Selective automatic load switching/sensing/prioritizing

[nonsquid]

How about selling a load sensing device that would help multiplex a small system inverter power between loads?  The unit would be downstream of the inverter and would sense when an AC electrical load demand (well pump, sump pump, refrigerator, air conditioning) is required.  Then the unit would - could be optionally set up to switch the load from the utility power to the solar inverter and then prioritize which load would be serviced from the inverter.  This would allow a small inverter to be time shared or prioritized between loads that when combined, would overload the inverter.  The unit would have multiple contactor relays that could be expanded out for load switching and a few zero point switches for bumpless utility to inverter transfer within on AC cycle.  AC load configurations could be predefined so certain big loads wouldn't trip the inverter for start up currents then small loads could added to keep the inverter running.  This unit could also be used for utility AC start of a big load then a solar invert run of that load.

Just the utility AC start and solar inverter run feature in itself would be a great product.

The unit would prevent dead heading a load against an off condition inverter.  It would only switch a load if the inverter is active.  It could also be used for controlling the inverter and turning it on and off to save inverter idle time with a DC contactor control.

There is all kinds of room for add ons and expansions.  This would be a great product line that would enhance all solar systems.

[dgd]

...  This would allow a small inverter to be time shared or prioritized between loads that when combined, would overload the inverter.

So why not just size the inverter to suit the potential loads?
The additional cost and complexity of this switching unit would likely far exceed the difference in cost between a smaller inverter and one suitable for the potential loads.

The unit would have multiple contactor relays that could be expanded out for load switching and a few zero point switches for bumpless utility to inverter transfer within on AC cycle.  AC load configurations could be predefined so certain big loads wouldn't trip the inverter for start up currents then small loads could added to keep the inverter running.  This unit could also be used for utility AC start of a big load then a solar invert run of that load.

Complex indeed and just the contactors/SSRs needed apart from the control computer and its programming will soon push the cost quite high.

Just the utility AC start and solar inverter run feature in itself would be a great product.

Not quite sure what you mean here, what would this feature be exactly?

...   It could also be used for controlling the inverter and turning it on and off to save inverter idle time with a DC contactor control.

Its generally not a great idea to power on/off and inverter too often. In your scheme this could be happening several to maybe dozens of times a day as loads kicked in/shut down.
Much, much better to leave the inverter powered up and just have the loads disconnected as required.
If your thoughts are to save idle power usage then its a matter of finding a very low idle power inverter something that has been well discussed in this forum for different inverter brands.

Overall an interesting idea and I have seen some fairly simple load control systems based on a small computer and usually an SSR or two.

dgd

[nonsquid]

Thanks for the reply dgd,

Re: properly sized inverter - for those times when your air compressor is running, then your well pump picks up and shoots past your surge current.

Re: complexity cost - selective load management is a feature to safeguard the reliability at the cost of complexity.  Complexity is simplicity twice.  How the loads are dynamically shifted lends itself to the total operability / functionality of the system.

Re: Utility AC start and solar inverter run - I am talking about the large AC start currents required to start an inductive load like a motor.  To start an inductive load under the utility power then switch over with a bumpless transfer to the solar powered inverter would save the running cost of the load.  Yes this may require synching up the inverter to utility AC, but now you wouldn't tax the reserve capacity of you inverter trying to start big loads.  As long as the inverter is within +-20 degrees phase angle difference of the utility power and the switching device can measure the phase angle difference, it could switch at an optimum time.

Re: Inverter on and off - you are right, but inverter dead head would be eliminated.  By dead head I mean starting the inverter under load and killing it.

Thank for the reply.

[dgd]

Nonsquid,

Ok, although I can follow your reasoning for this load control mechanism, I still can't see it offering any significant advantage over simply doing some sums on max load power requirements and sizing the inverter  appropriately.
Surge or inrush currents are usually well catered for as decent inverters will often manage significant overloads for certain times. My 6kW ozinverter will deal with 9kW for several minutes and 12kW for near a minute. Easily enough margin to let the inductive loads get underway.

Since you are already have grid power then is it not a function of a GTI with battery connected to monitor house/workshop loads and optimise use of battery power vs taking power from grid? or are they not that smart yet?  I wonder of the B17 will have that mode 

If you have figured out logic of how your proposed device would function then I'd be interested in some sort of flowchart showing the decision and outcome paths.
It probably would not be that difficult to implement for two or three oads using a a small CPU, Arduino, rPi, etc..  Maybe a good/interesting hobby project but as a commercially viable product I would be doubtful.

dgd

[nonsquid]

Here is an example of what I am talking about.

http://hackaday.com/2016/07/12/parallel-compressors-for-sandblasting/

[australsolarier]

maybe you should look at the victron or selectronic inverters.

[Eleceng1979]

How about a load shedding system from a genset.  It is required by code and they use a simple controller and 24vac contactors.  Probably closed spurce and not to adjustable.

You could design and build from scratch using a few ct's and a baby plc...  it wouldnt be hard.