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Try fieldlines.com. That is what the people there are all about. Lithium battery storage is a new thing, using salvage vehicle batteries, and, there needs to be a topic to investigate the best way to manage the battery cells, because of the 16+ voltage of 4 cells from vehicle batteries versus 13.4v of lead batteries.

I am very close to doing my house with Chevy Volt modules and a couple of smaller inverters. We don't have mandatory connections here, Costa Rica, and I am a very experienced power company ex lineman, so, understanding back feed issues from your house to the power grid is a very serious lesson to be learned.
 

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A few points in case they haven't been covered:

- any grid-tied arrangement needs to be either set up so it cannot deliver power back to the grid OR you must have the permission of the grid to send power back to them. It is not a given that they will take your power, and certainly not a given that they will pay you for it if they will
- a grid tied system needs to ensure that it will not try to send power to the grid when the grid is down, or it will potentially injure linesmen
- most want two separate meters- one for consumption, one for generation
- if you're going to do it illegally, i.e. without the knowledge of your grid supplier, you need to make sure you NEVER send power back to the grid. With some meters, when you run current in reverse, you will end up paying THEM for power YOU are sending to the grid, as if you were consuming that much power
- if you are going to use solar panels for your supply: if you have partial shading conditions, you're going to want to use microinverters on each panel rather than one big inverter or else you may not generate much power any time you're part shaded. This goes for any area where it snows, because snow generates part shading. Unfortunately, the microinverters I'm familiar with need a grid to sync to
- if you have no partial shading worries, you'll want to arrange things so that you can
- if you will end up with a single central inverter, there are inverters made that will handle the whole thing for you- they will watch your power production and consumption instant by instant, charge your batteries when you are making more than you need, disconnect from the grid when you don't need it, and draw from the grid exactly the amount of power you need if you're not quite producing enough. Regrettably I'm not aware of a microinverter arrangement which will do this for you
- conceptually, an easy way to isolate the two systems is by forcing all grid power to come in through your battery charger only, and all power going out to be produced by your single large inverter. However, that will waste energy, and battery life, by cycling your batteries needlessly. It will also not necessarily allow you to optimize your re-charging when you suspect you will need power, to times of day when power is cheaper (if you have time of use charges on your power bill)

Hope this helps, and hope others who do this for a living (which I don't) and hence know the most current gear much better than I do, will jump in and correct me where I'm wrong.
 

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Partial shading conditions are usually solved by so called optimizers. One for each panel. They're not expensive, about US$50 a piece.
Some panels perform well without optimizers, for instance Solar Frontier SF series thin film.

High power installations may not be able to feed full power to the grid on sunny days.
Especially in more rural areas (farmers).
 

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Discussion Starter · #24 ·
I dont have any shade where I plan to install. I dont currently have solar panels so that was all good info.

The last option of power flowing through the battery first wouldnt work for me because I also plan on using the battery for longer EV trips. I have the battery on a trailer and connect it to my car for longer distance road trips. But when I am home I would like to plug it in there to use to power the house. So the battery would have to be a removable part of the system.

If anyone has a page with products that you would recommend I would love to see them.
 

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If you are going to have all of the overhead costs of having a connection, why not use it?
Per his O/P, grid tie inverters are expensive. How long would it take to repay the investment of $15,000 at grid buy-back prices for his excess electricity?

Now, if they were cheap then he could justify it because he might sell enough back to cover the monthly cost of being forcibly tied to the grid...
 

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- conceptually, an easy way to isolate the two systems is by forcing all grid power to come in through your battery charger only, and all power going out to be produced by your single large inverter. However, that will waste energy, and battery life, by cycling your batteries needlessly. It will also not necessarily allow you to optimize your re-charging when you suspect you will need power, to times of day when power is cheaper (if you have time of use charges on your power bill)
Bold mine. Not necessarily. If the objective of the system is to be primarily off-grid and only consume from the grid during times of shortage (an intentionally under-sized system, which is cheaper) then it should be possible to allow the grid to charge the batteries in parallel with whatever power is still being provided by your solar setup (if any). So, you would need to set up your system so that the grid charger does not kick in until the battery reaches some point, perhaps 50% discharged.

Also, that setup would allow the use of less expensive off-grid inverters which would not need any fancy features at all.

I do not know what challenges there are when running two chargers in parallel, but if they are insurmountable (or very expensive) another option would be to have two battery packs and a switching system to isolate functions. At any given time one pack would be tied to the inverter and solar; the other to the grid charger which would only operate when needed.

Finally, to this setup could be added a smaller grid-tie inverter to "dump" excess power when both packs are approaching full and consumption is less than generation.

All of this would have to be controlled by some kind of smart switching system (a PC running sets of solenoids to control the busses, chargers, and inverters - but everything would be smaller (cheaper) and in times of low power AND no grid power you could even remove nonessential items from the bus (power saver mode).
 

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I dont have any shade where I plan to install. I dont currently have solar panels so that was all good info.

The last option of power flowing through the battery first wouldnt work for me because I also plan on using the battery for longer EV trips. I have the battery on a trailer and connect it to my car for longer distance road trips. But when I am home I would like to plug it in there to use to power the house. So the battery would have to be a removable part of the system.

If anyone has a page with products that you would recommend I would love to see them.
You may have some challenges finding one to work with your pack voltage. Most seem to be targeted and more "standard" 24/48v systems.
 

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Per his O/P, grid tie inverters are expensive. How long would it take to repay the investment of $15,000 at grid buy-back prices for his excess electricity?
...
First, that's a very high price for grid-tie inverter: in a randomly found listing of grid-tie inverters the highest-power inverter (11 kW) cost US$2736 and the most expensive was US$5863.

Then there's battery storage: the OP has a specific battery pack, but in general adding storage costs money, and using the grid connection avoids the need for storage, except as back-up.

Finally, the proposed scheme to which I was responding was to isolate everything except a token device (for legal purposes) from the grid: that would mean a solar-powered installation capable of handling the household's peak demand, which would be relatively expensive, instead of whatever size of solar system is desired and the grid providing any peak power desired. In a non-grid-tied system the inverter must be sized to handle peak demand; in a grid-tied system it only needs to handle peak solar output (which in most cases will be substantially less). Is the large non-grid-tied inverter much cheaper than a smaller grid-tied inverter matched to the solar system output?
 

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First, that's a very high price for grid-tie inverter: in a randomly found listing of grid-tie inverters the highest-power inverter (11 kW) cost US$2736 and the most expensive was US$5863.
I didn't go out and price the world. Just pointing out grid tie is probably more expensive than stand-alone - the difference was substantial last time I researched it. But good point, prices are definitely coming down from last time I looked.

Finally, the proposed scheme to which I was responding was to isolate everything except a token device (for legal purposes) from the grid: that would mean a solar-powered installation capable of handling the household's peak demand, which would be relatively expensive, instead of whatever size of solar system is desired and the grid providing any peak power desired.
Got that. My spinoff concept was saying, "if you are going to be stuck with the fixed costs for being hooked up anyway, why not buy a little power when you need it?" Usually your monthly hookup costs for taxes etc. are "fixed;" however, actually using a little electricity on a cloudy week is a small nominal amount since you have to pay the fixed costs anyway.

In a non-grid-tied system the inverter must be sized to handle peak demand; in a grid-tied system it only needs to handle peak solar output (which in most cases will be substantially less).
I freely admit it's been a while since I priced anything. How much is the difference between grid tie and non-grid tie these days? Is it enough to justify a "dumb" inverter which can handle your full load vs a "smart" one that does grid tie and allows selling back? Also, when I last looked many grid-tie inverters WOULD NOT FUNCTION if the grid was down. Have they fixed that?

Is the large non-grid-tied inverter much cheaper than a smaller grid-tied inverter matched to the solar system output?
Excellent question.

As in all things, the market changes quickly. You would need to perform a full analysis of your requirements and price a variety of solutions to fully optimize your results.
 

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Also, when I last looked many grid-tie inverters WOULD NOT FUNCTION if the grid was down. Have they fixed that?
That's what I recall, too; however, what I found when this thread came up was that grid-tie with battery backup is now available, which means that it does operate when the grid is down - a substantial functional improvement. :)

As in all things, the market changes quickly. You would need to perform a full analysis of your requirements and price a variety of solutions to fully optimize your results.
I agree!
 

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That's what I recall, too; however, what I found when this thread came up was that grid-tie with battery backup is now available, which means that it does operate when the grid is down - a substantial functional improvement. :)
So, there is a new category of Inverter which works in either grid-tie or stand-alone mode. I can probably search myself, but if you already looked it up can you tell me if it is smart enough to flip a breaker to isolate your home from the grid?

The ideal solution would be one where a computer somewhere in the system (could be in the inverter, could be stand-alone) acted as a programmable brain to determine when to pull from the grid (i.e. modify how much battery discharge to allow when, say, dawn is approaching so as to resist some "hard rule" that says "buy power" when in fact the sun is about to come up) and when to sell it back (batteries are almost full, sun is shining, still 6 hours to sunset so sell some portion during peak hours at a premium).

I can guarantee you that if you buy such a solution from the power company then the algorithm is going to favor the power company, not you. I think I can also accurately predict that such solution s WILL be sold, and marketed aggressively by the power companies.
 

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So, there is a new category of Inverter which works in either grid-tie or stand-alone mode. I can probably search myself, but if you already looked it up can you tell me if it is smart enough to flip a breaker to isolate your home from the grid?
I didn't keep links to specific hardware, but there's no way these things could be legally installed if they didn't isolate the power source from the grid connection in case of grid failure.

Now, of course, I need to do more research... :)

The ideal solution would be one where a computer somewhere in the system (could be in the inverter, could be stand-alone) acted as a programmable brain to determine when to pull from the grid (i.e. modify how much battery discharge to allow when, say, dawn is approaching so as to resist some "hard rule" that says "buy power" when in fact the sun is about to come up) and when to sell it back (batteries are almost full, sun is shining, still 6 hours to sunset so sell some portion during peak hours at a premium).
I was seeing descriptions as" grid-tie with backup", which suggests that the logic will just maintain the backup battery, and sell or buy net power production or demand as long as the grid is available; that wouldn't cycle the battery at all except in case of grid failure. I agree that a more optimal strategy is possible, but I don't know if it has been implemented.

An analogous situation is a gasoline-electric hybrid car: the most simplistic approach would shut the engine down (like a grid power failure) for coasting/braking and until the battery is run down, and use the battery only while the engine is shut down (regenerative braking) and for initial acceleration (until a switch to engine power). It would work, and would deliver some benefit (like any stop-start system, plus regeneration) but it's not worthwhile or at least not an optimal use of the hardware. Real hybrids use a more sophisticated control strategy to make use of engine power.

A utility might manipulate the logic of a grid-tied system with storage for a couple of reasons:
  1. to provide power the grid when needed to handle daytime peaks,
  2. to buy power from the end user when it is cheap and sell it when it is expensive, if the area has time-of-use pricing.
These two factors seem contradictory.

I can guarantee you that if you buy such a solution from the power company then the algorithm is going to favor the power company, not you. I think I can also accurately predict that such solution s WILL be sold, and marketed aggressively by the power companies.
Maybe, but utilities here in Alberta are required by regulation to allow grid-tied systems, with minimum buy-from-end-user prices, and I haven't seen any of them pushing any kind of system with storage. Perhaps the pricing is the reason: even with logic favourable to the power utilities, "microgenerators" (as end-user installations are called here) are probably not an attractive source. Also, we have a bizarre semi-regulated utility system in which energy generation utilities, energy distribution utilities, and energy retailers all separately operate - it might be difficult for any of them to deliver and manage a grid-tied system to their benefit.

According to the Solar Energy Society of Alberta, there are 2,343 solar installations in the province, with installed capacity of about 40 MW. This organization's website describes only the simple grid-connected configuration (no on-site storage, for backup or otherwise), so anything more sophisticated is at least not common. A local energy retailer offers leased solar systems, for which the description is clearly grid-connected, but it is unclear if backup or more flexible storage system is available. An Alberta solar-only company has this to say about storage:
The simplest and most cost-effective way to harness solar energy is with a grid-tie system. A grid-tied system allows you to use solar power when it is available during the day, and grid power when it isn’t, sparing you a huge cost in batteries, or from meeting any power requirements. Batteries are bulky, expensive and require regular maintenance, and won’t last as long as panels or inverters. Therefore we don’t recommend battery back-up systems unless you live or work in an area that experiences frequent power outages, and even then there might be more affordable solutions (such as back-up generators) than storage batteries.
... which implies that storage in a backup mode is available here, but doesn't suggest use of on-site storage while the grid is up.

Since pricing here essentially pays the solar system owner the same for energy as it costs them to buy energy, there is no incentive to cycle a local battery, so a battery is only for backup. Different pricing in other areas will drive different system choices.
 

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... which implies that storage in a backup mode is available here, but doesn't suggest use of on-site storage while the grid is up.

Since pricing here essentially pays the solar system owner the same for energy as it costs them to buy energy, there is no incentive to cycle a local battery, so a battery is only for backup. Different pricing in other areas will drive different system choices.
Ya, my original point was for those who effectively wanted to ditch the grid but couldn't. You are right it doen't make sense yet, but I think it will in the near future.
 

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Grid-tie with battery: example #1

So, there is a new category of Inverter which works in either grid-tie or stand-alone mode. I can probably search myself, but if you already looked it up can you tell me if it is smart enough to flip a breaker to isolate your home from the grid?
This is an example:
Solar Plus Storage - Grid-Tied Solar Power Systems with Battery Backup
As the title suggests, the battery appears to be only for backup...
When the grid is available, power produced by your solar system is used by the home and excess energy is sent into the utility grid. In the event of a power outage the backup inverter will automatically turn on to power critical appliances such as the fridge/freezer, lights, well pump, computer, phone and more. The combination of solar energy and battery storage works seamlessly to provide power to essential appliances during an outage, working similar to an off-grid system.
The system design addresses the isolation issues by using the normal features of a grid-tie system (using multiple solar panel powered microinverters), with a separate inverter for operation from the battery:
Magnum Energy’s MicroGT 500 Microinverters are paired with a powerful Magnum Energy MS4448PAE battery backup inverter.
The wiring diagram is part of the purchased package, so details are not freely available, but it appears that the "power center" connects the loads to the backup inverter when the grid-tie inverter automatically disconnects. How the battery is charged is not clear to me.
 

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Grid-tie with battery: example #2

Schneider offers two configurations using their inverters and control hardware for a grid-tied system with battery backup.
Solar Grid-Tie Inverters with Battery Backup
Diagrams with specific equipment models are provided, and which one is used depends on the metering method allowed by the grid connection.
  • FIT (feed-in tariff): all solar output goes to grid through one meter, all power used comes from grid (when up) or from battery (when grid down)
  • Net metered: one inverter provides AC power from solar, another inverter provides AC power from battery; power flow bi-directionally as required to absorb solar output and meet load

There is a pile of documentation on this Schneider site. One would need to plow through it to determine if the system can use battery storage in the desired way while also using a grid connection.

Schneider knows their stuff. Even without digging into the details, I expect their systems work well.
 

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Since pricing here essentially pays the solar system owner the same for energy as it costs them to buy energy, there is no incentive to cycle a local battery, so a battery is only for backup. Different pricing in other areas will drive different system choices.
You are right it doen't make sense yet, but I think it will in the near future.
Cycling a battery doesn't currently make sense in a grid-tied system here in Alberta, but it likely does in other areas, where the price paid for energy sent to the grid is much lower than the cost of energy from the grid.

Time-of-day metering matters as well, but may favour grid interaction rather than battery use.
 

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High energy storage also makes sense when for instance:

- you want to able to fast charge your EV at home;

- charging rates at public chargers are absurdly high in your region, solar is "free";

- as backup in case of power outages (I now have two UPSs with only a few minutes backup time);

- as storage for excess solar when you live in an area where the grid can't handle high power feed.

There are grid tied solar inverter / charger / storage combinations available but I haven't seen one (yet) that I like.
 
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