Lead-Acid Batteries for solar power storage

Common Lead-Acid Battery specifications

Specific energy

35-40 Wh/kg

Energy density

80-90 Wh/L

Specific power

180 W/kg

Charge/discharge efficiency

50–95%

Energy/consumer-price

7 (sld) to 18 (fld) Wh/US$

Self-discharge rate

3–20%/month

Cycle durability

<350 cycles

Nominal cell voltage

2.1 V

Charge temperature interval

Min. −35 °C, max. 45 °C

 

History of lead-acid batteries

In 1859, Gaston Planté invented one of the first types of rechargeable batteries, which is known as the lead-acid battery. The lead-acid battery had a poor energy-to-weight ratio and also a poor energy-to-volume ratio. However, the battery could supply high surge currents which gave a large power-to-weight ratio. With these benefits and with the relative low cost, motor manufacturers found an interest to use lead-acid batteries for motor vehicles.

Gaston Planté Lead-Acid Battery
Lead-Acid Battery Internals

Where lead-acid batteries are commonly used

The most common use for lead-acid batteries is in motor vehicles. Because lead-acid batteries are affordable when compared to modern batteries such as lithium-ion, the popularity of lead-acid batteries increased. Many people use lead-acid batteries in large quantities for energy storage in communication towers, some military equipment and solar implementations. Therefore, modifications have been made to the lead-acid battery’s standard cell which allow for longer energy storage durations and therefore, reducing maintenance requirements. The most common modified lead-acid batteries in these scenarios are Gel-cell batteries and Glass-mat batteries which are also commonly referred to as VRLA (Valve-Regulated Lead-Acid) batteries.

Materials used for lead-acid battery cells

Materials used for lead-acid battery cells

The active and main materials used to develop a lead-acid battery are lead peroxide, sponge led and dilute sulfuric acid. The positive plate of a lead-acid battery is constructed by lead peroxide which has a brown, hard and is a brittle substance. The negative plate of a lead-acid battery is constructed by pure led in a soft sponge condition. The dilute sulphuric acid used in lead-acid batteries, has a ratio of water is to acid equals to 3 is to 1(water: acid = 3:1). The lead-acid battery is formed by dipping the lead peroxide plate and sponge led plate in dilute sulfuric acid. There is a load connected externally between these plates. The molecules in the sulfuric acid split into positive hydrogen ions (H+) and negative sulphate ions (SO4 − −). When the hydrogen ions reach the PbO2 plate, the hydrogen ions receive electrons. Therefore, the hydrogen ions become hydrogen atoms. These hydrogen atom attacks the PbO2 and form PbO and H2O. This PbO reacts with H2 SO4 and forms PbSO4 and H2O. Or the led oxide reacts with sulfuric acid and forms lead sulphate and water.

Negative sulphate ions are moving freely in the solution that some of them will reach to the pure led plate where they lose their extra electrons and become radical sulphate. Radical sulphate cannot exist alone, it will attack pure led and form led sulphate. As positive hydrogen ions receive electrons from the lead peroxide plate and the negative sulphate ions give electrons to the led plate, there would be an inequality of electrons between the two plates. There would be a flow of current through the external between the plates for balancing the inequality of electrons. The process is known as discharging of a lead-acid battery. When the load is disconnected and lead sulphate covered lead and lead peroxide plate are connected with the positive terminal of an external DC source. The lead peroxide covered lead plate with negative terminal of the DC source.

 

How Lead-Acid Batteries Work Diagram

Simply, how lead-acid batteries work

A battery in its simplest form is a storage container of electricity for future use. The role of a lead-acid battery in automotive applications is to supply power to the starter and ignition system. This is to start the engine plus to supply extra power when the vehicle’s electrical load exceeds the supply from the alternator. Finally, it is to act as a voltage stabilizer and dampening device in the electrical system. A 12-volt car battery consists of a plastic case with six cells connected in series. Each cell is made up of negative sponge lead plates and positive lead oxide plates. The electrolyte is made up of a mix of 35% sulfuric acid and 65% water. The electrochemical reaction between the lead plates and the electrolyte produces DC electricity. One of the battery discharges active material from the plates reacts with the electrolyte to generate DC electricity. A byproduct of this electrochemical reaction is the production of lead sulfate which coat the plates. During recharging the lead sulfate should convert back to active materials, in essence, returning the battery to its former state.

Difference between AGM, SLA and VRLA batteries

VRLA and SLA are basically the same type of battery with different names. VRLA (valve regulated lead acid battery) and SLA (Sealed Lead Acid battery). Both of these batteries are resistant to leaks, maintenance and position insensitive. Also, VRLA and SLA batteries have vents to discharge build up gas for additional safety. AGM batteries or Absorbed Glass Mat batteries are an exclusive type of lead-acid or SLA/VRLA battery. An electrolyte is absorbed into separators in between the plates of sponge like fine glass fiber mats in AGM batteries. See our range of batteries at our  JC Solar Panels  online store.

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