Solar power - Tesla power wall question...

[shibumiseeker]

...
The hybrid inverter acts as 'The Grid', producing an AC sine wave form so grid tied inverters connect and allow production into the lines,
It also converts battery (DC) into AC the rest of the system uses,
And it acts as a 'Regulator' to keep Voltage/Amperage consistent throughout the system no matter how much, or how little the panels are producing.
Obviously 'Off Grid' this piece of equipment is needed because you don't have the 'Grid' as a fill in or dump for low/high power situations.
You also don't need the power company...

I do this as well in my older system on the old house, I haven't gotten around to doing it on my new system.

I have a timer that is connected to a current and voltage sensor. If the sun is shining and the battery bank is at high SOC then during the middle of the day when the timer kicks on it dumps my excess power into an electric water heater that is inline with my gas water heater, and a couple of window air conditioning units so I don't waste as much of my excess production. That way I got by with a much smaller battery tied inverter and any new panels I buy don't mean I have to upgrade my battery bank to be able to take advantage of the increased power.

In the winter I set the timer to fewer hours. I put a manual switch in the system to shut that part off so when I want to run the big power tools like the planer I am not competing with the water heater for inverter capacity.

Just some ideas from someone that's actually been through it, use it if you can.

Yeah, I love the people who tell me "you should do..." who have never lived with a system.

 

[JeepHammer]

Thanks for sharing your knowledge and experience JeepHammer. So are you using 24 or 48VDC for storage?

I started like everyone else did back then when messing around with RE,
12VDC, then 24, now 48.

I got stuck in the past (lead/acid batteries) when I switched to LFP, and I did a 2 year test on LFP before I switched over, and that LFP battery string had to meet my L/A voltage to be easily functional...

What I should have done was closer to line voltage, like around 240-250.
High voltage is hard to do with L/A, but with LFP it doesn't take a second thought, some of the new battery chemistry will do 900-1,200 volts without issues.
Not many 900-1,200 volt inverters out there, but a few places are making 96 VDC inverters, and even larger input.

If you compare this in automotive battery terms, multiples of 12, 12 × 8 = 96
The problem is we are still sticking with the 1900s automotive standards and not thinking in terms of what the new cells can do over Lead/Acid (L/A).

My biggest issue, and one of the more costly lessons is Lead/Acid batteries... A crap ton of money to learn those lessons...
First off, whatever the L/A is 'Rated' for, you can only use about 25% of that at any given time without damaging the battery.
1,000 aH battery can only provide about 250 aH without serious and permanent damage. L/A will only do about 25% DoD (Depth of Discharge).
That increases battery cost by a factor of 4 (4×) right off the bat, or you sit shivering in the dark...

Discovering old fork truck batteries helped that a bunch, they are TRUE 'Deep Cycle' batteries and you *Can* get up to 50% DoD...
The cost is reasonable because they are industral, you get them when they won't run a fork truck over a 12 hour shift anymore, but plenty for SLOW discharge with home use.

The draw back is WEIGHT! You will blow an ovary everytime you need to move one,
And it's Lead/Acid, constant maintenance in water, balancing and corrosion.
Not to mention the explosive/corrosive gasses...

They do come in the standard voltages, 12, 24, 36, 48.

Keep in mind the higher you drive the voltage, the higher internal resistance climbs and makes charging difficult.
Takes a LOT of amps that get converted into heat and gasses when you try to top charge L/A, the closer they get to 'Full Charge' the higher the internal resistance climbs...

L/A HATES anything than 100% State of Charge (SoC), anything under 100% and the battery is degrading in degrees.
You home system will RARELY be at 100% SoC (0% DoD) since things are running, consuming power all the time.

LFP doesn't care if it's 25%, 50%, 75% charged or not. It doesn't degrade until you get down to the last 10% or so (90% DoD/10% SoC).
L/A becomes unusable about 50% DoD because voltage falls off so quickly, while LFP holds voltage to about 80% DoD/20% SoC.
You get useable voltage supply down to the last 10% or 20% of capacity,
OR,
About 4-5 times the USABLE storage capacity of L/A, and you get it without significant damage.

I stumbled into a crap ton of LFP dirt cheap, cut them open and started fiddling with them... Not believing the 'Miracle Battery' worked,
2 years and a BUNCH of testing (abuse) later, I'm a believer and have switched everything but my golf cart (farm transport) over to LFP.

They take a little more wiring on the front end to get moving, but the maintenance is virtually zero and can have a useful lifespan of 10-15 years.
They are as close to 'Safe' as you can get, I've shot some with .30 Cal rifle, driven steel punches through the case, no fire/meltdown.

Tesla CAR batteries are more powerful than LFP, but they 'Vent With Fire', and that's no exaggeration.
You MUST put overcharge safeguards in place, and you must armor them.
Just a note if you see Tesla CAR batteries for sale.
LFP are damaged with over/under charge, but they don't catch fire.

You asked about batteries.... Again, use it if you can...