Africa’s great hydr
SOLAR-HYDRO HYBRID SCHEMES CAN HELP MEET AFRICA’S ENERGY NEEDS,WRITE
RIYAADH HASSIM & LOUIZA VAN VUUREN
THE evidence for climate change is clear worldwide. We see it in record heat levels, heavier rainstorms and severe droughts, increased tropical storms and hurricane intensity.
This reality has forced a new era of clean energy development.
Africa has great renewable energy potential and, since about 645 million people have no access to electricity, solutions to provide affordable, reliable and sustainable energy are crucial.
A lack of finance, project risks and unpredictable energy supply are barriers to developing renewable energy projects.
However, the integration of two or more renewable energy systems can overcome the limitations of individual systems. In particular, a hybrid system integrating photovoltaic (PV) and hydro-power deserve recognition.
To investigate this, we studied two African solar-hydro hybrid schemes in development to establish their viability from a technical, financial, environmental, developmental and energy-supply perspective.
A drawback of individual renewable energy systems is their intermittent nature. Fluctuations in cloud cover, for instance, result in plant capacity factors of 10-20% for solar plants.
The capacity factor is the plant’s average power generated, divided by rated peak power. To optimise output and improve returns, there are already examples of two or more independent renewable energy systems being integrated in places like Croatia, Canary Islands, Indonesia and China.
Existing systems in Europe prove Pv-hydro hybrids are technically and financially viable, even with capacity factors of 40% and 11% for hydropower and solar respectively.
Africa has an estimated capacity factor of 49% for hydro and 20% for solar, so there is great potential for solar-hydro hybrids.
PV systems are simple, easy to install, robust and low maintenance. The disadvantage is that they require an energy storage system or battery bank to provide stable energy supply on cloudy days and at night.
Batteries have a relatively short life span and add significant costs to the system. Including a hydro-power plant to the system allows for the reduction in the number of batteries or possible exclusion.
We studied two such Pv-hydro hybrids being planned in Africa. Due to the current status of the projects, details cannot be divulged. Project A is in western Africa and B in southern Africa.
Project A aims to develop a hybrid scheme from inception. B is a potential hydro-power scheme with environmental, developmental and economic limitations. B aims to develop a scheme to overcome these limitations while still realising a maximum power output with an integrated PV system.
There is a town (1) 20km southeast of the proposed site and another (2) 50km west. Average electricity consumption per capita in West Africa is 100kwh. Towns 1 and 2 have a combined population of 1 300, so the estimated generation capacity required is 1.3GWH.
According to growth estimates, energy generation of 2.4GWH will be required for the two towns in 10 years’ time. There are sub-stations at both towns and the extra energy generated could be sold into the electricity grid.
Preliminary verifications indicate that a 21MW hydro-power scheme could be developed and a 12MW PV plant, covering about 10ha, is viable.
Project B was initially earmarked as a potential hydro-power site with an installed capacity of about 40MW. However, due to inundation impact on upstream infrastructure, the dam height was restricted, resulting in a scheme with an installed capacity of 5.3MW.
To realise a higher output close to the initially intended capacity as well as economic viability of the project, a PV system was added. Topographic and irradiation data show the PV plant would average 12 hours of sunlight a day. Installed capacities of 6MW and 20MW were assessed.
The hydro-power plant is downstream of a cascade of dams that regulate flows, allowing for base flow conditions and thus base power output. Integration of a PV plant improves the system’s peak power output. The average annual energy output of a 5.3MW hydro-power plant is 46GWH. With the inclusion of a 6MW PV plant, the average annual energy is increased by 28% to 59GWH. With the inclusion of a 20MW PV plant, the average annual energy increases by 91% to 88GWH.
Traditionally, the PV and hydropower components of the hybrid system were developed either simultaneously, or the PV component was added to a hydro-power plant.
The construction and commissioning time frames for the PV component are short, compared to the hydro-power facility.
If, as in the case of project A, the PV and 21MW hydro components were built simultaneously, the hydropower plant would take three years to build. During this time, the PV plant and the sub-stations and transmission lines would also be installed.
This would be followed by two months of testing and commissioning of the hybrid scheme. With this development option, the project would only begin earning revenue after 38 months.
Commissioning the PV component of the hybrid system first means the PV component can generate revenue while the hydropower plant is built.
With this option, the PV component will be generating energy and earning revenue for over two years before the hydro-power component is operational.
Such small hydro developments with an integrated PV component