NiHaoMike

Building your own inverter is a huge undertaking. We had let the smoke out of ours more than once.

I've read your post though 3 times and still unsure to how this will work. Your indicating that you will be using a Prius Inverter but thats 3ph power stage. and you mentioned you will utilize some capacitors for a neutral tap. Hmmm

A method of sensing line current and offset to negate exporting power. Interesting!!

I will be interested following the build.

Randen

The reason why I'm looking at reusing a Prius inverter rather than building one from scratch, apart from it already having the hard work of all the gate drive and critical current path layout already done, is because it's actually cheaper to buy that rather than the parts to build a comparable inverter power stage from scratch!

DIY EV builders have pushed Prius inverters a lot harder than my application ever will. In fact, it will only get pushed to a fraction of what it would operate at in its original application.
https://www.youtube.com/watch?v=QRxbT9NQT4U

At this point, I'm building the PLC transmitter for the current sensor. It will use a pair of PLL synthesizers with a crystal reference to ensure the carriers don't drift due to component aging and temperature variations. (They'll be fairly close together in frequency so I need to make sure they won't drift into each other.) The signal will be applied to both phases and the inverter will use receive diversity to improve robustness to EMI.

First try at prototyping the PLC transmitter using 2x 74LV4046A. It works but the jitter is more than I like, giving a noisy signal. The CD4046, based on an older process technology, is rumored to have a better VCO section, which I'll be testing when I get them. (Digital circuits favor newer processes while analog circuits usually favor older processes.)
https://i.imgur.com/rQkvTZe.png
I used GNUradio to build a signal analyzer on my PC. In the actual application, the signal processing code will have to be ported to Verilog in order to run it on a FPGA, the sort of stuff Tiffany Yep is good at. Sadly, she's too busy to really help me with that, but she did give me a list of resources she used to learn how to do DSP in Verilog. (Now I get to have a bit of a feel of what it's like to be Tiffany Yep, but I don't think it would make me as good looking as her...)

I think I understand what you are trying to do. I'm still unsure how you are going to make this system undetectable from the grid. Here in GA if the power company sees PV's on the property they look for the signature of an inverter in the line. A few years ago several DIY systems ended up on craigslist after the power company shut them down.

use the solar system to power a grid-synchronized generator head? that won't have an inverter signature...

The high frequency noise it outputs is just like any other switching power supply, so simply trying to detect that will cause a lot of false positives. (I will also design the output filter to be very effective at attenuating noise, which is required in order for the PLC receiver to work.) Also, it never exports to the grid - in fact, the inverter will not completely offset the load. It also doesn't send impedance test pulses, since it doesn't need that with the lack of export.

Mike I would bet there are many wanting to do the same thing here but like me are not good at electronics. I had thoughts about going grid tie at one point. Its very convenient to be able to store that energy on the grid till you need/want it. In my case, the deciding factor to not go grid tie was the wording in the contract that basically gave my local government free access to my house to "inspect" when they deemed necessary. The other issue is you don't have access when power is out or even worse if the grid goes down. My goal now is low key urban partial off grid.

Storing some of that energy as heat is a good idea. I'm guessing you want it for domestic hot water and radiant heating maybe?

I'm going to be watching this thread with much interest. Perhaps one of the solar manufactures will also be reading and come up with a heat pump tied charge controller. Diverting to grow lights would also be another good source for many solar folks. There is a lack of load diversion controller options in the solar industry. Someone smart could find a good business nitch here.

I may adapt part of your idea. I like the idea of dumping some load for hot water. Resistive heating is a poor option. How about a simple charge controller that detects battery voltage and turns on a compressor/heat pump. If voltage still rises, it turns on another? Not as smooth as a variable but simpler to source parts. A large enough battery bank would smooth out the gaps in load size. Panels would be directly connected to the batteries as the controller would be purely diversion based. I would also include secondary load of LED grow lights once water temp was reached.

What are you going to do with the cold side of the heat pump? How about pulling heat from a cooler/freezer upstream from the source heat? Kill 2 birds with 1 heat pump.

How about going off the DC side? There are a few options with DC 3 phase brushless compressors. You could build a controller interface to pull power off of the batteries to control charge rate. It would be easy to make it a variable vs on/off. Thats basically what the newer inverter heat pumps are, 3 phase DC motors.

I like the idea of not having all your eggs in one basket. My systems tend to have lots of simple parts rather then one large device doing everything. That way I can move things around if there is a failure and keep things going. Its from a grid down self reliant angle. Down side is it requires more baby sitting.

Looking forward to see what you build

One thing that occurred to me, the ideal load diversion would also need to be fairly fast switching. Turning compressors just on and off has the problem of waiting for pressure to drop on the high side so the compressor doesn't stall at start up and also efficiency losses with pull down time. My setup would have to have a delay timer and multiple small compressors. Variable drive would solve allot of this.

Problem is with other large loads that come and go on the system.

Gadget

I as well am on the edge of my seat to see what Mike will come up with. The liquid cooled IGBTs will be a big help. When you start to draw current to keep an efficient home powered the resulted heat for the inverting will create a lot of heat localized in those semiconductors.

I understand what you are thinking trying soft start and multiple compressors and this is a valiant effort however these will only be subject to diminishing returns as the resultant steady draw will be the problem.

If you put your hotwater tank, cookstove clothes dryer and home heating on propane and operate the other loads on solar maybe!!!

It will always be not enough panels and not enough storage.

During the summer we usually have enough for everything the geothermal are air conditioning, cars are charging clothes are getting washed computers lights and all the creature comforts.

Put two or three days of overcast it all comes to a screeching halt.

Randen

So true, there is always plenty of solar when you don't need it.