Solar panel setup questions

[TRAIL TAILOR]

I scored 3-65 watt solar panels today. I'm no electrician, but I need a charge controller from what I've read. I think I have this right, but please help me out here.. 65w x 3 panels = 195 watts / 12 volts = 16.25 amps... I think a 20 amp charge controller would suffice with a 1.25 fudge factor.

I also have 3 new 12 volt 110Ah deep cycle batteries coming as well from the same source. How fast will this system charge the batteries and exactly how much can I run off this setup?

J

 

[george_tlc]

Well, it's not as simple as 65W x 3 = 175 / 12. Your max current could be 20% or 30% lower than your calculation.

Usually solar panels are rated at their maximum power point, which "MAY" be near 12 - 14V, but likely not.

Anyhow 20A charge controller will be fine for the 3 panels. I ASSUME they're nominal 17V (approx) panels and you plan to wire the 3 in parallel.

So, being conservative, if they deliver say 10 - 12A on a typical sunny day then you'll be harvesting around 120W - 140W per hour into your batteries (assuming they are been drawn down). So, you'll be able to draw about that much power while the sun shines without discharging them.

How fast it'll charge - depends on the state of the batteries and how many amp.hours you need to put back into them. If all 3 110A.hr batteries are fairly flat, then you need to put 330A.hr back in and if you're only getting say 10 12A.hr from the panels, it'll take quite a few sunny days...

Anyhow, all depends on what you are hoping to achieve in terms of powering various devices and charge time and # of sunny days and solar panels always aimed at the sun.... lots of variables

cheers,
george.

 

[TRAIL TAILOR]

George, thanks for the reply. Yes, I plan on a parallel system.Here is a picture of the back of the panel.

I plan on using these for off grid camping occasionally and only running a couple to 4-60 watt lights, a cell phone charger, and possibly a small fridge. Camping trips lasting maybe two--three nights max.

 

[george_tlc]

Ok, so a siemens panel, some info here http://abcsolar.com/pdf/sp65.pdf

Note that the Vmpp and Impp mean Voltage at maximum power and Current at maximum power.

So, that 65W happens at Vmpp which is 16.5V, i.e. you'll get less power at the 12 - 14.4V range of a typical lead acid. Not horribly worse, but certainly less than 65W. That 65W is also with nominal 1000W/m^2 or a somewhat "ideal" sun. Depending on latitude/haze in the air etc etc, you'll get less again.

My opinion is that I'm happy with an 85W panel feeding an 80A.hr aux battery (for camping etc). So, my rule of thumb (fwiw) is 1W per 1A.hr of battery capacity works well for me.

So, if **I** had 3 110A.hr batteries I'd be thinking something in the 330W range in terms of solar panel power. Again in **MY** opinion you have a lot more battery than solar panel at this point. That's just my experience camping out running a fridge & lights while camping for a couple of weeks.

Now, for just 3 nights, you have enough in a single one of those 110A.hr batteries to take care of your needs unless you need aircon in your tent too

A modern (within the past 5yrs or so) camping fridge is very power frugal if kept out of the sun and reasonably insulated with good airflow to the evaporator area. I'd invest in some LED lighting for your camping, that'll save you quite a bit of a.hr.

cheers,
george.

 

[TRAIL TAILOR]

George, you're the man! I will definitely look into the LED lights. I'm looking for a Engel, Wynter, or EdgeStar 12v fridge now, and in that order pending near future funds. I appreciate the feedback.

J

 

[TRAIL TAILOR]

So, got my 3-110Ah batteries and have 2- charge controllers now... my friend said to see if they worked, he didn't know the status/ condition of the controllers...

What is the best wire size to run from panels to controller to batteries?? 12 AWG or ?? For maximum performance that is.

Thanks guys..

J

 

[Bogo]

12AWG will work fine, 10AWG would be better, but not likely worth the extra cost. By wire amperage allowances, 12AWG is all that is needed. Your runs are also short. Note, get an automotive stranded wire. This is a good table for 5% loss in the wire at Amps and wire gauge: DC Wire Table

Now, for just 3 nights, you have enough in a single one of those 110A.hr batteries to take care of your needs unless you need aircon in your tent too

A modern (within the past 5yrs or so) camping fridge is very power frugal if kept out of the sun and reasonably insulated with good airflow to the evaporator area. I'd invest in some LED lighting for your camping, that'll save you quite a bit of a.hr.

With three 110Ahr batteries, No need for solar over a 3 night weekend. Yeah, a modern refrig/cooler will draw less than half that capacity over the weekend. Use a battery charger at home to charge the bank up and use it up over the weekend. I second the recommendation on getting LED lights. 8 of them will use less energy than one incandescent lamp of equal light output.

Adding in solar would extend trips to nearly any length, and automatically keep the battery bank topped off when not in use. The battery bank you have would allow a couple cloudy/rainy/tree covered days between good solar charging days. If run in that mode, then I'd only use in one day a maximum of 1/2 the daily solar charging capacity. The rest being available for recharging. Thant means about 225 Watt hours use a day. I assumed 80% efficient for flat mounting, and 80% efficient battery charging.

Aircon will draw 350 to 800 Amp hours in 8 hours at 12VDC. Depends on the air conditioning unit, and insulation. PS, insulation is nearly mandatory. Amp hour use is from a survey I did for myself on available units a few years ago. If you put DC powered air conditioning in, remove the engine driven air conditioner compressor. Use a second alternator in place of the engine drive air conditioner compressor to power the DC air conditioner, and recharge the house battery bank. It is not realistic to have enough solar charging capacity for air conditioner running.

 

[TRAIL TAILOR]

Bogo, Thanks.. I have access to wire from 6 to 14 AWG.. I will not be running an aircon unit, however I appreciate that input.

Mainly just lights, radio, cell chargers, laptops, and fridge on most trips.

J

 

[RHINO]

i run all my electric needs for camping off two 40 watt panels and a single 80amp hr battery. typically a fridge, a few chargers, LEDS at night for a couple hrs. i have been out several times with this set-up, the longest being 11 days, pretty sure i can stay out indefinitely.

 

[Bogo]

If you have cheap access to 10AWG, I'd use it if the device connectors will accept it. Less line loss in the wires. At 12VDC at mid day it will add up to a few percent loss.

I threw the bit in on air conditioning because George joked about it. Long haul truckers are putting in DC powered air conditioners because they allow them to sleep overnight in a sleeper cab without running the engine. That alone will pay for the unit in a year or less on a truck that sees a couple nights out a week. The thing is they use 4 group 31 deep cycle batteries to power it for around 8 hours use. That is a 400 to 440 Amp hour battery bank. They charge it with an upgraded or second alternator on the engine. I'm seriously considering it for the stalled Micro-RV project. One company that is uber expensive will supply you with a Li-Iron battery bank for powering their unit. Less than half the battery weight, but 10X the cost. From the numbers they quote, it looks like they have the most efficient system, but the numbers they quote don't easily compare against others numbers.

 

[TRAIL TAILOR]

i run all my electric needs for camping off two 40 watt panels and a single 80amp hr battery. typically a fridge, a few chargers, LEDS at night for a couple hrs. i have been out several times with this set-up, the longest being 11 days, pretty sure i can stay out indefinitely.

After doing some more research and reading the posts here, I think what I have is overkill for what I am going to use it for.

J

 

[TRAIL TAILOR]

If you have cheap access to 10AWG, I'd use it if the device connectors will accept it. Less line loss in the wires. At 12VDC at mid day it will add up to a few percent loss.

I threw the bit in on air conditioning because George joked about it. Long haul truckers are putting in DC powered air conditioners because they allow them to sleep overnight in a sleeper cab without running the engine. That alone will pay for the unit in a year or less on a truck that sees a couple nights out a week. The thing is they use 4 group 31 deep cycle batteries to power it for around 8 hours use. That is a 400 to 440 Amp hour battery bank. They charge it with an upgraded or second alternator on the engine. I'm seriously considering it for the stalled Micro-RV project. One company that is uber expensive will supply you with a Li-Iron battery bank for powering their unit. Less than half the battery weight, but 10X the cost. From the numbers they quote, it looks like they have the most efficient system, but the numbers they quote don't easily compare against others numbers.

I'll check the connectors and see if they will accept 10 AWG. I think they will.

J

 

[Cruiserdrew]

Did your charge controllers work? It would be awesome if they did.

You have a lot of battery, what do you need it for? To run a fridge, all you really need is 100 AH battery and about 100-120 watts of panel.

I'd install 2 of those panels, paralleled into whatever charge controller, and go for it.

But this is one of those situations where more can be better. So experiment and see what you get.