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The Tesla Powerwall 3 vs Enphase Energy’s System

Updated: May 21



Enphase, battery, backup storage, residential battery, backup power
Enphase Energy Battery System

I have attended several updates over the past few weeks on the new Tesla Powerwall 3

(PW3).  The PW3 seems better positioned then previous Tesla storage systems for a few reasons.  Before I begin this blog, it may make sense to go over a few terms and reference a few blogs, or in other words, lets place these concepts in our bag so we can pull them out later.

 

Tesla, Tesla Powerwall 3, Powerwall, Backup storage, backup battery, home storage
Tesla Powerwall 3

Battery Chemistry:  Older Tesla Power walls have used NMC chemistry, (nickel, manganese, cobalt) which was less safe and had significantly lower cycle rates, did not last as long.    With the new PW3, Tesla changed the technology to Lithium Iron Phosphate (LFP), which Enphase has always used.  The chemistry of the battery matters, both for production, the environment and even politics.  I have never been a fan of NMC – See Blog.

 

System Design Changes:  Last year, PG&E eliminated Net Energy Metering (NEM) and implemented Net Billing Tariff (NBT).  Under NBT solar users lose roughly 75% of all power exported, so it makes sense to minimize exports, making energy storage systems (ESS) mandatory in most designs – See Blog.

 



Coupling: Solar systems can be AC coupled or DC coupled.  The Enphase system is an AC coupled system while the Tesla PW3 can be AC or DC coupled.  While DC coupling can be easier when installing new solar with storage while AC coupling can be easier to configure with existing solar systems.  DC (direct-current) coupled systems mean the solar DC does not need to be converted to charge the batteries where AC coupling requires solar to go from DC to AC and back to DC to charge the batteries.  While DC-coupling can be more efficient, other factors like inverter efficiencies, power usage direct (not from batteries) and module level performance maximizing (inverters) can mitigate these efficiencies.

 

Inverters: This is one of the biggest differences in the two systems.  Tesla is a string inverter system while Enphase uses microinverters.  String inverters are less tolerant to shade, soiling or module mismatch then microinverters.  Thus, microinverters provide maximization of power per module over string inverters.  I wrote a blog about my 18-year history to remind me as to the benefits and challenges of both.

 

System Monitoring:  In the inverter blog above, I go into a great deal of the history of solar system monitoring.  In a nutshell monitoring was an option in the past, but it has become a requirement for most systems installations today.  Tesla uses their App for monitoring and monitors at a system level, total production.  With Enphase you can use their App or web-based monitoring and they monitor to the solar module level.

 

Okay our bag is packed, let’s begin the journey.

 

 

Executive Overview:

 

While there are many details that separate Tesla and Enphase, there are also several high

Santa Rosa Solar System, Enphase micro inverters, REC solar panels, Mission Solar Panel, Tesla Powerwall 3, Powerwall, Certified Tesla Installer
Santa Rosa Solar System

level differences.  Enphase requires you have both Enphase inverters on the roof to pair with their ESS solution.  Tesla on the other hand can be configured DC-coupled, where their PW3 can control both the solar and ESS or AC coupled to work with any solar system, including Enphase.  Cost can also be a big difference favoring Tesla especially in the DC-coupled solution.  Monitoring and support favors Enphase since it can monitor down to the solar module where as Tesla monitors the system, total power produced.  Module level monitoring makes systems easier to verify they are working, diagnosis problems and support.  I will cover these items in more detail below.

 

Next let’s look at the basic configurations of each system:

 

                                              Tesla                                         Enphase

                                                                                      PW3                                               5P

Total Storage capacity                                                   13.5 KWH                             5 KWH

Continuous Power                                                          11.5 KW                                 3.84 KW*

Maximum Configuration units                                   4                                           16           

Maximum Storage                                                           54 KWH                               80 KWH

Warranty                                                                          10-years                               15-years Cooling                                    Fans                    Passive

Installed Weight                                                               287 lb                                174 lbs                                    

 

*The Enphase system with IQ8’s for solar includes the power of both the 5P storage and the solar inverters during when the sun is shining.

 

For purposes of this blog, I will be comparing a new solar plus energy storage system, installed in northern California (PG&E territory).  In most new installations, under PG&E’s net billing tariff, I will be assuming the PW3 will be installed with 20 solar modules configures in a DC-coupled mode.  For Enphase I will assume we will be installing 20 modules paired with 20 IQ8M inverters configured with 2 Enphase 5P batteries.  In this configuration the PW3 has 3.5 KWH more storage, and the Enphase system has 2.8 KW more AC power.   I will compare in detail the following areas:

 

Cost

Design flexibility, expandability and solar performance.

Installation

Redundancy and reliability

Monitoring

Safety

Service and Support

Warranty and politics

Sunlight back-up, Sunlight quick start and generator integration

 

Cost –The main cost difference will be the cost of the Enphase solar inverters which are needed in addition to the inverters in their storage.  Up to 20 KW of solar can be supported by the inverter in the PW3.   Based on the configurations above, the ability of the PW3 to control both the storage and up to 20 KW of solar gives it a 10-15% up front cost advantage in most configurations.  Cost saving is probably the greatest benefit of the PW3.

 

Design flexibility, expandability and performance: 

 

One design Flexibility the PW3 offers over the Enphase system is it can be configured either DC-coupled or AC coupled.  The Enphase system can only be configured as an AC coupled solution and only works with Enphase solar microinverters.  Thus, both systems would work well in a new solar and storage situation.  But for a customer who already has solar, unless it has Enphase inverters, the only way to make this work with Enphase storage is to replace the existing inverters and rewire the modules.  In comparison, the PW3 system can easily be added to an existing solar, AC-coupled, without the need to rewire or replace the existing solar system.

 

Inverters - As mentioned in my blog on inverters, microinverters have a significant advantage with mitigating shade losses and design flexibility over string inverters.  The PW3 does have 6 maximum power point tracking (MPPT) strings, which does allow more flexibility than any string inverter I have worked with.  Each string on a PW3 can have between 3-12 modules with a maximum total of 20 kw of solar.  This design allows for maximizing string power with multiple orientations, roof pitches and some shading.  I could design one MPPT string to manage an east roof, one a west roof, and a third a south roof that has a tree that has rolling shade.  The MPPT’s allow each roof string to operate independently so each string can produce maximum power or losses by shade without effecting the others. Let’s take the example above where the 12 modules on the south facing array gets a rolling shade, a tree in the front yard that shades one side array in the morning, moving across the 12 modules through the day.  The challenge is if one module is shaded 10%, it could cause a 40% loss in production for the entire 12 modules.  This could be mitigated by breaking the 12 modules into multiple strings, but this increases cost and complexity.  On the positive side, the loss of power on the south roof will not affect the east or west roofs.

 

Enphase microinverters attached to each module can make design easier.  Since each module (as opposed to string) acts independently, they can be place in almost any quantity, orientation, or slope.  This has come in handy when a customer asks us to add a few more modules or change the design because the spouse wants a cleaner look in the front yard roof.  From a performance standpoint, microinverters produce more power especially with shading.  With microinverters, the only modules that are affected are those the shade touches, allowing the others to producing 100% power.  So, in the example above, with microinverters, the module that has 10% shade on it could be losing 40% of its power, while the others are unaffected.   Also, additional power improvements are harvested from microinverters with allowing for module mismatch and inconsistent soiling.  In an extreme example, if 11 modules are producing at 300-watts, and one module loses 1/3 of its cells (diode goes out) so it is producing 200-watts, with a string inverter all 12 modules are reduced to the lowest module, 12 modules at 200-watts, where with micro inverters it will just effect one module.  Excessive soiling on a module (think pigeons or chimneys) will also have this negative effect on a string. 

 

Battery expandability and incremental design: 

 

While Enphase is on their 4th generation system using Iron Phosphate or LFO chemistry, Tesla has abandoned the NMC chemistry of its first two generations of batteries and has joined the LFP world.  LFP batteries are safer and provide more longevity.  Likewise both systems are expandable, so let’s compare.

 

A single Tesla PW3 has 13.5 KWH of storage with 11.5 KW of continuous power.  Up to 3 additional PW3s can be configured for a total system size of 54 KWH of storage and power or 46KW.

 

A single Enphase 5P has 5 KWH of storage and 3.84 KW of continues power.  A total of 16 5P’s can be configured together for 80 KWH of storage and 61.44 KW of power.  One option Enphase IQ8 solar inverters have that the PW3 does not is during the day, the solar inverters aggregate with the storage inverters to provide additional power to the system.

 

Both systems will easily work with 95% of the homes in the US with Enphase having a slight advantage with more flexibility in incremental design and total storage and power.

Tesla full home backup, backup switch, Tesla Powerwall 3, Tesla Battery, Tesla home storage
Tesla Full Home Backup Switch

Installation: Both systems require roughly the same installation process, installing modules, connecting these modules to the energy storage system, and then connecting the system to the utility.  Enphase does require the inverters to be mounted below the modules and more mounting of the ESS components.   This favors Tesla in reducing the amount of time to install a system especially if a customer’s meter main allows for the new Tesla back-up switch, which allows a meter socket for easy whole home ESS installation connections to the grid.  This back-up switch often eliminates the need to replace meter-mains or move electrical circuits as is needed without it.  In a recent tour to the Enphase testing lab, they are also looking to reduce the number of components and have a meter-socket back-up switch soon (1st quarter 2025) which will lower their installation time as well.

 

Redundancy favors Enphase for a few reasons.  With the PW3 you have all your eggs in one basket.  The single inverter, batteries and controls are all in a single unit.  If the inverter fails, it is an all or nothing event.  And if this inverter fails, you lose both your back-up system and solar on the roof.  Enphase has several levels of redundancy.  While the inverters for the solar and storage do work closely together, they can also work separately.  If a solar inverter fails, it only effects on module, not the whole solar array.  Even the storage system has multiple inverters in each 5P, if one of the six inverters fails, the other five continue to provide you with back-up power. 

 

While the PW3 is just starting to be installed, I will use some inferred logic regarding the reliability between the 5P and the PW3.  The Enphase storage system has no moving parts (passive cooling) and separates system controls, and solar inverters from the actual ESS.  The PW3 has fans for cooling and is an all-in-one box which usually generates more heat.  In the old days of string inverters, the number one issue that caused inverters to fail was the fans failing, the only moving part in the system.

 

New regulations require all systems to have a rapid shut down, to keep first responders safe.  This shut down is located near the meter main and these two systems handle it differently.  Enphase requires a single rapid shut-down switch wire in their controller for the entire system.  The PW3 requires each battery to be wired into the rapid shut switch.  In addition, the solar array DC coupled to the PW3 requires the installation of an MCI (one per every 3 modules) – mid circuit interrupter leading to more complexity in design, longer installation time and questionable long term reliability issues.

 

Monitoring has been one of the greatest advancements in solar and storage and it favors

Tesla Monitoring, Tesla Battery Monitoring, Tesla Solar Monitoring
Tesla Monitoring

Enphase.  As mentioned above, Both Enphase and the PW3 come with system level monitoring.  System level monitoring is great to see how much power a solar system is using, when the storage is charging and discharging and even how much power a home is using.  When consulting with clients I can use this data to verify solar is producing within guidelines.  I can also see if the battery is discharging at the correct time to maximize financial benefit.  Being able to see how a home uses power has allowed me to diagnosis issues in homes that have excessive energy use.   If major issues exist, either monitoring

system will allow us to see we have a problem.  One thing Enphase offers that the PW3 does not is module level monitoring.  When I begin a consult with a client and find they have Enphase, it always makes my job easier.

Enphase per panel monitoring, Enphase system, Enphase battery
Enphase Monitoring

   In the last few clients I have worked with that had Enphase I was able to see one customer had a module not working, one had excess soiling near a chimney and another was getting excess shading from some bushes growing above the roof line.  In addition, because they had module level monitor, it was easy to see which microinverter was not working and which modules needed to get cleaned.  With system level monitoring, these issues could have gone unnoticed for years or even the life of the system.

 

Safety for installers and homeowners’ favors Enphase mainly due to working with higher voltages with DC-coupled systems.  Enphase converts the solar modules from DC to 240 volts AC, the same voltage our homes use.  The PW3 uses higher voltage, 600-volts DC coming off the roof and this voltage stays hot, even when the grid power is off.  This is one reason code requires all DC wiring form solar be enclosed in metal conduit trough an attic space while AC wiring does not need conduit in the attic.

 

Service and Support is a little mixed between the systems.  Let’s break it down into a few areas:

1)        Expertise in repair personal

2)        Ease of replacement

3)        Reliability

4)        Trouble shooting

5)        Customer Service

 

In most cases Enphase requires less expertise in repair, especially in issues related to the solar system.  The module level monitoring discussed above, makes it easy to locate the exact inverter/module on the solar system experiencing an issue.  No diagnoses required, just a truck roll to replace the inverter and often inverters can be fixed remotely by Enphase.  Usually, the time to drive to a job site, exceed the replacement time.  With the PW3 and system level monitoring, knowing I have an issue, is just the beginning.  I need a service call to figure out what the issue is, and even more time consuming where the issue is.  I remember the days of trouble shouting string issues.  They often required pulling several modules, to try to find which one was the issue, jokingly called battleship on the roof.  This could take hours and require expertise to find and repair the issue.  As mentioned above the bigger issue for a customer is often minor issues go unnoticed with string inverters and can have a significant affect over time.

Tesla Servicing, Enphase servicing, Tesla maintenance

The service and support of the storage systems seem similar.  One issue I do see is that since many of the components in the PW3 are not replaceable, it will require the 275 lb. unit to be removed requiring multiple people, multiple truck roles and/or specialty equipment.  Enphase being more modular will allow many of the replacements to be done by a single service person and is more component level replicable verses having to replace the entire unit.  For example, a failed inverter on a PW3 (only one) will create a total solar and storage system to be down.  With the Enphase 5P, failure of one of the 6 microinverters in the unit will have no effect on the solar, and allow the storage to continue to operate with 17% less power.   Also the monitoring will pinpoint which inverter failed, lowering the needed expertise in the field.  Enphase often asked for these parts to be returned for testing, allowing them to improve long term reliability.  We will have to wait and see how Tesla handles the actual return or recycling of their replaced units. 

 

Warranty and Politics: So the warranty of the products favors Enphase.  The PW3 unit comes with a 10-year limited warranty.  In a DC coupled environment, the PW3 controls the solar and storage unit.  Since most solar modules come with a 25-year production warranty, this means the PW3 would most likely need to be replace once, maybe twice, during the systems life cycle.  Enphase offers a 25-year limited warranty for the solar inverters and a 15-year storage system warranty.  While the storage warranty from Enphase does not last through the systems lifecycle, it does provide a 50% benefit over the PW3.

 

Politics can simply be stated as both companies are American.  The power wall name is better known, kind of like Kleenex for tissue. And finally many people I work with have a very strong opinion of Elon Musk, Tesla’s primary share holder.

 

Generator integration, Sunlight Backup and Sunlight jump start also favors Enphase. 

 

In a grid outage, most solar only inverters do not work (anti-island), as the solar inverter requires AC power from the grid to turn on.  This was a compromise with utilities and first responders to eliminate the need for a disconnect device (can use the solar breaker).  The two exceptions I know of this is the Enphase IQ8 solar inverters and Energy Storage systems (both require automated disconnects). 

Enphase monitoring, Enphase Solar, Enphase battery, Enlighten
Enphase Monitoring

The IQ8 inverter can work when the grid is up or down, Sun Light Backup.  When the grid is up it acts like other inverters, converting DC power to AC power and sending it to the home, ESS or grid.  When the grid goes down, the disconnect disconnects from the utility, PG&E, and the IQ8’s self-form a grid using the DC power of the solar modules (does not work at night).  Thus, with the IQ8 inverters, the customer could have power to the home during daylight hours, even without ESS. 

 

With most ESS systems, when the batteries drain, the are no longer available unless a customer has a generator that can recharge them, or the utility grid comes back on-line.  The Enphase IQ8 solar inverters offer one unique Sun Light Jump Start.   Since the IQ8’s can form a grid when the utility is down and the sun is shining, they can “wake-up” a drained battery system, allowing it to continue to work, even when the batteries are fully drained.  Once there is enough sunshine to turn on the IQ8’s, power can begin flowing again to the ESS for charging.  Usually the best approach to facilitate this option is to turn off all the loads to the house, until the ESS has established a good charge.  Once your ESS has a decent charge, slowly turn breakers back on to minimize surge.

 

About a month ago during a PW3 training, Tesla explained how their generator “integration” worked.  Integration is a stretch as the home is either on ESS or generator, but they do not work together.  If the PW3 fully drains (turns off), an automated disconnect would disconnect the PW3, connecting and starting the generator.  The battery would serve no additional benefit at this time.  The generator would continue to run until the grid is restored.  Once restored, the generator would disconnect and turn off, and the PW3 would reconnect and begin charging again.  We designed this for one of our Enphase Storage clients many years ago as a fix for an old generator not Enphase qualified, and while it works, I never thought of it as integrated. 

 

Enphase has true integrated between the solar, ESS and the generator.   Like my Sonnen ESS (see battery vs generator blog for savings)  you can set the ESS controls to start the generator if the battery’s state of charge reaches say 10% and to turn off when the batteries charge to 95%.  This can also allow a homeowner to set a lower storage reserve for backup, since the generator is available to recharge batteries, even if they are almost fully drainer when the utility goes down.  One thing the Enphase system does in addition is it will use the solar to cover the house loads, allowing more power availability from all three sources simultaneously – ESS, solar and the generator.

 

Summary:

 

Sometimes the choice between the Tesla PW3 and Enphase ESS can be simple.  It a customer has solar, and it is Enphase, use Enphase, any other vendor (i.e. Solar Edge or SMA) Tesla PW3 is the only current option Enphase is working on this).  If the customer does not have solar, and has significant shading, Enphase will most likely be your best bet.  Where it gets more complicated is around installing a new customer with solar and storage.  Deciding between Tesla and Enphase is like buying a new car, is your primary goals low upfront cost and basic, or do you want the upgraded version.  Tesla offers up front cost advantages since the PW3 is an all-in-one solution, one inverter runs both the ESS and solar.  The PW3 can also be easier to install since it has few components.  Enphase offers a system with more flexibility in design, more redundancy with multiple inverters, and a longer warranty.  For larger homes, Enphase can be configured with over 40% more power and storage and has a true generator integration.   Also the extended warranty, harvesting more power with microinverters and better monitoring, does offer more long term savings with Enphase.  As a guy who has been in the industry for over 18 years, module level monitoring from Enphase offers a level of security unmatched by system level monitoring.  For my next blog I will be looking at the 25 costs of ownership of these two systems.


If you have questions about either system please reach out to Dylan using the contact information below.


Dylan Mathias

Owner, First Response Solar

707.888.1243

License #: 1039876

 

 

 

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