120W panel potential on 48V system.

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120W panel potential on 48V system.

Postby Tarkin12 » Tue Oct 21, 2014 12:40 pm

Hello all, I am definitely a newb and here is my newb question.
I am wondering what effect a single 120W or 160W solar panel with 48V controller will have on a 48V system (6 x 8V deep cycle batteries). Ive attached one of the panels info pics. The batteries as far as Im aware are 150 - 180ah.

I am really just looking to assist this system and wanting to see what percentage of charge if any this might put back into the batteries. The space to fit the solar panel is limited so can only fit one panel.
Appreciate any feedback.
Thanks
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120W solar panel info.JPG
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Re: 120W panel potential on 48V system.

Postby Gordon-Loomberah » Tue Oct 21, 2014 12:54 pm

Welcome to the Energy Matters Forums Tarkin 12 :)

What sort of controller is it?

If the panel rating is to be believed then with MPPT you might expect about 100W under good conditions with the panel facing the sun, more for short periods if there is cloud edge effect increasing the radiation levels. If it's a PWM type, you'll get a bit less when the battery is near 60V, and significantly less when the battery is at 48V.
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Re: 120W panel potential on 48V system.

Postby Tarkin12 » Wed Oct 22, 2014 11:16 am

Thanks for the welcome and the reply Gordon.
The controller is an MPPT 30.
So under the best case scenario regarding panel position etc, is there a way to determine what percentage the 120W panel might put into that bank of 6 x 8V batteries (48V system) ?
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Re: 120W panel potential on 48V system.

Postby Gordon-Loomberah » Wed Oct 22, 2014 12:02 pm

I don't quite understand what you are asking ... percentage of what? If you leave it long enough, it will put in 100% of the charging required to 100% SOC! :)
On a daily basis, it really depends on the weather, sky exposure and tilt of the panel, time of year, and your location, and what loads and other sources of charging there are. Lots of unknowns make it a bit hard to give any sort of answer on your question at this stage.
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Re: 120W panel potential on 48V system.

Postby Tarkin12 » Wed Oct 22, 2014 12:47 pm

Sorry Gordon, I was assuming the obvious which wasn't that obvious at all ;)

I was looking for the possible percentage of charge that might go back into the batteries during one full day exposure to the sun (lets assume its the optimum re position and conditions etc).

The batteries are fully charged overnight by AC and at the end of a typical day they would have anything from 40% to 60% left in them (around 50% being the norm).

So I am looking to assist the battery bank during the day while this system is off the grid in hope of returning it back to the grid with less charging required.

Hope that helps to narrow it down a bit. Let me know if any other info needed and thanks again.
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Re: 120W panel potential on 48V system.

Postby Gordon-Loomberah » Wed Oct 22, 2014 1:15 pm

OK, that helps a bit, can you detail your loads? If you are able to run the load directly from the panels, then you don't lose energy in the inefficient process of charging Lead-acid batteries, so you might get a bit better performance than expected.

Of course, the amount of energy produced by the panel will vary significantly throughout the year, but lets use data from somewhere like Perth with ~5kWh/m^2/day annual average. So, on an average day, for a panel ideally mounted, you should get about (100W * 5hr) 0.5kWh/day, ignoring charge controller efficiency, actual vs claimed panel performance etc.
If your battery is 150AH (or is it 180?), then 48V * 150 = 7.2kWh
If you discharge 50% daily (not good for a long life expectancy), then that is 3.6kWh of energy used, so your panel, on average, might replace about 0.5/3.6, or 1/7th, of the energy in a day, not counting battery charging inefficiency factors. As mentioned earlier that inefficiency will be reduced if the PV is directly powering the load.

As a way of extending battery life and reducing mains electricity use, have a look at this thread:
solar-wind-gear/topic5064.html
you may be able to squeeze in 2 panels tipped well up, to get more even energy production throughout the day, reducing the amount of battery discharging.
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Re: 120W panel potential on 48V system.

Postby Bthree » Wed Oct 22, 2014 1:28 pm

Still a bit general and missing things like location but ...

Imp = 1.7amps x 5 hours on a good winters day = 8.5 ah x 48v = 408 watt hours

A solar panel is lucky to be 90% efficient so = 367 watt hours

MPPT regulator unless its a really good one 93% eff. = 340 watt hours

possibly double 340wh from Oct to march in AU

50% of 150ah ( battery capacity) is 75ah or approx. 3600watt hours (being conservative here)

So AT BEST your panel may contribute to battery capacity by 9% over a perfect day in winter MAYBE

Think about buying some more panels maybe 10 or so, the charge controller will handle it
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Re: 120W panel potential on 48V system.

Postby Tarkin12 » Wed Oct 22, 2014 8:35 pm

Moderator removed quoting of entire posting, which is just up there ^^ ;)

Gordon-Loomberah wrote:some stuff



Thanks for that Gordon. Not able to run the load from the panel. The space available for one only panel is very limited so it was more of an enquiry to see if we could gain any worthwhile benefit by adding solar to that limited space.
Appreciate your detailed explanation and showing how to work that out.
Will take a look at your other suggested threads as well.
Last edited by Gordon-Loomberah on Wed Oct 22, 2014 8:58 pm, edited 2 times in total.
Reason: removed excessive quoting
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Re: 120W panel potential on 48V system.

Postby Tarkin12 » Wed Oct 22, 2014 8:56 pm

Bthree wrote: something that is just up there ^^


Thanks very much Bthree,
Appreciate your input and the detailed formula and explanation is helpful.
Adding more panels is not really possible at this stage.
I think I have enough detail now to consider the options and no doubt will be back again with more questions down the track.
Last edited by Gordon-Loomberah on Wed Oct 22, 2014 9:02 pm, edited 1 time in total.
Reason: removed excessive quoting
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Re: 120W panel potential on 48V system.

Postby Tracker » Thu Oct 23, 2014 6:50 pm

further to what the others said

Bthree wrote:Imp = 1.7amps x 5 hours on a good winters day = 8.5 ah x 48v = 408 watt hours
A solar panel is lucky to be 90% efficient so = 367 watt hours

I have found my panels, in this MPPT battery charging mode, are actually very close to their rated power potential
Imp = 1.71
Vmp= 70V
Thus under the best conditions (1000w/m2) P = VI = 119.7W (hence 120W panels)

With Imp of say 1.7A, the battery charge current would be about 2.2A
but nothing will change the fact that 120W just won't do much, except perhaps for some LED lights..
eg.. Security Lights..?
The batteries as far as I'm aware are 150 - 180ah.


50V and 150AH gives 7500W and say 30% discharge (to give a fair life) - say 2250W

BUT - one panel CANNOT replace that power at say 5hrs and 120W

So - the proposed battery is massively larger than needed, but if used within the charge/discharge capability, would mean the batteries should really last...

Bottom line - what are you thinking about for an application..
..
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