Solis Seminar【Episode 13】Care of Your Storage System & Batteries During Winter

Introduction
Many residential hybrid solar PV systems need to (and will) work in the winter, but cold weather can negatively affect all batteries, including modern lithium-ion batteries. While lithium-ion batteries handle cold temperatures better than their older, alkaline counterpart, there are still precautions that should be taken to ensure your batteries survive the winter.
So how does cold temperature affect batteries? And what kind of O&M needs to be done? In this Solis Seminar, we will share with you how to care of your hybrid solar systems’ lithium battery in winter.

Why Cold Weather Affects Lithium-ion Batteries?
Before we discuss how to maintain lithium-ion batteries during the winter, let’s first look at why cold weather affects them in the first place.

The basic working principle of all lithium-ion batteries is similar. It is known as “rocking-chair” technology and involves the back-and-forth movement of the electrons and Li-ions during the charge and discharge process.
Low temperature will affect it in the following ways:
1. The lower the temperature is, the lower the activity of the positive electrode material is, and the external electric potential decreases;
2. Low temperature makes it difficult for positively polar lithium ions to diffuse in the internal channels of the material, showing increased impedance;
3. When the temperature is low, it becomes difficult for lithium ions to pass through the Solid Electrolyte Interphase (SEI) membrane, which is manifested with increased impedance.
4. At low temperature, the electrolyte activity will also worsen, and the diffusion ability of ions in the electrolyte decreases.

In short, low temperature reduces the potential energy of lithium-ion battery active substances when it is discharging, making the available capacity smaller. It also leads to greater internal resistance of the battery, making it difficult to discharge energy.

How to Maintain Lithium-ion Batteries During the Winter
Store at the correct temperature:  Avoid temperatures less than -20℃ and greater than 60℃.

As shown in the table above, proper temperature can extend the service life of lithium-ion batteries. For optimum performance, the recommended operating temperature range is between 15 and 25℃.

Do not install and operate the battery outside: Try not to use the battery in low temperature, because when the temperature is lower than 0℃, the battery will fail to charge. When the temperature is lower than -20℃, the battery will automatically enter sleep mode and will not function normally. Therefore, it is best to charge the battery indoors (temperature at 15-25℃) in winter.

Regularly clean your battery: Dirt and corrosion cause batteries to discharge faster, which will greatly decrease the lifespan of your battery. Gently clean your battery with a mixture of baking soda and water.
Regularly charge your battery: Lithium-ion batteries should never be fully discharged, if possible. During the winter months, it is easy to forget to charge your batteries. Please remember to never equate normal battery capacity with winter battery capacity.
Do not leave your battery charging for a long time: Charging time is generally only about 1.5 ~ 3 hours in winter. Do not leave too far away during it charging process, in case of emergency and timely treatment.
Keep the battery with 50%~80% State Of Charge (SOC) at all times: In winter, the lithium-ion battery needs to be kept in full charge, so as to extend the battery life.

Pay attention to the operating status of your hybrid solar PV system via its monitoring platform, especially the battery State of Health (SOH), SOC, etc. If the battery is out of power or has an abnormally short battery life, contact your local dealer or the manufacturer for inspection and maintenance advice. When the battery can no longer be charged or discharged, it should be replaced.