Battery Storage: How it Works and the Different Types
As more people choose to add solar panels to their home or office locations, the issue of storage is coming up more often. After all, if a storm knocks out the grid power, but the sun continues to shine, clients want to know if their solar energy can be stored and used later in an emergency. Even with a grid-tied solar energy system, battery storage can be invaluable for businesses that cannot handle a loss of electricity due to refrigeration needs or other systems that must remain running at all times, or that want to reduce demand charges. To understand the value of a battery storage system for your solar power array, it is helpful to understand the mechanism of a battery to begin with.
How do Batteries Work?
Batteries are chemical energy storage devices. Most of us know a battery as an encased unit that can retain potential energy to be discharged as electricity. The differences in batteries arise from the materials used to create their component parts, namely the electrolyte and the two electrodes of different materials. When connected into a circuit, ions from one electrode move through the electrolyte (the conductive material around the electrodes and between them) into the other electrode, creating a flow of energy that manifests as electrical current. Many modern advanced technology batteries are fully sealed, with the electrodes connected to an external anode and cathode that conduct the electricity in and out of the battery. Other batteries require the addition of water to maintain the optimum levels of electrolyte concentration.
Each cell (a unit containing the two electrodes and the electrolyte) in a rechargeable battery (made up of one or more cells) uses the two electrodes to generate energy. The materials have been chosen because they can react and produce electricity that flows out of the battery (called discharge) as well as reverse the chemical reaction by receiving electricity from another energy source (called recharging). Over the years, people have discovered different combination of electrodes that meet a few important criteria:
- How much they cost to produce.
- How long they last: this refers to both years of use and to the amount of discharges and recharges (known as cycles) they can last through.
- Depth of Discharge: how close to truly “empty” can they get without affecting the long-term ability for the battery to perform.
- Rate of “self-discharge” – when sitting on stand-by, do the batteries lose their charge quickly or slowly? You want a low rate of self-discharge to avoid having to use extra energy to replenish the batteries.
Types of Batteries
Nickel-Cadmium – An older type of battery technology, it has gone out of favor because of better alternatives that have less toxic materials (Cadmium is a heavy metal that requires careful disposal or recycling). Even today, they still have a reputation for lasting a long time as long as they are periodically discharged completely and are properly maintained. You may still find NiCd batteries in smaller solar devices, such as garden lights. Advances in other technologies, however, have made them less and less of a viable option for larger solar energy applications.
Nickel-Iron – Nickel-Iron batteries have an amazing quality, namely that they last for a very long time and don’t contain toxic metals like lead or cadmium in them. While they have been used with solar energy quite successfully, they have some downsides as a battery bank for a typical residential setting. They periodically need water added, require gas venting, and they aren’t produced in quantity in the United States. Historically they are also temperature sensitive and have high-self discharge, but newer versions of this very old technology may have a life of up to 50 years, which makes them an intriguing technology to be watched, especially for very large off-grid installations.
Lithium-Ion – Given their reputation for being smaller and lighter, as well as having long cycle lives, these batteries are becoming more common for residential battery storage. Mountain View Solar offers the DC coupled StorEdge/LG Lithium battery storage system and inverter, specifically because of how well-suited these batteries are to the task. The LG Chem RESU10H has a 10 year performance warranty, works well with a smaller critical load, and can now be doubled up for twice the capacity. They do need climate control to maintain peak operation, but overall these are perfect for running critical systems in a residential setting, such as refrigerator, electronics and other small appliances. Another lithium solution we recommend is the Discover AES battery with Schneider inverter, which can be stacked 10 high for much larger backup or off-grid applications. The Tesla PowerWall is also a fantastic battery, but being an AC coupled solution, is best suited for time of use shifting and self consumption, as compared to backup.
Lead-Acid – Highly consistent and the most common option, Lead-Acid batteries can be applied to any size project as they can be scaled up infinitely for the largest applications. They do have a lower depth of discharge than Lithium, so they require a larger overall capacity for the same true energy output, and they can be a bit complicated and require specialized labor to install. Some versions are flooded and require watering and maintenance, but for safety reasons Mountain View Solar will only install sealed, maintenance free batteries, so there isn’t a chance of gases or acid leaking from them. Lead acid batteries are a very well-tested, established technology. The DEKA Unigy II industrial grade batteries that we recommend and install were originally designed for backup in the Telecom industry, so they are very well suited for residential and commercial backup with extremely long stand-by lifespan. Although lead is a toxic heavy metal, the lead in DEKA’s lead acid batteries is recycled from dead batteries; the recycling system for lead-acid batteries is well established.
This brief overview only touches on the battery technologies out there, but rest assured that, as trained solar energy specialists, we have identified the most reliable and durable batteries for the typical applications in commercial and residential solar energy systems. We have also developed strategies to safely and efficiently retrofit batteries into older existing grid-tied systems using industry standard best practice.
Mountain View Solar has more experience with solar and battery systems than any other contractor in the Maryland, Virginia, West Virginia and Pennsylvania service area with 2 Megawatt-hours of installed residential battery capacity going back 10 years. Please fill out our quick and easy consultation form if you’d like to discuss your options with a seasoned professional today!