Smarter AGS for off grid?

BajaSolar

Hi,

I'm trying to set up a fairly advanced off-grid system and need suggestions to minimize automatic generator starting when solar is plentiful and loads are moderate. I haven't worked with AGS in the past and can't seem to find  many posts relevant to my specific concerns. Assume the client is not interested in learning the system or micromanaging the use of power like most of us with manual generators typically do. The client is not afraid to run the generator a lot when they feel that comfort is more necessary than fuel costs.

Assume the system is:
Aiming for all Outback, 48v (but outback is not set in stone if a more flexible solution is possible)
4000w of panels producing 3000+w for 5+ hours of most days (in sunny Baja)
600 AH (+/-) of batteries @ 48v
12kw Generator (+/-)
120/240 is undecided but doesn't seem relevant to this problem specifically.

Assume the loads are:
Typical energy efficient-ish off-grid beach home in Mexico (inverter refrigerator, sat internet, sat tv, led-lcd tv, several ceiling fans, led/CFL lighting...)(Expect toaster and electric coffee maker use on occasion)
Fluctuating moderate to heavy use of power without thought or regard to moment to moment conservation.
!! 6@ 1 ton inverter mini splits with heat pump !! (Mexico is cool/cold sometimes too)

The main question is how to properly balance the AGS so that it is coming on in the mornings when loads are moderate to high, but not come on in the afternoons when loads are moderate, but still come on when loads are high. 

Setting the inverter aux for AGS to start with loads of roughly 2500w would work well for sunny afternoons but would suck the batteries dry in the mornings and on cloudy days before the generator would start. 

Setting for low voltage would suck the batteries dry before the AGS initiates during moderate to heavy loads.

Using dual serial relays that sense for loads over 2500w from the inverter aux output, and 'low voltage' on the CC aux output would run the generator in the mornings with moderate to heavy loads if the batteries were already low-ish, but would not start the generator if the batteries were very low, and the loads are low to moderate.

Maybe I'm over thinking this or missing something. Is there no way for the system to sense the pv potential, battery state and loads, and make an intelligent decision as to whether to start the generator or not? Grid Zero and the other modes don't quite seem to cover this well enough, or my grasp of them is incomplete.

Thoughts and suggestions welcomed, thanks!

Estragon

Starting the generator bases on instantaneous load seems like a bad idea to me. You will have mini-splits, fridge, etc cycling at random times and with various cycle times. It would be hard to come up with a generator cycle time, not so short that the generator doesn't get warmed up and ends up constantly starting/stopping, and not so long that it's running unloaded for long periods.

Guessing at likely loads (especially HVAC), the bank/panel seem on the small side, so frequent generator use is likely. You didn't mention pumps for water, and the other loads shouldn't surge too badly. Maybe an AGS trigger based on voltage < Xv for > Ytime? The PV potential and loads are sort of factored in by way of battery voltage. It does mean batteries will draw down if loads > PV in morning, but voltage should trigger generator before they're "sucked dry".

You could develop some sort of SOC projection algorithm by sampling voltage and currents over time, but that's probably getting carried away.

Unless you have 240v loads (mini-splits?) or generator is far away, I would stick with 120v. Not really relevant to the AGS though.

mcgivor

That's quiet a challenge which would involve complexity in order to get it to work properly, would take some time to set all parameters to achieve the goal. Using a IO logic controller, current sensors, voltage sensors, and a basic program, would be one method, or using the aforementioned sensors and timers, with dry contacts, employing Boolean Algebra would be another. Would be a fun project to take on for the challenges, but not something to be attempted without experience in controls and certainly not something to hand over to a client without extensive testing and a fail safe default incorporated.

mike95490

Chris Olson had worked out a scheme to start the generator up after 4 minutes of some% of full load, so as to not start the genset when nuking a cup of 3 minute noodles.  The AGS has to be programmable.

jonr

There might be a market for an arduino kit with a couple of AC current transformers and a hall effect DC current sensor.   Combined with the ADC (battery voltage), some digital I/O, SSRs and some pre-written software, it would probably be useful for things like this.

Dave Angelini

If the design is right, where you live a generator does not need to be used except in really bad solar weather.

mike95490

Belive me, I like to avoid the generator, but weather changes:
 Genset Hours:
2013  53hrs
2014   227hrs
2015   104hrs
2016   134hrs

BajaSolar

Thanks for the comments. I finally had an in depth meeting with the client today and we're upping the panels and battery capacity considerably to move the generator farther out of the picture.

At my house nearby we're down to 8 hours of generator a year, except if it's too cloudy and the wife is having a laundry emergency. Then we usually just plug the washer directly into the Honda 2000.

I'm hoping that Outback eventually does design a smarter AGS system but I think the core of it will need to start on the charge controller side to be able to parse the potential output of the solar panels from moment to moment. This could help diversion load setups as well.