Thursday, 27 August 2020

WHY LOAD SHEDDING IS BACK


Following the need for repairs on two generators at Hwange Thermal Power Station, Zesa has pushed its giant Kariba South Power Station to generate 892MW as of Tuesday, filling much of the gap between demand and supply, but load shedding will continue until the repairs on the two Hwange units, which can generate 320MW, are complete.

The extra Kariba South generation is not enough to avoid load shedding as only 1 156MW is being produced from all sources against peak demand of around 2 200MW.

Extra imports are impossible with regional demand exceeding supply.

The upsurge in generation at Kariba South has to be done in a way that allows Zesa to remain within the annual water ration Zesa was given by the Zambezi River Authority, but the large storage capacity at Lake Kariba means that Zesa can temporarily run Kariba South well above the average required output at peak times and then cut back below average later, in off peak periods. 

In a statement, Zesa Holdings said there was limited power on the national power grid owing to a technical fault at Hwange.

“The depressed power supply has also been compounded by the unavailability of normal import levels due to constraints in the region,” read a statement from Zesa.

To that end, people have been advised to use available electricity sparingly while effort to restore services to optimum levels were underway.

Production at Kariba has remained at near maximum levels with the trend expected to continue into the year following an upward review of water allocation for power generating by the Zambezi River Authority. 

Kariba South, going flat out, can now generate 1 050MW of power following the commissioning of two additional units in March 2018, after an upgrade from 750MW, but even in a good year the maximum cannot be 24/7, although the station can go high in peak times and then drop right back at say 1am when demand is very low to maintain the required average generation.

Zesa, with base load largely met from Hwange, has been varying output from Kariba South significantly, using a major strength of a hydro station when generators can be brought online in a few minutes and switched off just as quickly.

Thermal stations can require more than an hour to bring a boiler-turbine-generator unit onto the grid.

ZRA increased water allocation for power generation for Zimbabwe and Zambia by a further 4 billion cubic metres to 27 billion cubic metres from 23 billion cubic metres earlier in the year.

ZPC acting manager Mr Kenneth Maswera said while production has been increased, it was being matched to water allocated by the Zambezi River Authority which manages Lake Kariba.

“We have increased production but we are still within the parameters given to us by ZRA. What we are doing is levelling out the production curve which allows us to increase production during peak hours and similarly reduce during off peak period,” he said.

Ideally, Hwange should run continuously with Kariba which can be revived up in a short space of time coming in to cover the deficit when demand increases.

With the allocated water ZPC can produce more than 300MW on average this year, which can be increased or reduced depending on demand.

At an extreme level that means Zesa could run Kariba South flat out for eight hours a day and switch off for the other 16.

In fact it runs at high levels for shorter periods, when domestic and production demand coincide, runs around the average levels for some other hours and cuts back to say just one generator at times of very low demand. Herald

0 comments:

Post a comment