Grid tie inverter parallel with MPPT chargecontroller on the same PV panel

[Justme]

Nowty,

Have you done any sums on what your PV offgrid energy costs per kWh to run? Especially the battery replacement side of things.

I think its fairly accepted that each kWh costs about 8p just for the battery replacements alone. By the time you add in inverter replacement & any other maintainance you could be better of using the grid mains.

[nowty]

Yes I am aware of the 8p'ish a kwh as a consumable cost of batteries before I started. I am fully aware its not financially viable, I knew that before I embarked on my off grid experiment and I have stated several times in my posts that it is not financially viable (if you have a grid power alternative).

I'm an electrical engineer, its techy, its fun, its green, it gives off grid resilience, its my hobby and I should still at least break even on the consumable batteries. If you get FITs for it then it should still be viable.

If I lump together my FITs on my main system with my electricity savings then I still get a total positive return on my solar PV costs.

And the way electricity (and PV) prices are going it may still eventually be viable without FITs.

[nowty]

Can you briefly explain how you do the automated / timed switching - and where does the SunnyIsland fit in? I vaguely remembered an earlier post of yours, and searched, finding this: http://www.navitron.org.uk/forum/index.php?topic=16866.30

However it mentioned your Victron Multiplus....?

Thanks

Start by looking at my thread,

http://www.navitron.org.uk/forum/index.php/topic,17834.msg203692.html#msg203692

I will update this thread soon with some more pics as I have changed some of the ways I do things.

The Victron was my first idea but I decided to go down the Sunny Island for a number of reasons. The Sunny Island is both an off grid inverter and battery charger system.

[jonesy]

At the expense of hijacking the thread, this 8p/unit is interesting for off grid.  As clockmanFR pointed out to me in a post recently, my grid purchase at €0.118/kWh is actually closer to €0.27 when you add in the standing charge.  I use about 500 units per year, so the standing charge makes a huge difference to the buying costs (say €60 of electricity, €72 standing charge per year).  From my 2 years of off grid days I still have batteries and inverters, but reasoned that my paid power would only go up if I started using the gear to save money!  In my mind, I can't clear my conscience about the batteries being green due to the mining and chemical production.  I used to use about 5 units/day and found the biggest power user was the fridge and freezer.  Buying a combined efficient unit and abolishing all stealth standby (timer, clocks, cordless base station, etc) has shed around 3 units/day.  Still got the usual dishwasher, bread machine and washing machine.  The fridge still  accounts for almost half my power usage.  The solar panels are grid tied and save about 0.8 unit/day.

Getting back to the OP, I agree with stephendv that the two MPPT devices will fight.  If you have a system voltage of around 150-250V DC, Billi I can't think of a technical reason at the moment why you cant use a standard switch mode power supply (SMPS) across the panels to charge the batteries.  Modern SMPS will operate 120-240VAC or around 150-250VDC (IIRC)  You'd need some sort of feedback loop to vary the charging current so you meet the FIT maximum, and a dump load for when the batteries are fully charged - or the GTI may have a setting for max power.

[billi]

Ok thanks , the idea is more , not having a Dump (sure in case the GTI fails , on needs a Plan B...) and sending all surplus to the Gti
so when the batteries are getting full the Gti feeds more and more power to the Grid


@Justme , i found the international Outback range  and yes they would work  but  in the Manual is written

Instructions on setting up individual FX systems, as
well as assembly of larger systems, are given in the International Series GTFX and GVFX Grid-Interactive
Inverter/Charger Installation Manual.

Note: This product is not CE compliant for grid-interactive operations.
.......
. The inverter can sell power to the grid after the batteries
are charged.

Hmm..... so  needs some more equipment , i suppose , to make this  legal , if at all possible  , something like this is required in Germany anyway called

ENS Grid Tie Protection

and looks


Other idea i have and not sure if it could work , is use a Diversion load controller like the Morningstar and  connect the GTI to the  dump load terminals instead of an immersion , but would the GTI work with this PWM signal  from the Morningstar ? Sure i am then very limited to inverter choice  cause low voltage DC ....  ( the dumping  in case Gti fails or  grid off, could be regulated by the off grid inverter ...)

I know , connecting a  GTI to a battery is not recommended , but would not the Diversion load controller then limit the amount of Amps the GTI wil get ?

Next idea would be , if one uses an intelligent off grid inverter , AC coupled on the "off-gid" side of the Install  ( i use my Victron as an example ) and use the internal programmable  Aux relays in the off grid inverter to switch over the GTI via a SSR onto the grid site of the installation  to exclusively  feed the Grid  , same i do here with Dumping into a AC heater  , say when battery is reaching 29 Volt , relays switches GTI over to Grid ,  when battery is  below 25 Volt , back to the "off-gid" side of the Install

Too much thinking i suppose 

Billi

 

[Justme]

Billi,


It might be worth checking with OB directly or via the OB forum as the info in the manual could be out of date.

Or find out what compliances it does have (like USA, Canada & Australia) & see if they match the needs of G83.

I would have thought that OB would have jumped at the CE market as they have had this solution for a long time.

You could also try Midnight Solar as they are virtually the same unit made by some of the original OB team.

[billi]

Ok .....  did that , i hope i get a response on the forum there ,

Interesting  charge controller , that could suit  http://www.colemanair.us/vp_asp/scripts/shopexd.asp?id=620

From the Manual

Extended Diversion Mode -- EDM
The basic operating philosophy of a diversion controller is quite simple. Monitor the battery voltage, and if it
should rise to a predetermined level, connect a diversion load, of sufficient size, to the battery or energy source
to prevent the battery voltage from increasing any further. The amount of time the diversion load is connected
is generally only 10 to 30 seconds. In this amount of time, the battery voltage will have dropped enough to be
back in the normal region. The controller will continue to engage and disengage the relays as often as necessary
to prevent battery overcharge. This is the normal mode of operation. The microprocessor uses several advanced
algorithms to prevent rapid relay cycle, yet it is common for the relays to be engaged and disengaged a few
times a minute. This constant attention keeps the batteries very close to (or just below) the trip point you have
set.
There are however, situations where you would really like the controller to engage the relays for a longer period
of time once the batteries get to a “Full” state. This is what we call Extended Diversion Mode. When you enable
this mode (see jumper settings below), and the batteries reach the trip point you have set (the same trip point as
the normal mode), the controller will engage the relays for approximately five minutes or until our batteries are
depleted by 15%, which ever comes first.
The EDM mode is very useful for running such items as water pumps or small grid tie inverters that you do not
want turning on and off every few seconds. When you enable the EDM mode, the wiring remains the same; the
difference is that the load you connect will be engaged for a longer period of time.

Sounds good

[uber39]

hello Billi and all,
     at my place I use a Latronics PV Edge 1200, does grid feed with solar direct, or turn off the MPPT and it starts to feed the grid at 54v,so first up in the morning the batts get a good charge then when volts get to 54 the gti turns her self on. Charge from any source - solar, wind,hydro even CHP. ( do wish I had hydro )
    They make a bigger brother PVEdge 2500but that runs at 96V+
    http://www.latronics.com.au/products/grid-connect-inverter-pv-edge-series
   
    We're only allowed to feed in 4500w of solar and get the max FIT,$0.70. Won't take my wind or CHP so these have to go to batts If to much goes to batts it just slips out via the gti javascript:void(0);

[billi]

Interesting , sounds good ,  an additional  off grid inverter is required  ,  and a full charge  every week or so ....