Homeowner Blog

Powervault 3 vs Tesla Powerwall 2: It's All In The Chemistry

Erica Charles 30 Apr 2018

I have an abiding memory from secondary school of our chemistry teacher pressing ‘play’ on an old video cassette, and there, projected onto the screen at the front of the room, was a video made by what must have been a desperately struggling actor, dressed in yellow tights and a white coat, dancing on a lab bench and singing the 'Periodic Table song'.  

The video served two purposes:

  • it put us off chemistry;
  • it put us off acting.

At least it put me off acting. Kristin Scott Thomas attended the school a few years before I did, and clearly, it didn’t put her off acting (credits include Four Weddings and a Funeral, The English Patient, and most recently Winston Churchill’s long suffering wife in Darkest Hour ). No dancing on lab benches for her just to pay the bills.

To the video’s credit, more than a couple of decades later, I can still remember the first two rows of the Periodic Table. Of course I’ve never used the knowledge, until the advent of home battery storage.

Today, as the second in our series of blogs on Powervault 3, we are studying Lithium Ferro Phosphate (Powervault 3) vs  Lithiated Nickel Manganese Cobalt Oxide (Tesla Powerwall 2).

Don’t worry, ‘Studying’ is over-egging it. We’re looking at the differences from a home battery storage point of view...


Ask many people which chemistry Powervault 3 or Powerwall 2 utilises, and you will get the same response, 'lithium-ion'.  However that hides the fact that whilst the anode of lithium-ion batteries is basically the same (carbon/silicon and graphite), the cathodes vary considerably, leading to trade-offs between energy density, life cycles and thermal stability.  

Powervault 3 uses a lithium ferro phosphate (LiFePO4) cathode (LFP for short) whilst Powerwall 2 utilises lithiated nickel manganese cobalt oxide (NMC)

In practical terms the key differences between these chemistries are as follows:

  • LFP (Powervault 3) has an expected life which is around double that of NMC (Powerwall 2). LFP typically has an expected life of 6,000 – 10,000 cycles compared to the expected life of NMC of 3,000 – 5,000 cycles: thus you end up with different levels of ‘minimum guaranteed lifetime storage capacity’ between Powervault 3 and Powerwall 2- see the table below;
  • the upfront cost of LFP (Powervault 3) per kWh of rated capacity is more than twice that of NMC (Powerwall 2).

LFP is also the less ‘energy dense’ of the two technologies, weighing more and taking up more space per kWh of battery capacity.

Overall the comparison between LFP and NMC is pretty much summed up in, ‘LFP means you double the lifecycles but you also double the weight and double the cost’.

Space aside, this effectively reduces the ‘chemistry’ buying decision down to one of ‘how many ‘kWh storage slots’ do you want to pay for upfront’? 

The answer to this question slightly depends on application (see last week's blog to understand the full possible range of functionality):

  • if the goal is simply to charge during the day from excess solar, and then discharge during the night, a typical battery will run through just under 300 life cycles a year, so NMC should last 10 years plus, and LFP should last over 20 years;
  • if the goal is to be more proactive – trading electricity or providing grid support services, the battery could cycle 500 times a year, and so NMC will last a minimum of 8 years, and LFP should last more like 16 years.

Of course, none of us know where battery technology will be in 10 years, let alone 20 years. If the expectation is for improvements and price drops, then paying less for a shorter life makes sense. But equally, it may be appealing to match the life expectancy of the battery system to the expected life of your solar panels.

Guaranteed and Expected Lifetime Storage Capacity

 

Powervault 3

Tesla Powerwall 2

 

Usable capacity:

2.5kWh

5.0kWh

7.5kWh

13.5kWh

 

Minimum guaranteed lifetime storage capacity:

17,300 kWh

34,600 kWh

51,800 kWh

37,000 kWh

 

Guaranteed lifetime storage capacity per kwh of rated battery capacity:

6.920 kWh

6,920 kWh

6,906 kWh

2,741 kWh

Powervault 3 offers more than twice the warranted output per kWh of battery capacity compared to Powerwall 2

Reasonably expected lifetime storage capacity taking into account End-of- warranty capacity guarantee:

19,050kWh

38,100kWh

57,050kWh

47,800kWh

Add 1000 cycles at the ‘End-of-life’ capacity % below

Equivalent cycles:

> 6,000

> 6,000

> 6,000

 

Tesla doesn’t talk in terms of cycles, preferring to focus on warranty term and minimum guaranteed output

End-of-warranty capacity guarantee:

70% of initial capacity: 1.75kWh

70% of initial capacity: 3.5kWh

70% of initial capacity: 5.25kWh

80% of initial capacity (10.8kWh) if used only for solar storage or if maximum usage during initial 10 years is 37MWh.

 

 

Spoiler Alert

Next week, the blog will give a 'back-of-envelope' economic comparison of the two battery systems: cost, payback, simple investment return %.

Now of course, like me, you may be one of those people who can't wait for the end of a story. You flick to the last pages of a book just to check your favourite character comes out OK in the end.

In that case, I'm guessing you can't wait to read our conclusions in the Powervault 3 vs Powerwall 2 story. If so, click on the link below to download our full Head-to-Head analysis of Powervault 3 vs Powerwall 2: 

 

Free Download

Head-to-Head Analysis:

Powervault 3 vs Powerwall 2

eBook_pink_pattern_L

 

Download now

 

 Otherwise, wait for next week's blog and see what unfolds.

 

Request a quote

If you would like a quote for Powervault 3, Powerwall 2, or indeed any other system, please get in touch.

Call 0118 951 4490, email info@spiritenergy.co.uk or request a quote:

Request free advice / quote 

 

 

 

Topics: Battery storage, Tesla Powerwall, Powervault

Leave us your thoughts on this post