So after reading part 1 of this blog, we now have a good idea what a grid-tied solar system means, what it can do for us and what not. The big issue of course is that it does not offer back-up power in case of power failure, which unfortunately is an issue South Africans are faced with frequently.
What is a back-up system?
A back-up system consists of an off-grid or hybrid inverter and a set of batteries. It is in essence a big UPS (Uninterruptible Power Supply), which is what IT companies use to protect their servers. Whereas a true UPS only supplies power for a few minutes so that a server can be shut down properly rather than it crashing by the sudden power interruption, a back-up system is designed with much more capacity, so that essential appliances can run from battery power for several hours. A back-up system, too, will protect your appliances from surge damage which can occur when the power is restored.
Depending on whether a household only wants to keep the lights on and perhaps be able to watch TV, or whether they want to use more appliances, or whether a business needs to keep their essential machines running, a back-up system can be sized for just about any requirement. There are several sizes of inverters available and also several sizes of batteries. The relevant inverter size and battery size will be determined according to every customer’s individual needs.
The batteries of a back-up system can be charged by mains while the power is on or by solar panels. So in order to have back-up power, it is not essential to have solar panels. If the system is re-charged by mains, you will have power until the batteries are depleted and if the power has not been restored before this happens, then you will be without power, i.e. please make sure not to purchase your batteries too small. If solar panels are connected, then the batteries will be re-charged by solar power while the sun is producing.
The difference between a hybrid system and an off-grid system
A hybrid system is the combination of a grid-tied system and a back-up system. You could have a fairly large grid-tied system with enough solar panels to produce enough power for your entire household or business, and only a small battery bank to carry essentials during the night or during power failures. You will keep your utility grid connection to supplement any consumption need which is not supplied by your own system. Sometimes we need more power than usual or the solar system might produce less because it is a rainy day.
Going off-grid means to really give up this utility connection. It is a big step to take if a utility connection is freely available! To be completely independent from the grid requires a great deal of planning and correct sizing of your own solar power plant. In this case a large enough battery bank size is absolutely crucial, as it must be able to store all the power your solar panels are producing and also supply enough electricity for the entire operation. The owner of an off-grid system must understand start-up power requirements from appliances with motors and ongoing consumption loads in order to avoid a system overload or running out of power. It will not be possible to just liberally run everything at the same time as we are used to when we have a well-functioning utility grid at our disposal.
Now which way to go?
You may have noticed that I am not in favour of going totally off-grid, if a utility connection is available. This is fact – I would really like to discourage everyone from considering this option, unless there is a good reason for it. A good reason for an off-grid system is living in an area where there simply is no utility power connection, or where it comes with a hefty price tag just for the connection regardless of consumption. These situations are usually found in rural and farming areas, but not in urban residential or industrial areas.
The preferred way to go for Mr and Ms Average is most definitely a hybrid system. Go as large as your budget allows with solar panels and a reasonable battery size to cover your power requirements during night time and power failures. This type of system will maximise savings as you will only purchase any surplus power requirements from your utility and you will not be left in the dark.
Choice of equipment
There is a wide choice of solar equipment out there, and a lot of companies with various offerings. Please make sure that you are dealing with an experienced and accredited solar supplier who can give you sound advice. The price range from cheap to expensive is not because one supplier is trying to make a killing whereas the other supplier is out there for the greater good, but because technology differs to a large degree, and technically superior equipment has a price tag attached to it. All systems will initially produce power as we would expect, but cheaper panels deteriorate much faster and produce less power within a couple of years. A good solar panel should come with a 10 years manufacturer’s warranty and a 20 – 25 years linear performance guarantee. Please check and compare the figures on the data sheet, which you must obtain.
As strongly pointed out in part 1 of this blog – please make sure you purchase a good inverter. Your inverter is the intelligent part of the system and responsible for smooth operation of your business or household.
You can either have a 2-inverter system consisting of a grid-tie and an off-grid inverter, or a hybrid inverter which combines both functions in one box. The pros and cons of these differences go beyond the scope of this blog and it gets rather technical, but please ask your supplier to explain the ins and outs of these. If they tell you it’s just a matter of price, then look for another supplier, it’s not that simple.
And lastly – the batteries: Batteries are the most expensive part of the system. They too come in lots of different shapes, sizes and materials. It is not necessary to purchase the most expensive batteries, aka power wall, but on the other side of the scale – a car battery just won’t do the trick. It is important to purchase a deep cycle solar battery. And the size of the battery bank must be considered carefully with a view to future extra needs, as you cannot just add another battery later. The expected lifetime of a good quality battery bank is 10 years plus, whereas cheaper UPS batteries will only last 1 – 2 years if they are used for the wrong application and cycled regularly.
The above mentioned 3 parts of equipment, namely solar panels, inverter and batteries, are at the core of a solar system. Your chosen supplier together with the installer will also advise you regarding management systems, panel mounting structure and other electrical requirements.
In closure, I would like to point out once more, that the sun radiation in South Africa makes for ideal conditions for solar power. Investing into solar is a wise decision, as it pays for itself in far less time than the projected lifetime of a system. The dividend of your solar system is the annual tariff increase not paid, it is kind of guaranteed and will not succumb to volatile economic conditions. Green loans are available from the bank for those who would like to invest but do not have the necessary cash flow. Wilster can also help with sourcing financing. Please contact us with your questions and requirements!