Solar Energy – some pitfalls
What is the deepest concern most people have wanting to install solar PV? Return on investment, initial capital outlay, eco-waste, weather not conducive to efficiency? There are lots of reasons for us wanting to possibly postpone the inevitable, but the reality is that with the rising costs of energy, it will not get cheaper – but renewable energy, specifically PV solar, is getting cheaper if we compare it to ten years back.
Much of what we see today encompassing solar energy has been with us for decades – solar geysers have been around since the 1960s. In fact the hospitality industry was one of the first industries to start cutting down on the exorbitant costs of heating water although the practice of heating water through collectors or storage tanks is nothing new and may go back a few centuries. Records from Bell Labs put three scientists in the forefront of Photo Voltaic energy, Calvin Fuller, Gerald Pearson and Daryl Chapin. However the photo voltaic effect was discovered something like 100 years prior by Frenchman Edmond Becquerel. And don’t forget that Albert Einstein won a Nobel Prize for his research into the photo voltaic effect in 1921 already.
Although solar PV has been around for some time there are some fundamental reasons takeoff has been slow until recently.
Scare Tactics by the Misinformed
So just how long do batteries really last? So you think that Lithium Ion is the way to go because your lead acid battery only has a live-span of five years. Interestingly enough the more mature of the two technologies has proven itself over and over again. Ask yourself why with RoHS car or auto batteries are almost always lead acid. What is more revealing is that years back NiFe cells were known to be extremely hardy although lower capacity than your deep cycle lead cell – both Lead Acid and Nickel Ferrous (Iron) have been used in the maritime industry with very positive results. Are batteries built differently these days – it’s not a secret that there are both NiFe and Lead Acid batteries that have clocked in over 50 years of service in various industries, most predominately in the telecommunications industry. What I can say is that batteries that last this uncanny length of time are well maintained and more importantly, can be well maintained because of the nature of their build. Sealed, gel etc are not in this category. And yes, they are costly.
Most of the installations that I personally have come across where the lead acid cells are still in good shape would definitely be where the cells are not discharged beyond a specific safe rating, the batteries contain an electrolyte which can be accessed either for topping up or a specific gravity can be read. The same applies to NiFe cells. I was in the merchant navy and most of the ships in early years had NiFe cells for emergency gear – 15 years on and no cells had been replaced and they all showed no sign of capacity loss. And I can promise you, there was a lot of abuse, especially overcharging. I put down the longevity to the fact that the technical staff had to keep a log, SGs had to be taken and the authorities would examine this log once per year or maybe in port spot checks. I do not know about today but guaranteed there are still stringent rules covering this. So the point I make here is clear, one may pay more for batteries that are modular but the results should be encouraging if you have the time for maintenance.
Your typical batteries used in solar installations are lead acid deep cycle batteries. I’ll veer off Lithium at this stage and get to that some other time, lead-acid is where users have problems. Do ensure you have proper software for monitoring your load power, battery discharge levels, this mean both in terminal voltage as well as capacity usage. More about this later!
Just to finish off on batteries, most battery banks fail because of the user having set discharge levels too low (potential difference across the bank) or running a system where the battery capacity was too low for the load. Usually the manufacturer would spec the inverter’s DC supply e.g. 5kVA would require 48V x 200A = 9 600W/Hr. We use a derater of 0.5 x 9600kW = 4800W/Hr. Even then try to reduce your current usage accordingly.
Are solar PV panels all the same?
With solar panels a question which often arises is why do some suppliers charge so much for their panels? P.V. panels are not all the same and here we can refer to Cleanenergyreviews – a good explanation of the panels available, efficiency level, warrantees, etc. Be mindful that an efficient solar panel does not mean better quality. One of the best quality panels in the South African market used to be LG whom sadly have shifted their focus to other business ventures (more profitable?).
A more costly approach to installing PV is to have an array constantly tracking for maximum light but this will improve the overall efficiency of the system. The pitfall here will be maintenance. Living in Cape Town in South Africa also has a huge advantage where irreadiance is high. Manufacturers and installers advise adding one extra panel in areas like Johannesburg or Durban. This same principle will apply to different parts of the world. Another very important factor is the output voltage versus ambient temperature. As the temperature drops the output voltage increases and if the array has not been configured properly the installer can damage the MPPT (max power point tracking). Very good write up here from Sunwize. There’s lots of information out there on this subject and I can promise you, information that most installers are not necessarily aware of.
Chinese panels are the most widely used globally.
Special note: Often I read about a circuit which “requires current to operate and not voltage”. e.g. To charge a lead acid battery bank “one needs current and not voltage”. This kind of statement to the layman is very confusing because it implies that there is no correlation between voltage and current. There is of course because the higher the terminal voltage (or the potential difference across the battery terminals) is the higher the current flow. In another way, if the terminal voltage of the battery is 12V and the charger is 8V there will be no current flow.
Inverters – rubbishing the Chinese imports
This is a very big problem area. It started with professional audio (and other sectors, like notebooks – but I am most familiar with audio and Behringer). In the entire electronics industry, yes, this includes Apple, most manufacture takes place in China. If China does not have the right engineers they buy them in. Why should we lambaste China now when the western world have been doing it for ages, just look at the amount of engineers working in the USA from India, China, Korea and even Russia. What has made the technology great is not just the design, actually more so in technogical improvements in semiconductors. Years back we had bipolar transistors, typically the tried and trusted 2N3055 NPN used to switch a 50Hz transformer. As the rating went up so did the weight. A 10kVA inverter had to be moved around by truck in the 80s – in 2022 we would be looking at possibly 20 to 30 kilograms. The big thank you goes to MOSFET and IGBT (metal oxide silicon field effect) and Insulated Gate Bipolar transistors. Just look at modern DC welders – under R2000.00 in South Africa ($140.00 US), for a 160A inverter welder where one is looking at a power switcher running at about 4kW at full power. And most of these are Chinese imports. Local manufacture and local supply will just not compete.
Competition in South Africa seems to be mainly between Victron and Axpert (Voltronics). The de facto website in South Africa to get your power solutions is Power Forum. A lot of queries one gets in the industry is answered on Power Forum by usually some pretty bright guys with lots of industry experience.
So where does one sit when looking to buy an inverter – number one, paying a hefty sum to have power backup at home is one thing but is this really necessary? No, it’s not. Axpert inverters are very popular and the fail rate is very, very low. Many of the specialistic installer companies will only insist on installing Victron because of this exact reason. Then we have the no-name brands and the Kodak inverters. Most of these are Axpert devices. Be cautious of the copy cats for Axpert – they do take short cuts and I read a lot on the forums about installers complaining about “cheap arsed Axperts” failing. They are not Axperts, they do not carry the right serial numbers nor the logo – they just look like Axperts.
Mecer and RCT are both reputed inverter importers in South Africa. Victron is imported from the Netherlands, the home of the manufacturer. Victron products are also illegally copied and distributed from China.
Doing your due diligence is very important before any installation – find out about the warranty on the individual components, the entire installation and the company doing the service and repair. Sometimes it may cost more but knowing you can have your product repaired locally is critical. I have heard of people in Cape Town having to send their product back to Johannesburg for repair which may take weeks.
What software are you using?
This is where things can become tricky. Why install a system which you cannot monitor. How does one optimise your solar system? These are questions often asked and frequently overlooked in an installation.
So here is a typical scenario in South Africa at the moment and as a result of the unreliability of our power commission, Escom.
(For the benefit of foreign readers, Escom (now Eskom) used to be in the top five biggest power generators globally prior to the current government. Lack of maintenance, theft and having no strategy has left this massive moneypit a headache for the current President).
Having any installation one needs to look at many factors, in the RSA one would be looking at the reliability of the power supply (not too good), cost per annum, future increases in energy prices and what the total cost of ownership over possibly ten years. If the solar panels have a 25 year warranty, the inverter can hold out for ten years then the only problem area is going to be your battery bank. Most installers are pushing a Lithium solution, more expensive but “possibly”more cost effective. Lithium Ion has been around for years but to be honest I cannot give you a a reliability report – it’s just too new on the solar market. Lithium Ion batteries or their equivalents are getting cheaper but bear in mind these are imported and subject to currency factors (the ZAR is just not strong), shipping and import charges.
Without software one cannot see the state of charge. If one is using their solar system strictly for keeping your rising energy costs down you will be in for a surprise if the battery bank is depleted by the time you really need it – in winter and when it is dark. The software will always mix solar, battery and mains. If you are using your system strictly as a backup in case the power goes down, then the solution would be to mix solar and mains and keeping the batteries fully charged. Your batteries will last longer of course.
In my case I don’t let the battery voltage drop below 48V and it’s set to solar, utility, battery. Battery cannot drop below 60% state of charge. Whether this is acceptable or not remains to be seen. The geyser is off the system because the battery capacity is only 9.6kW/Hr. Geyser power consumption about 150kW over thirty days. The battery supply is two independent banks 48V x 100A/Hr bridged through two Keto fuse / isolators (both + and -) – 35mm2 cable, common to inverter 50mm2. Axpert Max 8kVA. Panels are twelve 400W CNBN – are they any good? (split 6 panels per MPPT)
Part two – MPPT vs PWM and Power Inverters topology