Enphase Battery Is Impressive But Very Unlikely To Save You Money

Enphase AC Battery

The Enphase AC battery. image: Enphase

Until now, if you have been one of the highly intelligent and undoubtedly good looking people with a grid connect solar system and you wanted to add batteries, you were looking at spending at least $10,000.

But that will no longer be the case in August when the teeny tiny $2,000 Enphase AC Battery becomes available in Australia.

Each Enphase AC Battery only has 1.14 kilowatt-hours of usable storage, but up to 13 can be installed together giving a maximum total usable capacity of 14.8 kilowatt-hours.  The system is not designed to supply power during a blackout or be used off-grid.  It instead has one purpose only, and that is to save households money by letting them store solar electricity, or even off-peak grid electricity, for use in the evening or whenever household electricity demand exceeds the production of electricity from rooftop solar panels.

Enphase has a reputation for producing extremely reliable, well engineered systems, and their battery appears to be no exception.  Unfortunately, given its likely installed cost, the Enphase Battery is extremely unlikely to save anyone money.

The Enphase Battery’s Interesting Attributes

Nominal Storage Capacity per module 1.2 kilowatt-hours
Usable Storage Capacity per module 1.14 kilowatt-hours
Power output per module             260 watts
Maximum number of modules 13
Maximum Nominal Storage Capacity 15.6 kilowatt-hours with 13 modules
Maximum Usable Storage Capacity 14.8 kilowatt-hours with 13 modules
Maximum Power Output 3.38 kilowatts with 13 modules
Weight 25kg per module
Installation Location Indoors or enclosed only
Operating Temperature Range -20 to 45 Celsius
Type of Fixture Wall mounted
Warranty 10 years or 7,300 cycles at 80% of nominal capacity
Off-Grid Capable Not At All
Battery Chemistry Lithium ferrite phosphate
Required Inverter    Any
Enphase Envoy S Required Metered Communications Gateway              
Ease of Installation Piece of cake

The Enphase AC Battery Will Work With Any Existing Solar System

If your rooftop solar power system doesn’t use Enphase Microinverters, no worries. You can still use the Enphase Battery. Because the AC battery uses 240V AC for its power delivery and charging, your electrician simply connects into the 240V output of your solar panel system1.

What Are Enphase Microinverters?

Microinverters are tiny little inverters that are attached beneath individual solar panels and they convert the DC power that panels generate into the AC power that homes use. Because there is one inverter per panel, that inverter is able to lavish all its care and attention on that panel and so get the maximum output from it. As a result, panels with microinverters will typically generate about 5-15% more electricity than those that use the more common string inverters.  The drawback is microinverters are more expensive at the moment, but Enphase is working to change that.

The Enphase AC Battery Requires The Enphase Envoy S Metered Communications Gateway

enphase envoy-s

The Envoy-S comms unit. image: Enphase

The system’s interface, the Enphase Envoy S Metered communications gateway allows easy monitoring of solar power production and battery use and can be customized for a household’s individual solar energy production and electricity tariff to get the highest rate of return from the system.

If you already have an Envoy S then you are ready to go, but you definitely belong to a very small minority of Australian households.  If you don’t have one, it will be necessary.

The Envoy S has a warranty of 5 years, which is half that of the battery.

The Enphase AC Battery Warranty Is Good

The warranty on the system is one of the best available at 10 years or 7,300 cycles at 80% of the nominal capacity of 1.2 kilowatt-hours.  That is, at the end of ten years the battery will still be able to store at least 0.96 kilowatt-hours of usable energy.  The warranty covers 7,300 cycles which is two cycles a day for 10 years. The ability to cycle twice a day allows it charge on low cost, off-peak grid electricity overnight if desired.

Ease Of Installation

The Enphase AC Battery is the quickest and easiest energy storage system to install I am aware of.  Not needing to be connected to a hybrid inverter helps with this.  Unfortunately, it is still a fairly involved process that can’t be performed by typical homeowner themselves.  Enphase says a single person can install a battery in half an hour and they have made a video of one worker installing 4 batteries in 1 hour and 40 minutes.  Of course, you have to know what you are doing to install them that quickly.

The Enphase AC Battery Does Not Have A Lot Of Power

While each battery can hold 1.14 kilowatt-hours of usable electrical energy, they can only release that energy slowly and so their power output is not very high.  Each battery can only discharge a maximum continuous output of 260 watts. So to power a small 1,000 watt bar heater would take 4 batteries. While those 4 batteries can store enough energy to run the bar heater for over 4 hours, they would only have 40 watts of power left over to do anything else in addition to running the heater.

As the Enphase AC Battery will able to discharge a little faster than it charges, it will take almost 4.5 hours to fully charge and almost 4.4 hours to fully discharge. So if you come home to an empty house with fully charged batteries at 6:00pm and continuously drew power from them at the maximum rate, it will be 10:23 pm before they were flat. And this isn’t so great if your peak electricity rate finishes at 8:00pm, as they often do in NSW, because you won’t be able to use all your stored electricity during the period with the highest grid electricity price.

But They Are Pretty Cool

Because the batteries are low power they don’t produce much heat. One person told me they, “Don’t generate heat,” which is a statement that violated the laws of physics so hard it made me feel as though I was in a Doctor Who episode. But what he meant was, they don’t produce much heat and as a result they don’t have an active cooling system which means they have the advantage of never making any noise. Unlike some shield-shaped batteries I could mention.

The Enphase AC Battery And Efficiency

The Enphase AC battery has an excellent DC to DC round trip efficiency of 96.1%. I know this because it says so right here on this pamphlet I am holding and I must say that figure is bloody excellent. And it is also a bit bloody cheeky, because no where do I see any mention of the fact the system will also suffer additional losses that energy storage systems connected to string inverters do not. These additional losses are not large, but they do mean the system’s total efficiency is worse than that of most energy storage systems on the market, not better.

The Actual Efficiency Of The Enphase Battery

With DC Coupled energy storage systems, solar panels produce DC electricity which charges the batteries. When that stored energy is needed the batteries send DC power to the string inverter which converts it to the AC power our homes and businesses use. So there is a loss when charging the battery and again when discharging. There is also a loss when inverter converts DC to AC.

With the Enphase AC Battery, solar panels produce DC and the microinverter on the panel immediately converts it into AC and this results in a loss. When charging, the Enphase AC Battery converts this AC power into DC, because batteries can only be charged with DC, and this results in a loss. And when the stored energy is used it is converted from DC to AC which results in another loss. And these losses all add up.

When it comes to converting DC to AC current, the Enphase AC Battery is exactly as efficient as an Enphase S270 microinverter. This is because that is exactly what’s inside each battery. Its average efficiency is 95.6%, which is not bad, and I will assume the efficiency at converting DC to AC is the same.  So to work out the real efficiency of the storage system in practice, we take the efficiency of the solar panel’s microinverter at converting DC to AC and multiply that by the battery’s efficiency at converting AC to DC, and then multiply it by the battery’s DC to DC round trip efficiency of 96.1%.  We don’t need to include the final loss from converting DC to the AC used in the home, as other battery systems don’t include that loss in their efficiency figures and we want a result that can be compared to other systems.

All up this comes to an efficiency of 87.8%. This is less than the 92.5% round trip efficiency claimed for the Tesla Powerwall and considerably less than 95% figure claimed for the LG Chem RESU energy storage system.

The Lower Efficiency Is Not That Big A Deal

Obviously, the higher a system’s efficiency the better. But the Enphase AC Battery’s lower overall efficiency does not have a large effect on the economics of the system when it comes to storing solar electricity. This is because many people currently only get around 6 cents a kilowatt-hour for electricity they send into the grid. This means the cost of storing 1 kilowatt-hour of surplus solar electricity with 87.8% efficiency is only about 6.8 cents, which is only half a cent more than a system with 95% efficiency. So this has only a fairly minor effect on the overall economics of storing solar electricity.

Installation Cost Estimate

The fact that the Enphase AC Battery is easy to set up will help keep its installation cost down.  And another factor that will help is Enphase is known to produce extremely reliable products, so an installer can be confident that no more work will be required after the initial installation. And the fact that Enphase is a trusted company that is known to respond reasonably to any problems involving their products also helps.

As a result, Enphase claim you can get one battery plus the Envoy S installed for around $3,000 and each extra battery after that installed for $2,000.

How Many Batteries Do I Need?

If you want the highest possible economic return on your system then you will probably only want to install 2 or 3 batteries.  The reason why you would want such a small number is it makes it more likely you will use your battery storage at close to its full capacity.  The more energy storage you have, the less likely it is your rooftop solar power system will produce enough surplus electricity to regularly fully charge it, and the lower the chance that you will use all that stored energy during peak periods.

Why The Enphase AC Battery Is Not Likely To Save You Money

If a household installs 2 batteries they will have 2.28 kilowatt-hours of usable storage.  But because these batteries will degrade over time they might only average 2.2 kilowatt-hours of usable storage over 10 years.  If you cycle that once per day for 10 years until the warranty period is over and then the batteries are ripped off the wall and thrown out, it would come to a total of about 8,036 stored kilowatt-hours.  Dividing the $5,000 installation cost by that number comes to 62 cents per stored kilowatt-hour, which is pretty damn high.

Unfortunately, the real cost is even more than that because we have to account for the cost of capital.  This is the interest rate that people have to pay to borrow money to buy the system, or if money isn’t borrowed it is the return the money could have earned if invested elsewhere.  Using a fairly low figure of 5% for the cost of capital gives a cost of 81 cents per kilowatt-hour of stored electricity.  And that is not going to save anyone money.

However, there is actually no need for people to throw out their batteries once the warranty is up. They could keep operating for years after that. Just how long is hard to say. The more the batteries are used, the faster they will wear out, but they will also gradually degrade even if they aren’t used at all. Since in this example we are only cycling them once a day and I think it is likely to be a very reliable system, I will assume they last for a total of fifteen years, with degradation causing them to average 2.1 kilowatt-hours of usable storage a day. That would give a total of 11,505 stored kilowatt-hours.  If we divide the installation cost by that number it comes to about 43 cents per kilowatt-hour.   With a 5% figure for the cost of capital added in it would come to 63 cents per kilowatt-hour.  That’s still no where low enough for it to pay for itself, but at least it is getting closer.

Unfortunately, unlike the examples above, most households would be unlikely to use their energy storage at full capacity even if they only have 1 or 2 batteries.  This is because there were be days of poor weather or high electricity demand when there won’t be enough surplus solar electricity to fully charge the batteries or times when not all the stored electricity is used, such as when people are on holiday.  If they are only used at 90% capacity the cost per stored kilowatt-hour will be 10% more and if they are used at 80% of capacity the cost will be 20% more, and so on.

Charging With Off-Peak Electricity Can Help

Besides being charged with solar electricity during the day, the Enphase AC battery could also be charged with off-peak electricity in the early hours of the morning.  Unfortunately, this may not pay for itself.

For people on a time of use tariff in Western Australia, the difference between off-peak and shoulder electricity is 11.9 cents.  So people in Perth could charge the Enphase Battery using off-peak electricity overnight and use all the stored energy in the morning in the shoulder period that starts at 7:00am.  Then they could charge their Enphase Batteries  with solar electricity and potentially use it all during the peak electricity period that lasts from 3:00pm to 9:00pm, Monday to Friday.  Taking into account the Enphase Battery’s 87.8% efficiency, the peak electricity rate in Western Australia of 47.2 cents and their 7.1 cent feed-in tariff, when used at maximum capacity, 2 Enphase batteries could save a household an average of $1.03 a day.  That would come to a saving of 23 cents per kilowatt-hour of stored electricity.  Because the Enphase Battery is being cycled twice a day instead of once, over a 10 year period the cost of storage would be halved from 81 cents a kilowatt-hour to 40.5 cents.  Which means that under even these optimal conditions, cycling the Enphase Battery once on off-peak electricity and once on solar electricity each day clearly cannot save people in Western Australia money.

If the Enphase Battery lasts beyond its 10 year warranty period, which I am certain it will, the economic return will be even greater.  However, because it is being cycled twice a day instead of once, it might be overly optimistic to assume it would last 15 years.  I think 12 years would be a more reasonable figure and using that period of time, under the same conditions the cost of storage would be 35 cents per kilowatt-hour, which is obviously much more than the 23 cents per kilowatt-hour that would be saved.  In fact, the Enphase Battery would have to operate flawlessly for 23 years in order for it to pay for itself, and that is just not going to happen.

Charging With Off-Peak Electricity Can Also Make Things Worse

While there is a large difference between off-peak and shoulder rates in Western Australia, in NSW the difference is only a few cents.  So with a typical off-peak rate of around 9 cents a kilowatt-hour and a shoulder rate of 12 cents a kilowatt-hour, with the Enphase AC Battery’s efficiency of 87.8% it would cost 10.3 cents of off-peak electricity to save 12 cents worth of shoulder electricity.  And since the extra cycle will cause wear and tear on the battery and reduce its lifespan, charging with off-peak power in NSW is likely to cost more than its worth.

Dipping Into Battery Storage During The Day Can Help, But Not Enough

Households can draw upon the Enphase AC Battery during the day when their electricity consumption temporarily exceeds their rooftop solar energy production.  This can save a household from having to buy grid electricity while still allowing the battery storage to become fully charged for use in the evening.

Exactly how useful this is will depend upon a household’s electricity consumption patterns, the size and orientation of its rooftop solar system, and the electricity tariff used.  But while this could improve the economics of a system, it still will not be enough to make it worthwhile.  Cycling it once on stored solar electricity in the day and once on stored solar electricity during the afternoon and evening peak in Western Australia would be the ideal way to do this if it were possible, but it’s not as it would need 4.5 hours to charge after sunrise, 4.4 hours to discharge in the middle of the day, and another 4.5 hours to charge before sunset.  The day is only long enough to do this in the summer and even then, no one is going to have the necessary electricity production and consumption pattern.   Even if it were possible to do this, perhaps by slowing down the planet’s rotation, it would have to run at full capacity for 19 years to pay for itself which is another thing that is pretty impossible.

It Can Be Difficult To Get The Most Out Of The System When On a Time Of Use Tariff

There are many households in Australia on time of use tariffs that pay around 35 cents or more per kilowatt-hour for grid electricity during peak periods.  Using stored energy during these times will give the best economic return.  However, it can be difficult to use all the stored energy in an Enphase AC Battery during these times because it takes almost 4.4 hours to fully discharge and in NSW a typical peak period runs from 2:00pm to 8:00pm Monday to Friday.  This means to use all its stored energy during this time it would have to start discharging at its maximum rate at around 3:37 at the latest.  And this will often not be required as many household solar power systems will still be producing a considerable amount of electricity at this time, particularly in the summer, and especially if the solar panels face west.

Because of this, it is quite possible a household with Enphase Batteries would benefit more from having a fixed tariff than a time of use tariff.

Canberra And Adelaide City Council Battery Subsidies Help, But Not Enough

Canberra and Adelaide City Council offer subsidies for home energy storage that will cover up to half the installation cost of a system. The Canberra subsidy will be open to new entrants next year while the Adelaide City Council subsidy is available now, but it only applies to the Central Business District and a small area above it called North Adelaide.

Canberra has the cheapest grid electricity in Australia and with a peak price of around 21 cents in the evening and a 6 cent solar feed-in tariff, the total cost of stored energy would have to be under 15 cents a kilowatt-hour and so even with a subsidy paying half the installation cost the Enphase Battery won’t pay for itself.

Electricity prices are considerably higher in Adelaide. I can’t find a suitable time of use tariff available in the area where the subsidy applies, but a fixed tariff will cost households around 28 cents a kilowatt-hour for grid electricity and with a 6 cent feed-in tariff the cost of stored energy would have to come to under 22 cents a kilowatt-hour, and so a half price installation is not going to pay for itself there either.

The Enphase AC Battery Can Be Used For Electricity Arbitrage

The Enphase AC Battery may soon have an option to be retrofitted with a device that runs software from Reposit which enables it to sell electricity to the grid, at times for up to $1 a kilowatt-hour.  This can give an extra source of revenue for people with home energy storage, but just how much money people can make is not yet clear.  Personally, I doubt people will be able to make a very large amount of money, particularly with the Enphase storage system.  This is because periods of high electricity prices are usually quite brief and the system’s low power output makes it difficult to take advantage of them.  If a period when electricity sells for $1 a kilowatt-hour lasts for 15 minutes, a household with two batteries could sell 0.13 of a kilowatt-hour and make $0.13.  And these periods of high prices are quite rare.

The Non-Economic Case For Installing The Enphase AC Battery

Because the Enphase AC Battery does not realistically pay for itself anywhere in Australia at the moment, even in places that offer a hefty subsidy, there are only non-economic reasons to install it.  And one of those reasons could be to simply to own a nifty piece of technology that is probably very well made and likely to reliably serve you without problems for many years.

If you want to reduce greenhouse gas emissions, then you are better off buying rooftop solar for your grandmother or sister, expanding your own rooftop solar system, or investing in energy efficiency such as insulation, heat pumps, or double glazing.  While grid connected home energy storage can potentially reduce greenhouse gas emissions, its exact effects are not clear and will be quite limited compared to other options.

Footnotes

  1. You can do this no matter what inverter you have because it does not provide backup, and so does not need to talk to the solar inverter to throttle its output when the batteries are full. Any excess simply flows into the grid. This post explains why that is so.
About Ronald Brakels

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.

Comments

  1. Look it’s getting to the stage where I have to wonder do any of these producers have a grasp on what the public want and what they need and what they are prepared to pay ?
    I doubt it.
    Most of the solutions to power storage only do it by halves ,are too expensive and don’t really address what the people want.

    Its a bit like the salesman who comes to your door and tries to sell you solar and then goes on to quote the number of KW hours the system produces which is totally irrelevant to what you actually need.

  2. Ok Finn, great in depth article and a honest appraisal of a quality product … but falls down on the economics. Your assumption on tariffs don’t take into account any price rises. Over the passed 6-7 years tariffs have doubled, certainly in NSW, and I would expect a minimum rise of 50% over the next 7 years, unless Labor gets back in, then that could be 100%+ This changes the ROI and should be stated as such. Given an average life of 12 years, as you have accepted, I believe pay back will occur around 8 year mark. My peak tariff is 0.52 inc GST and off peak 0.11 so tariff shifting alone is worth 0.41 per kWh, with excess solar production and cycling twice a day (shoulder for breakfast loads and peak at dinner time) a value of 0.51 per kWh is achieved on today’s tariff rates, growing as we go forward.
    Keep up the good work …

    • Ronald Brakels says:

      Hello Lindsay, Ronald here, I wrote the article.

      I did assume for that grid electricity prices would not change in real terms over the life of the Enphase battery. I did this for two reasons. Firstly, because it was easy, and secondly because I doubt electricity prices will rise in real terms over that time. They have been declining here in South Australia.

      However, I don’t actually know what will happen, and NSW is definitely in a bad situation with regard to over investment in transmission infrastructure. It is certainly possible that electricity prices could continue to rise, but I definitely do not think electricity prices will rise by 50-100% or more over the next 7 years unless the electricity sector is in a big hurry to cut its own throat. But I’m certainly willing to consider what would happen with a very large price increase.

      Now I don’t know where you live, or why your electricity rates are so high. Your own individual circumstances may make the Enphase battery pay for itself for you much sooner than the typical household. But if we consider what the average family in NSW pays for electricity and assume they are buying an Enphase battery system now and not in the future when the cost of energy storage will no doubt be very different, and assume that electricity prices in real terms double over the next 15 years, then the Enphase battery is still not likely to pay for itself.

      If the doubling of electricity prices happens at a constant rate, and results in a straight doubling of off-peak, shoulder, and peak rates, a family in Sydney currently paying, after discounts are included, a typical peak price of around 40 cents a kilowatt-hour will pay an average of around 58 cents a kilowatt-hour for peak electricity over the next 15 years. Assuming the feed-in tariff stays around 6 cents, then cycling the Enphase battery once per day with solar electricity will save them around 51 cents per kilowatt-hour and cost them around 63 cents a kilowatt-hour. (Actually more than 63 cents due to the effect of lower return in the first 7.5 years, but let’s ignore that.)

      They could cycle it twice a day, once with off-peak energy, but as mentioned in the article, the difference between off-peak and shoulder in NSW is normally only a few cents. If that doubles to around 6 cents then a kilowatt-hour of storage cycled twice a day will save the household around 57 cents while still costing about 63 cents. And this is assuming the system lasts 15 years, despite being cycled twice a day.

      Assuming a greater increase in grid electricity prices can get a system to pay for itself, but there is still the problem of using all the stored electricity during the peak period which always seems to end at 8:00pm in NSW. Because it requires around 4.4 hours to fully discharge, a household discharging it at full power would have to start doing so at around 3:35 in the afternoon to use all its stored energy during the peak period. And many households are still going to be producing plenty of solar electricity at that time, especially in the summer. In order to use the Enphase battery at full capacity, a household’s electricity production and consumption would have to be really odd.

      So if there is a very high increase in electricity prices, buying an Enphase battery now could pay for itself. But a 100% increase over 15 years is not likely to make it worthwhile for New South Welsh people, though there could be some exceptions.

      • How are the numbers looking now. I currently pay 61c peak, 23c shoulder and 13c off peak? I know I could do a better deal, and will do shortly, but not as good as the figures you quote in this article.

        • Ronald Brakels says:

          Ouch! Those high rates make things better, but it still won’t pay for itself. But I expect its cost will come down in the future and unfortunately electricity prices could go higher still.

  3. Christine Fyfe says:

    My goodness. I have a 24 kWh lead acid Gel system (80% usable = 19.2 kWh) and it cost me the equivalent of about 3 of these installed (3.4 kWh). I appreciate that battery storage is improving, which is great, but why does it seem that lead acid has disappeared off the radar amongst all the disappointing hype? People have huge double garages these days-you’d struggle to find a battery bank in all that room. Perhaps including comparisons with lead acid in these type of articles would be of benefit to readers new to this (I have recommended this blog to many novices who, like I did, are starting out with no idea…about battery storage and electricity…although you could make further arguments…
    Thanks for the great blog!

    • Ronald Brakels says:

      People who are on-grid have several motivations for installing batteries. They include:

      1) Saving money
      2) Helping the environment
      3) Having latest technology
      4) Telling their electricity retailer to go jump

      At the moment lead acid batteries are really only able to do number 4, Installing enough lead-acid batteries to go off-grid certainly isn’t going to achieve number 1. And they won’t do number 2. And at over 150 years of age they’re not number 3 either.

      And so people are pinning their hopes on new developments, and as a result no one pays much attention to lead-acid batteries anymore. It may not seem fair, as they have stood by us for 157 years and are still providing plenty of service off-grid, but humans are a fickle bunch.

      But while the new batteries chemistries definitely don’t pay for themselves at the moment, I am hopeful that at some point they will make it possible to do 1,2, and 3. But I suspect that 4, going off-grid in towns and cities, may never pay for itself because electricity retailers have the power to ensure it doesn’t by removing supply charges on electricity bills.

  4. john nielsen says:

    Hi Ronald,
    Thanks for a very long and descriptive info about the Enphase AC Battery etc.,
    I have been using lead gel batteries for 15 months. They are 12 v, 250 Ah and I have 12 of them in 3 banks, i.e. voltage between 54.8 and 52 v. Presume I get a 2 volt drop, would I then not get 2 x 12 x 250 = 6 kWh ? and for say $5,000 how will this compare with Enphase and the Powerwall ? I will expect 10 years life from my batteries since they are mostly only DOD at no sun times as the 6 kW Enphase micro system provides plenty of power during the day hours.
    I cannot see any use for those expensive Li-ion bats and believe it will be years before people will go off grid with them.
    I am stand alone with my Enphase micro system, and I cannot see why the Enphase battery couldn’t be used off grid as long as you have a means of powering the system to 240 vac, but who would want to, at that price? Not I.
    Cheers,
    John Nielsen, Silkwood.

    • Ronald Brakels says:

      John, I have very little to do with lead-acid batteries apart from using one to start my car. (It’s also possible to use one to start a horse, but I really don’t recommend it.) But if you have a dozen 12 volt, 250 ampere-hour then you’d have a 36 kilowatt-hour bank of batteries. If you draw 6 kilowatt-hours from them that’s only a 17% discharge. If that is all the discharge they regularly receive then, fingers crossed, they should last a long time.

      If I had an off-grid lead-acid battery system I’d be in no hurry to replace it. But if I can understand people who are building a new off-grid home who don’t have any experience maintaining lead-acids using lithium-ion or zinc bromide flow batteries instead because of their extremely low maintenance aspect and the appeal of having a 10 year warranty.

  5. I’ve thought of a better way to use storage batteries.Instead of having a hard wired device with all the complications of working out when it should kick in etc this whole process can be eliminated quite easily similar to an UPS.
    You have a storage battery which is portable and you can have a number of these.What you do is plug it in during the day, just like an electric car and charge it from your solar.
    At night you plug the devices you are using directly into it.In my case the main power consumption I use at night is my computers and my big screen TV.
    So that means I have three batteries charging during the day and at night I use the storage as I see fit.being portable I either leave the computer connected to it or use it for some other appliance as I see fit.I can leave it for instance in my study,the computer during the day plugs into a conventional power outlet on the battery and at night I flick a switch to change to the storage, either that or the battery has an inbuilt timer which switches automatically to the stored power.
    Simple, easy, and I am waiting to see it happen as I know this will provide a much simpler solution.I am sure we can make a device similar to the UPS and much cheaper

  6. Just another thing in regards to the calculation on the use and cost of power from the grid.
    The rate in NSW on my system is the same whether its day or night its 22 cents a KWH plus GST less my discounts.
    I thought of changing to a heat pump hot water system to save money but this seems somewhat confusing in regards to tariffs.My present duel element system has its own meter and the tariff is 8 cents a KWH plus GST less discounts.
    My feedback price is 5cents a KWH so on my figures if I consume 10KW at night for water and feed back 10KW of solar during the day my actual cost per day is 3 cents so that’s $9.00 a month or $108.00 per year.
    Going to a heat pump hot water system may not save me anything at all as I am thinking this will be charged at 22cents a KWH ?

    • Ronald Brakels says:

      I’m in Adelaide, so I’m not completely familiar with conditions in NSW, but I understand people may not be permitted to run heap pump hot water systems during off-peak hours due to noise restrictions.

      How much you’ll be charged for running a heat pump hot water system all depends on how much it runs off solar electricity.

      But it will use only about 30% as much electricity as your electric resistance hot water heater, so you will come out ahead on electricity costs, even if you do pay 22 cents a kilowatt-hour for the electricity it uses.

      But if you put it on a timer so it runs when your home is exporting the most solar electricity to the grid, hopefully you’ll be able to run it mostly off solar electricity, so you’ll come out well ahead on electricity costs.

  7. David Ryder says:

    Does anyone know what became of the Vanadium Redox battery that was developed a few years ago? These had the potential to be very cheap to build and last for many years (indefinite) without loss of performance.

    • Ronald Brakels says:

      David, vanadium redox flow batteries are still around and have been used for large scale applications providing both energy storage and ancillary services such as voltage regulation to grids. But I am not aware of any vanadium redox batteries that are small enough for residential use. Perhaps someone will produce one suitable for use by households, but it will face stiff competition from battery chemistries already available including zinc bromide flow batteries.

  8. Ronald

    Back to the lead acid gel batteries – an installer in northern NSW is advertising that they can be cost effective. That is a payback in a few years, whereas the new lithium based batteries do not pay for themselves.

    I see the comments above but they seem to be confined to off-grid systems.

    As you point out the technology is old but that makes it “cheap”. Would they be a viable alternative to the Enphase or other systems until the new technology comes down to a cost effective price? (say in ten years??)

    Also, while lithium batteries are usually promoted as high discharge, I assume a bank of lead-acid batteries could provide a reasonable current.

    • Ronald Brakels says:

      Steve, for an off-grid system I can see a lot of people looking at the new battery systems that are on offer and deciding to go with lead-acid, particularly if that is what they are familiar with and know how to maintain.

      But for an on-grid system, which is the only way the Enphase Battery can be used, no battery storage available at the moment will pay for itself, whether it is lithium-ion, lead-acid, or a flow battery. This could change in a few years. But if you are on-grid and looking to cut your electricity bills now, your options include installing a larger rooftop solar system; or investing in energy efficiency such as insulation, heat pumps, and LED lighting. If, for whatever reason increasing your solar PV isn’t practical, and you have the roof space, you can consider installing solar hot water.

  9. TOU rates and demand-charge fees are going to change that. Solar PV + battery storage is the only way residential solar PV will be able to battle the utility monopoly on power. Hopefully, the grid-connect fees will be controlled and there will truly be a level playing field between residential solar + storage and C/I-utility solar+storage.

  10. Ron, Have a look at the newer lead carbon batteries which appear to address the maintenance issues you allude to with traditional lead acid batteries. They are also able to handle partial charging as well as rpid charging and discharge much better and cost between traditional lead acid and the newer chemistries with very long projected lifespan better in fact than the Lithium battery units. Also known as the Ultrabattery but there are other manufacturers. I think the Enphase battery is neat but simply way over priced particularly in Australia. As soon as the early adopters with too much money have spent their money Enphase will have move back to realistic pricing based on real rates of return. I do in fact have a 5kW solar system equipped with Enphase micro inverters due to shading issues and they work really well. At under A$1,000/battery unit Enphase would be in the ball park If they do not I am certain our friends in China will soon have something that is price competitive.

  11. David James says:

    Ron, Thanks for the article, just looking at the Enphase now but thought they may help in a blackout – obviously not. I guess the Tesla Powerwall would suit this more at 10kw? Can the Enphase be used at all off grid like in a blackout. E.g. just to run LED lights in the house that may amount to only 30 watts and perhaps another appliance? Would 2 batteries let you run say an LED TV for an hour? A quote I received was for $2300 for 1x Enphase 1.2KW batter and $4100 if I buy 2? As I’m 1 person at home and work during the day in SA (no time of day charging), I was told just an 8 panel 2.1 KW system would be enough to charge the battery… details.

    2.08KW 8 panel iDesign Solar Power System
    Average daily yield 8.0kWh
    Average annual yield 2905kWh
    Annual yield return $1055.00

    Total costs of system is $4,887 + $2,300 for the battery if I paid cash. This seems a lot compared to a DC panel system where I could probably get a 4-5kw system for that price (no battery)

    Would this be worth it for just an AC 2KW system?

    • Ronald Brakels says:

      David, unfortunately the Enphase battery can’t provide backup power during a blackout. But you could get a small generator. That will be able to provide you with a lot more electrical energy than one Enphase battery will and will be very useful if you are in a situation where a blackout lasts for days.

      As for paying a total of $7,187 for a 2.08 kilowatt solar system and battery, I look at it this way. If you have an 8 cent feed in tariff, then after losses, the energy stored in one Enphase battery is only likely to save you about 20 or so cents a day. If you instead spent the money getting a 5 kilowatt solar system you’d generate an average of about 12 extra kilowatt-hours a day which you would get 96 cents worth of feed-in tariff a day for. So economically you are a lot better off getting a larger solar system without a battery. And it’s better for the environment, since you’ll be generating a lot of clean solar energy and sending it into the grid.

  12. Further to my previous post I was reading Finn’s latest post about the new larger Tesla Powerwall which in fact seems to actually stack up as an economically viable item with at least the possibility of getting a return on your outlay. This is very good news as it will put huge pressure on the other players to become realistic with their pricing and make the renewable storage space a viable business area which does not require subsidies. As I said Enphase watch out as reality will mean price sensibly or you will be out of business.

  13. Rather a late posting – but better late, than never?

    Might I suggest discounting at an inflation adjusted (‘real’) interest rate?
    My actuarial studies from over a half century ago predating the current economic fashion of embedded inflation – the RBA annual target of some 2 – 3%.
    Historically [supposedly risk free] govt securities might have offered a ‘real’ 2 – 3% pa.

    Some may suggest a mortgage offset rate – but, arguably, this should be ‘real’.
    For retirees with bank interest no greater than inflation (also taxable :() – perhaps ZERO.

    Perhaps discount at 0 (LCOE), 2.5% pa [& 5% pa]?

    Cheers,
    I like your style 🙂

  14. Just a follow-up – poor memory with illness & old age 🙁

    A Tassie installer has mentioned a 25 year warranty overseas; & with this safe lithium chemistry (LiFePO4 – LFP) housed inside in air conditioned comfort, might a 25 year life [to say 80% capacity?], at LCOE [or even a real 2.5% pa] give a positive return?

    PS: Don’t think I will survive another 25 years tho 😉

    • Ronald Brakels says:

      Lithium iron phosphate (LiFePO4) are the toughest type of lithium battery around, but even they won’t come with a 25 year warranty. 15 years at 60% of original capacity is the best I’m aware of. What you might instead have is someone claiming batteries have a 25 year design life or can be expected to last 25 years, but I bet their written warranty doesn’t say 25 years.

      Any salesperson or installer who says their batteries have a design life of 20 or 25 years without a written warranty is on very thin ice with regard to the law, as those kind of statements can be counted as giving an express warranty the battery will last that long, regardless of what the written warranty says. I’ve written about the problem here:

      https://www.solarquotes.com.au/blog/battery-warranties/

  15. Mark Zammit says:

    Hi Ronald

    I have a 5.3kW enphase microinverter roof panel setup in a house with 3-phase electricity. The 20 panels have been divided roughly between the 3 phases. Any idea how an installer would install a battery system like the enphase batteries in such a setup (i.e. do I need separate batteries for each phase). Just a theoretical question at the moment, as the current cost of installation negates any benefit at the moment.

    Cheers,

    Mark.

    • Ronald Brakels says:

      Hi Mark. The easiest option would be to just put the batteries on a single phase, preferably the one that would be most used at night. But while that might be suitable for some applications, it would obviously be sub-optimal for how most people will want to use home storage. A separate battery could be put on each phase but that is clearly not an efficient way to use them and will result in a poor economic return. With the right equipment the output of batteries could be distributed across the three phases as needed, which is a function multimode (hybrid) inverters perform with DC coupled batteries. Personally, I am curious to see how Tesla’s 3 phase Powerwall 2s will be wired up when they start installing them next month – that is, assuming they have any.

  16. Finn, could you email me. I just tried to email you from the states and it bounced back. Also tried calling and said number was incorrect. Tried several times. thanks.
    [email protected]

      • Finn and to all cotributors too just a fascinating discussion– even as a lawyer I have to quell my emotions at power companies getting away with paltry 6 cents per kiilowatt and these Enphase batteries as cool as they are just don’t stack up economically but like many others and I agree with Ian the Chinese will inexorably drive prices inexorably down.

        1 thing not mentioned and it is impossible to quantify but all real estate agents agree having these sorts of technologies certainly adds to the ‘attractiveness’ particularly for younger generation buyers ( with families on the horizon)and probablyincreased price they will pay for a smart tech home.

  17. Geoff, 6-7c/kWh is close to the actual ex power station cost of generating power most of the rest of the costs are for underutilised capital in providing back up capacity for cloudy/windless days as well as the network of poles and wires. As a business proposition why would they buy power at more than their lowest possible self produced cost it would not make sense from a business point of view. The real answer is in storage at the point of generation in small scale solar generation setups like most domestic situations and these storage setups would be ideally accessible to the network providers so they could draw on them at peak demand times as well as recharge them at times of low demand when unfavourable wind/solar conditions are forecast. Add to this time of use tariffs and also have significantly higher feed in payments which the utility would pay for the use of your storage and everybody wins. with over 1.6 million domestic systems if they all had some say 5kWh attached that would represent a 8,000MWh of stored energy. That would be enough to run SA for 5 hours or so alone at full load. Obviously not all the domestic systems could support 5kW of storage and not all systems are connected to the Eastern grid as there are a few hardy souls still living in WA but this points the real way to energy independence as well as a more robust grid.

  18. Florent says:

    The emphase battery is the good concept of storage when you are connected to the grid.
    It is not dangerous with DC high voltage.
    With one battery you can have your light during the evening! For utility in France we can divide per 1.5 the nuclear central…good for the earth

  19. There can be 14 ACB’s on a single 20A DP circuit…

  20. Your quotes where done in early 2016, has the cost of enphase batteries changed since then? I ve heard they are forecast to drop 20% a year?

    • Ronald Brakels says:

      Hello Andy. I am not aware of any decrease in the price of the Enphase battery. Maybe they will lower their prices when AC coupled competitors are more widely available. (I’ve been hearing that will happen soon. In fact, I’ve been hearing it will happen soon for many months now.)

      • TJ Roberts says:

        Hi Ronald… the AC Battery has a 100% DoD… as for the Warranty Document Supplied, you state “No”, but Enphase’s warranty is very clear and easily found.

        [https://enphase.com/sites/default/files/AC-Battery-Limited-Warranty-AU-NZ.pdf]

        With regards to Total Warranted kWh and Cost per Total Warranted kWh, it should be noted that the AC Battery can cycle twice daily, thereby halving costs.

        Also, wouldn’t it be easier to have the batteries listed in alphabetical order, either by name or company. In that way, it would be easier to find the storage product you are looking for.

        This battery comparison table is very important, but please, please update the data for exactness. Thank-you.

        • Ronald Brakels says:

          Thanks for letting me know details of the Enphase battery have changed. The battery comparison table has been updated.

          • TJ Roberts says:

            Great going… that price on the Enphase ACB seems sort of stale. Are you including the 1-time cost of the Envoy-S communications gateway for the 1st ACB? Also, why aren’t the storage products sorted by alphabetical order by company or product name? ACB, Powerwall, RESU,… or Aquion, Enphase, LG, Tesla… only making the suggestion!!! Thanks for your diligence, Ronald… you guys do a great job as a central source for solar+storage int he Land Down Under! Cheers!

          • Ronald Brakels says:

            Hello TJ. As far as I am aware there has been no change in the price of the Enphase AC battery here. The price on the table doesn’t include the Envoy. (The exchange rate has been pretty stable over the past year.) If you could tell me how much it is in the US, I’d be interested to know that.

            As for why the batteries aren’t in alphabetical order, I don’t know. I’ll have to ask Finn.

  21. Kim Ryan says:

    I just got a quote for an Enphase installation. Battery price hasn’t changed, but the installation cost was $450, less than half of your original figure. And AGL have just announced a 20% tariff hike. Which would mean 60c/kWh peak rate in Sydney starting from July. So I think a reasonable pay back period could now be achieved.

  22. I already have 2 Enphase batteries and had an add-on offer from my installer on 10/6/17 of $2180 for 1 battery $4120 for 2 etc. Looks like they are reacting to the market, if a little slowly at the time. Given the current energy price hike of 20% perhaps they could have held on but the offer is out there now.

    Thanks for the material above Ronald, it really cleared the cobwebs, not to mention the marketing fog thats out there. There are a few other sources of confusion like the discounts and the seniors allowances not to mention the variations in time of day rates, its a field day for market differentiation.

  23. I’m having 3 enphase batteries and 3.4kw panels added to my existing 1.3kw system. $4490 for 12 panels, inverter, monitor and 1 battery plus $1800 each for 2 additional batteries.

    I’m in Sydney faced with a 20% increase. Informative discussion thank you.

    • Ronald Brakels says:

      Hi MikeP. Just to make sure you go in with eyes open, I’ll mention the increase in NSW feed-in tariffs more or less cancels out the increase in electricity prices as far as home battery storage is concerned. But if you are getting the batteries for non-economic reasons, that won’t be a concern.

  24. Just wondering if anyone knows about Hello Solar. They are offering free enphase battery + controller + monitoring system worth $3000! Too good to be true?

  25. I can see some controvesial reviews about the company from your website and whirlpool forums (links below). I’m not quite sure what to think. Their quote seems to be quite good though – I was quoted $5990 for 13xJinko 290w panels + Frunios Primo 3kw inverter + Enphase battery + controller + monitoring.

    https://www.solarquotes.com.au/installer-review/hello-solar/
    http://forums.whirlpool.net.au/archive/2637940

  26. Mali Honzik says:

    Dear Ronald (& all contributors): you have all been extremely helpful.
    I live in NSW. I have recently had an offer to join a “subsidised field trial program” by a so-called reputable solar battery expert company. They stated that they would install a single Enphase battery at “half price” at $4,516 (they state an installation normally costs $7,300). I asked for a few more quotes, and had a comparable $5,390 for 2x Enphase batteries from another company. Had I not read your blog, I might have fallen for what is clearly an outright con.
    I wish there was a way to make the public more aware of all this.
    Reading Ronald’s excellent advice, I am convinced I will rather invest in upgrading my insulation instead!
    Thank you Ronald. 🙂

    • And they are still going.
      I’ve just been offered to join the same sort of “Subsidised Energy Independence Initiative”: a single Enphase battery for $5600(!) installed.

      For a battery with a 1.2kWh capacity…. I could save:
      1.2kWh * 35c/kWh (peak) = 42c per day (ok… per cycle, which will be nearly 1 per day) = $150 per year.
      Hmmm. and that is at maximum 270W output.
      Er… and doesn’t include the cost of putting the power into the battery.

      Points of differentiation:
      – “It comes with a 5 year maintenance program — ?what needs maintaining?”
      – “We’ll monitor your usage and tell you when and how you can modify your energy usage.
      Maybe I can sell myself out as a $5000 energy-use coach 😉

  27. Man I wish I had read this article couple of months ago. I’ve been, apparently duped, and paid $5790 for a 1.2 Enphase and just been offered a 1.6 for $3999. Going to get me completely of imported powers they said. Mmmm. Me thinks not. And not getting my money back by the looks of it.

    • Ronald Brakels says:

      Hello Sara

      Any product you buy (that’s under $40,000) is protected by Australian consumer guarantees:

      https://www.accc.gov.au/consumers/consumer-rights-guarantees/consumer-guarantees

      One of these consumer guarantees says products must:

      “meet any extra promises made about performance, condition and quality, such as life time guarantees and money back offers”

      So if you were told things about the batteries performance by the people who sold it to you and and the product failed to live up to them you are entitled to a remedy. This remedy could be a repair, a replacement, or a refund.

      If you wish to pursue this matter I suggest contacting a consumer affairs organization in your state.

  28. If anyone wants to have a look at a single Enphase battery’s performance I have started pushing the data from mine to pvoutput (level of charge is under extended data)
    https://pvoutput.org/intraday.jsp?sid=56467

    Total system with battery included under usage
    https://pvoutput.org/intraday.jsp?sid=56468

    I have worked out most the kinks in the software doing the pushing now but before February the data has quite a few issues.

    My quick back of envelope calculation shows it will take about 28 years to earn back $2000.

    • My “back of envelop” calculations

      Power Consumed 28.1kwh
      Power Returned 22.6kwh
      Power Consumed price 11.1c (my feed in tariff, some power is drawn overnight at flat rate but I’m ignoring that)
      Power Returned price 25.5c (my flat rate after “discounts”)
      monthly savings $2.64 = (22.6 * 0.255) – (28.1 * 0.111)
      double that in case February was a bad month $5.28
      annual savings $63.36 = 5.28 * 12
      payback 31.6 years = 2000 / 63.36

      Anyway my data is at the links above (and growing every 5mins 🙂 ) if anyone else wants to have a go at the maths I’d be interested.

      Solar panels are a completely different kettle of fish. First 4kw of panels were earning+saving about $100.00 a month and will pay themselves off in under 5 years.

  29. I can’t agree having the enphase system installed since August 31, 2017.
    My observations here;
    https://plus.google.com/+MichaelPotts/posts/N8sXWFq1VeF

    • My Enphase system as a whole also does well too but at least in my case that’s almost entirely down to the panels. When I looked at the battery alone the batteries economics aren’t good

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