Different Solar Systems and their Pros and Cons

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.

Off-Grid Solar Systems

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!

A thought...

So everything begins with a thought. That’s obvious. The fact that some basic foundations are in place already is a huge bonus, but today I decided to start a blog on our website. I have had it for almost 2 years now, and have procrastinated and avoided just about all I can manage, and so today, I had the thought of starting to take our business a little more seriously. So I decided to write a blog.

The thought thing is only pertinent because I have experienced so many times, how important it is to think about something long and hard before action is taken, if you want that action to make some sense, and hopefully convey the original thought purely and without corruption. This can lead to overthinking things if you aren’t too careful, and in this case I hope to avoid that by taking action sooner than later. Well, by writing at least. The real action might have to wait. But at least it has begun. The rock is moving just a tiny amount, the great wheels are finally turning….