Adding an ESS to Enphase Enlighten System

[svetz]

$720 - 12x iQ7+ @ $60 from eBay used
$ 10 - NodeMcu
$ 16 - 16-Channel Relay, 2 kW/channel
$280 - 4x 400W chargers
$3000 = At 30¢ Per Wh a 10 kWh battery is $3000, if you go cells and your own BMS 20¢/Wh + 55 - BMS = ~2100.
======
~$4,000 (or $3,000 with DIY cells)
+ 20% for breakers, wifi switches, wire
======
~$5,000

Occurred to me that for nighttime usage, for the cost of MC4 splitter cable ($7) and SPDT remote switch you could reuse an existing microinverter. That is have the existing microinverters hooked up to both the solar panel and the battery with a cutover switch to isolate them (e.g., microinverter can only ever be connected to one or the other). That essentially eliminates the microinverter costs. With the number of wireless switches and cable complexity it might not be worthwhile. Possibly replace the switch per panel with a diode to prevent backflow into the panel and use the main battery switch or relay bank?

 

[GXMnow]

Battery Hookup has a few 10S Li NMC EV batteries. They should be a decent fit to feed a single iQ7. 30 volts dead to 42 volts fully charged. Right now the 7.9 KWH pack is going for $790 or just $100 per KWH. That would run a 240 watt iQ7 for 30 hours. Will it work to parallel on 2 iQ7's??

 

[newbostonconst]

As microinverters are current sources, when connected to a battery they output their continuous maximum power. In the diagram below, a relay is used to power individual microinverters, so if you had 300W microinverters and needed 800W, you'd turn on 3 relays providing 900W. Enphase would then throttle other inverters back to reduce the energy by 100W.

If the microinverters could be throttled and controlled by Enphase (e.g., IQ7s or IQ8s) you'd only need a single relay rather than a bank of them. Unfortunately, the Enphase system would prioritize the battery-powered microinverters over other non-solar energy sources, so even though they could be throttled to zero output you'd still want at least one relay to only output power when you wanted to.

I have tried to get a IQ7x working on a battery for over a year and haven't been able to. I can get it working on the bench with a small battery but as soon as I hook it up to my main 35kwh pack I get a error for to low of resistance between the battery and the AC side. I bought a toroid isolation transformer to totally isolate the AC and DC side and I still get the error. I would love to get rid of my 300watt base load with this method and add inverter capacity.

When the IQ7 runs off the battery is produces full power if your providing it good voltage....Once the IQ7 warms up it drops to the guaranteed wattage which is like ~20 kw lower....I added one cell at a time to see how it reacted and once it has enough battery voltage to produce full power it gives a constant output. There is a thread some where in this forum on it.

 

[svetz]

... error for to low of resistance between the battery and the AC side...

I'm assuming the error is from the microinverter. Possibly a "safety" feature to ensure it's not a dead short on the DC?

For my LG panels Vmpp = 34.5 and Impp = 9.86, so the Rmpp is ~ 34.5 / 9.86 ~= 3.4Ω.

Have you tried a blocking diode (or two to get ~2-3Ωs) resistance?

Update: Possibly measuring impedance, might try an inductor.

...I bought a toroid isolation transformer to totally isolate the AC and DC side and I still get the error...

It was probably very efficient, that is < 1Ω resistance.

When the IQ7 runs off the battery is produces full power if your providing it good voltage....

That's what I'd expect from a current source.

Interesting it works with some batteries and not others. Most batteries have pretty low resistances, what sort of battery were you using when it worked? ncsolarelectric has it working with a Hoymiles microinverter using a Drok power supply. Not sure if he's attempted to connect it directly to a battery yet.

 

[Shimmy]

Logically it would do some kind of check to confirm the DC is below its maximum interrupting current. Pretty hard to run the inverter if you cannot switch the DC.

 

[ncsolarelectric]

I have not tried the Hoymiles microinverter directly from a battery because I only have one 12V, 50Ah battery on hand. I need 2 more.

The IQ7 is probably looking for a specific Amps per Volt slope and it's too steep with the larger battery. It could also be the battery BMS that is cutting out, Idk what the ratings are of the BMS you're battery is using.

 

[newbostonconst]

I'm assuming the error is from the microinverter. Possibly a "safety" feature to ensure it's not a dead short on the DC?

For my LG panels Vmpp = 34.5 and Impp = 9.86, so the Rmpp is ~ 34.5 / 9.86 ~= 3.4Ω.

Have you tried a blocking diode (or two to get ~2-3Ωs) resistance?

Update: Possibly measuring impedance, might try an inductor.


It was probably very efficient, that is < 1Ω resistance.


That's what I'd expect from a current source.

Interesting it works with some batteries and not others. Most batteries have pretty low resistances, what sort of battery were you using when it worked? ncsolarelectric has it working with a Hoymiles microinverter using a Drok power supply. Not sure if he's attempted to connect it directly to a battery yet.

The small battery is just a subset of the larger battery so I am guessing because there are more cells in parallel there is less resistance....The resistance off memory was still in the maga ohm range. The micro does work fine with a solar panel connected. I could try a blocking diode but not sure I would want that across my 35kWh battery bank.

From Enphase Manual
DC Resistance Low – Power Off Condition For all IQ Series models, a solid red status LED when DC power has been cycled indicates the microinverter has detected a DC Resistance Low – Power Off event. The LED will remain red and the fault will continue to be reported by the Envoy until the error has been cleared. An insulation resistance (IR) sensor in the microinverter measures the resistance between the positive and negative PV inputs to ground. If either resistance drops below a threshold, the microinverter stops power production and raises this condition. This may indicate defective module insulation, defective wiring or connectors, moisture ingress, or a similar problem. Although the cause may be temporary, this microinverter condition persists until the sensor is manually reset.

The toroidal transformer is a isolation transformer so the AC in and AC out are not connected thus are infinite resistance.

https://www.mouser.com/datasheet/2/410/VPT230_2170-781527.pdf

After reading the manual above again maybe it is because I have no ground connected but it works fine with a solar panel connected without a ground connected.

 

[ncsolarelectric]

Do you have a ground on the Neg or Pos terminal of your battery, or is the battery voltage floating wrt ground?

 

[ncsolarelectric]

You could add a 300W DC-DC converter between the battery and the inverter. It will provide current limit and act like a constant current source. It will add cost, but that's probably the most efficient solution to your low Z problem.

 

[WildLeg]

This thread went deep quick, glad i’m showing up relatively early. I had the idea years ago to bypass the microinverters when the grid was down with inline mc4 t connectors on the dc panel wiring for off grid use. Then i wondered about a small battery under each panel in parallel with the inverter dc wiring. Its all very cerebral when comparing the option of another IQ10T.

Enphase Energy ENCHARGE-10T-1P-NA Enphase Encharge 10

The Enphase Encharge 10 all-in-one AC-coupled storage system is reliable, smart, simple, and safe. It is comprised of three base Encharge 3 storage units, has a total usable energy capacity of 10.08 kWh and twelve embedded grid-forming microinverters with 3.84 kW power rating. It provides backup...

www.cityelectricsupply.com

$6850 For an IQ10T...The simplicity of plug and play has much value.

Enphase has a new form factor battery coming out 1H 2023 with double the peak and continuous power at 5kWh of energy. Will this drive down costs for the 10T further? Doubtful as enphase manage their channel inventory quite diligently. Will the new 5P battery work on our older system? Will it require a new controller? Enpahse did say the new form factor will have a wired CANBUS communications protocol instead of the ZIGBEE. This lead me to believe it will require some new equipment all around.

Re: IQ7 and IQ8 on the same circuit.… as long as you don’t need enphase monitoring and you are only using them grid tied/ac coupled they will both work on the same branch circuit. They have no choice but to work. I hope to be testing this soon.

 

[svetz]

Costs - not worth it if you want the equivalent of adding an IQ10
An IQ10 is 10 kWh of energy and 3.8 kW power for about $8k...

The prior analysis showed the costs were about a wash. Have things changed?

Let's put together all the thoughts from the thread so far and combine them with some new products (first bullets) and see how it works:

First, let's look at the modified design to the right: PIC activates relays (green) turning the chargers or inverters on/off Series of small chargers instead of one larger charger Cheaper, less heat loss, no fans so more efficient, but takes more space Provides more reliability/resiliency Allows excess solar to be consumed intelligently in small amounts by turning single chargers on/off. Envoy throttles inverters when off grid While on-grid, the microinverter relay bank can activate a portion of microinverters to minimize the night-time base load, or the pic can control the number activated to match power consumption. If operated at night, sun-powered microinverters do not count towards the IQ Battery microinverter limits. No need for IQ8s or a new Envoy. PIC can match battery SoCs by turning micros on/off PIC can also operate remote devices wirelessly based on excess solar Excess solar determined by IQ Battery SoC.

...An IQ10 is 10 kWh of energy and 3.8 kW power for about $8k...

Since then the IQ10 price has dropped, it's about $7k now.

• The new IQ7PD72 is $79 and handles 200W ($0.38/watt), for 3.8kw of power you'd need 19 of them, so $1500.
• The IQ7PD84 an IQ7, so you don't need a new Envoy and it will throttle power
• Two EG4 batteries would give 10 kWh for $3k.

Technically, you don't need additional microinverters because at night time the ones on your roof are idle. But the wiring and switching for that would probably be more of a tangled mess for that than it would be worth. For ground mounted panels with a nearby ESS it might be viable.

Let's add in $500 for the balance of systems, that's $6k. So probably still not worth it to DIY your own IQ10 unless you pick up some used microinverters. For example, if you could pick up IQ7As off eBay for $50, then it would cost about $600 for the micros so not much savings.

But... if you can't shell $7k out right now, you could go in smaller increments and build up over time. For example, a single EG4 battery and five IQ7PD84s would provide 5 kWh of energy and 1 kW of power for a cost of ~$2k. Unlike adding DC batteries, there are no age/impedance concerns when piecemealing a system together, so you could add to it a little bit at a time.

 

[svetz]

Found an interesting thread where people have turned the theory of connecting micros to a battery into practice!

Another aspect anyone should consider before going this route is that Enphase's bi-directional charging will be out next year. That will allow the massive battery in your EV to be used.