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rondurrans
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« on: July 27, 2011, 08:34:14 AM » |
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If you were off grid and assuming losses of up to 20% from your batteries, would it be advisable to convert straight away from DC to AC and back to DC to store in batteries to ensure maximum return from the FiT? Am I right that there are no OFGEM/MCS approved DC meters.  |
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Justme
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« Reply #1 on: July 27, 2011, 09:40:39 AM » |
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You might be better off financially but worse off for actual usable power.
Ok in summer when you will be making more than you use but for the rest of the year you will be under producing.
array-charge controller(95%)-bat(80%)-inverter(95%)-meter = total losses 27.9%
array-inverter(95%)-meter-mains battery charger(90%)-bat(80%-inverter(95%) = total losses 35.01%
So roughly 8% net power worse off per year. Now you need to run it the other way & see how much extra FIT's payment you will get. Dont forget that you also now have an extra link in the chain so increase install & replacement costs need factoring in. I would guess that over its full lifetime your way would be better for monitary reasons even after needing to top up the supply in winter from a genny (separate CU)
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
200w (250w peak) 12v turbine as a tester
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h @12v
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EccentricAnomaly
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« Reply #2 on: July 27, 2011, 10:22:18 AM » |
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What inverter would one use on the output of PV to create 240 V AC?
A grid-tie inverter wouldn't work without a grid. An off-grid inverter wouldn't do MPP tracking and it would be a worry whether it'd tolerate the range of voltages from the PV as the sun and load vary.
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rondurrans
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« Reply #3 on: July 27, 2011, 12:07:05 PM » |
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Thanks guys.....
My simple mind was convert DC to AC (FiT meter) – supply AC demand – what was left convert back to DC and store in battery; when batteries full dump excess AC into element in water tank. Is there something fundamentally wrong with this?
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« Last Edit: July 27, 2011, 12:17:19 PM by rondurrans »
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Justme
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« Reply #4 on: July 27, 2011, 01:15:00 PM » |
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I think thats almost what Russ has from the Sunny boy range (sunny Island?) & is changing to a more normal set up due to issues.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
200w (250w peak) 12v turbine as a tester
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h @12v
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Mike McMillan
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« Reply #5 on: July 28, 2011, 06:48:28 AM » |
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I am off grid and use a morninstar relay driver to open circuits to use surplus power. It is working really well. It measures the DC voltage from the batteries and as that rises, it opens 4 circuits sequentially. It is programmable. I have it turning on 2 dehumidifiers, then storage heater and finally oil filled radiator. Very pleased with the result.
Mike McMillan
IOW
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billi
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« Reply #6 on: July 28, 2011, 07:28:42 AM » |
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Hi there is not an awful big difference between a DC-AC with charge controller Battery and Off grid inverter to a DC--AC with an Gridtie inverter (replaces the charge controller and coupled to an Off Grid inverter picture attached is from here http://www.studer-innotec.com/?cat=whitepapers ( click on "Partial AC-coupling in Minigrids" , if you want to read ) Billi @ Mike , that sounds good is it AC you transfer ? You seem to have a big AC Inverter then  |
Guinness no Grid comes near
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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camillitech
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« Reply #7 on: July 28, 2011, 10:30:40 AM » |
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Most interesting links Billi,
Cheers, Paul
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http://lifeattheendoftheroad.wordpress.com/12kw Lister 11m turbine tower 10 hundred ah 48v battery bank 900' pennstock 8kw woodburner 7kw Lister 6 bladed Rutland 50w of solar 4 and a half Kw inverter 3kw Lister 2 hydro turbines and a Proven in a pear tree :-) Raasay, 57 27 537 N 06
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Mike McMillan
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« Reply #8 on: July 28, 2011, 02:10:17 PM » |
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Billi, yes, My 2.5 KWH studer is not enough, so I am trying out a cheapo (£300) 4 kw modified sine wave jobbie (otherwise the studer trips when the hoover is used!) 3WKH panels in the garden charging some pretty hefty 15 year old yacht batteries through 3 controllers. FIT meter is from the Inverters. Here's the relay driver. http://www.morningstarcorp.com/en/relay-driverMike |
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rondurrans
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« Reply #9 on: July 28, 2011, 03:35:45 PM » |
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Mike do you convert DC to AC and then back to DC when the AC demand does not need it and then store in your batteries to ensure maximum return from the FiT?
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Mike McMillan
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« Reply #10 on: July 28, 2011, 05:36:46 PM » |
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No, the controllers are only charging the batteries and the inverter is 24v to 220. I was worried that I would be dragging 3 kw out of the batteries but in practise, the controllers are feeding the correct charge into the batteries and the surplus just skips across the terminals into the inverter. let's put it this way, I am not topping up with water any more frequently than before, so in effect it's not discharging and charging the batteries during daylight hours. At the moment, I am consuming around 14 kw of power on a sunny day, £6 revenue a day! Brill.
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