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- Last Updated: Thursday, 08 November 2018 23:56
Integrating Batteries in Renewable Energy Systems, the Dilemma
This note briefly discusses some aspects related to the genuine role of electric batteries in renewable energy (RE) systems as compared to the one sought by industry and facile business. It tackles some of the misconceptions of RE technologies and their impacts on the role of constitutive elements of RE systems, e.g., the storage concept and storage medium (here the battery). The misconceptions seem to drift the technology development from the correct path, towards technologies that are rather more suited to short term profitable business. The reasons of the drift are outside the scope of this discussion. But in general, one can say that the origin is mostly the conservative view of many technologists whom remain attached to the old technologies of large power plants, energy transport, and energy distribution. These, in my opinion, are leading RE to an uncertain path, and as such, could be fatal for the future of these nascent technologies.
Regardless of my own creed about the approach for the energy technology orientations and the optimal design of renewable energy systems, let’s look at battery issues when used as a regulator device in power grids and in energy systems that endure much fluctuations at the sources. I plan to discuss in a series of short papers various cases, where batteries are the moderator device. Readers are invited to participate in his endeavor.
In a daring paper titled "Battery technology will define the future of renewable energy" the author, a CEO of a battery company and advisor to industry in the field, has gone too far in concluding that without batteries renewable energy technologies will not succeed, altogether. But for energy infrastructure, electric batteries are only used to support renewable energy sources, thus must not be considered as a “deep intermittent energy source”, and we must not think that we are obligated to store harvested energy. As such, batteries will not directly solve the energy production issue, the main problem for the success of renewable energy technologies. Therefore, batteries will not boost the alternative energy technologies; their effect will remain indirect and secondary. To give batteries a larger role than a regulator, would be wrong, as it is going to be a dangerous technology pathway that could mislead researchers, investors, and policy makers. Batteries will only support renewable energy systems for smoothing the energy delivery. They must be sized to exactly compensate for the fluctuations induced, for instance, by variations of sunlight or wind input energies and fluctuations of the consumption. Therefore, battery size must be kept to a minimum. Optimization of battery size will prevent exogenous problems due to batteries themselves, and will leave the tiny bits of harvested energy to be used by the electric loads. Statistics and machine learning can help finding proper size and battery configuration, on the case by case basis.
Electric batteries seem to be easy solution at the design level as well as for system installation and operation. However, if the economics and the materials sustainability are still problematic for batteries, compensation of energy fluctuations can still be done using either small diesel or gas turbine powered electric generators. The diesel is suitable for a micro- and small grids, while gas turbine would be for larger grids.
Going back to the basics; I strongly believe, that renewable energy technologies, except Wind, CSP and Wave energy sources, cannot be designed to work in the old fashion, referring here to the old power generation technologies and energy distribution systems. This is basically due to the fact that RE are diluted by nature. It would be waste to centralize it, recondition it (increase voltage), transport it, dilute it, then distribute to the consumer. Therefore, making large power plants that require transport of the energy is fundamentally wrong. Only, for the above listed cases are exception to this “rule”, one can still design small power plants for which only transport (over a short distance, the shortest possible) to the local consumer is conceivable. The rational for the wind is as follows. Because more wind energy is harvested if the mill sweeps a large volume of air and if the mill is tall, large mills are more efficient. Recall that the wind speed is higher at high altitude than on the ground. Also on large scale production, wind technology is more manageable if a wind farm is set-up. Wind farms are suitable for powering small cities or suburbs. Studies showed that for wind energy production centralization is conceivable and economic. Also by design CSP has to be centralized, but the plant must not be necessarily very large. In the contrary, photovoltaics (PV), solar windows, solar skins, biomass systems, water solar heaters, solar ovens, solar dryers,… should be designed to produce the energy where it is exactly needed. That way the energy production is directly connected to the consumption, which results in more saving and an increased overall efficiency. In that scheme, battery will have a little- to no-role in the energy system. Excepting some applications, for PV, there is no need for concentrating the harvesting operation, which otherwise induces enormous losses before the energy reaches the application. Imagine PV used in each home (rooftop PV modules or PV tiles), only small batteries will be eventually needed, which cancels related complexities and results in further energy saving.
In an article that appeared in this website, I argued that batteries have limited purpose in energy systems, and cannot be employed to power energy-centered applications, such as powering heavy duty vehicles, or cities,… As an intermittent source of energy, batteries will neither work for large scale transportation nor in large residential grids. One must not forget that batteries main purpose in RE systems remains a regulator device, and should not be regarded as a massive intermittent energy source.
A. Karoui