Is this the first concrete solution for renewable energy storage?
We look at the difficulties of storing renewable energy: essential if the uptake of low-carbon alternatives is to gather pace.
1 October 2018
For most of its existence, storage of energy has been the biggest limitation of renewables. The problem with the two most prominent sources of renewable energy (wind and solar) is simple: energy output from sunlight and wind does not overlap with demand for energy consumption. As a result, without storage, those renewable sources cannot supply more than 20% of power demand. Figure 1 illustrates the discrepancy between photovoltaic, or solar, energy production and consumption for the average household. Most solar energy is produced between the two peaks of home demand. Most wind energy is generated during night, when demand is lowest and energy prices, at times, are even negative. The incentives for efficient energy storage are plenty.
Today, several types of energy storage exist and provide varying advantages and disadvantages. In general, technologies can be split into electrochemical, mechanical, chemical, and thermal energy systems. Examples include:
- Lithium-Ion and Sodium Sulfur batteries (electrochemical) - mainly used in electric vehicles (EVs) and home electronics (Li-Ion), and bulk storage and space shuttles (Sodium-Sulfur), respectively.
- Pumped hydroelectric and compressed air storage (mechanical) – using gravitational force and compression to store large amounts of energy.
- Hydrogen and methane storage (chemical) – stored underground or as liquid in high-pressure refrigerated tanks for future use.
- Heat and thermo-chemical storage (thermal) – such as solar thermo-chemical energy storage (TCES), during which thermal energy is used to drive a reversible endothermic chemical reaction, storing the energy as chemical potential.
Figure 1. Solar energy production versus energy demand
Source: Solar Choice, December 2017
The quality of each type of storage varies. Pumped hydroelectric (Figure 2.) has become the dominant solution for bulk storage, due to its large-scale applicability and high energy efficiency of more than 80%; accounting for almost 100% of bulk storage globally.
Figure 2. Share of global renewable energy capacity by technology
Source: Quartz, June 2018
In times of excess energy production, the energy is used to pump water from a low-level reservoir into a high-level reservoir. Once demand increases, the water is released to the low-level reservoir, driving turbines that generate energy. However, this solution is not always viable. Regions of water scarcity cannot afford to use water to store energy and geography does not always allow building the large dam constructions needed to create the required economies of scale. Consequently, pumped hydro storage has been restricted to mostly 10 countries so far.
Figure 3. Product price per KwH
Source: Chemistry World, July 2017
An alternative solution is currently under development by a Swiss startup. Instead of using water, the startup used concrete and cranes. Excess energy powers a crane to stack concrete blocks on top of each other, increasing the potential energy level. Once energy demand increase, the crane unloads the blocks, using gravity to transform potential into kinetic energy, which in turn drives a generator producing electricity. With a roughly 85% conversion rate (li-ion batteries have 90%) and the advantage that concrete is a lot denser than water – hence storing more energy per unit of volume – this concept might turn into a viable solution for large scale energy storage in areas where pumped hydro storage doesn’t work. Additionally, other forms of energy storage are gaining traction, particularly distributed home-scale storage and even EVs that are being used as home batteries. With cost of storage continually declining across most technoligies, decentralised storage is expected to become economically ever more attractive.
Overall, the sole solution might not lie in stacking blocks of concrete alone, but energy storage on both large-scale bulk storage as well as smaller battery levels will be fundamental to successful mainstream application of renewable energy.
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