Home » Industry » Zesa Electricity Exports Progressive [editorial]

MANY consumers will be startled to hear that Zesa exports electricity, but oddly enough, at least until the extensions to Kariba South are finished or our industries move towards full use of capacity, it is not a bad idea and will cut costs to Zimbabwean consumers without depriving them of electricity.At the moment Zimbabwe has a very large gap between peak demand and minimum demand. This means that we are very short of power during much of the working day and especially in the early morning and early evening when domestic, industrial and commercial sectors are all functioning and the domestic demand, in particular, reaches its peak.

The problem facing Zesa is that energy cannot be stored, or at least cannot be stored at the moment. This changes when the 300MW extension to Kariba South comes on-stream. This will add to Zesa’s capacity to generate more power at peak periods, but will not add to the total energy Kariba South can generate. We already use all the water the Zambezi River Authority allocates to Kariba South. So when the extension is in place Zesa will be able to run the 1050MW power station full-blast at peak periods but will have to cut back below the present 750MW in the slack periods, such as the middle of the night, to balance the water consumption.

This will force Zesa to stop treating Kariba South as a base-load station, which has always been odd, and allow it to do what hydro stations are supposed to be used for, coping almost instantly with fluctuations in demand.

But at the moment, since Kariba power is so cheap to generate, it makes sense to run the station flat-out 24 hours a day so long as there is someone, somewhere, who wants to buy that power with Zesa’s mark-up.

Hwange Thermal, the other main Zesa station, has a quite different economic profile. It takes quite a long time to fire up a boiler until steam is produced, then start spinning the turbines and then align the output to the grid. While a Kariba turbine can be supplying the grid within a couple of minutes of a “switch-on” order, well over an hour is needed before a Hwange turbine can do the same, and to fire up all six of the present Hwange turbines and bring them onto the grid can take most of a day. You cannot just switch a coal thermal station on and off.

Coal stations run most efficiently, economcially and with the least maintenance when they run continuously. This is why most countries with both coal thermal and hydro use the thermal for the base load, that is what is required throughout every 24 hours, and use the hydro to cope with the huge fluctuations during the day. Unfortunately, Zimbabwe’s base load is very low at the moment and the fact that Hwange power is several times the price of Kariba power has tempted Zesa to run the system the wrong way round, which is bad engineering and bad economics.

So if Namibia and DRC can use night power, when Zimbabwean demand is so low, that gets the base load up and it makes a lot of sense to export. When the extra 600MW of Hwange Extension are commissioned, and this extension no doubt will fix the cooling problems that stop the present station going flat out, then Zimbabwe will have a peak capacity of 2 470MW, although quite a lot of the time this will be 120MW to 300MW less depending on which of the 16 generators is under routine maintenance.

But Zesa will only be able to generate a maximum of less than 2 000MW off-peak due to the need to manage Kariba water. That might still allow Zesa some night exports. It will all depend on how Zimbabwe industry continues to recover.

Our verdict is that Zesa should export at night so long as Zimbabwean consumers do not go without but that long-term contracts should take into account a likely boost in the Zimbabwean economy and a return to night shifts in factories.

Source : The Herald