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| Photovoltaics: incoming light from the sun converts to electricity |
What is the quickest way to add a gigawatt of capacity to the South African grid?
Small-scale solar power on homes, institutions and business.
I am talking here about making electricity from the sun, not heating water. That is another whole issue.
Photovoltaic panels or PV for short produce electricity as long as the sun is shining, Modern PV systems even produce some electricity in cloudy weather.
A single panel is generally about 300W – so how do we multiply that to 1GW – a million watts? That would take about 3.3-million solar panels. This is how we can get there:
- 1 million single panels on RDP houses – in total 300MW
- 4 panels on half a million homes (totalling for each 1.2kW) – in total 600MW
- 50 panels on 5000 businesses (totalling for each 15kW) – in total 45MW
- 100 panels on 2000 public institutions (totalling for each 30kW) – in total 60MW
Where would you get those work crews? See my article Eskom – Restructure or Destructure?
This solar power will not all be available at once. None of it will be available at night and output reduces radically under cloud. If it is widely spread out of the country, a substantial fraction will be available most of the time – cloud cover shifts around the country.
And this is just a start – once this first phase is installed, there is no reason not to gradually spread it out to all RDP houses and all homes, businesses and institutions that can afford it.
How can it be paid for?
The poor should receive it free on RDP houses, with some of the cost recovered from power generated. Just as an RDP house has to be occupied for 8 years before ownership transfers, there can be a transfer phase when the solar power unit is generating electricity partially to recover its own cost and to cover the cost of the free allowance of electricity for the poor. Eventually it should be fully paid off.
For private premises, the payback time is relatively short – about 6 years. The ability to feed excess power into the grid makes this a great investment. And that is where reform is needed. Municipalities are reluctant to encourage solar power because it cuts into their profit on selling electricity. The remedy is simple: a grid-connect fee calculated to be equivalent to the amount the municipality would have earned as their share off the electricity cost had they sold Eskom power. If done right this can be revenue-neutral for municipalities while reducing their dependence on Eskom.
Without the ability to feed into the grid, solar power is only useful for cases where much of your power usage is in daylight hours or if you use batteries to store power for use at night. Batteries are expensive and limit the usefulness of solar to backup systems or to those who have to live off grid.
Employing solar PV seems like a practical solution to reducing the demand on the Eskom grid, but in reality things become a bit more difficult. The first hurdle is determining the rules and regulations around installing solar PV. These vary depending on whether you buy your electricity directly from Eskom or pay your local municipality. The City of Cape Town supplies my electricity and they have loads of rules that must be followed before the installation of solar PV. You cannot buy any inverter - you must ensure you buy one that is on their approved list. You also need to have the installation signed off by a professional engineer which costs thousands of Rands. You also need to make a decision whether you want to export surplus electricity to the grid or want to use all the energy generated yourself. Even if you want to export surplus energy to the grid, the CoCT has a rule that says you must be a net user of electricity - ie during the year nobody is allowed to export more electricity to the grid than they buy from them! They also charge users around R2 per unit electricity and only pay around R0.50 for surplus electricity.
ReplyDeleteThe biggest problem with solar PV using standard grid tied inverters is that the inverter automatically shuts off if the grid electricity goes down. This means the solar PV panels cannot produce electricity during load shedding! This is a safety measure to prevent solar PV systems feeding electricity back to the grid when the grid has been taken down for maintenance.
If people want solar PV to continue working during load shedding they need to fit a hybrid inverter. The hybrid inverter is more expensive and is used in conjunction with a battery bank. The big advantage of going down the hybrid inverter/battery bank route is having a back-up source of electricity during load shedding. The disadvantage is increased cost which will push the payback period to around a decade. Traditional lead acid batteries are cheapest to initially purchase but they have several disadvantages:
1) Lead acid batteries should only discharged to 50% depth of discharge (DoD) for maximum life
2) The batteries are heavy, bulky and some of the battery technologies release hydrogen gas when charging so are better to be in a garage or well ventilated outside enclosure
3) The charging/discharge cycle is only around 75% efficient
4) The battery bank will need to be replaced after around 3 years
The lithium ion batteries cost much more initially (roughly 2.5x the price of decent VRLA lead acid batteries. They do offer several advantages over lead acid:
1) They can be discharged to 80% or 90% DoD
2) They are smaller and lighter than lead acid. They don't emit hydrogen gas when in use
3) The charging/discharging cycle is around 90% efficient
4) They have a design life of around 10 years
So if break-even payback time of a hybrid PV system is approaching 10 years, you'll have recouped your initial costs by the time the lithium batteries are starting to become less efficient and be down to around 80% of original capacity. Also cheap inverters may need to be replaced every 5 years and even decent inverters may have had required a repair during 10 years of use.
I think that if possible the ideal would maybe be a modular solution. 0.5kw solar panels with 1-5kwh battery storage built into the panels and each with a hybrid microinverter. Then all you need is a central connection box for all of the modules you wish to install to connect to and switch function between grid connected and grid outage mode.
DeleteIdeal because modular and scaleable with less points of failure that can bring the whole system down. Plug and play. Even allows mobile applications like for camping, remote work sites, etc.
My own system is a hybrid that is not grid-tied because that is not allowed here. It charges enough battery to take me through a load-shed if I avoid running very much. It helps that I have LED lighting and my computers have very low standby power. I haven’t had it a full month yet to assess the effect on my electricity bill; if usage over the last 9 days is an indication vs. April last year, usage has dropped about 40%. However one month isn’t really indicative as there are circuits not covered like hot water and that one is highly variable (we have a water crisis now so I use a lot less; if the month is sunnier than average, the electric backup for solar heating is less needed).
DeleteRegulatory issues people run into e.g. in Cape Town are unnecessary hurdles. I lived in Brisbane (Australia) for a while and it was pretty straightforward to get a system installed.
There are people claiming to sell modular systems, though I haven’t seen a detailed spec of one yet.
DeleteWhile I like your concept in general terms, there are three significant factors that have to be taken into account for mass deployment of grid-tied solar PV:-
ReplyDelete1 Peak Eskom demand is around 06h00 in the morning, and 18h00 in the evening. Solar PV generates zero power during those periods. Instead, it is capable of supplying significant power during about 10h00 to 16h00. During this time, power demand is significantly lower, so excess PV power can even mean throttling back existing baseload stations, with a loss of efficiency and hence an increase in overall costs.
2 Something often forgotten by zealous advocates of "renewable" power is the requirement for maintaining system stability. The simplistic version of this is considering the frequency of supply. The large rotational inertia of many turbines and generators makes the network as a whole relatively immune to sudden changes in load - they all slow down a bit, until the control systems bring them back up to speed with a sudden increase in load, and ditto for a reduction in load. No such inertia exists in electronic systems such as PV-driven invertors. Yes, systems do exist to mimic this behaviour, but they add hugely to the cost.
3 Grid-tied PV invertors, by definition, cease operating when there is no mains power. Thus, a simple grid-tied invertor is useless when one is afflicted with load-shedding. A much more expensive hybrid system, usually involving very expensive batteries, is required to solve that problem.
On the other hand, the point that solar PV distributed over the whole country is less sensitive to localised cloudy weather is well made.
Adding more storage to the network would help. Batteries are still expensive but gradually getting less expensive. On of the problems Eskom has run into is pumped storage cannot be topped up if non-peak load is too high; solar could help with that (capacity is nearly 3GW). Another thing: the Cahora Bassa hydro plant could be relatively rapid dispatch and is very cheap. With more solar online during the day time, there would be less need to use hydro out of peak time.
DeleteIn the longer term, finding creative ways of adding storage such as Vehicle to Grid V2G is the way to go (one of the better arguments for electric cars). The more batteries there are on the grid for whatever reason, the easier this gets. A hybrid system under current regulation feeds nothing to the grid from batteries. If e.g. 10% of homes had hybrid systems as cover against power outage and they were switched into backup mode – or even feeding into the grid – during peak time (avoiding draining the batteries far enough to prematurely age them), that could help with dealing with peak demand.
We need a lot more work on creative approaches to managing variability of supply by managing demand.