Solar yields at various times and locations in US

mash2

In an effort to help out, I  sat down and calculated estimated yields from solar panels of different wattage.  Obviously these are rough estimates, assuming clear days, no obstructions, sea level (ignoring altitude variations), for horizontally mounted panels.  Its from a solar calculator on the web.  

This doesn't tell you how large your system needs to be.  You need to match up these yields with your battery capacity, anticipated amps you plan on using daily (based on heater, lights, and other appliances plus potential inverter needs as well.   I'm hoping that it gives everyone a sense of the size of solar panels needed to meet your needs.  One side is usage, the other side is potential yield.  I think this should give everyone a sense of the potential yield from various configurations.  Remember, this is a simple sizing exercise.... given weather, shade and other issues, the actual yield is less.   Just trying to give a sense of what sizes of panels means.  Picked prototypical locations and calculated yields in early August.  The second table is the adjustment factor for different times of the year.  For instance, in detroit, the yield in January would be (18.7 X .32) or slightly less than 5 AMPs daily.   Hope this helps.

You need to calculate anticipated demand to determine the yield that you need to stay charged (This is also ignoring the battery capacity that you have to accept the charge).

Daily solar panel yield (in daily AMPS) assuming various panel sizes (August 7th for each)

Latitude 35 37 42 Watts Memphis San Francisco Detroit 40 Watts 19 19 19 80 Watts 38 38 37 100 Watts 48 47 47 120 Watts 57 57 56 160 Watts 76 76 75 200 Watts 95 95 93
Cloudless, horizonal mountiing, no obstructions at sea level, ignoring temperature

Time of year adjustments 

Latitude		35	37	42
Location		Memphis	San Francisco	Detroit
January		42%	40%	32%
February		53%	51%	44%
March		68%	66%	61%
April		87%	86%	83%
May		100%	100%	100%
June		114%	112%	112%
July		113%	112%	112%
August		100%	100%	100%
September		85%	80%	81%
October		67%	65%	60%
November		51%	48%	41%
December		41%	39%	32%

calculated using http://www.where-rv-now.com/Notes/Solar/index.php?lat=32.63851&month=November&mday=7#Calculator


Others can chime in ....

jkjenn

Thanks, @mash2

mash2

Part 2:     Other side is usage.

Construct a table of amps required by your appliances and estimate hours used in day (will depend on time of year).   This will give you your AMPs usage per day.

I have an '06 so the numbers won't apply to LG trailers (they should be in manuals or could be measured).

For me, here was my load assuming a fall outing.

FALL APPLIANCE USAGE	DM 2006
Appliance	Amp	# Hours/day	Total Use
2 way Refrig	2.7	8	21.6
Furnace ('06 TAB)	3.4	2	6.8
Fan (assuming half speed)	1.25	2	2.5
Lights (AAA battery powered in general)	0.05	3	0.5
Exterior	0.1	2.5	0.3
Alarms	0.25	24	6.0
Stereo (use primarily lithium charged)	1	1	1.0
Misc	1	3	3.0
Water pump	?		1.0
Total			42.6

Maximum load is probably mid winter when the yield is lowest on the panels as well so you need to decide when you are going to be using.  Total up and you have your needs.  Add battery capacity to determine when you run into issues.

In my case I have 200 AMP in batteries.  Could draw down to 50% (AGM batteries).   How long could I go in November (I'm in San Francisco)?

Total AMP in BATTERIES		200
SAFE AMPS AMOUNT		100
Day	Starting Available	AMPS used	Solar added	Ending AMP
1	100	43	30	87
2	87	43	30	74
3	74	43	30	61
4	61	43	30	48
5	48	43	30	35
6	35	43	30	22
7	22	43	30	9
8	9	43	30	-4
9	-4	43	30	-17
10	-17	43	30	-30
11	-30	43	30	-43
12	-43	43	30	-56

As the chart indicates... without any other adjustment (TV charge, generator, more judicious use), I can go about a week totally off grid and still have remaining capacity.  I could TV charge on day 6 (or use generator to increase available AMPs) and be able to go longer.  In my case, I planned on moving on about once every six days with the TV charge boosting my AMPS for longer boon docking.


Hopefully this is clear.   Again, others can chime in on power usage of LG trailers.  

Nomad

mash2 - that second is real useful, could you review your setup here for reference.

jkjenn

@mash2- you have inspired me. I have been on a hunt to track down power usage of some of the newer products.


Here is what I found:

mash2

Pxlated.  

SOLAR YIELD:
On the solar yield side, I used a solar calculator assuming the various wattages on the 7th of each month.   Developed a general ratio comparing the other months to August 7 (no significance to the month or day, just easier to calculate on the calculator if I accepted some standard inputs from the calculator).

I actually calculated yield at each location at each wattage for each time of year.  The table was a bit unwieldy so I figured I'd just use a ratio to translate to other months.

Thus, if you want to get an idea of yield on October 7 in San Francisco, for a 100 watt system, start with August number (47 AMP) and use the September factor for to convert yield to an expected September yield   (47 AMP X 80%).  So in San Francisco on September 7 you should be able to count on about 38 amps (no rain, flat panels, in the sun, and at sea level).

The number for my usage vary a bit because I have a different panel configuration (136 core watts -- with a plug in 68 watts that I did not consider in these numbers.  


DRAWS ON SYSTEM
The daily use for appliances overall is the rated amperage for the appliance (these are hourly amps)  times the number of hours per day that the appliance will be in use.  The use is the amount of time that the appliance is on.   So for instance, if your refrigerator is actually running for 4 hours throughout the day (with the various on and off cycles just count the time that the appliance is on.  For the refrig, I just spent a few hours keeping track of when the ref rig was actually running the compressor.  This depends on the appliance and the time of the year (more furnace in colder weather, for example).   I just estimated for each appliance and then add them up.


These are the draws on the battery.  The second table translates this draw to the amount of AMPS remaining in the batteries.  In my case, starting with 200AMPs of power, I feel I can drain down to about 50% before I have significant battery issues (I try to get no lower than 75% in reality).   I have a 40 AMP drain daily and on a normal day in November, I can usually count on about 30 AMP's of solar charging making it back to the battery.  In other words, in November with my 126 watt panels, I can count drawing down 10 net amps per day (40 amps usage - 30 amps solar added).  

My numbers didn't match exactly to the first set of number that I presented was because my system doesn't match any that I presented (standard systems available in the  market seemed like a better benchmark for people trying to gauge solar).

As my example showed, for me with 136 watts of solar in the San Francisco Area (I used 37.7 latitude, actual latitude in SF), I can make about a week without compromising my batteries.  Again, this is a rough gauge.  I have a northern breeze fan (not very efficient, but I using run on far less than 1/2 speed.   In reality, since I was calculating for november, the heater would probably be on more than 2 hours in the evening - but not a lot more.   I added a miscellaneous category to account for solar charger use (I have an MPPT controller that uses about .25 AMP as I recall).  



Jenn, I would assume that even in LP gas mode, there is some electrical use for the 3 way....don't know them that well, but they do require a fan to circulate...1 AMP seems high to me, but if it is an Atwood, their appliance don't seem particularly efficient.  

 If the batteries are battery drive, I would accept the number, but if they use battery power, there is some drain (admittedly minor).  

On the furnace, if it is a 3010, the manual indices that DC power requirements are about 1 amp per hour.  

Two-way frog's are definitely more efficient when operating on LP gas (but true electrical hogs on DC current only where the rating appears to be 11 AMP's).  At that rate, they would suck up all the solar when in DC mode.  I understand why people complain of battery problems with 3-way frogs.  For those of you out there ...if the frig is permanently operating, the thing is probably consuming the entire solar gain in the autumn when on DC.  

I would generally buy Jenn's number (although if I had to guess, I would put it closer to 30 AMPS with normal use.





Pxlated, sorry for the long winded explanation but I hope this helps.  If this isn't clear as mud, just ask me any direct question and I'll provide another long winded  indirect answer.

For what it is worth, while I can't match your extended travels, I did spend a couple of months on the road last year and my performance was pretty close to the numbers presented here.  

mash2

Didn't answer some of part 2 setup.  A combination of manuals, measuring time operating (vs on) and some slop allowance because the systems are never as efficient as advertised.  Again, these are from a DM T@B and I also scoured the Yahoo group for measurements by others with meters (I have a multimeter and taken a few reading to augment, but what I really know about electricity could fit on one piece of paper-- double spaced and 24 point text.

jkjenn

How do you about measuring yourself? Start with the voltmeter (12v) with nothing on and then get subtract the reading from the original reading?

mash2

Jenn, in general that is the approach.  A full audit would give you a more accurate measure of the system and individual components.  There are several articles on full audit procedures for RV systems (measure base load, moving circuit by circuit through the system measuring each component with a multimeter).  I wanted a good sense of need for my system, so I "cheated" with ratings.  IN fairness, I did meter readings on ref rig and fan (my two biggest users of electricity) taking meter readings to confirm my guesses.  

If you want to conduct a detailed audit of your system, there are some good articles on it on the web.  My goal was to give those without a background a better sense of the electrical needs for a solar system, not a full outline of individual requirements.  I think there is a lot of confusion about how much solar is enough; a rough sense of need and sizes of panels to meet their needs.  

A separate discussion on the needs for individual appliances would help people develop specific information for sizing.

II had two goals in my entry.
   1.   How do solar panel sizes translate to capacity in your electrical system.
   2.   How do specific appliances impact your needs.

In my case, there were a few things that accounted for my real sizing need.   The 2 way frig (I could switch to 3-way to extend boon docking but then need I'd need to work around the DC draws of the 3-way).  Heating requirements for the propane system in m T@B (not nearly as efficient as the Alde system) and fan (I could swap out to a more efficient 7350 fantastic vent).  

If your numbers are correct, the TV and radio use is potentially significant.  Watching a movie and listening to the radio for a couple of hours would add up to 16 amps of power needs, something new users should consider when trying to determine power needs for their systems.  

I also use these estimates to help me when I'm out boon docking.

Again, others can chime in on their experiences or specific numbers.  Maybe I'll drag out the multimeter to make some specific estimates, but my goal was a bit more broad in nature.  I probably tossed in 10 AMPS of need in my initial sizing exercise to ensure that I had enough power to cover contingencies (the misc category and I had already swapped out an inefficient CO alarm from the original DM system and use a lithium powered speaker system on my IPOD/IPAD to limit radio draw as well as AAA background lighting to augment the LED replacement lights in the T@B).  

jkjenn

Thanks!

mash2

Jenn.  According to the 3163 manual, the 3-way refrigerator draws .34 amps when in propane mode (.1 for the electronic ignition and .24 for fan).  Unfortunately when in DC mode it draws nearly 12 amps, the cause of so many drained batteries in the discussions on this and other forums.  For newbes watch out for your batteries when using 3 way in DC mode.

jkjenn

mash2 said:

Jenn.  According to the 3163 manual, the 3-way refrigerator draws .34 amps when in propane mode (.1 for the electronic ignition and .24 for fan).  Unfortunately when in DC mode it draws nearly 12 amps, the cause of so many drained batteries in the discussions on this and other forums.  For newbes watch out for your batteries when using 3 way in DC mode.

Thanks!

I noticed that the manual actually calls out the significant DC power draw.

mash2

Only for DC operation.  It's very frugal in propane mode.

jkjenn

mash2 said:

Only for DC operation.  It's very frugal in propane mode.

Agreed.

I created a simple Excel tool for calculating my usage if anyone wants to use it you can download it here.

jcfaber1

Another factor to consider is the angle of the panel to the sun by geographic location and time of year in order to optimize the performance of the panel.  I created the attached table so that I  would know how to set it up. I use a Ridgid digital level on my phone for the frame that I made to support my home made 200watt flexible Renogy suitcase.  I hope this helps.

John

gooselady

Gosh, my head hurts.......  :-)

Nomad

gooselady - Ain't that the truth!  Gotta be a solar nerd to get thru this thread. Glad we have some but it certainly ain't me ;-)

mash2

Gooselady.  Just squint at the stuff.  I was trying to show that 100 to 120 watts will meet the needs of most of us.  If you're going camping in late spring, summer or early fall, a 100-120 system will probably give you enough power to not worry about having an AC hookup (unless you want air conditioning).  For most folks, 200 watts is probably overkill.  Just think about how you want to use your trailer and match it to wattage.  Basic stuff is 100 - 120 watts; full out use is probably up to 200 watts.  As to angles for the panel, mine are attached permanently to the T@B so I couldn't do much with the solar angle if I wanted to.  But I don't have any setup time so there is no setup time.  Just stop, angle for the where the sun path is (the T@B's so light, I can rotate the whole vehicle), and get on with life.

But yeah, there are some of us who are solar nerds...forgive us.

Verna

And some of us who don't want to run out of power when their favorite college basketball team is playing

jkjenn

Verna said:

And some of us who don't want to run out of power when their favorite college basketball team is playing

Or college football

Nomad

Roller Derby for me - Or beach Volleyball :-)

mash2

robot wars for me.

Nomad

I could see "robot wars" - There was a "B" movie I saw featuring big robots during it out. Have no idea what it was named though.

mash2

Current incarnation is Battlebots brought back by ABC this year.  

jkjenn

In all seriousness, having a good grip on what you have in terms if battery and charge capacity in relationship to what you, "spend" reduces the stress when dry camping. I think I have a decent battery budget planned for my trip, next month.

Nomad

You're trying to get us back on track? ok, maybe.

jcfaber1

Hey I have always disliked coming up short.  I recently purchased an ARB and I use a CPAP at night so that like 200 plus watts!  
John