Tesla Powerwall vs. Enphase AC Battery

powerwall and Enphase AC battery

How the Tesla Powerwall and Enphase AC battery specs compare.

Tesla Powerwall
Approx $10,000 fully installed on compatible solar system
6.4 kWh
3.3 kW
single or 3 phase
no inverter included
no UPS features included
10 year Warranty
350 – 450 volts DC
Enphase AC Battery
About $2,000 fully installed on any existing solar system with any brand inverter
1.2 kWh
260W continuous, 270W peak
single or 3 phase
micro inverter included
no UPS features included
10 year Warranty
240 volts AC

In terms of good marketing in Australia, two batteries stand head and shoulders above the rest in Australia right now: the Tesla Powerwall and Enphase AC battery. Both of which are due for mainstream release in 2016.

(There are lots of alternative batteries around – many of which are worth considering – but this article is about Tesla vs Enphase due to the volume of enquiries we get about them.)

So we are getting a lot of queries along the lines of:

“I’m getting a solar system and I’m keen for it to be as ‘battery-ready’ as possible. Do I get an Enphase System or a Powerwall-ready system?”

These folks have the foresight to specify a solar system that can accept batteries with as little modification as possible. If they want to be ready for the Enphase AC battery, then they should get an Enphase micro inverter system and specify to the installer that they want to upgrade the system-controller (known as the Envoy) to the “Envoy-S” for an extra $300 or so. The “-S” means it is ready for the AC battery to plug into and also includes monitoring of your electricity consumption. Which is essential if it is to control the battery to minimise your bill.

But while having an Enphase-based solar system makes installing the batteries drop dead simple – I should point out that the Enphase system will work with any existing solar system and and brand inverter. You simply buy an Envoy-S controller (approx $500) which can AC-couple into any inverter.

If a Powerwall-ready system is on the shopping list, then at time of writing, the only 2 inverters at the that I know of  that allow easy installation of the Powerwall are either a SolarEdge system or the Fronius Symo Hybrid Inverter. Both these inverters are definitely able to talk to the Powerwall.

So which option should you go for?

Cost

Enphase: Installers I have spoken to tell me that the AC batteries are likely to cost AU$2,000 each if installed into a compatible Enphase system or an extra $500 for the first battery if it is not an Enphase system. This is $2000 per 1.2kWh. To get close to the 6.4kWh available in the Powerwall you’ll need 5 batteries at a total cost of $10,000.

Powerwall: Installers I have spoken to – who Telsa are allowing to quote on Powerwall installations – are quoting about AU$10,000 to add a Powerwall to a SolarEdge or Fronius Symo Hybrid system.

So not a lot of difference in price, with the Powerwall looking a little cheaper (depending on how much of the 7kWh is usable). Enphase have said that their battery can be discharged 95%, twice a day for 10 years. Tesla are not too forthcoming with similar info!

Winner: Dead heat if you know that you need EXACTLY 6kWh.  Enphase wins if you want to add 1.2kWh at a time – which is a very sensible way to go as the chances of your home needing exactly 6kWh is very unlikely. 

Ease of use / Software smarts

The Enphase batteries will all be controlled by Enphase software. Enphase control the whole experience – a bit like Apple control their hardware. Their software supports PV systems, storage, consumption monitoring and, in the future, load control. With Tesla, you will use SolarEdge or Fronius control/monitoring software interfacing with the Tesla unit..

Winner: Enphase (probably – although I have not seen any of the interfaces yet!)

Power Output

On the surface – the major disadvantage of Enphase’s offering seems to be its power output. Each battery only has a 260W (260VA if you want to be totally accurate) continuous rating.

But thinking about it – it is not such a big deal:

To charge a single 1.2kWh AC battery will take a minimum of 1.2 / 260 = 4.6 hours.

But you can put multiple AC batteries together and they will charge in parallel (i.e. you add the powers). So no matter how many kWh of AC batteries you have the whole shebang will take 4.6 hours to charge from empty at full power.

For example 5 Enphase AC batteries (6kWh) can charge in 4.6 hours at a rate of 1.3kW.

A single Powerwall is rated at 3.3kW, so will take about 2 hours to fully charge.

The longer charging (and discharging) time of  Enphase AC Battery systems will limit the flexibility of the battery to be in a fully charged state when you need it to be, and to cover every consumption peak. The importance of this will completely depend on your electricity consumption profile and your local weather. The moral of the story is – to make a decision on batteries you should have at least a quarter’s worth of 1-5 minute consumption data (and ideally a year’s). Then you can run an analysis which will show you if the Enphase’s power limitations will be a problem for you or not.

Where the power restriction of Enphase is s definite disadvantage compared to the grunty Tesla is if you want to sell your power to one of the new breed of ‘grid support’ services such as Reposit Power. In a nutshell, Reposit  allows you to participate in the wholesale electricity market which means you get paid more for exports when there is a higher demand for electricity. This typically gives you much better average rates that the typical Feed In Tariff of 6-8c per kWh.

Unfortunately for Enphase, when selling into serves such as Reposit,  power (kW) is more valuable than energy ( kWh) [click here if you think kW and kWh are the same]  So if you want to use these services in the future, Tesla may allow you to make more money.

Winner: Tesla

Battery Backup

If you want to have your lights and some of your appliances backed up so they can run off your battery when the grid goes down, then you should choose the Powerwall. Both Solar Edge and Fronius claim they can run without the grid. Although be ready to pay your installer extra to configure this and rewire your switchboard to allow this.

The Enphase AC battery does not allow grid backup.

Winner: Tesla

Status

If you a hang a Powerwall on your house – preferably where the neighbours can see it, you’re gonna get some serious street cred! The Enphase units, while looking cool probably don’t have the same effect on your social status. But if that is the reason you are buying a battery, save your self $10,000 and read this book instead!

Winner: Tesla

Modularity.

The main difference with Enphase’s solution is that it is modular. You don’t have to buy the whole 6.4kWh at once. You can dip your foot in the whole battery thing $2,000 at a time. You can see how well the first battery works, pore over the analytics that Enphase produce and decide if another battery is worth it. Recent analysis by Warwick Johnston at SunWiz shows that the first kWh of battery will always pay back faster than subsequent kWhs, which makes a modular system such as Enphase’s very compelling.

Winner: Enphase

Heavy Lifting

The Powerwall weights a whopping 100kg. So you are going to need a very strong wall to hang it on. The Enphase units weigh about 20kg each.

Winner: Enphase

Ease of Installation

Installers I have spoken to are telling me the Tesla is a bit of a ‘raw product’ and a bugger to configure once it’s be hoisted on to the wall. Enphase promise me that the first AC battery can be installed in under 2 hours, and subsequent batteries are plug and play.

Winner: Enphase

Conclusion

Both batteries are going to be very well made, safe and easy to use. They will both be supported well in Australia. I think both are good choices. If you know that 6.4kWh is a good size for you and you want grid backup plus the option to participate in future energy-trading services, then the Powerwall is worth considering. If you want panel level monitoring and optimisation (and why wouldn’t you!) then a Powerwall ready SolarEdge system looks very compelling right now if you have $10k burning a hole in your pocket.

If you are not sure how many kWh of battery you need and want to benefit from, experience, geek out or simply play with solar+storage on your home, then Enphase will save you a lot of money in hardware initially and comes with very powerful software that will help you control your home and monitor your consumption to identify low hanging energy efficiency opportunities. And the price of the batteries is only going to come down, so when you want to add more kWh, it should be cheaper than $2,000 to plug in subsequent AC batteries.

[updated on Feb 23 2016 to include details of multiple AC batteries’ power output]

[The author’s super fund has shares in Enphase]

About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of SolarQuotes.com.au. My last "real job" was working for the CSIRO in their renewable energy division.

Comments

  1. regardless neither are cost effective at this price.
    One thing everyone seems to overlook is the age of the persons buying solar which also influences decisions on whether the pay back period is viable.
    For me if the battery can’t repay its purchase price in 3 to 4 years it is of no use, so my price that I would pay is around 3 to $4,000 for a battery that will store enough power for my overnight use which is 6KW.
    Easy to see that if it fails after the warranty then you have to buy a new one so a 10 year payback or even 8 might just make it more expensive than just paying for your grid power.
    Also is the warranty pro rata ? or is it a full replacement warranty ?

    • Agreed Eric – for most people batteries do not make sense economically yet. Hence lots of people are thinking of buying a system that can be easily upgraded 2-3 years down the line when batteries have come down the cost curve!

  2. Bruce Whitfield says:

    Hi Finn, good article on Tesla vs Enphase, although I wouldn’t entirely agree that the storage answers lie just with these two manufacturers.
    The amount of research into PV storage happening in China right now is staggering, driven by their desire to be in front with modestly priced EV’s. Couple this with a huge country that will/is also leading the charge on the application of microgrids, China will play a huge part in the supply of PV storage solutions. At the moment SolaX and Growatt solutions are just the beginning of many more entrants into this exciting aspect of micro generators and micro power grid . technology.

  3. Jonathan Brooke says:

    any info on the powerwall and being compatible with other brands of inverters? If not how would you see other inverter makes being modified to be able to accept the powerwall?

    • If an inverter can talk ‘modbus’ then it should be able to talk to the Powerwall. But Telsa are so bloody opaque it is really hard to get any technical details from them. So the safest bet right now is to get the Fronius Symo Hybrid or SolarEdge.

      The alternative is to get a cheap budget inverter now and when it fails in 2-3 years you’ll have a much bigger choice of batteries and compatible inverters to replace it with!

  4. Hi Finn – good article!

    Enphase is nice, but despite what they say, it’s hard to install due to its’ use of powerline communications. It’s especially hard to install on sheds which are pretty common out here in regional Australia.

    So that’s why I offer my customer Solaredge. Like Enphase it offers panel level optimisation and panel level monitoring. It’s also cheaper than Enphase, easier to install and has 25 year warranty on the optimisers and 12 years on the inverter vs 10 years for Enphase. And as you say, Solaredge speaks fluent Tesla.

    The other Tesla compatible option is as you say Fronius Symo – but that’s only suitable for 3 phase installations. If you want panel level optimisation and monitoring, either add Tigo or use Trinasmart modules which come with Tigo factory installed.

    Just my 5 cents worth 🙂

    Cheers

    Tony

  5. David Brien says:

    Finn,
    based on the above. have you any comments about Redflow fitting within this category now that it is available in Australia? Or is it more suited to Farm and small scale commercial applications?
    http://redflow.com/products/zbm/

  6. Nice analysis, guys! I am still in the research phase:

    I want to find the best PV system that will give me enough stored power to run a heat pump at night for a few hours to warm water to about 30+ C.

    This is to supplement my solar evac. tube heater (60 tubes) feeding my hydronic heating when the sun don’t shine…

    I’ll probably find that it is probably easiest to just get a decent heat pump and run it off bought ‘green’ electricity!

    Cheers

    LMH

    • Michael says:

      Carioca, This is also what I need. How did you go with it?
      I assume 5 kw is minimum. I have to use Enphase micro converter (complex roof, shading etc), and an inverter to 3 phase for the heat pump, I assume.
      The best air to water heat pump is the NIBE F2120. I fear it costs about $10,000 but waiting on costing. Nice solution, but expensive…
      Battery: still too expensive.

  7. Peter Thornton says:

    G’day Finn,

    Thanks for the article. Perhaps one aspect that should also be considered is the multiple conversions and the efficiency drops that would occur with the DC-AC-DC-AC conversions that would be inherent in the Enphase system (i.e. conversion of DC to AC at the panel, conversion of AC to DC to charge the battery(s), conversion of DC to AC when power is drawn from the battery).

    The SolarEdge system utilises a straight DC-DC interface for the battery connection and so the only conversion to AC appears to be when power is finally drawn for consumption. One could imagine (depending upon inverter efficiencies) that a 5-10% drop in efficiency could be incurred, let alone other loses.

  8. David Colley says:

    Hi Finn

    Any thoughts on this product ?

    http://www.aquionenergy.com/

    Cheers
    David

  9. David Brien says:

    Finn,
    Myquestion seems to have disappeared I work in an prganisation with a large ESD team. They are showing a lot of interest in Redflow (we have no connection with the manufacturer but I am always interested in the direction our ESD team seems to head in.) I would be interested in soem comparison with this solution to Powerwall and Enphase. I current have micro-inverters installed and up to this point was leaning towards their battery solution. The Redflow does not look like a consumer item ( in fact it is an exceptionally heavy and industrial looking design) but the newer systems are being presented as such.

  10. john nielsen says:

    Hi Finn,
    Thanks for your Powerwall Enphase comparison. While I have Enphase micros and very pleased with my system, I don’t think the ACbattery (there is no such thing as an AC battery) will be my choice as they seem far too powerless and too dear. As for the Powerwall: if it is a battery, power in and power out, I would consider it, but I don’t think it is. I believe they have monopolized the use of this battery in that you can only use specific inverters to use the thing. Also, I believe there will be built in software to stop me from using it such: power in power out. I see also that in order to give a 10 year warranty, they will have built in a ssr (solid state recorder, not solid state relay) which will monitor the temps, discharge, cycles etc., so after 5 years use your Powerwall is dead, they will just remove the ssr and print out a misuse statement, and here begins the litigation.
    There are some li-ion batteries on Ebay, car size, no software, just straight power in power out, however they are far too expensive at the moment,,, wait a couple of years.
    Unless I learn some more about the Powerwall, I will just live with the air con running from the grid. Why anyone wants to quit the grid altogether is beyond me. My 6 kW system is a standalone, and the reason is that the grid wouldn’t let me have 5 kW but said that I could have as much solar power as I like as long as I don’t export to the grid. I am independent of the grid, but can still on a separate circuit use the grid if need be, like night time air con. My power bill was about $3,000 a year, 6 person household, now the bill is less than $300 a year and that is only because of the 5 months air con. Keep up the good work Finn, Cheers.
    John Nielsen, Silwood.

  11. Kalinya says:

    Hi Finn,
    I found your article very interesting. I already have solar plumbed into the grid with good feedback, but on a matter of principal object to a huge multibillionaire taking my money while hiking the prices of the power i use. Is it possible to retain my existing setup (thus getting maximum money for the power my system creates) and run an independent system off grid? i.e. with switch over if i need to? I am not sure how it would switch over.

    • Yes it is. A good way to do this is to take your lighting circuit off grid (make sure you have all LED lights first). You can segregate your lighting circuit and unit entirely of a small panel array and small battery.

      Then you can add stuff to the off grid circuit that will not require grid backup, like pool pumps or hot water boosting.

  12. rumtytum says:

    I have a micro inverter system (LG panels) and I’m contemplating a Tesla car. Can the Enphase battery be used to charge the Tesla car without complications or will I need to buy a DC-type battery system? My solar installer did a good job for me but is useless when asked questions like this, and I can’t find any way to communicate with Enphase without becoming an installer myself.

    • Yes it can. The Enphase battery simply converted the DC to AC inside the battery box. The Tesla charger will then convert it back to DC.

      If you had a powerwall, the car charger would still use AC, so you’d still have the 2 conversions (DC -> AC -> DC).

      But.. the Telsa Cars have 60-90kWh which is the equivalent of 55-80 Enphase batteries. It would make more sense to have solar where the car is parked during the day so you can store the solar directly into the car battery.

  13. Great comparison analysis. There are so many DC batteries coming on the market as DC provides a 2-14% increase in efficiency over AC. The incremental Enphase AC is handy but not a practical capacity except for brownout/blackout events unless your house has whole controls that can shut off non-critical loads automatically.

    For such features, look at LumenCache. It’s a DC nanogrid platform. Does not use the old AC type wiring so it’s mostly for new construction (sorry). It can directly feed from the Tesla or any other DC power source with peak efficiency. Of course there is an AC adapter but LED lighting is electronics so why convert to AC just to convert back to DC at every lightbulb?

  14. Hugo Ramirez says:

    I have a 3kw enphase system with micro inverters , if i buy the 3 kw battery backup system , will I be able to disconnect the DWP power off the grid and use DWP for backup only.

    • Ronald Brakels says:

      I am afraid it won’t be possible to go off grid. A 3 kilowatt solar system won’t be enough for a typical household and a 3 kilowatt battery system won’t be either. The batteries, generator, and other hardware required to go off-grid are substantial and expensive.

  15. PV systems are improving rapidly, the AC micro panels are definitely the future with their ability to operate independently and not reduce input on to the bus bar therefore ensuring constant mains frequency, 50Hz-240v ac.

    The cost of the entire system is the main point to consider, it must pay for itself in the shortest possible time ie 3-5 years which by then the panels will be at there extreme life on a hot or cold roof, glass tarnishing, seals opening up & moisture entering shorting circuits, solder starting to break away etc.

    Batteries are costly again, plenty of storage power means they last longer by not having to discharge them to their extreme which will reduce their life with too many cycles. In other words bigger the tank the more reserve you have but that also means you must have enough panels to fill up those batteries to cope with demand from the premises they have to power.whilst also been able to charge up those batteries providing you have plenty of sunlight.

    So the best is 50% panels 50% mains, control how much electricity you use by.turning on equipment only as required and ensure basic items like fridge is alway on H VACS on when in those rooms and not left on for more than an hour if rooms to be vacated etc.

    The bigger the system the more you have to pay and trying to recover that cost off the panels will not outlast the expense plus interest on the loan.

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