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Place of renewables in national power grid



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Power engineers are justly concerned about the problems of integrating renewable resources into the power networks designed to operate with conventional generating plants.

Ironically, in this country, the problems of the large-scale integration of renewables to our ageing or a modernised national electricity grid has not attracted the attention it readily deserves, mainly because it is unlikely to be faced in the next 10 to 15 years.

But what are the likely challenges of a future Smart National grid with such a massive integration of renewables?

My fellow power engineers will agree with me that power systems are designed to cope with substantial variability of demand. If a variable source is added in small amounts, there will be negligible consequences since its variability will be swamped by that of the demand.

A number of studies have shown that supplying up to 20 per cent of the demand from renewable sources will require no modification in the way the systems are run at present.

For the larger penetrations, however, the energy from the renewable sources will become increasingly less valuable unless appropriate policies are implemented to enable the co-ordination of the output from a variety of renewables.

The penalties to be paid if the penetration from say, wind and tidal (if in future this is exploited on the Kenya coastline) will be substantial due to the following reasons:

Cycling losses due to the increased start-ups and shut-down of thermal plants; Reserve costs arising from the need to ensure that the system can respond adequately to unpredicted changes; and discarded energy when the available variable input exceeds the amount which can be safely be absorbed while maintaining adequate reserve and dynamic control of the system.

Variable power sources – solar, wind, and tidal are all characterised by high costs and very low operating costs.

Therefore, it is quite possible to make them base plants par excellence, that is, that their output could be easily accepted whenever it is available.

It is notable that solar and wind are actually intermittent resources, which means that they require some additional resources for their own stabilisation and reliability.

In the power system of the future containing supposedly all the three types of plants, with the gradual phasing out of the capacity-limited ones, the policy, in my view, should to be to fully maximise the use of renewables with the energy-limited plants supporting variable power sources and capacity-limited plants used as little as possible.

The hydrogen generated from the renewables can thus be used to power the remaining capacity –limited plants and also provide portable fuel for transport and industrial use in future.

Mr Chesoli, a practising electrical engineer and an Energy and Regulatory Board-registered graduate engineer, is also a lead energy auditor. [email protected]