help for existing grid tied system to add battery

[BigEdHB]

Hello, I have the following:
System Size: 10.140 kW -
Module: CanadianSolar CS3N-390 (26 panels, I Believe)
Inverter: Enphase IQ8+ Microinverters

Here's where I need help. The system is not producing close to a $0 balance because of the "time of use" by So Cal Edison
I Would love to add a battery to help offset the usage at night a bit.
I have seen articles stating that it is a simple procedure. However, I don't even know where to start, in terms of what battery and is my inverter sufficient to just add a battery. So many questions, hoping someone can lead me in the correct direction.

Thank you all in advance.

 

[sunshine_eggo]

You can add a very expensive enphase storage system.

You can add a separate off grid inverter and battery solution to AC couple to your existing GT system - also very expensive.

Don't be surprised if the ROI on battery storage is on the order of 30-50 years.

 

[BentleyJ]

Simplest Solution: Use Enphase batteries that are designed for Enphase IQ microinverters. You may need a system controller and a load controller installed if you don't already have them. If the system is configured for Sunlight Backup then those devices are already present. Unfortunately this is the most expensive choice.

Generic Solution: Add UL1741SB compliant hybrid inverter and batteries. This is more complicated and there is already much information on this forum regarding AC Coupling.

 

[1201]

Sorry to jump in on this thread but I have a question for @BentleyJ and @sunshine_eggo

If the goal is to use batteries at night and he already has a sell back agree meant wouldn't it be far easier to install the new inverter in parallel with the existing system, instead of ac coupling?

 

[Hedges]

What are your on and off peak rates?
What are your credits for backfeed? Same as rate to buy power, or less?

Some rate plans have a spread of $0.20 to $0.30/kWh for off-peak credit vs. on-peak. Others may differ $0.50, not sure.

There are batteries which can cost around $0.05/kWh over projected 16 year life (for instance EG4 PowerPro, which is 14 kWh). I think the EG4 inverter would double that cost, if used with just one battery. So I think about $0.10/kWh for such equipment if you use it for AC coupling and time shifting.

Maybe this will give about 8 year ROI.

As 1201 says, doesn't have to be a battery inverter that supports AC coupling, just an "AC battery", charging with the goal of hitting zero export from your PV system, discharging to supply loads during peak rates. A "power wall".
But with AC coupling, it can work together during extended outages.

I'm presently trying out Sunny Boy Storage with LG RESU-10H. (Not that I'm recommending it, has some issues, but it does perform the time-shifting function.)

 

[zanydroid]

IIRC I calculated 8-10 year ROI with PG&E with self installed PowerPro and 18kpv

Unfortunately this is the most expensive choice.

Is this really more expensive than a PowerPro with 18kpv? I believe the IQBAT are cheaper in isolation, however I am not sure about the all in cost of the system. And I believe some things can be omitted for time shifting use case (IE can the MID be omitted; in principle you should just need CTs and a coordinating controller to provide self consume signals and controls)

 

[solar8484]

What's the typical monthly electric bill? On NEM3?

 

[zanydroid]

That was going from NEM2 -> NEM2+Storage with forced exports at peak as a net electricity consumer.

The house is basically all-electric (haven't done the WH but that's $40/month of gas) with one EV. I need 3.5 MWh/year just for heating,1.75 MWh/year for EV (though I'm getting free charging right now at EA).

Most of the consumption is in the winter so forced export in the summer is the linchpin of the 8-10 year ROI. Forced export is still done during non-summer rates to harvest a little bit more $cheddar$.

I have not bought the system used in that ROI modeling.

 

[solar8484]

Since the OP has 10kW iQ8's, the cheapest home battery solution for backup power usage is likely a single Enphase 5P (~5kWH) and maybe 3T (~3kWH) based system. Other home battery or hybrid inverter systems would require a much larger (~20kWH) battery bank to support reliable and safe off-grid AC coupling with the 10kW iQ8's. This is because when iQ8's are used with Enphase batteries they work (via proprietary comms/control) in the voltage source mode (i.e. like a typical off-grid inverter that supports parallel operation) when off-grid instead of the standard current source mode (i.e. like a typical grid tied inverter). Too bad Enphase does not provide the open API/control to allow third-party home battery/hybrid inverter systems to control the iQ8 mode. Another way to help Enphase battery sales.

 

[zanydroid]

Current source is somewhat far from accurate , I think people jump to it because the voltage source analogy is clearly correct and like sexy but inaccurate opposites

It is more like a voltage source with slow speed voltage/phase adjustments to maintain a constant power target.

A true current source would slew the output parameters much more quickly.

 

[zanydroid]

FWIW off grid operation was not crisply specified by OP. So the max charge/discharge speed is determined more by parameters like how much production they want to capture and supply for self consuming.

Overshooting the capabilities when on grid just pushes more out or pulls more in.

This however is academic in comparing small IQBAT to hybrid/AC batteries. In the 3-10kWh range IQBAT are not that badly priced (ignoring balance of system). And there are very few grid tie approved systems competing at the 3kWh and 5kWh size nodes anyway.

 

[BigEdHB]

Simplest Solution: Use Enphase batteries that are designed for Enphase IQ microinverters. You may need a system controller and a load controller installed if you don't already have them. If the system is configured for Sunlight Backup then those devices are already present. Unfortunately this is the most expensive choice.

Generic Solution: Add UL1741SB compliant hybrid inverter and batteries. This is more complicated and there is already much information on this forum regarding AC Coupling.

What's the typical monthly electric bill? On NEM3?

average $125. was told that Time of use was the reason for this. I'm hoping to be able to draw from a battery source once the sun goes down but still be on the grid

 

[BigEdHB]

You can add a very expensive enphase storage system.

You can add a separate off grid inverter and battery solution to AC couple to your existing GT system - also very expensive.

Don't be surprised if the ROI on battery storage is on the order of 30-50 years.

just paid $1500.. on my year end to Edison. are we really thinking $45,000 on the low end?

 

[zanydroid]

just paid $1500.. on my year end to Edison. are we really thinking $45,000 on the low end?

Sunshine eggo is in a normal energy cost state, while some of the other folks on the thread are in a crazy energy cost state like California.

You can do your own math and add up 1 or two PowerPro batteries and one 18kpv inverter

Or one IQBAT 3/5 (pick yer poison) and that gives a bottom bound (does not include all support components)

 

[BigEdHB]

What are your on and off peak rates?
What are your credits for backfeed? Same as rate to buy power, or less?

Some rate plans have a spread of $0.20 to $0.30/kWh for off-peak credit vs. on-peak. Others may differ $0.50, not sure.

There are batteries which can cost around $0.05/kWh over projected 16 year life (for instance EG4 PowerPro, which is 14 kWh). I think the EG4 inverter would double that cost, if used with just one battery. So I think about $0.10/kWh for such equipment if you use it for AC coupling and time shifting.

Maybe this will give about 8 year ROI.

As 1201 says, doesn't have to be a battery inverter that supports AC coupling, just an "AC battery", charging with the goal of hitting zero export from your PV system, discharging to supply loads during peak rates. A "power wall".
But with AC coupling, it can work together during extended outages.

I'm presently trying out Sunny Boy Storage with LG RESU-10H. (Not that I'm recommending it, has some issues, but it does perform the time-shifting function.)

mid peak generation and delivery 0.61 per kwh
I think they give me back 0.10 but this is the winter rates I would have to dig up summer rates

 

[zanydroid]

FWIW there are occasional fire sales on grid tie code compliant batteries on eBay etc. That might significantly boost your ROI.

Note however that batteries and inverters are joined at the waist in the current regulatory environment. So you have very little freedom in mixing and matching (it’s not zero, but also not free market)

IOW buying a battery on fire sale without understanding the inverter you are allowed to use it with will be a sad day potentially

 

[BigEdHB]

Sunshine eggo is in a normal energy cost state, while some of the other folks on the thread are in a crazy energy cost state like California.

You can do your own math and add up 1 or two PowerPro batteries and one 18kpv inverter

Or one IQBAT 3/5 (pick yer poison) and that gives a bottom bound (does not include all support components)

would this system allow me to use battery when the panels are not generating and still remain on the grid?

 

[BentleyJ]

So you want to save that $1,500 every year. For example, a 5 year pay back gives you a budget of $7,500.
How many Enphase IQ batteries does that buy and would they provide enough capacity to offset 90%+ of the kWhrs listed on the year end catch up?

 

[zanydroid]

would this system allow me to use battery when the panels are not generating and still remain on the grid?

All of those will.

Some will also let you defer export at the peak rate. Normally you export 90% of solar at the off peak rate. It depends on what modes are supported. 18kpv has the mode. I am not sure it is legal to turn on in all POCO in California.

 

[zanydroid]

So you want to save that $1,500 every year. For example, a 5 year pay back gives you a budget of $7,500.
How many Enphase IQ batteries does that buy and would they provide enough capacity to offset 90%+ of the kWhrs listed on the year end catch up?

$7500 + 30% federal