Trailer Power - Solar vs. Generator???

[Robert Bills]

My solar vs. generator question relates specifically to offroad trailers. If this thread should be in the "Power Systems-12v, solar, gen." forum, I'm sure the Moderator will move it.

Before I start, I have already read every thread about solar power and generators in the "Expedition Trailer" and "Power Systems-12v, Solar, Gen." forums here.

My issue: Determining the most cost effective/simplest/least bulky means to provide electricity to my Bantam trailer for recharging the "house" battery, running an ARB/Engel fridge (sometimes for extended periods), powering 12v lights, radio, laptop, etc. Also, I am a complete dummy when it comes to electricity and designing circuits.

What I have now: ARB model 45 fridge, Group 27 Wallyworld Everstart 27DC-6 deep cycle marine trolling battery (115 amp hours, 720 marine cranking amps, 600 cold cranking amps) in a battery box/power station that looks like this:

The battery box is mounted in my trailer next to the fridge, the only space I have for a battery:

I also have an el cheapo 300w inverter, not shown.

The battery is charged by tow rig while in tow (through 6-pin connector), otherwise at home by my battery charger. (Your basic "throw together" system.) Amazingly the cheap Wallyworld battery (manufactured 2/05, cost $56.95 in 2005) has lasted 3 years without any trouble, although it is getting tired and in the best of times would only run the fridge for 2 days before reaching the 50% discharge limit. I have forgotten to charge it on occasion and run it down to almost nothing, but it still seems to come to life on my home battery charger.

My upgrade options:

Solar - Using a panel that can be stored inside the trailer and set up a few feet away by use of an extension cord (I like to keep my trailer in the shade, if possible), with enough capacity to keep up with the fridge and not draw down the battery more than 30%.

Small Generator - Most likely a Yamaha EF1000iS (best price 2/5/08 on Amazon.com is $684 including shipping), or Honda EU1000i.

Putting aside for a moment the debate between "silent" solar and "noisy" generators, it appears that the cost per watt is the same or more for a portable solar charging system of adequate size than for a small inverter generator. Is this correct? If so, then it seems that a small generator might be the answer as it can produce 110v, charge the "house" battery, and be used for other purposes than camping or expeditions. Also, space is at a premium inside the trailer and my thinking (at least for now) is that a 18"Lx9.5W"x15"H generator will actually consume less space than solar components, and at 29 lbs. will weigh less.

For those of you who already have solar in your trailers and Engle/ARB fridges, what are you using for panels and charge controllers, where did you source the parts, and how much did you have to invest? (Many of the previous posts are not particularly specific about the brand/model of solar panel, and some of the panels mentioned are no longer available.) Please bear in mind that as a long time jeeper (Just Empty Every Pocket), I've learned that to continue jeeping without domestic strife that I must scrounge parts whenever possible and never pay retail if I can avoid it. Cost is an object (otherwise I would just buy a system from Mario and Martyn).

For those of you who have a small Honda or Yamaha inverter generator and ARB/Engle fridge, how long do you typically run your generator each day to keep your house battery charged? (Seems to me that unless one is running 110v stuff at night, the generator wouldn't be required after dark or in the early morning, and could be operated in a manner that wouldn't disturb other people.)

Everyone's thoughts?

 

[Martyn]

Robert

Your power requirements are not that big, so it depends on what you mean by "extended periods". If you are not moving and recharging the battery via the alternator, then you may need more power in the form of storage or input.

If you are driving the vehicle every 3 or 4 days then you should be able to recharge the battery in the trailer. If you want to increase the recharge capability then may want to think about a dedicated 6 gauge system from the main battery in the vehicle to the deep cycle in the trailers. This would shorten the time needed to achieve a full charge.

I also think you need to do an assessment on which deep cycle battery you use. Not all batteries are created equal and cost analysis over time might surprise you. You would also want to get an idea of how much charge the batteries you already own are capable of holding. Their efficiency may have decreased with time.

In general it's less expensive to run two deep cycles to provide for your needs than a generator or a solar system. But you need to do an assessment of your power requirements before you try to make this decision.

The big issue in power requirements must be based around the longest period of time you will be in base camp without running the tow vehicle to recharge the trailer battery.

Most people think that their power requirements are much greater than they actually need.

IMHO I don't think that 110 volt accessories belong in the backcountry, and I don't believe generators do either.

 

[UK4X4]

There are some simple load calculations that you can do, but I've found that
most of the calcs do not take into account of mismatched equipment and you usually need more than you think.

I have designed and built solar panel systems for remote monitoring systems in the past.....but money was not an issue but going to visit after install was a major pain...so I over spec'ed them all.

No real time right now but i have a spreadsheet calculator somewhere....I'll post tommorow.

My trailer will have these panels....not the most effective but rubust for off road usage.

http://www.alphasolar.com/alpha_solar_046.htm


This site has some good prices and products and here's a link to some of the calculators and advise...

http://howto.altenergystore.com/Solar-Panels/a4/

 

[elcoyote]

All things being equal i.e. price of a 1000 W genset = 80 watt panel & controller, IMHO, the cost per watt over the lifetime favors solar because the panel does not require maintenance or fuel & oil to operate. Most of the high quality 80 watt panels that we use such as Kyocera, Seimens & Carmanah come with robust warranties for output of 15-20 years. Keep in mind this is based upon 24/7 exposure to the elements. Even once the warranty period is up, they still continue to produce.

Most importantly, evaluate your needs. If you want to run an Engel, some lights, laptop, recharge camera batteries and the occasional 110V inverter driven appliance, solar will do it. If 110V and high high wattage loads are more important, go with a generator.

 

[pete.wilson]

Robert Bills,

Instead of using a generator for 110vac; why not consider a DC to AC converter of about 2K watts powered by two good 12v batteries with about 200min ea. of reserve power to get your 115vac. Even though you will lose some efficiency, they are quiet (digital), suply enough current for Fridge, microwave, etc. The one I use is a Cobra electronics 2200W/4400W and use two series 31 trolling motor batteries and get several days useage before needing a recharge. You could use a couple of 15watt solar panels/controller to help with charging duties. System works good....Only downfall is the weight of the batteries and that they need to be evenly distributed weight wise in the trailer.

Pete Wilson

 

[Robert Bills]

I've edited my original post to show photos of my current setup and accurately describe the "house battery" in by Bantam trailer. Probably won't change the comments thus far, but who knows?

 

[Robert Bills]

Robert
Your power requirements are not that big, so it depends on what you mean by "extended periods". If you are not moving and recharging the battery via the alternator, then you may need more power in the form of storage or input.

My "extended periods" range from 2 1/2 to 5 days between charges from my tow rig.

If you are driving the vehicle every 3 or 4 days then you should be able to recharge the battery in the trailer. If you want to increase the recharge capability then may want to think about a dedicated 6 gauge system from the main battery in the vehicle to the deep cycle in the trailers. This would shorten the time needed to achieve a full charge.

I currently use 8 ga. for the charge wire. It seems to work fine, and my trailer battery charges in a relatively short time now (i.e., may not be worth the effort to increase to 6 ga.)

I also think you need to do an assessment on which deep cycle battery you use. Not all batteries are created equal and cost analysis over time might surprise you.

One of my limitations is space. I already have a propane tank on the trailer tongue, which eliminates that location for a battery. The only available space will hold one battery. (I tried to shoehorn in a Group 31 and a 4D, but no dice.) The Wallyworld Everstart 27DC-6 deep cycle trolling battery I am using now is rated at 115 amp hours and cost $56.95 when I bought it in March 2005. I chose that battery after pricing a number of alternatives (Interstate, Trojan, Optima, etc.), and after reading numerous posts on the Internet by RVers, bass fishermen, etc. singing the praises of the relatively inexpensive Everstart 27DC-6 (manufactured by Johnson Controls, which also manufactures Optima). But now that it's time for battery replacement, I am certainly open to suggestions.

You would also want to get an idea of how much charge the batteries you already own are capable of holding. Their efficiency may have decreased with time.

Please forgive me, but I warned you that I'm a dummy when it comes to electricity. How does one test for how much charge a battery is capable of holding?

In general it's less expensive to run two deep cycles to provide for your needs than a generator or a solar system. But you need to do an assessment of your power requirements before you try to make this decision.

Unfortunately, I don't have the room to run two batteries, otherwise that is what I would be doing instead of struggling with how to charge the one battery I have room for when I am away from a 110v source.

The big issue in power requirements must be based around the longest period of time you will be in base camp without running the tow vehicle to recharge the trailer battery.

I estimate no more than 5 days. More typically 3-4. On the rare occasion that the trailer would be in one spot without my tow rig longer than that (I recall one time in Baja and another at a Boy Scout summer camp), those left in base camp may just have to muddle on without a fridge.

Most people think that their power requirements are much greater than they actually need.

I agree. However, I'm having some trouble calculating just how much electricity an Engle/ARB model 45 fridge actually uses. The amp draw listed at the Engle website is 0.7-2.5 amps @12.7v. Do I average that (to guesstimate fridge vs. freezer use) or figure in a 50% duty cycle or both??? It makes a big difference to the bottom line.

Also, for purposes of calculating how much time I can run my fridge with my current 115 amp hour rated battery, I am first subtracting 10% (11.5 amp hours) to account for manufacture over rating or less than 100% actual charge, and then calculating that my battery can supply approximately 46 amp hours before reaching the 50% charge threshold (based on original 115 amp hour rating). Does this make sense? I'm so confused.

IMHO I don't think that 110 volt accessories belong in the backcountry, and I don't believe generators do either.

We are on a slippery slope here. We already participate in mechanized travel in the backcountry, much to the ire of the Sierra Club and the Center for Biodiversity, so none of us can make a principled argument that internal combustion engines don't belong. Where does one draw the line between a Jeep or Land Rover and a small generator? That being said, I have never been a fan of generators.

My trailer is set up more as a field kitchen for larger groups than as a trailer for traversing Dusy Ershim or the Rubicon. On those trips I pack for economy of space and weight and can manage two passengers and all of our food and gear for 3-4 days in my CJ-7. My trailer stays home.

My trailer serves two main purposes - base camp for 4WD trips where there are often underhood welders and other noise makers operating in the late afternoon or early evening (and sometimes, unfortunately for the poor guy with a seriously damaged rig, into the night), and also as the kitchen for adult leaders at Boy Scout events. A generator would not be out of place in the former situation, but would be inconsistent with Boy Scout camping or in wilderness situations where it could disturb the peace of others.

 

[Robert Bills]

No real time right now but i have a spreadsheet calculator somewhere....I'll post tommorow.

Thanks. I look forward to it.

My trailer will have these panels....not the most effective but rubust for off road usage.

http://www.alphasolar.com/alpha_solar_046.htm

This site has some good prices and products and here's a link to some of the calculators and advise...

http://howto.altenergystore.com/Solar-Panels/a4/

Thanks for the links. Now to figure out just how many watts I really need????

 

[Robert Bills]

All things being equal i.e. price of a 1000 W genset = 80 watt panel & controller, IMHO, the cost per watt over the lifetime favors solar because the panel does not require maintenance or fuel & oil to operate. Most of the high quality 80 watt panels that we use such as Kyocera, Seimens & Carmanah come with robust warranties for output of 15-20 years. Keep in mind this is based upon 24/7 exposure to the elements. Even once the warranty period is up, they still continue to produce.

I would prefer solar over a 1000 watt inverter generator for a number of reasons, lack of moving parts and silent operation being just two of them. I started thinking generator out of sheer frustration.

Most importantly, evaluate your needs. If you want to run an Engel, some lights, laptop, recharge camera batteries and the occasional 110V inverter driven appliance, solar will do it. If 110V and high high wattage loads are more important, go with a generator.

I found these links while researching small solar charging systems. Nothing esoteric, just simple systems for a truck camper and a pop up camper. (Used to have a link for a VW Westphalia solar system, but the site is dead now.)

http://www.otherpower.com/popup.html

http://www.backwoodshome.com/articles2/yago93.html

The tough part is calculating the capacity I really need and then finding a panel that will withstand rough roads and that doesn't cost a small fortune. The Alpha Solar link has some promising possibilities.

 

[Robert Bills]

Instead of using a generator for 110vac; why not consider a DC to AC converter of about 2K watts powered by two good 12v batteries with about 200min ea. of reserve power to get your 115vac.

Actually, my primary goal is a source for recharging my "house battery" so that I can run the Engle/ARB fridge and single light for 3-4 days, and up to 5 days, without discharging the house battery more than 50%. I am not so much worried about charging or running a laptop as I only use one for GPS mapping and even then not often. I don't take a lot of digital photos and seldom go through more than 2 sets of batteries on a trip.

[I use] two series 31 trolling motor batteries and get several days useage before needing a recharge.

I wish I could carry two batteries, but alas I cannot. I only have room for one Group 27 or 29 battery box and thus far the highest rated battery is 115 amp hours. Also, I want to keep the weight down as sometimes I have to manhandle the trailer myself and at my age I have to be concerned about injuring myself or my heart.

You could use a couple of 15watt solar panels/controller to help with charging duties.

So the real question is, how many watts of solar panel do I really need, considering my anticipated current draw and battery limitiations.

 

[Martyn]

Robert

I think your fridge would be pulling 1.75 amp for 12 hours out of 24. If you pack it correctly, open it infrequently, keep it out of direct sun, and keep it full at all times you shouldn't go over that. I believe how one uses the fridge is a big factor in how much power it draws,

Judging by the amount of time you expect to spend in one place I'd say you could manage 3-4 days on a good deep cycle battery, 5 days would be pushing it. I'm guessing on your power consumption and usage for your light, camera and lap top.

As you say you don't have room for a second battery (I'm puzzled that you would have room for a generator), I'd suggest an 80 Watt panel with a simple none LED control panel.

If you want us to quote the solar panel with stand, electrical cables, and control panel we'd be glad to. If you have a fair understanding of DC it's not too difficult to wire up, or we can arrange for that as well.

Alternatively you have some good sources for all the parts, then it's just a matter of making a stand for the panel and wiring the whole thing up.

 

[Robert Bills]

I think your fridge would be pulling 1.75 amp for 12 hours out of 24. If you pack it correctly, open it infrequently, keep it out of direct sun, and keep it full at all times you shouldn't go over that.

Thanks. That ends my confusion over calculating the draw from the fridge.

Judging by the amount of time you expect to spend in one place I'd say you could manage 3-4 days on a good deep cycle battery, 5 days would be pushing it. I'm guessing on your power consumption and usage for your light, camera and lap top.

My "seat of the pants" test has been 3 days before the battery charge indicator shows a weak charge. If I had a real voltmeter instead of the LEDs, I would know exactly. I suspect that I am taking the battery far below 50% charge after 3 days, thus diminishing battery life.

As you say you don't have room for a second battery (I'm puzzled that you would have room for a generator), I'd suggest an 80 Watt panel with a simple none LED control panel.

If you look at this photo, you'll see my battery box. If I added some kind of shelf over the area where the battery box is located I could conceivably strap down a small Honda or Yamaha inverter generator, which has approximately the same "footprint." However, I would far prefer solar.

If you want us to quote the solar panel with stand, electrical cables, and control panel we'd be glad to. If you have a fair understanding of DC it's not too difficult to wire up, or we can arrange for that as well.

Sure, quote it. I could spend hours sourcing the parts which would probably be better spent earning a living (and paying your shop.) Send me a PM or e-mail.

So my question remains, do I really need an 80 watt panel or can I use something smaller?

 

[Bergger]

So my question remains, do I really need an 80 watt panel or can I use something smaller?

That's my question too. I've heard of people using a 15 watt panel to maintain a single deep cycle. That is what I was thinking of doing. Those can be had with a controller for about $150.

 

[oldcj5guy]

I had the popup setup with 2, 6 volts stacked and used a charger setup for a boat to charge it when I was close to a 110 source. Looking at what you have, you might consider going to a custom battery box and stack 2 batteries. I could get about 6 days running my large norcold freezer and lights for a few hours every evening. Before we sold it I added 2 smaller solar panels 45 watts each. We did 14 days in Missouri without plugging in and the battery gauge never got below 55% and we ran the lights and radio way into the night.

 

[Martyn]

Sure, quote it. I could spend hours sourcing the parts which would probably be better spent earning a living (and paying your shop.) Send me a PM or e-mail.

So my question remains, do I really need an 80 watt panel or can I use something smaller?

Robert

The reason I suggested an 80 watt panel is it's the best bang for the buck. As you start to get smaller the cost per watt goes up.

Again the size of the solar panel you need will all be guess work until you do an energy assessment. I've ball parked your fridge, now we need to know what the power consumption on your lights, camera, and computer are, and an average per day usage.

Once we have those numbers we could say exactly what size panel you need. We can talk all day about what size panels are available and what size panels other people have used successfully, but we need to find out what is going to work best for you.

Here is a selection of the panels we can provide;
10 Watt Panel providing 0.65 amps
20 Watt Panel providing 1.3 amps
50 Watt Panel providing 3.1 amps
80 Watt Panel providing 4.6 amps
110 Watt Panel providing 6.7 amps