Solar panel efficiency
Understand the difference between different technologies and avoid pitfalls and comebacks
Tests carried out on 160+ different solar panels by the internationally acclaimed research organisation Solartechnik Prufung Forschung (SPF) found that the gross efficiency of flat plate collectors was considerably higher than evacuated tube collectors…… http://www.sustainability.ie/solar.html
Your Solar Tips:
Flat plate is the most suitable solar technology for human water consumption at approximately 60◦C. When offering your customer the solar solution look at the temperature range required and make sure to apply the correct type solar panel for the application
Using a manifold of evacuated tubes in direct contact with water is lethal. Sooner or later the manifold paths will develop scale, causing rapid decline in efficiency and ultimately complete clogging of the manifold, rendering the whole system ineffective.
The distorted structure of government incentive schemes pushed many Evacuated tube suppliers to oversize their system, causing severe overheating once installed. The overheating of such systems causes a variety of problems such as geyser failures, valves failure, circulation pumps failure, safety problems with boiling water etc. Make sure to verify that the solar system you install is not prone to such problems.
Solar tips for the plumber
Right-sizing solar geysers and solar panels
Give your customers sufficient solar capacity to provide for their daily consumption.
Being an active plumber, you often find yourself in a position of having to recommend to customers the correct type of solar geyser installation.
As the South African solar heating market is not yet standardised you are very often exposed to suppliers trying to promote a variety of product and solutions, many of them not tried-and-tested under South African conditions.
Here a number of solar tips which will help you decide on making the right choice for your customers and avoid the frustration of having to deal with unsatisfied customers:
Facts and Figures
- Average middle-income South African family consumes 200-300 litres of hot water per day.
- Heating and maintaining such volume of water at 60C requires energy input of 10-15 kWh.
- The South African sun radiates approximately 6 kWh per m2 per day onto the earth surface. Modern collectors are capable of converting 50%-70% of this energy into heat.
- Following this logic, most collectors will produce approximately 3.6 kWh per m2per day.
- Producing 10 kWh to heat up a daily consumption of 200 litres will therefore require collector area of not less than 2.8 m2
- Producing 15 kWh to heat up a daily consumption of 300 litres will therefore require collector area of not less than 4.2 m2
Understand Different Systems
Solar tip for the plumber – Indirect, thermosyphon (natural circulation) solar geysers – Understand the working of such systems and avoid pitfalls and comebacks
Indirect solar geysers use heat transfer fluid (normally glycol) to carry energy from the solar collector and transfer the energy to the water through a heat exchanger. The purpose of using this technique is to prevent environmental damages to solar collectors such as freezing damages, corrosion and clogging.
Natural circulation systems are preferable to pumped systems in many instances due to their relative simplicity, lower cost and higher level of reliability. However, many of these systems fail to operate in a satisfactory manner due to faults related to wrong installation.
Natural circulation in solar geysers is weak in comparison to pumped circulation and is therefore sensitive to wrong system setup.
The following errors are most common:
1. Small leaks of glycol which are not detected during the installation
2. Incorrect pipe slopes, causing local high points and consequent air locks in the primary heating circuit
3. Incorrect glycol filling procedures, leaving unwanted air pockets and causing reduced efficiency
4. Incorrect glycol/water mixing ratios, causing freezing and consequent cracking of collectors
5. Insufficient service intervals – glycol level in Indirect systems should be checked regularly. The recommended interval is once a year. Systems which are not serviced are likely to experience reduced efficiency and ultimately stop functioning.
Your Solar Tips
- The only indirect storage tank which is suitable for natural circulation system is the double jacket type, with both supply and return points placed in the lower part of the jacket and the air bleeding outlet on top. Serpentine type heat exchangers are not suitable for natural circulation systems as they present a variety of challenges relating to problem free circulation.
- Special care must be given to correct pipe slope in split installations where the storage tank is placed inside the roof. The point where the collector – tank supply pipe penetrated the roof is specifically sensitive. The installer must ensure that there is no local high point and that all the air in the system is allowed to flow naturally and release from the top of the double jacket. The only way to achieve this reliably is to ensure that all pipes slope upward constantly from the collector to the storage tank. No local high points can be allowed in these pipes.
- Always fill the primary circuit from the bottom of the collector in order to make sure that all the air is removed from the circuit systematically.
- Use a pressure pump to pressurise the primary circuit and ensure that it is free of leaks.
When testing, take special care not to exceed the specified pressure rating of the jacket.
- Before leaving site, feel the temperature difference between collector bottom and collector top to make sure that the circulation is healthy. The bottom inlet of the collector should feel COLD, meaning that cold Glycol is flowing in from the tank jacket.
- Mix the glycol according to manufacturer’s specifications to make sure that the collector mixture can not freeze under any circumstances and the viscosity is suitable for natural circulation.
Following the above principles will prevent comebacks. The tips provided are based on the natural laws of physics and not on municipal by-laws. Therefore, failure to meticulously follow those guidelines will guarantee installation failure, frustrated customers and loss of reputation for the installer and the technology.
Don’t hesitate to contact email@example.com if you require technical assistance