Eng. Matshela Koko
On November 3, 2019, the Zimbabwe Electricity Supply Authority (Zesa) increased power cuts to a punitive Stage 2 of load-shedding, where consumers spent up to 18 hours without electricity because it had lost 251MW from Hwange Power Station.
On November 12, 2019, the eastern part of the country lost electricity for almost three hours from 1am when a regional inter connector carrying 280 megawatts (MW) tripped and stopped generation at Kariba South Power Station.
At the time of the incident two Kariba units were connected to the national grid and were generating about 240MW.
The technical fault affected the eastern parts of the country, and included Harare, Mashonaland, Masvingo and Midlands.
The power crisis in Zimbabwe is a long-term problem and the country is looking at distributed photo voltaic (PV) generation to minimize the amount of unserved energy.
The Government of Zimbabwe has set a target to get at least 2 000MW of power from solar PV generation by 2030.
This is more than the amount of electricity the country produces today from a range of sources and it is over 20 percent of the projected capacity of 10 000MW in 2030.
The Zimbabwe Energy Regulatory Authority (Zera) has already processed 39 utility-scale solar PV projects, which have capacity to generate up to 1 150MW by 2024.
With behind-the-meter distributed generation (renewable energy generation facility) considered, solar generation technologies would easily contribute over 30 percent of the projected generation capacity in 2024.
This scenario will lead to a compromised transmission and distribution network and more blackouts unless mitigated.
If Zera continues to license new solar PV projects in an unmitigated manner, then the systems operator will have no choice but to rely on Kariba Power Station and increased imports for grid stability to prevent blackouts.
However, Kariba South Power Station is currently generating around 100 to 300MW against an installed capacity of 1 050MW due to low dam water levels.
Kariba Dam is a victim of drought conditions over the last three years.
The drought conditions are expected to become more prevalent as the world continues to be affected by the impact of climate change.
The immediate alternative to Kariba is thermal power generation from coal, but Hwange Power Station is old and its performance is unpredictable.
At best it can only generate 500MW of the 920MW installed capacity.
The major expansion of Hwange Thermal Power Station will see an additional 600MW on project completion in 2021, but this will not resolve the grid instability issues introduced by deeper solar PV penetration of up to 30 percent.
If the licensed solar PV projects deliver more than 1 500 W as planned and Hwange Power Station also delivers an additional 600MW in 2021 also as planned, Zimbabwe will need more electricity imports to stabilise the power system and to prevent the grid from collapsing.
The increased imports of electricity will require significant capital investment in the transmission infrastructure to facilitate energy transfers, as well as to improve wheeling through the Zimbabwean network.
Currently, wheeling operations from north to south on the Zimbabwean network are limited to 400MW because of the limited capacity of the transmission network.
Zesa will have to increase its tradable energy from 400MW to at least 1 000MW and address some constraints on its network, but it cannot afford this.
Zesa does not have the required financial resources to do this.
Zimbabwe could learn from case studies from South Africa, South Australia and Northern Ireland that transmission network is one of the greatest roadblocks to continued development of renewable energy projects.
Given these case studies, Zimbabwe can manage the transition to renewable energy technologies much better than many other countries, but it will need good planning, good networks, energy storage and better matching of energy demand to when the energy is generated.
As distributed PV generation becomes a bigger portion of energy generation in Zimbabwe, utility-scale solar power projects will need to provide firm, flexible energy commitments even when the sun goes down, as well as critical grid services like frequency regulation and spinning reserves to stabilize the grid.
Matshela Energy is one of the companies licensed to build a solar PV power plant, which is expected to produce 100MW of electricity, in a bid to ease electricity supply crisis in Zimbabwe.
The company has evaluated the main reasons for adding energy storage to its 100 MW solar PV project, and the main reason to add energy storage is frequency control to enhance grid stability.
A major consideration for Zesa in terms of reliability and efficiency of the power system is the required operating reserves in the presence of high solar PV penetrations.
Adding a lot of distributed PV to the system increases the requirement for operating reserves.
These reserves are normally required to step in within 10 minutes when the system’s frequency drops rapidly due to major system disturbances such as breakdowns at Hwange and Kariba and when regional interconnectors trip.
When the system’s frequency drops, distributed PV generation will trip offline due to the prevailing anti-islanding schemes on inverters.
This exacerbates the drop in frequency, so Zesa is obliged to take necessary measures by increasing the available operating reserves to avoid the collapse of the power system.
Energy storage installed with PV systems increases the available operating reserves on the system without decreasing the efficiency of conventional generators.
Distributed energy storage can also be used towards this purpose, provided that a minimum discharge level is set so that some energy is always available for reserves.
Decision-makers and network planners in Zimbabwe should realize the urgent need to build up the operating reserves to support the rapid expansion of distributed PV generation.
These reserves must be accessed within 10 minutes when there is a disruption to power supply.
Energy storage in Zimbabwe should be implemented urgently to provide spinning reserves required to secure the power grid from collapsing in the event of major system disturbances.
We must fight energy poverty in the region by building a sustainable and resilient power system in Zimbabwe.
After all, Zimbabwe lies at the epicenter of the SAPP (Southern African Power Pool) transmission grid.
Therefore, the power system in Zimbabwe must be modernized and expanded in a sustainable manner to support energy trading in the region.
Engineer Koko is former acting chief executive of South Africa’s power utility Eskom. He is also the managing director of Matshela Energy, which is implementing a US$250 million solar power plant project in Gwanda.
Source:The Sunday Mail