Technical

Solar Collectors absorbing efficiency, heat looses and total heat transfer efficiency.
Type of collector	Conversion factor	Thermal loss factor (W/m² °C)	Temp. Range (°C)	Heat transfer efficiency %
Uncovered absorber	0.82 - 0.97	10 - 30	Up to + 40C⁰	Up to 50%
Flat plate collector	0.66 - 0.83	2.9 - 5.3	From +30C⁰ to + 70C⁰	From 55 to 75%
Evacuated tube collector	0.62 - 0.84	0.7 - 2.0	From +60C⁰ to + 120C⁰	From 70 to 86%

Daily, Monthly and Annual Radiation Inputs in Johannesburg, South Africa.
Nearest location for weather data	Latitude	Slope of solar collector°	Latitude of project location°	Annual, average.
Nearest location for weather data	Latitude	Slope of solar collector°	Latitude of project location°	Daily radiation on horizontal surface (kWh/m²/day)	Daily radiation in plane of solar collector (kWh/m²/day)
Johannesburg	-26,1	from 26,0 to 40,0	North	5,18 (kWh/m²/day)	4,45 (kWh/m²/day)
Month		Monthly average. Day radiation on horizontal surface (kW/h/m²/d)	Monthly average. Day temperature (°C)	Monthly average. Relative humidity (%)	Monthly average. Day radiation in plane of vacuum tube solar collector (kW/h/m²/d)
January		6,44	19,7	70,1%	5,53
February		5,83	19,4	71,1%	5,01
March		5,19	18,4	70,3%	4,46
April		4,57	15,8	64,7%	3,93
May		4,03	13,1	54,2%	3,47
June		3,66	10,1	52,1%	3,14
July		3,93	10,0	51,3%	3,37
August		4,66	12,7	46,4%	4,00
September		5,53	16,0	48,8%	4,76
October		5,79	17,2	59,6%	4,98
November		6,19	18,0	66,3%	5,32
December		6,43	18,9	70,2%	5,53
Annual average		5,18	15,8	60,4%	4,45 (kW/h/m²/d)

Annual Radiation Inputs in a major South African cities
Nearest location for weather data	Latitude	Slope of solar collector°	Latitude of project location°	Annual average.
Nearest location for weather data	Latitude	Slope of solar collector°	Latitude of project location°	Daily radiation on horizontal surface (kWh/m²/day)	Daily radiation in plane of solar collector (kWh/m²/day)
Bloemfontein	-29,1	29-39,^o	North	5,86 (kWh/m²/day)	4,55 (kWh/m²/day)
Cape Town	-34,0	34-44,^o	North	5,19 (kWh/m²/day)	4,10 (kWh/m²/day)
Durban	-30,0	30-40,^o	North	4,41 (kWh/m²/day)	3,51 (kWh/m²/day)
Kimberley	-28,8	29-39,^o	North	5,89 (kWh/m²/day)	4,60 (kWh/m²/day)
Nelspruit	-25,5	25-35,^o	North	4,99 (kWh/m²/day)	3,97 (kWh/m²/day)
Pietersburg	-23,9	24-34,^o	North	5,85 (kWh/m²/day)	4,72 (kWh/m²/day)
Port Elizabeth	-34,0	34-44,^o	North	4,92 (kWh/m²/day)	3,84 (kWh/m²/day)
Johannesburg	- 26,1	26-36,^o	North	5,18 (kWh/m²/day)	4,15 (kWh/m²/day)
Pretoria	- 25,7	26-36,^o	North	5,46 (kWh/m²/day)	4,35 (kWh/m²/day)
Upington	-28,4	28-38,^o	North	6,17 (kWh/m²/day)	4,84 (kWh/m²/day)
(For more detailed Daily, Monthly and Annual Radiation Inputs please refer to: www.retscreen.net or contact our office.

E-Solar diagrams for traditional geyser EXPENSES vs. SAVINGS with advanced E-Solar vacuum tube solar
Total annual EXPENSES with your traditional 200L geyser	Total annual SAVINGS with E-Solar 200L solar geyser

Savings tables for E-Solar 200L solar water heating system with 2,7 m2 vacuum tubes solar collector.


Average annual electricity consumption by traditional 200L geyser (per house holding p/day)	13,93 kW p/day
Annual electricity consumption by traditional 200L geyser (per house holding)	5 098,4kWh p/annum
Average Annual solar power heat output (kW per day) on surface of E-Solar 200L solar geyser with 2,7m² vacuum tube solar collector	11,7 kWh p/day
Annual solar power heat output (kWh) on surface of E-Solar 200L solar water geyser with 2,7m² vacuum tube collector	4 282,2 - kWh p/annum
Average daily electricity consumption by 200L E-Solar geyser with 2,7m² vacuum tube collector p/day	2,23 kWh p/day
Annual Geyser electricity consumption per household by 200L E-Solar solar geyser	816,2 kWh p/annum
Annual Geyser electricity SAVINGS per house holding with 200L E-Solar geyser	4 282,2 kWh
Annual Geyser electricity SAVINGS per house holding with E-Solar 200L geyser for water heating	84,50%
TOTAL annual electricity SAVINGS per house holding with E-Solar 200L solar geyser	46,00%
Payback Period	3-4 years
Your SAVINGS over period of 20 years (in current electricity price)	R 80 000,00

Comparison of Solar collectors efficiency

TYPE 1

Uncovered absorber (usually plastic tubes for swimming pool) - Low solar absorption efficiency and low conductivity Solar Heat Collectors, Greater heat loss.

Up to 75-85% solar radiation absorption, about 15-25% solar radiation emission. Reach max. temperature up to 55^oC. Usually used for swimming pool heating. Does not accept high pressure. Uncovered collector consists few hundred plastic tubes assembled into solar absorber. Does not consist of any frame, cover and insulation. Absorber itself does not protects from adverse weather conditions.

TYPE 2 - Flat Plate solar collectors:

Up to 80-85% solar radiation absorption, about 15-20% solar radiation emission.

Reach max. temperature up to 60-70^oC. Not for use in frost areas. Accept high pressure.
A flat-plate collector consists of an absorber, a transparent cover, a frame, and insulation. Usually an iron-poor solar safety glass is used as a transparent cover, as it transmits a great amount of the short-wave light spectrum Simultaneously, only very little of the heat emitted by the absorber escapes the cover (greenhouse effect). In addition, the transparent cover prevents wind from carrying the collected heat away (convection). Together with the frame, the cover protects the absorber from adverse weather conditions. Typical frame materials include aluminium and galvanized steel. The insulation on the back of the absorber and on the sidewalls lessens the heat loss through conduction. Insulation is usually of polyurethane foam or insulating materials like fiberglass. Flat collectors demonstrate a good price-performance ratio, as well as a broad range of mounting possibilities.

TYPE 3 - All glass vacuum tube solar collector - High solar absorption efficiency and high conductivity Vacuum Tubes solar collectors with minimal heat loss.

All Glass Vacuum Tube Solar Collectors usually used in integrated Solar Water heating systems and call Thermosiphon system. All Glass Evacuated tubes contain water inside the tube.

The Advantage feature of high conductive All Glass evacuated tube solar collectors:

Sensitive and high speed of heat reaction. No additional fluid such as Glycol is used to transfer heat into the water. No movable parts, no noise. Power-free, durable more than 15 years. Water temperature can reach up to 95^oC in summer and 75^oC in winter. No electricity, no electric pump in use. Need only clean water supply. Very affordable price and are most welcomed by local communities across African continent.

The Disadvantage feature of high conductive All Glass evacuated tube solar collectors:

Can be used only in non freezing areas with lowest temperature not below -10^oC.

When tubes are broken, water from storage tank will leak out.

Needs clean water only. (tubes can be blocked with mud and sand)

TYPE 4 -Glass, superheat vacuum tube with heat pipe solar collectors:

At these types of solar collector vacuum tubes consists of a copper heat pipe to transfer heat from absorber to the water. Heat pipe incorporates a special fluid, which begins to vaporize even at low temperatures (+25C). The steam rises in the individual heat pipes and warms up the carrier fluid in the main pipe by means of a heat exchanger. The condensed liquid inside the heat pipe drops back into the base of the heat pipe. The pipes must be angled at a specific degree above horizontal so that the process of vaporizing and condensing functions. There are two types of collector connection to the solar circulation system. Either the heat exchanger extends directly into the manifold ("integrated") or it is connected to the manifold by a heat-conducting material ("separated"). A "separated" allows to exchange individual tubes without emptying the entire system of its fluid. Evacuated tubes offer the advantage that they work efficiently with high absorber temperatures and with low radiation. Higher temperatures also may be obtained for applications such as central heating.
Vacuum Tube Solar Collectors with Heat Pipe adopts superconductive heat pipes, and there is no water inside the evacuated tubes, which assures protection against freezing and hail. The water tank has better heat-preservation and strong pressure-bearing ability, with long service life and without pollution intelligent control and automatic operation, providing hot water throughout 24 hours. Reliable, durable and convenient performance.

Superconductive heat tube has a low heat capacity, and has rapid heat conducting medium (up to 500 times faster than copper heat conducting medium), so it is very efficient in heat conduction. The heat conduction rate is up to 99%. It starts up fast, and collects solar energy completely. At 25^oC, it can conduct heat at 5 seconds. The evacuated heat collector functions as solar energy absorption and heat preservation. Even if it is located in disadvantaged conditions (such as windy and cold areas), it can keep the heat from any loss. It also functions as heat conductor.

We use All Glass Vacuum tube and Heat Pipe technologies, which has been an advanced technology in Europe, America, Australia and Asia.

Smallest 12 tubes integrated collector (for 100L storage tank) is our typical type of this series and we manufacture and supply the collectors up to36 vacuum tubes in single unit . Many sets in series or parallel connection can produce a large collector for commercial use such a block of flats, hospitals, hotels, restaurants or mines.

Glass Super Heat Vacuum Tube Solar with Heat Pipe can be used for open and close loop systems.

Heat Pipes (Heat transmitting copper pipes)

Structure and Principle

The heat pipe is hollow with the space inside evacuated, much the same as evacuated solar collector tube. Inside the heat pipe there is a few purified water and some special additives. 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 our solar collectors have a boiling point between 25- 30^oC. So when the heat pipe is heated above 30^oC the water vaporizes. This vapour rapidly rises to the top of the heat pipe and transfers the heat. As the heat is lost at the condenser (top), the vapour condenses to form liquid (water) and returns to the bottom of the heat pipe at once and then repeats the process.

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 affect 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.

Often heat pipes use a wick or capillary system to aid the flow of the liquid, but for the heat pipes used in our solar collectors, no such system is required since the interior surface of the copper is extremely smooth, allowing efficient flow of the liquid back to the bottom. Also our heat pipes are not installed horizontally. Heat pipes can be designed to transfer heat horizontally, but the cost is much higher. The heat pipe used in our solar collectors comprises two copper components, the shaft and the condenser. Prior to evacuation, the condenser is brazed to the shaft. The condenser has a much larger diameter than the shaft, which can provide a large surface area where heat transfer to the header can occur. The copper used is oxygen free copper, thus ensuring excellent life span and performance.

Freeze Protection

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

Heat pipes, in its simplest form, a heat-pipe is a sealed Pipe containing a small quantity of a volatile liquid with no air or other "permanent" gas present. If such a pipe is placed vertically and the lower end is heated, liquid will evaporate and the vapour so formed will travel to the cooler parts of the pipe where it will condense and give up its latent heat of vaporisation. The condensate will then run back to the heated end where it can re-evaporate. This is illustrated below:

Because the heat transfer within the pipe comes from boiling liquid and condensing vapour, both of which processes have inherently very high heat transfer coefficients, and because the amount of material which has to move from one end of the pipe to the other is small the effective thermal conductivity of the heat-pipe is very large. To illustrate the magnitude of these quantities imagine that the heat-pipe is transmitting one kilowatt using water as the working fluid. The mass flow would be just under 0.5 g/s. At a temperature of 100⁰C in a 20 mm diameter pipe this would correspond to a vapour velocity of about 2,5 m/s.
In more sophisticated versions, the pipe contains a capillary wick to assist the return of the liquid from the condenser end to the evaporator end. Such pipes will work without the aid of gravity, for example in spacecraft. However, for terrestrial applications the far cheaper and simpler two-phase thermo siphon, as the gravity return heat-pipe is usually known, is often adequate. The maximum operating temperature of a heat pipe is the critical temperature of the used heat transfer medium. Since no evaporation/condensation above the critical temperature is possible, the thermodynamic cycle interrupts when the temperature of the evaporator exceeds the critical temperature.

The main useful characteristics of the two-phase thermo siphon are:
(1) the thermal conductivity is extremely high: about a thousand or more times that of copper,
(2) the thermal conductivity is almost independent of the metal that the heat-pipe is made from,
(3) the device acts as a thermal diode. That is, the conduction is very high in one direction (upwards) and very low in the other (downwards),
These characteristics make heat-pipes useful wherever a large amount of heat needs to be conducted through a small cross-section. They have been used in cooling space-craft components, in cooling plastics-forming dies, for the construction of air-to-air heat exchangers for industrial and domestic energy recovery, and in cooling electronic components mounted in confined spaces.

In Solar Energy Industry, heat pipes are widely used for the following purpose:

1. To setup pressure boundary;

2. For anti-freezing purpose;

3. To accelerate heat transfer.

For inquiries contact us: Tel/Fax: 035 7535 345, Cell: 082 293 8081 Email: info@easysolar.co.za