Enlarge /. A new hydropower plant on the Ivory Coast.
There has been much discussion about how areas with explosive renewable energy growth can cope with the large amount of intermittent power sources. However, these mainly focus on regions with mature electricity grids and relatively static growth in demand. What would happen if you tried to grow renewable energy while trying to build a grid?
A team of researchers from the EU and the US have decided to find out what a good renewable energy policy could look like in West Africa, an area that is similar in size to the 48 neighboring US states but consists of 16 different countries. Some of these nations already source a significant portion of their renewable electricity from hydropower, but demand is expected to roughly double in the next decade. Although renewable energies such as sun and wind are likely to play a role only because of their price, the researchers' analysis suggests that an intelligent international network can balance water, wind and sun to create a much more environmentally friendly network.
Hydro as a giant battery
The new work has a mix of focal points. This is happening against the backdrop of the expectation that West Africa's electricity demand will explode in the next ten years. The region currently has nearly 400 million residents who use slightly more than 100 terawatt hours per year (compared to 4,000 TWh per hour in the United States). By 2030, this demand is expected to be more than 200 TWh – a fourfold increase over the demand in 2015.
Large hydropower plants in West Africa currently produce about 20 percent of the region's electricity. The rest is mainly supplied by a combination of natural gas and oil power plants. Other hydropower plants are in various planning and construction phases, and the first large solar plants have been opened there in recent years.
Beyond the increasing demand, however, researchers are interested in finding out how to make the best use of the renewable resources available in West Africa. To this end, they are analyzing how well existing and planned hydropower can serve as a battery-like resource for adding intermittent renewable electricity such as wind and sun. This requires balancing a combination of retaining sufficient water behind the dams to maintain their function and allowing sufficient flow from the dam to keep the river catchment area viable. However, within these limits, the dam can absorb and use a sufficient amount of water to compensate for any shortcomings in production from other renewable energies.
Time to model
To understand the potential here, the researchers created a computer model that contained data on the basic statistics of the individual dams (or planned dams): incoming flow and precipitation, evaporation of the reservoir, minimum required outgoing flow and the minimum amount of water The dam has to be updated every hour for one year based on previous data. They then used this to calculate an hourly measure of the dam's electricity generation limits – how much more could be expected when renewable energies run out?
Against this background, the researchers have adjusted this capacity to different potential wind and solar projects under different scenarios. This included a fundamental case where the use of renewable energy was simply expanded to match Hydro's capacity for security. one that takes into account the effects of climate change on rainfall; one in which wind and solar plants were strategically oversized to increase production in moderate conditions; and one in which different nations interconnected and managed their networks to maximize renewable production.
Good for now, not with growth
The good news is that, at least for the immediate future, climate change is not a problem for such a hydro-focused plan. There will be some changes in rainfall over the next ten years, but they will be minor and mainly due to the drier regions becoming drier. Since hydropower plants are not initially located in dry areas, this has only a very limited impact.
Another conclusion is that "over-provisioning" – building more renewable capacity than is technically necessary – can be very effective. This approach ensures that at times of maximum productivity, renewable production exceeds demand and needs to be limited. In the research model, however, overproduction of 25 to 30 percent avoided the use of hydropower that could be used at times when it was urgently needed. The net result is that this scenario increased total renewable energy consumption by 20 percent. In other words, even though part of the renewable energy generation was wasted, the total loss at the system level was quite small.
And in general, the system is effective. Even in the baseline scenario, the researchers estimate that in a good year it could cover almost half of the region's current electricity needs. Oversizing solar energy could increase this number by 20 percent. By adding cross-border network connections and management, production could be maximized to around 70 percent of the region's current needs.
The downside is that in just a decade, the number is expected to drop from 70 percent to about 32 percent. That is, the northern parts of West Africa border the Sahara and have the potential for a massive increase in solar productivity, and the authors have not considered the potential for pumped hydropower that can reverse the water flow at dams in order to generate storage potential for later. The combination of excess solar production and dams that act as giant batteries could significantly increase the productivity of renewable energies.
Sharing is taking care
In any case, the report makes it clear that it is not only rich industrialized countries that can benefit from the continuing fall in prices for renewable energies. Despite the additional cost of overproduction, the authors estimate that the system could be operated at a price that is about 10 percent cheaper than increasing the cost of natural gas.
However, one of the challenges will be to reconcile the needs and political expectations of 16 different countries. Those with access to good water resources are currently planning to meet their climate protection commitments. It will undoubtedly take a lot of work to get them to export part of this electricity to get renewable electricity that is generated by plants in another country that are yet to be built.
Nature Sustainability, 2020. DOI: 10.1038 / s41893-020-0539-0 (About DOIs).