Lithium-Ion Batteries for Solar Street Lights

Over the last decade, lithium has been proven to be an extremely reliable and dominant energy storage technology.  Lithium batteries are widely used in diverse areas to operate electric vehicles, mobile phones, laptops, digital cameras, medical equipment and other portable devices and are used for energy storage in the electrical grid as well.  Lithium is the lightest of all metals and lithium batteries have high energy density, which means they produce a lot of energy without being heavy.

Electropositivity is the measure of how easily an element can donate electrons to produce positive ions.  Lithium is the most electropositive chemical element; this means lithium battery can easily produce a lot of energy.  A Li-ion battery consists of several individual cells that are connected to one another.  Each cell contains a cathode (positive electrode), an anode (negative electrode) and an electrolyte.

In a lithium-ion battery, electricity is generated through chemical reactions of lithium.  Lithium is unstable in its element form, so a combination of lithium and oxygen (lithium oxide) is used for cathode, which acts as an active material.  When a lithium-ion battery is charged, lithium ions from the cathode move to the anode through the electrolyte and the electrons return during discharge.  This is a constantly growing technology and there is a lot of research going into enhancing every part of these batteries to make them safer and less expensive.

Lithium-ion batteries and solar street lights


Lithium-ion batteries have been in use since 1990s for commercial applications and now, they are the most popular rechargeable batteries used in solar lighting applications.  As they are lightweight and their lifespan is longer than traditional lead acid batteries, they work perfect for solar street light.  Li-ion battery has an average lifespan of around 5 to 6 years.

Lithium iron phosphate batteries are a new variant of lithium-ion batteries using   a graphitic carbon electrode with a metallic backing as the anode and LiFePO4 as the cathode material.  LiFePO4 lasts for almost 7 to 10 years and this premium battery technology influences the total life of a solar street light.  They are compact in size and to power them, small-sized solar panels are sufficient.

Modern solar street lights use built-in lithium-ion or LiFePO4 batteries.  Solar street lights with LiFePO4 batteries can sustain their brightness for longer hours, a quality that is helpful in keeping the installed area illuminated during non-sunny days.  LiFePO4 has good electrochemical and thermal stability and relatively better environmental compatibility with less toxicity.  LiFePo4 batteries have high quality cells and recharge faster.  LiFePO4 batteries have a higher DoD (depth of discharge) of around 80% which means more of the battery capacity can be utilized.

Traditional solar street lights used lead acid batteries, which needed constant refill; however, lithium batteries demand almost no maintenance during their operating life.  Both lithium-ion and LiFePO4 batteries charge effectively with as less voltage as 3.2V or 3.7V and solar panels do not have to generate a lot of current to charge these batteries.  Lithium batteries are priced slightly higher but they have higher efficiency and extended lifespan and do not require replacement or repair for a long time.

The life expectancy of a solar battery is mainly determined by its cyclic life or usage cycles and lithium batteries are expected to give around 2000 cycles.  A good quality battery decides the performance of a solar street light; therefore, it is important to know which battery is being used in solar lights and always purchase your solar street lights from a reputed manufacturer.