Proposed 1,200 MW Floating Solar PV Plant In Zimbabwe Could Increase Generation By 44%

China Energy Engineering Group has proposed to construct a 1,200 MW DC Floating Solar PV (FPV) plant on Lake Kariba to help alleviate Zimbabwe’s unprecedented electricity crisis.

Zimbabweans are currently experiencing some of the worst electricity rationing in the country’s history, going up to 18 hours without electricity everyday as the utility company struggles to generate enough electricity due to several reasons. The country’s largest generation station, the 1,050 MW Kariba hydropower plant, has had to throttle generation due to low water levels resulting from lower than normal rainfall over the past few years. Late last year, ZPC, the generating company that operates the hydropower plant on the Zimbabwe side of the shared resource, had to throttle generation to a maximum of around 300 MW.

Zimbabwe also has aging coal power plants in Hwange that break down quite often, leaving a large deficit, hence the utility company has to implement load-shedding. There is of course the Southern African Power Pool (SAPP), where Zimbabwe gets some imports from its neighbors, but South Africa, which is part of the SAPP, is also experiencing generation shortfalls and hence the crisis in the region is more widespread. Zimbabwe also doesn’t have enough foreign currency at times to pay for more electricity imports from some of its neighbors.

Zimbabwe now has an installed capacity of about 2,500 MW, if we include the new 300 MW Hwange Unit 7 coal power plant that was recently synchronized to the grid. Another, Unit 8, will add an additional 300 MW, bringing the installed capacity to about 2,800 MW, however all the old coal units at Hwange (920 MW) are underperforming and are prone to breakdowns. There are plans to take them out of service once the new Unit 8 comes online, in order to refurbish them. Coupled with the periodic low water levels at Kariba, Zimbabwe will be facing an electricity generation deficit for quite a while.

The country’s power utility recently said it has received applications for new connections from the mining sector and other heavy energy consumers that are close to 3,000 MW. This means that the current peak demand which ranges from 1,700 MW to 2,200 MW, depending on the season, will soon be close to 4,700 MW to 5,200 MW, therefore Zimbabwe needs as much new generation capacity as soon as possible. This is one of the main drivers for the proposed 1,000 MW floating solar plant at Kariba.

Here is an overview of Kariba Dam:

Kariba Dam is shared between Zambia and Zimbabwe and was constructed between 1955 and 1959. The dam extends for about 280 km. It holds about 185km³ of water. On the Zimbabwe side, (Kariba South), the hydropower plant now has an installed generation capacity of 1,050 MW. The dam is a major tourist attraction for the country, second only to Victoria Falls. Lake Kariba is also now home to the world’s most productive reservoir fishery, and therefore a source of employment for the artisanal fishing industry. Any floating solar PV plant would need to take this into consideration in order to ensure their business continuity. Other environmental considerations for FPV that have been discussed in a paper by Rafael M. Almeida et al., include shading from floating panels resulting in reduced light disturbing photosynthetic organisms such as aquatic plants and phytoplankton However, this shading could also help reduce the proliferation of harmful algae in reservoirs.

Kariba dam was primarily built for power generation and there are several significant opportunities to optimize power generation from the installation of FPV, bringing wide ranging economic benefits as listed in a paper by Javier Farfan et al.  These include:

• Providing cooling effect for solar panels increasing their efficiency
• Panels will provide shading, reducing evaporation from the reservoir and also reducing algae growth, improving water quality. Reducing evaporation also provides the potential to produce additional power from the water saved.
• Reduced soiling in water environment compared to dusty land based areas
• Less shading on PV panels as they will be placed away from trees, buildings and other objects that are usually a source of significant shading.
• Co-location of FPV plants with already existing hydropower plants provides significant cost reductions through maximising existing grid connectivity infrastructure such as transformers and transmission lines.
• The reservoir will now act as a virtual battery, unlocking more value from the colocated floating variable renewable solar energy. During the day, the power generated from the floating solar plant be could be used directly whilst the water in the reservoir will be allowed to accumulate from inflows and/or saved for later use during the evenings and at times of  lower PV production due to cloud cover etc.

The proposed 1,00 MW (AC) (1,200 MW DC), FPV for Kariba dam will use 1,832,069 PV panels covering 25km². These will be 655Wp mono crystalline bifacial dual glass modules. This will be for a 25-year period. The initial estimated annual production is 2,640 GWh. The total project price is estimated to be around $987 million. China Energy Engineering Group Co. Ltd (China Energy) says it has done several projects in China including 250 MW, 200 MW, 100 MW, 150 MW, and  130 MW floating PV plants from 2017 to December 2022.

Several studies have shown that some reservoirs in Africa, including Lake Kariba, present some of the best opportunities for floating PV plants. A study covering 146 hydropower reservoirs in Africa by Rocio Gonzalez Sanchez et al, indicates that with just 1% coverage, the installed capacity of existing hydropower plants could be doubled, producing an additional 46.04 TWh per year. They add that water savings could be up to 743 million m³/year.

The study also looks at optimizing existing grid infrastructure through the Equal Installed Capacity (EQIC) scenario where the FPV is sized to match the existing installed  hydro capacity. In this way, the FPV can feed the maximum possible electricity into the existing grid infrastructure. Rocio Gonzalez Sanchez et al, also looked into a case study for Zimbabwe. The data is looking into the period before the recent addition of 300 MW at Kariba to bring the installed capacity to 1,050 MW and thus uses an EQIC scenario of about 680 MW. This still gives us some very interesting insights into the power of FPV. For a scenario covering just 8.42 km² , which is 0.45% of the area they considered as the “total reservoir’s area” (1,862.3 km² ), they found that there will be an additional generation from the FPV of 1,595.2 GWh of electricity which works out to be 34% of the 4,686.3 GWh from the hydropower plant during that period. How cool is that!

The proposed 1,200 MW (DC)/ 1,200 (AC) floating solar plant for Kariba will  cover 25km² (about 1.34%) of the total reservoir’s area using the figures considered by Rocio Gonzalez Sanchez et al., providing  an estimated annual production of 2,640 GWh. In 2021, Kariba generated 6,067 GWh on the Zimbabwe side, according to the Zimbabwe Energy Regulator’s (ZERA) annual report. The annual production from the proposed FPV would work out to be 44% of that, excluding any extra generated from reduced evaporation.