The batteries of battery storage
- Oct 9, 2019 7:01 pm GMT
- 2297 views
The introduction of battery storage equipment solutions to the PV solar industry has captured intense interest, confusion, and skepticism throughout the worldwide energy industry over the last several years. Some claim batteries will greatly assist in the ongoing transition of the energy grid and that they answer the intermittency limitations associated with wind and solar energy generation. Others view batteries as yet another complicated and expensive renewable energy solution with concerns from the regulatory and authorities having jurisdiction parties as to certain lithium-ion batteries potential safety risks.
While much is written about the rate of battery storage installations, how large those installations are and which country is leading the pack in installations, the types of batteries which can be used for storage projects are less well understood. So we ask the questions today, what are the batteries which comprise the world of battery storage, what do they do well and not so well and what are some of the key considerations when choosing given battery chemistries?
The batteries of battery storage
While people tend to use the one type fits all term, “lithium-ion battery”, these types of batteries comprise a surprising number of varying compounded chemistry which produces a range of lithium-ion batteries with unique operating performance and cost structures. Here is a list of better known and marketed lithium-ion compounded batteries:
Source: Synergy Files
Here is a view from battery supplier, Simplifi, in a comparative table as to the operating characteristics of these batteries:
Lead-acid, the old standby of batteries
As in the case of lithium-ion batteries, there are several types of lead-acid deep cycle batteries that have been used for many years for battery storage applications, most commonly for emergency backup power applications. This is considered the general list of commercially available in inventory lead-acid battery types as organized here by Battery Stuff.com:
Flooded Batteries - This is the traditional engine start, tractor, and deep cycle-style battery. The liquid electrolyte is free to move in the cell compartment. The user has access to the individual cells and can add distilled water as the battery dries out. Popular uses are engine starting and deep cycle designs. Flooded batteries are common and found in many applications, such as automotive starting batteries and flooded batteries for solar and emergency backup systems.
Sealed - This term can refer to a number of different constructions, including only a slight modification to the flooded style. In that case, even though the user does not have access to the cell compartments, the internal structure is still basically the same as a flooded battery. The only difference is that the manufacturer has ensured that a sufficient amount of acid is in the battery to sustain the chemical reaction under normal use throughout the battery warranty period.
VRLA - This stands for Valve Regulated Lead Acid battery and this is also a sealed battery. The valve regulating mechanism allows for a safe escape of hydrogen and oxygen gasses during charging. VRLA batteries are common and found in many applications.
AGM - Otherwise known as Absorbed Glass Mat construction which allows the electrolyte to be suspended in close proximity with the plate's active material. In theory, this enhances both discharge and recharge efficiency. Actually, the AGM batteries are a variant of Sealed VRLA batteries, just a more advanced design. Popular usage includes high-performance engine starting, power sports, deep cycle, solar and storage batteries and UPS and Telecom batteries for use with generators.
GEL - The Gel Cell is similar to the AGM style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a Gel Cell has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of a lead-acid battery. This is probably the most sensitive cell in terms of adverse reactions to over-voltage charging. Gel batteries are best used in deep cycle applications and may last a bit longer in hot weather applications.
A big advantage of lead, in addition to its on average lower price, is it is completely recyclable which will generally result in dollars paid back to the owner when the lead-acid batteries are turned back into the battery manufacturer’s recycling smelter operations.
How the lead-acid and lithium-ion batteries compare in terms of energy density
This said it’s clear the varying types of lithium-ion batteries dominate the battery storage sector:
Choosing the right battery for a battery storage application
Solar Power International in its annual installer surveys has found the following to be key and often overlooked factors when it comes to installing batteries in solar plus battery storage projects:
Battery sizing - is essential but often not always given full consideration by users and installers. Batteries in PV systems are routinely undersized due to cost or because the system loads were underestimated. It’s important to know the client’s power needs and correctly plan. Many online calculators provided by battery manufacturers and other software are available in determining battery capacity for load requirements.
Consider the cost of ownership - There are several factors that should be taken into account when determining the total cost of ownership over the life of the battery.
• Price: A battery with a low price is always attractive, but if low price comes at the expense of quality and battery life, the need for frequent battery replacements could boost the cost over time. That’s why it’s important to consider issues other than price when making the decision.
• Capacity: Battery capacity is important because it’s a measure of the amount of energy stored in the battery.
• Voltage: The battery bank voltage must be considered to ensure it matches the system requirements. The battery bank voltage is often determined by the inverter specifications if installing a DC-to-AC system or by the voltage of the loads in a DC system.
• Cycle Life: The most critical consideration is cycle life, which provides the number of discharge/charge cycles the battery can provide before capacity drops to a specified percentage of rated capacity. Batteries from different manufacturers may have the same capacity and energy content and be similar in weight. But design, materials, process, and quality influence how long the battery will cycle.
Getting the right battery for the project as they say in the industry is crucial to project success.
Robert Magyar is the Technical Managing Director of Navitus Strategies, a consulting services firm in the battery storage, inverter and PV solar market segments and located near Philadelphia, PA. Robert has consulted with BP Solar, Shell Solar, Princeton Power Systems, VARTA Storage GmbH, Green Mountain Energy and Darfon Electronics among other clients in the renewable energy field.