There are a few disgruntled people out there who have had a solar system installed, only to find that they are left in the lurch, and without the power they thought should be coming from their solar panels, when we have load-shedding. They believe they have been duped, and worse still, some have become disenchanted fans of solar power. I can think of few sadder scenarios…..:( Then there are others who have had a solar system put in, and are left with the impression that when the sun shines, they will have the power they need, regardless of how big their requirements are compared to the size of their solar system.
The problem here starts with a lack of understanding, which has led to unfulfilled expectations and then of course, disappointment. The answer is simply to understand the difference between the different types of solar systems, their pros and cons, and to figure out which one suits your needs and your budget. Then one needs to ensure that the size of the system marries up with the electrical requirements. Making an informed choice from the start, should at least ensure that your expectations are met, and if there is any disappointment, it should only be that you didn’t go solar sooner.
The first type to discuss is the ‘Grid-tied’ solar system. This consists of a PV array (a group of PhotoVoltaic panels, usually facing in a common direction, grouped and wired together), and a Grid-tied Inverter. Fairly simple, and therefore the cheapest option, largely because this type of system has no storage. As the name implies, it is very much part of, and tied to, the Grid, and this is important to understand. ln South Africa, where load-shedding is becoming a part of life, the grid fails often. Because these systems are grid-tied, they do not function when the grid fails. This is due to a built-in safety mechanism within the inverter, so that power is not inadvertently fed onto the grid, when it is though to be ‘dead’. However, in areas where there is a feed-in tariff (currently Cape Town and surrounding municipalities, Joburg), and one can get credit for energy fed back onto the grid, this kind of system can help reduce electricity bills substantially, and will usually be spec’d to match the electricity usage, so that the system operates optimally and thereby gives the quickest payback, usually 2-4 years in most cases.
In SA, Eskom and the municipalities have made it that the end-user must still be a net user, so one will never get paid out for energy fed back to the grid, best case scenario is that you have a very small monthly bill. So this will be beneficial to high usage customers, who have a large space to place panels with good efficiency - like factories with large, suitable roof-space, and where most if not all of their electricity usage is during the day.
The next type is called a Hybrid Solar system. This still maintains a connection to the grid, but with the addition of a battery, for stored electricity to be used either at times of grid failure, or for self-consumption of excess solar power. So this comprises a Hybrid inverter (preferably with a built-in ‘anti-islanding’ system, to comply with regulations), which is either AC- or DC-coupled to an array of panels, and, importantly, connected to a battery. This gives this type of solar system energy storage capability, and therefore can operate when the grid is down. It will usually also use the grid to charge the battery via the inverter/charger when necessary.
I feel that in most residential South African homes, this is the most sensible and suitable system because it offers the best of both worlds - maximising one’s solar potential, and giving one power security from a solar-assisted backup system that supplies power when the grid fails. The proviso here is that the size of the battery determines how much backup time one has, relative to how much electricity is used, especially important when the grid is down, and there is no charge coming from the panels (ie. at night). The battery is the most expensive single component of this system, and this makes the payback a little longer, usually 5-6 years, pending usage and system efficiency.
The third type of system is an Off-grid solar system. This is essentially a Hybrid system without the grid being available. In this scenario, it is most important to recognize that the sun is simply not always going to shine, and if electricity is used consistently, then either one needs a very large battery (usually not financially viable) or some other source of electricity, like a generator, to keep the batteries healthy, even when the sun can’t. Usually an off-grid system will be spec’d to provide electricity for 95% of the time, and the other 5% may require generator support. This keeps the system within reasonable limits both financially and practically, because besides a budget, there is usually only so much suitable space available for panel mounting.
This last type is usually reserved for places where it is difficult to get a grid connection, or very high-cost standing/availability fees from the provider. These are often the more expensive type of solar system because it is the sole source of electricity for a particular dwelling, or load, and one would usually need to slightly over-spec PV size and battery to take care of extreme eventualities. Having said that, if it is spec’d right, even these systems should provide a cheaper-than-grid solution in the long run, and the lithium ion batteries are getting more and more affordable, reliable and lasting longer. One should see a payback in 8-10 years, pending usage and system maintenance costs.
But certainly in my experience, the most fantastic aspect of an off-grid system, and one which is impossible to put a price-tag on, is the feeling of having control over one’s own power, of never having to worry about load-shedding, and knowing and understanding the future of my energy costs, both to myself and to the planet.