Useful Info,Solar Water Heater

��

��1. Solar Glossary

��

��2. Solar FAQ

��

��3. Expert Guide

Expert Guide

1. Energy calculator & Collector sizing

Energy calculator

These information may help you to calculate the energy you can get.
Insolation Level - Before you calculate your energy output, you must know your solar insolation level,This is available from the insolation page.My Insolation level)
1 kWh/m2/day = 317.1 Btu/ft2/day=3.6MJ/m2/day
Collector Size - 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 xianke 20 tube = 1.6m2 absorber area
- 58/1500 = 0.067m2 per tube
Energy Cost - 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
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 xianke 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 30-40?.
- 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.

Collect size choose

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 12,15. 20, 24.30.32.34 or 36, 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 60^oC / 140^oF, when showering a temperature of between 42^oC / 107^oF and 45^oC / 113^oF is normally used. Therefore 300L of hot water at the tap may only draw 220L of hot water (at 60^oC / 140^oF) from the storage tank.

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

Apart from the three key factors used in the calculation above, you may also need to consider:
1. Annually/daily shade patterns
2. Angle/direction of installation (a less than ideal angle will reduce efficiency)
6. Installation site (Do you have enough room for the collector(s)?)

The estimations above are just a guide and are based on a average summer performance level of 70%. As explained above it is best not to oversize the system. Your local distributor may need to complete a onsite inspection to accurately assess your requirements and design a solar water heating system which suits your needs. For more information about performance and heat energy output please

Back Top