The Tesla Powerwall 2: How it Works

Solar Panels With Battery Backup
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Although known for electric vehicles, the Tesla solar product line has gained significant traction. Many people have particular excitement over the company’s solar shingles and home battery.

Although solar shingles have struggled to take off, the Tesla home battery, the Powerwall, has become the best battery storage batteries on the market. The Powerwall illustrates Tesla’s passion for progression as a forward-thinking company.

Basic Tesla Powerwall 2 Features and Specs

As a leader in battery backup technology, Tesla has updated its original design. The new model can store twice as much power, has a built-in inverter, connects seamlessly with their app, has updated liquid cooling technology so it can perform in a range of temperatures, and it can mount both on the floor or the wall. 

Powerwall 2 has the following features, making it an optimal energy conservation method for homeowners. Tesla Powerwall 2 + Gateway Entails:

  • 5 kW Max Continuous Charge/Discharge
  • 13.5 kWh capacity
  • 7kW Max Peak for 10 seconds
  • Dimensions: 45.3in x 29.6 in x 5.75in
  • 30 amperes or less with 1 Powerwall
  • 2+ typically needed for whole-home backup.
  • Gateway = Brain of the Powerwall system
  • 10-year limited warranty.
  • Weight: 276 lbs.
  • Mounting Types: Floor and wall mount
  • AC Voltage (Nominal): 120/240 V
  • Internal Battery DC Voltage: 50 V
  • Grid Frequency: 60 Hz
  • Total Energy: 14 kWh
  • Usable Energy: 13.5 kWh
  • Max Continuous Power: 5 kWh
  • Peak Power: 7 kWh
  • Round-Trip Efficiency: 90%

How the Tesla Powerwall Works

While lots of energy storage options exist, home batteries typically use one of two main battery technologies. These include lithium-ion and lead-acid batteries.

Lead-acid batteries typically cost less. However, they also have a lower depth of discharge, a shorter lifespan, and weigh significantly more than lithium-ion batteries. So, although the lead-acid battery doesn’t cost as much up-front, in the long run, it costs more, which contributed to Tesla’s decision to use lithium-ion technology when it created their home battery.

How Many Powerwalls Needed to Power a Home

How many Powerwalls a home needs depends on how much energy the house typically uses. It’s also dependent on whether the homeowner wants to power essential loads during an outage or the whole home and how regularly this storage would be consumed.

Powering Essential Loads

If the customer determines they only want to power a couple of items in an outage, one Powerwall will do the trick. The combined power needs of the homeowner’s essentials need to equal less than the continuous power supply rating of the battery for it to power these loads for long periods.

Power for the Whole Home

Whole-home power refers to the number of batteries needed to keep a home running normally during an outage. The home battery needs of a house for a couple of hours won’t cover the home’s continuous power needs. Battery needs for both whole-home and continuous power depend on the energy usage of the house.

Mounting Styles for the Powerwall 2

The Powerwall 2 can mount either side-by-side or front-to-back. The number of Powerwalls and the mounting area determines the best mounting method.

Side-by-side mounts install each Powerwall along a wall. For this mount to work, the Powerwall needs room for ventilation and on each side for electrical connections.

Front-to-back mounts attach to the floor and a wall. Each stack can hold up to three Powerwalls.

The Tesla Mobile App

Once installed, the customer can use the Tesla mobile app to monitor their Powerwall. This app keeps track of the Powerwall’s use and allows owners to control it.

Federal Incentives for Battery Backup

If a customer purchases a Powerwall 2 with their solar array, they can qualify for the Federal Investment Tax Credit. Businesses purchasing solar and battery backup can also qualify for the Modified Accelerated Cost Recovery System (MACRS).

These incentives cover a chunk of the cost. Customers will want to remember it when they file their taxes the following year.

While available for all energy storage systems, these incentives have a couple of stipulations.

Qualifying for the Solar ITC

To qualify for the ITC, customers need battery backup and solar, or another qualifying renewable energy source, on-site. The combination of battery backup with solar passes the battery as part of a renewable energy option. Since batteries can store electricity no matter how it’s generated, batteries don’t qualify as a renewable energy option on their own.

Customers also have to own their solar arrays and battery backup solutions to qualify for the ITC. This requirement is one of the reasons why it’s better to own a solar array rather than leasing one.

Photo Credit: NREL

Determining the Powerwall’s Tax Credit

How much recharge the renewable source provides determines the incentive amount for the battery. To qualify for the tax credit, at least 75 percent of the battery needs to charge with a renewable source.

The battery will receive the same percentage of the ITC that it uses from renewable energy. For example, a home battery that pulls 75 percent of its charge from renewables will get 75 percent of the tax credit.

Battery Backup and MACRS

Only a private entity can qualify for the MACRS. Tax-paying businesses include one qualifying example.

Powerwall owners can have the MACRS regardless of whether they have solar. Those who only have battery backup can accept a 7-year MACRS, which equals 20 percent of the battery. Those who also qualify for the ITC can get a 5-year MACRS, equaling 21 percent of the battery costs.

The Downside of Waiting for Battery Backup

If an individual can qualify for solar, it’s in their best interest to install solar and battery backup sooner rather than later. One of the reasons for purchasing these products sooner rather than later has to do with the ITC phase-down.

In 2019 it decreased from 30 to 27 percent and after December 2020, it will decrease again to 22 percent. This could mean thousands of dollars of savings lost by not taking advantage of the opportunity sooner.

Lithium-ion Home Battery Competitors

While the Tesla Powerwall may come to mind first when thinking about home batteries, other home batteries also have a place on the market. Customers considering a home battery for their home have several different battery types and a selection of brands within each to consider.

Five categories help customers accurately compare competitors. These categories include capacity, depth of discharge, round trip efficiency, chemistry, and warranty. 

Capacity includes usable energy that the battery can hold. The depth of discharge tells how much energy it can use before the battery needs another charge. Round trip efficiency tells us how much power the battery loses each time it recharges. 

Chemistry, as stated earlier, can make a difference in the longevity of the battery. Most batteries use either Li-ion or Lead-acid technology. Lastly, interested parties should consider the battery’s warranty; a quality warranty has a long life and quality protection against possible issues.

Comparison of the Sonnen Home Battery

Sonnen currently has two home battery options. These include the Sonnen eco and the Sonnen ecoLinx.

The Sonnen eco has 5-20 kilowatt-hours of usable capacity. The Sonnen ecoLinx has usable capacity between 12 – 20 kWh.

The Sonnen eco has a continuous output of 3,000 – 8,000 watts of alternating current, which equals 3 to 8 kWh. The Sonnen ecoLinx has a continuous output of 8,000 watts of alternating current.

The peak efficiency of the eco and the ecoLinx equals 95 percent. However, each has differing cycles and warranties. The eco has a 10,000 cycle 10-year warranty, and the ecoLinx has a 15,000 cycle 15-year warranty.

Both of these batteries use Li-ion technology. They weigh less and have a higher depth of discharge and lifespan than comparable lead-acid batteries.

Sonnen EcoLinx Full Specs

  • Weight: 936 lbs.
  • Dimensions: (26 in x 84 in x 19 in)
  • AC Voltage: 240 volts
  • Grid Frequency: 60 Hz
  • Usable Energy: 12-20 kWh
  • Max Continuous Power: 8 kWh
  • Peak Efficiency: 95%
  • Warranty: 15-year or 15,000 cycles

The LG Chem RESU Home Battery Options

The LG Chem RESU batteries have gained a lot of traction lately. To better determine if this traction as any merit, let’s look at the specs for this battery.

LG offers five different battery sizes. These include RESU3.3, RESU6.5, RESU10, RESU7H and RESU10H.

Depending on the model, the LG Chem batteries have a capacity between 3.3 and 9.8 kWh. However, the depth of discharge ratings ranges from 2.9 to 9.3 kWh.

All LG Chem batteries use Li-ion technology with a 95 percent round trip efficiency. These batteries also have a 10-year 80 percent capacity warranty.

LG Chem RESU10H Full Specs

  • Weight:214-220 lbs.
  • Dimensions: (29.3 in x 35.7 in x 8.1 in)
  • Voltage range: 350-450 V and 385-550 V
  • Total Energy: 9.8 kWh
  • Usable Energy: 9.3 kWh
  • Max Continuous Power: 5 kWh
  • Peak Power: 7 kWh
  • Round Trip Efficiency: 95%
  • Warranty: 80% after 10 years

What Sets the Powerwall 2 Apart From the Competition

As a Tesla product, the Powerwall already has a reputation for quality. However, taking a closer look ensures that this home battery has everything you need.

The Tesla Powerwall has a usable capacity of 13.5 kWh with a continuous power supply of 5 kilowatts. It also has a depth of discharge of 100 percent, which means Powerwall owners can use all the energy from the battery before it needs to recharge.

The Powerwall also has a round-trip efficiency of 90 percent. The battery uses Li-ion technology and comes with a 10-year warranty. Although warrantied for 10 years, less use could make the battery last much longer.

Cost Savings of the Tesla Powerwall

Consumers care about the cost, especially for large purchases such as a home battery. However, the customer needs to consider how much of the price savings will cover the cost of the installation and product first.

How the Powerwall Pays for Itself

Even with incentives, a Powerwall will require some investment. When homeowners purchase a Powerwall, they invest in solar storage and the freedom and future savings it will offer.

A solar system can generate electricity all day, but as soon as the sun goes down, it can no longer produce power. Often people make up for this by staying connected to the grid.

However, those who stay connected to the grid without battery backup have net metering programs that don’t always benefit the customer. Often, utilities pay less for customer solar generation than what they charge for power pulled from the grid.

When you install a Powerwall, excess power is stored for later use, meaning you don’t have to worry about losing money to the utility. In fact, over time, you will recoup the money you spent on the home battery through savings on electric bills.

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