In a recent blog I queried whether it was wise to award a contract to Karpowership to supply 1220MW of gas turbine power at 3 sites around South Africa. This objection was based purely on the costs that seemed to have been accepted by Eskom which I believe is overpriced by 50%. Setting that objection aside, I am fully in favour of a land-based turbine solution.
Main picture: Five of Ankerlig’s 148MW open cycle gas turbines
When evaluating the various options for power generation, I believe that the priorities in order of descending importance are:
- Noxious pollution
- Carbon footprint
All the objections that I have heard of thus far have focussed on the last and, in my mind, the lowest priority. That does not mean that I don’t consider CO2 to be a problem. Far from it. I actually propagate for the limitation thereof. However, SA is not in an economic position to be precious about this. That is why cost is at the top of my list.
In terms of CO2 emissions, we might be 17th largest emitter (with international shipping at 8th and aviation at 13th) but we are a pimple on the arse of the world – no more than an irritant. We were only responsible for 1.26% of the CO2 in 2017. If you dig further and consider our per capita emissions, then we were only 26th on a per capita basis at 8.2 tons per year. Some notable countries ahead of us are Qatar (37.1t), Australia (16.5t), USA (15.7t), Japan, (10.4t), Norway (10t) and Germany (9.7t).
Given our negligible contribution to the problem combined with our precarious economic position and that we are a developing nation, we need not unduly worry about this. Nevertheless, while gas turbines are not as green as renewable power sources, they emit 1.74 times less than coal for the same thermal output. Since their thermal efficiencies of turbines and coal power stations are similar at around 35%, this also means that they emit 1.74 times less for the same electrical output. This is a bonus.
Our coal power stations emit prodigious amounts of noxious gases which pose immediate health risks to the whole of Mpumalanga. Gas turbines only produce a small amount of nitrous oxides which are easily dealt with.
Immediacy has a high priority as the country is in a crisis that is seriously hampering our economic growth. Apart from loss of business confidence and production cycle interruption, businesses have to provide backup generation capacity which is capital that predominately lies idle. We have seen the long lead times of coal power, particularly in the hands of Eskom and nuclear is even longer. SA demonstrated that it could build 2000MW gas turbine plant in 18 months when we constructed the Ankerlig and Gourikwa power stations starting in 2006. The fast lead times are because the turbines are modular power packs that are manufactured in their 100’s each year (900 worldwide in 2015). Locally you must mainly provide the foundations, switchgear and transmission transformers, transmission lines to the grid and a gas storage tank with piping to a harbour or an offshore gas terminal point. This is still a lot of work but it is all easy stuff.
Above all, it must be affordable. Eskom has ruined its balance sheet over the last 10 years to the point that they can’t undertake even the smallest capital project. All their resources are devoted to repair and maintenance. This totally rules out the nuclear option and any serious coal power stations. Although the capital cost of renewables sound seductive sometimes, once you realise that the output quoted is the nameplate (peak) capacity which is more than 3 times higher than the actual average capacity, the capital cost can exceed that of a coal power station. Obviously they win back with the zero fuel costs to come out slightly cheaper overall. Gas is the cheapest option from a capital point of view, although the fuel costs of up to 3x the cost of coal makes the two options roughly equal.
However, what I like most about gas turbines is their extreme flexibility. They can operate as a base load and as a peaking plant because of its quick start up time (less than 10 minutes to synchronise to the grid). It has a further advantage which can make a huge impact when used in conjunction with renewables. Its low capital cost means that we are not too concerned if we are not sweating the asset. This enables it to act as a battery for when the renewables are not producing. Whether we like it or not, the sun is only effective for around 10 hours out of 24 due to the atmospheric absorption at low angles. Then there is the variability. Even without inclemency, the solar radiation daily insolation is nearly 40% lower during winter when we need it most. Batteries can only deal with diurnal variations, but not seasonal. Gas turbines can do both and are probably cheaper from a capital cost point of view.
For the carbon-phobes, the case for the gas turbine can be sweetened by reducing the carbon dioxide emissions per kWh by 70% without increasing the fuel usage by converting it to a combined cycle gas turbine. The gas turbine runs at a thermal efficiency (conversion of thermal energy to mechanical output) of 35%, same as a typical coal power station. But it leaves a lot on the table as the exhaust temperature is around 600°C which is ideal for running a steam turbine for free. In practice, they do a small amount of reheat to push the temperature up slightly, but the overall thermal efficiency is pushed up to 60 to 65%. The combined cycle turbine emits 3 x less CO2 than a coal power station for the same output.