Wind and solar power – the two major forms of renewable energy – are intermittent power sources because the wind is not always blowing, nor is the sun always shining. This explains why a large country like the United States has been unable to generate 20 percent of its power from this energy. Nonetheless, new storage technologies such as the lithium battery have made it possible for homes to power their houses through solar energy round the clock. In this post, we review the use of lithium batteries to power an off-grid system and give you some tips on picking a battery system for your home.
What Is a Lithium-Ion Solar Battery?
A lithium-ion solar battery is a rechargeable energy storage solution that can be used to store excess power by pairing it with a solar energy system. You can find lithium-ion batteries in common electronics like laptops, electric vehicles, and cellphones.
Tesla announced a new lithium solar battery in 2015 called Tesla Powerwall 1. The battery was inspired by their electric vehicles, and its launch sparked debate about cost-effective solar energy storage solutions while making the company one of the top battery manufacturers in the country.
The Tesla Powerwall was instrumental in laying out the future of lithium solar batteries. It convinced investors to invest in the energy storage sector, established the pricing for the batteries, and affirmed that battery systems could be made affordable for the average residential consumer.
Before this technology, most off-grid systems were powered by lead-acid batteries. Now, however, there are many lithium-ion options on the market, and the average homeowner can pick the right energy storage solution for their needs.
Pros and Cons of Lithium-Ion Solar Batteries
The invention of the lithium battery storage unit was crucial to the world of solar energy because the technology offers several benefits over the alternative – lead-acid batteries. Let’s review the pros and cons of the lithium-ion solar battery:
Pros
The top advantages of this energy storage solution include:
- Higher DoD
The Depth of Discharge (DoD) of a battery refers to the amount of usable stored energy in it concerning its total capacity. Because they are deep cycle storage units, lithium-ion solar batteries usually have a high DoD – around 95 percent. In contrast, most lead-acid batteries have a 50 percent DoD. This means that you don’t have to charge a lithium-ion battery as many times to use most of its stored energy.
- High Efficiency
The efficiency of a battery is how much usable energy you can get out of it compared to the amount you used to store it. With an efficiency of 90 to 95 percent, lithium-ion solar batteries have higher efficiency (roundtrip) than other options in the market.
- Long Lifespan
Most lead-acid batteries come with a minimum warranty lifespan of approximately 5 years. On the other hand, lithium-ion solar batteries usually have a 10-year lifespan or around 10,000 cycles.
- High Energy Density
In a battery, the energy density refers to the amount of power it can hold compared to its physical size. Lithium-ion solar batteries tend to take up less space and store more power than their lead-acid counterparts. This is a great plus for homeowners looking to maximize space usage.
- Less Maintenance
Lithium-ion solar batteries require less maintenance than lead-acid batteries.
Cons
Potential pitfalls of using a lithium-ion battery system include:
- Costlier Option
Lithium-ion batteries are the most expensive power storage solution. Fortunately, they usually qualify for government incentives like the federal tax credit, cutting some of their cost. Additionally, lithium-ion batteries last longer than lead-acid batteries, which makes them more affordable in the long run.
- Thermal Runaway
These batteries are more likely to experience thermal runaway and catch on fire. That said, if they are properly installed, the risk is negligible or non-existent.
Lithium Vs. Lead in Off-Grid Systems
Lithium-ion and lead-acid batteries are often pitted against each other for use in off-grid systems. What are the differences, and which is better? By definition, an electric battery is an energy-storing device that can convert energy into electrical power. This means that while all batteries can supply energy to off-grid systems, some can handle the cycling schedule and power demands better than others.
The focus when it comes to off-grid systems is more about the usage and less about the battery type. Lead-acid batteries will serve you great if you only need backup power for outages or power failures because they don’t cycle regularly. However, if you need a primary demand charge power source, you are better off installing a lithium-ion battery system.
A lead-acid battery is best suited to short-term, occasional power backup needs, while lithium-ion batteries are the ideal choice for going off-grid. This is especially true if you wish to avoid using the grid for a long time. You will need deeper, more frequent cycles than a lead-acid battery can offer. Simply put, you can live off-grid on either battery, but lithium-ion is more efficient.
How Do Batteries Power Off-Grid Systems?
An off-grid solar energy storage system runs the utilities and electrical appliances in a home through the power stored in its battery units. The energy supply needs to be constant – not a backup – which means that the batteries in the unit must be charged and discharged daily. Typically, multiple cycles are employed where one charges the batteries during the day then discharges the stored energy in the evening. More discharges mean deeper cycles.
The reason lead-acid batteries are not ideal for off-grid systems is that they degrade further with each cycle. Lost lead-acid batteries will peak at around 2,500 cycles on a 50 percent discharge rate. In contrast, many lithium-ion batteries offer a guaranteed 10,000 cycles when discharged to 95 percent.
In terms of economy, an off-grid system will use fewer lithium-ion batteries than lead-acid ones for the same application since the former offers higher discharge and charge rates. This means that lithium-ion batteries are more cost-efficient in the long term.
When Is a lithium-ion Battery the Ideal Choice?
We have already established the benefits of using lithium-ion batteries to sustain your residential off-grid system. They take up less space, store more energy, and have high discharge rates. Moreover, they last longer and don’t need to be replaced as regularly, making them the more economic option.
In some cases, however, homeowners might benefit from other battery types, such as lead-acid batteries. This is especially true when you only need a backup energy source to be used on occasion and don’t want to spend too much money on a lithium-ion system.
Lead-acid batteries may also be ideal for an off-grid system that is only used occasionally, such as a vacation cabin. That said, a lithium-ion solar battery will serve you best for regular or everyday use.
Factors to Consider When Choosing an Off-Grid Battery System
As mentioned earlier, there are currently many solar battery systems available on the market, meaning it can be difficult to pick the best one for your home. The situation is made even worse by the fact that the residential energy storage industry is still fairly new. Here are some pointers on what to look for in a solar battery system for your household:
1. Battery Lifespan
The first factor to consider when looking for a battery system is lifespan. You can measure the lifespan of a battery through the expected cycles, expected throughput, or expected years of operation. Through the cycles, you can determine the number of times you can charge and discharge your battery. The throughput – expressed in kWh – tells you the amount of electricity you can move through the battery before it dies. You can convert the expected throughput of a battery into a projected lifespan through the following formula:
Throughput (in kWh) ÷ Usable capacity = Number of full cycles
Number of full cycles ÷ Number of days in a year = Expected lifespan
For example, a 10,000 kWh throughput warranty on a 10 kWh battery equals 1,000 expected cycles. This is equivalent to one cycle per day for 2.7 years. Most lithium-ion batteries offer a guaranteed lifespan of at least 10 years or 10,000 cycles.
2. Power Rating
Measured in kilowatts (kW), the power rating of a battery is the amount of power it can produce at once. Simply put, this measurement tells you the number of appliances you can run on the battery simultaneously. Different appliances have different power needs, and the average battery has a continuous power rating of 5kW.
When choosing a solar battery system, you should keep in mind that solar batteries usually have two power ratings – an instantaneous power rating and a continuous power rating. The former tells you the amount of power the battery can produce in short bursts.
If you have appliances that require a lot of power to start but run on low power, you will need a battery system with a high instantaneous power rating.
3. Roundtrip Efficiency
The roundtrip efficiency of a battery system is a measurement of how well the system stores and converts electricity. An energy storage system consists of the battery and inverter. When you invent DC electricity to AC electricity or charge and discharge your battery, it loses some power. A battery with a high roundtrip efficiency provides more electricity for every unit you put into it, which means it loses less power. You should buy a battery system with a high roundtrip efficiency.
4. Storage Capacity
Another thing to look at is the storage capacity. The size or storage capacity of a battery refers to the amount of electricity it can store and provide to your off-grid system. Although battery power is expressed in kW, battery capacity is power multiplied by time and is expressed in kWh (kilowatt-hours). As such, this rating can tell you how long a battery system will power your home.
Tip: Always review the usable capacity of a battery because it tells you the amount of electricity from the total stored that you can actually access.
5. Chemistry
The chemistry of a battery refers to the primary compound which the battery uses to store electricity, such as lithium-ion or lead-acid You should always consider the chemistry of a battery because it determines the properties of the battery, such as power density and storage capacity. Some compounds like lithium-ion enable a battery to produce more power for more years and store more electricity in a smaller battery space.
6. Safety
It is important to note that all the batteries installed in the United States are safe. Solar batteries in the country usually have to meet set safety standards to receive installation certification for commercial or residential use. That said, some chemistries have been tested more extensively than others, usually beyond the requirements set by the government. This means that some battery chemistries are somewhat safer than others. In terms of safety, a well-installed lithium-ion battery is the safest choice for your home and has little to no risk of catching on fire.
7. Number of Batteries Needed
The last factor to consider when setting up your off-grid system is the number of batteries you need to run it. This will depend on the type and nature of your appliances, how long the battery will be running, the number of appliances that will remain on at a time, and the type of solar panels you have. If you are unsure of how many batteries you will need for your system, you should consult a professional.
Conclusion
So, what is the best lithium-ion battery for your off-grid system? Generally, the ideal battery for your setup will depend on several factors, including the type of solar installation you have, the size of your home, and your budget. If you are looking to power a large house with many appliances, your best bet is a high-capacity battery that will provide power 24/7. However, if you have a limited budget, you can optimize your solar energy storage system by purchasing a smaller unit with excellent integration. Either way, a lithium-ion battery system is a way to go.
