining, then more gas or electric boosting may be required to keep the water at the desired temperature. This system is automated, so you won't have to worry about running hot water on a rainy day.

6. Can I connect a solar collector to my existing hot water system?

Usually, yes. Simple retrofit valves can often be used to allow solar energy to connect to your existing cold water supply. If your tank cannot accept the solar inlet directly, an additional storage tank can be installed to preheat the cold water before it enters the existing tank.

7. Are the solar collectors noticeable on the roof?

If only the collector is mounted on the roof, it should be well integrated into the roof structure. Solar collectors are very thin and can be mounted on a roof without any visible gaps. From a distance, they look a bit like a skylight. You may need to check with your local council regarding building restrictions when installing your solar system.

8. Can solar collectors be mounted on a flat surface?

Yes, they can be mounted on a flat roof or on the ground using a stainless steel flat roof system. The collector should be installed at an angle of at least 20 degrees to ensure optimal heat transfer.

9. How do I protect my solar system in sub-zero temperatures?

If you have a system operating in areas with sub-zero temperatures, then frost protection must be implemented. The simplest way to prevent freezing is to use a controller with a low-temperature setting. When the manifold temperature falls below a certain preset temperature (5°C/40°F), the pump will circulate, heating the collector with water from the bottom of the storage tank. The pump does not run continuously, but only periodically, its frequency depending on the outside temperature. In extremely cold regions, a closed loop using a glycol/water mixture may be appropriate.

10. Will the solar collector pose a fire hazard in hot, dry weather?

No, all solar collector components are rated for high temperatures and are non-flammable. Therefore, even in strong sunlight with the circulation pump switched off (stagnation), the system will not catch fire or produce sparks. The majority of solar collector components are made of stainless steel, aluminum, glass, or fiberglass. The manifold outlet should be fitted with a T-rated connector. 

A temperature relief valve prevents overheating if the temperature exceeds 99°C/212°F.

11. Can the solar collector heat water to a sufficiently high temperature?

Yes, in good weather, the solar collector can heat water to the boiling point. Generally, this is unnecessary, and the system should be designed to provide a daily temperature increase of approximately 25-30°C (45-54°F) in the summer. Sizing a domestic system to heat water up to 60°C/141°F in a single day is not practical, because if hot water is not needed for one day, the system will boil the water the next day and then dump hot water through the temperature relief valve. This is a waste of both energy and water! Please size your solar water heating system appropriately to ensure optimal performance and minimal water waste.

12. What maintenance is required for the solar collector?

Under normal circumstances, no maintenance of the system is required. Due to the shape of the tubes, regular rainfall and wind should keep them clean. Should a tube break, it should also be replaced. However, this is an inexpensive and simple task. Any handy person can replace a tube (while adhering to local health and safety regulations). Solar collectors can operate with several broken tubes, but the efficiency will be slightly reduced.

13. Can solar collectors be used for large-scale hot water production?

Yes. Solar collectors can be connected in series or parallel to provide large-scale hot water production for commercial environments such as schools, hotels, or office buildings. There is virtually no limit to the size of the system, but collectors must be installed in banks of no more than 150 tubes (in series); otherwise, the water may boil.

14. Can I heat my swimming pool or spa with a solar collector?

Vacuum tube collectors are high-temperature collectors and are therefore ideal for spas, as the water volume is small and temperature requirements are high. For swimming pools, however, the water volume is large and the required temperature increase is only a few degrees. The cost of heating a pool with vacuum tube collectors (for residential use) can be prohibitively high. For large-scale swimming pools, however, the collector can be an extremely practical supplement to gas or electricity.

15. Are vacuum tube collectors more efficient than flat-plate collectors?

When comparing peak efficiency levels, it may seem that there is little difference between flat-plate and vacuum tube collectors. In fact, flat-plate collectors may actually be more efficient, but this is under minimal heat loss conditions. When averaged over a year, vacuum tube collectors have a clear advantage. The main points are:

A. Due to the cylindrical shape of the evacuated tube, the solar tubes can passively track the sun throughout the day. Flat-plate collectors only deliver peak energy output at midday when the sun is perpendicular to the collector's surface. To learn more about IAM and performance, click here.

B. Air is evacuated from the solar tube to create a vacuum. This reduces conductive and convective heat loss from inside the tube. As a result, wind and cold temperatures have less of an impact on the efficiency of the vacuum tube collector.

C. Solar collectors can often be used in sub-zero temperatures without the system suffering damage. Flat-plate systems often require expensive and complicated antifreeze systems to be installed.

D. Vacuum tubes are strong, long-lasting, and should one break, they are inexpensive and easy to replace. If a flat-plate collector panel is damaged, the entire system must be replaced.

E. Due to the high efficiency of absorbing solar radiation, even under cloudy skies, combined with the excellent insulating properties of the solar tube, solar tube collectors can heat water year-round (securing gas and electricity is still required).

F. Due to the numerous advantages of vacuum tube collectors over flat-plate collectors, a smaller collector can be used to provide the same heating output. For example, a standard household of 4-5 people would typically need a 250-300L hot water storage tank. Depending on your location, only 30 vacuum tubes would be needed to provide hot water all summer and a significant portion during the other seasons.

G. Flat-plate solar collectors can produce similar heating output to vacuum tube collectors, but usually only during hot, sunny conditions. When averaged over a whole year, the heating output of a vacuum tube collector per square meter of net absorber area is between 25% and 40% greater than that of a flat-plate collector. 

Solar collector.

16. Which collector offers the best value for money?

Instead of focusing solely on peak efficiency levels when comparing solar collectors, the cost per unit of energy produced is much more logical. For example, even if collector A is 20% more efficient than collector B, if collector A is 30% more expensive, then collector B might actually be a better choice because it produces less energy per kWh per day. Since payback time is important, not only the price per kWh of the product is significant, but also the final system cost. In this respect, solar collectors offer a further advantage as they are very easy to install, and this can make a huge difference in terms of overall installation time and cost. For more information on comparing collector performance, please click here.

17. What is the solar irradiance (insolation) level where I live?

Learn more about solar irradiance and find out the values for your region.

18. How do I calculate what size collector I need?

Please click here to visit the collector sizing page.

19. Where can I purchase a solar collector?

Solar collectors are available through an official distribution network. Click here to find your nearest agent.

20. Can solar collectors be used in a drain-back configuration?

Yes. The end-port version of the solar collector is well-suited for drain-back use. A common question is whether the solar collector will be damaged when the pump is turned off and the solar system is in good saturation. No, it will not, as the collectors are designed to withstand stagnation. However, the insulation of the piping used near the collectors must be considered, as it must withstand stagnation temperatures.