How solar energy could replace coal in SA - TechCentral

How solar energy could replace coal in SA

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South Africa should consider concentrated solar power (CSP) with storage for base load energy since it has the capacity to replace Eskom’s ageing coal-fired power stations.

This is the message of Nandu Bhula, CEO of the Bokpoort CSP plant near Groblershoop in the Northern Cape. Bhula believes the performance of this plant proves his argument.

Bokpoort, with a nameplate electricity generation capacity of 50MW, has the capacity to store enough energy for 9,3 hours of electricity generation at the level of 50MW, once the sun sets.

If it reduces the output to 30MW as the electricity demand drops after the evening peak, it can run 24 hours per day.

This was illustrated when Bokpoort ran nonstop for 14 consecutive days, ended 31 March, at an average load factor of 66%. (Load factor measures efficiency and is the ratio of actual electricity output divided by maximum potential output.)

The assumption in South Africa’s Integrated Resource Plan (IRP) is that the typical load factor for a CSP plant with nine hours of storage capacity would be 43%, but Bhula believes it should be at least 60%.

According to Eskom spokesman Khulu Phasiwe, the load factor of Eskom’s coal-fired power station is between 78% and 90% and for the Koeberg nuclear power plant it is 90%. In its previous annual report, Eskom said the average load factor for all renewables connected to the grid was almost 31%. That includes various technologies.

Bhula says it is essential to have the IRP reviewed if South Africa wants to utilise CSP to its full potential.

In the IRP it is further assumed that the lead time to completion of a CSP plant with nine hours of storage is four years. The Bokpoort experience shows that an average load factor of 60% and lead time of three years is realistic, Bhula says.

The R5bn Bokpoort plant that started commercial operations on 19 March, consists of eight solar fields with 241 920 mirrors with a combined reflective surface of 658 000sq m. The mirrors follow the sun like sunflowers and concentrate the solar energy on tubes filled with oil.

The oil is heated to 400 deg C and transported to heat exchangers where it is either used to generate steam for generating electricity for direct output or to bank the heat in a huge salt tank to be used later when the sun is no longer available, to generate electricity.

It takes about 30 minutes to switch from direct output to generation from stored energy, Bhula says.

Based on the outdated IRP assumptions, CSP is regarded as a peaking technology and tariffs are set accordingly. That means that CSP tariffs provide for a base tariff during the day, that is multiplied by 2,7 times during peak and a zero tariff from 10pm to 6am, Bhula says. The tariff therefore incentivises the reduction, rather than the increase of storage capacity, he says.

The effect of the tariff signal is clear from the fact that Bokpoort in the second round of the department of energy’s renewable energy procurement programme was designed with 9,5 hours of storage, Redstone in round three with 12 hours storage and CSP1 in round for with a reduced 7,5 hours of storage, Bhula says.

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“Why would you provide it (storage capacity) if it cannot earn you money?” he asks.

Bhula says Eskom will have to start decommissioning its older power stations by 2020. If South Africa changes its approach to CSP and expands the CSP allocation, CSP with proper storage could replace these decommissioned stations, he says.

He says as a technology, CSP plants are probably less prone to sudden load losses than coal-fired plants. The only reason for load losses is the weather and that could in most cases be fairly well predicted from the viewpoint of the system operator.

The country has some of the best solar resources in the world and more than enough space to build enough CSP plants. A big CSP drive could provide the necessary economies of scale to develop a proper local supply chain and the location of the plants in rural South Africa could go a long way to reverse the deterioration of rural economies, Bhula says.

In the tiny town of Groblershoop with a population of about 9 000 for example, Bokpoort has created 1 300 jobs at the peak of construction and 62 permanent jobs during operations. This makes a huge difference in the small rural economy.

The huge high temperature fluid overflow and expansion vessels for the plant were built in Johannesburg and the metal components for the two salt tanks, both 14m high with a diameter of 40m, were constructed and assembled on site by a firm from nearby Upington.

Bokpoort further supplied 305 homes in Groblershoop with solar energy for running their lights, television and radio to the value of R1,2m and installed a water reticulation plant and connected 77 houses in nearby Topline village with running water for the first time.

Bhula said the tariffs agreed upon for CSP has dropped from about R3/kWh from the first bid round to R1,20/kWh in the fourth round, which makes it competitive with Eskom’s new coal power stations. He believes CSP tariffs could drop further if an expanded programme could provide further economies of scale.

Bokpoort is a ring-fenced company with the Saudi power developer ACWA Power (40%) as controlling shareholder. The other stakeholders are Lereko Metier through different vehicles (25%), the Public Investment Corp (25%) and a community and BEE trust with a combined 5%.

  • This article was originally published on Moneyweb and is used here with permission

6 Comments

  1. Dr KG Kennedy on

    Thank you for this ‘wake up call’. While undoubtedly more of a track record is needed for the annual assessment – including winter months to be taken into account – the concept that brings into question SA’s need to be mining for so much coal and to be burning same is a good one – as it also brings to the forefront the question and rationale for it’s need for more nuclear. Surely those in most small to mid-sized communities in South Africa can become more aware and supportive of the tremendous advances that we are seeing. Our ‘SA solar beneficiation potential [SASBP]’ applies not only to the massive CSP-type installations in the Northern and Northwestern Provinces, but also to local community-based and micro-grid suburb-type installations and local infrastructure services. Both can support municipalities who can get their local infrastructure processes in order and realize that they can be innovative to provide their own income from solar resources we have here in southern Africa.

  2. As it seems so common in articles about CSP, the picture on top looks to me to be of PV solar panels.
    CSP is a very interesting technology, especially combined with heat storage.But it always appeared more expensive than PV solar, and the CSP + heat storage will be difficult to compete with nuclear for base load power.
    There would not be a need to pay power generators so much extra for power during peak hours, when there would be a far more concerted effort to reduce the demand for power during these hours with introducing differential rates for consumers with time linked electricity meters, and clamping down on illegal power consumption and connections.
    It seems very unlikely, users of illegal connections will ever bother about reducing their consumption during peak hours. The 17-21h peak has every thing with domestic use. In this small rural town 85% of the households are not paying for electricity or any rates or taxes, acc to the local unit manager.

  3. Ben Franklin on

    The picture above is of the Seville CSP plant https://en.wikipedia.org/wiki/PS20_solar_power_plant — where nearly flat (slightly curved) mirrors (heliostats) reflect the sun onto a high temperature receiver atop the tower shown.

    Time-of-use tariffs (and eliminating illegal connections) would indeed go a long way to improve SA’s electricity net.

  4. TC corrected he photo.Time of use tariffs is indeed the correct expression for it.
    There is just not enough political will and courage to tackle illegal connections and non payment of legal connections on a grand scale it seems.

  5. Andrew Newman on

    “Bhula said the tariffs agreed upon for CSP has dropped from about R3/kWh
    from the first bid round to R1,20/kWh in the fourth round”

    Both of the Department of Energy reports give much higher rates for the forth round Bid Window CSP. (also referred to as Bid Window 3.5)
    R1-70 /kWh base rate and R4-58 /kWh peak rate.
    An average rate of R2-77 /kWh (2015 price)

    Bokpoort is a Bid Window 2 project (BW 2)

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