The debut of the Tesla Powerwall has made quite a splash in many circles. Claiming to outperform current battery systems for solar, it has the potential to make a large impact on the storage side of the production of solar energy. I had the chance to speak with Christopher LaForge, a PV battery expert with more than 20 years of experience working with many types of PV systems and the instructor of the HeatSpring course Batteries in Solar PV Systems. He is the CEO and founder of Great Northern Solar as well as a NABCEP certified solar PV installer. He’s been living on his property, completely powered by solar, in northern Wisconsin for more than 24 years. You can click on the following clip to listen to the full interview, or read a written summary of Christopher’s responses below.



Q: What’s different or what does the Powerwall change?

Elon Musk and Tesla are taking on climate change head on. He made it very clear in the keynote debut of the product that this is very much aimed at helping combat climate change. The new batteries, which are lithium ion, will hopefully bring the price of systems down, as well as making installation and maintenance more amenable to users and help make the systems easier to implement.

Q: What makes this technology different than current battery systems?

Lithium-ion batteries are dry cell batteries, so, unlike lead-acid batteries, you don’t need to add distilled water to them, making it a bit more user friendly. While lithium-ion batteries have the possibility of overheating when they discharge too quickly, reports so far seem to indicate that this risk is controlled for in the batteries. The Tesla is also guaranteeing 10 years for the Powerwall battery, which could be as much as 2-3 times the life of lead-acid batteries, depending on user maintenance.

Each battery is listed as a 10 kWh unit, meaning that one battery is about one-third of the 30 kWh that the average residential household uses each day. The system’s ability to connect several batteries and scale is a major positive aspect of the unit, but then this means that price becomes much more of a factor.

Q: How does the price point compare to current battery systems?

It’s about a 30% premium, but if the estimates of the new battery having 2-3 times more cycles than a lead-acid battery are accurate, then the new battery becomes much more cost effective over the lifetime of the battery. A way to visualize a comparison model of lead-acid vs. lithium-ion battery systems would be to think of: [number of cycles per amp hours per year] or [# of cycles/amp hour/year]

It’s worth noting that this technology will likely get more affordable as the Tesla battery factories come to scale. Along the same line of bringing the factory to scale, handling spent batteries and recycling them at scale is also of importance. They appear to have an innovative recycling program that’s been talked about in using batteries from the Tesla cars and recycling them, making them viable for use within the Powerwall.

Q: In what applications does it make the most sense?

Being able to use this system as a supplement for peak usage periods seems to be one of the best applications of this system, whereas using it as a back up battery just for an emergency situation probably isn’t the best use of the unit considering the price point. In using the system as a supplement during peak usage periods, it could be a major positive step toward a smarter grid. Installing it in medium-large facilities, due the battery’s ability to link multiple units together and to scale, is likely where the biggest energy savings will be seen. Big facilities can use these batteries to ease their electrical load coming from utilities during peak hours.

One thing to note: There is a “glitch” between the National Electrical Code (NEC) and the operating system. The operating voltage of the battery is between 300-450 volts DC. Currently, the NEC says that you can’t deploy a battery in a residential application higher than a nominal 48 volts. Tesla hasn’t addressed this yet, but because they’ve said that 300 units have already been installed and are in use, they may have found a way to work around this.

Q: Do you think this could provide market disruptions to the utility sector?

As it stands now, it’s a solid backup and supplemental system. That being said, if utility companies don’t decide to implement technology such as this and oppose residential production of energy, then this battery system could be scaled and could become very competitive and potentially disruptive.

If the price point of the system comes down a bit more, it will be very competitive for people that want to be completely off-grid, as well as the market that is simply interested in solar for the long term investment and savings. Allowing consumers to have the ability to be completely independent of external energy needs through solar can be a very democratizing feature.

To hear Christopher’s more in-depth responses, listen to the interview above. If you would like to learn more about batteries and solar PV systems, you can download the free Load Calculator for Battery-Based Solar Projects tool.

The related free lecture Battery Capacity – The Basis of Storage may also be of interest. To get the most in-depth information on battery storage and solar PV systems, you can take Christopher’s full 6-week online course, Batteries in Solar PV Systems.