The progress already seen in the negotiations with Skypower Global of the United Arab Emirates to invest in 500 megawatt solar stations in Zimbabwe promises to keep the accelerated growth we are now seeing in our economy to continue after the Hwange Extension comes on line over the next few months.

Solar has always been an obvious green energy option for Zimbabwe, considering that we are in the tropics and receive a lot of sunlight almost every day.

As with hydropower, solar has low operational costs, basically just maintenance, but high capital costs to build a station and hence the welcome news that an experienced investor in large solar stations is keen to come into Zimbabwe with the funds.

The first set of negotiations are almost complete, the framework agreement between the Government and Skypower. This is basically the sort of agreement between any investor and the Government, and with the present investment drive these are becoming routine.

We already have the necessary legislation allowing for private investment into power stations, what are called the independent power producers, so licensing Skypower is just ticking the boxes.

There are obviously special conditions needed for each sort of investment, but there is unlikely to be any delay before the Skypower framework deal is signed.

Then comes the far more detailed agreement, the one between Skypower and Zesa. There are several aspects here.

First Skypower needs to be assured it has a customer for its stations, that Zesa will buy what it generates. This requires some rather good estimating of future demand.

Zesa does not want a gap in what is available and what it needs, but neither does it want to close units on one of its own power stations to buy more expensive private power.

Fortunately Skypower are interested in phased development of the power stations it is likely to build. Solar has the advantage that once the basic infrastructure of a station is in place, the security, staff housing, cleaning systems and the huge substation and its transformers needed for the connection to the national grid, adding more banks of solar panels and more transformers can be done quickly. So estimates probably only have to cover a year or even less.

The second part of the Zesa deal will have to involve the pricing, how much will Zesa pay for Skypower power. By now there are internationally accepted formulas for settling prices.

These have to cope with the costs of the actual investment, an agreed and reasonable return on that investment, and the fairly low operational costs.

The big items in the investment are likely to the banks of solar panels, the transformer banks to connect to the grid, and the equipment needed to maximise output by allowing the panel alignments to be shifted.

When you consider that the sun appears to move across the sky between dawn and dusk every day, it is obvious that output can be maximised by reorientating the panel banks. Then there is the seasonal movement.

In midwinter, the sun in Zimbabwe is around 60 degrees above the northern horizon at noon, but in mid-summer it is around 92 degrees above the southern horizon.

Obviously these pricing calculations will need to be checked, so both sides are convinced they are talking the same language, but that is not a major delay.

A third factor will be storage of energy. Solar works directly when the sun is shining. If energy generated during the sunny periods is needed at other times it has to be stored, and here some detailed work will be needed to agree on how much should be stored and how it should be stored.

Very large battery banks are very pricey. But Zesa does have some storage options using Lake Kariba and its oversized Kariba South Power Station. The river flows are never likely to allow Kariba South to be run flat out 24/7 at its maximum output of 1 050MW.

That output, and the very few minutes it takes to bring a hydro unit onto the grid, was designed to give Zesa flexibility, running Kariba South flat out at peak periods, but cutting back sharply at other times. The lake is the largest storage dam in the world.

So, especially as the first banks of solar cells come on grid, Zesa can cut back output a bit at Kariba South in bright sunlight, store the water and then crank up the hydro station during the dark hours since there will be enough water. There are obvious limits to this, but it is a start.

Other storage options include finding a suitable mountain, having a modest reservoir at the top and another at the bottom and a pump and generator station near the lower reservoir.

The pump motors and the generators are the same equipment; they just spin in different directions when use switches. This set-up allows water to be pumped up to the top in bright sunlight and then allowed to come down in the dark. Several of these exist round the world, the closest is the Drakensberg in South Africa.

Zesa, and Zimbabwe generally, would also have to look at when solar power is used most as the output grows. As more solar units come on line, irrigation can be a daylight option, and industrialists can align their shifts to the sun.

As electric cars become more common we need to ensure that charging points exist in parking garages and the like so the cars can be “fuelled” while the motorist is working or shopping, in daylight. All this sort of activity can help reduce storage requirements and so costs.

As the Cabinet noted as it gave the go-ahead for pushing forward with the negotiations with Skypower, solar complements the thermal and hydro capacity in Zimbabwe. It cannot replace it but can add to it.

We still need the big thermal stations to handle our base load since these do operate 24/7 and are not dependent on how much rain falls, or does not fall, in river catchments.

We still need hydro, but more and more for its almost instant flexibility, its capacity to meet peak demand rather than base load, and its high level of reliability.

And we need solar to complement these two and also to ensure our economic development accelerates but also fits in with our commitments to move to net zero carbon emissions.

A limited number of thermal units can be covered by planting forests, but we need the clean energy as well.

As multiple sources come on stream the pressure will grow for Zesa to have exceptionally good operational management, to ensure that the right mix of generation options are available every hour of every day.

This becomes ever more complex as more stations and more types of generation come onto the grid, and Zesa needs to be ready itself to have the required management skills and equipment to cope.

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