Power bills are killing me. Ohhhhh it’s so high. This is the minimum bill.

Wall mount pulley from Lowe’s. But it had a bronze bushing. I swapped it for a 2-1/2” garage door wheel that has real bearings. Should last a lot longer.

Salt & Water - Barbara O'Neill

The European mind cannot comprehend this level of freedom.

My wife went to our local walmart yesterday and found the shelves pretty picked over. She also noted that they have made the aisles wider... like twice as wide. That means 1/2 or 1/3 fewer aisles in the store. And that means they have less inventory. Anyone remember during covid time that stores did creative things to fill the shelves like put folding chairs in the empty spaces in shelves? Things are happening folks.

The way AC coupling throttling works is that our AC electrical system runs at 60hz (50hz). If there is more power being made that the house needs, the power goes to the battery as if it was a surge tank and within about 1 second, the system frequency changes toward 62hz. The idea for this comes from gasoline and diesel generators... they are made to idle at 62hz (3720rpm). As you put load on them they pull down to 60hz. now imagine a balance where your generator is just idling providing a very small amount of power to your house and you turn on the stove and it bogs the generator down from 62 to 61.3hz. You solar system would see this and wake up and start making a little extra power. Now imagine we simulate the loading and unloading of the generator with a battery inverter's software. BOOM... now you know how the UL1741SA frequency control works.

So the best of both worlds is to combine the two methods of coupling. Use your existing grid tied inverters if you have them and if you need more power, just add MPPT DC chargers.

My system here has two PV inverters that make a total of 10kw. They are able to be throttled and during the day, they run my house and charge my batteries via the battery inverter.

My system also has two 48v MPPT chargers that make a total of 6kw.

If I didn't supplement my sytem with DC coupling, I'd be stuck at 10-12kw of PV power at most.

The other way to connect your solar panels is what's called AC coupling. If you, like me, started with a grid tied system you already have solar inverters to make 240v. 99% of systems installed to sell to the grid are this way. Problem is they don't make power when the grid is down. If you get a battery inverter that says it is UL1741SA (or SB) rated, it can trick these grid tied inverters into coming on. Further, an inverter with UL1741SA can throttle the solar inverters if they are making more power than you need at the moment.

Something that's slick about setting up a system this way is that your solar inverters run your house directly when the sun is out. This means less wear and tear on your battery inverter. As the sun goes down, the battery inverter will begin to transition to making the power that runs your house.

Another advantage is that you effectively double the amount of power available to your house in the day time. Let's think about this for a moment... I have 12kw of battery inverter and 10kw of solar inverters all making 240v. So in the day time I have access to 20kw of 240Vac and at night I have 12kw. If the house is pulling more power than the solar can make the battery inverter makes up the difference.

The final adavantage for most people is..... that they already own the solar inverters and panels. Just like rednecks racing.... run what ya brung.... if you have a grid tied system you can more than likely just add the battery inverter and the batteries.

The disadvantage of AC coupled.... in a special case you might want to NOT have a net metering agreement and make enough power to run your house but not enough to export. In this case the way that AC coupled inverters are throttled is incompatible with controlling how much power they produce.

Another disadvantage is that some solar inverters can't frequency shift. One such is my older Solar Edge 11.4kw unit. It is kinda sorta compatible with the throttling method in that it'll just stop making power... so it's either running 100% or off.

Another issue with AC coupling is that your battery inverter must be able to accept 100% of the solar power. Let's think about it... your water heater is running and using all your solar power. All the sudden the water heater shuts off.... your system has been making 5kw. Where does that power go until the throttling can happen? The quick answer is that your battery will act as a surge tank... but the battery charger built in to your battery inverter has got to be able to take it. So the rule of thumb is that your AC coupling can't be larger than your battery inverter's power capability.

What's a battery management system (BMS)? Here's a primer to fill in gaps I'm sure some of you have...

It used to be simply a battery monitoring system that would monitor the individual cell voltages in a battery pack. For example there at 16 cells in a 48v LFP battery and you have to keep tabs on each one making sure it doesn't go over 3.6v or under 2.5v.

Next they added a relay to the BMS so that if it did detect something wrong it could disconnect the load or the charger.

Next they added the ability to put a small resistor across a cell that was charged higher than it's peers. This is balancing. There's a point where a cell's voltage rises rapidly as it gets close to full much like gas in a gastank rises rapidly in the filler neck. It is not advisable to try to balance a battery that's not "up in the filler neck" at >3.4v. So balancing is enabled as each of the 16 cells get higher than 3.4v. JK BMS is the only BMS I know of with what's called "active balancing". It actually takes extra voltage from one cell and uses a capacitor to move it to another cell. So if cell 10 is too high, it connects a capacitor to 10 and then connects that capacitor to say, cell 5 that is the lowest. The advantage of this is 1)no heat, 2)everything that comes out of the highest cell goes to the lowest cell. WIth a passive balance system all you can do is burn off extra voltage from the top 15 cells waiting for that 16th straggler to catch up.

Next they added directional MOSFET switches to BMSs so it could shut off the charger OR the load OR both.

At this point, you have a normal everyday BMS that is madde today. It protects the cells from overcharging and stops charging if a cell is >3.6v or it's too cold.

The next step in evolution is BMS that actually communicates with your inverter. It tells your inverter the State of Charge of the battery and to slow down or stop the charging amps. You see if a cell is between 3.4v and 3.6v, we want charging to simply slow so it doesn't get ahead of the balance circuit. So the BMS can talk to your inverter over a network connection called RS485 or CANBUS.

The next step is to have several BMS units talking to each other and one of them keeping tabs on all that data, collecting the data and combining it all together to present to the inverter. So you can have 10,12,16 batteries combining all their SOC readings into one reading for the inverter. Neat stuff.

What my neighbor and I did was to let the individual BMS units do their jobs monitoring each group of 16 cells and we have a separate Victron Smart shunt that talks to the inverter.

So there's a kit I just posted on here last night that is a metal case and a BMS. This bms looks good except it only has passive balanacing. Truth is, once a battery is balanced initially, it usualy stays pretty close.. JK BMS makes a server rack BMS that has active balancing. Both the basengreen and JK server BMS can talk to other units and present one collective SoC to the inverter.