Tesla drives towards domestic battery storage

8 October 2015

The US electric car manufacturer Tesla Energy has launched a range of rechargeable lithium-ion storage batteries scaled for homes and businesses. It can, says Tesla, also be scaled to much larger sizes for use by utilities. The basic packs are intended to enable owners to store cheap rate electricity or renewable energy to manage power demand, provide backup power and increase grid resilience.

It is designated 'Powerwall' and consists of Tesla's battery pack, a thermal control system, and software that receives dispatch commands from a solar inverter. The unit mounts on a wall and is integrated with the local grid. Its benefits to the customer are said to be in power costs and flexibility. They include load shifting - charging during low rate periods and discharging during more expensive rate periods - increasing the self- consumption of solar power generation by storing surplus solar energy not used at the time it is generated, and back-up power, to use in the event of an outage.

The Powerwall is available rated at 10 kWh, primarily for backup applications, or 7 kWh for daily cycling. Both can be connected to solar generation or to the grid and both can provide backup power. Both are rated at 2 kW continuous power, 3 kW peak power with a round trip efficiency of >92%. Operating temperature range is -20°C (-4°F) to 43°C (110°F). Tesla's USA selling price to installers is $3500 for the 10 kWh unit and $3000 for 7 kWh, excluding the inverter and installation cost. Deliveries are due to begin in late summer in the USA and in the UK before the end of the year.

Type of cell

Tesla has not yet specified the kind of Li- ion cell to be supplied (LiCoO2, lithium iron phosphate, lithium manganese oxide lithium sulphur etc) although it is known that initially at least it will be supplied by Panasonic, which is a Tesla shareholder. Tesla is believed to be negotiating with other suppliers owing chiefly to the high volume of demand that it anticipates.

Battery lifetime (ie the number of discharge cycles) is implied by a warranty of 10 years and a suggestion of daily cycling, but not specified. A recent study (by Andreas Gutsch, Karlsruhe Institute of Technology) suggests that Li-ion storage battery lifetime could vary by a factor of five, from 1000 cycles to 5000 cycles. The study estimated that batteries with lifespans of 3000 cycles would be needed for profitable operation.


In February last year the California Public Utilities Commission ordered the state's investor-owned utilities to jointly purchase more than 1.325 GW of electricity storage by 2020, virtually creating a market overnight. Later that same month Tesla CEO Elon Musk revealed his plans to open a US$5 billion 'gigafactory', at an unspecified location in America's southwest, to make advanced batteries for its next generation of vehicles, and to supply lithium-ion batteries for stationary storage applications. Reportedly at about that time Tesla started a rumour that the new factory would be needed to manufacture batteries because Panasonic would not be able to keep up with Tesla's demand. There is some warrant for this - Elon Musk's ambition is to produce 500 000 plus cars a year eventually, but even the present rate of production is using up all the cells it can supply, according to Panasonic.

Tesla sees the giant plant as key to reducing battery prices and making electric vehicles more affordable. By the time it reaches full production in 2020, the proposed plant would annually produce enough batteries for 500 000 cars while its economies of scale could cut battery costs by more than 30%.

Industry reaction

The reaction from industry and business has sounded warning notes. Monica Giulietti of Warwick Business School in the UK said: "This is an interesting development ... Tesla's involvement in the stationary storage market can support the progress towards affordable storage by [exploiting] their expertise in battery technology ... but there are ... risks involved, that the battery technology is superseded by more efficient systems such as fuel cells and that the majority of potential consumers will not be prepared to invest ... due to the risk of being locked in with an obsolete technology."

Lux Research in Boston believes that to truly disrupt stationary energy storage, Tesla would need more partnerships and acquisitions in power electronics, software, and with utilities.

“Cheap cells ... are only part of the puzzle," said Dean Frankel of Lux Research. "Unlike electric vehicles, in stationary batteries there is more of a relative cost contribution coming from power electronics, software, and installation. Without more vertical integration - and perhaps even some acquisitions and Gigafactory-like efforts dedicated to inverters - Tesla is limiting its growth potential here."

At $350/kWh, Tesla is the industry's current price leader for stationary Li-ion packs. Consumers will also need to pay for an inverter, installation, and other costs, which altogether will nearly double the $3000 price of the entry-level unit. Tesla, says Lux, will need to push their power electronics and installation partners to cut their costs further - or do that itself, either in-house or via acquisitions.

Business and utility

Tesla offers systems based on its electric vehicle components that integrate batteries, power electronics, thermal management and controls into a turnkey system. These are aimed mainly at businesses with solar arrays, to create a hybrid that can reduce costs by storing excess solar energy for later use, especially at times of peak demand. Last year, the company supplied battery packs of this kind to SolarCity in San Mateo.

For utility scale systems, 100 kWh battery blocks are grouped to scale from 500 kWh to 10 MWh+. These systems are capable of 2 hr or 4 hr continuous net discharge power using grid tied bi-directional inverters. Systems support applications include peak shaving, load shifting and demand response for commercial customers and renewables firming and a variety of grid services at utility scales - increasing resource capacity via instantly available distributed power, to add grid resiliency, ramp control by providing a buffer while the power output from a large generation source is ramping up or down, and improving power quality by preventing fluctuations from propagating to downstream loads.

Utility projects

Tesla aleady has storage projects ongoing with a number of utilities including Oncor (microgrid) and AES (solar hybrid) but the most advanced seems to be that with Southern California Edison which has developed the USA's largest battery storage system and has contracts in place for an additional 264 MW of storage, including projects using Tesla batteries. SCE is working with Tesla on three demonstration projects that are intended to help drive down the cost of battery storage systems.


First published in June 2015

Battery The Powerwall unit
Battery Table 1. Powerwall specifications
Battery Utility scale battery storage

Linkedin Linkedin   
Privacy Policy
We have updated our privacy policy. In the latest update it explains what cookies are and how we use them on our site. To learn more about cookies and their benefits, please view our privacy policy. Please be aware that parts of this site will not function correctly if you disable cookies. By continuing to use this site, you consent to our use of cookies in accordance with our privacy policy unless you have disabled them.