Techie Top Tip 1

Techie Top Tip 1 

Winter considerations for battery energy storage systemsgn
Techie Top Tip 1

It can’t be denied, winter is most definitely upon us. Whilst winter weather and plummeting temperatures provide its own challenges for the physical nature of our industry, with installers out and about, up on roofs and exposed to the weather, it’s also important to think about cold ambient temperatures when designing and installing Solar PV & battery energy storage systems.

We shall initially look at battery systems.

Cold temperatures and Battery Energy Storage Systems
Over the last year, Segen has experienced massive growth in the supply of Battery energy storage systems, as you’re all now incorporating more and more battery systems into installs than ever before.

Typically , for LFP (LiFePO4) battery systems, cold temperatures are not our friend. On the Segen Tech Support phones in mid-Dec 2022, whilst it’s been bitterly cold outside, there have been numerous queries relating to an observed drop in performance of battery systems in the cold snap.

Ultimately, it’s the internal chemistry of the battery that determines the characteristics of the battery, and the BMS works to operate the battery at optimum performance whilst (most importantly) protecting the battery. If you push too much current through a battery which is too cold when charging, then you can cause irreversible damage to the battery cells.

Lithium ‘plating’ can occur on the anode side of the cell, where Lithium ions help to deposit metallic lithium, which can cause dendrites to form.

Thermometer in snow

Dendrites are an interesting, but a wholly undesirable phenomenon – they are a ‘growth’ that occurs on the anode of a battery cell – these little critters occur naturally over the long term, but misuse of the battery (such as trying to charge it at higher C rates at very low temperatures) can accelerate the formation and growth of dendrites. In the worst case scenario the dendrites can grow to ultimately short circuit between the anode and cathode and the battery cell dies which, in many cases, results in an unusable battery.

Dendrites are ‘den-wrong’.

Battery manufacturers therefore wish to limit the formation of dendrites as much as possible to maximise the life of the battery.

When the battery is cold, manufacturers can manage the battery conditions via the BMS so that the conditions for dendrite formation and acceleration is avoided. This means the BMS will reduce the C rate during charging to protect the integrity of the battery, therefore customers may experience their battery systems seemingly failing to charge, or at least charging at an extremely low rate when the ambient temperature is in single digits.

So, what can be done to maximise the performance of a battery system in respect to the cold?

Location, location, location.

Locating a battery system is clearly a difficult tightrope to walk – you must consider the wishes of the end user, as not all customers want a battery on show in their living room. Residentially, whilst lofts are a popular location for both inverters and battery storage, they are often subject to both hot and cold extremes of temperature, depending on the season.

Likewise, where an external garage/carport or similar may be an ideal location out of the way, exposure to cold temperatures will affect the battery performance. IP ratings are something that can potentially cause incorrect assumptions. Clearly the IP (ingress protection) rating of an object determines its ability to withstand ingress from moisture and dust. However, even if a battery has a protection rating of IP65, which would typically be considered as an ‘outdoor’ product, you do still need to consider how extreme ambient temperatures will affect the performance of the battery. In the same way that you don’t want a battery exposed to extreme hot temperatures in the summer (e.g., installed in direct sunlight), when designing a BESS system, you need to consider protection from the extreme cold. Constant use of a battery system will at least maintain some inherent heat within the battery to stop it getting too cold internally.

In the build-up to a cold period, you may even consider increasing the minimum state of charge in the battery to encourage the grid to top up the battery and maintain that constant use. This has an added advantage in cold weather as battery voltage itself (and therefore SOC) is related to temperature. For certain battery systems, a cold snap may cause the battery SOC to drop beyond the desired SOC which could cause some comms issues for certain types of system.

Additional insulation of battery systems is unlikely to yield any significant results, therefore if you can at least consider the potential ambient temperature of the desired location when designing systems, it should help to reduce the chances of an installer reporting a poor performing battery system at this time of year. Whilst our growing Tech Support team are always happy to speak to you, very often there is little we can advise in this sort of scenario, other than helping to manage expectations.

Remember, to find the contact details of your allocated Tech Support contact, please go to your portal home screen, where you will find our phone number or alternatively use the ‘Contact Us’ form.

– the Technical Team

Glossary of terms
• SOC – State of Charge
• Voc – Open Circuit Voltage
• Vmpp – Maximum Power Point Voltage
• BMS – Battery Management System
• STC – Standard Test Conditions
• LFP – Lithium Iron Phosphate, LiFePO4
• BESS – Battery Energy Storage System
Dendrites – small growths on the battery anode
IP rating – Ingress Protection rating

Techie Top Tips so far:
No.2. Installation Addendum – Solis EH1P Hybrid Inverter – only available on the Segen customer portal
No.3. Cold Temperatures & String Design

– the Technical Team

Glossary of terms
• Voc – Open Circuit Voltage
• Vmpp – Maximum Power Point Voltage
• STC – Standard Test Conditions

Techie Top Tips so far:
No.1. Winter considerations for battery energy storage systems
No.2. Installation Addendum – Solis EH1P Hybrid Inverter

Your technical contact is Adam Jackman , Adam.jackman@segen.co.uk

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