After receiving quite a lot of feedback on the previous article on this subject, some of the valid points made by various commentators are addressed here.
For those that haven’t read the previous article, it can be summarised as follows:
Load shedding is caused by an instantaneous deficit in power occurring on the grid, which requires immediate reduction in consumption to match available supply, to prevent protection systems tripping and blacking out the grid.
This video below explains the issue quite well, using a recent actual event. The thing to take away from the video is one needs to understand the fact that regardless of the situation, instantaneous supply MUST keep up with demand, otherwise the AC wave frequency starts deviating beyond tolerances allowed by the grid protection switches, which automatically disconnect when they detect wave deviations. A catastrophic cascading uncontrolled shut down of the entire grid is a potential consequence. And in those circumstances, the ONLY option for the grid control authority, is to shed load. So load shedding will continue in SA until we have sufficient generation capacity to supply instantaneous demand, night or day, in any weather.
Wind and solar generation simply cannot meet that criteria. And thus those energy sources are not the solution to our problem, as desirable and fashionable as they might be.
The points below should be understood within that context, and are meant to refine the previous article, as well as address a few points which were implied, but not made explicitly in the original article.
The points I will address below are:
- If a solar power system is a viable option to alleviate load shedding when installed on my house (which it definitely is), then why will that not be a solution for the country as a whole?
- What about large scale battery systems?
- If everyone puts a solar system on their roof wouldn’t that solve the problem?
- How are other “more enlightened” countries able to add large amounts of wind and solar generation to their grids? If it works for them, why not us?
One of the things I think is confusing many people in this debate, is the fact that one way of insulating ourselves from the scourge of load shedding at home, is to install a properly designed domestic solar power system to our homes. This will definitely allow you to ride through even prolonged load shedding in most cases, provided you have enough battery storage, and also provided you do not experience an extended cloudy period.
So many people are assuming the same is true at a national grid level. Which is an understandable point of view.
Why should large scale solar power arrays, that we see being built in the Northern Cape, for example, not be a solution to load shedding? After all, we are told that we are short of about 6,000 MW (I suggest much more is needed to properly stabilise the grid), so why doesn’t the power generated from all those solar array installations offset that deficit on an accumulated basis? They should all add up, right?
The problem lies in one word – INTERMITTENT. The power available from a solar array is by its very nature intermittent. The biggest single problem are clouds (ignoring the fact that the sun doesn’t shine at night). The power generated by a solar panel is very significantly reduced by a cloud coming out above that panel. The power drops off down to about 40-10% of rated capacity, or even lower, depending on the thickness of the cloud. And a cloud can come out over a solar array at any time. So it’s a bit like relying on a car that, by design, surges to full power and then cuts out unexpectedly for some random length of time, and then surges back to full power, at random intervals. Just because that car has enough power at times, doesn’t mean it is suitable for the task at hand. You cannot run a country, in circumstances where supply needs to be very delicately balanced on a second-by-second basis with demand, using a power source like that. It simply will not solve the problem. In fact, you will be adding to the grid instability, not reducing it.
If one cannot rely on that power being available, from renewable sources, second-by-second at all times of the day and night, in all weather, then additional power has to be available from some other more reliable source, to step in and take over immediately. Which ends up meaning that what ever investment you made into a solar power array, that investment will need to be duplicated in some other form of generation, which can be relied upon to step in and take over, when the weather is bad. Which in turn ends up meaning you should have invested in that other more reliable source of power FIRST, to ensure you had sufficient power at all times (which is our current problem – we do not have sufficient power to meet supply, at all times).
Most of those large solar arrays are grid tied systems, which supply power directly onto the grid, so when the sun shines, that power is available for use, and when the sun does not shine, then no power is supplied.
But what about large scale batteries? In a domestic solar system, batteries absorb the intermittent power from the solar panels during the day and then provide a constant supply to our homes throughout the day. Surely they can do the same at a national level and save the day?
A good way to understand this problem, is use a large factory as a case study. There is a reason why large factories, many of which have large solar array’s on their roof, install internal combustion generators, and not a massive bank of batteries instead. And that is because as the scale of the demand increases, a generator becomes the only really practical choice, in comparison to a massive battery bank, certainly for most factory managers.
In most factories, the generator is installed to ensure that there WILL be power available, whenever required.
The solar array is installed for a different reason – to save daily energy costs, where some of the power that would normally have been supplied by the council, can be offset by that generated by the solar panels during the day. When the sun shines you save money. But it doesn’t matter from a power supply point of view, whether the sun shines or not, because the council supply makes up the difference.
The two systems (generator vs solar panels on the roof) serve completely different functions. Both systems perform those functions very well, which is why financially astute business men make those investments.
In a large factory, the generator is there to step in and take over the FULL load, when the power from the council goes off. It can can do that for as long as its fuel tanks are kept filled. And with careful maintenance, will last many decades. Generators do not take up a lot of space. Plus the capital and operating costs of a generator are manageable. Large battery banks lose on most of those comparison criteria. Which is why they are not seen as a practical solution. A few limited batteries may be included, to power UPS systems, to supply uninterrupted power for critical systems, but these only need to last for as long as it takes for the generator to start up, and those typically supply power to only a few small systems, such as critical computers and control systems etc.
The same is even more true, when you scale the power and energy requirements up to enormous national levels.
In your home, you accept those compromises when installing a solar system with battery storage, mostly because the noise of a generator can be very irritating. Plus, the amount of energy needed to run your home from a solar/battery system can be managed down to quite a small amount, which then makes supplying that energy from batteries viable. So you are prepared to pay extra for that luxury of silence. But many people have a generator as well, as a backup, for the exact same reasons described above.
The other question asked, was surely as more and more people install their own solar systems at home, or on their factory roofs etc, surely that reduces the demand deficit, and thus in that way load shedding becomes unnecessary, or at least far less of a problem? Which again is a reasonable question to ask.
The unfortunate problem lies (mostly) again in that problem of INTERMITTENCY.
Essentially this objection is based on the hope that the reduced demand from users who are now using renewable energy sources, instead of the Eskom grid, will reduce the deficit experienced by Eskom in terms of its ability to satisfy instantaneous demand.
And while the sun is shining that will be true.
But as soon as a cloud comes out (again ignoring the problem of the sun not shining at night), well then all those solar system users (unless they are relying on completely off-grid systems), will then automatically switch to requiring power from the Eskom grid, which then means the demand shoots up massively in a few seconds. Which in turn means load shedding becomes suddenly necessary again.
The point is that the intermittency of solar power still remains the core problem. As that waxes and wanes, some other source of power needs to be available to step in and take over, to prevent load shedding becoming necessary.
So yes, while the sun is shining, the additional power generated from many installed solar power systems in various places in the country, should help with the deficit between supply and demand, in theory. That is UNTIL a cloud comes out somewhere over any significant number of such solar systems. And then, if enough generation is lost, we are right back to where we started, in our current predicament. And obviously this will not help at night.
And this also ignores a completely different esoteric technical oddity – which is that grid-tied systems shut down when the grid power is lost, or the grid becomes unstable. They cannot produce power without a stable grid being present to synch with. The reason for that is another whole technical discussion on its own (as well as safety reasons). So your factory roof top solar system does not produce any power for you, or anyone else during load shedding, it shuts down.
Many people counter this argument by pointing out that it’s unlikely that there will be clouds over all the solar installations in the country at once, so the stop-start effect is mitigated by geographical distribution, which is true. But unfortunately, even neglecting the transmission grid limitations, (which alone are enough to make this suggestion impractical) the overall problem remains. The only way to prevent load shedding, is to keep the grid stable, where supply is very delicately balanced with demand, on a second by second basis. Unfortunately, what we are talking about here is an inherently unstable grid, no matter how you present the case. The idea that excess power which randomly is available at one point on the grid, can easily be sent to another part of the country, which has suddenly lost the power it needs, and where that whole situation randomly changes, as clouds move across the county, is just not a viable solution to the problem of nation wide load shedding. Certainly not in our very advanced state of the disease, in any event.
During the times when the sun is shining, and the nation’s demand exceeds supply, which lately it almost always does, then all that accumulated solar generation, installed across the country (but mostly in the Northern Cape) will of course help, but only to the extent that it reaches those without power (who may be far away), as long as solar power is available at the precise time that load shedding may have been necessary and does not fade away unexpectedly thereafter.
And all of that assumes that the transmission grid can randomly send any power generated in one part of the country, to another part of the country which had just lost their supply (which of course it cannot -there are very real limitations to the existing network cables).
Now my question in return, is even if the transmission grid limitations can be solved, thus allowing power to be sent from one part of the country where solar power is currently available, to another part which is about to experience load shedding, can one view that as a valid solution to load shedding?
To use the analogy of the car that surges and splutters randomly, by design, again. Would you be able to trust such a car in normal traffic, where it could suddenly stop in a dangerous situation (like right in front of an oncoming truck) and leave you without any power for an unknown length of time, and definitely throughout the night), before surging to power again? Could you run a steel smelter, for example on such a power source? If you were a factory manager, could you run a factory on such a system?
However, the random intermittency of renewable energy can be tolerated if there is sufficient non-renewable power available to step in and take up the load. What I mean is, when you have sufficient excess capacity of non intermittent reliable power sources available on the grid, then in that case, the grid does not risk going into an potentially unstable state, when a cloud comes out over a significant solar installation somewhere, due to the fact that there is sufficient non-renewable power available to easily step in and take up the load, available at strategic points in the grid, during that sudden loss of solar generation.
This is what is done in those countries which are presented as role models for renewable energy adoption. They already have a stable grid, with sufficient excess base and peak load capacity from reliable non intermittent sources. So they have the luxury of scaling back those base load or peak load generation systems, as the renewable sources come on line each day, but always have the spare capacity from their non-renewable sources to step in as required.
For this reason, most of those “more enlightened” countries struggle to get more than 30-35% of their power from renewable sources.
The arguments above are focused on solar power as the source of renewable energy, but apply almost equally to wind power.