It can be hard to decide what solar battery type is right for your needs. What do you need the solar battery to do? What size will it be? How much are you willing to spend? This article will help answer these questions and compare lead-acid batteries with lithium-ion batteries so that you can make a well-informed decision based on your unique needs.
What solar battery do I need?
The two main types of solar batteries are lead-acid and lithium-ion. Lead-acid batteries have been around for the longest and are known for their low prices. Lead-acid can be the best choice in some instances, like vacation homes. Lithium-ion batteries are the best choice for full-time residences due to their higher efficiency and cycle life.
When you build your solar system you will have a choice of 2 different types of lead-acid batteries and lithium-ion batteries.
Lead-acid vs. Lithium Solar Batteries:
Flooded Lead-Acid (FLA)
FLA batteries have metal plates that are submerged in water. For FLA batteries to work properly, the plates need to be submerged in water and checked every 1-3 months. If you neglect this upkeep, then it can shorten battery life or void your warranty!
Sealed Lead-Acid (SLA)
There are two types of lead-acid batteries, AGM (Absorbent Glass Mat) and Gel. AGM and Gel batteries are both spill-proof, maintenance-free, rechargeable types of battery. The key difference in AGM vs. gel is that they differ in charging rates and output, where the gel is lower in both.
Gel batteries take longer to recharge and output less power, as they cannot handle as much charge current as AGM batteries.
Lithium-Ion
The best lithium battery chemistry for solar applications is Lithium Iron Phosphate, abbreviated to LiFePO4 or LFP batteries. This new technology lasts longer and can withstand deep cycles without maintenance or venting as lead-acid batteries do.
Lithium batteries cost more upfront, but the extra efficiency means you will have to spend less over time because of their increased capacity.
What size should my solar battery be?
Calculate Inverter size
To figure out the size of inverter you need, we have to find your peak load– or maximum wattage. This is determined by adding up all the watts from appliances and devices that can run simultaneously (including microwaves, lights- anything). The sum will tell you which size inverter is needed.
For Example:
If you have 3 x 20 watt led lights as well as a 500-watt heater in a room then:
The inverter size is 500 + (3* 20 watt) = 560 watts
Calculate Daily energy use
To find out how much energy your home consumes in a day, figure out the number of hours each electronic device will be on and multiply its wattage by that amount. Add up all these values to estimate total power consumption, which is probably too low due to efficiency losses; you can get closer by multiplying it by 1.5 (to account for performance decreasing as temperature increases).
For Example:
Led lights run for 5 hours a day. The heater runs for 2 hours a day.
(60 watts x 5 hours) + (500 watts x 2 hours) = 1300 watt-hours.
1300 x 1.5 = 1950 watt-hours
Choose the number of days of autonomy
You can choose how much energy you want to store in your battery bank, although most people generally keep it at two or three days’ worth. This will determine the size of your battery bank.
Determine the size of your solar battery
Finally, we can calculate the minimum battery AH capacity that we need. Take your watt-hours per day and multiply them by the total in 3 above to represent a 50% depth of discharge on your batteries.
So then you would convert kilowatt-hours into amp hours using this formula: divide by voltage for each battery type which is 12V, 24, or 48 volts, respectively, to estimate how many amp-hours (AH) is required.
For Example:
If you want your batteries to last for 3 days:
1950 watt-hours x 3 days = 5850 watt-hours
5850 watt-hours / 48 volts = 121.8 AH
You will thus need 121.8 AH of battery capacity.
It must be remembered that if you opt for lead-acid batteries, they can only be discharged 50 % before they need to be recharged. What this means is that you may not have enough power storage capacity on a lead-acid battery bank for the desired number of days (in this case, three)
You will then have to get double the battery capacity in lead-acid batteries to meet your power requirements:
Lead-acid battery capacity
121.8 AH x 2 = 243.6 AH
Lithium -ion battery capacity
121.8 AH
If you opt for lithium-ion batteries, you will only need the estimated 121.8 AH of capacity, as lithium-ion batteries can be discharged to 80%. What this means is that you will have a better battery life because more charge cycles are available.
What to look for in a battery
There are lots of different potential decision criteria and comparison points to make. The battery specs matter most if you want to use an energy storage system with a battery. There are several different criteria to evaluate your energy storage options. What’s best for you depends on your specific needs.
The key decision criteria for solar batteries are:
Cost
The batteries for your solar system will be a significant upfront cost and will be a key consideration when installing your solar system. What you should look for in a solar battery is what it will cost over its lifetime. What’s the best option, then?
You can expect lithium-ion batteries to last 10 years or more. They have almost no degradation from age: lead-acid batteries may only last about six years before their capacity starts dropping by half every three years.
Performance
What is the battery’s power rating (amps), and how much energy can it store? What type of discharge cycle does it have– 50% or 80% depth of discharge? What are its operational characteristics, such as charge voltage and recovery rate after deep cycling? What is the battery’s amp-hour capacity, and how much does it cost?
Durability
How well will the solar batteries stand up to extreme temperatures (cold or hot)? What materials are used in its construction? What is this battery’s tolerance to vibration and shock loads during installation–in transit, on-site, throughout operation?
Lifespan
How long will the solar battery last before it needs to be replaced? What are its expected years of life, and what’s the warranty on this number? What is a typical power output degradation rate over time (typically expressed in percent)?
Maintenance
What are the maintenance requirements, such as how often they should be checked and what kind of care you need to give them? What is their self-discharge rate (typically expressed in percent or amp hours)? What kinds of additives does this solar battery have for electrolyte fluid loss protection–is a specific additive needed on top of distilled water?
Warranty
What is the solar battery warranty? What are the terms of the warranty for this type of solar system component, and what does it cover–power output and capacity or just replacement parts?
What is the difference between lead-acid batteries and lithium-ion batteries?
Below is the comparison for battery cost for a 5 kw solar system over a 10 year period.
Solar Battery Comparison
(10 years of ownership)
| Flooded Lead-Acid (FLA) | Sealed Lead-Acid (SLA) | Lithium-Ion | |
|---|---|---|---|
| Upfront Battery Cost | $2800 | $3900 | $9600 |
| Total Battery Cost (10 Years) | $8500 | $11800 | $9600 |
| Depth of discharge (DoD) | 50% | 50% | 80% |
| Number of Cycles | 1200 | 1000 | Unlimited |
| Maintenance | Yes | No | No |
| Battery bank weight | 970 lbs | 1010 lbs | 380 lbs |
| Warranty | 3 years | 3 years | 10 years |
The lead-acid batteries will have to be replaced 3 times over the 10 year period, while the lithium-ion batteries will last the whole period.
Differences between lead-acid and lithium-ion batteries
Upfront battery cost
The upfront cost of lithium-ion batteries is much more than lead-acid batteries. This means that you will have a higher initial cost for the lithium-ion solar battery, but over time it saves money because there are fewer replacement costs.
Total battery cost over 10 years
Although the upfront cost of lead-acid batteries is much less than the upfront cost of lithium-ion batteries, the cost will be about equal over time because lead-acid batteries have to be replaced at least three times.
The warranty on lithium-ion batteries is much better than the warranty on lead-acid batteries. This means for a lithium-ion solar battery, any defect during the 10 year period will be covered by the warranty. This means for a lead-acid battery that you have to pay out of pocket for any repairs needed on it during the ten-year period.
Cycle life
When you discharge a battery and then charge it back up with your solar panels, referred to as one charge cycle, we measure the lifespan of batteries not in terms of years but rather how many cycles they can handle before they expire.
Batteries used at a vacation home can typically last 4 years before their cycle count reaches 100; however, if used in full-time residences where they are cycling hundreds of more times per year than at vacation homes (300+), these same batteries will most likely not survive as long because this use creates higher loads on them during each charge/discharge cycles–the battery’s life is significantly reduced when it sees high numbers of cycles over its lifespan.
Depth of Discharge (DoD)
Depth of discharge means how much of the battery’s overall capacity is being used before recharging. This means that if you use more of the battery’s capacity, it will last longer because there are fewer cycles on it.
This means for a lithium-ion battery that if you discharge it to 80%, then the battery life cycle will be much more. This means that lead-acid batteries have less depth of discharge, and any usage over 50% could shorten its lifespan.
Battery efficiency
Lithium batteries are more efficient than lead acid. This means that you can store and use up to 95% of your solar power instead of only 80-85%.
For example, if there were 1,000 watts of energy coming in from the solar panel, only 800-850 watts are available in lead-acid due to a higher percentage loss; using lithium would mean having 950-watt hours available for use because they have less amount lost during this process.
Charge Rate
With higher efficiency comes a faster charge rate, which is an advantage of lithium-ion batteries. They can also handle higher temperatures from chargers, meaning they can be charged a lot faster than lead-acid battery systems.
Weight
Lithium-ion batteries weigh more per battery, but offer far more storage capacity per single battery.
The result is to get the same amount of storage capacity from your batteries, and there will need to be more lead-acid batteries resulting in much more weight.
Which one is better for me, lead acid or Lithium-Ion?
Lithium-ion batteries have a much higher upfront cost and will be recommended for full-time residences with a high cycle rate on the batteries. This means that if you plan to use your solar panels at a vacation home most of the year, then lead-acid batteries would be better because they cost less upfront and do not need to go through as many cycles.
Here are our recommendations for different types of residences.
Solar Battery Type Recommendations
| Residence type | Solar Battery |
|---|---|
| Grid-tied Full Time | Lithium-ion |
| Off-Grid Full Time | Flooded Lead-Acid (FLA) or Lithium-ion |
| Vacation home | Sealed Lead-Acid (SLA) |
| Battery Backup Only | Sealed Lead-Acid (SLA) |
How do I know what battery I need for my solar system?
As a homeowner, you need to know what kind of battery your solar panels are compatible with. Lithium-ion batteries are more efficient than lead acid but they’re also more expensive and can only be used in full time residences where there will be high cycle rates on the batteries (300+).
Lead-acid is less expensive upfront and if you plan to use your system at a vacation home then lead-acid would be better because they cost less upfront, and do not have to go through as many cycles like lithium ion systems.Especially sealed-lead acid (FLA) batteries can be a viable option because they offer most of the benefits of lead-acid without the maintenance.
