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Author Topic: Using an Immersion type device with an off grid system  (Read 4279 times)
nowty
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« on: November 01, 2014, 07:39:42 PM »

I have had an Immersun working on my grid tie system for a couple of years now and this has worked very well dumping over 3000 units to storage heaters, but I have thought it (or a similar device) must also work equally well on my AC coupled off grid system. bike

The problem with my off grid system (and most off grid systems) is that once the batteries are nearly full the solar generation throttles back and the system is underutilised, especially in summer. I know some of the regulars use a manually controlled dump load but I wanted something automatic that I could leave running all summer. fume

My off grid inverter + batteries is effectively similar to the grid so putting the current sensor clamp on the live wire going into my Sunny Island must be the same as putting it on the live wire going from a grid tied consumer unit to the incoming grid elecy meter. tumble

I have not seen any device claim they could be used with an off grid system and I have never seen a thread about anyone else trying it. I decided to bite the bullet and reinvest some of my FITs in the cheapest immersun type device I could find for £165 off fleebay and wired it up using a simple electrical convector heater.  Tested it today as the November sun has been fairly reliable all day. The results are it works exactly as I hoped it would.

No export from my batteries and seemless automatic proportional diversion to my convector heater as the clouds came and went. My Sunny Boy has been maxed out most of the day instead of throttling back to almost nothing with the batteries on float. extrahappy

Very happy bunny, so thought this would be of interest to all the off gridders who have been thinking like me it must be possible but wanted someone else to risk their own cash first !  ralph
« Last Edit: November 01, 2014, 09:32:49 PM by nowty » Logged

11kW+ of PV installed and 56+ MWh generated.
Lithium battery storage of 50+ kWh.
Hot water storage of 15+ kWh.
Heat storage of 15+ kWh.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
260,000+ litres of water harvested from underground river.
Home grown Fruit and Veg.
clockmanFR
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« Reply #1 on: November 01, 2014, 08:27:09 PM »

Well done Nowty.

Glad you spent the money and experimented.   genuflect

Thanks.  extrahappy

An Immerson type device is now definitely on my agenda for my SI and its AC coupling inputs from Sunny Boys.

Not sure how I get the cabling from my SI up 100m to the house.  banghead 
 
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biff
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« Reply #2 on: November 01, 2014, 09:55:40 PM »

Strewth,friend Nowty,
                          Our own off-grid system is also totally automatic, Our 3.8 solar pv travels in 4 strings through 2 Chinese wind turbine controllers which are set to dump at 138.9 vdc, Each controller redirects the excess into the immersions that heat our d.h.w.t and water storage/heater. Bank remains full while the tanks get heated.. and it works very well,leaving me another happy bunny
                                                       Biff
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Tinbum
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« Reply #3 on: November 01, 2014, 09:57:32 PM »

That's interesting. I'm planning on doing something similar soon but with sunny backups but also I'm grid connected.
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« Reply #4 on: November 01, 2014, 11:22:01 PM »

I did consider it, and yes it has been done before but I decided to go DC and PWM, probably more expensive in the end as I'm using rather a lot of 70mm and 50mm square cable but 'I know a man'  whistlie

The problem with my off grid system (and most off grid systems) is that once the batteries are nearly full the solar generation throttles back and the system is underutilised

Not if you alter the parameters on your SI so a PWM in diversion mode heats the water first. Of course I'm saying all this as if I actually know what I'm talking about but in truth I've got no further than installing the SI, batteries, controllers and cabling. If it actually works you'll be the first to know  Grin

Good luck, and great result, Paul
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« Reply #5 on: November 02, 2014, 04:45:46 AM »

cool   Nowty  

good to know  another  method of utilizing  all surplus power when battery is full , in an off grid setup
Are you certain , that  enough  Sunny Boy s power flows backwards into the Sunny Island to charge the batteries ?

My "overproduction"  is done with the  relay  built into my Victron Inverter  in relation to battery voltage

Or sure much more clever with the Outback MPPT charge controller , that allows a 100 % granted  full charge of the batteries  , but to use every surplus from the PV trottled back  during absorption  and float charge

Billi



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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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« Reply #6 on: November 02, 2014, 07:02:08 AM »

Cracking job nowty  genuflect
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biff
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« Reply #7 on: November 02, 2014, 08:06:43 AM »

I have often wondered just how much energy our bank looses,
                                              Our controllers are set to divert to the immersions @ 138/9vdc which is almost the same as 14volts in a 12volt system. So that is not terribly high yet low enough to give the bank a decent charge overnight when the house is using less energy. Yet to get to that stage,and stay up at that voltage I assume a lot of the solar pv power and the wind turbine power drifts off into cyber space,in the big effort to keep the voltage up so there must be massive loss,s.
   I am guessing that with a lower voltage and smaller bank the modern Outback and Victrons would win the day but with a bank like mine where the cells are different they would be utterly confused trying to take a reading from one minute to the next. I am guessing that there would be a lot of delays and little warning lights and signs telling me that I have "ERRORS" hysteria.
   Nowty,s method sounds the business and like Billi says, "It is good to know another method of utilising all surplus power when the battery is full"
                                        Biff
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billt
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« Reply #8 on: November 02, 2014, 09:04:34 AM »

My off grid inverter + batteries is effectively similar to the grid so putting the current sensor clamp on the live wire going into my Sunny Island must be the same as putting it on the live wire going from a grid tied consumer unit to the incoming grid elecy meter.

The trouble is that you are likely to end up with flat batteries if you are using the Sunny Island as a charger.

The aim of diverters is to ensure that no power is sent to the grid, if it's working properly then the SI won't get enough power to charge the batteries.

There are a few ways to achieve this without a diverter.

The bigger SIs have a couple of relays that can be programmed to switch on battery SOC, so one of them could be used to drove a load switching relay.

Use one or more frequency sensitive relays. I think Heatherhopper uses this method.

I'm going to try a modified OEM PLL diverter arduino sketch to act as a frequency sensitive switch. http://openenergymonitor.org/emon/pvdiversion/pll/features
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Tinbum
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« Reply #9 on: November 02, 2014, 09:45:07 AM »

My off grid inverter + batteries is effectively similar to the grid so putting the current sensor clamp on the live wire going into my Sunny Island must be the same as putting it on the live wire going from a grid tied consumer unit to the incoming grid elecy meter.

The trouble is that you are likely to end up with flat batteries if you are using the Sunny Island as a charger.

The aim of diverters is to ensure that no power is sent to the grid, if it's working properly then the SI won't get enough power to charge the batteries.

There are a few ways to achieve this without a diverter.

The bigger SIs have a couple of relays that can be programmed to switch on battery SOC, so one of them could be used to drove a load switching relay.

Use one or more frequency sensitive relays. I think Heatherhopper uses this method.

I'm going to try a modified OEM PLL diverter arduino sketch to act as a frequency sensitive switch. http://openenergymonitor.org/emon/pvdiversion/pll/features

Its all very complicated as there are many scenarios. As nowty has the clamp on the sunny island the addition of a frequency switch could be employed. As soon as the frequency goes higher (batteries charged, (but that could only be part charged!)) then the frequency switch energises  (timed) and the immersun is powered. I think the immersion has a setting, doesn't it, to allow some power back to the grid so that could help with charging.

There are commercial frequency switches for the SI but they are about £90 and they are just on/off.

As Billt says something like an arduino is probably the best bet but it takes some learning and trial and error. I use one for my normal diverting and was going to add to that. So when I'm off grid it does like you suggest frequency controlled and when on grid it will only divert when no power is coming from the batteries.




 
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85no 58mm solar thermal tubes, 28.5Kw PV, 3 x Sunny Backup 5048, 3x Sunny Island 5048, 2795 Ah (135kWh) (c20) Rolls batteries 48v, Atmos wood gasification boiler, Brosley wood burner, 2000lt buffer tank and 250lt DHW
nowty
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« Reply #10 on: November 02, 2014, 10:00:15 AM »


QUOTES
“Are you certain , that  enough  Sunny Boy s power flows backwards into the Sunny Island to charge the batteries ?”

“The trouble is that you are likely to end up with flat batteries if you are using the Sunny Island as a charger.”



I won’t end up with flat batteries because when I have wired the system up properly the immersun type device won’t be able to turn on until the batteries are fully charged.

I already use the Sunny Islands multifunction relay when the batteries are 90% (highest setting the SI will allow) + cascade that with an external time delay relay of 1 hr to switch my grid circuits to “off grid” early in order to increase the yield. This has worked very well over this summer.

I will add in another 1hr time delay relay, so the immersun type device will only turn on when the batteries are 90% + 2 more hrs charge. From that point the immersun type device will guarantee no discharge from the batteries, even when the sun goes behind clouds.

In the summer months 90% + 2 hrs will still be reached mostly before midday. Still plenty of time left to heat up a 150 litre water tank with 10 units or so.

I did note in my experiment yesterday that the immersun type device was allowing nearly 200w to flow into the Sunny Island so it should also keep it nicely topped up on float too.
« Last Edit: November 02, 2014, 10:02:27 AM by nowty » Logged

11kW+ of PV installed and 56+ MWh generated.
Lithium battery storage of 50+ kWh.
Hot water storage of 15+ kWh.
Heat storage of 15+ kWh.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
260,000+ litres of water harvested from underground river.
Home grown Fruit and Veg.
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« Reply #11 on: November 02, 2014, 10:43:18 AM »

Nowty,
Please do keep stuff coming regards the Sunny Island, because the stuff you, Tinbum, Paul, billt, Heatherhopper, Stephen and others with operating SI systems, are seriously filling in my knowledge about the SI.

SMA are clinical with there specs and operation, but they could give some working examples which would be very useful for dim wits like me.

Hopefully by the time I switch mine on, I should be able to plan out its full working possibilities.

 Thanks Guys and Gals.
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heatherhopper
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« Reply #12 on: November 03, 2014, 11:34:50 PM »

Interesting trial Nowty.
I would certainly like an AC side PWM diversion and briefly looked at the Immersun a couple of years ago but decided it was not really compatible with my set-up. I regard PV and wind as power generators first, battery chargers second and heating is just a necessity (albeit with great fringe benefits) to keep the generators loaded.

Some issues I would have with it (although I may have misunderstood the Immersun set up):
Activating the Immersun using an SI relay based on SOC of 90% is going to be at odds with the SI charge regime. There can be a considerable and increasing SOC error when in Float mode which is only corrected when the mode changes to Boost and Boost voltage will not be achieved with only leakage past the Immersun. 90% is not necessarily 90% and starving the batteries of potential charge when it is available is not a good idea when off-grid. Similarly Full and Equalisation modes will also not complete.
Activating only at 90% +  SOC the Immersun would not provide the diversion required for loading an AC coupled 6kW Proven.

If the Immersun could be frequency shift activated I can see this would work fine in an Island grid. Would the clamp sensor work on the live to a separate frequency shift relay activated load?

I think I'll stick with frequency controlled diversions for now – the on/off nature may be a bit crude but they are simple, fast and reliable (thus far) and the PV and Turbine are always loaded with no adverse effects on battery status, plenty of hot water and heating too!

I would be interested to hear how the final working Immersun set up goes over time – I could be tempted to try it.
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nowty
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« Reply #13 on: November 04, 2014, 05:15:50 PM »

Activating the Immersun using an SI relay based on SOC of 90% is going to be at odds with the SI charge regime. There can be a considerable and increasing SOC error when in Float mode which is only corrected when the mode changes to Boost and Boost voltage will not be achieved with only leakage past the Immersun. 90% is not necessarily 90% and starving the batteries of potential charge when it is available is not a good idea when off-grid. Similarly Full and Equalisation modes will also not complete.

That would be correct but I am using additional time delay relays so the immersun would only get activated 2 hours after the batteries achieve 90%, so they would generally finish their absorption charge and be in float when the immersun kicks in. And I would not use it at all from Nov to Feb as I have a winter setting where I disable the multifunction relay.

For EQ charging which I do manually anyway, I can simply turn off the immersions, in fact I can turn the immersions off manually anytime I thought the batteries needed a good fry or if the weather forecast for the next day was not so good to give greater chance of the batteries finishing absorption.

I thought about using a frequency controlled switch but I dont like devices which are only on or off. Also using one to switch on the immersun would have it come on too early, then it would be continually switching on and off.
« Last Edit: November 04, 2014, 05:39:09 PM by nowty » Logged

11kW+ of PV installed and 56+ MWh generated.
Lithium battery storage of 50+ kWh.
Hot water storage of 15+ kWh.
Heat storage of 15+ kWh.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
260,000+ litres of water harvested from underground river.
Home grown Fruit and Veg.
biff
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« Reply #14 on: November 04, 2014, 06:40:04 PM »

Nowty,
         Thats exactly how I boost the bank, I turn off one 2kw immersion and let the voltage climb and sit at 146v for 20 mins or so.
                                                                         Biff
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