This is the third article in our series on solar powered billboards by Kevin Conlin.  Conlin is President of Autonomous Power Solutions.    You can reach Kevin at kconlin@autonomouspwr.com or 281-202-9629.

Batteries are the single most important, and least understood, component of any solar powered billboard. Every watt of energy used at night has to be stored in your batteries.

This discussion is centered around lead acid batteries, the most common, and cost effective type found in solar billboard lighting systems.

There are 2 types of lead acid batteries: wet and “sealed”.

• Sealed batteries, though not truly sealed, are generally considered maintenance free, and are a good choice for smaller solar systems and systems in cooler climates, since high temperatures shorten their life. In hot climates, such as the southwest US, high temperatures can shorten sealed battery life to 2-3 years, while in cooler climates, they may last 6-7 years.

• Wet batteries are a good choice for hot climates and larger systems due to their lower cost. Although they require occasional maintenance, usually less than 1 hour per year, they last twice as long, and cost half as much, as sealed batteries.

Autonomy is the number of days a solar system can operate without sun, typically during winter, when days are short and cloudy and often stormy.

Because batteries are expensive, most battery banks are undersized for cost saving reasons. This is the “kiss of death” for reliability, and for the batteries themselves.

We recommend at least 7 days autonomy, even in the desert southwest. Winter storms and extended cloudy periods can tax batteries even in the sunniest cities, such as Las Vegas, Phoenix and San Diego.

Too little autonomy means your solar lighting system will fail frequently in winter, resulting in customer complaints, shortened battery life and higher operating costs for the billboard owner.

Battery life expectancy is affected by two things: temperature and daily depth of discharge.  High temps dramatically shorten sealed battery life due to increased internal corrosion and loss of electrolyte.  Wet batteries are less affected, and since lost water can simply be replaced, they have double the life of sealed batteries in hot climates, up to 10 years.

The Bottom line: Don’t skimp on batteries. While initial cost savings may be attractive, in the long term you’re going to have higher operating costs, frequent system failure, and unhappy clients.

Next week: Controls and lights

Paid Ad