Is grid connectivity inverter really worth it?

[1201]

Without some sort if credit, you probably want batteries. But just 25% credit and you're better off buying more panels and forgoing battery.

Do you mind sharing some math on this?

 

[Brett V]

I will add that based on what I can do with the 3kw of ground mount panels I put in for the off grid system, I'm pretty confident that if I could utilize the 9kw of grid tie panels on the roof for whatever I want, I could have a very comfortable life off grid in a SHTF scenario.

 

[Hedges]

Do you mind sharing some math on this?

GT PV hardware costs about $1.00/W, maybe $1.10/W with RSD.
5 hours effective sun per day, I come up with $0.025 to $0.03/kWh amortized over 20 years.

I can overpanel GT PV for just the cost of PV panels and hardware, maybe $0.25 to $0.50/W. Multiple orientations, less clipping.


Lithium batteries look like they cost at least around $0.05/kWh over their cycle life, plus inverters that work with them cost more (unless a hybrid that is also your PV inverter.)

So I might as well add up to 200% maybe 300% more GT PV, no more than the cost of batteries.
Desire for grid-backup of course changes the equation.

If you pay for turnkey GT PV install, cost is more like $2 to $4/W, so battery may be more attractive in comparison.
Much less work, I think. Especially if just a Powerwall or similar AC coupled battery.

Watch out for bad panels that degrade, however. Counting on 25 to 40 year life. Or at least 20 year with above math.

 

[DIYrich]

I will add that based on what I can do with the 3kw of ground mount panels I put in for the off grid system, I'm pretty confident that if I could utilize the 9kw of grid tie panels on the roof for whatever I want, I could have a very comfortable life off grid in a SHTF scenario.

You could put in a switch to move the power from the grid system to the off-grid.

 

[Zwy]

GT PV hardware costs about $1.00/W, maybe $1.10/W with RSD.
5 hours effective sun per day, I come up with $0.025 to $0.03/kWh amortized over 20 years.

I can overpanel GT PV for just the cost of PV panels and hardware, maybe $0.25 to $0.50/W. Multiple orientations, less clipping.


Lithium batteries look like they cost at least around $0.05/kWh over their cycle life, plus inverters that work with them cost more (unless a hybrid that is also your PV inverter.)

Assuming you pay $0.12/KWh, can you ever come out ahead going full offgrid?

That's an impressive motor. Pretty massive but the price reflect that also..

diysolarforum.com

 

[Zwy]

You must not be married.

I just replaced a perfectly good electric dryer with a gas version, simply so I didn’t have to break down the how/why for my wife.

Clearance price $400 LG with smart features felt cheaper an easier. Hell I’d happily spend $400 to avoid the look on her face when I say to only dry clothes at certain times

My wife uses the electric dryer at least every 2 days.

She is The Official Loads Tester when it comes to checking inverter output.

 

[Brett V]

You could put in a switch to move the power from the grid system to the off-grid.

My grid tie system is SolarEdge. The optimizers aren't compatible with anything else.

 

[Brett V]

My wife uses the electric dryer at least every 2 days.

She is The Official Loads Tester when it comes to checking inverter output.

I've never been able to train mine to not use the microwave and toaster oven at the same time while making a pot of coffee when the air conditioning is on. Upgrading to a bigger inverter than I need was the end solution.

 

[Watts Happening]

I've never been able to train mine to not use the microwave and toaster oven at the same time while making a pot of coffee when the air conditioning is on. Upgrading to a bigger inverter than I need was the end solution.

Your wife is my wife’s spirit animal

 

[DIYrich]

My grid tie system is SolarEdge. The optimizers aren't compatible with anything else.

Would it work if you bought a SolarEdge inverter and hooked it up to your off-grid system. Then switch the PV from one Inverter to the other?

 

[Quattrohead]

My wife uses the electric dryer at least every 2 days.

She is The Official Loads Tester when it comes to checking inverter output.

I was told I can do whatever I want, as long as when she hits the on button it turns on. WAF Wife Acceptance Factor lol

 

[1201]

I've never been able to train mine to not use the microwave and toaster oven at the same time while making a pot of coffee when the air conditioning is on. Upgrading to a bigger inverter than I need was the end solution.

That's why systems like this exist ?

 

[Hedges]

Assuming you pay $0.12/KWh, can you ever come out ahead going full offgrid?

That's an impressive motor. Pretty massive but the price reflect that also..

diysolarforum.com

Your calculation for batteries is $0.0264/kWh. My rough number was $0.05/kWh. That changes the PV panel to battery calculation a bit.
Most commercial battery systems are much more expensive, but DIY with cells and server rack batteries might reach this range.

All based on manufacturer's claimed cycles. There are a few forum members with actual experience of high cycle life. Many more with failure?
Tests have not shown many manufacturers reaching claimed life. Those were operated around 1C continuously, so results may be better with our gentle cycling.

Are LFP prices artificially high?

Cost is irrelevant to sale price. market value is king. profit drawn from building, marketing, future sale reduction pricing, etc. I would be EXTREMELY surprised if sales were anywhere close to material and labor and manufacturing costs... It's like the cannabis market. It costs MAYBE $50 to...

diysolarforum.com

I don't like putting a lot of money into chemistry that degrades with time.
Electronics, I think main degradation mechanism comes from electrolytic capacitors and semiconductors, both strongly affected by temperature.
I have some experience with electronics still operating decades later.
Fans, of course, need replacement. I just ordered a 24V fan for VFD that I've had for 20 years.

For grid-backup batteries I went with AGM 3 years ago. 1/5th the cost of lithium (that I knew about) for 1/5th the cycle life.
If I get pushed onto NEM 3.0 I'll consider changing that system to LiFePO4 and moving the AGM to another system on NEM 2.0

 

[Crowz]

The hybrid grid connection is the only reason I got back into solar so to me its not only useful its required.

Plus if someone was starting out and wanted to get into solar on the cheap side it seems required too since you can start with thy hybrid and grow as money allows. No batteries required to get started.

 

[1201]

GT PV hardware costs about $1.00/W, maybe $1.10/W with RSD.
5 hours effective sun per day, I come up with $0.025 to $0.03/kWh amortized over 20 years.

I can overpanel GT PV for just the cost of PV panels and hardware, maybe $0.25 to $0.50/W. Multiple orientations, less clipping.


Lithium batteries look like they cost at least around $0.05/kWh over their cycle life, plus inverters that work with them cost more (unless a hybrid that is also your PV inverter.)

So I might as well add up to 200% maybe 300% more GT PV, no more than the cost of batteries.
Desire for grid-backup of course changes the equation.

If you pay for turnkey GT PV install, cost is more like $2 to $4/W, so battery may be more attractive in comparison.
Much less work, I think. Especially if just a Powerwall or similar AC coupled battery.

Watch out for bad panels that degrade, however. Counting on 25 to 40 year life. Or at least 20 year with above math.

How many cycles are you using for battery calc? I get about 2 to 3 cents per kWh with my calculations.

Grid tie has some major benefits but for many people is not as inexpensive as initially expected. Grid tie requires ul components and usually an engineered design, so sld cost is a factor, engineered racking is more expensive, required shutoffs etc , and of course it may have additional monthly fees.

doing some estimates for my particular use case, it seems I can actually get into a battery system cheaper than a grid tie system for the same monthly bill. I havent lived in this house in the winter so this is just based on summer months. Im sure winter number will change the equations.


the spreadsheet is a little difficult to decipher but with engineering and solar panels and racking, it looks like I end up spending more to go grid tied than to go off grid

 

[Hedges]

That's why systems like this exist ?

Couple "5000W" autotransformers. (likely able to transfer 2500W)
I wonder how those are wired, all 120V loads downstream, protected so they never lose neutral? Way more inverter than transformer in that setup.
Do they fix all the ground reference issues we've tried to has out?

Having battery storage bench blocking grid breaker panels probably violates code.
You're supposed to have a certain distance in front of them, not blocked.
When operating a breaker, you should stand to the side with metal door shielding your face from it. Just in case.

 

[Hedges]

How many cycles are you using for battery calc? I get about 2 to 3 cents per kWh with my calculations.

Maybe 2500 cycles from DIY 280 Ah battery, or 6000 cycles from 100 Ah server-rack.

Easy enough to cut cost in half with optimistic cycle life expectation, and for cells all we have is a number on a sheet of paper. Not like there will be any warranty. Cycle life may be valid for EV grade cells used in busses. DIY is going to to be reject cells which may die sooner. Or maybe gentle use more than makes up for that.

I would assume 25% of expected life when making financial decisions, based on that 3rd party test where only maybe 5% of brands reached cycle life.

Grid tie has some major benefits but for many people is not as inexpensive as initially expected. Grid tie requires ul components and usually an engineered design, so sld cost is a factor, engineered racking is more expensive, required shutoffs etc , and of course it may have additional monthly fees.

True, off-grid can be a 100W system from harbor freight consisting of PV panel, SCC, battery, inverter for $300.
Grid-tie can be 3000W system with Sunny Boy and panels for $3000

I think batteries-optional hybrid grid-tie is the way to go. Other brands out there already, but I expect to use SMA Smart Energy in place of Sunny Boy when it is on CEC list. Compatible batteries unfortunately are 2x the price of server rack. But as a listed ESS it will be the way to go for my sister. For DIY, others compatible with cheap batteries, to be added once inspection is done.

doing some estimates for my particular use case, it seems I can actually get into a battery system cheaper than a grid tie system for the same monthly bill. I havent lived in this house in the winter so this is just based on summer months. Im sure winter number will change the equations.

With my figures of GT PV costs $0.025/kWh and LiFePO4 costs $0.05 (and my Sunny Islands for $0.25 on the dollar), I could certainly come in way under the $0.25 to $0.50 PG&E rates.

Likely relying on gas for heat. But all the A/C I could ever want, powered by the sun.

 

[1201]

Couple "5000W" autotransformers. (likely able to transfer 2500W)
I wonder how those are wired, all 120V loads downstream, protected so they never lose neutral? Way more inverter than transformer in that setup.
Do they fix all the ground reference issues we've tried to has out?

Having battery storage bench blocking grid breaker panels probably violates code.
You're supposed to have a certain distance in front of them, not blocked.
When operating a breaker, you should stand to the side with metal door shielding your face from it. Just in case.

That's funny because I was wondering the opposite- why not just one transformer? Most large loads are 240v so I wonder what large 120v loads they plan to power

Btw the inverters don't appear to have a grid connection. Just battery and pv

 

[Zwy]

I've never been able to train mine to not use the microwave and toaster oven at the same time while making a pot of coffee when the air conditioning is on. Upgrading to a bigger inverter than I need was the end solution.

Best thing that ever happened when we moved into this house about 8 years ago was the microwave was on the same 20A circuit as the window air in the kitchen and the refrigerator.

Breaker might trip if she used the microwave at the same time the window air was on and the fridge kicked in. She learned the lesson real quick about running too many things at once. I have changed it since by splitting up the circuit but never told her.

 

[n2aws]

The inverters that have grid connectivity, are they worth having? If you are never planning on selling back to the utility company but instead just have a transfer switch / sub panel to power your house?

The price difference is substantial, so if you are not planning on connecting to the grid should you still get a on-grid inverter?

My simple-minded thoughts without knowing your specific scenario.

If you have grid available, I'd consider a grid-capable inverter. Even if you don't intend to sell back to the grid itself.

In my case, I don't have an NEM. I've moved critical loads to a subpanel that is fed from my inverter. HOWEVER.. with the use of a set of CT nodes on the grid mains into the primary panel.. I can do "zero sell" or "grid zero". (essentially, whatever word your vendor chooses to use, to describe.. sending enough energy back to the main panel to offset costs, but not so much that it goes back to the grid.

Between that, and the ability to power things even when you're doing maintenance on the inverter/charge controllers/battery banks.. etc.. it's a "small" price to pay, for a lot of additional flexibility.

Obviously, your use-case may vary.. but IMO.. if you can swing the budget, I'd consider an inverter that was capable of it, even if you don't *currently* plan to use it. The future always changes.. and that "small" upfront cost now, may prevent your need to replace an entire inverter or system in the future should your needs change.