As we explained in our previous article, high temperatures challenge the lifespan of batteries and pose potential safety issues. This article will be focused on proposing possible solutions to mitigate these issues.

Roughly speaking, there are two main solutions: the first one is cooling the system down and the second one is using a chemistry that is resistant to high temperatures.

Cooling the system down

For cooling the system down below the ambient temperature, it is necessary to use specific cooling solutions (such as air conditioning or liquid cooling) for lowering the battery temperature. Such a cooling solution will always keep the battery bank at our desired temperature (which will be typically between 25 and 30 degrees).

Fans and passive cooling are also cooling options; however, they are not able to bring the battery temperature below the ambient temperature level (as they only extract the heat generated internally by the batteries). This is important as many manufacturer warranties require the battery to be operated within a certain temperature range; if the battery is placed in a site with a very high ambient temperature, a fan might not be enough to fulfill this operating requirement. The main advantage is its low energy consumption.

However, such a system consumes much energy. To have an idea of the amount of energy consumed, let us assume that a containerized lead-acid battery, which has a usable capacity of 1 MWh, is fully charged and discharged (up to its usable capacity) once a day. For making these calculations, we will assume that this battery is installed both in Dar es Salaam (Tanzania, with tropical climate) and Riyadh (Saudi Arabia, with desert climate).

By using a fan, the energy consumption in both locations would be approximately 0.5 kW, which equals ~12 kWh/day – or 1% of the usable energy capacity.

By using active cooling, the energy consumption in these locations are shown below:

• In Dar es Salaam, Tanzania (tropical climate)

As it can be seen on [Fig. 1], in this tropical location, the seasonal difference in cooling power required between is small, whereas the day/night difference is relatively large. It is expected that every day, around 6 – 7% of the battery capacity will be used to keep the system cooled.

• In Riyadh, Saudi Arabia (desert climate)

As it can be seen in [Fig. 2], in this desert location, both the seasonal differences and the day/night differences in cooling power required are very large. It is expected that in summer, around 12% of the battery capacity will be used to keep the system cooled, whereas in winter, this figure would drop to 5%, approximately.

However, it should be reminded that using a cooling system presents additional issues other than its high energy consumption. First of all, it increases the upfront CAPEX of the project. Secondly, it creates an additional possible failure point for the system as it is a critical requirement. Last but not least, it needs to be properly maintained, which can be an issue in remote locations where adequately trained personnel may not be available or where it may be costly to have such people travel to.

Using specific chemistries for high temperatures

Another solution is to use specific chemistries that are suited for high temperatures, so the need for using an active cooling system is eliminated or reduced. For example:

• If the temperatures are not extremely high (so they do not exceed 30 degrees often), the LFP (lithium-iron-phosphate) Li-ion chemistry can be a suitable candidate, as it offers a high lifespan, good thermal stability, and the ability to provide both energy and power functionality. Furthermore, the CAPEX of this kind of battery is reasonable.
• If the temperature is expected to often exceed 30 degrees, and high discharge is a requirement of the project, advanced NiMH (nickel metal-hydride) batteries, able to withstand very high temperatures, may be a good alternative. Even though the CAPEX might be higher than for LFP, they are more temperature stable, and their lifespan is much less sensitive to high temperatures.
• Na-S batteries are resistant to high temperatures, have a long lifespan, and are very good at providing energy services; however, they are not good at providing power services. Usually, these batteries have a very big size (>200 kWh). Therefore, this type of battery are suitable for large projects if power services are not a priority, as its CAPEX is not very high. However, it should be kept in mind that the operating costs associated to this kind of battery are relatively high. Even though in general they are considered safe, there have been some issues due to the violent reaction that is produced when sodium and sulphur get in contact.
• Zn-Air batteries are resistant to high temperatures, very safe and have a low CAPEX. Like sodium-sulphur batteries, they are also good at providing energy services but not adequate for power services. However, it should also be mentioned that currently Zn-Air is a young and not very well tested technology, and present some important issues (e.g. very low round-trip efficiency and important uncertainties in their lifespan). However, this market is evolving fast and it is worthwhile to keep an eye on how this technology evolves during the next few years.
• Flow batteries are resistant to high temperatures and offer extremely long lifespans. In the same line as Na-S and Zn-Air, they are very good at providing energy services but not adequate for providing power services. However, their CAPEX is still very high, and like Zn-Air, they have not been tested enough yet, so even though they might be an interesting technology in the future, we do not believe that the microgrid market is ready for this kind of storage technology yet.
• There is a specific zinc-based chemistry, zinc-bromine, that usually is presented in the form of a flow battery, however, certain flowless models are commercial as well. The latter ones are showing good potential, with high levels of safety, relatively low prices and a long lifespan. Main challenges to be overcome by this technology are to boost the round-trip efficiency (moderate at this stage) and to make sure that the application chosen is compatible with their high self-discharge rate (e.g. such a high self-discharge rate is not a significant issue for daily cycling, but makes these batteries unsuitable for back-up applications).

As it can be seen, choosing an adequate battery solution is a complex task, which requires a detailed case-by-case analysis. In Gommyr, we will offer our expertise to assist you in selecting the most suitable battery solution for your microgrid projects.

Disclaimer: the whole content of this article is for general information purposes. Gommyr Power Networks makes no representations or warranties of any kind, express or implied about the completeness, accuracy, reliability, suitability or availability of this information. Any reliance you place on such material for making any business, legal or any other decision is therefore strictly at your own risk.