what size solar panel to charge a 110Z battery in 6 hours ?

Submitted: Sunday, Jul 07, 2013 at 17:53
ThreadID: 103135 Views:2021 Replies:2 FollowUps:5
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can anyone recommend what size solar panel is required to charge a 110X car battery in a day , or allowing 6 hours charge time , assuming 60 - 70 % discharge when beginning recharging ?

the battery is for a trolling motor in a boat and trying to weigh up if i can recharge with solar instead of lugging a genset

180 watt solar will fit on the vehicle roof without hogging too much space from my rooftop tent :)

any suggestions ?

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Reply By: olcoolone - Sunday, Jul 07, 2013 at 18:10

Sunday, Jul 07, 2013 at 18:10
Your panels will put out about 10amps under ideal conditions.

We recently did a Northern Simpson trip along the Madigan Line and under ideal conditions from our 95w panel we got 5.6amps, if the panel was off axis to the sun this would drop down to around 2amps.

On over cast days it varied between 1 to 3.5amps.

We only had on average 2-4 hours per day under ideal conditions.

I've been pretty conservative with the figures and I sure someone will say different.

We used a Redarc BMS to monitor charge.

My use was under real world conditions over 21 days with varied weather conditions adjusting the panel to follow the sun.
AnswerID: 514448

Reply By: VroomVroom - Sunday, Jul 07, 2013 at 18:19

Sunday, Jul 07, 2013 at 18:19
i have done some homework and i have space for a 250 watt solar panel with 30 amp charge controller

can someone tell me how to calculate the charging time on a 110 battery from that ?

ty :)
AnswerID: 514449

Follow Up By: olcoolone - Sunday, Jul 07, 2013 at 18:48

Sunday, Jul 07, 2013 at 18:48
What happened to your 180 watt panels....... if you work on between 13 to 17 amps and your battery was depleted by 70% you need to put back in around 60 to 80 amps...... grab you 13 to 17 amps from the panels and divide it into the 60 to 80 amps you need to bring your battery back up to 100%.

That will give you how long under ideal conditions nor real world conditions.

There are so many variables to your question.

And to answer you question....... somewhere between 4hrs and 3 weeks to charge your battery.
FollowupID: 793467

Follow Up By: VroomVroom - Sunday, Jul 07, 2013 at 18:53

Sunday, Jul 07, 2013 at 18:53

i thought there might be some sophisticated formula to work it out with efficiency factors and lots of big words.

yeah . cloudy days and angle of panel to the sun will give big variations but i will base it on worst case and a 250 watt should cover me


best wishes
FollowupID: 793469

Follow Up By: olcoolone - Sunday, Jul 07, 2013 at 20:55

Sunday, Jul 07, 2013 at 20:55
There are correct formulas to work it out but I will leave it up to the professors of EO to tell you more about everything you don't need to know.

In a mobile situation it is hard to give a better figure, in a stationary setup you are dealing with more constants so you can be a bit more accurate.

When we were away we had 4 days where the panel was reduced to 30% capacity and we could only use the panel for about 3hrs a day before the dark clouds rolled in.
FollowupID: 793486

Follow Up By: The Bantam - Sunday, Jul 07, 2013 at 20:58

Sunday, Jul 07, 2013 at 20:58
Yeh there are sofisticated formulars but they require information like the location within Australia so it can be related to a solar radiation map and the time of the year....and of course shading factors due to overcast and tree cover.

The actual output of solar panels varies a great deal depending on the situation.

If you where located in the highest radiation areas in the country in summer with clear skies , you could expect to get pretty close to 100% of the rated output of your panels in the 3 hours either side of solar noon and useful charging at a reduced rate for up to 12 hours total.

If however you where in Tasmania in winter, even with clear skies you would be doing well to get 30% of the rated capacity and for no more than 4 hours and less than 12 hours of daylight so maybe 8 hours of useful charging total..

When calculating for reliability, its not unreasonable to work on 50% of the rated capacity over an 8 hour period each day in middle Australia...in good weather.

the question is will this panel be on the boat or back at camp.

Remember people are general far to optomistic about solar, depth of discharge and how long batteries take to charge.

FollowupID: 793487

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