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Lead-Acid vs Lithium Batteries: Which Are Best For Solar?

Lead-Acid vs Lithium Batteries: Which Are Best For Solar?

Lead-acid vs. Lithium Battery Comparison

Lead-acid batteries cost less up front, but they have a shorter lifespan and require regular maintenance to keep them running properly. Lithium batteries are much more expensive up front, but they are maintenance-free and have a longer lifespan to match their higher price tag. This article offers a side-by-side comparison of both options.

Welcome to our Solar 101 series! This article goes over a choice you’ll need to make if you buy a battery-based solar system, either to move off the grid or to add energy storage to your grid-connected home.

Specifically, we’re going to look at lead-acid vs. lithium-ion batteries — the two main battery types used for solar. Here’s the summary:

Lead-acid is a tried-and-true technology that costs less, but requires regular maintenance and doesn’t last as long.

Lithium is a premium battery technology with a longer lifespan and higher efficiency, but you’ll pay more money for the boost in performance.

Let’s go over the pros and cons of each option in more detail, and explain why you might choose one over the other for your system.

Lead-acid vs. Lithium Solar Batteries: The Basics

When you build a solar system, you have three main battery options:

Flooded Lead-Acid (FLA)

The distinguishing feature of FLA batteries is that the plates are submerged in water. These must be checked regularly and refilled every 1-3 months to keep them working properly.

Falling behind on upkeep can shorten the life of the batteries and void the warranty. FLA batteries also need to be installed in a ventilated enclosure to allow battery gases to escape.

Sealed Lead-Acid (SLA)

SLA batteries come in two types, AGM (Absorbent Glass Mat) and Gel, which have many similar properties. They require little to no maintenance and are spill-proof.

The key difference in AGM vs. gel batteries is that gel batteries tend to have lower charge rates and output. Gel batteries generally can’t handle as much charge current, which means they take longer to recharge and output less power.

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Lithium

The best lithium battery chemistry for solar applications is Lithium Iron Phosphate, shorted to LiFePO4 or LFP batteries. This new technology lasts longer and can be put through deeper cycles. They also require no maintenance or venting, unlike lead-acid batteries.

Lithium batteries cost more up front, but the extra efficiency means you can potentially spend less per kilowatt-hour of capacity over the lifespan of the battery.

Lead-acid vs. Lithium Batteries: Pricing Breakdown

Let’s look at how much it would cost to build a battery bank with all three options.

We’re not just interested in the up-front cost, but also the cost of ownership over the life of the system. As an example, we’ll look at how much the batteries would cost to power this 5.13 kW off-grid system, which we sell for $12,899 at the time of publication.

In an off-grid environment, you want to look at the estimated cycle life since you are cycling your batteries on a daily basis. This system would produce an estimated 23.08 kWh per day in the summer and 11.54 kWh per day in the winter.

Here’s how much it would cost to buy batteries for that system over the first 10 years. We are comparing the following battery banks:

Lead-Acid vs. Lithium Batteries: Cost Breakdown

A Few Notes About This Chart

We are estimating that the lead-acid batteries will be replaced 3 times over a 10 year period, the lifespan of 1 lithium battery. This comparison is based on the length of the warranty offered by the manufacturers.

We’ve done our best to give an apples-to-apples comparison of these batteries based on their printed specs. However, in real-world applications, factors like discharge depth, temperature, charging source, overall system design, and your willingness to perform regular maintenance will affect the true performance of your batteries.

5 Key Differences Between Lead-acid and Lithium Batteries

1. Cycle life

When you discharge a battery (use it to power your appliances), then charge it back up with your panels, that is 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.

Think of it like putting mileage on a car. When you evaluate the condition of a used car, mileage matters a lot more than the year it was produced.

Same goes for batteries and the number of times they’ve been cycled. A sealed lead-acid battery at a vacation home may go through 100 cycles in 4 years, whereas the same battery might go through 300+ cycles in one year at a full-time residence. The one that has gone through 100 cycles is in much better shape.

Cycle life is also a function of depth of discharge (how much capacity you use before recharging a battery). Deeper discharges put more stress on the battery, which shortens its cycle life.

2. Depth of Discharge

Discharge depth refers to how much overall capacity is used before recharging the battery. For example, if you use a quarter of your battery’s capacity, the depth of discharge would be 25%.

Batteries don’t discharge fully when you use them. Instead, they have a recommended depth of discharge: how much can be used before they should be refilled.

Lead-acid batteries should only be run to 50% depth of discharge. Beyond that point, you risk negatively affecting their lifespan.

In contrast, lithium batteries can handle deep discharges of 80% or more. This essentially means they feature a higher usable capacity.

3. Efficiency

Lithium batteries are more efficient. This means that more of your solar power is stored and used.

As an example, lead acid batteries are only 80-85% efficient depending on the model and condition. That means if you have 1,000 watts of solar coming into the batteries, there are only 800-850 watts available after the charging and discharging process.

Lithium batteries are more than 95% efficient. In the same example, you’d have over 950 watts of power available.

Higher efficiency means your batteries charge faster. Depending on the configuration of your system, it could also mean you buying fewer solar panels, less battery capacity and a smaller backup generator.

4. Charge Rate

With higher efficiency also comes a faster rate of charge for lithium batteries. They can handle a higher amperage from the charger, which means they can be refilled much faster than lead-acid.

We express charge rate as a fraction, such as C/5, where C = the capacity of the battery in amp hours (Ah). So a 430 Ah battery charging at a rate of C/5 would receive 86 charging amps (430/5).

Lead-acid batteries are limited in how much charge current they can handle, mainly because they will overheat if you charge them too quickly. In addition, the charge rate gets significantly slower as you approach full capacity.

Lead acid batteries can charge around C/5 during the bulk phase (up to 85% capacity). After that, the battery charger automatically slows down to top off the batteries. This means lead acid batteries take longer to charge, in some cases more than 2x as long as a Lithium alternative.

5. Energy Density

The lead-acid batteries featured in the comparison above both weigh around 125 pounds. The lithium battery checks in at 192 pounds.

Most installers can handle the extra weight, but DIYers might find the lithium batteries more challenging to install. It’s wise to enlist some help lifting and moving them into place.

But that comes with a tradeoff: the energy density of lithium batteries is much higher than lead-acid, meaning they fit more storage capacity into less space.

As you can see in the example, it takes two lithium batteries to power a 5.13 kW system, but you’d need 8 lead-acid batteries to do the same job. When you take the size of the entire battery bank into account, lithium weighs less than half as much.

This can be a real benefit if you need to get creative with how you mount your battery bank. If you are hanging an enclosure on the wall or hiding it in a closet, the improved energy density helps your lithium battery bank fit into tighter spaces.

Lithium vs. Lead-Acid: Which Should You Choose?

Lithium and lead-acid grade out at comparable prices over the life of ownership, but lithium is a much steeper investment up front. We wouldn’t recommend it unless you use your system on a daily basis.

Here are the battery types we’d recommend for a variety of applications:

Full-Time Off-Grid Residence

Flooded Lead-Acid or Lithium.

If you live off the grid full-time, your best bet is FLA (if you don’t mind regular maintenance) or the premium Lithium option for heavy use.

Off-Grid Cabin / Vacation Home

Sealed Lead-Acid.

If you own something like a hunting cabin or a vacation home, you’ll only be there a few times a year. That means you won’t be able to keep up with the maintenance required of FLA batteries.

Spend a bit extra on SLA instead. They’re zero-maintenance, so they won’t die if they sit idle for a few months.

Battery Backup System

Sealed Lead-Acid.

Let’s say you are building a system with battery backup for emergency power outages. Ideally, you will only use those batteries once a year (a few times if you live in an area with an unreliable power grid). They won’t see enough use for you to invest into lithium, and you don’t want to perform maintenance on FLA batteries you use once a year.

Go with SLA, which (again) don’t require upkeep.

Remote Industrial Use

Sealed lead-acid or lithium.

The decision-making process is pretty much the same here. Lithium could be worth it to power an industrial site that sees heavy use. If you are powering basic monitoring equipment at a remote outpost, SLA will get the job done cheaper, and you still won’t have to worry about maintenance visits.

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Grid-tied vs. off-grid solar: are you sure you want to live off the grid?

Grid-tied vs. off-grid solar: are you sure you want to live off the grid?

Let’s clear up one of the most common misconceptions in the solar industry: the idea that you must go “off the grid” to go solar.

This article will explain the different types of solar power systems: grid-tied vs. off-grid.

Many people call us looking for help going “off the grid.” But when we explore their motivations a bit more, we find that what they actually want is to ditch their utility company.

Really, they want to go solar to be independent, generate their own power, and stop paying money to the utility every month.

If this sounds like you, read on. Because you can accomplish all these things without going off the grid. It’s called grid-tied solar, and it’s the preferred type of solar system for any property that has access to power lines.

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Why? Because it’s cheaper. No, really, it’s a lot cheaper. You should always build a grid-tied system when you have the option to do so.

Let me explain why.

Grid-tied vs. off-grid: what do these terms really mean?

The difference between grid-tied and off-grid solar revolves around where you store the energy you generate.

Every system needs a place to store energy so that it can be used on demand. Your panels only generate charge when the sun is out during the day, but you still need a way to turn the lights on in the evening.

With grid-tied systems, the energy you generate is sent into the utility grid. Your panels feed electricity into the grid, which can be distributed to other people in your area.

In return, you receive a credit for the energy you generate, which you can use any time. Think of it like a transaction at the bank: you are allowed to withdraw as much as you deposit. This is what allows you to keep the power on when the sun goes down.

Off-grid systems are different. With no access to the utility grid, you must find another solution to store energy.

For that, you’ll need to add a battery bank to your system. Batteries provide dedicated energy storage. Without any access to power lines, batteries are mandatory for off-grid solar systems.

In summary: grid-tied systems store energy in the power grid, while off-grid systems store energy in batteries.

When in Doubt, Go Grid-Tied

It doesn’t cost anything extra to store electricity in the grid. But adding batteries to an off-grid system is a significant extra cost.

In fact, batteries are the most expensive part of a solar system. They represent as much as 30-40% of the cost of an off-grid system.

Batteries alone are a 4-5 figure investment. For that simple reason, we always recommend connecting a grid-tied system if you have the option.

Why spend thousands of dollars on batteries if you don’t need them?

Browse grid-tied system packages in our shop.

What about Energy Storage Systems?

Right now you might be thinking, “what if I’m connected to the grid but still need energy storage?”

For that, there’s a third system type. It’s called grid-tied with battery backup (a.k.a. energy storage systems).

These systems connect and store energy in the grid, but they also include batteries. There are two reasons you might want to add energy storage to a grid-tied system:

  • Store backup power in case of outages (useful if you live in an area with an unreliable power grid or severe weather)
  • Store energy so you can use it or sell it later (useful if you live in an area with a certain utility billing structure, such as time of use rates, high demand charges, or no net metering)

The same caveats apply: batteries aren’t cheap, and adding them to your grid-tie system lengthens your payback period. But in some places, it’s invaluable to add security against harsh weather, outages, and inflated electricity costs.

Energy storage systems provide extra peace of mind and help you get the most out of the electricity you generate. It’s up to you to decide if it’s worth it to spend more on your system for the added flexibility.

Browse grid-tied systems with battery backup in our shop.

Continue Your Research

Have any more questions about the process of going solar? Check out our Getting Started Guide, a crash course on the basics of designing and installing your solar energy system.

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What is a kilowatt hour?

What is a kilowatt hour?

Kilowatt hours measure energy usage and production.

If you’re thinking about going solar (or just want some advice on how to reduce your energy consumption), you’ve probably come across the term kilowatt-hours.

But exactly what is a kilowatt hour? And why do we need to know how many we use each month?

First things first: What is a kilowatt hour?

A kilowatt-hour (kWh) is a measure of how much energy you use over a set period of time. It determines how much you pay for electricity each month, since the utility company bills you on a cost-per-kWh basis.

Here’s how it works.

Every appliance has a rating which measures how many watts of power it uses. For example, an oven may be rated at 2000 watts, or 2 kilowatts. (1 kilowatt equals 1000 watts.)

If you cook something in that oven for 30 minutes, here’s how to calculate the total energy used:

2 kilowatts x 0.5 hours = 1 kilowatt-hour (kWh) of energy used.

To determine how many kilowatt-hours an appliance uses, simply estimate how long you use it each day, then multiply by the wattage rating.

Easy so far. But how can you use this information?

Measuring Electricity Cost Per kWh

Utility providers track your usage with a meter and bill you based on total kilowatt-hours consumed.

In America, the average cost of electricity is about 12 cents per kWh. However, that can fluctuate based on where you live as well as what time of day you use the electricity.

Many utility providers bill variable rates for Time of Use (called TOU rates). If you are familiar with the concept of surge pricing, that’s what this is: electricity costs more when lots of people are using it.

There’s less demand during the day, so the rate is lower. When people come home from school and work, the rate goes up because the demand is higher.

You can usually find the breakdown of TOU rates on your utility provider’s website, or right on the electric bill.

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But it might be quicker to measure how those costs average out based on your usage patterns. Divide your monthly payment by your total kWh usage to get your average cost of electricity:

$130 electric bill / 1,237 kWh used = 10.51 cents per kWh

How Kilowatt Hours Factor into Solar System Sizing

Understanding kilowatt hours is key to being able to design a system that works. Without that information, your system might be too small to cover your entire energy bill (or too large, in which case you’re just throwing money away and diluting the value of your investment).

So we use your kilowatt-hour usage as the starting point in the system design process. Once you know how much energy you use, you can size your system components to match usage demands.

Our solar cost calculator can provide a ballpark system size and cost based on your kWh usage. You can also read about the math behind this formula in full detail in our article: “How Many Solar Panels Do I Need?”

To get an accurate calculation, there are a few things to take into account:

  • Average monthly usage
  • Peak usage (it will spike when it’s snowing or 100 degrees outside)
  • Future changes in energy usage patterns

Your system should be sized to cover you year-round. Make sure to take a year’s worth of usage into account, since freezing winters and 100+ degree summers tend to skew the usage data.

Also, carefully consider whether your usage will increase in the future. If you plan to have kids, build a new shed on your property, or buy an electric vehicle, those things will eat up a lot more energy and your kWh usage will climb.

You don’t need to build for future usage now, but it helps to plan your system with expansion in mind. Certain pieces of equipment are designed to facilitate expansion, like microinverters and lithium batteries.

Read more: Best Grid-Tie Solar Inverters >> | Best Solar Batteries >>

Why Kilowatt Hour Usage Is So Important For Off-Grid properties

When you’re connected to power lines, finding all this information is simple. Just grab your latest electric bill. Your provider prints your kWh usage on your bill every month, and some list their cost-per-kWh rates as well.

This makes it easy to do the math on system size. You can also drop the number into our solar cost calculator for a quick ballpark cost and sizing estimate.

Off-grid systems are different.

When you go off the grid, you likely won’t have a precedent to figure out how much energy you will use. Instead, you’ll need to fill out a load evaluation sheet, listing each appliance manually and estimating how much you will use them each day.

Daily kWh usage is crucial to building a system that can supply uninterrupted power to your off-grid property.

You don’t want to look at your yearly usage, but rather your needs on a day-to-day basis. The goal is to store enough power to cover yourself if any problems arise (like severe weather or equipment failure).

People tend to store about a day’s worth of power in their battery bank, and lean on a generator for backup. But you can plan for more cushion with your battery bank if you want the extra peace of mind.

To estimate daily usage, find the kWh usage (wattage x hours in use each day) for every large appliance in your off-grid home and add them all together.

The total is your daily usage, which can be used as the basis to size your system:

Daily kWh Usage ÷ Sun-Hours ÷ 0.9 (inefficiency factor) = Minimum Solar Array Output

How to Estimate Solar Cost Based on Kilowatt Hour Usage

Got your kWh usage on hand? Plug that info into our solar cost calculator to see how much it might cost you to go solar.

Grid-tied systems tend to pay for themselves quickly. It’s reasonable to expect to break even on your investment within 5 years.

Off-grid systems cost more and come with different expectations. Unlike grid-tie systems, the value in off-grid systems isn’t necessarily making a profit from your investment.

Instead, it should be viewed as a means to generate energy where there is no access to power lines. To determine whether off-grid solar is the right choice, you should compare it against the cost of other methods to generate power, like wind turbines or gas generators.

Interested in solar, but not quite sure where to start? Download our Getting Started Guide to get up to speed with the essentials.

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