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Solar Knowledge

Aug 29, 2012

Solar Engery FAQ (II)

Solar Engery FAQ (II)
Category: news
Posted by: jarryq

2-1. Can the solar collector heat water to a high enough temperature?
Yes, in good weather the 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.

2-2. 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. However,this is an inexpensive and easy job. Any "handy" person can install a new tube (while adhering to local health and safety regulations). Solar collectors can operate with several broken tubes, however the efficiency will be reduced slightly.

2-3. Can solar collectors be used for a large scale hot water production?
Yes.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.

2-4. Can I heat my swimming pool or spa using an solar collector?
Our solar 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,solar collectors may be an extremely viable supplement to gas or electricity.

2-5. 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. 
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. 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.

2-6. 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 our solar collectors provides a fruther dvantage as our solar collectors are very easy to install, and that can make a huge difference in terms of total install costs.

2-7. What is the Solar Radiation (Insolation) level where I live?
Click here to learn more about Insolation.

2-8. How do I calculate what size collector I require?
Please click here to visit the collector sizing page.

2-9. Where can I purchase solar collector?
Click here to contact us.

2-10. Can solar collectors be used in a drainback configuration?
Yes. The end port version of the solar collector is well suited to drainback use. The question is often asked if the solar collector will be damaged 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.