Another solar question

[Nwcid]

I have been doing tons of reading on solar stuff. While there is quite a bit of info out there on it much of it just seems to be the same info over and over again.

So I am trying to set up a solar charging system in my enclosed trailer.

I currently have 2, 6v batteries with 225ah (20 hour) reserves. They are wired in series to give me 12v and if I understand correctly I still only have 225ah reserve.

I have installed 2 fans (fantastic's) that draw 3A each for a total of 6A. I would like to be able to run these all day to pull warm air out and probably most the night to pull cool air in. I have some interior lights that will run for short bits (under 30 min) in the evenings and morning. I have no plans of using much else for power on a regular basis most the time. Just to be on the safe side I have been saying I want to pull 10A, 24hr/day on the couple calculators I could find online. I know my batteries are just undersized for that.

I am trying to figure out how many panels I will need. I found a 235 watt panel for a good price but according to the calculator I would need 3 to do what I want. The calculator I could find would not convert voltage and amps. The panel I am looking at is rated at 30v to get the 235 watts that is 7.8 amps which I know does not work. If I am reading right if I get a MPPT controller that will bring it back to 12v but that will also give me about 19.5A to get the 235 watts. Am I understanding that right?

So that leads to the next part. This time of year we have 14 hours of daylight. I know the panel will not put out full power that whole time but is it reasonable to believe there is 7hr of good sun this time of year?

Can I get by with 1 panel or do I need 2? Obviously the price of 2 doubles my cost. Plus MPPT's are not cheap either.

I know I am missing some info and some questions in there. Any help getting this straightened out would be nice.

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[Mark W.]

look up "Ohms law" it will give you the math to convert from volts to watts to amps.

You need more voltage then the storage batteries in order to get them to charge. (like in a car 12V battery 13.8V charging system).

To greatly reduce your demand look at replacing your lighting with LEDs the difference in amps is amazing.

having a system that will tip the panels to face the sun will greatly increase the production of electricity during the day. This can be something automatic $$$$$ or something as simple as a manually adjusted mounting bracket (PITA)

Have you been looking on RV web forums for advice?

 

[HenryJ]

I am just south of you and not far off the longitude. 5 hours is the average sun for charging. Our latitude determines that on the charts I have seen.

Conservation is the best investment. The suggestion above to go LED is a very good one. Look around, you don't have to spend $15 per fixture to go LED. I installed 21 LED panels in all the fixtures in my whole trailer for about $40 , also including indirect floor lighting.

I too an running two six volt batteries and have the same reserve. I don't run roof vent fans, but have considered them.

I am using a 40w solar suitcase that I put together.



It does all I need. My batteries are topped off each day by 10am with decent exposure. In the trees and shade I am charged back up by early afternoon. Plenty of cushion , IMO.



I have been watching for a few friends. I am convinced that you don't have to buy a huge system to go solar. 30w-40w is a great start. Chase the sun a little and you will be fine.
Here are some that I have found:
Instapark 30W Solar Panel
Coleman 36 Watt Folding Solar Panel

I would suggest the second one that I linked. It is easier to transport. The first one has a cheap controller, but for under $20 that can be replaced with a Morningstar controller. Either looks like a great investment.

If you are wanting to hard mount the panels and forget them you will need at the very least twice as many panels since they will not be optimized for capturing the available sun. Play the sun dance and move the panels around camp a little during the day. a couple moves is all it takes.

Keep in mind that you can always add more panels later if you find that you need them. I think most tend to add enough solar to run everything all the time. That is not usually the case. Lights are not on all day.

 

[Nwcid]

I looked into LED lights but they are not my main draw so would be very little return on my investment. The trailer now has 3 fluorescent fixtures that each have 2, 18" 15 watt bulbs. I looked into replacing them with something else but cost vs output was not there for me.

When I am using the set up this way I will not be able to rotate the panel(s). I will be using it this way when on wildland fire assignments where the trailer will be basically sitting out in a field in the sun all day. I am planing on building a bracket that I can angle the panel(s) south. When I am out I can be gone anywhere between a week and a month so need to be self sufficient. I know I can drop usage in a pinch if I need to.

Basically since it is hot out in the summer I want to be able to vent the trailer all day then pull cool air in at night. I am sure at some point during the night the fans will get turned down/off as they have thermo controls built in. They are my biggest draw.

A 30 watt pannel will only put out 2.5A at best. If my math is correct I need at least 10A.

 

[OFADAN]

Be advised depending on your mission for this trailer if you break one of those flo lights you've got a potentially contaminated environment and all youre valuables inside are tainted. If your using this away from home at a remote location then LED is going to be more robust and you don't have breakage or bulb burn out issues. Look at the LED lights from a Marine shop used for boats. Rugged, reliable, designed for tough conditions and 18 individual LED lamps which will illuminate a 14' trailer are going to only draw around 1 amp/hr.

Also be advised a 225 amp/hr battery bank is for all practical purposes 1/2 that capacity. According to my professional solar sources (not Internet resources) they only advise draining or drawing down ones battery bank no more than 50% to preserve the banks long term integrity. You can periodically go below 50% but only on occasion. They recommed for the long haul stick to a threshold of 50 max. You'll find those who use solar are amp mizers. Any way you can save milliamperes eventually adds up.

Also what takes 4-6 hrs now in the summer to recharge could take 2-3 days to recharge in the middle of the winter. Don't ask me how I know this!!!

 

[HenryJ]

Replacing the fluorescent with LED is a good investment. Power consumption will be greatly reduced. LED are measured in millionths of a watt. Shop around. there are affordable solutions.

Use it while you need it.
You wouldn't leave a light on all day and night if you were not there, why leave a fan on? Convection will naturally draw. Open the vent and let the heat escape. It will not take long to vent it with fans when you return. All that "away" time will restore reserves quickly.
I run two fans to circulate air in the summer while camping and our furnace runs lots when we spring camp. I ran a 12V refrigerator with no problems on only a single 12v 90ah battery. That fridge alone averaged a 2.4 amp draw in 24 hours.
I have done the math and consulted the charts. After real world testing with my panels and several years experience using them, I am comfortable leaving the generator home. We have never needed it.
If you have $1k to spend on panels and room to mount them, by all means go for 200w or more panels.

I totally agree that if you have high demands, don't expect the solar to maintain the load. You need a greater storage and reserve, Invest in a couple more batteries before a bigger solar panel.

BTW, don't get excited about the amount of Mercury in a fluorescent bulb. Newer bulbs have much less than they used to and the amount is almost insignificant. The amount is very small. Don't eat it or snort it. Don't have your three year old clean it up. Clean it up carefully with a small broom and dust pan. Vacuums without the HEPA filter can just blow it into the air. Bag the debris and dispose it it. We get these calls all the time. I am a 20+ year Hazmat tech for region 10 in Oregon.

 

[Nwcid]

I understand LED and why but when it is going to be 5% of my consumption seems like the last place to spend money. When I got the trailer and the batteries set up this spring I left all the lights on and the forced air heat (was about 40* out at the time) on and the radio (car deck) on for over 24hrs and still had 11.9V in my batteries. If I was being efficient I am sure I could easily get several days out of it.

I will have to play with the fans at home while it is plugged in and see what if any difference in cooling having the fans on during the day.

A local shop (going to stop by today) has a 235 watt panel on sale right now for $400 which is why I am looking at it. If I am reading about MPPT's right I would have more then enough power.

My mission is to have a multi use trailer and so far so good. In the role I am talking about now it will be for me to sleep in at night between shifts for up to a month.

 

[ZigZagZeke]

Volts = E
Amps = I
Resistance = R

E=I*R Substitute as necessary (e.g. R=E/I, I=E/R)

Watts = P

I*E = P Substitutions: (I=P/E, E=P/I)

Ampere Hours = Ah = I*Hours

 

[Redcap]

 

[EMP9596]

I have carried one of these since they came out.

Uglys.net

 

[HenryJ]

I understand LED and why but when it is going to be 5% of my consumption seems like the last place to spend money.

It is cheaper to conserve 5% than it is to generate it.

When I got the trailer and the batteries set up this spring ...over 24hrs and still had 11.9V in my batteries. If I was being efficient I am sure I could easily get several days out of it.

11.9 volts is very nearly dead. Just over 0% of charge and requires 370 minutes at 10 amps to recharge.

A local shop (going to stop by today) has a 235 watt panel on sale right now for $400 which is why I am looking at it.

That is a reasonable price of it is durable and of good quality. That panel should be about 3'x6' , do you have room for that? Keep in mind that all your eggs are in that basket should it get damaged. Usually those large panels are used on fixed facilities where they will not see the flex and twist of an RV application. You may be better served with two or four smaller panels. If one gets damaged you are not out of business.

 

[OFADAN]

It is cheaper to conserve 5% than it is to generate it. 11.9 volts is very nearly dead. Just over 0% of charge and requires 370 minutes at 10 amps to recharge.

Indeed! Amen, on the first statement. Regarding the second, even with 300 watt panels this time of the year you can sqweak out 6 hours of recharge time to top off your battery bank. However, starting in late October early November that isn't going to happen.

Also remember if you're cycling your batteries deeply (80 to 100%) on a daily basis this will shorten the battery's life. Using only 25 to 50%of the storage capacity of your batteries will put less strain on them and increase their useful life. So it behooves you to not to discharge any greater than 50% max on a regular basis.

Also it will behoove you to have a system that has the capacity to have either a scheduled manual or automatic equalization to maintain long term health of your battery bank. You've never stated (or I just didn't see it) but I'm assuming your batteries are AGM for this application?

Thanks HenryJ for the clarification on the LED/Mercury issue. This I did not know...now I'll go back and start using my portable Flo lamps in my camp kit!

 

[Nwcid]

The only long term off grid use I have planned is during fire season. So generally August and September but it can be a little earlier or later. If it is the later the highest power use will be to run the blower on the heater.

I am running 2 Trojan 105's which are wet batteries but come highly recommended for this application. I guess I did not pay good attention before when reading, Deep Cycle Battery FAQ and now see my 11.9 has dropped my battery to 40%. Right now I am using a Inverter Charger | Freedom HF Inverter/Charger | Xantrex 1000/20 to keep them charged.

So unless I want to spend almost $2000 for 2 more batteries and a 500 watt + kit I am just really going to have to watch my power use. I was hoping to be in the $500 range.

 

[RVTECH]

Ohm's Law Calculators

This might make it a little easier. I use this at work a lot when working on similar issues. We talked about your issue a while back if you remember.

 

[mjbskwim]

I just got a head ekk reading all this.

 

[Nwcid]

Well after more and more and more reading I did order some stuff today.

I found some 128 watt flexible panels. I have read the good and bad about them vs flat panels. Sounds like for my application they are a better choice. Lots of people like them on their Airstream. I can run one down each side of my slightly curved roof and if I can park N/S then I would be able to get sun on them most of the day. Since they are 24v with they are rated at 200 watt at 12v. I got a 45a MPPT controller so I can add up to 3 more panels if needed. I easily have room for 2 more if needed.

I do live in an area that has quite a few power outages in the winter. Might make a nice little extra back up if I need it.

 

[HenryJ]

Sounds real good. Get us some pics when you get all set up.

 

[19 Adam]

Sounds real good. Get us some pics when you get all set up.

Yes, pictures!

I am planning on building a portable solar generator. A friend built one with two solar panels on lawn mower wheels and a long cord that runs to a hand truck that has the electronics and batteries. He can plug cords directly into the electronics and run items for several hours on the batteries without going below 50%. It has very nice digital readouts so you know the charging rate and the discharge rate.

 

[WhyteCheddar]

I looked into LED lights but they are not my main draw so would be very little return on my investment. The trailer now has 3 fluorescent fixtures that each have 2, 18" 15 watt bulbs. I looked into replacing them with something else but cost vs output was not there for me.

When I am using the set up this way I will not be able to rotate the panel(s). I will be using it this way when on wildland fire assignments where the trailer will be basically sitting out in a field in the sun all day. I am planing on building a bracket that I can angle the panel(s) south. When I am out I can be gone anywhere between a week and a month so need to be self sufficient. I know I can drop usage in a pinch if I need to.

Basically since it is hot out in the summer I want to be able to vent the trailer all day then pull cool air in at night. I am sure at some point during the night the fans will get turned down/off as they have thermo controls built in. They are my biggest draw.

A 30 watt pannel will only put out 2.5A at best. If my math is correct I need at least 10A.

IMHO, 'costeffectiveness' is a relative term when referring to solar power.
You could completelyremove the lighting load from your PV system by going with LEDs that have theirown internal battery. Some of those can go a very long time on their ownbattery, and provide a great deal of light. You can always keep a few sparebatteries on hand but I could see them lasting for several months base on thedescription of your usage.
Would love to seepictures of your trailer when you are finished outfitting it.