Newbe needs help trying to reduce the power I buy from the power company

[thomBangor]

Hi, I'm trying to design a diy solar system to put on my garage roof in Maine, that will reduce the power I buy from the power company.

I think I would like to include an outdoor-type battery like the outdoor EG4 powerpro, so that I can store my solar power for use at night.

I would prefer not to net-meter for the moment. I believe that means I need a gadget that prevents power from backfeeding to the grid.

What gadget do I need to prevent the backfeeding?

What I have in mind so far is three groups of: 5-hyperion-400W-panels-in-series. Put that into the three (??) DC inputs of the Growatt 6000 or 7600 MIN TL XH-US. I would mount the Growatt inverter on the outside wall of my garage (is this ok?).

Plug the Growatt Min's battery charger into a EG4 PowerPro WallMount AllWeather.

I read in this forum the Growatt Min has a battery output and input, and read some about it in the spec, but would really appreciate knowing whether this actually works?

The spec for the EG4 PowerPro claims that it is seamless with Growatt - is this true for the MIN?

The Growatt Min claims it has a shutoff for arc faults in the panels- is this true and if so do I still need a DC fuse/breaker for the panels?

My final question: SignatureSolar calls this Growatt Min a grid-tie inverter. Since it does batteries isn't it a hybrid inverter? Is there somewhere one can go to learn what off-grid, hybrid, and grid-tie really mean in technical terms?

Any thoughts on which is inverter better for my situation - off-grid, hybrid, or grid-tie, and if so which one?

Lots of questions, thanks for your patience.

 

[sunshine_eggo]

off-grid: An inverter that can form it's own grid to provide power, typically from a DC source (batteries). It may use grid or generator as a backup source. Some off-grid inverters can be used as the grid needed for grid-tie inverters. They must be of equal or greater output power than the grid-tie system and capable of frequency shifting, or "AC Coupling"

hybrid: An inverter that can form its own grid, be powered my multiple sources (battery, direct PV), may operate batteryless and may provide grid-tie function. It may typically also be setup as an off-grid inverter, and it may also use grid or generator as a backup source.

Grid-tie: An inverter that must be connected to an existing grid to function. It expects to be connected to an infinite grid and will output it's maximum available power at all times.

Grid-tie also means "grid interaction," i.e., your equipment will interact with the grid. This requires you have a contract with your power company.

Since this is being pursued as a cost savings effort, it's very important to understand the ROI. Using typical numbers, even with DIY, you may not break even for many years unless your power is VERY expensive. I have helped someone work through their Victron system in Maine, and their power is pretty cheap. I would expect your break even to be on the order of 10+ years.

 

[thomBangor]

Since this is being pursued as a cost savings effort, it's very important to understand the ROI. Using typical numbers, even with DIY, you may not break even for many years unless your power is VERY expensive. I have helped someone work through their Victron system in Maine, and their power is pretty cheap. I would expect your break even to be on the order of 10+ years.

Thanks for the reply. I think our power costs are around 20 to 23 cents / kWh, which seems expensive to me. I used https://pvwatts.nrel.gov/pvwatts.php to estimate the kWh (5-7 kWh/yr) I would get from a 6kW system (15 panels) and did an ROI calculation. It came out to 3.5 years with a battery, 4.5 years without a battery. Are my numbers reasonable given the components I'm looking at?

https://signaturesolar.com/growatt-6kw-grid-tie-inverter-min-6000tl-xh-us/ 1 @ $900
https://signaturesolar.com/hyperion-395w-bifacial-solar-panel-black 15 @ $119
https://signaturesolar.com/eg4-powerpro-14kwh-all-weather-lithium-solar-battery-wallmount/ 1 @ $3600
Unistrut/EasyStrut/SuperStrut 8 @ $40
Wire 2 @ $100

 

[thomBangor]

off-grid: An inverter that can form it's own grid to provide power, typically from a DC source (batteries). It may use grid or generator as a backup source. Some off-grid inverters can be used as the grid needed for grid-tie inverters. They must be of equal or greater output power than the grid-tie system and capable of frequency shifting, or "AC Coupling"

hybrid: An inverter that can form its own grid, be powered my multiple sources (battery, direct PV), may operate batteryless and may provide grid-tie function. It may typically also be setup as an off-grid inverter, and it may also use grid or generator as a backup source.

So if I want to run ~50% solar inverter power, 50% grid power at all times, do I want an off-grid with freq-shift/AC couple? Hybrid sounds neat (esp. since I have a gas generator) but they are really expensive.

 

[Mkgough]

I Maine, I expect angle and direction will be a concern, also snow build up, so maybe trackers that you can tilt better than roof mount to get more bang for your bucks vs more inefficient roof mounts at a poor angle and snow build up issues?

 

[sunshine_eggo]

Thanks for the reply. I think our power costs are around 20 to 23 cents / kWh, which seems expensive to me. I used https://pvwatts.nrel.gov/pvwatts.php to estimate the kWh (5-7 kWh/yr) I would get from a 6kW system (15 panels) and did an ROI calculation. It came out to 3.5 years with a battery, 4.5 years without a battery. Are my numbers reasonable given the components I'm looking at?

https://signaturesolar.com/growatt-6kw-grid-tie-inverter-min-6000tl-xh-us/ 1 @ $900

Guessing you missed this needs a 400V battery, and the list of "compatible" batteries that does not include any E4 batteries?

https://signaturesolar.com/hyperion-395w-bifacial-solar-panel-black 15 @ $119
https://signaturesolar.com/eg4-powerpro-14kwh-all-weather-lithium-solar-battery-wallmount/ 1 @ $3600
Unistrut/EasyStrut/SuperStrut 8 @ $40
Wire 2 @ $100

Where is all your hardware for NEC compliance? You need rapid per-module shutdown. You need to know what the utility requires to allow you grid-tie to them.

 

[sunshine_eggo]

I Maine, I expect angle and direction will be a concern, also snow build up, so maybe trackers that you can tilt better than roof mount to get more bang for your bucks vs more inefficient roof mounts at a poor angle and snow build up issues?

This is an excellent point. The aforementioned Maine user relies heavily on grid for backup in the cold months.

 

[Solar Guppy]

You will never earn your investment back building a solar system in a high latitude location not even getting into the issues with cold weather in your location would require a sheltered and insulated environment, no inverter or battery will handle Maine winters outside.

Here is an exercise for you, add up the full cost to build your system, then see how many kilowatts you can buy at your current rate divided into your annual usage. I suspect you will find nothing will replace your grid connection for a lower net price.

 

[thomBangor]

Here is an exercise for you, add up the full cost to build your system, then see how many kilowatts you can buy at your current rate divided into your annual usage. I suspect you will find nothing will replace your grid connection for a lower net price.

I already did this. Please see my post above: Friday at 8:27 AM. If there are holes in the math, please point them out specifically. Thanks

 

[thomBangor]

I Maine, I expect angle and direction will be a concern, also snow build up, so maybe trackers that you can tilt better than roof mount to get more bang for your bucks vs more inefficient roof mounts at a poor angle and snow build up issues?

I think this concern is already factored into the calculation I performed at https://pvwatts.nrel.gov/pvwatts.php. Is that correct or no?

 

[thomBangor]

You will never earn your investment back building a solar system in a high latitude location not even getting into the issues with cold weather in your location would require a sheltered and insulated environment, no inverter or battery will handle Maine winters outside.

"You will never earn back your investment..." could you please elaborate and be specific? I don't know what 'issues with cold weather' means.

For sheltered/insulated, it looks to me like EG4 PowerPro Allweather would be suitable in Maine's weather. Spec says -4 F. We do get one or two days colder than that I guess, but does that mean the system instantly self-destructs? Seems like keeping it at -4 F for a day or two in the winter would be a reasonable problem to solve, rather than give up on?

 

[thomBangor]

Guessing you missed this needs a 400V battery, and the list of "compatible" batteries that does not include any E4 batteries?

Yes, I missed this. tidbits like that are part of the reason I'm posting here. The EG4 allweather pro spec says it is compatible with GroWatt inverters, so I assumed it was compatible with the Growatt MIN. Is that incorrect? Could you please suggest an inverter suiting my purposes better?

 

[thomBangor]

Where is all your hardware for NEC compliance? You need rapid per-module shutdown. You need to know what the utility requires to allow you grid-tie to them.

What is NEC, and why is it important to comply with them? Why do I need rapid per-module shutdown? We have no permitting required in my town for solar. I did ask the utility what they require to grid-tie, but at the moment I don't want to grid tie. I just want about half of my power to come from solar, and the other half to come from the grid-- mixed so that the grid can flex up when my wife turns on 4 stove burners, for example.

From a functional perspective, what is rapid per-module shutdown, and what purpose does it achieve?

 

[thomBangor]

Thanks for the reply. I think our power costs are around 20 to 23 cents / kWh, which seems expensive to me. I used https://pvwatts.nrel.gov/pvwatts.php to estimate the kWh (5-7 kWh/yr) I would get from a 6kW system (15 panels) and did an ROI calculation. It came out to 3.5 years with a battery, 4.5 years without a battery. Are my numbers reasonable given the components I'm looking at?

https://signaturesolar.com/growatt-6kw-grid-tie-inverter-min-6000tl-xh-us/ 1 @ $900
https://signaturesolar.com/hyperion-395w-bifacial-solar-panel-black 15 @ $119
https://signaturesolar.com/eg4-powerpro-14kwh-all-weather-lithium-solar-battery-wallmount/ 1 @ $3600
Unistrut/EasyStrut/SuperStrut 8 @ $40
Wire 2 @ $100

To add some more data:
My power cost will be between 28 cents/kWh and 30 cents/kWh in 2025 (I can't find on my bill whether I'm hydro or public district)
My kWh used in 2023 was about 10,000
in 2025 my est. power bill will be ~$3000.

My costs for the solar project (that I know of) are those listed in my prev post, which add up to ~$7000 total (not including rapid shutdown modules, which I'm not convinced are a good thing).

My estimated return/year based on pvwatts.nrel.gov is ~6000 kWh/year, which is ~$1800/year.

My ROI estimate is $7000/$1800/yr = 3.8 years.

Thanks

 

[1201]

@thomBangor

Really the best way to not need an interconnection agreement is to do a subpanel and power that subpanel with pv and battery. That way you are not worried about exporting to the grid and you can size accordingly.

Before I got my connection agreement this is what I did. I selected some circuits (in my case about 90% of my monthly use) and setup a system to run that.

It would run from solar and better during the day, and at night if the better for low enough it would switch over to the grid and run from the grid.

You might say, well I don't want to have to install a sub panel. If that's the case then get a connection agreement.

Zero export is not really zero export and without permission you might get a visit from the poco

 

[sunshine_eggo]

What is NEC, and why is it important to comply with them? Why do I need rapid per-module shutdown? We have no permitting required in my town for solar. I did ask the utility what they require to grid-tie, but at the moment I don't want to grid tie. I just want about half of my power to come from solar, and the other half to come from the grid-- mixed so that the grid can flex up when my wife turns on 4 stove burners, for example.

National Fire Protection Association (NFPA) National Electric Code (NEC).

Even if permits aren't required (my city is the same), they often require compliance with certain standards. Unfortunately, if not installed by a licensed contractor, my city requires a permit.

I checked the city of Bangor permit requirements, and "permits are usually required for the following: Electrical systems"

The permit application references NEC 2020.

From a functional perspective, what is rapid per-module shutdown, and what purpose does it achieve?

690.12(A&B) Rapid Shutdown of PV Systems on Buildings.

Rapid shutdown provides the first responder with a simple method to de-energize the PV system conductors easily and quickly to ensure a safe condition on the roof of a building during a fire.

www.electricallicenserenewal.com

It's purpose is to protect firefighters on your roof from high voltage DC sources.

 

[Solar Guppy]

Yes, I missed this. tidbits like that are part of the reason I'm posting here. The EG4 allweather pro spec says it is compatible with GroWatt inverters, so I assumed it was compatible with the Growatt MIN. Is that incorrect? Could you please suggest an inverter suiting my purposes better?

The MIN requires a proprietary growatt battery that is ~400V and on a cost per kWh is ~ $400 which is significantly more than the 48V batteries, the inverter itself is low cost.

 

[Solar Guppy]

"You will never earn back your investment..." could you please elaborate and be specific? I don't know what 'issues with cold weather' means.

Your 15 panels in PVwatts shows @7500 kWh annually, but this assumes you are gridtie ( or can use all of it on site each days harvest ). With your storage of 14kWh, a significant amount of your best months of harvest could be lost with nothing to consume it as your average maybe 20 kWh day, but that's actually 27kWh / day in July and 14kWh day in December generated so averaged math doesn't work in this case.

The balance of system can cost as much as the main pieces of the system, wire has become very expensive, and there is conduit, breakers and hardware that all adds up. If your doing a 48V system wire cost is VERY expensive.

You need a spreadsheet with your daily loads at least per month to see what size storage you need to utilize the full harvest, a budget that has all the NEC stuff you may not realize is required and a plan on how to split the usage as the Growatt MIN likley can't power the whole home so that needs to be understood.

 

[Hedges]

Is net metering available, if so what terms?

You can store power in a battery, but only about 1 day's worth before it becomes impractical in terms of size and cost.
With net metering, you can store a summer's worth of production for use in the winter.

If you DIY GT PV, it will cost $1.00/W +/- and make power for $0.025/kWh +/- (amortized over 20 years)
If you buy an economical LiFePO4 battery (e.g. EG4 PowerPro), it will store power for $0.05/kWh (amortized over 6000 cycles, 16 years.)
The inverter with supports battery as well as powering loads and optionally doing grid-tie net metering may make system cost more than sum of the above, or maybe not.

If you do an offgrid system you can make power as cheap, but if you waste it by not consuming, cost per kWh is more.
If you don't waste any but don't make enough so have to buy from the grid, that will cost you your $0.20/kWh or so rate.

If your main objective is to save money, don't dismiss net metering without evaluating it.
The system can also provide backup during grid failures. You might want a backup generator for winter.
If you have gas, oil, etc. heat available, you can use electric and net metering when the grid is up, and have economical backup.

 

[SoggyShoes]

Here is something I have been wondering about relating to what the OP wants, where they basically want to produce as much of their own power and then supplement as necessary from the grid.

Why not build basically an RV system using the grid like shore power?
Could a person have all the AC and DC circuits paneled off a charger/inverter system with solar and batteries. Then the grid connection is just a panel with a 50A 14-50 plug.
I imagine many jurisdictions would red tag a system like this if they found it, but I have worked with smaller communities that have a PUD that are pretty flexible. It sounds like the OP's area is pretty reasonable.

 

[Citlalatonac]

Here is something I have been wondering about relating to what the OP wants, where they basically want to produce as much of their own power and then supplement as necessary from the grid.

Why not build basically an RV system using the grid like shore power?
Could a person have all the AC and DC circuits paneled off a charger/inverter system with solar and batteries. Then the grid connection is just a panel with a 50A 14-50 plug.
I imagine many jurisdictions would red tag a system like this if they found it, but I have worked with smaller communities that have a PUD that are pretty flexible. It sounds like the OP's area is pretty reasonable.

As long as the AC generated from the panels/batteries is fully isolated from the grid AC, it is at least generally fine by utility. You basically need to go AC>DC>AC to accomplish that. Zero export setups exist, but will always have a little leakage back to the grid just because of how electricity is. Some utilities reportedly can detect very small changes will take action. Generally, please don't be the person who zaps a linesman with a bodgejob.

Local code enforcement also matters for fire/electrical/building and is separate from utility.

 

[SoggyShoes]

So does that mean if the power goes out at an RV park, then all those RVs hooked up to shore power with charger/inverters will be leaking current back into the grid?

 

[SoggyShoes]

l guess I would have thought they have something that disconnects the connection or something that prevents back flow.
Or do they all take all the shore power make it DC then convert back to AC to send to the A/C panel? That seems like it would loose a lot of efficiency.
And do they all do the same thing. I have Victron so I am especially curious how they work.

 

[thomBangor]

The MIN requires a proprietary growatt battery that is ~400V and on a cost per kWh is ~ $400 which is significantly more than the 48V batteries, the inverter itself is low cost.

Any idea what the EG4 Manual means on pdf page 33? Protocol P02-GRW?

 

[thomBangor]

@thomBangor

Really the best way to not need an interconnection agreement is to do a subpanel and power that subpanel with pv and battery. That way you are not worried about exporting to the grid and you can size accordingly.

Before I got my connection agreement this is what I did. I selected some circuits (in my case about 90% of my monthly use) and setup a system to run that.

It would run from solar and better during the day, and at night if the better for low enough it would switch over to the grid and run from the grid.

You might say, well I don't want to have to install a sub panel. If that's the case then get a connection agreement.

Zero export is not really zero export and without permission you might get a visit from the poco

I agree this is the best, for a single person. In my case it is not the best. Solar generated power through my system is going to vary wildly with snow/clouds/etc. My wife has made it clear that this project can only proceed if she cannot tell the difference in the power. It is my belief that using a subpanel one of two things will happen:
1. That subpanel will be at some point underpowered and my wife will never let me do a project like this one again (not acceptable)
or
2. That subpanel will be conservatively designed, so power is not efficiently used, so the ROI time for this project goes up to the point where it makes no sense to do it.