Which solar kit do I need?

[Cakeman2253]

Ok i have read lots on solar but still a little confused. Electric does that to me.
I have looked at several kits on line. We are only camping 1 or 2 nights in a row without power when we go out on the beach. I have 1 (deep cycle battery) but am going to install another 12v deep cycle battery (so I will have 2 in series). The motor battery is separate. I only run lights when needed and a 4 inch oscillating fan when sleeping. How many watts do you think I need? Need to know which kit to order? Do I need 20W or 30, 45W?

Main goal is to keep my batteries charged? I am not using the inverter so no major modern appliances.

These are what I have looked at
http://cgi.ebay.com/RV-SOLAR-PANEL-KIT-45-WATT-12-VOLT-45W-/310327071267?pt=LH_DefaultDomain_0&hash=item4840ef5223

http://cgi.ebay.com/RV-SOLAR-PANEL-KIT-30-WATT-12-VOLT-30W-/280699893057?pt=LH_DefaultDomain_0&hash=item415b047541

http://cgi.ebay.com/RV-SOLAR-PANEL-KIT-20-WATT-12-VOLT-20W-/280699893076?pt=LH_DefaultDomain_0&hash=item415b047554

I am open to suggestion on other kits or ideas also, There seem to be many qualities out there and pricing is all over the place.

Thanks for your help, as always Bradley

[Stewartfan]

Try looking up Power Film, they roll up for easy storage and are very durable.

[DaveVA78Chieftain]

1st, thats two 12VDC batteries in parallel not series.

2nd, size of solar array needed should be based on the amount of usage you expect to have .

Calculating Amp hours per day requirement (Ah = Amp hours):

Amp hours per day = Amps x Quantity of item (ie: 3 lights) x hours of operation per day

Item	Amps   x	Qty    x	hours   =	Amp Hours
Lights	1.5 amps	3	4 hrs	18 Ah
Water Pump (Includes 2 Showers	5 amps	1	0.75 Hrs	3.75 Ah
TV	4 amps	1	2 hrs	8 Ah
Misc (Clocks, etc.)	Various	Various	Various	2 Ah
Total Ah per Day				31.75 Ah

For 2 days of usage thats a total of 63.5 Ah (31.75 x 2 = 63.5 Ah)

It is unfortunant that they list Solar size in watts for marketing puposes.  It confuses the issue for many people.  You need to use one reference value for caluculations so the fist thing to do is convert to maximum rated amperage.  A 45W solar unit provides 3.75 amps of energy (45W / 12DC = 3.75 amps).   Now you have to compute the total amount of amp hour capability per day. For desert camping, thats approximately 45 amp hours of energy (3.75 amps x 12 hours).  For camping in the woods that will be drastically reduced because of tree shade (Mommy wants maximum AC effciency so having the RV shaded is required).  You may only get 3.75 x 4 hours = 15 Amp hours.  On a cloudy or rainy day you may not get any Solar array benifit (0 Ah). 

When camping in the desert, the 45W solar unit (45Ah) will cover the 31.75 Ah usage requirement.  When camping in the woods though, that 31.75 Ah requirement may not be meet because the shaded array can only produce 15 Ah of energy.  Your battery would have to provide that additional 16.75 Ah of energy.

You do not want to discharge a true Deep Cycle battery to less than 50% charge.  A Typical Group 27 12VDC deep cycle battery is rated for 105 Ah.  50% discharge would be 52Ah.  52Ah would cover the usage for one day (with no recharge capability).  Two Group 27 batteries (2 x 105Ah = 210Ah) would cover 2 days.  If you are in the woods camping for 2 days, the solar array (for the 15Ah example I am using here) would only provide 30 Ah of the total.  The batteries would have to supply additional 33.75 Ah of the total needed.  As you can see, it is not just the size of the array but also how effeciently the array will be in a given situation.  You would have to use a generator to restore the additional 17-20 amps per day needed.  However, if the battery bank is big enough to provide the additional Ah's needed fo a 2 day trip, then that can they can be charged either on the drive home (engine alternator) or at home with a seperate battery charger.

Most Group 24 (approx 80Ah) or Group 27 (approx 105Ah) 12VDC batteries are Marine Deep Cycle batteries which are not true deep cycle batteries.  It is typically said those should only be discharged to around 75% to 80% capacity.  At 75%, that only provides you with around 25 Ah per day per battery.   For now at least, I just treat my Marine Deep Cycle as true deep cycle batteries because I do not have the $ to put out for true deep cycle batteries.  It takes 2 6VDC deep cycle baterries in series to produce 12VDC.  You only double the voltage with 2 of those not the Ah so two 6VDC 105Ah batteries in series only = 105Ah not 210Ah.  Two 12VDC 105Ah batteries in parallel do = 210Ah.

Hope this helps,
Dave

For AC via Inverter: DC Amps = ((AC amps x 120) / 12) * 1.1
AC Watts = AC amps x 120
DC Amps_a (100% Inverter Efficiency) = AC Watts / 12VDC
DC Amps @ 90% Inverter Efficiency = DC Amps_a x 1.1

The table contaiins both AC and DC information used for computing power consumption requirements.



   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

ITEM	Watts	AC Amps	DC Amps
Air Conditioner, 7,100 BTU	1020	10	93.5
Air Conditioner, 13,500 BTU	1700	14.16	156
Air Conditioner, 14,800 BTU	1920	16	176
Air Conditioner, Heat Strip	1920	16	176
Blender	300	2.5	27.5
Bulb, #1141, Incandescent	18	N/A	1.5
Bulb, #1003, Incandescent	10.8	N/A	0.9
Bulb, 8W DC Fluoresent	8.4	N/A	0.7
Bulb, 15W DC Fluoresent	14.4	N/A	1.2
Bulb, 30W DC Fluoresent	24	N/A	2.0
CB	6	N/A	0.5
Coffeemaker	900	7.50	82.5
Computer, Desktop	100	0.83	9.2
Computer, Printer	240	2	22
Converter/Charger 20 amp	420	3.5	N/A
Converter/Charger 30 amp	552	4.6	N/A
Converter/Charger 40 amp	660	5.5	N/A
Converter/Charger 75 amp	1040	8.66	N/A
Drill, 3/8"	350	2.91	32.1
Fan, 3 Speed Roof Vent    Brand & Speed Dependent	21.6 - 87.6	N/A	1.8 - 7.3
Fan, Wall Mounted    Brand Dependent	14.4 - 60	N/A	1.2 - 5.0
Fan, Bathroom Vent	24	N/A	2.0
Fan, Range Hood	24	N/A	2.0
Fridge (LP/DC/(AC) LP Mode	12	N/A	1.0
Fridge (LP/DC/(AC) 12VDC Mode	180 - 420	N/A	15.0 - 35.0
Fridge (LP/DC/(AC) AC Mode	300	2.7	27.5
Fridge AC/DC Compressor 12VDC Mode	72	N/A	6.0
Fridge Portable Type AC Mode	47	0.39	4.3
Furnace	60 - 96	N/A	5.0 - 8.0
Hair Dryer	1200	10	110
Heater, Elecric, 1500 Watt	1500	12.5	137.5
Heater, Elecric, 1250 Watt	1250	10.41	114.6
Iron	1300	10.83	119.2
Microwave, 450 Watt	900	7.50	82.5
Microwave, 650 Watt	1300	10.83	119.2
Saber Saw	300	2.5	27.5
Sewing Machine	150	1.25	13.75
Stero, Automotive Style	20.4 - 72	N/A	1.7 - 6.0
Toaster	900	7.50	82.5
TV, 9" Color, AC Mode	54	0.45	4.95
TV, 9" Color, DC Mode	36 - 48	N/A	3.0 - 4.0
TV, 13" Color, AC Mode	70	0.58	6.4
TV, LCD, 19" Color, AC Mode	250	2.1	23
TV, 5" B-W, DC Mode	12 - 18	N/A	1.0 - 1.5
TV Sat Receiver	170	1.41	15.6
Vacuum Cleaner, Hand held	240	2	22
Vacuum Cleaner, Canister	350	2.91	32.1
VCR/DVD 12VDC Mode	18	N/A	1.5
VCR/DVD AC Mode	90	0.75	8.25
Water Pump	48 - 96	N/A	4.0 - 8.0
Washer/Dryer, RV Type	1920	16	176

[ibdilbert01]

"A 45W solar unit provides 3.75 amps of energy (45W / 12DC = 3.75 amps)."

And don't forget because most panels are actually 20 to 22 volts plus other losses, you won't get anything near 3.75 amps unless you use a MPPT controller.   Realistically you'll see 2 to 2.3 amps on a nice sunny day with a standard charge controller and a 45 watt panel.       

$199 seems a bit hot in price.

[Cakeman2253]

ibdilbert01
-----Did you get a chance to put any of the solar pannels together?