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A place where you can learn about solar
 
If this is your first time visiting Sawan Solar Systems online, then this page is designed as a starting place for you. It will direct you to the key areas of this site which provide easy to read information about the technology and science behind thermal solar, and details of the AP solar collectors and related product range. Please follow the links below to find out more.



 


What is Solar?
 
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.

Thermal energy obtained from the sun can be used for a number of applications including producing hot water, space heating and even cooling via use of absorption chilling technology.

Using solar and other forms of renewable energy reduces reliance on fossil fuels for energy production, thus directly reducing CO2 emissions. CO2 emissions contribute to global warming, an environmental issue which is now of great concern.

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.




What is an Evacuated Tube?
 
Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry. Sunrain collectors use the most common "twin-glass tube". This type of tube is chosen for its reliability, performance and low manufacturing cost.

2

Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al) which features excellent solar radiation absorption and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.
Please
Why a vacuum? As you would know if you have used a glass lined thermos flask, a vacuum is an excellent insulator. This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don't want to lose it!! The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 150oC / 304oF , the outer tube is cold to touch. This means that evacuated tube water heaters can perform well even in cold weather when flat plate collectors perform poorly due to heat loss (during high Delta-T conditions).

In order to maintain the vacuum between the two glass layers, a barium getter is used (the same as in television tubes). During manufacture of the evacuated tube this getter is exposed to high temperatures which causes the bottom of the evacuated tube to be coated with a pure layer of barium. This barium layer actively absorbs any CO, CO2, N2, O2, H2O and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintaining the vacuum. The barium layer also provides a clear visual indicator of the vacuum status. The silver coloured barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition. See picture below.

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The Getter is located at the bottom of the
evacuated tube.

3

Left Tube = Vacuum Present
Right Tube = Faulty

Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of your location. In a North South orientation the tubes can passively track heat from the sun all day. In an East West orientation they can track the sun all year round.

The efficiency of a evacuated water heater is dependent upon a number of factors, one important one being the level of evacuated radiation (insolation) in your region.

Evacuated Tube Basic Specifications

Length (nominal)
1500mm /1800mm
Outer tube diameter
58mm
Inner tube diameter
47mm
Glass thickness
1.6mm
Thermal expansion
3.3x10-6 oC
Material
Borosilicate Glass 3.3
Absorptive Coating
Graded Al-N/Al
Absorptance
>92% (AM1.5)
Emittance
<8% (80oC)
Vacuum
P<5x10-3 Pa
Stagnation Temperature
>200oC
Heat Loss
<0.8W/ ( m2oC )
Maximum Strength
0.8MPa




How strong is the solar radiation (insolation) in my area?
 
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





What is a Heat Pipe?
 

Heat pipes might seem like a new concept, but you are probably using them everyday and don't even know it. Laptop computers often using small heat pipes to conduct heat away from the CPU, and air-conditioning system commonly use heat pipes for heat conduction.

The principle behind heat pipe's operation is actually very simple.

1


Structure
and Principle

The heat pipe is hollow with the space inside evacuated, much the same as the solar tube. In this case insulation is not the goal, but rather to alter the state of the liquid inside. Inside the heat pipe is a small quantity of purified water and some special additives. At sea level water boils at 100oC (212oF), but if you climb to the top of a mountain the boiling temperature will be less that 100oC (212oF). This is due to the difference in air pressure.

Based on this principle of water boiling at a lower temperature with decreased air pressure, by evacuating the heat pipe, we can achieve the same result. The heat pipes used in AP solar collectors have a boiling point of only 30oC (86oF). So when the heat pipe is heated above 30oC (86oF) the water vaporizes. This va pour rapidly rises to the top of the heat pipe transferring heat. As the heat is lost at the condenser (top), the va pour condenses to form a liquid (water) and returns to the bottom of the heat pipe to once again repeat the process.

At room temperature the water forms a small ball, much like mercury does when poured out on a flat surface at room temperature. When the heat pipe is shaken, the ball of water can be heard rattling inside. Although it is just water, it sounds like a piece of metal rattling inside.

This explanation makes heat pipes sound very simple. A hollow copper pipe with a little bit of water inside, and the air sucked out! Correct, but in order to achieve this result more than 20 manufacturing procedures are required and with strict quality control.

Quality Control

Material quality and cleaning is extremely important to the creation of a good quality heat pipe. If there are any impurities inside the heat pipe it will effect the performance. The purity of the copper itself must also be very high, containing only trace amounts of oxygen and other elements. If the copper contains too much oxygen or other elements, they will leach out into the vacuum forming a pocket of air in the top of the heat pipe. This has the effect of moving the heat pipe's hottest point (of the heat condenser end) downward away from the condenser. This is obviously detrimental to performance, hence the need to use only very high purity copper.

Often heat pipes use a wick or capillary system to aid the flow of the liquid, but for the heat pipes used in Sunrain solar collectors no such system is required as the interior surface of the copper is extremely smooth, allowing efficient flow of the liquid back to the bottom. Also Sunrain heat pipes are not installed horizontally. Heat pipes can be designed to transfer heat horizontally, but the cost is much higher.

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The heat pipe used in Sunrain solar collectors comprises two copper components, the shaft and the condenser. Prior to evacuation, the condenser is brazed to the shaft. Note that the condenser has a much larger diameter than the shaft, this is to provide a large surface area over which heat transfer to the header can occur. The copper used is oxygen free copper, thus ensuring excellent life span and performance.

Each heat pipe is tested for heat transfer performance and exposed to 250oC (482oF) temperatures prior to being approved for use. For this reason the copper heat pipes are relatively soft. Heat pipes that are very stiff have not been exposed to such stringent quality testing, and may form an air pocket in the top over time, thus greatly reducing heat transfer performance.

 

 

 

 

 

 

 

 

 

 

Freeze Protection

Even though the heat pipe is a vacuum and the boiling point has been reduced to only 25-30oC (86oF), the freezing point is still the same as water at sea level, 0oC (32oF). Because the heat pipe is located within the evacuated glass tube, brief overnight temperatures as low as -20oC (14oF) will not cause the heat pipe to freeze. Plain water heat pipes will be damaged by repeated freezing. The water used in Sunrain heat pipes still freezes in cold conditions, but it freezes in a controlled way that does not cause swelling of the copper pipe.





I don't know what insolation, IAM or absorber area are! Visit the Solar Glossary.
 

Solar Glossary

Here are a list of some terms you may encounter when reading through our web site.
We have tried to make explanations as easy to understand as possible, but if you are still un-clear please feel free to contact us.

A-B-C-D-E-F-G-H-I-P

A

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.

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. The Sunrain solar collector does not use reflective panels.

B

BTU - Stands for British Thermal Units. This is an imperial unit of measurement for heat widely used in the US and also in the UK. The conversion to the metric unit kWh is: 1 kWh = 3412Btu, and for surface area values, 1kWh/m2/day = 314Btu/ft2/day

C

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. The Sunrain AP model is separate from the tank as so is a solar collector.

Celsius - The metric unit for temperature measurement. Convert as follows:
Fahrenheit = (oC x 1.8) + 32
Celsius = (oF - 32)/1.8

For Delta-T measurements the relative temperature difference is needed.
Eg. Delta-T = 7oC turn pump on, Delta-T 2oC turn pump off. How much is that in oF??
The conversion from Fahrenheit to Celsius is simple:
Fahrenheit = oC x 1.8
Celsius = oF / 1.8

 

D

Delta-T Controller: 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.7oC / 12.7oF) and off again when the temperature difference drops below another setting (Eg. 2oC / 3.6oF). 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 5oC.

E

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.

Efficiency testing is usually completed by testing bodies such as SPF, SRCC and other government approved testing bodies.

Tm* is the x axis value on performance graphs for solar collectors.
Tm* is calculated as:
(water temp - ambient temp)/Insolation
Eg. (44oC - 20oC)/800Watts = 0.03

F

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 = 0.264 US Gallon/min

G

Gross Area: 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.

H

Heat Pipe: An evacuated rod or pipe used for heat transfer.

I

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.

Insulation: The ability to protect against transfer of heat/cold. Sunrain solar collectors use compressed glass wool 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.

Irridance, Irridation: Basically the same as Insolation - explained above.

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 0o, with negative and positive angles in the morning and afternoon respectively. Collectors with a flat absorber surface, which includes some types of evacuated tubes, only have 100% efficiency at midday (0o), whereas Sunrain solar tubes provide peak efficiency mid morning and mid afternoon, at around 40o from perpendicular. This results in good stable heat output for most of the day.

P

Pressure: Refers to the water pressure in the system. The conversions for the most commonly used units are: 1 bar = 1.02kg/cm2 = 14.5psi = 100kPa = 0.1Mpa = 10m water head





How much energy can a solar collector produce?
 

Energy Calculator

Using this energy calculator you may determine how much energy solar collector will produce each day/month/year. The way you utilize this energy is up to you. You can heat water for showering and washing clothes, or central heat a building. In fact one integrated system can complete both these functions.

You can also use these values to help you calculate how much energy you can save by using an Sunrain solar collector.

In order to calculate energy output you must input the following variables:
Insolation Level - Before you calculate your energy output, you must know your solar insolation level. This are available from the insolation page. Take note of your max and min levels throughout the year as well as the annual average value. When assessing potential energy savings, input annual average insolation, and take note of the "per year" energy output value.
Energy must be input in the unit kWh/m2/day. 1 kWh/m2/day = 317.1 Btu/ft2/day

Collector Size - You must enter the collector size in absorber surface area.
The absorber surface area of the various tubes sizes are as follows:
- 58/1800 = 0.08m2 per tube. Therefore an Sunrain AP 20 tube = 1.6m2 absorber area
- 58/1500 = 0.067m2 per tube

Energy Cost - Enter cost per kWh in your local currency
(may need to convert from m3 or Therms)
1 therm = 29.3kWh = 100,000Btu = 105.5MJ
Natural Gas is 39MJ/m3 = 10.83 kWh/m3
LPG Propane (liquid) = 25.3MJ/L = 7kWh/L
LPG Propane (gas) = 93.3MJ/m3 = 25.9kWh/m3

Insolation Level =
kWh/m2/day
Absorber Area =
m2
Electricity Cost =
$// per kWh


(click twice)

Energy Output

Per Day = kWh
Per Month = kWh
Per Year = kWh
= Btu
= Btu
= Btu

 

= $//
= $//
= $//

Please note:

- Collector peak efficiency is only achieved when ambient temperature and water temperatures are the same. During normal use, this is only likely to happen for a short period of time each day, and usually only when ambient temperatures are high (summer). Therefore during normal use, the solar collector can not always perform at such a high level of efficiency. This is true for all evacuated tube and flat plate collectors, not only Sunrain collectors. In order to provide more realistic figures, the above calculations are based on "normal" operating conditions under which the difference between ambient temp and manifold water temp is around 30-40oC.


- When making comparisons with other products please take the above point into consideration. Do not simply use the peak efficiency values for energy output, as this will provide inflated figures. IAM values also play an important role in determining total energy output from a solar collector. Please click here to learn more about how to interpret IAM figures.

- Monthly and annual values are calculated using 28 days and 336 days respectively to account for days of very low solar radiation.

- Energy output values are approximations. Actual energy output and overall system efficiency will depend upon installation location, climate, insulation, system configuration and many other factors. On rainy or heavily overcast days energy output will be greatly reduced.

- Energy is produced in the form of heat. In transporting and converting this energy, such as for air conditioning or central heating, some energy (heat) will be lost, as no system or insulation is 100% efficient.




What size collector do I need?
 

When determining what size collector you need, you must consider two key factors: insolation level and energy requirements. Energy requirement will usually take into consideration the volume of water and rise in temperature required. Once you know these factors you can determine the size collector you require. The bigger the collector you have, the more hot water, but you should make an economically sound decision. Generally it is wise to select a size which will provide you with 90% of your hot water needs in the summer.

Although it may seem strange to use a value of only 90% for summer solar contribution, it is for good reason. It is normal to size based on 100% of your summer hot water energy needs, with a percentage provided throughout other months, lowest obviously in winter. That is based on normal water usage, but often, and particularly in the summer, water usage patterns may not be that normal, with cooler than normal showers taken in hot weather, and greater possibility of the house being vacant for one or two days each week (weekends). As such, using a target value of 90% will probably actually result in a system that is able to supply more than 100% of your hot water needs in the summer, without excessive heat production, which can lead to water loss via pressure release and a waste of energy.

The calculator below can help to determine how many evacuated tubes you require given your energy requirements. Solar collectors come in a set of standard sizing of 10, 20, 22 or 30, depending on your region. Of course you can also combine collectors to increase the size. If you get an answer that is not a standard size, as a general rule, select the next size down - this will prevent having too much heat in the summer.

Depending on your preference, either Metric or Imperial values may be used to calculate the number of tubes required. Please note: 1 kWh/m2/day = 317.1 Btu/ft2/day

Metric Calculation

Insolation: kWh/m2/day
Water Volume:* Litres
Temp Rise:** oC
You Require:
Evacuated Tubes

Imperial Calculation

Insolation: Btu/ft2/day
Water Volume:* US Gallons
Temp Rise: ** oF
You Require:
Evacuated Tubes

*Water Volume = This should represent the actual volume of hot water used at the tap in total each day.
Although most hot water systems have target temps of 60oC / 140oF, when showering a temperature of between 42oC / 107oF and 45oC / 113oF is normally used. Therefore 300L of hot water at the tap may only draw 220L of hot water (at 60oC / 140oF) from the storage tank.

**Temperature Rise = target tap hot water temp - average mains cold water temp.
Target hot water temp should usually be around 42oC / 107oF to 45oC / 113oF
Cold water usually fluctuates by about 10oC / 18oF between winter and summer. A check of your local weather records should provide you with an idea of average cold water temperatures (normall about 10oC / 50oF in winter and 20oC / 68oF in summer, in mild regions).





How does using solar help the environment?
 

Solar Water Heating Reduces CO2 Emissions

Currently solar collectors are reducing CO2 emissions by more than 13,000 tonnes / 28.6million pounds per year, with collectors installed in the UK, USA, New Zealand, Germany, France, Sweden, Italy, Hungary, Portugal, Jordan, Lebanon, Australia, Canada, Mexico and many other locations.
(One metric tonne = 2200 pounds)

There has been a great deal of information in the media over the past few years about global warming and the role of CO2 emissions. 2003 saw extreme weather conditions and a heat-wave throughout Europe, clear evidence of the realism of this problem, commonly referred to as the "green house effect." Burning fossil fuels such as coal for electricity production, and gas for water heating both release large amounts of CO2 into the atmosphere, thus contributing to this environmentally harmful phenomenon.

By using renewable energy sources such a Solar Thermal, Solar PV, Wind, Hydro and Geothermal, reliance on fossil fuels can be minimised, thus directly reducing CO2 emissions. On average for every 1kWh of energy produced by a coal power station, 1kg (2.2pound) of CO2 is produced. Burning natural gas for electricity production or water heating produces about 450grams of CO2 for every kWh of energy produced.

In the average household, water heating accounts for around 30% of CO2 emissions. By installing a solar water heater, which can provide between 50-70% of your hot water heating energy needs, you can reduce your total CO2 emissions by more than 20%.

Below are two calculators which can be used to estimate how much you can reduce CO2 emissions by installing an Sunrain solar water heater together with either an electric or natural gas water heater. Just enter your average annual insolation level and number of evacuated tubes and click on calculate.

Electric Water Heater

Metric Calculation

Insolation: kWh/m2/day
Number of Tubes:
Reduction of kg of CO2/year
Imperial Calculation

Insolation: Btu/ft2/day
Number of Tubes:
Reduction of pounds of CO2/ year
 


Natural Gas Water Heater

Metric Calculation

Insolation: kWh/m2/day
Number of Tubes: (1.8m tubes)
 
Reduction of kg of CO2/year
Imperial Calculation

Insolation: Btu/ft2/day
Number of Tubes: (1.8m tubes)
 
Reduction of lb of CO2/year