Battery systems have come a long way in the past few years. And Enphase, the world’s leading microinverter manufacturer, is shaking up the market with its innovative, modular AC battery system. For off-grid consumers living in small homes, units and townhouses, there are many benefits of the Enphase AC battery.
A Quick History of Battery Systems
Winding back to 2012 the only option for a serious battery system was to install some ‘wet cell’ batteries that may last ten years and put up with a tedious maintenance schedule. The sizing of these systems was based on a ‘depth of discharge’ of 40% meaning that 60% of the battery was left sitting there unused. To make matters even more complicated, the batteries were installed in ‘strings’ and a single failure or change to system capacity, often meant that the entire string had to be replaced.
At the same time, lithium-ion solutions were entering the market at exorbitant cost. Utilities and analysts cried that it would be decades before the technology became competitive whilst innovators such as Elon Musk projected seemingly impossible advances. Generation One was released with poor temperature characteristics which often meant that systems shut down over summer. They also required advanced Battery Management System algorithms which only communicated with certain inverters. The market responded with claims of ‘battery ready’ which only further confused consumers.
Enphase – The Quiet Achiever
Whilst all this was happening, Enphase was quietly working away on a genuinely new concept. They call it the AC battery, and at its heart are Enphase’s key design criteria of modularity (ensuring no single point of failure), extremely long lifespan and an almost DIY ease of installation.
Since then Tesla has come out claiming a ‘world first’ inverter driven battery technology, but the clear fact remains that not only did Enphase do it first – they did it with a longer lifespan and a far easier installation process that is suitable not just for new, but also for any old inverter on the market.
The Benefits of Enphase AC Battery
The benefits and true beauty of the Enphase AC battery can be quite hard to understand. At first glance, many were underwhelmed by its small discharge rate and capacity. Over time a few things have changed this opinion and we’re now at the stage where Enphase have not only a decisive market niche but also a solid chance at taking a key percentage of the mass market alongside front runners, LG Chem and Tesla.
1. Compatibility and Ease of Installation
The Enphase AC battery key advantage is compatibility. It will work with any inverter old or new. It is so simple to install that a unit can be up and running on the wall in less than 10 minutes.
2. Reliability
Its other key advantage is modularity. Whilst its small size can sometimes be a disadvantage, system integrators need to be aware that no single point of failure and endless upgrade options are something that many battery systems simply can’t offer.
Remember what happens if a ‘string’ of batteries fails? Well, the same thing can happen if you lose your Powerwall. If that happens in an Enphase system, the rest of the batteries keep on operating and the overall effect is minimised. This has large implications not just for the consumer market, but also the commercial sector where uptime can be critical.
3. Battery Longevity
Even less apparent is the charge and discharge advantage. At first, the solar market cried out for faster discharge rates completely ignoring the effect this could have on battery life. These discharge rates are specified as ‘C ratings’ and both LG and Tesla are capable of C1. What this means is that the battery can be discharged to zero in one hour. Anyone who has seen the internal temperature of these batteries as they attempt that sort of discharge rate will know that they run internally above 40 degrees Celsius and that no amount of air conditioning will keep that temperature stable. An Enphase battery has a C4 rating which means that it will charge and discharge over a leisurely 4 hour period which leads to a much longer service life. This is illustrated by the Enphase AC battery’s impressive warranty of 7300 cycles. By way of comparison, competitor products specify 6000 cycles, but this figure could be significantly less if discharged at higher rates.
4. Upgrade Freedom
Enphase batteries can be expanded in small or large quantities at any time without affecting another battery in the system. This makes them perfect for adding onto installations large or small where only partial upgrades are required. They’re also suitable for people that want to ‘test’ battery technology with the aim of adding further units at a later date.
5. Safety
There are no DC isolators required as there are no hazardous DC voltages. The fire risk from DC systems is well documented. Enphase completely removes this DC fire risk.
System Suitability
What has become clear over the past few years is that comparing batteries is no easy task and that no battery is suitable for all applications. Key criteria include cycle life, depth of discharge, environmental factors (often overlooked) and discharge rates.
The Enphase AC battery seems very suitable and even cost effective in smaller applications such as townhouse or unit developments. It also has application in low energy use homes such as retired or working couples with no kids. The large LG and Tesla batteries are generally more suitable for more energy intensive environments.
ROI Considerations
Unfortunately, what many system designers don’t understand is that the ROI of a battery in an on grid hybrid situation is determined by its use. Whilst this sounds obvious, most designs seem to include additional capacity which effectively cannot be included in an ROI calculation. If we look at the typical home’s nighttime demand, most customers use between 200-400Wh of energy each hour as their ‘baseload’ consumption. If one is looking at achieving a maximum ROI outcome, a battery pack should be designed around this baseload output, and not the facilities maximum demand. How many Enphase batteries would it take to meet that demand?
There are two things to consider here. One is the maximum demand. Each Enphase AC battery will put out up to 270W. So just two batteries will easily cater for demand. To meet that demand all night long would require the Wh x the number of hours. Once again we are calculating around the lowest total demand which is the shortest day of the year.
Excess capacity will result in lower if not absurdly poor ROIs.
Therefore 300Wh @ 8 hours = 2.4kWh of energy which is equal to 1-3 Enphase batteries.
It’s worth noting that these calculations do not include heating or cooling requirements, however once again, sizing a battery system to these peak demands will result in extremely poor ROIs.
Recently we found yet another application for Enphase batteries and it’s one that has huge applications in the off-grid sector. Enphase AC batteries will AC couple into island systems. This means that an old wet cell pack could be compensated with lithium ion technology as it fails and if need be, in modular steps. Another key advantage is that Enphase batteries can be AC coupled on top of other lithium batteries such as LG Chem to provide increased maximum demand and a protective buffer between the C4 and C1 ratings.
Enphase AC Battery System Installed by Ecoelectric
The system pictured, installed October 2016, shows an off-grid system installed in a world first configuration by Ecoelectric. The LG Chem 10kWh units are used for bulk storage and are illustrated in the logging as ‘the grid.’ The 4 Enphase AC batteries clip the top of the load and take priority when charging or discharging. This provides another 1kW or so of additional demand and will ensure that ‘the grid’ lasts far longer than it would have otherwise. Temperature rises are minimised and redundancy is further increased. EchoGlobal
Overall it is always important to consider application and requirements. There are too many people shopping for brands which will never result in the best outcome, nor the best ROI. Furthermore, it is imperative that designers understand that batteries come in many different sizes with many different design factors. These factors must be understood before it is possible to recommend a truly unique and integrated design.
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I agree, enphase batteries dont have enough out put, over priced.Very frustrating to consumer waiting for this company to catch up with capacity & price.
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Yes that is correct, but Enphase are introducing backup capability in 2020.
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Enphase does not provide backup capability. Therefore, if backup is a priority, the LG or Tesla options would be better. Is that correct?
Hi,
I am amod from loom solar.
I saw your video and its now imaginative but i believe this is future, In next years whole world would be living with solar energy only.
this is not easy job but also its not impossible job.
Going forward, we would need educate more people to accept it.
I recently had the good fortune of reading your post regarding “ac batteries and modular-battery”. It is perfectly written and, contained sound, practical advice with valid facts and figures. I look forward to read your next informative write-up.
Enphase aren’t doing it right with their battery system, as far as I am concerned. Their ROI is poor because their cost per kWh put through the batteries over the cycle life of the system can easily be double that of a simpler and higher capacity system like LG chem. The larger, cheaper, batteries also allow much better energy arbitrage, ie on cloudy days, they allow customers on a time of use tariff to buy electricity at off peak rates and put a decent amount back in the evening when the time of use tariff is higher. 1-2 kWh of enphase storage is piddly amounts if you’re looking to make us of your batter this way.
I wish I want to avail this service because the weather here is very sunny and good timing to use PV panels.
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Great to see some discussion around this blog. Some valid points been made but all it really underlines is that every situation is different. Having looked at hundreds of real life load profiles I can assure you that a very significant segment of the market simply doesnt require 10kWh of storage. Where most designers go wrong with these systems is they think that a larger battery will produce move savings. It wont. For these systems to have any hope of ROI at all, the battery must be cycled every day. Even a shortage of charge on overcast days, or lower night time usage over temperate nights will up to double the payback period on large batteries. As per usual, everything is site specific and other factors such as backup requirements can change the product selection. The short answer is there is no correct answer – talk to the customer, analyze their unique situation and then make a recommendation. Enphase’ niche is the townhouse/unit space (ie a very large proportion of urban population) and we have also proven another in regards to repairing off grid systems.
Enphase originally annouced these batteries in a two inverter (peak load focused model) and a one inverter (baseload targeted model) at a price point in Australia for first adopters of $1,150. The peak load model never arrived and the launch price model was closer to $2,500 installed. At the same time Telsa announced the PW2 – with 13.5 kWh useable storage coupled with 5 kW inverter and off grid capability model. This model could support both Peak and Base load. Economic return for anyone on a time of use tarrif means you might only have to supply peak power for 1-2 hours in the evening cooking – but that could amount to 5-6 kWh. It would take sixteen Enphase batteries costing over $30K to supply this peak load – and each battery couldn’t fully discharge its power in this short timeframe – so you would have to over purchased unused storage capacity – at a price of more than double its nearest competitor – to make up for a woefully small inverter on each AC battery pack. Sonnen uses the same excellent battery chemistry as Enphase – even they went with a much bigger central inverter with 1-7 batteries per unit (but their unit without any batteries is drastically overpriced – about $7K for just the unit and inverter). If one wanted to spend that much on an inverter alone – get a top notch selectronics one of double the output power and just use the same (or an) battery technology. If Enphase doubled there output power per each battery unit (i.e. put two S275 inverters to allow 540W per unit) and brought each unit’s price down below AUD $1,000 then Tesla would have some great competition. With all Enphase’s executive turnover and redundancies it might be a while before it can make some great moves in the storage market like it has done in the micro inverter space.