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Lets get some solar power

This is a discussion on Lets get some solar power within the Broken Arrow forums, part of the Gun Forum category; So, I end up with for my main system 520 watts of solar. Up to 187.5ah of stored power. And a 1500watt inverter. By no ...


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Old January 3rd, 2012, 04:51 AM   #121
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So, I end up with for my main system 520 watts of solar. Up to 187.5ah of stored power. And a 1500watt inverter. By no means a large system but people run remote cabins on less.
And for times when solar panels can't keep up with use, there is charging the batteries from generator or the truck but the main thing is not having to use fosil fuel to have power. And if fuel is readily available, I still don't have to run generator at night drawing off the batteries to have electrcity.
But with the storm shelter, I would rather restrict myself to power use to what is stored in the batteries & what the solar panels can provide.
Absolutely wouldn't have trouble providing power for lights, fans, tv/radio, etc but to run the small chest freezer I will need plenty of good sun.

HH

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Old January 3rd, 2012, 06:28 AM   #122
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When calculating building a system there are many things to take into consideration. For the batteries, its number of days you have sunshine. Where I live its 300 which is pretty good. But that means 65 days a year you'll produce little to no power from the solar panels. And that is part of calculating batteries for storeage. You want atleast 48 hours of stored power according to your estimated useage. But then again, that is one of the reasons you want a backup generator.

But it all comes down to how much you can afford to financially put into the system you intend to build.

HH


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Old January 4th, 2012, 10:43 AM   #123
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Exclamation Harbor Freight 45 W Set-ups - $149.99 W/Coupon

The February 2012 issue of "Guns and Ammo" has a one page Harbor Freight advertisement in the last few pages and there is a coupon for the 45 W Solar Panel Kit for $149.99.

The coupon can me used online, by phone, or in-store.

Just thought I'd pass that along.

Peace - Patrick ><>

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Old January 5th, 2012, 09:44 AM   #124
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Well, this morning seemed like the right time. Moved the four solar panels back & ended up shortening the 6gauge wires by 6ft. So the wires from the solar panels to the controller are right at 11ft which is well within specs for 20amp.

Next is building the frame for the two 80watt panels.

HH

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Old January 5th, 2012, 10:26 AM   #125
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HH-

According to my calculations, your 520W solar array is overmatching your battery bank by quite a bit.

If you use the recommended C/8 charge rate, your batteries can absorb 187.5 / 8 = 23.43A of charge current. Your array is capable of putting out ~35A of current. Even figuring in losses for wiring and partial shading, you're losing a lot of the potential of your array.

I'm currently charging my 235Ah battery bank (4x Trojan T105, wired for 24VDC) at 35A. A full charge can be had in ~3 hours. My charge current usually starts dropping in absorption mode after about an hour.

I'd recommend a 4th battery, when you can afford it. You'll increase your standby time and more effectively use your array.

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Old January 5th, 2012, 02:09 PM   #126
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No money right now. One of my rescue dogs goes in for surgery on the 17th & property taxes close to due.

But I do have space on the rack for a fourth battery.

HH

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Old January 5th, 2012, 06:57 PM   #127
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I already know I can run the small chest freezer with what I have. But do have the concern of draining the batteries too much. Adding two 80watt panels & an additional 125ah battery will make me feel better about leaving the chest freezer hooked up to the system permanently.

HH

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Old January 6th, 2012, 07:03 AM   #128
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With the two 80watt panels added & the fourth battery, the C/8 would be 31amps & figure panels at about 30amps(maybe alittle more) so close to a perfect match. But very much doubt I would ever come close to the calculated rating for the panels of 35amps.

HH


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Old January 6th, 2012, 10:37 AM   #129
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Figures I would buy a set of bed frames last week & find a free set at the dump today.

HH

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Old January 6th, 2012, 10:55 AM   #130
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Keep in mind that the C/8 figure is your maximum charge rate. If you can obtain a full charge in three hours at 35A, but you have five hours of full sun, you have leeway to charge at a lower current.

Before buying more array, see what your full charge time is on the current system, and see if you have some overhead in your available sunlight.

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Old January 6th, 2012, 01:48 PM   #131
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A problem with the C/8 is the higher the percentage the charge on the batteries the less the controller allows to the batteries so as not to damage the batteries.

HH

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Old January 7th, 2012, 05:57 AM   #132
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BTW, when I add the fouth battery I will have 250ah of useable stored power using the 50% rule. Means for instance I can draw 10amps of power for 24 hours.

HH

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Old January 7th, 2012, 06:52 AM   #133
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Quote:
Originally Posted by huntinghawk View Post
A problem with the C/8 is the higher the percentage the charge on the batteries the less the controller allows to the batteries so as not to damage the batteries.

HH
I don't understand what you mean by this.

The closer the batteries are to fully charged, the less current they can absorb. This is what causes the charge current to drop as the batteries charge. The controller will happily put out as much current as you set it for. The batteries absorb all they are capable of.

If you've determined to use a C/8 charge rate, the batteries will absorb current at that amperage as long as they are able, then they will self-limit. The current will remain constant throughout the bulk mode, then drop slowly during the absorption mode. But the transition between bulk and absorption isn't determined by the controller, it's simply a phenomenon of how batteries charge.

If one uses a C/1 rate, for example, with 100Ah battery, the battery will absorb 100A as long as it can, then the current willI drop as the battery becomes charged. This charge cycle will be much shorter than the C/8 rate, but will damage the battery.

A C/20 rate will work exactly the same way- the 100Ah battery will absorb 5A as long as it is able, then the current will fall off as it reaches a state of charge that limits the charge current.

C/8 is just a way of determining the bulk mode charge current. It is one eighth of the battery's Ah capacity.

The other controller determined settings are:

The charge voltage
The float voltage
The set point for the switch to float mode
The equalize voltage
The equalize schedule (if applicable)

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Old January 7th, 2012, 08:09 AM   #134
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My understanding is the controller allows current to the batteries by the voltage it reads from the batteries. If its reading real low like 11V it will probably allow maximum current to the batteries. But if the controller were to read 12.6V it would allow very little current to the the batteries. Same as a car battery charger operates.

HH

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Old January 7th, 2012, 08:14 AM   #135
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I got weld blinded alittle while ago so done working for the day. Frame is coming along though.

HH

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