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Old 02-23-2015, 06:31 AM   #21
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Re: Solar???

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Originally Posted by daveb

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For the money a +/- 200 watt solar array coupled with an adequate battery bank provides a good balance for a Sportsmobilers needs. I just run the engine to supplement the load requirements when running my microwave which pulls about 80 amps @ 12vDC on high. If I use a lower setting, I can still warm something that needs only a minute or so to heat up with out running the engine. With my 400AH battery bank I still never reach 50% of discharge by morning and have plenty to spare throughout the night to power my Espar heater or a fantastic fan, the stereo, a DVD player and LED lights. My batteries are usually charged to full by 9am even in partial shade. I have 270 watts worth of solar on top of my van and enough room for a cargo pod. It's a good balance and works for me.
Dave, do you find your battery-bank versus solar-array capacity well balanced?

If I installed 400AH bank with the intent to regularly use 200AH, and the solar made a little over 20 Amps, it would take all day to recharge assuming there were no ongoing loads. In your case if you are recharged by early morning, does it mean you are using very little battery capacity, like maybe 10 to 20 percent or so?

Is it cheaper to oversize battery bank at expense of solar capacity (assuming a fixed total budget), or did cost have little to do with your ultimate ratio of battery versus array sizes?

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Old 02-23-2015, 07:17 AM   #22
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Re: Solar???

Hi Chance, Dave can answer for his particular usage, but here is the way I am looking at it (which may be off base as I have never done a solar install or had an RV with solar) for our upcoming solar install:

Parameters: Typical daily hourly usage of about 4 amps per hour from 10 AM to 8 PM , and 2 amps per hour from 8 PM to 10 AM. Total = Battery bank of 350 aH = 175 aH max usable. 300 watts of panels, 30 amp MPPT Charge Controller. available charging 300w/12v = 25 amps, Camping style= stay put for a few days.

Arrive campsite afternoon 5 pm, 100% charge from driving, solar, etc. Assume engine off, no solar due to late in day. By 10 AM battery bank is down 4 amps x 3 hrs, plus 2 amps x 14 hrs = 40 amps total. Solar starts charging at 10 am (will be a bell curve for charging with max of 24 amps (25 amps max available form solar for charging x 80% efficiency) during middle of day. Ongoing usage of 4 amps/hr is covered and somewhere between 10 to 15 amps/hr residual is available for charging the battery bank. By noon / 1 pm the battery bank should be back to full theoretically (I know this is not reality as the battery charging will be going into float, etc and the smart charger will be reducing the amps delivered to the battery depending on state of charge) but the solar will get batteries topped of by 5 pm when the cycle starts over.

With moderate to great sun, we should be fine with solar charging more than covering our daily needs (excess solar amps could be dumped into 12v element electrical hot water heater) so solar amps are harvested for something . The 175 ah usable gives us about three days of zero solar if solar availability is really bad (not sure I would stay for three days in those conditions = engine running), and likely four to five days if the available solar is only mediocre. We have 220 amps worth of alternators on the clackty-clack engine as back up.

Just my attempt at analyzing electrical usage and how solar plays into our camping routine. There are lots of variables: shade, ambient temp, how packed is the freezer/fridge, how cold at night = demanding more heater fan, how hot at night demanding roof vent fan, water pump usage, time of year, etc.

Hope that sheds some sunlight as to how solar can help one's camping experience with properly sized panels and battery bank. Really interested on feedback as to my analysis and if reality mirrors what I am thinking.
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Old 02-23-2015, 10:57 AM   #23
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Re: Solar???

I've never really done the math to figure out what I need. I started with a single 4-D and 180 watts worth of solar. My average usage was the heater or a fan, the fridge and pre-LED lights that pulled about 2amps each. The fridge cycled on and off at about 3 Amps and the fan pulled more than the heater cause it pulls a constant 3 amps where the heater cycles. In sub freezing temps I always run the engine water heater for 2 hours before the sun comes up. Most of the time I pulled the battery down to about 12.3 volts but there were those times where I left a light on and woke to voltages below 12.2. The solar put me back to full charge by about 10 AM most of the time. If I used the MW, I always ran the engine.

Then I added a second 4-D and like today I rarely drop below 12.4v. The Solara panels failed so I put up a 135w glass panel. I was usually charged by 11AM. After adding the second 135w panel I started to get to full by 9AM. Like Ray mentioned, there are so many variables that I'm just giving an average. Where the second panel helped was during overcast. At least I can get a few amps out of both of them. I rarely see more than 14amps in full sun and early morning sun usually produces about 2 amps then quickly ramps up. Seems like 6-9 amps is an average number I see these days around 9AM. The charge tapers off as the batteries reach full charge so even in full sun if the batteries are 100% the solar only reads a few amps unless something is running.
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Old 02-23-2015, 05:02 PM   #24
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Re: Solar???

Boywonder makes a good point about new vs. 3-year old house batteries. Back when our van was new, we tended to drive at least 3 hours a day. With a new 200ah house battery, that was fine. Now we tend to drive much less.

We are now on our fourth or so house battery and it is 3 years old. Our 240 or so watts of solar keeps the battery charged during the day (without any driving) but when the sun goes down, so does the house battery voltage. Our Isotherm refrigerator won't pull it down to critical during the night and usually the sun is up and recharging the battery by the time the propane heater comes on (with its fan).

Cover your roof with solar and you have one less thing to worry about.

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Old 02-24-2015, 07:04 AM   #25
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Re: Solar???

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Originally Posted by 1der
300 watts of panels, 30 amp MPPT Charge Controller. available charging 300w/12v = 25 amps
I would say that your thoughts are correct, but you do start with one flawed piece of data. Your panel is rated at 300 watts for the STC (Standard Test Conditions), since pretty much what all panel producers use, is good way to compare from panel to panel. But, the standard test does not reflect reality, fortunately your panel choice also gives data for NOCT (Normal Operating Cell Temperature) and that data is much closer to reality.
For your panel STC data says Vmpp =32V and Impp = 9.40 Amps = 32 X 9.4 =300.8 watts
NOCT data says Vmpp = 29.3V and Impp of 7.50 Amps = 29.3 X 7.5 ==219.75 watts

So when you size your expected output from the panel you should start with NOCT data if provided. That is a better starting point, it does not take in account the efficiency of your controller or voltage loss in wires.

The good news for you, is the difference between STC & NOCT exist for all panels, not just the one you selected. It is also very nice that they include the data in their spec sheet.

for more data on the topichttp://www.amsolar.com/home/amr/page_164

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Old 02-24-2015, 07:25 AM   #26
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Re: Solar???

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Originally Posted by 1der

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Camping style= stay put for a few days.

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Hope that sheds some sunlight as to how solar can help one's camping experience with properly sized panels and battery bank. Really interested on feedback as to my analysis and if reality mirrors what I am thinking.
Thanks for sharing your plans. I think you hit on why I keep having a hard time justifying solar at all. We are more travelers than stay-in-one-place campers, and have never (that I can recall right now) stayed more than two nights and the day in between at a site that didn't have shore power. Most often it's just the one night without shore power.

Granted, our present van is extremely basic and uses practically no power when not on shore power, and we are hoping to change that when we upgrade to a much bigger and nicer van, but even when we had a Class C and also rented on many occasions, our travel habits don't change much. The biggest difference was that we ran the generator to power the microwave, or maybe the roof AC while eating lunch. But these were so short in duration that I plan to run off house battery and inverter and then recharge as soon as we start driving again. For what it's worth, none of the RVs had an inverter.

As much as I'd like to find a use for solar for our next van, I'm having a hard time if I remain objective. It seems that if I apply the funds towards more house battery capacity I come out ahead for our intended use.
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Old 02-24-2015, 08:04 AM   #27
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Re: Solar???

Quote:
Originally Posted by Scalf77
.....cut.....

for mare data on the topichttp://www.amsolar.com/home/amr/page_164

-greg
Thanks for posting link, there is a lot to review there. Under rules of thumb they address the balance between battery and solar capacity. They seem to recommend in range of 1 amp-hour battery to 1 watt solar. I'm sure that changes some by camping style.

I'm going to keep reading on this subject since I'm now interested in controllers. When array produces power at near 30 volts, does the controller do a good job at preserving power by charging batteries at nearly twice the current (I would hope), or does it "essentially" reduce voltage to that of battery while keeping current in and out constant (I hope not). Any idea on overall controller efficiencies under varying conditions?
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Old 02-24-2015, 08:24 AM   #28
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Re: Solar???

Quote:
Originally Posted by Chance
I'm going to keep reading on this subject since I'm now interested in controllers. When array produces power at near 30 volts, does the controller do a good job at preserving power by charging batteries at nearly twice the current (I would hope), or does it "essentially" reduce voltage to that of battery while keeping current in and out constant (I hope not). Any idea on overall controller efficiencies under varying conditions?
Chance: I haven't done a deep dive into solar controllers, I imagine Gregg can enlighten us further on this.

There appears to be 2 basic types: the cheap ones are PWM type controllers and the expensive ones are MPPT (max power point tracking); these convert volts into current and apparently do other things to maximize efficiency.
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Old 02-24-2015, 08:50 AM   #29
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Re: Solar???

We're looking to add a Solar panel to our EB this spring for extended off-grid travels coming up.

Given all the recent improvements and advances in Solar Technology - what is the recommended setup in this current day? Thinking of just one 150-180 watt panel right now. Don't mind spending a few extra $$ for longterm reliability etc... Will install myself

FWIW - I have a fresh Deka 4D house battery that I installed late last fall. Mostly powers the Fridge, lights and a bit of fan for the furnace on the chilly am's. Live in UT and no shortage of sunshine

thanks for the recs
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Old 02-24-2015, 09:05 AM   #30
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Re: Solar???

Quote:
Originally Posted by alta825
We're looking to add a Solar panel to our EB this spring for extended off-grid travels coming up.

Given all the recent improvements and advances in Solar Technology - what is the recommended setup in this current day? Thinking of just one 150-180 watt panel right now. Don't mind spending a few extra $$ for longterm reliability etc... Will install myself

FWIW - I have a fresh Deka 4D house battery that I installed late last fall. Mostly powers the Fridge, lights and a bit of fan for the furnace on the chilly am's. Live in UT and no shortage of sunshine

thanks for the recs
When I installed mine I decided to go with 300W (3x100W) of panels.. because it's not that much more expensive, and the labor is basically the same.. And more is better. If you do 150W, and then decide you need more, it's more work to retrofit more panels on..

I have the same draw, fridge, LED lights, furnace fan, charging devices. My 4D is always topped up every day even in partial shade.. Which is what I wanted.
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