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Solar Panels:
Q 1: What is the best angling for my PV array
A1: Some debate on this, but in S.A. we usually go with the line of latitude as the measure for angle. Some, in Gauteng, believe that angling for summer months (flatter angle) is better because there are more clouds in the summer ‘fronts’ that come through, and thus less actual sun than in the Highveld winters – where there are virtually no clouds for several months. Roof angles usually dictate for most domestic installations.
Q 2 :What is the best orientation for my PV array
A2: As a rule of thumb, in the southern hemisphere, facing north is best. We have seen higher yields from slightly north-east facing arrays in summer months, due to the fronts that often limit afternoon sun in Gauteng.
Q3: Are Mono panels better than Poly, in African conditions
A3: Up until several years ago, Mono panels were preferred for African conditions where UV rays are very strong. However, the manufacturers of Poly panels appear to have 'upped their game' and are giving the same sort of performance warranties as Mono panels over the past few years. In the broader scheme of things, Poly panels have a better temperature coefficiency than Monocrystaline panels and will generate more power throughout the year.
Q4: Can I mix different types of panels
A4: This again is not a recommended practice. Mixing Mono and Poly would be less critical than Poly and Thin film – which actually should never be done - due to the differences in output voltages (thin film voltages are much higher than Mono or Poly panels).
Q5: Can I mix different sizes of panels
A5: Another No-No in the world of solar disciplines. Mixing panels of differing voltages and amperages will bring the ‘string’ down to the lowest common denominator – the weakest panel. If it is a simple 12V system with say 2 panels of similar Watt rating wired in parallel, it will not be as detramental as when they are strung in series.
Q6: What are the benefits of Thin film panels over ‘conventional’ ones
A6: Thin film panels, particularly of the CIGS variety (not Amorphous Silicate), have started to become quite popular in the past few years. They are purported to give anything between 10-15% greater yield - depending upon location, climatic conditions and ambient temperatures. They are now also giving similar guarantees to the more popular Mono and Poly panels and their roof ‘footprint’ is not all that much different these days as the technology has been perfected since the first panels hit the market some 10 years ago.
Q7: Does your geographical location affect PV yield (coastal, inland, desert, etc.)
A7: Indeed! The further south you are the less solar charging hours you tend to achieve – so the best performance would be on the equator (although high temperatures, humidity and rainfall would have some negative bearing on nett yield). Coastal areas are not as good as inland deserts at the same latitude.
Q8: How much do dirty panels affect PV yield
A8: More than you would imagine! Dirty panels can lose as much as 35% of their potential yield. Thin film panels much less so as they are not as susceptible to shading as Mon and Poly panels.
Q9: How much does temperature affect PV yield
A9: Quite a lot, is the simple answer. It may seem counter-intuitive, but solar panel efficiency is affected negatively by temperature increases. Photovoltaic modules are tested at a temperature of 25 degrees C (STC) – about 77 degrees F., and, depending on their installed location, heat can reduce output efficiency by 10-25%. As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly. In fact, the voltage reduction is so predictable, that it can be used to accurately measure temperature. Thin film CIGS panels are much less affected by higher temperatures.
Q10: How often should I clean my panels
A10: It depends how often it rains in your neck-of-the-woods, as well as how dusty an environment your PV array is subjected to. They should ideally be cleaned at least monthly by you, or by nature. Use only fresh water with no detergents – spraying with a garden hose is quite adequate as a rule.
Q11: How much yield can I expect from my roof (watts per Sq.M)
A11: Again this depends upon the location of your site. As a rule-of-thumb for Gauteng area we use a figure of 1000Watts per hour, per square meter – although it can be slightly higher depending on air temperature and weather conditions.
Q12: How much does shading affect PV yield
A12: A great deal! Just because your panel is only shaded by say 10%, you could easily be losing up to 80% of your potential yield. (It is much less with thin film panels). Winter shading is a big issue for many solar systems installed in the summer and where the installer did not allow for a drop in the angle of the sun in winter. Obstruction such as neighbouring buildings, masts, turrets, high trees, etc. can all lead to shading and a reduction in PV yield.
Q13: Can I install panels flat against my roof
A13: If you place panels directly onto a roof, especially corrugated iron and IBR roof types, the the heat generated from of the back of the panels has no decent means of escape thus trapping the heat. As we know, panels start to lose power after 25 degrees centigrade and thus you can lose a lot of power from their being ‘over-heated’. Mounting the panels with a minimum airgap of 10cm is the correct way of ensuring proper airflow and maximising PV yield.
Q14: What is the best sizing for a roof-mounted panel
A15: In ‘the old days’ you saw many 80-100 watt panels mounted on roofs but today the normal roof-mounted panels are between 200-270W. This is still a practical size for handling using ladders. For ground-mounted system one can obviously go larger (Refer Q 53)
Q15: What is the maximum size for a ground-mounted panel
A15: Ground mounted panels can go up to 350W and more these days – although the industry is very dynamic and more powerful panels could well come on-stream in the future.
Q16: What is the difference between Amorphous thin film and a CIGS panel
A16: With both of them being refered to as thin film panels, the main difference is that the CIGS panels contain no Silicone or silicates whatsoever. Amorphous type panels are known to be flexible and have a quite a larger footprint than that of CIGS panels.
Q17: Is winter yield much lower than summer yield
A17: That really depends where you are located. In Gauteng some of the highest yielding months can often be in October time when temperatures are still quite cool – but it does vary a lot and will be influenced by the angle of your panels as well as your location. Even though the arc of the sun is lower during Winter months, the cool temperatures and clear skies result in very good power yields from PV systems.
Q18: What do I lose in yield if my roof is East/West facing
A18: During Winter months one will see a considerable drop in yield with an East/West split array due to the sun's path and azimuth. Summer months will see the yield increase exponentially due to the much higher arc of the sun. However, one would need 2 x MPPT/PWM regulators for a East/West split array so as not to let the one array pull the other down.
Q19: How do I know if a panel is under-performing
A19: This is where a system monitor comes into its own. By tracking yield throughout the year you can compare days, months and years. If your yield is dropping off it can be due to many reasons:
Dirty panels
Not utilising full potential of array (poor system design)
Battery bank not holding charge
Connection issue with panels
Faulty MPPT or regulator
Poor Power Management (use heavier appliances during solar charging hours)
Faulty panel, or string of panels
Incorrect cabling used (some installers use solid AC copper wire for DC applications)
Poor programming of Inverter (brings in Mains or Genset too quickly)
Mixing panels of different types, or sizes
Inadequate battery bank for application
Q20: Do I need to earth my panels – if so, what is the best method
A20: This is very critical, particularly in lightning-prone areas such as Gauteng (third highest strikes in the world, it is said). You can use a lightning rod/stake or an earth Mat (prefered method) which will limit the danger of a strike doing too much damage to your panels and Charge controller.
Q21: Do surge protectors really work
A21: They definitely help and lower the risk of damage to a PV systems components. However, very little will protect you against a direct lightning strike – so make sure you are insured under your policy for this!
Q22: What is the best way to clean my panels
A22: use only water as a rule. If you have spilt something that requires a detergent, use sparingly as they may damage the panel if too strong a solvent or cleaner is employed.