1. Is solar water heating a viable alternative to gas or electricity?
Solar should not be seen as a alternative to gas or electricity, but rather a supplement. Solar cannot totally replace the need for gas or electric heating as there are sometimes days when there is little sunlight. When averaged over a year, a correctly sized solar system can provide 60%-70% of a household’s hot water needs. Providing more than this is unadvisable, as too much heat will be produced in the summer. The hot water system system can easily be automated so hot water is guaranteed regardless of sunlight levels.
2. How long will it take to recoup my investment?
RIWATT solar collectors are much more affordable than many other solar hot water heaters. For a household of 4, the price of a full system may not be too much more than a new electric or gas system. Depending on you location (solar levels) and current hot water usage the annual electricity or gas saving will differ. However in a normal household that spends 25% of its electricity bill on hot water heating, the full cost of the purchase may be recouped as quickly as 4-5 years in reduced bills. You will definitely make considerable savings during the life of the solar hot water heater.
3. Can RIWATT solar collectors be used in cold conditions?
Yes.RIWATT collectors can be used in temperatures as low as -30oC, although performance is greatly reduced in such extreme conditions. Good heat output is still achieved in mild sub-zero conditions.
4. What happens if one of the solar tubes is broken?
Firstly, tubes are very strong and not easily broken, but if the worst should happen, solar tubes can be replaced very easily. They are inexpensive and available though your local RIWATT distributor.
The RIWATT solar collectors can operate with several broken tubes, but the efficiency will be reduced, so it is recommended that broken tubes be replaced immediately.
5. Will water be heated on a cloudy day?
Yes. Although the heat output of the solar collector is reduced on overcast days it will still be able to provide heating. If it is a heavily clouded day or raining, then more gas or electric boosting may be required to maintain water at the required temperature. This system will be automated so you don’t have to worry about running out of hot water on a rainy day.
6. Can I use a solar collector with my existing hot water system?
Normally yes. Simple retrofit valves can often be used to allow solar to connect to your existing cold water inlet. If your tank cannot accept the solar input directly an additional storage tank can be installed to pre-heat the cold water prior to entering the existing tank.
7. Are the solar collectors noticeable on the roof?
If only the collector is mounted on the roof it should blend into the roof design quite well.RIWATT solar collectors are very thin and can be flush mounted on a roof. From a distance they look somewhat like a skylight. You may have to check with your local council regarding building restrictions when installing your solar collector. Click here to view installation photos.
8. Can RIWATT solar collectors be mounted on a flat surface?
Yes they may be mounted on a flat roof, or on the ground by using a stainless steel Flat Roof Frame. The collector should be installed at a minimum of 20o angle to ensure optimal heat pipe operation.
9. How do I protect my solar system during subzero temperatures?
If you have a system that is operating in areas with subzero temperatures then freeze protection must be implemented. The easiest means of preventing freezing is to use a controller with a low temperatures setting, so when the manifold temperature drops below a certain pre-set temperature (5oC/40oF), the pump will circulate, warming the collector with water from the bottom of the storage tank. The pump will not run continually, just periodically, the frequency of which will depend on the outside temperature. In extremely cold areas, a closed loop using a glycol/water mix may be appropriate.
10. Will the RIWATT solar collector be a fire hazard during hot, dry weather?
No. The RIWATT solar collector’s components are all high temperature rated and non-flammable so even during strong sunlight with the circulation pump turned off (stagnation), the system will not catch alight or give off any sparks. The majority of the solar collector’s components are stainless steel, aluminium, glass or glass wool. The manifold outlet should be fitted with a temperature relief valve, which will prevent the manifold temperature from exceeding 99oC / 212oF.
11. Can the RIWATT solar collector heat water to a high enough temperature?
Yes, in good weather the RIWATT solar collector can bring water to boiling point.
Generally this is not necessary and so the system should be designed to provide a daily temperature rise of around 25-30oC (45-54oF) in the summer. Sizing a domestic system that can bring the cold water up to 60oC/141oF in a single day is not logical, because if hot water is not used for one day, the following day the system will be boiling and dumping hot water via the temperature relief valve. This is both a waste of energy and water! Please sensibly size solar water heating system to ensure optimal performance and minimal wastage of water.
12. What maintenance of the solar collector is required?
Under normal circumstances no maintenance of the system is required. Due to the shape of the tubes regular rainfall and wind should keep the tubes clean. Should a tube even be broken it should be replaced. This, however, is an inexpensive and easy job. Any “handy” person can install a new tube (while adhering to local health and safety regulations).RIWATT solar collectors can operate with several broken tubes, however the efficiency will be reduced slightly.
13. Can RIWATT solar collectors be used for a large scale hot water production?
Yes. RIWATT solar collectors can be connected in series or parallel to provide large scale hot water production for a commercial settings such as a school, hotel or office building. There is really no limit to the size of the system, however 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 using an RIWATT solar collector?
RIWATT collectors are high temperature collectors, and are therefore ideal for spas, as the volume of water is small and temperature requirements high. For swimming pools, however, the volume of water is large and the temperature rise required is only several degrees. The cost of heating a pool using solar tube collectors (for domestic purposes) may be prohibitively high.
For large scale swimming pools, however,RIWATT collectors may be an extremely viable supplement to gas or electricity.
15. Are solar 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 evacuated tubes,
in fact flat plate may actually be higher, but this is during minimal heat loss conditions. When averaged over a year evacuated tube collector have a clear advantage. The key points are:
1). Due to the cylindrical shape of the evacuated tube, the solar tubes are able to passively track the sun throughout the day.
Flat plate collector only provide peak energy output at midday when the sun is perpendicular to the collector’s surface. To learn more about IAM and performance click here.
2). Air is evacuated from the solar tube to form a vacuum. This greatly reduces conductive and convective
heat loss from the interior of the tube. As a result wind and cold temperatures have less effect on the
efficiency of the evacuated tube collector.
3). RIWATT solar collectors can often be used in subzero temperatures without the system sustaining damage.
Flat plate systems often require expensive and complicated “antifreeze” systems to be installed.
4). Evacuated tubes are strong, long lasting, and should one be broken, inexpensive and easy to replace. If a
flat plate collector panel is damaged the whole panel must be replaced.
5). Due to the high efficiency absorption of solar radiation even during overcast conditions, combined with
excellent insulative properties of the solar tube, solar tube collectors can heat water all year round (backup
from gas and electricity is still required).
6). Due to the various advantages of evacuated tube collector over flat plate collectors, a smaller collector
can be used to provide the same heating performance. For example, a standard household of 4-5 people
would usually require a 250-300L water storage tank. Depending on your location, only 30 evacuated
tubes would be required to provide all summer hot water needs and a large percentage in other seasons.
7). Flat plate solar collectors can produce similar heat output to evacuated tube collectors, but generally only
during hot, sunny conditions. When averaged over an entire year, evacuated tube collector heat output per
net m2 of absorber area, is between 25% to 40% greater that a flat plate collector.
16. Which collector is the best value for money?
Rather than looking at just peak efficiency levels when comparing solar collectors, cost per unit of energy produced is much more logical.
For example: Although collector A may be 20% more efficient than collector B, if collector A is 30% more expensive, then in fact collector B may be a better choice, as per kWh of energy produced per day it is cheaper. When payback time is of concern, not only price per kWh of the product is important, but also of the end system. In this regard RIWATT solar collectors provides a fruther dvantage as RIWATT solar collectors are very easy to install, and that can make a huge difference in terms of total install costs.
For more information comparing collector performance please click here.
17. What is the Solar Radiation (Insolation) level where I live?
Click here to learn more about Insolation, and to find out values for your region.
18. How do I calculate what size collector I require?
Please contact with our sales team to get the latest collector sizing info.
19. Where can I purchase an RIWATT solar collector?
RIWATT solar collector are available through an official distribution network.
Click here to find your closest RIWATT agent.
20. Can RIWATT solar collectors be used in a drainback configuration?
Yes. The end port version of the RIWATT solar collector is well suited to drainback use. The question is often asked if the solar collector will be damanged when the pump turns off and the system stagnates in good sun – no it won’t, as the collectors is designed to withstand stagnation. What must be considered though is the insulation used on the piping close to the collectors, as this must be able to withstand stagnation tempertures.
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