Batteries provide the DC that is to be converted to AC by the inverter for use in appliances. In hybrid solar power systems however, that is, systems that incorporates both solar panels and a battery bank, they mostly serve energy storage purposes. In other words, they store energy produced from solar panels for use by the appliances in the absence of production from the solar panels.
All batteries have essentially the same components: electrolytes, positive and negative terminals and separators integrated into 'cells'. These components are often differentiated based on the nature and/or type of the chemical material from which they are made.
Flooded Lead-Acid
In an FLA, the acid electrolyte is 'poured' into the battery encasement and is free to move about. In most cases, the electrolyte is sulphuric acid diluted with distilled water. They are the most common and cheapest type of deep cycle batteries. They have been in use for a longer time than any other battery technology and therefore have a greater history of field use and testing.
Lithium-ion
In a Lithium-ion battery, graphite is mostly used in the negative electrode. The positive electrode is generally one of three layered materials of lithium salts. (Recently, graphene containing electrodes [based on 2D and 3D structures of graphene] have also been used as components of electrodes for lithium batteries.) And the electrolyte is typically a mixture of organic carbonates containing mixtures of lithium salts. (A modified variant of Li-ion batteries, the lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), uses a polymer electrolyte instead of a liquid electrolyte.)
FLA Vs. LIB
Depth of Discharge (Winner: Lithium-ion)
The depth of discharge of a battery is the percentage of a battery that can be discharged without damaging the battery. Lithium-ion can withstand discharge of about 86-98% while FLA batteries can only handle 30-50% discharge and sometimes even lesser. In lead-acid batteries, over-discharging causes sulphate at the electrodes and this can reduce the performance of the battery.
Performance (Winner: Lithium-ion)
Battery efficiency, also known as round trip efficiency, is the how well a battery charges or discharges when being used. Lithium-ion batteries are more efficient (up to 98%) than FLA (80%).
Energy Density (Winner: Lithium-ion)
Li-ion batteries have the highest energy densities of any battery technology today (100-265 Wh/kg or 250-670 Wh/L). This means that they can store more energy per mass than their FLA counterparts and thus require lesser installation space. This means they weigh lesser and lighter while providing the same amount of output than FLA counterparts. However, being sensitive, Li-ion batteries require additional safety systems as part of their battery management systems to limit voltage and internal pressures. This can inadvertently increase their weight and, in some cases, limit their performance.
Lifespan (Winner: Lithium-ion)
Though Li-ion batteries are subject to aging, they very well outlast FLA. Regardless, a well-maintained FLA can last long.
Safety (Winner: Lithium-ion)
FLA batteries emit hydrogen gas and acid fumes when in use and have higher ventilation requirements. They are thus to be installed in well-ventilated spaces in order to avoid the risk of explosion of the hydrogen gas. The regular maintenance in form of topping the battery with distilled water and performing equalization charging are generally hazardous exercises and they have to be performed at least once every three months and by a professional. LIBs are maintenance-free for life. They come with safety mechanisms that protect them and users. They are generally safer and can be installed in living spaces.
Warranty (Winner: Lithium-ion)
Typically, manufacturers can back their lithium-ion batteries with up to 10 years, whereas other battery types generally are backed by a maximum of only 6 months to 1 year.
Cost (Winner: FLA)
Lithium-ion batteries cost way higher than FLA batteries. The upfront price of a LIB can reach up to 20X that of the FLA battery. The lower cost of FLA batteries is why they have remained in the market. However, over their lifetime, LIBs are more economical.
Overall (Winner: Lithium-ion)
The primary advantage of FLA batteries is that they have the lowest cost of all deep cycle battery technologies. Since cost is the most practical consideration for majority of buyers and since FLA batteries are more common, FLA batteries may be regarded as the most practical choice of the two. Lithium batteries are more expensive up front, regardless, the cost over their life cycle are the cheapest of all battery types. Regardless, costs of lithium batteries have dropped by 60-70% in recent years. This will continue as the industry expands. The kings of mass-market-directed products, China is anticipated to manufacture over 73% of all lithium-ion battery storage.
FLA is the oldest battery technology. This means that installers and users have more experience with FLA batteries than the new Lithium-ion batteries. It has been argued that a well-maintained FLA battery has the prospect of lasting up to a decade. But the additional burden and costs of maintenance and the attending hazards counter that argument.
There are other factors besides the battery technology that are to be taken into consideration by the user and the system designer when deciding which battery type to use in designing a system. Among those, the users budget, power needs and power environment play decisive roles in the type of battery type users will ultimately choose to invest in. The nature of appliances that will run on the system and the expected lifespan of the system are also significant factors.
Solarkobo often recommends FLA batteries for its clients, especially when cost is the chief consideration, which is often always the case. Also, in designing systems to backup power during brief power outages, FLA batteries come highly recommended as good options because they would be used only for small periods of time. Regardless, another battery type, AGM batteries, can provide a sort of middle-ground between FLA and LIB in costs and performance. Though an AGM battery typically cost more than an FLA battery, it costs less than a LIB but offers a performance that is closer to that of an LIB while removing the need for constant checks and maintenance. With the most research effort being invested in optimizing Lithium-ion battery technology than any other battery technology (the 2019 Nobel Prize in Physics was awarded for research in Lithium-ion battery technology), and even as costs is being driven down to meet the boom in demand, we consider lithium-ion batteries the batteries of the future.
An already large and still increasing range of available options can lead to information anxiety that can result in a poor decision. In situations like this, Solarkobo has university-trained engineers who have acquired years of field experience to help users make the best choice of battery type that fit their budgets and meets their power needs.