[Battery] What’s the best energy storage technology for solar lighting?

An off-grid solar streetlight comprises a PV panel, an LED light unit, a pole with crosspiece and a battery. The battery stores the energy produced during the day and releases it at night in a cleverly controlled way.

There are three main kinds of batteries on the market: lead acid (absorbent glass mat or valve regulated types), lithium, and nickel-metal hydride (NiMH). Only NiMH batteries are really suitable for off-grid solar streetlights. Here’s why…

Optimally suited to solar lighting

10-year service life

The service life of a battery varies, depending on the type. It’s calculated on the basis of how many cycles the battery can usefully complete. In other words, the number of days the battery can charge and discharge. NiMH technology allows up to 4,000 cycles, equivalent to more than 10 years of everyday operation. By comparison, lithium batteries last about five years and lead-acid batteries only one or two years.

Plus, NiMH batteries can completely discharge without damage. If they overcharge, it doesn’t affect their useful service life. And the better the battery performs, the less maintenance will be needed!

Unaffected by temperature extremes

The ability to withstand temperatures when charging and discharging is different for each type of energy storage technology. Here are the figures for each type:

While charging

• Lead-acid battery: 0°C / +35°C
• Lithium battery: 0°C / +30°C
• NiMH battery: –40°C / +70°C

While discharging

• Lead-acid battery: –10°C / +45°C
• Lithium battery: –20°C / +70°C
• NiMH battery: –40°C / +70°C

NiMH is the only technology able to function optimally across such an extreme range of temperatures. Four years ago, Fonroche installed solar-powered streetlights at Kuwait International Airport and along a 20 km stretch of road in the Middle East where the mercury reaches +68°C in the summer. At the other end of the scale, our solar streetlights have been installed on ski runs in Switzerland and in a residential neighbourhood in Canada, where temperatures can plummet to –40°C.

Eco-friendly also means recyclable parts

For a lighting solution to be truly environmentally friendly, its component parts must be recyclable. Fonroche solar streetlights are 98% recyclable, including the battery. Lead-acid and lithium batteries are excessively harmful to the environment, because the recovery industry is highly polluting. And unlike NiMH technology, they contain toxic heavy metals.

Lightweight energy storage

NiMH batteries are light and compact, which is essential for solar streetlights because it means they can be located at the top of the pole, where the power is needed. By contrast, lead-acid batteries are heavy and need to be placed at the base, which can lead to vandalism and theft.

Power365 battery for smart storage and management

A solution developed by Fonroche’s R&D teams

Using NiMH technology, our R&D teams developed the Power365 battery system. Specially adapted for solar lighting, it ensures that our streetlights operate 365 nights a year, with no maintenance for the first decade. What’s more, the built-in smart energy management system allows optimal storage and programmable lighting schedules. Power365 is unlike any other battery in the world and guarantees 365 nights of lighting a year, even on cloudy or rainy days!