10 Things Being Missed Regarding Tesla’s Powerwall Battery

There is a lot of hype about the announcement of Tesla’s Powerwall Battery. Most of the press and social media postings are missing a few key points / questions.

Here are some important points to remember from a BC perspective:

• Battery storage for homes is not something new. It has been around for decades. There are probably hundreds of homes and cabins in BC with renewable energy and battery storage. We have installed a few of them ourselves. These include both off-grid and on-grid homes that use the batteries as a back-up when the grid goes down.
• Tesla’s battery is not cheaper than current options (despite what the press is saying). The 10kW battery pack is US$ 3,500. I just priced a battery pack of that size for a customer at C$ 2,100. It is not clear from Tesla’s announcement if this includes the the charge controller / battery automation system (BAS). This could add a considerable amount to the cost. Not to mention the costs of re-wiring for a critical loads circuit (which you normally need for battery back-up).  Lithium Ion batteries do have some advantages over lead acid batteries but there is an additional cost.
  Update: More recent information from Tesla indicates that the price does include the BAS.
• It is not the only game in town. From my perspective Enphase’s new battery pack is more interesting (works with micro-inverters and has a built in inverter!) although it doesn’t have a ship date yet: http://enphase.com/ac-battery/
  Update: Enphase has release more information and they won’t have an off-grid option which Tesla will.
• Many people are saying this battery will help people “go off the grid.” It might be good for people who are already off the grid. But for most people who are on the grid it is NOT a good idea to go off-grid. Going off grid means you need to size a system for the worst season (winter) and this means the system is over-sized for the summer. So you end up wasting energy. And this is bad for climate change, your bank account and the environment.
•  The spec page lists it as UL certified but not ULc or CSA. That will make it difficult to use in Canada (although new press reports say it will be available here in 2016).

There are also some technical questions that I have not seen the answer to yet:

• Is it just a battery pack or does it include a charge controller / BAS?  Some reports say it does but there hasn’t been much information on the specifications for this.
• What inverters will it work with? One report states that they will work SolarEdge inverters. But will it work with current models? Or just new models? There are hints it will work with other manufacturers as well. Will it?
• The battery pack has a high voltage 350-450 V which is good for AC conversion but higher than what a typical off-grid / grid inter-eactive inverter uses. So how will it work with current off-grid / grid-interactive inverters?
• If it is designed to work with regular grid inverters (which could accept the higher voltage) how does it handle things like the anti-islanding shut-down? The current SolarEdge inverters aren’t designed for the two circuits and automatic switch-over that you need for grid-tied battery back-up.
• Is a battery that is good for automotive use the best one to use for stationary storage? Some experts think not: http://blog.aquionenergy.com/three-reasons-why-the-lithium-ion-battery-chemistry-is-challenged-for-long-duration-energy-storage-applications (UPDATE: it seems that the Powerwall battery chemistry will be different then the car battery).

But hey, the battery pack does look cute.

This doesn’t mean that there aren’t some very good reasons to use this battery pack. In fact, we have already submitted a request to become an installer.  But as with any product we want to make sure customers understand the limitations and determine if it is the best solution for their needs.