We have a E350 van we use for car camping. I've got two deep cycle batteries that are charged via the vehicle alternator (while driving) or via a battery charger plugged into shore power. Am thinking of adding solar to the mix for off the grid camping....
The issue is when we aren't driving and don't have power nearby. The flooded batteries are rated at 105 amp hours and the fridge has a peak usage of 45 watts (its slightly larger than a dorm fridge -- not full size). When camping I turn the fridge way down and am careful to to open it too often. Still in about 2 days, it runs through the charge in batteries ... so 210 amp hours over 48 hours.
How do I calculate the how large a panel I will need to break even .. ie: when boondocking, my solar panel will restore my batteries during the day (or at least extend my off grid time) .. 120w, 200w, 400w system?
Also, because I have a battery charger for shore power and vehicle alternator providing recharging capabilities, I am assuming that most solar panel controllers have a diode that prevents back charging ... ie: if driving, the alternator isn't trying to also charge the solar panel. What to a look for or ask about to make sure the solar panel controller has this one-way curcuit?
Thanks !!
Nat
Jack Mayer said
02:49 PM Aug 3, 2013
Well, in "theory" a 45 watt appliance can be "run" with a 45 watt panel. In practice, of course, it does not work that way. So having the battery bank "buffer" is critical. You do not want to run your batteries lower than 50% of their capacity -they will not last long if you routinely use more than 50%. So your usable capacity is at most 50% of your total capacity. That is assuming that you have deep cycle house batteries, not regular automotive starting batteries.
Since solar panel cost is pretty cheap these days, I would put on the largest single panel that you can. If money is not a major object then a high voltage panel with an MPPT controller (that can utilize the higher voltage) is what I would do. Panel form factor (shape) will be a major consideration. Look on wholesalesolar.com at panels that are high voltage (over 21 volts Vmp). Or, if you wnat to stick to "12-volt" panels look for panels 21 volts Vmp or under - these will not require an MPPT controller (which costs more than a PWM controller). Then, look at the Imp for your panel - that is the number of amps it outputs in max sun....and size your controller for that.....except always put in more controller than required, you may want to add a panel.
If I was doing it I'd put in probably something around 200+ watts, high voltage, and add a Morningstar MPPT45 amp controller. That would handle all your future needs and easily keep the batteries up in sun. But it is a higher-end solution. That is just one suggestion....more info could result in a different solution. Also, it is wise to put in a battery monitor if you are gong to come near the capacity of your battery bank. I like a Trimetric 2025RV. But it does add to cost.
Bill and Linda said
03:53 PM Aug 3, 2013
Hello Nat, welcome to the forum.
Well, I had typed up a response saying what Jack said and also recommend 200+ watt panels, closer to 300, IMO if you can make them fit, because you probably use 12 volt lights in the van at night. Also, on some days you can't get that many hours of good charging and you need more "collectors" to get all the sun you can.
Anyway, Jack beat me to the post.Good for you.You really need this stuff he outlined to make this work well. Might need a very small generator as well but that's another discussion.
What Jack left out is the following:
Highly recommended reading to help with your questions more fully than space here permits:
GREAT. Thanks for your input guys. Do most solar panel controllers (PWM and MPPT) come with a anti-back charging diode that prevents a generator, the vehicle's alternator or shore power from sending current through the solar panel when those systems are operating?
Thanks for your thoughts on sizing the system. I had done the math and was thinking around a 200w system but will think about upgrading that. Given that we don't (or at least haven't yet) done long term boondocking I was initially thinking about a PWM controller, but I do fine that even on shore power (Intelipower 9160A battery charger) it takes quite a while to recharge the battery bank from 50% (as in more than overnight). Perhaps a higher volatage MPPT-based system would allow it to recover quicker.
I do have a Trimetric battery monitor that I use for the batteries and they will give me a good idea of where I am in terms of full charge or not.
-- Nat
Bill and Linda said
09:23 PM Aug 4, 2013
Nat:
If you want it to do the best possible job in the limited physical space you have, I would suggest you need a MPPT charger, such as the model jack recommended, I have one, and some ~22+ volt or so panels. Best physical size vs. output naturally in your situation. That’s why the MPPT is so important as are higher voltage panels. PWM chargers can work, but are probably not going to cut it in your situation.
With this charger you don’t have to worry about the generator “charging” the panels.No “diodes” required.
You will probably need a small gas generator at times to supplement the panels.Just reality IMO30-45 minutes with a generator and a high current (smart) charger can do a lot of initial bulk charging and then the solar can finish the last ~25% in the absorption mode.On some days you may not need the generator at all.Naturally, “it depends.”
Jack has a lot of links on his website I gave you the link to which can provide a source.AM Solar is a good place for one-stop shopping with reasonable prices IMO. They have “packages” that can save you a few dollars.
Hi,
New to forum ... hoping you can help out.
We have a E350 van we use for car camping. I've got two deep cycle batteries that are charged via the vehicle alternator (while driving) or via a battery charger plugged into shore power. Am thinking of adding solar to the mix for off the grid camping....
The issue is when we aren't driving and don't have power nearby. The flooded batteries are rated at 105 amp hours and the fridge has a peak usage of 45 watts (its slightly larger than a dorm fridge -- not full size). When camping I turn the fridge way down and am careful to to open it too often. Still in about 2 days, it runs through the charge in batteries ... so 210 amp hours over 48 hours.
How do I calculate the how large a panel I will need to break even .. ie: when boondocking, my solar panel will restore my batteries during the day (or at least extend my off grid time) .. 120w, 200w, 400w system?
Also, because I have a battery charger for shore power and vehicle alternator providing recharging capabilities, I am assuming that most solar panel controllers have a diode that prevents back charging ... ie: if driving, the alternator isn't trying to also charge the solar panel. What to a look for or ask about to make sure the solar panel controller has this one-way curcuit?
Thanks !!
Nat
Since solar panel cost is pretty cheap these days, I would put on the largest single panel that you can. If money is not a major object then a high voltage panel with an MPPT controller (that can utilize the higher voltage) is what I would do. Panel form factor (shape) will be a major consideration. Look on wholesalesolar.com at panels that are high voltage (over 21 volts Vmp). Or, if you wnat to stick to "12-volt" panels look for panels 21 volts Vmp or under - these will not require an MPPT controller (which costs more than a PWM controller). Then, look at the Imp for your panel - that is the number of amps it outputs in max sun....and size your controller for that.....except always put in more controller than required, you may want to add a panel.
If I was doing it I'd put in probably something around 200+ watts, high voltage, and add a Morningstar MPPT45 amp controller. That would handle all your future needs and easily keep the batteries up in sun. But it is a higher-end solution. That is just one suggestion....more info could result in a different solution. Also, it is wise to put in a battery monitor if you are gong to come near the capacity of your battery bank. I like a Trimetric 2025RV. But it does add to cost.
Hello Nat, welcome to the forum.
Well, I had typed up a response saying what Jack said and also recommend 200+ watt panels, closer to 300, IMO if you can make them fit, because you probably use 12 volt lights in the van at night. Also, on some days you can't get that many hours of good charging and you need more "collectors" to get all the sun you can.
Anyway, Jack beat me to the post. Good for you. You really need this stuff he outlined to make this work well. Might need a very small generator as well but that's another discussion.
What Jack left out is the following:
Highly recommended reading to help with your questions more fully than space here permits:
http://www.jackdanmayer.com/rv_electrical_and_solar.htm
Bill
Thanks for your thoughts on sizing the system. I had done the math and was thinking around a 200w system but will think about upgrading that. Given that we don't (or at least haven't yet) done long term boondocking I was initially thinking about a PWM controller, but I do fine that even on shore power (Intelipower 9160A battery charger) it takes quite a while to recharge the battery bank from 50% (as in more than overnight). Perhaps a higher volatage MPPT-based system would allow it to recover quicker.
I do have a Trimetric battery monitor that I use for the batteries and they will give me a good idea of where I am in terms of full charge or not.
-- Nat
Nat:
If you want it to do the best possible job in the limited physical space you have, I would suggest you need a MPPT charger, such as the model jack recommended, I have one, and some ~22+ volt or so panels. Best physical size vs. output naturally in your situation. That’s why the MPPT is so important as are higher voltage panels. PWM chargers can work, but are probably not going to cut it in your situation.
With this charger you don’t have to worry about the generator “charging” the panels. No “diodes” required.
You will probably need a small gas generator at times to supplement the panels. Just reality IMO 30-45 minutes with a generator and a high current (smart) charger can do a lot of initial bulk charging and then the solar can finish the last ~25% in the absorption mode. On some days you may not need the generator at all. Naturally, “it depends.”
Jack has a lot of links on his website I gave you the link to which can provide a source. AM Solar is a good place for one-stop shopping with reasonable prices IMO. They have “packages” that can save you a few dollars.
www.Amsolar.com
Bill