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Old 02-11-2013, 01:12 PM   #1
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Solar Size Calculator

For a couple of years I've been messing with calculations to see how much solar I need. The attached excell spreadsheed has been pretty helpfull in totaling up my loads and visualizing how solar and a genset can work to provide my needs.

This is pre-populated with the data for my '63 Overlander - pretty minimal electrical demands, no central heat and a fridge that uses no 12 Volt. I found on my 34' that the small load from the fridge, only about 1 amp, was one of the larger users of power since it pulled 24 hrs a day.

Keep in mind that this provides a 'best case' since clouds, solar angle and other stuff make a huge impact.

No warranty, no return, no customer service number if you have questions, if you don't like the spreadsheet you can more it to your trash bin and restore harmony...
Attached Files
File Type: xlsx Dolly Amp Hour Model.xlsx (55.5 KB, 149 views)
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Old 02-11-2013, 01:22 PM   #2
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Originally Posted by HiHoAgRV View Post
For a couple of years I've been messing with calculations to see how much solar I need. The attached excell spreadsheed has been pretty helpfull in totaling up my loads and visualizing how solar and a genset can work to provide my needs.

This is pre-populated with the data for my '63 Overlander - pretty minimal electrical demands, no central heat and a fridge that uses no 12 Volt. I found on my 34' that the small load from the fridge, only about 1 amp, was one of the larger users of power since it pulled 24 hrs a day.

Keep in mind that this provides a 'best case' since clouds, solar angle and other stuff make a huge impact.

No warranty, no return, no customer service number if you have questions, if you don't like the spreadsheet you can more it to your trash bin and restore harmony...
Most owners are not aware of the fact that "solar panels" only produce maximum energy, if the sun is direct over the panel, namely 90 degrees.

The output is reduced whenever the sun is at an angle to the panels.

Andy
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Old 03-01-2013, 12:43 AM   #3
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...or that most calculations figure on only receiving 5 hours of "peak" sunlight per day
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Old 03-01-2013, 06:35 AM   #4
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Originally Posted by HiHoAgRV View Post
This is pre-populated with the data for my '63 Overlander - pretty minimal electrical demands, no central heat and a fridge that uses no 12 Volt. I found on my 34' that the small load from the fridge, only about 1 amp, was one of the larger users of power since it pulled 24 hrs a day.

Keep in mind that this provides a 'best case' since clouds, solar angle and other stuff make a huge impact.

WE have a similiar situation with the 61 Tradewind. With LED lighting etc our normal consumption is under 20 amp hours per day even with some TV watching, ham radio time and various light loads like the MiFi.

The continuous small loads are the ones that count.

One of these days i may be forced to a modern refrigerator. I assume the one amp load would only be during the ignition cycle? A constant load would almost be a deal breaker for our solar system as it would be more than we use for everything else.

I think someone actually did some measurements on this and found it not to be as bad as it first appeared as there were a couple features that could be turned off but it would be in my files at home and we are in South Florida now ( on solar).

Does anyone still make a thermo couple fridge that doesn't require power?
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Old 03-01-2013, 06:52 AM   #5
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Does anyone still make a thermo couple fridge that doesn't require power?
No such thing. Most refrigerators contain a thermocouple. A thermocouple is just a temperature-sensitive switch, not a cooling system in its own right.

But you can get a fridge that doesn't require power, and doesn't contain a thermocouple. It's called an ice chest if portable, or an icebox is built-in. Just add ice, and voila!
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Old 03-01-2013, 07:12 AM   #6
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No such thing. Most refrigerators contain a thermocouple. A thermocouple is just a temperature-sensitive switch, not a cooling system in its own right.

But you can get a fridge that doesn't require power, and doesn't contain a thermocouple. It's called an ice chest if portable, or an icebox is built-in. Just add ice, and voila!
Didn't mean it as a cooling system. Simply meaning the older systems where the thermocouple provided the voltage to open the main gas valve without the need for a 12 volt source and the burner flame was on all the time and just turned up or down by the thermostat. ( like my current dometic RM60)
A few years ago Norcold still had one in the line but don't know if that is still available.
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Old 03-01-2013, 08:39 AM   #7
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Rick,
On my modern Dometic, it pulls about 1 amp all of the time. The first ignition is a small spike but there didn't seem to be any difference between high and low flame (it never really turns 'off', just shifts into a lower flame).

The fridge in my '63 is from the 70's and has NO power draw and still shifts high to low flame using the old style gas valves. I have not seen any new fridges that are sill like this. If it has auto ignition, it pulls power.

I used the spread sheet to see what it would take to run a 110V fridge/inverter in my '63. I used a Kill-a-watt to measure the power draw from my dorm fridge and it equated to a 2.21 Amp load for 24 hours. If you stick that into the spreadsheet, it's a huge deal. I went from 60 watts and a pair of 6V batteries being adequate all the way up to 4-6V batt's and 180watts of solar.

Keep in mind that 60W of solar will only approach that level when the sun is at 90 degrees to the panel, thus the spreadsheet is an absolute best case.
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Old 05-11-2013, 08:21 PM   #8
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Hi, I have a new to me 2006 19' Bambi CCD. I will be starting my Summer Season of 20 weekends of 3-4 nites boondocking at venues for work. My previous rv had an 80 watt panel and worked ok, except when it was way over 90*. I am not vacationing on the weekends, really work til late at night, shower, read, sleep, prepare my own food for the day, work. So my question is....(and I have no idea how hot an AS can get in the Summer)...would it be better to park in shade and use battery very conservatively or get solar setup and always be parkwd out in the Sun trying to catch the few hours of good charging sun each day? Also if the fridge is working great, and by day 3 my battery is getting low, can I add ice(in a container of course) to the fridge and use it as an ice chest? I would think my biggest drain would be over night fan, but even there I could use battery fan.

Sometimes I think the shade is better than solar in full hot sun...thank you in advance for all help.
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Old 05-11-2013, 08:53 PM   #9
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Sun or Shade?

That is a big question. Since the time I got a solar system installed (2 - 160 watt panels, 3 Lifeline batts), my answer for summer time has tended to be sun in the morning and shade in the afternoon, if I can get a place like that. I actually scout camp sites with satellite images, so I can try to pick such a place in advance.

That way the trailer cools down over the afternoon / evening and the fans, lights, etc. run on battery power over the course of the late afternoon and night. If I do this right, I always seem to be fully charged again by about 10 in the morning on sunny summer days. Also by then, the coach starts getting pretty warm. So then as the coach heats up, I'm outside sitting under the awning, hiking, fishing, etc. I leave a Fantastic vent running all day to keep the inside temps under control, and by late afternoon when I'm back in the shade, things start to cool down for the evening.

I guess if it were gonna' be HOT like desert southwest hot, etc., then I'd probably not boondock - but would try to find a "commercial" site with electricity for the AC, or I'd use my generator. But I'd rather not do either of those things, so I try to stay further north and find trees!
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Old 05-11-2013, 10:05 PM   #10
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Didn't mean it as a cooling system. Simply meaning the older systems where the thermocouple provided the voltage to open the main gas valve without the need for a 12 volt source and the burner flame was on all the time and just turned up or down by the thermostat. ( like my current dometic RM60)
A few years ago Norcold still had one in the line but don't know if that is still available.
The Dometic RM 2510 5 cu ft is still available (Google it) and it uses NO 12 volt power while in operation. It still uses the old hi/low flame system that was used in the past. Yes, there is a 12 volt connection on it, which is only used to operate the initial spark lighter, but after that, it draws absolutely no current as long as the refrigerator is on propane.

Dometic does not list it on their main web site for some strange reason, but it is available and a current model. It is around $900. I bought mine 3 years ago for my Argosy.
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Old 05-12-2013, 12:05 AM   #11
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I appreciate you supplying the spreadsheet, as well as the solar tab. A couple of questions if you don't mind. I understand the sun hours you have posted as a total, in this case 5.4 at 70% efficiency, but what about the allocation of sun time for various times of the day? How did you derive those, such as 0.75 etc., are these estimates of the portion of the given hour that the sun was effectively charging the system during that time period? And the Gen Set of 50% throughout the day, could you shed a little more "light" on that per centage? You may have addressed this somewhere, but I can't seem to see where. I have looked at all the cells in that row and don't see a link to another spreadsheet or cell. Thanks in advance for any answers you can give me. I need all the "learnin" that I can get.
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Old 05-12-2013, 06:09 AM   #12
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Also if the fridge is working great, and by day 3 my battery is getting low, can I add ice(in a container of course) to the fridge and use it as an ice chest?
Any fridge works best when it's cooling something other than air. If you have any space in the freezer at all that's not being used, fill it with ice cube trays, or blue ice packs, something. Any space in the fridge that's not being used should be filled with bottled water. That also serves as a hedge against days when it's not working as efficiently, because a brim-fill fridge will stay colder, longer (as long as you don't open the door) than one that's only partly filled.

Something I learned from hurricane season, where power outages affecting my home fridge are expected for every storm, including the ones that aren't strong enough to evacuate for.

And a handy hint for monitoring your freezer when you're not there: on one ice tray, after it's frozen, lay a dime on one of the ice cubes in the tray. If the freezer ever gets warm enough for the ice to melt, and then refreezes, the dime will be inside the ice cube and not on top of it anymore. If that happens, it's time to throw out all the food, because if it got warm enough for the ice to melt, it got warm enough for the food to spoil.

Also a hurricane season trick, for monitoring a fridge left behind when I evacuate.
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