FAQ's

What is the Collector?
Collector - A solar collector is not really a solar water heater. A solar water heater is a system which may include a tank, pump, controller and solar collector panel. A solar collector is that part of the system which absorbs the sun's energy and converts it into heat.

What is Delta T?
Delta-T refers to the difference in two temperatures. This term is often use in relation to a solar controller. In such case the Delta-T is the difference between the solar collector temperature and the temperature of the water in the solar storage tank. A Delta-T controller can be configured to turn on the pump when the Delta-T difference exceeds a certain level (Eg.7'C) and off again when the temperature difference drops below another setting (Eg. 2'C). The controller turns on the pump when there is heat potential in the manifold. A Delta-T controller can also be used to provide freeze protection by circulating warm water from the tank through the manifold when the manifold temperature drops below 5'C.

How is the Solar Collector Efficiency measured?
Efficiency: Solar collector efficiency is usually expressed as a percentage value, or in a performance graph. When assessing a collector's performance make sure it is based on the correct surface area values. Eg. If performance values are based on gross area, then the gross area must be used when determining total heat output. IAM values have a significant influence on actual heat output throughout the day, and should be considered. Looking at just the percentage efficiency value will not give a true indication of daily heat output.

What is a heat-pipe?
Heat Pipe: An evacuated rod or pipe used for heat transfer.
What is Insolation?
Insolation: Don't confuse this with insulation - the one letter change makes a big difference. Insolation refers to the amount of sunlight falling on the earth.

What is Insulation?
Insulation: The ability to protect against transfer of heat/cold. Solar collectors use compressed glass wool or polyurethane insulation to insulate the header from heat loss. Glass wool has excellent insulation properties, is very light and can withstand high temperatures, making it an ideal choice for a solar collector. It is made from a least 80% old glass bottles and can be recycled so is very environmentally friendly.
What is Irradance?
Irridance, Irridation: Basically the same as Insolation

What is IAM?
Incidence Angle Modifier (IAM): refers to the change in performance as the sun's angle in relation to the collector surface changes. Perpendicular to the collector (usually midday) is expressed as 0', with negative and positive angles in the morning and afternoon respectively. Collectors with a flat absorber surface, only have 100% efficiency at midday (0'), whereas solar tubes provide peak efficiency mid morning and mid afternoon, at around 40' from perpendicular. This results in good stable heat output for most of the day.

What is the Aperture? The part of the collector through which light enters. For evacuated tubes this refers to the cross-sectional surface area of the outer clear glass tube measured using the internal diameter, not the outside diameter.
(Eg. 0.0548m x 1.72m = 0.094m2). 1.72m is the exposed length of the evacuated tube.

What is Absorber?
Absorber: The part of the collector that actively absorbs the light rays. For solar tubes this is defined as the cross-sectional area of the inner tube (selective coated) measured using the outside diameter. (Eg. 0.047 x 1.72m = 0.08m2) This value is used when calculating efficiency values. For solar tube collectors with reflective panels, the entire circumferential surface area of the inner tube is often used when calculating absorber area, as the reflective panel is supposed to reflect light onto underside of the evacuated tube.

Are Vacuum Tube Collectors Better than Flat Plate?
Flat plate thermal solar collectors have been in use for several decades, but only in relatively small numbers, particularly in Western countries. Evacuated tubes have also been in use for more than 20 years, but have been much more expensive than flat plate, and therefore only chosen for high temperature applications or by those with money.
In recent years the production volume of evacuated tubes has exploded, resulting in greatly lower manufacturing and material costs. The result is that evacuated tubes are now similar in price to flat plate, but with the insulating benefits of the evacuated tube, they are set to become the default choice for thermal solar applications worldwide.

Is solar water heating a viable alternative to gas or electricity?
Solar should not be seen as an 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 can easily be automated, so hot water is guaranteed regardless of sunlight levels.

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

Can solar collectors be used in cold conditions?
Yes. collectors can be used in temperatures as low as -30'C, although performance is greatly reduced in such extreme conditions. Good heat output is still achieved in mild sub-zero conditions.

What is Flow Rate?
Flow Rate: The volume of water flowing through plumbing in a given period of time. Usually measured in volume/minute or volume/hour. 1 Litre/min

What is the gross area of a collector?
The total surface area of the collector including the frame, manifold and absorber. This area is often used when comparing collectors, but a better comparison to use is value for money. Roof size is not usually a limiting factor for domestic solar water heating installations, so the size of the collector is not really that important.

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 The Solar Shop. The solar collectors can operate with several broken tubes, but the efficiency will be reduced, so it is recommended that broken tubes be replaced immediately.

Will water be heated on a cloudy day?
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.

Can I use a solar collector with my existing hot water system?
Normally yes. But it depends on your existing system.

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. Our 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.

Can 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 20' angle to ensure optimal heat pipe operation.

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 (5'C), 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.

Will the solar collector be a fire hazard during hot, dry weather?
No. The 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


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 ever 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.

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 setting 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. 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 pool, the volume of water is large and the temperature rise required is only several degrees, so it prove an extremely viable supplement to gas or electricity.

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 but when averaged over a year, evacuated tube collectors have a clear advantage. The key points are:
- Due to the cylindrical shape of the evacuated tube, the solar tubes are able to passively track the sun throughout the day. Flat plate collectors only provide peak energy output at midday when the sun is perpendicular to the collector's surface.
- 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.
- 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.
- 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.
- Due to the high efficiency absorption of solar radiation even during overcast conditions, combined with excellent insulation properties of the solar tube, solar tube collectors can heat water all year round (backup from gas and electricity is still required).
- Due to the various advantages of evacuated tube collectors 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.
- 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 much greater that a flat plate collector.
- When considering the difference, it is also important to think about other points like installation. With vacuum tube collectors installation is very much easier. One can construct position and fix the frame and header manifold first, installing the tubes individually after you have connected the system. Flat plate collectors are installed as one large and often heavy piece.

What is solar energy?
Solar energy is the cleanest and most inexhaustible of all known energy sources. Solar radiation is the heat, light and other radiation that is emitted from the sun. Solar radiation contains huge amounts of energy and is responsible for almost all the natural processes on earth. The suns energy, although plentiful, has been hard to directly harness until recently.
Solar Energy can be classified into two categories, Thermal and Light. Photo-voltaic cells (PV) use semiconductor-based technology to convert light energy directly into an electric current that can either be used immediately, or stored in a battery, for later use. PV panels are now becoming widely used as they are very versatile, and can be easily mounted on buildings and other structures. They can provide a clean, renewable energy source which can supplement and thus minimize the use of mains electricity supply. In regions without main electricity supply such as remote communities, emergency phones etc, PV energy can provide a reliable supply of electricity. The disadvantage of PV panels is their high cost and relatively low energy conversion rate (only 13-15%). Thermal solar on the other hand has average efficiency levels 4-5 times that of PV, and is therefore much cheaper per unit of energy produced.
Thermal energy can be used to passively heat buildings through the use of certain building materials and architectural design, or used directly to heat water for household use. In many regions, solar water heaters are now a viable supplement or alternative to electric or gas hot water production.

What is solar insolation?
The amount of electromagnetic energy (solar radiation) incident on the surface of the earth. Basically that means how much sunlight is shining down on us.

Why is knowing the insolation level useful?
By knowing the insolation levels of a particular region we can determine the size of solar collector that is required. An area with poor insolation levels will need a larger collector than an area with high insolation levels. Once you know your region's insolation level you can more accurately calculate collector size and energy output.

What units are used to express Insolation levels?
The values are generally expressed in kWh/m2/day. This is the amount of solar energy that strikes a square metre of the earth's surface in a single day. Of course this value is averaged to account for differences in the days' length. There are several units that are used throughout the world.
The conversions based on surface area as follows:
1 kWh/m2/day = 317.1 btu/ft2/day = 3.6MJ/m2/day
The raw energy conversions are:
1kWh = 3412 Btu = 3.6MJ = 859.8kcal

Is my region's insolation level low, moderate or high?
The following scale is a basic guide for insolation levels. Although a value of 5 is not considered very high during the summer months, as an average annual value this is very high. You will see that in central Australia, which is a hot, sunny place, the annual average insolation is 5.89.
You may compare you location to the following two extreme locations.
Average annual insolation levels:
Central Australia = 5.89 kWh/m2/day - Very High
Helsinki, Finland = 2.41 kWh/m2/day - Very Low