Requesting opinions/feeback on this 6.12KW Off-Grid System

[Bala]

if it were me I would connect to the grid, buy a generator that will run what you need if the grid is down, you will need the generator either way.

This will mean you can have you aircons or what whatever else you want and work all night if you need to.

Your costs over a long time will likely be similar, but the grid and back up generator will be a lot easier to live with than stand alone solar.

[Mike90250]

...The only constraint on charging lithium batteries is the maximum charge rate....

Boy, are you going to be in for an expensive surprise some day.

And what is that comment supposed to mean?

Because you can charge at a low rate, 30V on a 12V pack and end up .... (wait for it....) Surprised ? Max Charge Rate (amps) is NOT the only recharge constraint.

[karrak]

Because you can charge at a low rate, 30V on a 12V pack and end up .... (wait for it....) Surprised ? Max Charge Rate (amps) is NOT the only recharge constraint.

Try putting 30V on a 12V lithium pack and one of the follwoing will happen.

1. You will exceed the batteries maximum charge current
2. The power supply will current limit and the charge voltage will drop down to around 14V
3. The battery BMS will disconnect the battery from the charger.
4. The power supply will blow up
5. If the battery is full the battery voltage will go above its maximum rated voltage and will be damages

It is up to the system designer to make sure that the maximum charge current is not exceeded. It is also up to the system designer to make sure that the maximum battery voltage is not exceeded.

The discussion was about charge current not voltage, taken in context I see no problem with my comment

Simon

[Mike90250]

karrak
you keep throwing out "factoids" at neophytes and I will call you on it, A good power supply wins over battery every time, I don't use toy supplies that fry.

And you have no idea what a creative neophyte can throw at a batch of Li cells with no BMS, because YOU said it can't hurt. So be warned you will be challenged when you make a "blanket statement" when a neophyte is asking questions. You may not care if they roast their gear, but the mods do.

[inetdog]

Try putting 30V on a 12V lithium pack and one of the follwoing will happen.

1. You will exceed the batteries maximum charge current
2. The power supply will current limit and the charge voltage will drop down to around 14V
3. The battery BMS will disconnect the battery from the charger.
4. The power supply will blow up
5. If the battery is full the battery voltage will go above its maximum rated voltage and will be damages

It is up to the system designer to make sure that the maximum charge current is not exceeded. It is also up to the system designer to make sure that the maximum battery voltage is not exceeded.

The discussion was about charge current not voltage, taken in context I see no problem with my comment

Simon

Note that you did not mention anything about monitoring the temperature of the cells. I guess you figured that the BMS would take care of that too?

You will find some very detailed and well thought out descriptions from members PNjunction and Sunking about why, for PV storage purposes, it can be safer and better for battery life to carefully control charging voltage to stay within the selected operating range of an initially balanced bank of bare cells than to use some popular BMS strategies.

Anyway, please do NOT assume that the typical new DIYer will be using a safe, well-designed BMS or that they understand its limitations.
Boeing had a very sophisticated BMS for their hibachi-replacement 787 battery. It just was incompetently designed and badly configured, and the choice of battery chemistry and mechanical construction was riskier than they realized.

[John Galt 1]

I expect the BMS would monitor the cell temperatures because Lithium batteries have a lot more fire hazard. If it was my setup I'd also occasionally use a separate temperature sensor and keep an eye on the batteries. IMO lithium batteries are still not developed enough to put in my house. Maybe some day but not until they have a longer track record.

[Sunking]

And what is that comment supposed to mean?

That you are an idiot and not welcomed here. Take a hint from both moderator and get lost. You have no credibility here.

OP do yourself a favor and ignore Karrak. He is dangerous and does not know what he is talking about.

Stay away from Lithium batteries. Bad enough going off grid is going to cost you 5 times more than buying electricity. Do it with Lithium and you double your cost and replacement frequency. Do not learn that lesson the hard way with your cash.

[Sunking]

I expect the BMS would monitor the cell temperatures because Lithium batteries have a lot more fire hazard.

That is true if they used LCO or LMO lithium batteries, but you would use cheap Chi-Com LFP lithium batteries which require no temp monitoring. If you know how they operate does not even require a BMS as you never fully charge them, or fully discharge them.

. IMO lithium batteries are still not developed enough to put in my house.

I agree a long ways off. With the batteries available to consumers, the economics do not work plain and simple not to mention really no equipment on the market to work with Lithium unless you know how to interface with them by changing equipment parameters. Even if you do the expense factor still remains. If you have an application that demands Lithium high charge and discharge rate capabilities, AGM is a better solution as they do not cost as much and last as long as Lithium. Even with AGM you increase your long term battery cost 400% over Flooded Lead Acid.

There are not many applications where using Lithium Batteries can be justified. That would be Electric Vehicles and Power Tools. The irony is Joe Consumer doe snot have access to the same quality batteries OEM's use. We have to use Chi-Coms that cost 1/3 of good lithium batteries. You get what you pay for.

[Sunking]

Try putting 30V on a 12V lithium pack and one of the follwoing will happen.

1. You will exceed the batteries maximum charge current
2. The power supply will current limit and the charge voltage will drop down to around 14V
3. The battery BMS will disconnect the battery from the charger.
4. The power supply will blow up
5. If the battery is full the battery voltage will go above its maximum rated voltage and will be damages

You just proved you do not know WTF you are talking about. Anyone who knows how a battery charges, knows you can charge a 12 volt 100 AH battery with a 100 volt 10 amp current limited supply any day of the week. All you have to do is terminate the charge when the battery voltage reaches 14.4 volts on a LFP battery you moron.

That is what allows a manufacture to make a multi-voltage battery chargers. DUH! Use any 30 volt GT panel and you can charge any 12 volt battery with no issues whatsoever. You just disconnect when you hit a target voltage. Only thing that is required is controlling current and monitoring battery voltage. It is child play. In fact is exactly how solar was done when it started. A Charge Controller was nothing more than a Relay that connected the panel directly to a battery. When battery voltage reached 14 volts, the Relay disconnected the panel from the battery. In fact they still make and sell those controllers today made by Coleman and some other antiquated controllers like PWM which is basically the same thing.

Ignore Karrak, he is a fake.

[karrak]

I agree a long ways off. With the batteries available to consumers, the economics do not work plain and simple not to mention really no equipment on the market to work with Lithium unless you know how to interface with them by changing equipment parameters. Even if you do the expense factor still remains. If you have an application that demands Lithium high charge and discharge rate capabilities, AGM is a better solution as they do not cost as much and last as long as Lithium. Even with AGM you increase your long term battery cost 400% over Flooded Lead Acid.

There are not many applications where using Lithium Batteries can be justified. That would be Electric Vehicles and Power Tools. The irony is Joe Consumer doe snot have access to the same quality batteries OEM's use. We have to use Chi-Coms that cost 1/3 of good lithium batteries. You get what you pay for.

Installation of the Powerwall 2 start next month in the USA and Canada. This system is a consumer grade maintenance free battery system that is warranted for up to 10 years. The home owner does not to have any technical knowledge to operate this battery system.

If you don't like Tesla try one of the many other lithium ion based systems available. All the cheapest battery systems listed are based on lithium ion batteries.

These costings are is AU$, to convert to US$ multiply by 0.75




Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger
Latronics 4kW Inverter, homemade MPPT controller

Admin Note, removed link. please dont link to that site.

[Sunking]

Here are some costings for batteries from this article https://www.solarquotes.com.au/blog/...ll-2-warranty/

Now that is some funny chit, I don;t care who you are. A sales pitch made by a salesman who works for a Solar Distributor in Australia.

Here is the Punch Line folks:

Karrak is the salesman. Get it?

If not maybe this will help. The Tesla Powerwall V2 does not exist. As of now is pure Vaporware like the Tesla Powerwall V1 that never existed but was for sale. It is a make believe sales pitch. You gotta be pretty stupid to believe a battery that cost 4 to 6 times more than FLA and only last half as long cost less.

[bberry]

Hi folks, although I've been consuming myself with reading up and down about solar I'd still like to get any opinions or feedback on this set up from some of the Pro's here on the forums...its a big investment so I'm looking for some warm and fuzzies since this is not my area of expertise.

A little background on the situation. We are building in an area with 5.5 to 6 sun hours year round, warm climate so no freezing batteries or snow covering the panels to worry about. Maybe the occasional tropical storm or hurricane but we can deal with those gaps with a small generator (question on that later). Cooking and dryer will be LP, No Air Conditioners, minimal appliances, etc...

I would pay for the grid connection and plan to go solar plus battery for relaibility/ cost reduction as the battery market matures. I would be willing to pay a lot an unreliable grid connection to avoid running a generator.