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Author Topic: To use solar or a generator.  (Read 6183 times)

gizmothing

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To use solar or a generator.
« on: March 08, 2010, 09:05:12 AM »
Well as per the advice in the other thread, here is a new thread with a different title.

I am going to skip the boring into and such, and get right to it.

We have just purchased a 24' travel trailer, and I am looking to find the best option for power.

I am leaning towards a Solar set-up, but I have zero experience towards what I need, or how much I need. On the other hand, I could just buy a generator for it, and not worry too much.

Power demands are:

water pump, furnace, fridge, few lights and a small 12v car stereo (head unit and 2 indoor speakers and 2 outdoor) that I will be installing.

With that, the trailer has an old 12v deep cycle that I think I will be replacing.

I have heard something about using golf cart batteries as well.

with what I want to be using, how much will I require with a solar set up? and is it cost effective versus a generator? I am hoping to avoid the generator because of the noise, but, I can learn to ignore it for the right price...

any help or advise that can be imparted is greatly appreciated!

bigskymt

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Re: To use solar or a generator.
« Reply #1 on: March 08, 2010, 09:50:12 AM »
   Two 6 volt batteries will not provide much reserve if your furnace is fan forced. I hope you don't plan on running the fridge on 12vdc if it is so equipped, that will kill batteries quickly.
  Normal lights, stereo, water pump should be OK with two 6Vs.
  IMO one 130 watt (about 8.5 amps) solar panel should be sufficient for 2 6V.
  A small Honda or Yamaha 1000 or 2000 watt generator is quiet, efficient and dependable. It would be a good backup to batteries and solar or great on its own.
 
 

donn

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Re: To use solar or a generator.
« Reply #2 on: March 08, 2010, 10:04:25 AM »
Refer runs on Gas and normally only needs a very small 12VDC power to work.  So, solar= silent power, does not work on cloudy days or in the shade is very expensive per watt of power.
Generator= can be a noisy depending on the brand purchased, less costly per watt of power.  Does not care what the weather conditions are or where you are parked.  They can sprout legs and walk off unless secured.
I have and use both.  250 watts of solar panels, 4 batteries, soon to be upgraded to 6 and a 2800 watt generator.  When boon docking I carry both.
Solar is not good for high amperage draw items like AC units, coffee makers, toasters.  Solar is good for recharging the batteries if in the sun, running a TV and or Sat receiver or DVD player for a few hours a day when not hooked to shore power.
Decide what is important and how much money you want to spend.

tennsmith

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Re: To use solar or a generator.
« Reply #3 on: March 08, 2010, 10:46:41 AM »
Seems to me that either way, solar or generator, you have to have enough battery capacity to last you through the night using the furnace and powering the fridge 12vdc control/ignition circuitry (this assumes propane for the actual cooling process).  You simply can't discharge the batteries completely each night and expect them to live very long.  There are rules and likely people on this forum who can help you size your batteries for what you wish to power.  Solar, in the capacity needed is going to rival, I think, the cost of a small "inverter style" generator.

Generator technology has come a long way since the advent of portable units.  Today's "inverter" generators are not bad, at all on the noise scene and their speed is proportional to load and they don't run "wide open" like the generators of old.  However, the inverter generators are more expensive than the older styles.  Honda and Yamaha both manufacture small inverter generators that are "favorites" amongst most campers.  Honda makes both a 1000 watt and a 2000 watt small inverter generator and they can be found on Ebay sometimes in the 500 dollar (1000 watt) and 1000 dollar (2000 watt) ranges.  My guess would be that you'd spend 500-700 getting enough solar array to keep  your batteries charged and then you still have to consider cloudy days and shade which you can't do anything about.
Bob Smith
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2000 Itasca Horizon 36LD
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gizmothing

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Re: To use solar or a generator.
« Reply #4 on: March 08, 2010, 01:58:21 PM »
well, would it be better to run 2x12v deep cycle batteries then? how big or how many solar panels would i need to be able to keep those charged?

I don't know if i am even asking the right questions, or if I am asking them correctly.

we don't plan on needing to run a laptop, and obviously the lights won't be used much in the day. We don't winter camp, so the furnace probably won't get used that much. The fridge we will run off propane, but the circut boards apparently still need power, and there is a grand total of 3 lights. additionally, I will be adding a 12v stereo with 4 speakers.

I am not sure how much of a drain that would be on the batteries, or what kind of solar panels would be needed, or if i need a charge controller or should I go 6v or 12v or a mixture of the 2, or, or, or.

I am completely at a loss here. I am used to tenting. This is my first trailer, and I got no clue...

enough to make me want to pull my hair out and sacrifice some poor sheep to a trailer god...

donn

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Re: To use solar or a generator.
« Reply #5 on: March 08, 2010, 02:56:03 PM »
Being conservative two high capacity deep cycle batteries should last two to three days.  The least expensive way to recharge them would be to get a 1000 watt Honda generator and a good battery charger.  Using solar panels a 125 watt panel in full sun would probably take 8 to 10 hours to recharge from 70%.  Like I said before I have both and use both all the time.

bigskymt

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Re: To use solar or a generator.
« Reply #6 on: March 08, 2010, 03:07:26 PM »
  I misunderstood your first post to say you were going to run the fridge off 12vdc. Current draw on gas is minimal, some refers have D.C. cooling fans for the coils.
  You will need a charge controller for your solar, any solar panel above the small maintenance (5-10watt) needs a controller.
  You can compare amp/hours on two 6V vs 2 12V deep cycle. There are numerous topics here on batteries etc. How much room do you have?
  As an example you could use 2 12V Deep cycle with 1 130watt panel and a 20 amp controller. You could then add another 130 watt panel if desired using the same controller. A 1000 or 2000 watt inverter is another option.
   Should you decide on a 2000 watt Honda or Yamaha Gen. it would also work well and if necessary power a 12,000 BTU A/C (a 12,000 BTU A/C is about 1600 watts)
   Solar panels are upgradeable by adding panels if the controller is sufficient. The gen. you're stuck with unless it can be daisy chained to a comparable gen to boost output.
     Hope this answers your questions.

gizmothing

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Re: To use solar or a generator.
« Reply #7 on: March 08, 2010, 03:51:56 PM »
well, the battery is on the tongue of the trailer behind the propane tanks. would not be hard to weld in a second plate to house a second battery.

well, lets use this scenario.

with 2x12v deep cycle batteries, with minimal draw for lighting and regular use of fridge and furnace ect, how many solar panels and what size would be recommended to bring these batteries back to full power with 8-10 hours of sunlight?

bigskymt

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Re: To use solar or a generator.
« Reply #8 on: March 08, 2010, 04:20:44 PM »
 I've done what you're proposing with 135 watts of solar but also ran coffee maker, TV, microwave and 3 12 V deep cycle batteries
  IMO a 130 watt should be sufficient. Don't forget 130 watts is maximum: clouds, shade, indirect sunlight all lower solar output.
   The second 50# battery will sure add to tongue weight.
  There are some solar experts on this forum and several discussions if you want to try a search.

Gary RV_Wizard

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Re: To use solar or a generator.
« Reply #9 on: March 08, 2010, 04:39:19 PM »
I gather, but you did not say, that you plan to do all your camping in places that do not have electricity available?  Many campsites have electrical power, even if only a 15A household outlet, and you don't need any battery or charger as long as that is available. Your trailer has a 12v power converter that will supply all the 12v needed and will also re-charge the battery(s) while doing so..

Assuming you will not have 120v electric (aka shore power) available, there are two questions to be answered:

(1) How many battery amps you will use each day (amp hours) and how many days you will need to go without recharging.

(2) What is the easiest and most cost effective way to recharge, assuming no external electric source is available



First the battery amp hours question: 
12v light bulbs use 1-2 amps per hour, depending on size. The furnace fan uses about 5-7 amps while it is running, but usually runs only part time (depending on temperature, of course). The fridge power draw is negligible, as long as the interior light stays off.  The water pump runs only for short times, so it too contributes very little over the course of a day, maybe only  one amp/hour. Your stereo is something you will have to figure. Bottom line is that you can figure each light x 1.5 x hours of use and get a number of amp-hours (AH). Ditto for furnace run time and your stereo system.  Throw in another 2 AH for fridge and water pump and that's the amp-hours you use every day.  You need enough battery capacity to get you through 24 hours.  With that modest load, you won't need much, but most people end up using more electric than they estimate, so you might want to double the estimate to have some reserve.

Batteries come in various sizes (amp capacity). A typical Group 24 size holds about 85 amp-hours (AH) when used lightly - less if a big load is applied. A Group 27 (slightly larger in physical size) holds about 105 AH.  Golf cart batteries are 6V and have to be wired in pairs to make 12v, but they are high capacity and very rugged and long-lasting. A pair will store about 220 AH.  In practice, you can only use about half the available AH in a battery - using more will severely stress it and greatly shorten its lifetime. So figure that your total battery capacity needs to be about 2x what you expect to use daily.

Now the charging question:
Without external power source, you can charge the battery with a generator or with solar  power. You need to replace the amp-hours you used the previous 24 hours, so you need enough charging time to produce the same number of AH that you used.

With the generator, you can charge whenever you (and your neighbors) don't mind the noise.  You don't actually charge with the generator in most cases - you plug the trailer into the generator and let the trailer recharge itself. This is nearly always more efficient than using the generator's 12v output, if it has one. We don't yet know the size of the charger that is built into your trailer (what year make & model trailer is it?), but it is likely in the 20-40 amp range. That means that it can put about 20 amps back into the battery in an hour (amps x hours of run time). The charge rate slows as the battery gets full, but you might reasonably expect to re-charge 40 amp-hours back into the battery over a 3 hour period. You get the idea...

Solar, of course, is available only when the sun shines and is at its peak power only when the sun is directly overhead of the panel. You may get a few hours a day of solar charging or you may get 10-12 hours in some locations.  For solar, you need to guess how much direct sun you will get (don't forget tree shade) and use that to calculate the size of the panel(s) needed to re-charge the amps that were used.  A 100 watt solar panel produces about 7 amps @ 13.6v (charging voltage), so you would need about 6 hours of direct sun to replace 40 amp-hours. A bigger panel (more watts) produces more amps, so needs fewer hours of sun to produce the same 40 amps.

At this point, you probably have more questions and also need to get some more data, so I'll cut the lecture short for today and see what you have to say.

In the RV Forum library in the Newcomers section there is a beginner's primer on RV Electrical Systems. You might want to read up on that.

RV Electrical System Primer
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

gizmothing

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Re: To use solar or a generator.
« Reply #10 on: March 09, 2010, 09:03:48 AM »
in response to an earlier question, our trailer is a 1976 24' Prowler (not top of the line, or prettiest, but it will work for now), and I believe everything inside is original. I have already fixed most of the things that needed attention ASAP, but still have a few smaller jobs left.

Without knowing my exact draw, and using a rough estimate using a guide Tennsmith gave me, Huge read, but alot of info, if i figgure on going way high in estimate, I will go with 10amp hour draw, of course that is not constant, but a good usable number to work with. I am not going to be using this 24 hours a day, but either way, good number to use.

so, using a formula Tennsmith gave me:
10amp hour draw X 24 hours a day = 240 amp hours
so needing 240amp hours of recharge in an arbitrary 10 hour day of sunlight = 24 amp charge rate
solar array produces 15 volts X 24 amp charge rate = 360 watts for a solar array.

so, I am thinking since I probably won't even use that much, that if i get 3x110 watt solar panels and the charge controller and second appropriate deep cycle, I should be fine.

Am I even in the ball park by this thinking?


donn

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Re: To use solar or a generator.
« Reply #11 on: March 09, 2010, 09:10:18 AM »
The numbers you are using for the panels is based on ideal conditions, IE full sun and panels tracking the arc of the sun all day.  Cut that number in half and you will probably be far closer considering the panels will probably be screwed down to the roof, flat, and likely have at least partial shade.  Or am I mistaken in assuming you are not parking in the Mohave desert and have some form of panel tracking system?

gizmothing

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Re: To use solar or a generator.
« Reply #12 on: March 09, 2010, 09:18:45 AM »
no, I won't be fixing these to the trailer, I plan on fabricating a small aluminum stand and adjusting a couple times during the day as needed.

I guess I am stuck in the thinking that my power requirements are not that high, and as such, am having a hard time with thinking I can't make solar work. I want to make every effort to make solar work, but if it just isn't feaseable, well, I will get the generator. I just hate the idea of the sound of the engine and filling with gas all the time when I am in nature...

donn

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Re: To use solar or a generator.
« Reply #13 on: March 09, 2010, 09:27:19 AM »
Solar does and will work.  Heck, I have 250 watts on my roof and use it all the time.  But I do not rely on it for all my power needs.  I realize the limitations based on where I park.  I personally do not like full sun, so I try to find shady places, reducing my panels capacity by more than 50%.  Thus the generator if necessary.  For the cost of solar per watt, it is really not practical.  Like I said before, consider the Honda 1000 watt generator for starters and add the solar when money becomes available.  With the panels on the ground you better plan on some method of securing them in place otherwise they might grow legs and walk away.

Gary RV_Wizard

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Re: To use solar or a generator.
« Reply #14 on: March 09, 2010, 11:42:59 AM »
An average of 10 amps/hour for 24 hours is a huge amount for the sort of usage you described. You might use 10A/hr during the evening and near that overnight on a cold night due to the furnace (and the desert or mountain nights can be cold even in summer).  For what you describe, I would guestimate 10 amps x 5 hours and 2A x 8 hours 1A x 11 hours for a daily load of  77 amp-hours.

If you really think you will need 360 watts of solar panels, you also are going to need  a lot of batteries to store that energy. At least 4 6v golf cart bats or 4 x Group 27 or 29 12v bats. You need about a 400-440 amp-hour battery bank to have 240 AH for daily use.
Gary
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Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Wendy

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Re: To use solar or a generator.
« Reply #15 on: March 09, 2010, 12:21:12 PM »
We have 4 6V golf cart batteries and 2 120-watt solar panels. We use a lot of electricity and even on a good solar day we usually still need to run the generator for an hour. My parents are minimal electricity users, using much the same as you describe. They usually made due with one 120-watt panel that was in a frame that he moved around to face the sun.
 
Why not start out with one panel and 2 6V batteries and see if that keeps up with your needs? You can always decide to add more later. I really think 360-watts is overkill for what you're going to be doing.
 
You might also think about skipping solar altogether and just get a small generator. Solar is more desire for quiet than it is money-saving thing. We bought our solar because we enjoy boondocking but I don't like listening to the generator, not because we thought we would save money.
 
Enjoy your travels.
Wendy
 
 
Wendy
Wendy, Mike, and Gordon
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Here's where we are http://map.datastormusers.com/user2.cfm?user=2276
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gizmothing

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Re: To use solar or a generator.
« Reply #16 on: March 09, 2010, 01:22:38 PM »
We have 4 6V golf cart batteries and 2 120-watt solar panels. We use a lot of electricity and even on a good solar day we usually still need to run the generator for an hour. My parents are minimal electricity users, using much the same as you describe. They usually made due with one 120-watt panel that was in a frame that he moved around to face the sun.
 
Why not start out with one panel and 2 6V batteries and see if that keeps up with your needs? You can always decide to add more later. I really think 360-watts is overkill for what you're going to be doing.
 
You might also think about skipping solar altogether and just get a small generator. Solar is more desire for quiet than it is money-saving thing. We bought our solar because we enjoy boondocking but I don't like listening to the generator, not because we thought we would save money.
 
Enjoy your travels.
Wendy
 
 
Wendy

That is where I am at Wendy.

I am willing to spend a bit more if it means i don't have to listen to a generator, or worry about others having to listen to it in the next site(s) over. When camping I like the quiet time.

I would really like to make solar work for that reason alone, but if there ends up being that much of a cost difference then I will get a generator.

And RV Roamer, I agree with you, i think what i am estimating my usage to be is way overkill, but I would rather be way high, then way low, if you know what I am getting at. But it looks like I just found some 110 watt panels (used) for $110 per panel. If they are in good condition and work properly, I think I might go grab em.

gizmothing

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Re: To use solar or a generator.
« Reply #17 on: March 09, 2010, 01:25:14 PM »
An average of 10 amps/hour for 24 hours is a huge amount for the sort of usage you described. You might use 10A/hr during the evening and near that overnight on a cold night due to the furnace (and the desert or mountain nights can be cold even in summer).  For what you describe, I would guestimate 10 amps x 5 hours and 2A x 8 hours 1A x 11 hours for a daily load of  77 amp-hours.

If you really think you will need 360 watts of solar panels, you also are going to need  a lot of batteries to store that energy. At least 4 6v golf cart bats or 4 x Group 27 or 29 12v bats. You need about a 400-440 amp-hour battery bank to have 240 AH for daily use.

Gah, i didn't think about the battery. now I have to see what is available for that...


gizmothing

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Re: To use solar or a generator.
« Reply #19 on: March 09, 2010, 01:36:58 PM »
you know what, never mind.

Adding up cost, and such, this is going to go way over the cost of a generator by leaps and bounds.

I was mistaken, those panels i mentioned earlier were not 110 watt,  :-[ ,they were 15 watt for $110.

I promise to go back to school and learn to read again.

Gary RV_Wizard

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Re: To use solar or a generator.
« Reply #20 on: March 09, 2010, 04:24:13 PM »
Either of those batteries would do the job, I think.  If buying in the USA, it might be worthwhile to join Sams Club or Costco. They both have excellent golf cart deep cycle batteries at great prices.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Gary RV_Wizard

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Re: To use solar or a generator.
« Reply #21 on: March 09, 2010, 04:27:00 PM »
I agree with Wendy - start smaller and see how it goes. 2 batteries and 210-225 AH and one or two 100 watt panels (if your bargain deal comes through). Don't forget you will need a charge controller for the panels as well.  If you will be camping mostly in Canada, your solar output will be decidedly less than optimal - you guys just don't get enough sun up there!   ;) Two panels is probably a necessity with the lower output.

Have you listened to one of the available inverter-type generators like the Honda eu1000i?  It just purrs - amazingly quiet!
 
« Last Edit: March 09, 2010, 04:28:56 PM by RV Roamer »
Gary
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Summers: Black Mountain, NC
Home: Ocala National Forest, FL

SwampChik

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Re: To use solar or a generator.
« Reply #22 on: March 09, 2010, 10:39:16 PM »
I just wanted to thank everyone who is participating in this discussion.  A lot of my questions are being asked.  And answered.  Thank you all!  I've found the power/solar/battery information to be extremely confusing in general, and usually by the 3rd paragraph of an article I'm zoned out.  I'm "getting" it here.  Yippeeee!

-Bev

RVRoadTrip

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Re: To use solar or a generator.
« Reply #23 on: March 10, 2010, 08:11:05 AM »
We have 270 watts of solar our our 19' travel trailer. Total cost was just under $1800 with us doing the installation. It can be done for a lot less but we wanted name brand equipment with long warranties and good reputations. Now we have clean, quiet power for at least the next 25 years... probably longer. I think the solar will outlast us - LOL. No gas to buy, no oil to change, nothing to load and unload, no worries about theft, etc. The drawback is I cannot run my A/C or microwave on solar but that doesn't bother me one bit.

Jerry n' Cynthia
« Last Edit: May 31, 2010, 05:16:59 PM by Tom »
The Adventures of Jerry n' Cynthia

Gary RV_Wizard

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Re: To use solar or a generator.
« Reply #24 on: March 10, 2010, 08:58:31 AM »
One thing that is often overlooked is that you don't actually run anything on solar. You run your stuff on batteries (may require an inverter if 120v stuff) and then recharge the batteries with solar power during sunny afternoons.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

 

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