There's been a lot of discussion about how areas that are seeing explosive renewable growth can manage the large amount of intermittent electricity sources. But these mostly focus on regions with mature electric grids and a relatively static growth in demand. What would happen if you tried to grow renewables at the same time you're trying to grow a grid?
A EU-US team of researchers decided to find out what a good renewable policy might look like in West Africa, an area similar in size to the 48 contiguous US states but comprised of 16 different countries. Some of these nations already get a sizable chunk of their power from renewables in the form of hydropower, but they are expected to see demand roughly double in the next decade. Although renewables like solar and wind are likely to play a role purely based on their price, the researchers' analysis suggests that a smart, international grid can balance hydro, wind, and solar to produce a far greener grid.
Hydro as a giant battery
The new work has a mix of focuses. It's run against the backdrop of the expectation that West Africa's demand for electricity will explode over the next decade. Right now, the region has nearly 400 million inhabitants who consume a bit over 100 terawatt-hours a year (compared to the United States' 4,000TW-hr). By 2030, that demand is expected to be more than 200TW-hr—a fourfold increase from where demand was in 2015.
At the moment, large hydro facilities in West Africa produce about 20 percent of the region's electricity. The remainder is mostly supplied by a combination of natural gas and oil-fired generating plants. Additional hydro plants are in various phases of planning and construction, and the first few large solar facilities have been opened there in recent years.
Beyond the rising demand, however, the researchers are interested in figuring out how to get the most out of the renewable resources available in West Africa. In order to do this, they analyze how well the existing and planned hydropower can serve as a battery-like resource for the addition of intermittent renewable power like wind and solar. This requires balancing a combination of retaining a sufficient amount of water behind the dams to keep them functioning, as well as allowing a sufficient flow from the dam to keep the river basin viable. Within those limits, however, the dam can hold a sufficient amount of water and use it to balance out any shortcomings in the production by other renewables.
Time to model
To understand the potential here, the researchers created a computer model that incorporated data on each dam's (or planned dam's) basic statistics: incoming flow and precipitation, reservoir evaporation, minimum required outgoing flow, and the minimum amount of water that must be retained by the dam, each updated on an hourly basis for an entire year using past data. They then used this to calculate an hourly measure of the limits on the dam's electricity generation—how much more could it be expected to generate if renewables came up short?
With that in hand, the researchers matched this capacity to various potential wind and solar projects under a range of scenarios. These included a baseline case of simply expanding renewable deployment to match hydro's capacity to back it up; one where the effects of climate change on precipitation were considered; one where wind and solar facilities were strategically oversized in order to boost production when conditions were mediocre; and one where the different nations linked and managed their grids in order to maximized renewable production.
Good for now, not with growth
The good news is that, at least for the immediate future, climate change doesn't pose problems for a hydro-focused plan like this. There are some rainfall changes over the next decade, but they're minor and are largely a case of the drier regions getting drier. Since hydro plants don't tend to be situated in dry areas to begin with, this has a very limited impact.
Another conclusion is that "overprovisioning"—building more renewable capacity than is technically needed—can be highly effective. This approach ensures that, at times of maximum productivity, renewable production will exceed demand and need to be limited. But, in the researchers model, a 25-30 percent overproduction avoided the use of hydropower that could be deployed at times when it was needed more urgently. The net result is that this scenario boosted the overall use of renewables by 20 percent. In other words, even though some amount of renewable generation was wasted, the overall system-level loss was pretty small.
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