Solar batteries to help you survive any power outage

Lead-acid batteries are the same type of battery you have in your car. The main difference is that for a solar power system you'll need deep-cycle lead-acid batteries – they can withstand deeper discharges than those used in cars, hence the name.

Deep-cycle lead-acid batteries have four main components:

• Positive plate covered with a paste of lead dioxide;
• Negative plate made of sponge lead;
• Separator – an insulating material between the two plates, needed to enable conduction without the two plates touching;
• Electrolyte, consisting of water and sulphuric acid, which helps conduct electricity.

These constituents are enclosed in a plastic cell which keeps the electrolyte in. When the battery discharges, lead and lead dioxide react with sulfuric acid in the electrolyte to form lead sulfate. When the battery recharges, lead sulfate reverts back to lead, lead dioxide, and sulfuric acid.

The voltage difference between the two plates is approximately 2 volts. That's why a 12 V battery, for example, has six single cells linked in series.

Lithium-ion batteries are literally everywhere – from laptops and cell phones to hybrids and electric cars. They offer great capacity and current output for a lightweight and small size. Lithium-ion batteries are deep-cycle by origin, so they can be fully charged and discharged, and thus used for solar energy storage.

Lithium-ion batteries have four main components:

• Anode (positive cobalt-oxide electrode) and cathode (negative graphite electrode) which store the lithium;
  
• Separator which blocks the flow of electrons inside the battery;
  
• Electrolyte carrying positively charged lithium ions from the anode to the cathode and vice versa through the separator;
  
• Two current collectors (positive and negative).

While the battery is discharging, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When the battery is getting charged, lithium ions are released by the cathode and received by the anode. The battery is fully charged when no more ions flow. If all the ions have moved back, it means that the battery is fully discharged.

There are three types of lithium-ion batteries: cylindrical such as in a remote control, pouches such as in smartphones and tablets, and prismatic such as in electric vehicles. The former type often has corrugated sides, which create air gaps between adjacent cells and can aid in cooling. This feature makes them suitable for solar energy storage.

Lithium-ion refers to a variety of lithium-based battery chemistries. Lithium iron phosphate (LFP) batteries are considered to be the best solar battery type. Unlike regular lithium ion batteries, LFPs have a higher cell density, which makes them more compact. Moreover, they last longer due to the electrolyte's properties, and are not classified toxic.

Flow batteries are relatively new to the battery storage market, but their use in long duration storage is steadily growing. They boast a 100% depth-of-discharge, greater design flexibility and an ability to last for decades at zero charge.

Flow batteries have four main components:

• Two electrolyte liquids (positive and negative) enclosed in two tanks;
  
• Pumps, which push the electrolyte through two independent loops to the core to generate electricity;
  
• Reaction cell, divided into two half cells;
  
• Membrane, separating the two half cells to prevent the electrolyte liquids from coming into direct contact with each other

In flow batteries, the charges are stored in the electrolyte liquids, which are contained in external tanks. The charge-carrying electrolytes are pumped through a reaction cell, containing two electrodes (one positive and one negative) separated by an ion-conducting membrane. During discharging, ions are reduced at the positive electrode and oxidised at the negative electrode. When charging, the process reverses.

Since the external tanks have no size limit, the storage capacity of a flow battery can be easily adjusted to the needs by simply adding more electrolyte. That's what makes them ideal for storing large amounts of power, for example, for off-grid systems, which aren't connected to the grid.

The membrane of flow batteries degrades little over time, which makes them capable of withstanding full discharges, storing power for longer periods (four hours or more), and lasting for decades with almost no maintenance.

Flow battery manufacturers offer a range of chemistries including vanadium, iron chromium, zinc bromine, zinc iron and others. Flow batteries can also be redox (reduction oxidation), hybrid and membraneless. The most common types for solar installations are the vanadium redox (for commercial solar systems) and the Zinc-bromide hybrid (for residential solar systems).

Nickel-cadmium (NiCd) batteries are rechargeable batteries with a high cycle life expectancy. They are typically used in stand-alone solar PV systems where large capacities and high discharge rates are required. Their strongest point is a broad operating temperature range (-4 F to 140 F, compared to around 32 F to 102 F for many lithium-ion batteries).

Nickel-cadmium batteries have four main components:

• Anode (positive nickel-hydroxide (NiOOH) electrode)
  
• Cathode (negative cadmium (Cd) electrode)
  
• Separator, to ensure that the anode and cathode do not physically touch
  
• Electrolyte (alkaline potassium hydroxide (KOH)), enabling electron transfer

During charging, the negative plates lose oxygen and begin forming metallic cadmium (Cd). The active material of the positive plates, nickel hydroxide, becomes more highly oxidized. When a nickel-cadmium cell is discharged, the nickel hydroxide changes its form (Ni(OH)2) and the cadmium becomes cadmium hydroxide (Cd(OH)2). The concentration of the electrolyte does not change during the reaction.

Nickel-cadmium batteries can be a highly reliable energy storage solution for solar PV systems, especially under extreme weather conditions. In fact, they are the only batteries capable of performing well even at low temperatures (up to -40°F). Due to their robustness and low maintenance, they are favored for off-grid megawatt-sized projects in harsh environments.

To wrap it up, a lithium-ion battery is an absolute leader. It will be a good option for both off-grid and hybrid systems. Lead-acid batteries will suit low-cost solar projects with no space constraints. The other two types of solar batteries - flow and nickel-cadmium - are ideal for large-scale solar installations, but are more difficult to find on the market. Check out what solar batteries we have in our store today.