Hi, All, I would eventually like to install panels but it’s not in the budget yet.
What I DO have is 15 kW of LIFEPO4 cells, several electric car self-conversions and a very inexpensive TOU rate from midnight to 6 AM… 9 cents. that’s cheap for San Diego. Peak rate is 53 cents.
I’ve done the math and 15 kW is plenty for most days. If I have to eat a few high cost kilowatts on the few days that I run an air conditioner, I’m OK with that.
I would like to rate shift. The bottom line is, I would like to always charge the batteries from midnight to 6 AM, then run on the inverter until the batteries run low, then run off the grid until midnight. Most days I probably won’t run out of battery power.
I am looking for an inverter that can perform this. I have been looking at the Schneider SW4048. I have read the owners manual pretty thoroughly. But it contradicts itself when talking about what happens when the batteries run out.
In one place, it says it will connect to the grid and start recharging the batteries immediately. Which is not what I want. I want the grid to feed the load, and the charger to sit idle until midnight.
In another place, it says the batteries will not ever charge while the charger block is on.
Under the Time-of-Use Metering heading, it says that if charging is required during the charger block period, then it will use solar to charge the batteries. But it doesn’t say what it will do if I don’t have solar input.
Batteries low, no solar input, charger block on. Does anybody know what this inverter will do in this situation? Will it feed the load with pass-through from the grid?
Alternately, can someone recommend an inverter that will do what I want it to?
I am a DIY guy and I would tackle the problem a bit different.
First off, they make battery chargers that turn off when the charge is full and also some of them turn on automatically when the battery get low on on charge. I even seen chargers that can be programmed to come on at a specific time.
Me, I would get a charger for it and a time relay that tells the charger to come on and off at a specific time. This would turn your charger on after midnight and off at 6AM.
If you should get solar power at a later time just hook the solar power in parallel to the charger unto the battery, the solar charge controller will start to charge and stop the charge as needed. Midnight til 6 the grid is charging your batteries and then the sun takes over and continue to charge the battery throughout the day.
If the battery voltage is too low the inverter will shut down so in that area there will be no damage done to the battery.
Another thing is.....you can not get 15 kw out of a 15 kw battery unless you discharge the battery voltage and amps down to zero/nothing at all, that is where Peukert's law come in. In reality it is more like around 80% of that. You only can take 80% of power max from those batteries without killing the battery early and you have to check the max charging and discharging amps those batteries can handle. Go over those specs and you shorten the life of the battery.
Chargers and batteries have losses. Lets say you took 10kw out of the battery, it may take 14 KW or more to put it back because of heat losses and losses when the chemical change takes place while charging takes place.
6 hours may not be enough to charge those batteries, because in order to keep batteries alive you should not go over the charging amps that is listed on the battery.