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.

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 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.

Over the weekend I found that you can buy chinese server rack batteries for $689. Check the Energy Storage System on Alibaba app👉 https://x.alibaba.com/AwqpgJ?ck=pdp

I can’t vouch for these but $688 for 100ah server rack with canbus BMS. I think the 200ah (10kwh) variants are $1200.

Batteries are getting really really cheap. There will come a day where the lower prices will be eclipsed by the diminishing value of the USD. So thread the needle folks.... when you see the value of the dollar dropping, if you want batteries or any other things that aren't made here, start buying.

The difference between PWM and MPPT charge controllers. PWM is limited to the amps the solar panel can provide. MPPT can convert the higher voltage of a panel to even more amps. See attached picture.

Thermostat for direct hot water heating from solar panels. 3 250-275w panels and this thermostat and you’ll have hot water.

Is it hot in your attic? Why not run a bunch of pipe up there to soak in the heat all day? When you take a shower the hot water heater inlet can be connected to the pipes in the attic and you can refill the hot water heater with 100F water instead of 50F water.

if you use 2" PVC pipe, be sure to slope the lines in such a way they will drain completely in winter. hint: 250' of 2" PVC will give you 40 gallons of warm water.

This week is "clean up and organize the workshop". We sold our house 2 years ago, moved here and built the shop. We haven't stopped long enough to organize anything. I've got fence parts in three places (basement, barn and workshop) for example. Consolidation and organization is my thing this week.

If I think of something off griddy I'll post, but there won't be an "off grid" project this week.

Cleaning up in shop. My first bus bar before I knew better.

My 3 layer wood working screw tool box

Top drawer out

Second drawer out

The box has a simple old elec cable drilled and a knot inside the box and swivel castors on the bottom
I pull it to where i am working and voila'
No walking up and down

Its about 25 years old. Great thing is you not carrying screws up n down in tins and having to put them back.
Its also easy to do inventory and see what you need at anytime.

I have different "stock box" tool boxes for various things

https://www.youtube.com/watch?v=qpPYkqpe-Ms

This guy is the real deal. Back 6 or 7 years ago, he bought a crashed tesla battery and used it to replace his old lead acid batteries.

Family
@survival4u

World's most expensive strawberries

Waking up with 68% battery since sundown last night. Here's energy generation (dk blue), export(lt blue) and usage for HVAC(purple) and my car(orange) yesterday. Note that export takes off sharply after 1pm... that's when the batteries got full from the previous night and 100% of my system was dedicated to export.