Battery Backup Comparison: Power eVault vs. Powerwall

Fortress Power eVault vs the Tesla Powerwall 2: Solar Battery Product Comparison

The Powerwall has become the battery associated with residential solar. However, it isn’t the only home battery option. Fortress Power has come out with a line of solar batteries. Let’s compare their home battery, the eVault, and see what it has to offer.

Comparing Battery Backup Types

First, it’s important to note that while both the Powerwall and the eVault use lithium batteries, they aren’t the same type. Each lithium battery type performs a little differently. This difference in function makes knowing the battery type vital for those trying to decide which battery to use. 

Power eVault Battery Type: Prismatic Lithium Iron Phosphate

The Fortress Power eVault uses a prismatic lithium iron phosphate battery. Prismatic battery cells use a layering approach to optimize space. While this packaging saves room, it can also have reduced thermal efficiency and shorter life cycles. As a Li-iron battery, the eVault uses Iron phosphate as the cathode. This battery type has better longevity and safety than other ion batteries. However, it also has lower specific energy, with an average voltage of 3.2V/cell, than cobalt blended lithium-ion batteries and a tendency to self-discharge. 

Tesla Powerwall 2 Battery Type: Lithium-Ion NMC Battery

The Tesla Powerwall uses lithium nickel-manganese-cobalt-oxide (NMC) batteries. These batteries use the combination of nickel manganese and cobalt as the cathode. These batteries have overall good performance. They have become the preferred choice for electric vehicles and now solar batteries.

Solar Battery Capacity and Power Ratings

While many factors go into a battery, those deliberating over their solar battery options should consider the capacity and power ratings. Capacity shows how much electricity the battery can store. The max power rating on a battery indicates the maximum withdrawal rate. Together these ratings help customers determine which battery will work best for their energy needs.

What Are KWhs (Kilowatt Hours)?

In understanding solar batteries for the home and in comparing these 2 products, let’s break down what this term means first. Kilowatt-hours are an expression of the capacity of an equipment’s run time and, in a sense, power. E.g., if you have a 5-kilowatt solar system installed on your home, and it runs for 12 hours while the sun is shining, that is 60 kilowatt-hours of solar energy produced by that solar array in the allotted timeframe. To learn more about solar definitions and terminology, visit our glossary page at the button below.

Fortress Power eVault Ratings

The eVault has 18.5 kWh (kilowatt-hours) of total capacity. This capacity has the potential to expand to 222 kWh when multiple batteries are conjoined. Additionally, power in this battery can withdraw at a rate of 9 kW.

Comparing Tesla Powerwall Specifications

The Powerwall has 13.5 kWh of usable capacity with the ability to expand to 135 kWh. It can discharge at up to 5kW, which increases with each additional battery to a max of 50 kW.

Other Features to Consider

While capacity and power help homeowners determine how many batteries they would need, they aren’t the only factors to consider. The warranty, round-trip efficiency, and usability of each battery also play a role in the buyer’s decision.

Tesla Vs. Fortress Power: Warranty Comparison

Tesla offers a 10-year limited warranty at 70 percent. Fortress Power offers a 10-year or a throughput warranty of 6,000 cycles at 80 percent or 2,000 cycles at 100 percent. Because the eVault has more storage capacity, each cycle would provide more power, but the guarantee of ten years, regardless of how many cycles the battery has, is hard to beat.

Comparing Round-trip Efficiency

Round-trip efficiency includes the percentage of usable storage. The eVault has 97 percent round-trip efficiency, whereas the Powerwall offers 90 percent.

Considering Battery Usability

Often ease of use factors into the buying decision. If two products have similar specs, but the other has features that allow for easy use, it often outwins its competitor.

Battery Weight and Size

The weight and bulk of each battery contribute to the ease of use. Each Powerwall weighs 276 lbs. and takes up 45.3 in x 29.6 in x 5.75 in. The eVault weighs 476 lbs and takes up 38.8 in x 19.2 in x 21.3 in. Thankfully, the eVault also comes with casters, but it’s still tremendously heavy and bulky.

Monitoring Apps

Monitoring apps allow the owner to see battery activity and remotely control when it charges and discharges. The Powerwall connects to the Tesla app, where it can easily monitor and control the Powerall and prep for potential threats with the storm watch feature and preheat or cool the battery during inclement weather. Currently, the eVault has closed-loop communication between the battery, the inverter, and other connected batteries. These batteries don’t have a monitoring app yet, but Fortress Power plans to create one.

The Best Application for Each Battery

The Fortress Energy home battery has a larger capacity and withdrawal rate. However, depending on the homeowner’s needs, this much power in one battery may go to waste when applied to residential solar.

The eVault works best for commercial applications. However, if you use a lot of electricity and have a home that already has or will have one of Fortress Power’s approved hybrid inverters, the eVault is worth considering.

The Powerwall does a better job at tackling home battery energy needs in manageable chunks. Homeowners who want to power their entire home often install between two and three Powerwalls; for a total capacity between 27 and 40.5 kWh. The large storage potential of each eVault makes accurately scaling power harder for homeowners.


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