The Tesla Powerwall: How it Works

Solar Panels With Battery Backup
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Although Tesla is known for its electric vehicles, its solar product line has gained significant traction. Many people are excited about the company’s solar shingles and home battery.

Although solar shingles are struggling to take off, its home battery is rated one of the best on the market. Taking a look at the Powerwall illustrates why Tesla is such a forward-thinking company.

How the Tesla Powerwall Works

The Powerwall is a home backup battery. It, however, isn’t the only battery on the market.

In fact, there are not only different competitors. There are also different battery types.

Lithium-ion Batteries Vs. Lead-acid Batteries

There are two main battery types used for home battery backup. These include lithium-ion and lead-acid batteries.

Lead-acid batteries are cheaper. However, there are some pretty obvious reasons why.

Lead-acid batteries are large and heavy. They also have a lower depth of discharge and a shorter lifespan.

This means that although the lead-acid battery is cheaper, in the long run, it actually will cost more. This is why when Tesla created their home battery they made sure it was a lithium-ion battery.

Inner Workings of the Powerwall: a Lithium-ion Battery Par Excellence

Let’s take a look at the basics of how a lithium-ion battery works. In a lithium-ion battery, this movement is set in motion by the movement of lithium ions across the battery. For reasons beyond the scope of this piece, using a Li-ion battery is the better option.

The Powerwall is a Li-ion battery. Inside the Powerwall, there is a connection point, a liquid-cooling inverter, and a battery pack.

The connection point allows the Powerwall to connect a home to the solar array. The liquid cooling keeps the battery from overheating. Lastly, the inverter converts direct current in the battery to alternating current for home use.

How Many Powerwalls Needed to Power a Home

How many Powerwalls needed depends on how much energy the home typically uses. It’s also dependent on whether the homeowner wants to power essential loads during an outage or the whole home on a regular basis.

Powering Essential Loads

If the customer determines they only want to power a couple of things in an outage, one Powerwall will do the trick. The combined power needs of your essentials need to be less than the continuous power supply of the battery.

Power for the Whole Home

Whole-home power refers to the number of batteries needed to power an entire home during an outage. This is still less than the number of batteries needed to continuously power a home.

Mounting Styles of the Powerwall

There are several ways to have the Powerwall mounted. These include side-by-side and front-to-back mounts. The number of Powerwalls and the area it is being mounted to determines which method is best.

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

Front-to-back mounts are mounted to the floor and a wall. There can be up to 3 Powerwalls in each stack.

The Tesla Mobile App

Once the Powerwall is installed the customer is ready to use the mobile app. This app keeps track of when the Powerwall is being used and allows owners to control its use.

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 and the Modified Accelerated Cost Recovery System.

This is a huge chunk of the cost. Customers will want to remember it when they file their taxes the following year.

These incentives are available for all energy storage systems. There are, however, a couple of stipulations.

Qualifying for the ITC

To qualify for the ITC customers need battery backup and solar, or other qualifying renewable energy, on-site. This is because batteries are not considered a renewable energy option on their own.

To qualify customers to have to own their solar array and battery backup. This is one of the reasons why owning a solar array is better than leasing one.

Photo Credit: NREL

Determining the Battery’s Tax Credit

How much of the incentive a battery will qualify for is determined by how much of it is recharged with renewable sources. To qualify for the Tax credit at least 75 percent of the battery needs to be charged with a renewable source.

The battery, however, will only get the percentage of the ITC that it pulls from renewable energy. For example, a battery that pulls 75 percent of its charge from renewables will get 75 percent of the tax credit. Because the credit is currently 30 percent this would equal 22 percent of the battery covered by the tax credit (.75 x .30 = .22).

This credit will not give the owner more than they own in a tax year. To compensate for this, the tax has a rollover period of 5 years.

Battery Backup and MACRS

To qualify for the MACRS the owner needs to be a private entity.  Taxpaying businesses are one example that would qualify.

Battery owners can get the MACRS regardless of whether they have solar. Those that only have battery backup can get a 7-year MACRS. Which is equivalent to 20 percent of the battery. Those that also qualify for the ITC can get a 5-year MACRS. This equals 21 percent of the battery costs.

The Detriment of Waiting on Solar Backup

If an individual can qualify for solar, it is in their best interest to get solar and battery backup sooner rather than later. This is because the ITC is going to phase out.

In 2019 it is set to decrease from 30 to 27 percent. This could mean thousands of dollars of savings lost by not taking advantage of the opportunity sooner.

Home Battery Competitors

Although the Powerwall is the best home battery on the market, it isn’t the only one. To determine which home battery is best, there are six categories to compare. These categories include capacity, depth of discharge, round trip efficiency, chemistry and warranty.

Capacity is the amount of usable energy that the battery can hold. The depth of discharge tells how much of that energy can be used before the battery needs to be recharged.

Round trip efficiency is how much power is being lost each time the battery is recharged. A high charge round trip efficiency is ideal.

The chemistry of the battery, as stated earlier, can make a difference in the longevity of the battery. Most batteries are either Li-ion or Lead-acid. The last thing to consider is the battery’s warranty; a quality warranty is long-lasting and will protect the customer 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 5-15 kilowatt-hours of usable capacity. The Sonnen ecoLinx’s usable capacity is between 10 – 20 kWh.

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

The efficiency of the eco and the ecoLinx is 93 percent. However, their cycles and warranties are different. The eco has a 10,000 cycle 10-year warranty and the ecoLinx has a 15,000 cycle 15-year warranty.

Last of all is the chemistry of the batteries that Sonnen offers. Both of these batteries are Li-ion batteries. This means that they are lighter and have a higher depth of discharge and lifespan than comparable lead-acid batteries.

Sonnen EcoLinx 20 Full Specs

  • Weight: 950 lbs
  • Dimensions: (26 in x 83 in x 14 in)
  • AC Voltage (Nominal): 120/240 volts
  • Grid Frequency: 60 Hz
  • Usable Energy: 20 kWh
  • Max Continuous Power: 8 kWh
  • Round Trip Efficiency: 86%
  • Warranty: 15-year or 15,000 cycles

Taking a Look at the LG Chem RESU Home Battery

The LG Chem RESU batteries have gained a lot of traction lately. Let’s take a look at the specs for this battery to better determine if this traction has any merit.

There are five different sizes of batteries available. These include RESU3.3, RESU6.5, RESU10, RESU7H and the RESU10H.

Depending on the model that is chosen, the LG Chem batteries have a capacity between 3.3 and 9.8 kWh. However, the depth of discharge is less. LG’s smallest battery’s depth of charge is 2.9 kWh and the largest battery has a depth of charge of 9.3 kWh.

All LG Chem batteries are Li-ion. They have 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 Apart From the Competition

Because the Powerwall is a Tesla product, it already has a reputation for quality. However, taking a deeper look ensures that this home battery really is the top of the line in terms of what you personally 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. This means Powerwall owners can use all the energy from the battery before it needs to be charged.

The Powerwall also has a round-trip efficiency of 90 percent. The battery is a Li-ion battery with a 10-year warranty. Although it is warrantied for 10 years, depending on how regularly it is used, the battery could last much longer.

Tesla’s Powerwall 2 Full Specs

  • Weight: 276 lbs.
  • Dimensions: (45.3 in x 29.7 in x 6.1 in)
  • 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%
  • Warranty: 10-year

Cost Savings of the Tesla Powerwall

How much something costs is one of the most pressing questions that consumers have. This is especially true for large purchases such as a home battery. However, what needs to be taken into consideration is how much of that price is going to be made up for in the savings.

How the Powerwall Pays for Itself

Even with incentives, purchasing a Powerwall is an investment. However, this is an investment that is well worth the money. When homeowners purchase a Powerwall for their home they are investing in solar storage.

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

The problem is that net metering programs are not always fair to customers. Often, utilities pay less for customer solar generation then what they charge for power pulled off the grid.

When you install a Powerwall, you are able to store your excess power for later use. This means you don’t have to worry about losing as much 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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