Caution needed on renewable energy


Generating electricity from renewable energy rather than fossil fuels offers significant public health benefits.

Charles Frizzel

IT is apparent that Zimbabwe, like South Africa, is suffering from a crisis in the supply of electricity, due to a total lack of forward planning and investment over at least the past 20 years.
There has been quite a lot of speculation in the media and I feel that there is a danger that decisions that are neither rational and economically nor technically sound could be made.
Decision-makers who are not engineers are in danger of being hoodwinked by unscrupulous people pushing their own interests at the expense of national interests.
Let me explain the various sources of energy and their advantages and disadvantages.
The first thing to understand is the nature of the load; i.e. what consumes the electricity. This of course varies throughout the day with peaks and troughs in demand.
With domestic consumption, there is usually an early peak as people use electricity to cook breakfast. This then falls off rapidly during the day and then rises again in the evening for both cooking and lighting.
Late at night, the domestic consumption drops to almost nothing.
For office and light industry, the load rises at around 7:30am and remains fairly steady until around 5:00pm.
With heavy industry, mining, electro-refining and so forth, the demand is usually fairly constant throughout day and night.
It should be remembered that disruptions in electricity supply for industrial use wreaks havoc to production.
Agriculture can also use large amounts of electricity, particularly for irrigation. This is usually done during daylight hours, but of course the demand is very seasonal.
Now we need to consider the various sources of energy. What is particularly important, other than cost, is availability and response time.
Some sources have very slow response; needing a considerable time to come up to full output and also needing time in order to reduce output safely.
Nuclear reactors are usually considered slow response systems. These systems are ideal for supplying the base load as they are generally less costly than others.
Coal and gas-fired power stations that rely on steam to drive the turbines have an intermediate response time and, at present, form the backbone of power generation worldwide.
Hydro-electric power generation has an extremely fast response which can go from virtually nothing to full output in a number of seconds as more water is allowed to flow through the turbines.
A disadvantage is that adverse climatic conditions can limit the amount of water available and also over time even a large dam like Kariba will silt-up and thus the amount of stored water is reduced.
Another disadvantage of hydro power is that the dams and power stations are costly and take a long time to build.
Gas turbines are widely used where a source of natural gas is available. They have a fast response time and are economic, especially if situated near to a source of natural gas. They do, however, require more maintenance than a hydro power station.
A lot has been said in recent years about so-called “renewables” and “green energy”.
There are a number of different systems around, but all suffer from a fundamental problem, and that is that at present there is no economically viable method of storing significant amounts of electrical energy from these sources.
Research is going on in this field but at present I cannot think of any viable system. That is one reason that there has been a rapid reduction in support and subsidies in the First World. These systems sound good, but are just not practical or economic.
Wind power is not feasible in Zimbabwe because thankfully we have very little wind. In places like the United Kingdom, subsidised wind turbines are often spinning but not actually generating any power for consumption.
Even in Europe the amount of wind energy is very variable and cannot be relied upon. It is there when the wind blows, which is not necessarily when you need it.
A lot has been said about solar power. Unfortunately, this is even less attractive than wind energy. The power available is directly proportional to the amount of sunlight falling on the panels and will rapidly drop to a low level should a cloud pass over the array.
Of course no power is generated except when full sunlight is falling on the panels, and the power that is generated cannot be easily controlled as with conventional systems.
At least wind turbines can generate power at night!
Until mass storage of electrical power is available and economically feasible, both wind and solar can only be described as “vanity projects” and certainly not suitable for Zimbabwe.
The most promising future storage system would seem to be the flow battery, but as yet this is not a commercial reality.
For decades, water has been pumped up to a high dam when power is available and then allowed to run down when power is needed. This is called pumped storage. It works, but is not very efficient. It also requires two dams near to each other, one at a high altitude and another much lower down. The turbines act as generators when the water flows down and then as pumps to pump the water up again.
In coastal countries, attention is now being paid to generating electrical power from tidal sources. This also varies in a cyclical manner, but those cycles are reliable and well understood.
Geo-thermal power is also reliable but only viable where the hot rock is not too far below the surface and adequate water is available to turn into steam. Attempts have been made to use wave energy in maritime nations, but again they have not so far proved to be viable.
In Zimbabwe, we only have two sensible choices; either conventional coal fired power stations or to use the vast resources of natural methane gas in the Lupane area.
Both of these have mature technologies readily available from a large number of sources in Europe, Scandinavia and China.
Natural gas has the advantage of being quite a lot cleaner than powdered coal used at Hwange. It should be possible to have coal or gas-fired generation up and running relatively quickly because these are available “off the shelf”.
Past experience in Zimbabwe tells us that we should avoid the United States or Canadian suppliers because their electrical and mechanical standards are very different from ours.
Their use of 60 Hertz (Hz) and not 50Hz has caused many problems because their standard production items are just not suitable for use in Zimbabwe.
As well as the 50Hz and 60Hz problem both these countries use Imperial (inch) size nuts and bolts and measurements which are actually illegal in Zimbabwe.
The lure of “renewables” and “green energy” must be avoided at all costs because they are just not suitable for us.
We should let the rich countries play with these at least until such time as an economic system for the storage of large amounts of electric energy is developed.
We should stick to known, tried and trusted technology that can be obtained at a reasonable cost.