(Re posted from April 2010)
One of the biggest problems the consumer in South Africa has is knowing which Solar Water Heater to select.
In spite of the fact that there are now a great many systems available on the Eskom subsidy list to choose from, it is difficult to separate the good from the ugly, since even the bad systems are accepted onto the scheme. By bad I mean systems which deliver a very low energy replacement.
The public perception is that if a product is listed on the Eskom subsidy scheme it must be OK, right? And certainly if it has SABS Mark approval it should be fit for purpose. Unfortunately, in my opinion, this is not the case.
See our article published back in March 2010. http://www.busrep.co.za/index.php?fArticleId=5387996
The value of rebate a system was eligible for, started out being directly proportional to the energy it could replace. The revised scheme announced in January this year departed from common sense in favour of something purportedly aimed at enabling a five year ROI (return on investment) on systems of different prices, regardless of their energy displacement capability.
So now the situation exists where a 300L system delivering 9kwh of energy receives almost 30% more subsidy than a 200L systems delivering the same energy, this, in spite of the fact that the 200L system will provide better water temperatures and represent a better ROI.
So how can one evaluate the best buy in solar water heating products?
In South Africa this is very difficult since the SABS and Eskom both consider test results and system ratings confidential and do not require a supplier to disclose this information.
We find this rather odd since other countries have open policies on such information.
New Zealand have the Energy Efficiency and Conservation Authority http://www.energywise.govt.nz/solarcalc
The United States for example has the SRCC
http://www.solar-rating.org/
Which also advocates labelling to indicate the efficiency of various solar products.
Fortunately with the benefit of having access to our own reports and certain others from reputable suppliers, we are able to reverse calculate the Q factor (performance rating) of any product in the Eskom scheme from its subsidy value.
With knowledge of the products Q factor and tank capacity it is possible to level the playing fields and gain the ability to compare apples with apples. To this end Sky Power have developed a calculator which we call the “Product Performance Evaluator”.
The calculator simplifies this calculation and produces comparative data specific to the products whose details you have entered which you can then use to make your decision.
Open the Product Performance Evaluator here.
In a separate window browse the Eskom suppliers list and select the products you are interested in from this site. Eskom Suppliers list
On the product Performance Evaluator enter the:
Total installed price of the product
Subsidy value in Rands
Capacity of the system in litres.
The calculator will return:
The Q factor of the product
The Rand value per kWh used to calculate the rebate
The energy required to produce a 40 degree temp rise
The percentage of required energy the product will supply from Solar Input at the SABS test datum.
Cost effectiveness of the product in Rand’s per kWh.
A rating of the products performance.
Having completed this exercise you may be interested to take the next step and get an estimate of product performance throughout the year.
You may then also plug the Q factor, geyser volume and product price information into our Expected Temperature graph tool and you will be able to see the expected temperature delivery of the product month by month according to your location, roof slope and other variable information.
The same tool also allows you to estimate a ROI based on the current and escalated price of electricity, replaced energy and your initial investment.
If you have any difficulty in using the tool please drop us a line and we’ll do our best to help you.
Sky Power is a South African supplier of advanced Solar Thermal and Solar Electric systems. We offer a money back performance guarantee on all of our installations.
Showing posts with label solar geysers. Show all posts
Showing posts with label solar geysers. Show all posts
Wednesday, February 2, 2011
Monday, September 13, 2010
Anomalies of efficiency
Certain SWH systems apparently demonstrate over 100% efficiency!
This of course is clearly not possible and can only come about as a result of an error in measurement or calculation however, there are certain products on the Eskom subsidy scheme which are listed with subsidy values and therefore Q factor measurements, which appear to have been mis-calculated.
It should be noted that this is not a Eskom fault but does possibly indicate an oversight with the issuing of test reports.
In any solar water heating system (as with all other systems) there are theoretical maximums.
SABS test procedures typically issue Q factor measurements relative to 16MJ/sqm/day of solar input.
The maximum Q factor for any product with a collector size of 1 m2 is therefore 16MJ and this would imply 100% efficiency. Energy received being equal to energy delivered.
In the real world, of course, this is not possible since there will always be losses in any energy conversion.
As a case in point one product is calculated to have a 154% efficiency. With a 1.1 sqm collector area and its calculated Q factor of 27.221MJ.
The theoretical maximum of such a product is 16MJ x 1.1sqm = 17.60MJ
It is essential then that, before purchasing a system, you check the measured Q factor for reasonability.
Using the Sky Power product performance calculator available here. http://www.skypower.co.za/content/calculators/Product%20Performance%20Evaluator%201.1.xls
Enter the subsidy value as published by Eskom. The calculator will return the Q factor of the product in kWh. Multiply the kWh figure by 3.6 to convert to it MJ.
Ask the supplier to tell you the absorber area of their product. Divide the Q factor by the absorber area to get energy delivery /sqm
Then divide energy delvery /sqm by the 16MJ X100 (the figure used as the test datum).
The result will be the efficiency of the product as a percentage.
Using Sky Power product as an example:
Q Factor 33.227 MJ and Absorber area 2.4 sqm.
(Q Factor / Absorber area ) = energy/sqm
(energy/sqm /16) x 100 = % collector effeciency
33.227/2.4 = 13.84
13.84 /16= 0.865
0.865 x 100 = 86.5%
Anything over 90%, should be questioned as being unlikely and anything over 100% as impossible.
If in doubt, please call us at Sky Power and one of our technical staff will help you.
This of course is clearly not possible and can only come about as a result of an error in measurement or calculation however, there are certain products on the Eskom subsidy scheme which are listed with subsidy values and therefore Q factor measurements, which appear to have been mis-calculated.
It should be noted that this is not a Eskom fault but does possibly indicate an oversight with the issuing of test reports.
In any solar water heating system (as with all other systems) there are theoretical maximums.
SABS test procedures typically issue Q factor measurements relative to 16MJ/sqm/day of solar input.
The maximum Q factor for any product with a collector size of 1 m2 is therefore 16MJ and this would imply 100% efficiency. Energy received being equal to energy delivered.
In the real world, of course, this is not possible since there will always be losses in any energy conversion.
As a case in point one product is calculated to have a 154% efficiency. With a 1.1 sqm collector area and its calculated Q factor of 27.221MJ.
The theoretical maximum of such a product is 16MJ x 1.1sqm = 17.60MJ
It is essential then that, before purchasing a system, you check the measured Q factor for reasonability.
Using the Sky Power product performance calculator available here. http://www.skypower.co.za/content/calculators/Product%20Performance%20Evaluator%201.1.xls
Enter the subsidy value as published by Eskom. The calculator will return the Q factor of the product in kWh. Multiply the kWh figure by 3.6 to convert to it MJ.
Ask the supplier to tell you the absorber area of their product. Divide the Q factor by the absorber area to get energy delivery /sqm
Then divide energy delvery /sqm by the 16MJ X100 (the figure used as the test datum).
The result will be the efficiency of the product as a percentage.
Using Sky Power product as an example:
Q Factor 33.227 MJ and Absorber area 2.4 sqm.
(Q Factor / Absorber area ) = energy/sqm
(energy/sqm /16) x 100 = % collector effeciency
33.227/2.4 = 13.84
13.84 /16= 0.865
0.865 x 100 = 86.5%
Anything over 90%, should be questioned as being unlikely and anything over 100% as impossible.
If in doubt, please call us at Sky Power and one of our technical staff will help you.
Wednesday, July 21, 2010
Don’t pay for capacity you can’t use.
Why do some solar geyser suppliers recommend bigger tanks than normal geysers?
These are invariably systems based on thermosyphon, the type of systems where you have a tank up on the roof.
This is because of the way thermosyphon works.
The fact that hot water rises and that the thermosyphon process is very slow, the hot water in such systems rises to the top of the tank leaving markedly colder water at the bottom. This design is unable to heat the lower volume of water in the tank.
Click on image to open PDF version.
In large bodies of water such as lakes for example a similar effect is noticed. Divers will witness what is known as the thermocline, a point where the water temperature suddenly drops. The same thing happens in smaller volumes of water where there is no stirring of the upper and lower layers.
What this means is that if you buy a thermosyphon system you can’t really use the full capacity of the tank. So you need a bigger tank than you would have done.
One supplier states that their 300L product has a solar delivery of 240L and their 180 L product can only deliver 160L from solar. This suggests that approximately 20% of the capacity is not usable.
This phenomenon however only applies to thermosyphon systems.
The more modern designs which are actively circulated by the use of small pumps, does not suffer from this loss of capacity. As such it is perfectly acceptable to use your existing geyser or one of the more common geyser sizes that will suit your water demand needs.
These are invariably systems based on thermosyphon, the type of systems where you have a tank up on the roof.
This is because of the way thermosyphon works.
The fact that hot water rises and that the thermosyphon process is very slow, the hot water in such systems rises to the top of the tank leaving markedly colder water at the bottom. This design is unable to heat the lower volume of water in the tank.
Click on image to open PDF version.
In large bodies of water such as lakes for example a similar effect is noticed. Divers will witness what is known as the thermocline, a point where the water temperature suddenly drops. The same thing happens in smaller volumes of water where there is no stirring of the upper and lower layers.
What this means is that if you buy a thermosyphon system you can’t really use the full capacity of the tank. So you need a bigger tank than you would have done.
One supplier states that their 300L product has a solar delivery of 240L and their 180 L product can only deliver 160L from solar. This suggests that approximately 20% of the capacity is not usable.
This phenomenon however only applies to thermosyphon systems.
The more modern designs which are actively circulated by the use of small pumps, does not suffer from this loss of capacity. As such it is perfectly acceptable to use your existing geyser or one of the more common geyser sizes that will suit your water demand needs.
Wednesday, July 7, 2010
Solar Water Heaters Overheat
Overheating of certain solar water heating designs is a growing concern in the industry. Dangerously high water temperatures, even boiling can be achieved with the associated risks of injury.
Such system designs rely on a passive principle known as thermosyphon to enable heated water to naturally rise into a storage vessel. These are the systems that typically require a tank on top of the roof.
The problem with such simple passive designs is that there is no mechanism of controlling maximum temperature as the thermosiphon process cannot be turned off.
Example of the type of system which can be prone to overheating.
Particularly when the home owner is away, on holiday for example, without water being drawn off the system will heat untill the safety valve blows. At other times of low water usage tank temperature can reach scalding temperatures.
Whilst the problem can be reduced by adding thermal tempering valves, which mixes cold water with the hot, to avoid excessive temperature at the tap. Extra cost and additional maintenance are incurred which make these often low priced systems less attractive.
The challenge with using solar energy is that the sun is a highly variable power source, a fact which is exacerbated in a country such as South Africa, due to its great variances in latitude from the north to the south of the country.
Because of such variances the ability to provide control becomes all-important so that systems can deliver acceptable performance from the low sun conditions of winter whilst not overheating in summer. The alternative is to undersize collectors which reduces overheating but does not deliver any significant benefit in winter when hot water is needed the most.
Particularly prone to this problem are integrated or compact vacuum tube versions of these designs. (Pictured above) It should be noted however that it is the integrated close coupled system design, rather the vacuum tubes themselves, that create the problem.
Conversely the system design known as an "active split system" where in many cases the existing geyser can be employed and with the water circulated by use of a pump, is not prone to overheating since it is able to harness the power of the more efficient technology by providing failsafe control. It also has aesthetic benefits, not requiring roof top tanks.
This is the design advocated by Sky Power as it resolves the issue of overheating and simultaneously enables year round performance through its ability to provide control.
More advanced technology which permits control of maximum temperature safetly.
The ability to control circulation effectively provides the ability to throttle back thermal delivery once the desired temperature has been achieved. In this way systems remain safe even when left unused for extended periods. Such as when the owner is away on holiday for example.
Such system designs rely on a passive principle known as thermosyphon to enable heated water to naturally rise into a storage vessel. These are the systems that typically require a tank on top of the roof.
The problem with such simple passive designs is that there is no mechanism of controlling maximum temperature as the thermosiphon process cannot be turned off.
Example of the type of system which can be prone to overheating.Particularly when the home owner is away, on holiday for example, without water being drawn off the system will heat untill the safety valve blows. At other times of low water usage tank temperature can reach scalding temperatures.
Whilst the problem can be reduced by adding thermal tempering valves, which mixes cold water with the hot, to avoid excessive temperature at the tap. Extra cost and additional maintenance are incurred which make these often low priced systems less attractive.
The challenge with using solar energy is that the sun is a highly variable power source, a fact which is exacerbated in a country such as South Africa, due to its great variances in latitude from the north to the south of the country.
Because of such variances the ability to provide control becomes all-important so that systems can deliver acceptable performance from the low sun conditions of winter whilst not overheating in summer. The alternative is to undersize collectors which reduces overheating but does not deliver any significant benefit in winter when hot water is needed the most.
Particularly prone to this problem are integrated or compact vacuum tube versions of these designs. (Pictured above) It should be noted however that it is the integrated close coupled system design, rather the vacuum tubes themselves, that create the problem.
Conversely the system design known as an "active split system" where in many cases the existing geyser can be employed and with the water circulated by use of a pump, is not prone to overheating since it is able to harness the power of the more efficient technology by providing failsafe control. It also has aesthetic benefits, not requiring roof top tanks.
This is the design advocated by Sky Power as it resolves the issue of overheating and simultaneously enables year round performance through its ability to provide control.
More advanced technology which permits control of maximum temperature safetly.The ability to control circulation effectively provides the ability to throttle back thermal delivery once the desired temperature has been achieved. In this way systems remain safe even when left unused for extended periods. Such as when the owner is away on holiday for example.
Monday, July 5, 2010
Response to Star Consumer Watch Article
In response to the Star Consumer watch article. Monday 28th June.
http://www.iol.co.za/index.php?click_id=3027
One critical point which has been omitted from this article is that the problems that have been encountered are entirely with flat plate systems. There has been no mention of that fact that Evacuated tube systems are more than adequately frost tolerant.
We have not had a single problem with the recent cold weather. Said Barry Cribb MD of Sky Power.
As mentioned in the article quite correctly, flat plate systems are notoriously prone to freezing because of their design. The very thin fluid channels in contact with the flat sheet of metal can only be protected by an antifreeze solution, typically propylene glycol and configured in what is referred to as an indirect configuration.
Evacuated tube systems conversely use a similar alcohol within a sealed copper pipe which will withstand temperatures down to minus 30 degrees. This is one reason why they are becoming more popular in the consistently colder climates of northern Europe.
http://www.iol.co.za/index.php?click_id=3027
One critical point which has been omitted from this article is that the problems that have been encountered are entirely with flat plate systems. There has been no mention of that fact that Evacuated tube systems are more than adequately frost tolerant.
We have not had a single problem with the recent cold weather. Said Barry Cribb MD of Sky Power.
As mentioned in the article quite correctly, flat plate systems are notoriously prone to freezing because of their design. The very thin fluid channels in contact with the flat sheet of metal can only be protected by an antifreeze solution, typically propylene glycol and configured in what is referred to as an indirect configuration.
Evacuated tube systems conversely use a similar alcohol within a sealed copper pipe which will withstand temperatures down to minus 30 degrees. This is one reason why they are becoming more popular in the consistently colder climates of northern Europe.
The above two photographs above were taken in Rivonia, Johannesburg.
The tubes can be seen clearly covered in ice. Outside roof temperature was measure at -7 degrees Celcius.
No damage was caused to either of the systems inspite of the fact that the electronic frost protection mechanism had been disabled as proof of resilience.
It is important to understand the difference in performance of the various system designs and not brand all solar water heaters as frost sensitive. The more efficient evacuated tube systems are inherently frost resistant.
How long untill I get my money back
What about financial payback?
Approximately 5 years
A typical 200L geyser uses an average of approximately 11-13 kWh per day to maintain the temperature at 60 degrees. At the current 39c/kWh this resolves to R4.29 per day or 1565.85 per annum.
With projected Eskom tariff increases of 30% per annum the recovery point for a system delivering 9.23kWh into a 200L tank will be reached between 5 and 6 years based on the installed price of the 9.23kWh product of R17, 300
Anything less powerful than 9.23kWh into 200L will take correspondingly longer to recover.
kWh Cost Annual Saving
Year 1 R 0.39 R 1,575.89
Year 2 R 0.51 R 2,048.65
Year 3 R 0.66 R 2,663.25
Year 4 R 0.86 R 3,462.22
Year 5 R 1.12 R 4,500.89
Year 6 R 1.46 R 5,851.16
Total R 20,102.07
See the Sky Power Payback Calculator: -
http://www.skypower.co.za/content/calculators/power_demand.asp
Any 200L product with a lower Q factor forecasting a shorter payback will be overly optimistic.
Approximately 5 years
A typical 200L geyser uses an average of approximately 11-13 kWh per day to maintain the temperature at 60 degrees. At the current 39c/kWh this resolves to R4.29 per day or 1565.85 per annum.
With projected Eskom tariff increases of 30% per annum the recovery point for a system delivering 9.23kWh into a 200L tank will be reached between 5 and 6 years based on the installed price of the 9.23kWh product of R17, 300
Anything less powerful than 9.23kWh into 200L will take correspondingly longer to recover.
kWh Cost Annual Saving
Year 1 R 0.39 R 1,575.89
Year 2 R 0.51 R 2,048.65
Year 3 R 0.66 R 2,663.25
Year 4 R 0.86 R 3,462.22
Year 5 R 1.12 R 4,500.89
Year 6 R 1.46 R 5,851.16
Total R 20,102.07
See the Sky Power Payback Calculator: -
http://www.skypower.co.za/content/calculators/power_demand.asp
Any 200L product with a lower Q factor forecasting a shorter payback will be overly optimistic.
The true cost of an Installation
Cost per kilowatt-hour(for the capital cost of the system)The true cost of the system.
Using the Eskom web site as the source of data. Indicated installed pricing for solar water heater varies from R22, 700 down to R14, 900.
The Q factor explained earlier is used by Eskom to determine the value of the subsidy for which the product will be eligible. The subsidy has recently been revised and no longer applies linearly relative to Q factor.
Nonetheless a products Q factor can be determined from its subsidy value, though the calculation is more complicated than before.
Please visit our web site for our product performance evaluator. This allows you to calculate the Q factor and an estimate of how much energy any system will deliver from solar input.
The calculator also provides a "cost per kilowatt hour" comparison to help you select a suitable product by comparing apples with apples.
http://www.skypower.co.za/content/calculators/power_demand.asp
It is imperative that purchasing decisions be made on performance/price rather than just price.
But which is the most cost-effective product to buy? Divide the Q factor by the indicated pricing and you come up with a price per Kilowatt-hour. Figures range from R1874 to R3995 per kWh.
Still be wary however of any very low offerings as this might indicate the supplier is allowing insufficient funds to provide a reliable after sales service.
Using the Eskom web site as the source of data. Indicated installed pricing for solar water heater varies from R22, 700 down to R14, 900.
The Q factor explained earlier is used by Eskom to determine the value of the subsidy for which the product will be eligible. The subsidy has recently been revised and no longer applies linearly relative to Q factor.
Nonetheless a products Q factor can be determined from its subsidy value, though the calculation is more complicated than before.
Please visit our web site for our product performance evaluator. This allows you to calculate the Q factor and an estimate of how much energy any system will deliver from solar input.
The calculator also provides a "cost per kilowatt hour" comparison to help you select a suitable product by comparing apples with apples.
http://www.skypower.co.za/content/calculators/power_demand.asp
It is imperative that purchasing decisions be made on performance/price rather than just price.
But which is the most cost-effective product to buy? Divide the Q factor by the indicated pricing and you come up with a price per Kilowatt-hour. Figures range from R1874 to R3995 per kWh.
Still be wary however of any very low offerings as this might indicate the supplier is allowing insufficient funds to provide a reliable after sales service.
Retrofit or New Geyser
Retrofit to existing or complete replacement
Solar geysers for which you pay a premium are required to have a better standing loss performance than a standard geyser.
The SABS spec states that a 200L Solar geyser must achieve 2.26 kWh or better. That’s only 0.04kWh better than a popular brand of standard geyser. A good argument in itself to uses a system that will fit to your existing geyser rather than buy a new one.
In terms of losses there is often no significant difference between a solar geyser and a good standard one with adequate insulation. Greater losses come from un-insulated pipe work.
Almost invariably it's the suppliers who market integrated systems (though with built in tanks ) that decry the use of existing geysers.
Solar geysers for which you pay a premium are required to have a better standing loss performance than a standard geyser.
The SABS spec states that a 200L Solar geyser must achieve 2.26 kWh or better. That’s only 0.04kWh better than a popular brand of standard geyser. A good argument in itself to uses a system that will fit to your existing geyser rather than buy a new one.
In terms of losses there is often no significant difference between a solar geyser and a good standard one with adequate insulation. Greater losses come from un-insulated pipe work.
Almost invariably it's the suppliers who market integrated systems (though with built in tanks ) that decry the use of existing geysers.
Thermosyphon vs. Active Circulation
Thermosyphon vs. Active Circulation.
The most common image one has of a solar heater is of a roof tank with a flat plate collector positioned beneath it in what is known as a close-coupled configuration. This is the most common configuration. Known as thermosyphon, it relies on the fact that hot water rises.
Whilst this is the simplest of all configuration options, like many older designs, it has a number of disadvantages when compared to current technology.
Firstly the heat transfer rate is very slow. Secondly and more importantly it has no means to control top end temperatures.
For this reason many thermosyphon configurations are sized to prevent overheating and even boiling in summer conditions.
Being undersized to prevent overheating also prevents them from offering adequate performance in winter.
Conversely correctly sized systems having no control often present dangerously hot water temperatures.
Active circulation mechanisms however whilst being slightly more complicated are able to control temperature delivery and so can provide superb winter performance without the problem of overheating in summer or if the system is unused when the property is vacant for example during holidays, etc.
This is achieve by one of two methods, either diverting water flow to a heat dump to dissipate the excess energy on large scales systems or by allowing the collector to stagnate in the case of small systems.
Whilst it can be possible to locate a thermosyphon tank out of sight in a “separated” configuration, another benefit that active circulation brings is that the storage tank or geyser can be placed anywhere as opposed having to be above the collector.
In many cases active systems can employ the existing geyser as the primary storage tank rather than having to install a second or new one.
Although flat plate systems are more commonly used in close-coupled arrangements, certain manufacturers of evacuated tube systems also offer a close-coupled thermosyphon arrangements.
These systems however are equally as prone to overheating for the same reason having no means to turn off the energy delivery once the water is at the required temperature.
The result again is that such systems are under specified in order to prevent excessively high temperatures being reached in summer.
Not withstanding this these systems can still boil if left unused during holiday periods. This is of course is potentially dangerous as well as being wasteful of water, as ultimately the systems safety valve will discharge the entire volume of water to bring the temperature under control.
To borrow a statement from a Pirelli advertisement: – Power is nothing without control.
Conclusion: Active circulation provides control to achieve year round performance and protect against overheating.
The most common image one has of a solar heater is of a roof tank with a flat plate collector positioned beneath it in what is known as a close-coupled configuration. This is the most common configuration. Known as thermosyphon, it relies on the fact that hot water rises.
Whilst this is the simplest of all configuration options, like many older designs, it has a number of disadvantages when compared to current technology.
Firstly the heat transfer rate is very slow. Secondly and more importantly it has no means to control top end temperatures.
For this reason many thermosyphon configurations are sized to prevent overheating and even boiling in summer conditions.
Being undersized to prevent overheating also prevents them from offering adequate performance in winter.
Conversely correctly sized systems having no control often present dangerously hot water temperatures.
Active circulation mechanisms however whilst being slightly more complicated are able to control temperature delivery and so can provide superb winter performance without the problem of overheating in summer or if the system is unused when the property is vacant for example during holidays, etc.
This is achieve by one of two methods, either diverting water flow to a heat dump to dissipate the excess energy on large scales systems or by allowing the collector to stagnate in the case of small systems.
Whilst it can be possible to locate a thermosyphon tank out of sight in a “separated” configuration, another benefit that active circulation brings is that the storage tank or geyser can be placed anywhere as opposed having to be above the collector.
In many cases active systems can employ the existing geyser as the primary storage tank rather than having to install a second or new one.
Although flat plate systems are more commonly used in close-coupled arrangements, certain manufacturers of evacuated tube systems also offer a close-coupled thermosyphon arrangements.
These systems however are equally as prone to overheating for the same reason having no means to turn off the energy delivery once the water is at the required temperature.
The result again is that such systems are under specified in order to prevent excessively high temperatures being reached in summer.
Not withstanding this these systems can still boil if left unused during holiday periods. This is of course is potentially dangerous as well as being wasteful of water, as ultimately the systems safety valve will discharge the entire volume of water to bring the temperature under control.
To borrow a statement from a Pirelli advertisement: – Power is nothing without control.
Conclusion: Active circulation provides control to achieve year round performance and protect against overheating.
Does Solar Really work ?
Whether a solar water heating system will provide any real benefit is purely a function how much energy the volume of water in question requires and how much energy the collector can deliver and when.
The energy required to heat for example, a 200L geyser by 40 degrees Celsius is 9.13kWh.
Systems currently listed on the Eskom web site show products with energy delivery ratings from 3.74kWh to 9.23kWh for 200L systems.
This rating is known as the Q factor. It is produced from SABS test measurements and indicates the heat output from an insolation level of 16MJ or 4.44kWh/m2/day of sunlight energy.
This means that the 3.74kWh product will provide 41% of the energy required whereas the 9.23kWh product will deliver 101% of the energy required to achieve a 40-degree temperature rise in the 200L of water.
Many systems available on the subsidy scheme are, in my opinion, under powered some of which are even S ABS Mark approved. Unfortunately, mark approval in the case of Solar Water Heating equipment does not indicate that the product is fit for purpose.
The minimum output energy rating required for approval being only 2.5kWh regardless of the volume of water into which the energy is being delivered. Typically in a 200l geyser 2.5kWh is just enough to keep the water hot. It will not provide sufficient energy to reheat the water used.
Make sure you select a product with a High Q Factor and compare it to the required to heat the volume of water in question.
See the Sky Power Product Performance Evaluator:http://www.skypower.co.za/content/calculators/power_demand.asp
The energy required to heat for example, a 200L geyser by 40 degrees Celsius is 9.13kWh.
Systems currently listed on the Eskom web site show products with energy delivery ratings from 3.74kWh to 9.23kWh for 200L systems.
This rating is known as the Q factor. It is produced from SABS test measurements and indicates the heat output from an insolation level of 16MJ or 4.44kWh/m2/day of sunlight energy.
This means that the 3.74kWh product will provide 41% of the energy required whereas the 9.23kWh product will deliver 101% of the energy required to achieve a 40-degree temperature rise in the 200L of water.
Many systems available on the subsidy scheme are, in my opinion, under powered some of which are even S ABS Mark approved. Unfortunately, mark approval in the case of Solar Water Heating equipment does not indicate that the product is fit for purpose.
The minimum output energy rating required for approval being only 2.5kWh regardless of the volume of water into which the energy is being delivered. Typically in a 200l geyser 2.5kWh is just enough to keep the water hot. It will not provide sufficient energy to reheat the water used.
Make sure you select a product with a High Q Factor and compare it to the required to heat the volume of water in question.
See the Sky Power Product Performance Evaluator:http://www.skypower.co.za/content/calculators/power_demand.asp
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