eBusiness Weekly
With the scientific evidence for worse global warming than previously predicted, it is obvious that everyone needs to accelerate their plans for a net-zero carbon economy, and that includes Zimbabwe, small as the country is and with very low emissions.
The main problem for Zimbabwe is the need for reliable energy with development particularly dependent on reliable electricity, and by reliable we mean not just 24/7 but 24/7 for the full 52 weeks of the year. And at the moment this means coal has to take the lead, and that we need to build more coal stations.
Renewables are important but only two, hydro and solar, can make any impact on Zimbabwe.
Hydro is already centre stage with Kariba South at 1050MW, although we cannot generate that amount consistently since there is not enough river flow in the Zambezi.
We are lucky to get an average output of around a third of that, but the extra capacity does give both the flexibility to handle peak surges and with the giant volume of Lake Kariba to allow us to use other hydro schemes and solar power a lot more efficiently.
Hydro potential in Zimbabwe, excluding some tiny potential schemes on other dams, is limited to the Zambezi, the only major river flowing throughout the year. Any big hydro stations we build have to be on that river. And the problem with the Zambezi, as we are aware, is that a serious drought in eastern Angola means the flow is reduced, sharply.
Batoka Dam and its two power stations is the planned next hydro scheme. It will be extremely useful but will not solve all our problems.
Storage is limited so when the river is in flood we can use the power stations flat out, but come low water we get a lot less power. Because Lake Kariba has the volume for a lot more storage and because Kariba South and Kariba North are both oversized, Zesa and Zesco can operate the two dams as a pair.
When the river is in flood the two authorities can run their Batoka stations flat out, and cut back sharply at the their Kariba stations allowing the lake to fill. As water flows ease off the Kariba stations can be progressively opened to generate more using that stored water and can run far closer to flat out as a result.
So Batoka South does not add 1 00MW to the average generation capacity, although it can add that to peak output, but will more likely be adding half, and even that assumes that the drought in Angola is not crippling. So once again we need coal for the base load, since a coal station can operate 24/7 regardless of the rainfall, whether the sun is shining or any other external factor.
Solar is an obvious renewable for Zimbabwe, and a lot of businesses and homeowners have installed the panels and batteries and owners of the larger installation have taken advantage of Zesa’s new smart metering to sell power when the sun is blazing and buy power when the sun goes down.
As more solar is installed, and it does not matter whether we have 1000 businesses with surplus or a single giant solar station, Zesa can use Lake Kariba to store the surplus power when the sun is shining. This is possible when we consider the big lake and the oversized Kariba South station.
With a lot of solar on the grid the output from Kariba South can be cut right back in the middle of the day, and the water stored and as the sun goes down then Kariba South can be ramped back up, in effect using most of the day’s water ration in just 10 to 12 hours, so being able to run more generators at any one time.
The other three renewables of wind, tide and biofuels are never going to amount to much in Zimbabwe. We are not on the coast so forget tide. Winds only blow hard enough during brief gales or when a cyclone hits, and it is hard enough to find enough irrigation for food, let alone adding in the raw material for biofuels.
Other options to reduce carbon emissions but not eliminate them do exist. Methane and natural gas stations emit just over half the amount of carbon dioxide as a coal station.
Already, investment is now coming through to start tapping the coal-bed methane in the Lupane and Hwange areas. And the main use of that methane will be a gas power station.
Test drilling in Muzarabani is due to start soon.
The probability of exploitable natural gas is higher than the probability of petroleum, and considering that most major car makers are looking at switching over to electric vehicles within the next decade natural gas would be more useful.
While any petroleum deposit will take several years to bring on line, and then build the refinery to get useful products, gas can be exploited a lot faster. And processing is largely just cleaning the gas so a useful product can be obtained without an expensive refinery. So the Muzarabani power station can be feeding the grid long before we are even pumping petroleum, let alone refining it.
Gas stations are fairly simple in engineering terms, largely being a jet engine in a shed, an over simplification but one that gives the idea.
From start to finish a gas station can be built in well under a year using off the shelf technology that most suppliers can make quickly. And the stations are a lot cheaper than coal ones.
If the methane and natural gas deposits are in the order we all hope, we thus can use gas stations more and cut back on the number of coal stations we have to build, but unfortunately we cannot eliminate coal or even stop building coal stations. We just build fewer.
The arrival of the electric cars will increase demand for electricity obviously, and for electricity without load shedding.
But we win in a sharp reduction in carbon emissions, even if we use coal stations. Internal combustion engines are not efficient.
Electric motors are and modern power stations are.
So we burn a lot less carbon, even using coal, to get the same number of kilometres travelled by cars and trucks when we use electric motors.
So some of our efforts must be in locking up the carbon our coal and future gas stations will emit.
Already, a great deal of research is being done in how to scrub carbon dioxide out of the flue and exhaust gases from these stations. The theory is there but viable engineering is still to be developed.
Obviously as these technologies become available they must be made available to developing countries, and some of the promised aid money being sought for climate purposes can be used to make them affordable or even free.
But we already have one low tech way of locking up carbon, with the main technology being a spade. We can plant trees, millions of trees. Generating a kilowatt hour, a single unit on a meter, in a coal station sees just over 1kg of carbon dioxide emitted, or about 300g of carbon once we exclude the oxygen that a tree converting the carbon into wood will emit. But even that needs a lot of trees.
This would be in addition to the trees we need to plant to convert firewood into a renewable resource, and that includes the firewood we use to cure tobacco. Fortunately the final wood does not have to be stored in a tree. It can be stored as timber in the form of roof trusses, panelling, furniture and the like. So we can use the extra timber we grow.
Tree growing is also needed, in any case, to modify climate change by shading more of our land and providing the mulches and the like that our farmers need for the more drought-resistant conservation farming. And while we plant the technology to scrub carbon from power station flue gases will be progressing.
So why we need coal stations, and if we find gas then gas stations, we need to push our renewable energy sources as hard as we can and we need to make major national efforts to keep our net carbon footprint as near zero as possible.
If we get it right, we can do this.
