Off-grid with Grid Backup
This is our most popular system for residential customers. This system gives you the freedom of being off grid, but because you have a grid connection available, you do not have to have a massive battery bank to get you through days with no or little sunshine. In other words the significant expense you have to go to in order to make provision for 3-5% of the time of poor weather in a total off grid system is avoided.
As battery storage becomes better and more cost effective, the battery capacity can be increased over time to move to a total off grid scenario.
The MPPT solar charger provides power to the inverter and charges the battery bank. The inverter is programmed to use battery and solar power to power the house / office. Should the battery voltage drop below a set value, the inverter will seamlessly switch to grid power, protecting the batteries from discharging further. It is important to design the system so that the PV panels, the batteries and the loads are well balanced to ensure that the system only goes to grid power in poor weather conditions or exceptionally high use of electricity (outside the usage the system was designed for).
The biggest advantage of this system is that you are protected against power outages, while you are saving on electricity. The downside is that the system is more expensive than a normal grid tied system due to the batteries and the more expensive battery to AC inverter.
Pure Grid Tied
This is the most popular system in most parts of Europe where generous power buy back schemes are in place. In South Africa, this system is not that popular for the following reasons:
It provides no protection against power outages (when Eskom goes down, the solar power goes down as well)
We do not have favorable net metering (power buy back) schemes to our disposal yet. There are some programs in place, but they do not make financial sense to small consumers.
The one anomaly is the Drakenstein Municipal area in the Western Cape. They have a VERY good system in place. See our dedicated page for this. Because we do not have good net metering schemes, this system does not make a lot of sense if you are not going to consume the power as you generate it (during the day). So it makes a lot of sense for most businesses, but not so much for residences.
Having said all that, if your objective is to save money and you are a day time consumer of electricity, this is the best system for you.
The difference in the Drakenstein area is that you can offset all your Eskom electricity with a solar system, if you use it during the day or night, because the system allows you to “store” your unused power during the day and consume it during the night. This means it makes as much sense for a large home that uses most of its electricity in the evenings as it does for an office block that uses almost all its energy during the day.
Ironically it is batteries, and not inverters or solar panels or charge controllers etc. where the biggest mistakes are made in solar system design and installations. If off grid solar systems, batteries are normally the most costly component of the system, yet not many people realise the enormous pitfalls there are in selecting the correct battery type for the application and conditions (such as ventilation, temperature, charge and discharge times and peak current requirements to name a few).
We have invested countless hours studying batteries and still spend hours weekly reading up and contacting manufactures and peers in the industry in order to give our customers the correct advice on battery choice.
This is a very complex topic and there are good resources available online to educate yourself, but be warned, prepare to spend quite a few hours and then go back for more studying, as new questions will emerge as you start delving into the battery world. One such good resource is
www.batteryuniversity.com. The fact this a site like this even exists should help you understand this is a minefield to be negotiated carefully.
This is also where the biggest advances are happening at the moment, and we are (in South Africa at least) seeing very interesting developments in Lithium battery solutions, specifically targeted at the residential and commercial solar energy and backup power market. The key is to find a battery manufacturer that is trustworthy and backs up their warranty. We have found such a supplier and is very proud to be associated with their product.
What makes the modern Lithium battery landscape very interesting is that we are able to offer the technology at prices better than lead acid over the life of the battery. In other words, for the energy stored and extracted for as long as the battery lasts, Lithium beats lead acid. This is major news, because the price of Lithium has the potential to fall by a large margin in the coming years where lead acid costs are actually going up.