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Author Topic: Maximum charging current  (Read 5861 times)
Justme
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« Reply #15 on: April 29, 2009, 10:00:48 PM »


i am planning a solar/ wind off grid system to provide 2.5 kw a day, in the winter i was thinking that the solar would provide most of the power most of the time with the wind giving the battery's a good long drink of leccy when it blows.
And a dc genny as a last resort, i was thinkin 24 volt because i want alot of the system dc to minimise inverter losses and 24 volt truck stuff is readily available.

I have a similar system.

Mine is 12v & I use about 3kwh per day
I have 800watts solar
200 watts wind
6kva genny

 So far the wind has not been worth it (but it is a bad site for wind)
The solar will NEVER give me enough power in winter (infact I worked out on current performance I would need 26kw to cover december)
So I worked out a sweet spot that will give me just over enough in summer & ok in spring & autum, winter will be a genny every couple of days.

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
Justme
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« Reply #16 on: April 29, 2009, 10:09:48 PM »


And a dc genny as a last resort, i was thinkin 24 volt because i want alot of the system dc to minimise inverter losses and 24 volt truck stuff is readily available.

Makes sense.

Until you want to power an item that would use to much peak power or be on for to long for the inverter / battery. Far better to have a genny at mains power so you can utilise it directly (also IF the inverter fails or the bank fries you still can run the genny for a few hours each day so you have some redundancy built in). Also then when its on ALL the items in the house are powered direct from the genny (with a pass through inverter) so that the charger & inverter are not trying to do both at the same time so more of the charge actualy get into the bank. You can also use the inverter & genny together to power even larger items so it allows you to have a smaller genny & inverter than you think (victron power assist I think its called).


Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
daftlad
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« Reply #17 on: April 29, 2009, 10:45:33 PM »

Justme, looks likes a really good site that has been saved to my favourites, i will have to come back to this one next week, i am off to see the earthship in Brighton tomorrow.
I do agree with you both about wind but i was planning enough pv to get me through 10 months and for the other 2 be economical (turn fridge off etc), only wash clothes etc when the wind blows and fire up the genny as a last resort.
The reason why i don't want to go genny too much is because i want to be as near zero carbon as possible and am prepared to make a few lifestyle sacrifices to do it.
You may think that i am wasting your time asking dumb ass questions but I really want to build this house partly as an experiment, partly as a blue print of what can be done, I have the money just not the site or health at the moment, so i am spending my time doing research and asking dumb ass questions.
The reason i was thinking dc generator was because of what happened to Frotters generator when he connected it to a big inductive charger, the plan as far as inverters is concerned is to have a dinkey one for most stuff and a big modified sine wave one for other big stuff.... Aghhhhh i hear you say not msw inverters.
do you think i should start a new post for this one?
laters
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I WILL KEEP BANGING ON ABOUT MASONRY STOVES
Justme
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« Reply #18 on: April 29, 2009, 11:38:42 PM »

To give you some idea of how much you will have to give up here are my monthly totals
month                           daily average
         amp/h    kw/h       amp/h    kw/h      Days with no power         
dec    214        1.6         6.9        0.05             16 (6 in a row)
jan     315        2.9        10.16      0.09             7 (4 in a row)
feb     656        6.9        23.42      0.24             3
mar    1830      21.2       61          0.7               0 (min power 0.1kwh)
apr     3311      40.5       110.36    1.35             0 (min power 0.2kwh)



The best day I have had was 2.4kwh (april 27th) & 184 amph (april 18th). Peak watts 760 (but not on a high total output day)





Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
Justme
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« Reply #19 on: April 29, 2009, 11:42:20 PM »


I do agree with you both about wind but i was planning enough pv to get me through 10 months and for the other 2 be economical (turn fridge off etc), only wash clothes etc when the wind blows and fire up the genny as a last resort.

You may think that i am wasting your time asking dumb ass questions

Have you worked out how much power you actualy need yet?

Nah keep em coming.


I have a spread sheet that you can play with that shows the affects of diff sizes & costs of panels at diff levels of power consumption if you want a copy.

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
daftlad
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« Reply #20 on: April 30, 2009, 01:30:42 AM »

All really good stuff, see you next week
laters
ps seems the on line calculator i used might have been a little optimistic
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billi
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« Reply #21 on: April 30, 2009, 08:07:03 AM »

Hi
The only real reliable components in my system  was and is the PV panel  , the inverter , and the solar charge controller and a DC Diesel generator  and  a big second hand forklift battery

The 1 kw windgenerator blew away last winter not a expensive one  but still including materials and helpers wage  2500 euro gone
I started with a small but expensive (1500 euro ) gel leisure battery as a greenhorn ( was the recommendation from my inverter sales person )   gone after a year     Roll Eyes

I went trough 2 cheapish diesel AC generators(1500 euro ) perhaps repairable ?connected to my inverter to be switched trough the dirty juice into our house  , but they didnot manage to survive

I might have had bad luck , but i learnt   some lesson

So my conclusion  is (with my history)  the 5500 euro i lost and the diesel i burn  will (would have ) buy me a nice additional PV panel  to provide 90 % of my needs  and who cares if i have too much in summer  (always can heat water  via a small heatpump)

Im not saying AC generators are bad no  , but they have to work much harder to supply the varying needs in the house then a smooth DC charging generator
And nothing against windgenerators either  , we miss it  Angry

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
daftlad
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« Reply #22 on: May 05, 2009, 04:20:02 PM »

Any thoughts welcome.
I have estimated The size of my PV system based on the following website
http://sunbird.jrc.it/pvgis/apps/pvest.php
Compared with the results that Justme has posted they seem a little unrealistic.
Not really knowing what i was doing i left the variable perameters alone and left it at 1kw of panels and the results for south Cumbria were as follows (monthly average)
jan 0.8kw
feb 1.5
mar 2.2
apr 3.1
may 3.8
jun 3.5
july 3.6
aug 3.0
sep 2.5
oct 1.6
nov 1.0
dec 0.6
This is for a fixed inclination of 37 degrees and an orientation of 0 degrees.
So why are the results so much better than Justme's?
The penel selected was crystalline silicon with losses of 14 percent.
I realise Just me has 800 watts but still?
laters
PS Justme, can you send me the spreadsheet info you mentioned, i have sent you a personal message, cheers.
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Justme
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« Reply #23 on: May 05, 2009, 04:34:39 PM »


PS Justme, can you send me the spreadsheet info you mentioned, i have sent you a personal message, cheers.


I did it the same day (30th April).

Justme
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
stephend
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« Reply #24 on: May 07, 2009, 11:07:55 AM »

Daftlad, check the losses, these differ a lot depending on how your system is setup.  I.e. if you're calculating the power from a grid connected system, then you'll have losses in the DC cabling of the panels, the inverter and the AC cabling.  In an off-grid system the efficiency is much worse: losses in DC panel cabling, losses in charge controller, losses in charging the battery, losses in discharging the battery, losses in inverter and AC distribution.  For off-grid, using an MPPT tracker you could probably estimate losses of about 30-40%, depending on how your load is distributed, i.e. you get higher efficiencies the more power you use during sunshine.
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