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Solar Inverter - Load sensing

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veggie:
I would like to be able to feed power from ten X 220w panels into my cabin electrical system to help offset demand from the grid powered electric baseboard heaters in winter. I am not interested in "net metering" or selling power back to the utility company. When all heaters are on at the same time the total load is 4kw.
That creates a mess of paperwork and meter changes which in the end will not be worth my effort.
I am wondering if anyone is aware of a grid tie inverter that modulates it's contribution to the home circuit according to the current entering the house main breaker panel from the utility.
The idea being that my solar panels would contribute to the loads when the heaters ( or other loads) are on, and scale back (or divert the AC to a dump load like a water heater) instead of back-feeding to the grid when there is low demand.
These type of inverters are readily available from non-approved (and probably poor quality) suppliers on Ebay.
They have a donut current sensor which clamps to the incoming grid wire at the breaker box which is wired back to the inverter for monitoring the incoming grid amperage. The unit throttles accordingly.
They also claim to have "island protection" which will shut down the inverter if grid power goes out. Thus preventing back feed during outages.

I am wondering if any North American brands are capable of output modulation or load diversion based on mains current draw.
Anyone else using solar to help reduce electrical loads without backfeeding the grid?.

Summary:
I want to offset the power used by my baseboard heaters without back feeding the grid

veggie:

Here is an example of grid tie inverters with current limiters based in incoming grid power...

https://www.ebay.ca/itm/3000W-5000W-String-Solar-Power-on-Grid-Tie-Inverter-with-Limiter-PV-Connected/192559414466?hash=item2cd56f7cc2:m:m4yQjN6VOMcb2tnj10Bk5ZQ


https://www.ebay.ca/itm/1000W-MPPT-Solar-Grid-Tie-Inverter-with-Limiter-Sensor-DC45-90V-to-AC190V-260V/163780592807?hash=item26221584a7:g:mLQAAOSwPVFcCe7f


Very little information available for these units.
Also, No UL or CSA certification.

mike90045:
For sure, crunch the numbers before you buy anything.   

  There are several PV estimating sites on the internet, you enter your location, size, tilt and azimuth of your array, and you get a month by month output, adjusted for weather.  I'm north of San Francisco, and a sunny day in winter, I can easily harvest 18Kwh with 5kw of panels.  Cloudy days, I run the listeroid generator and top off my Edison Cells (48V 800ah bank)

https://pvwatts.nrel.gov/

Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | 3Kw 15, Evergreen 205w "12V" PV array on pole on a Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)|  Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister

veggie:

Thanks glort, I was not aware of the term "zero export".
I ran the numbers some time ago and the outcome is not very exciting.
However, I have these panels sitting on a shelf doing nothing at the moment.
This would be a "winter only" application with the panels almost in a vertical orientation and facing due south (for north American orientation).
The big problem is the cost of a "zero export" inverter rated at 3kw.
This system would NEVER pay for itself in 30 years when contributing only in winter.
(In summer the power usage is almost zero at this site so no need for solar).
I suppose the best application for spare panels is to heat a domestic hot water tank on a year round basis.
I can easily match the impedance of an element to the best efficiency point of my panels.
I also have an MPPT tracking converter which converts Panel power to a electric element sweet spot.
I bought one of these units a  year ago and plan to install it. I is designated for my hot water tank.
https://www.youtube.com/watch?v=YkPtPXfhiYk
I think it is meant to achieve what you are working on.

I think you are right, the amount of energy I would produce trying to offset my space heater consumption would not be worth the effort.
Keep us posted on your water heating project. This is something where PV panels can really do well.
I have several water heating applications that would benefit from solar so if you come up with a good DIY solution for tracking PV power points it would be very interesting to see it.

22kw of panels ... wow! that's a good sized array you have there mate! That's more than my house uses per day. Which brings up the burning question of excess energy storage. We really only have two options. Store in batteries or store as heat.
Charging a small electric vehicle would be very feaseable with your system.

BruceM:
The Techluck is only a DC PWM unit, with no voltage shifting ala boost converter, so wattage to element depends entirely on the panel array and element voltage.  Open circuit max PV voltage is 250V, and max operating PV voltage is 200V.   Frankly MPPT is a waste of circuitry and complexity for this application, and a simple DC solid state relay driven from a non-load carry thermostat would perform similarly and without any EMI, at a small fraction of the price.

Your scheme will have the same limitation, Glort, in that 90V applied to a 230V, 4500 watt element (11.5 ohm) will only consume 704 watts.  You must either increase panel voltage or use a DC-DC boost converter (or other DC-DC transformer based design) to raise the panel voltage to match heating element, or find a lower voltage, high wattage element.  Ohms law lets you calculate it.

Most cheap hard switching and badly designed devices make me cringe; EMC is typically ignored, the cables to the panels will likely obliterate radio reception in the home.  Sadly it is now normal to have hobbyist design level switching power supplies in appliances of all sorts and this does not bode well for public health since conducted EMI goes back on all the home wiring.  Our home's wiring is typically totally unshielded, thus acts as a radio transmitter for high frequencies and is literally wrapped around us as we sleep.  Switching supplies were unheard of in appliances and HVAC just 50 years ago, so now we are in the midst of a huge public health experiment; both wireless and EMI levels  in homes are now typically 100,000 times higher than 50 years ago.  Neurodegenerative diseases, autism and other chronic illnesses are on the rise.  Hmmm.

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