WHAT ARE THE DIFFERENT TYPES OF SOLAR BATTERIES?

There are various types of batteries suitable for solar systems. The generally common factor between these batteries is that they are deep cycle batteries [3]. A deep-cycle battery is any battery that has been designed and manufactured to withstand regular discharging, using up most of the battery’s capacity [1]. These batteries are different from ordinary car or generator batteries which are only designed to “crank” or start an engine for short periods. Therefore you generally can NOT use a car battery on a solar system. It will barely last more than a month as it was not designed for deep discharge applications.

The batteries used for solar systems include: Lead Acid, Lithium-Iron, Lithium-polymer, Nickel-Based and salt-water battery. We will look at the two most popular types in the industry: Lead Acid and Lithium Iron

(1) Lead Acid: These are the oldest (invented in 1859)2 and most widely used battery that has been used for several decades, being continously improved.

How it works: Chemical energy of the battery is stored in the potential difference between the pure lead terminal at the negative side (anode) and the Lead Dioxide on the positive side (cathode), with aqueous sulphuric acid electrolyte.

This type of battery should always be stored at full state-of-charge (fully charged, even in shop storage warehouses!!). A low state of charge causes a condition called sulfation, which results in a degradation of battery performance.

The most popular group of this battery is the “sealed lead acid” battery, as it is maintenance free and does not require regular topping up fluid. The two most common sealed lead acid batteries available are the Gel (also known as Valve-Regulated Lead Acid (VRLA)) and the Absorbent Glass Mat (AGM) 2

The gel type is made up of a gel (silica based) that suspends the elctrolyte in a paste [2], whilst the AGM suspends the electrolyte in a specially designed mat [2]. How do the two compare in performance? The AGM battery fades gradually with use (meaning year 2 will be slightly less than Year 1, and so on until end of life-span), whilst the Gel maintains high performance for a long period then just suddenly drops off towards end of life... so you can take your pick there :)

Please find below the advantages and disadvantages of Lead Acid Batteries:

(i) Advantages:

· Dependable and been tested over time (more than 100 years of use)

· Relatively lower up-front costs

(ii)Disadvantages:

· Shorter life-spans (4 to 5 years)

· Life-span and performance sensitive to temperature (ideal operating temperature for VRLA reported to be 25 deg C, with performance degraded as temperature increases)

· Relatively high charge times (between 10 and 16 hours of charging needed)

2. Lithium Iron: This battery type is relatively new, becoming commercially available in the 1970s.

How it works: Lithium-ion utilises a cathode (lithium metal oxide), an anode (porous carbon) and electrolyte as conductor2

Please find below the advantages and disadvantages of Lithium-Iron Batteries:

(i) Advantages [2]:

· High specific energy (meaning that the amount of energy that you get per kg of weight is relatively higher)

· Long life-span (average life-span of 8-10 years).. and long shelf life

· Relatively short charging time

· Very deep discharge (some batteries can even be discharged to 100%)

· Low self-discharge

(ii)Disadvantages:

· Requires strict protection of the circuit, and as such cannot be connected to any system. The design and matching has to be accurate

· Relatively much higher upfront costs (though cheaper if looked at on the long-term)

We will talk about selection and sizing of a battery for your system in future posts… watch the space!!

SOURCES:

1. https://en.wikipedia.org/wiki/Deep-cycle_battery

2. https://batteryuniversity.com/

3. https://www.altestore.com/

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About Author:

Lovewell Chitiyo is a Mechanical Engineer with 15 years experience in the building services Engineering consultancy, renewable energy systems and sustainable design fields. He is currently studying Masters in Renewable Energy at Stellenbosch University in South Africa

Lovewell is an Accredited Professional with the Green Building Council of South Africa for Existing Buildings Performance and New Buildings; Interiors, holding several qualifications and certification in Renewable Energy and Sustainability.

Lovewell also has vast experience in design, supervision, installation and commissioning of several projects locally and regionally in the last 15 years.