The term ‘Off-Grid’ has become a popular phrase these days, and many people use the term quite loosely when referring to domestic solar systems in general. There are, however, different kinds of solar systems and some solar arrays (a group of solar panels working in unison) are actually grid connected, and rely on the grid to work. So it is important to understand some basic terms, and to use them accurately to describe what one has, or would like to achieve.
The ‘Grid’ that is referred to is the national electricity system that exists in any particular country. In South Africa, this is primarily Eskom’s electricity network, but in some areas it is managed by local municipalities, who simply buy the power from Eskom and sell it on to the final end user.
So to be off-grid, means exactly that - to provide one’s own electricity, without being connected to the national grid. A well designed off-grid Solar PV (PhotoVoltaic) system will supply you all your required electrical energy, day and night. It must therefore have generating capacity (panels) as well as storage capacity (batteries).
An off-grid solar PV system comprises a set of PV panels, a charge controller, an Inverter, and a battery (or many batteries, in the case of lead-acid). This is assuming that the house (or system being supplied with the electricity) is running a 230Volt electrical system, which most households in South Africa would be. Note here that one can run a 12Volt system directly off a battery (no inverter, therefore cheaper), but then all appliances in this system would need to run on 12Volts, and these light bulbs and appliances can be more difficult to source.
The panels gather the energy in the sunlight, the charge controller (these days, usually a Maximum Power Point Tracker, or MPPT) modulates the charge from the panels to the battery to optimise what sunlight is available, as well as making sure the battery doesn’t get over-charged. The inverter then takes the DC (Direct Current) from the battery and/or MPPT, and supplies AC (Alternating Current) to the house.
All the components can vary in size and a system can therefore be tailor made to suit one’s specific requirements. There are some fairly common numbers, though, and the best way to estimate what size system one would require, is to work back from how many kWh’s are used, on average, per day.
An average suburban household will use around 25-30kWh’s per day. A solar system that can provide this, on average, will cost around R250k. Bear in mind that this is a very broad generalisation, as there are so many factors that will affect this figure. For example, some areas of South Africa have heavy cloud in the afternoons, and that is when a solar system is usually producing a lot of its energy, so location will play a role. Likewise, some houses might be on the shady side of a mountain, and see much less direct sun than others. And some houses have very little suitable roof space for enough solar panels. So it is always necessary to have a proper evaluation, preferably by a solar installer, before one assumes too much about what their solar potential might be.
It is also important to advise that one should always have a backup generator when going completely off-grid, approximately the same size as the solar system inverter, to help manage loads during long periods of inclement weather, as well as to charge up the battery. One can get away without one, but this means building a bigger system, which costs more, and as a result, wasting more power when the sun is shining. One would want to build a system to manage 95% of the time, and use load management and/or run a generator for the remainder. To cover that last 5% with only solar can mean spending insensible amounts of money.
Living off-grid will give one a genuine feeling of self-reliance and power security, and the fact that one will never again have to contemplate the hassles of load-shedding, is hugely satisfying. More importantly, the clean energy that one lives with is not polluting (each kWh that is not used from Eskom, saves just under 1kg of CO2 going into the atmosphere!) and you are in control of your electricity entirely. With good equipment, I do believe solar is more reliable than Eskom’s grid in most parts of the country, and with average usage, one should get a payback on investment in approximately 7-8 years. I would encourage anyone who can afford it, to take the leap, the sooner the better!