Solar, gas needed quickly in energy mix

01 Feb, 2019 - 00:02 0 Views

eBusiness Weekly

Zimbabweans are now waking up to the opportunities of alternative energy sources and are not just waiting for the Government to do something; they are going to do it themselves and the result will be a far more robust economy.

Solar is an obvious energy source in a tropical country like Zimbabwe where the sun shines strongly most days of the year. The cost of solar cells is continually falling, so the capital cost grows less each year. The one problem with solar is that it can be intermittent; the sun does not shine at night and cloudy days can see sharp reductions in output, even in day time.

There are two solutions. One is to live with the intermittent supply and the other is store the energy. Zimbabwe can do both, depending on what is needed.

Sable Chemicals, for example, is now planning a solar installation. This company can cope with intermittent supply but, to be viable, needs a lot of very cheap electricity. Sable was set up when Kariba South had surplus capacity. Zesa and its predecessors could either allow surplus water to go through the floodgates or flow it through turbines that were not needed for general use and sell the resulting extra power cheaply to Sable. Better to get some money than just waste the capacity and extra water.

Sable used their cheap energy to produce nitrogen by liquefying air and hydrogen by electrolysis from water. The gases were then used to make ammonia, the first stage in the production of ammonium nitrate. Neither process had to be continuous. But the electricity had to be cheap. Both hydro-power and solar-power are cheap, once the capital costs are sorted out, because both use free fuel, water in a river and he sun shining in the sky. There was the useful waste product at Sable, oxygen from both processes, but that is why Sable was set up in Kwekwe, so the oxygen could be sent in a pipeline to Zisco. And when the steelworks is rebuilt then oxygen will again have a market.

Others could also use intermittent solar. Irrigation farming is an obvious sector. When the sun shines the pumps are on and when night falls they go off.

Farmers might want electricity 24/7 but again they managed quite well in the past on cheap surplus Kariba power, usually sent out at night when no one else wanted much, because the prime requirement was cheap power, not continuous power. And when it is very cloudy in the daytime it is probably going to rain, so clouds do not devastate solar irrigation farmers.

Since a lot of irrigation is done by blocks of farmers sharing a dam or other water source, sharing an associated solar station should not be a problem and, in any case, solar stations come in modest units. You can have a 50kW station just as easily as a 50MW station.

But big investors into potential solar stations and Zesa can come to other arrangements. With Kariba South upgraded to 1050MW there is no way the flows in the Zambezi River can give Zesa enough water to run all turbines 24/7. What the extensions to the station mean is that Zesa can run all eight turbine-generator sets at peak hours and then cut right back to say just two in the early hours of the morning.

But if there is solar power available Zesa can take what is on offer and cut back a bit at Kariba South while the sun shines, storing the unused water in the dam, and then open up more turbines in the early hours. Lake Kariba in this scenario becomes a giant storage battery in effect.

The other new source of power is gas. IT is now almost certain that there is natural gas at Muzarabani, although almost a kilometre underground. But flows are probably good enough to run a decent power station .

But there is also coal-bed methane at Lupane that has never been exploited for reasons that are difficult to understand. Now potential investors are showing interest there. The coal-bed methane is closer to the surface, in fact almost at the surface, and can be tapped quicker.

Natural gas power stations are not renewable energy, but their carbon footprint is a lot smaller than an equivalent-sized coal station. And they can be switched on and off fast and can be commissioned quickly from off-the-shelf technology.

Basically a gas power unit is a jet engine, the same as the one under the wing of a large airliner, connected to a generator and transformer. The civil engineering is little more than a shed to keep off the rain. It is not unusual to have such a station running a year after the contract is signed.

Zimbabwe has been talking about solar and gas power for decades. We now need to move from the talk to the action.

Neither technology will answer all needs nor provide all the answers for all users. But they can answer many needs and have the potential to satisfy requirements of many users.

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