Advice on my system

System

Hello all! I'm in need of some guidance/advice on the system I recently installed on my RV. I have 4-Kyocera 205 watt panels (7.71a @ 26.6v)

4- 12v Concorde 258 AH SunXtender AGMs

1- TS-MPPT-60 Tri Star charge controller w/remote meter
(all purchased from NAWS )

and a Magnum MS 2812 inverter.

4/0 inverter cables (5'), and #2 welding cable from roof to charge controller & batteries (11' +5')

I do not have the RTS for the controller (I actually thought I did, but it was for the inverter).

I live in central Indiana, and it has been warm & sunny (extremely) the past couple weeks. I have been staying in the RV as a "test run" because I'll be living in it full-time.

I do not have the loads I'd used to figure when I started, but I live alone, have a 7 cu ft freezer with the t-stat conversion to use as a 'fridge (which the Kill-a-watt shows running right at 100 watts), a 26" flatscreen, a laptop and wireless router, 4 fluorescent (13w or smaller) and a 12vdc water pump. I'm good about not turning things on/leaving them on, and if the TV is on I seldom need to use any lights. The 'fridge running is a given, and I watch TV and get online of an evening for a few hours, shower once a day, and use lighting very little. Appliances are plugged into surge protectors which are shut-off when not in use to prevent phantom loads (except 'fridge).

If I recall, I figured I should be able to go 5 days with little sun before reaching the 50% mark on DOD. I feel I'm not getting the full benefit of the panels considering how clear the skies have been. After initial installation of the panels, the meter showed an output of 31v.

It seems I "lose ground" voltage wise from the battery bank whereas I feel as light as my loads are, I should be able to keep-up, perhaps I'm expecting too much?

I set the dip switches (#4-5-6/off-on-on) or the designated AGM setting per charge controller instructions. Switch #7 is off (for manual equalization)

I may not have provided enough information for any suggestions, and I'm not overly technically-inclined regarding electronics, so I will try to provide any additional info I can.

Thanks in advance for any help, advice, or suggestions anyone might have.

icarus

Re: Advice on my system

It really is a series of pretty simple equations. First, you must get an accurate load profile. Guessing just leads to more guessing. Either log everything by hand over a number of days/weeks or killawatt everything, or monitor your amps in/amps out with something like a trimetric.


As for your Pv capacity. Assuming that your panels are somewhat oriented correctly (and that is a big if) if they are mounted on an RV, my rule of thumb is as follows.

Take the name plate rating of the PV, divided by two to account for all cumulative system loses/efficiencies, then multiply that number by 4 to represent the average hours of "good sun one can expect. People often think it should be more, but in most cases 4 works out to be a pretty good average.

So in your case, 820/2=410*4=1640 watt/hours/day. That would be the starting point as to how much you can sort of count on day in/day out. (That said, in an RV set up with less than optimal panel orientation I would predict less.)

So that 1.6 kwh/day, let's look at your loads,

Fridge, 100 watts, duty cycle 50%== 1200 wh
TV 200 watts, duty cycle 4 hours 800 wh
Lap top/router ect 75 watts 2 hours 150 wh
Water pumping WAG 50 wh
Lighting 15 watts*4*2 120 wh

So that totals~ 2300 wh or about 1.5 times as much as you are able to produce on an ideal day. My guess is that you are chronically undercharging your batteries, leading to an early death. I would really recommend getting a accurate count on your loads.

Good luck,

Tony

Ps Also note that PV production will drop off significantly in hot temperatures. If your panels are mounted on the roof of the RV with little or no air space under them, you could be seeing panel temps that are very high, perhaps near 180f maybe. This will drop production off a hell of a lot.

Cariboocoot

Re: Advice on my system

Did I read this right? You're using #2 from the panels to the charge controller? Why?
With an MPPT controller you should have those four panels wired for higher array Voltage and make use of the down-converting ability of the controller. Smaller array-to-controller wire and less line loss (probably not a big consideration given the short distance).

Another issue may be how those four batteries are paralleled. Check the diagrams at SmartGauge against your configuration: http://www.smartgauge.co.uk/batt_con.html

It is highly doubtful that your panels are ever at ideal angle to the sun. This could be losing you a lot of potential 'harvest'.

System2

Re: Advice on my system

Hi Tony, and thanks for the reply! Let me add my system has only been up & running for a bout a month. During the past couple weeks, I have been plugging-in the charger in the Magnum inverter daily to charge the batteries, this is the 1st time that hasn't been done (since Friday) as a test-run, so this is the 1st time the batteries have been even close to the 60% charge point, so no worries about damaging them.....which I want to keep that way. I will have a gen for that very reason before hitting the road.

I did figure my loads prior to selecting components (as mentioned I just don't have those figures in front of me..if I still have them at all), and I actually estimated them on the "heavy" side as not to cut myself short on capacity.

I have a deck on the entire roof of the bus, and park facing north, so the panels run long-ways east to west, with no shadowing whatsoever. The panels are spaced 1" off the deck (which is composite material) for air spacing underneath. We are back into temps approaching the 90* mark.

Thanks again for the help.....

System2

Re: Advice on my system

Hi Marc, I used #2 because that's what the charts I saw suggested (@12v of course), and I prefer to be over-sized instead of under, and it leaves room for expansion later-on.

My batteries are wired as per example #4 on the link you provided...I've been a lurker here for a while

I'm not trying to claim I have perfect alignment on the panels, and understand there are a fair amount of "loss" throughout the system, that I realize. My panels will tilt (manually) from either end, but because of health issues it's not the easiest thing for me to do.

Having no experience with solar, I just had nothing to base any expectations on, which is what's behind my questions.

Thanks

icarus

Re: Advice on my system

" so this is the 1st time the batteries have been even close to the 60% charge point, so no worries about damaging "

The issue of damaging them is not eh 60% soc, but rather the failure to bring them back to full charge quickly and regularly.

I am not very familiar with AGMs, but I suggest that you read and understand the following links: http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Tony

Cariboocoot

Re: Advice on my system

I'm afraid Tony's right about the chronic under-charging. Even in a best-case scenario you don't have enough panel to properly recharge 1032 Amp/hrs of battery. But you are nearly at the limit for the charge controller (not including inefficiency losses).

Try disconnecting 1/2 the batteries and see how well the panels can keep up two instead of four.
This will of course reduce your available power capacity by 50%, but it might just save those expensive batteries.

#2 is over-kill for the panels, even in a parallel configuration. Less than 8 Amps each, * 4 = 32 Amps. 8 gauge would handle that with no problem, and be easier to work with. But if you've already got the #2 installed, why mess with it?

You have got fuses on each panel, haven't you?

ronpozoromo

Re: Advice on my system

I know this is an older thread, but this sounds much like the system I'm designing for my off grid cabin. My question is about the watt hours used on the chest freezer converted to a refrigerator. 1200 watt hrs per day sounds high compared with what I've read on other sites & posts. People say they're using 100-400 watt hours per day. If this is as efficient as it gets, I'll have to go with a propane frig!

Cariboocoot

Re: Advice on my system

There are a lot of variables in the energy consumption of any refrigeration equipment. Not the least of which are ambient temperature and how often you open the door. Strangely, size doesn't have as much affect as you might think: smaller units have less thermal mass and actually consumer more energy per cubic foot of capacity. And of course some people may not be calculating correctly. :roll:

1.2 kW hours per day is about all my standard 'frige uses, +/- up to 20%. A converted chest freezer should use less. But not necessarily.

Sometimes a propane unit is a better option, especially if it is an "occasional use" location. The extra expense of putting in enough solar to run refrigeration (as opposed to a few lights) can buy a lot of propane (although they cost more to begin with).

Search this forum for "refrigeration", et cetera and you'll find quite a bit of discussion about the pros and cons of different solutions.