RV Solar Design Requested

E350 4x4E350 4x4 Registered Users Posts: 8
OK folks, your design assistance would be appreciated.

I have a Ford E350 extended van with a 20"-tall fiberglass top on which, five years ago, I mounted four PV solar panels. My previous solar charge controller failed and, without naming names, I wasn’t all that impressed with it anyway. So, I now have the opportunity to re-think and re-design my PV solar system.

My two primary electric loads are as follows:

1. Engel Combi Fridge Freezer combo
Model: MT60
Volume: 34 Qt Fridge / 26.5 Qt Freezer
Power Source: 12V DC / 24V DC / 110V AC
Power Consumption: Variable from 0.7 - 2.8 Amps (12V DC)

Daily Amp Hr Usage 24x4= 96 Amps per day
So aren’t watts 12x4= 48 W
Engel: Daily Watt Usage 24x 48= 1152W

http://www.engel-usa.com/index.php?page=shop.product_details&flypage=vmj_genx.tpl&product_id=26&category_id=1&option=com_virtuemart&Itemid=59

Note: I have had the Engel for 5 years. My actual experience, regardless of what the manual says regarding duty cycle or amp usage, is that my BMV 600S battery monitor says that it draws 4 amps continually around the clock at least when outside temperature is 100F.

2. Webasto Dual Top diesel furnace/hot water heater
Model: RHA-100
Power Source: 12V DC; operating range 10.5 to 15V DC
Current Input at 12 V DC: 0.5 to 7 A
Power Consumption in use: 15 to 65 W
Power Consumption standby: >1 W

Daily Amp Hr Usage: 6x7= 42 Amps/ day
Daily Watt Usage
24x(15+65/2=40)x 24= 960 W

Similar to:
http://www.webasto-outdoors.com/heating/dual-top/dual-top-evo-6.html


Battery: I have a 250 Amp Hour sealed AGM house battery (electrically isolated fr the starting batteries)
Universal Power Group
UB-8D AGM 9925089 250aH 12V DC
20.5" x 10.5" x 10" 167 lbs.


PV Solar Panels:

I have four BP 380J panels flat mounted on the roof (and can fit and would like to add a fifth)
BP 380
Rated power (Pmax) 80 W
Power tolerance ± 5%
Nominal voltage 12 V
Maximum power (Pmax)3 80 W
Voltage at Pmax (Vmp) 17.6 V
Current at Pmax (Imp) 4.5 A
Warranted minimum Pmax 76 W
Short-circuit current (Isc) 4.8 A
Open-circuit voltage (Voc) 22.1 V
Temperature coefficient of Isc (0.065±0.015)%/ °C
Temperature coefficient of Voc -(80±10)mV/°C
Temperature coefficient of power -(0.5±0.05)%/ °C
NOCT (Air 20°C; Sun 0.8kW/m2; wind 1m/s) 47±2°C
Maximum series fuse rating 20 A
Maximum system voltage 600 V


Additional facts:

My home base is Sacramento, CA. My usage is usually around Latitude 38.

The Engel Combi Fridge Freezer runs the hardest in the Summers camping, etc. when the outside temperatures are 90 to 100F during the day. Again, my actual experience, regardless of what the manual says regarding duty cycle or amp usage, is that my BMV 600S battery monitor says that it draws 4 amps continually around the clock at least when outside temperature is 100F.

The Webasto Dual Top diesel furnace runs the hardest in the Winter (I use the sportsmobile as an rv every weekend at Kirkwood Ski Resort where the outside temperatures can run from -17F to +50F.


My Load calculations:

You shouldn’t have to do my homework. I should have to do that, but could you check it? I am not a numbers person and I probably screwed up something below, or my assumptions are wrong for my flat panel mounted panels for my latitude, or I didn’t even see the elephant in the room which is obvious to you. Accordingly, your correction of my homework as well as any additional comments and suggestions would be greatly appreciated.

1. Assuming I will run both the Engel and the Webasto during the Winter:

Load: 96 A (Engel) + 42 A (Webasto) = 138 AHr/day

Four PV Panels (what I have now):
Voltage at Pmax (Vmp) 17.6 V
Current at Pmax (Imp) 4.5 A
4.5 A x 4 = 18 A derate 50% = 9 A
9 A x 10 hours of effective sunlight/day = 90 AHr/ day

This leaves a deficit of 48 AHr per day (90-138=48 AHr). Thus, 4 panels will not be able to replenish the usage via the PV array each day. Accordingly, running a generator will be required.

Five PV Panels (max that can fit on the van roof):_
4.5 A x 5 = 22.5 A derate 50% = 11.25 A
11.25 A x 10 hours of effective sunlight/day = 112.5 AHr/ day

This leaves a deficit of 25.5 AHr per day (112.5-138=25.5 AHr). Thus, even 5 panels will not be able to replenish the usage via the PV array each day. Accordingly, running a generator will be required.

2. Assuming I will run only the Engel in the Summer:

Load: 96 A (Engel) alone = 96 A/day

Four PV Panels (what I have now):
4.5 A x 4 = 18 A derate 50% = 9 A/Hr
9 A x 10 hours of effective sunlight/day = 90 AHr/day

This leaves a deficit of 6 AHr per day (90-96=6 AHr). Thus, 4 panels would not replenish the usage via the PV array each day. Accordingly, running a generator will be required.

Five PV Panels (max that can fit on the van roof):
4.5 A x 5 = 22.5 A derate 50% = 11.25 A/Hr
11.25 A x 10 hours of effective sunlight/day = 112.5 AHr/day

5 panels would replenish the usage via the PV array each day. Accordingly, running a generator should not be required


Questions:

Assuming that money is no object (which it is not but I want purely electrical advice) what is the best solar charge controller for my needs?
Would an MPPT charger actually (rather than theoretically) increase my charging amps per day?
Should I wire my panels in series or parallel?
(I previously wired them in series but I can easily re-wire them in parallel.)
In the event that I have killed my battery because it is five years old and I have undercharged it and over-discharged it, what would you recommend. I can fit golf batteries in parallel or in series.
Finally, please correct my abbreviations/nomenclature.
Do you have any other suggestions?

Thanks. Your time and knowledge would be greatly appreciated.

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    welcome to the forum.

    i first off have to correct you on your units here some for amps is a measure of current and going for a period of time referenced to one hour would be amp hours. same with watts and watt hours. so 4 amps for 24hrs is 96 amp hours. at 12v this is 4a x 12v for 48w and over 24hrs it's 1152 watt hours.

    your big problem is the flatness of the pvs in the winter. the pvs will be off angled by your latitude, 38 degrees, plus the winter offset angle of 23.5 degrees for a total of 61.5 degrees. at around 45 degrees only half of the solar insolation reaches the pvs and you're beyond that. my guess would be about 75% lost before it even gets started. after that subtract for stc figures at about 77% and you have a dilemma.the 5th pv wouldn't bring this in line to make it operational for the loads you have in mind.

    mppt controllers do help a tad, but you will be giving it little to work with in the first place with pvs flat on a roof. it may be worthwhile to put a separate remote pv and a separate controller to supplement your system rather than mount another pv on the roof. the remote pv could be angled and placed into the sun while your vehicle is parked in the shade. in winter park in the sun. maybe get 2 of the higher wattage pvs out there in the 200w+ area and use a small mppt controller like the rougue, that's good to about 30a if memory serves. this would make a big difference. worst case would be to drag out a small generator to supplement the charge.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: RV Solar Design Requested
    E350 4x4 wrote: »
    1. Engel Combi Fridge Freezer combo
    Model: MT60
    Volume: 34 Qt Fridge / 26.5 Qt Freezer
    Power Source: 12V DC / 24V DC / 110V AC
    Power Consumption: Variable from 0.7 - 2.8 Amps (12V DC)

    Daily Amp Hr Usage 24x4= 96 Amps per day
    So aren’t watts 12x4= 48 W
    Engel: Daily Watt Usage 24x 48= 1152W

    1152 watthours is huge for a 2 cubic ft fridge. Have you allowed adequate ventilation for the condenser?
    E350 4x4 wrote: »
    2. Webasto Dual Top diesel furnace/hot water heater
    Current Input at 12 V DC: 0.5 to 7 A
    Power Consumption in use: 15 to 65 W

    12 volts x 7 amps is not 65 watts
    E350 4x4 wrote: »
    9 A x 10 hours of effective sunlight/day = 90 AHr/ day
    <snip>
    11.25 A x 10 hours of effective sunlight/day = 112.5 AHr/ day
    <snip>
    9 A x 10 hours of effective sunlight/day = 90 AHr/day
    <snip>
    11.25 A x 10 hours of effective sunlight/day = 112.5 AHr/day

    Even with a tracker you won't get that many hours of effective sunlight each day.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Neil: Thank you for your helpful suggestions. Are there higher wattage panels out there which could make this work? I would be willing to sell the BP 380J's and buy different panels if there will be a significant improvement. However, when I looked at wattage per square inch five years ago, all the panels were about the same. But if there will be a significant improvement, I could upgrade or plan and prepare to upgrade.

    My Thule tracks are about 48" apart, so the BP 380J (48" L) mounted sideways fit perfectly. I don't know about dimensions of newer panels, they all seem bigger designed for larger residential roofs. I am thinking about design/building a way to angle my panels when parked, but it sounds like I will still not have enough energy even if angled.

    I will look at the rogue charger. I assume that your suggestions will depend on the type of panels I plan to buy in the future. If you do have a recommendation for a type of higher wattage pv panel, could you recommend a charger to go with it? That way I could buy the charger now, and replace the panels in the future? I know I need a charger now, because I don't have one.

    vtmaps: Thank you for your reply and your criticism. Any additional recommended solutions? I blew the dust out of the compressor with compressed air a few months ago, but I will check it again. The 3.5 to 4 amp draw is from the BMV 600S battery monitor mounted on the battery, so it is taking into account line loss in addition to fridge freezer use. My battery runs are 4.0 welding cable about 6 feet long.

    Again, thank you both for your time and knowledge. More would be appreciated.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    i should also mention you don't have enough battery capacity for the loads as 50% of battery capacity is usable to keep battery life making 125ah x 12v = 1500wh available. finding the physical room for more batteries is a problem you have to work out or get used to driving the battery you have into the ground. i'm surprised that battery went for 5yrs.

    maybe, on another thought, with higher pv wattages you could load shift while charging, but you'd need excess pv to do that. i can't comment on what fits on your vehicle, but if size is problematic then going to monocrystalline would shrink the size a bit. you can look over some pvs our host has available to see if any are good for your roof.
    http://www.solar-electric.com/hiposopa.html

    i still think having a pv or 2 remote would be good to supplement what you have. these could be positioned in the sun at the proper angle while you sit in the shade. when done fold them up and put inside. a means of wiring that is polarity protected on an extension cord that won't get confused with any ac connections would need to be incorporated that can be unplugged and rolled up to be placed inside with the pvs when done.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Niel: (Sorry for the earlier misspelling.) I may in fact have driven that battery into the ground. At full charge it holds about 12.6v. What do you recommend for batteries? Five years ago, as my first welding project I welded an under the side barn doors battery mount which attaches to the vehicle frame. I have room for more or different batteries. What do you recommend?
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    well i'll leave the battery choices up to you and i would suppose you may like to stay with the agm type so in this link you can see choices from upg and concorde.
    http://www.solar-electric.com/batteries.html
    note that mk/deka also has agms as do other battery manufacturers, but they aren't necessarily better than the concorde and are higher priced. upg is inferior to concorde and won't generally last as long.
    my guess may be 2 of the 4d size batteries wired in parallel. this will give about 200ah of usable current and 2400wh of load capability over a 24hr period.

    you will need to be sure to use very heavy cables to interwire the batteries and be sure the interconnects are equal in length to keep the charge/discharge equal or run risk of over-taxing one of the batteries. this link goes into paralleling batteries and you can use method #2 or #3 with method #2 more common with just 2 batteries. note that the connections for loads or charging always tap opposite batteries to help distribute currents evenly.
    http://www.smartgauge.co.uk/batt_con.html

    i guess i better note that at a minimum you would want to see at least a 5% rate of charge into any battery. for 400ah of batteries the 2 4d sizes would give needs at least 20a. higher currents would be even better and around 10% is typical for many batteries noting that agm batteries like more than that. this means that above all losses and deratings from pvs this kind of current should be realized to the batteries. if you go with another one of a similar 250ah then go even higher in the pv power noting that some loads may be run via the excess power and thus be able to stretch the battery to a more acceptable overall power consumption over 24hrs.

    as you said, finding room for more pvs is problematic when you are mobile.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Niel: Dude! That smartgauge article was fantastic. I am not wedded to AGM. In fact, I wonder if I would get a longer life out of an unsealed battery bank because I could equalize them. I think I can fit 5-6 Trojan golf cart batteries sideways if I remember my design correctly. I don't remember the model of the Trojan. But when I drop the battery tray I will re-measure how many I can fit and then explore the batteries at WindSun on the link you provided.

    While we are talking about batteries. My fancy pants expensive inerter/charger broke. I am now over having a combined inverter charger and want a separate deep cycle charger and a separate 1500-1800w pure sinewave inverter. Any suggestions on either?

    Also, did you have a recommendation (maybe not on size but on make or model) of higher wattage pv panel?

    Thanks, again.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    the chargers are available on the naws website as well.
    http://www.solar-electric.com/bach2.html

    the choices for pvs are many, but would depend if the physical size of the pvs are acceptable to you otherwise watts are watts noting that they are all rated by stc. only other differences may be warranty or how long in business and both of those are quite similar for all excepting the chinese made pvs as they jumped into the market later. a pv rated at 200w with a price tag of $255 will output the same power for a 200w pv at a price tag of $321. these higher wattage pvs do have higher numbers of cells and are usually not compatible with pwm controller useages unless the cell number of 36 cells for 12v pv and 12v battery and 72 cells for 24v pv and corresponding 24v battery bank is present. the odd voltages will mandate an mppt controller to cut the losses presented by the higher voltages these pvs produce.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Interesting chargers. I am out of pocket for the next few hours and will look into them more later. I definitely want a 3-stage plus equalization and a remote monitor would be nice to see what is going on and to commence equalization.
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: RV Solar Design Requested

    There are similarities in our set up. I am using a Weaco refrigerator with a similar current draw and an Espar diesel heater. There is a high voltage 185W solar panel attached to the top of the teardrop feeding a Morningstar MPPT.

    Attachment not found.

    Attachment not found.

    The refrigerator is wrapped in a layer of the bubble reflector insulation which does help and sits inside the TV when traveling fed by the alternator. I have a 150 AH Lifeline AGM monitored with a Victron battery monitor. I also took along a 144W Unisolar panel that plugs into a STECA controller and it stayed in the tongue box on our month long trip. Even in Big Basin Redwoods we never got below 70% SOC in part because even in shade you get usable current. The other part of the equation however is conservation and our tear has all LED lights and while we have a flat screen TV/DVD and Sirius fed stereo current usage is and can be very low. If all else fails the battery can be fed from the TV with jumper cables (made weld cable:)). We spend 7 days off grid in our month long trip.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Shadowcatcher: Thank you for your reply. 1. What Morningstar are you using; 2. Do you recommend wiring multiple panels in series or parallel? 3. What Steca are you using (I am entirely unfamiliar with them); 4. I will admit some real stupidity here, based on your comment, and the fact that my Engel Fridge Freezer is actually inside my van when I am driving there is no reason why I cannot use a ship to shore or other selection switch to use starting batteries to run it when I am driving and use the house battery when I am parked. I will need to either hook up my Victron BMV 600S to my starting batteries or some other monitor maybe the smartgauge referenced in the link posted by Niel otherwise I know I will pull in to sleep and leave the fridge connected to the starting batteries and then not be able to start the next morning! Please keep your thoughts coming!
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: RV Solar Design Requested
    E350 4x4 wrote: »
    Shadowcatcher: Thank you for your reply. 1. What Morningstar are you using; 2. Do you recommend wiring multiple panels in series or parallel? 3. What Steca are you using (I am entirely unfamiliar with them); 4. I will admit some real stupidity here, based on your comment, and the fact that my Engel Fridge Freezer is actually inside my van when I am driving there is no reason why I cannot use a ship to shore or other selection switch to use starting batteries to run it when I am driving and use the house battery when I am parked. I will need to either hook up my Victron BMV 600S to my starting batteries or some other monitor maybe the smartgauge referenced in the link posted by Niel otherwise I know I will pull in to sleep and leave the fridge connected to the starting batteries and then not be able to start the next morning! Please keep your thoughts coming!

    I was a little puzzled by Shadowcatcher's reference to (I thought) putting the bubble wrap from around the freezer into the TV (which was just a flatscreen!) while traveling. Then I realized he meant Tow Vehicle. :-)
    SMA SB 3000, old BP panels.
  • CATravelerCATraveler Solar Expert Posts: 98 ✭✭✭✭
    Re: RV Solar Design Requested

    Certainly today's larger panels cost less per watt than smaller panels. But since you have existing panels there may not be any reason to change. For my future panels it's basically a no brainer. While I won't save due to the higher MPPT cost I'll have a "better" system.

    My take on MPPT is that you could get about a 10% improvement. The mfg claims of higher seem to be based on a short duration event like a cloud edge effect.

    12V panels in parallel might produce little or no power to the batteries while a serial connection would have a much higher voltage into the CC for a given lower light or shadow condition. Assuming your panels have bypass diodes then that could be beneficial for a serial connection since RVs are more prone to be in various degrees of shade from rooftop equipment to trees etc.

    Partial shading on a 4x9 panel could bypass half of the panel for example but still produce full power from the other half. Serial and MPPT controllers can take advantage of that while a parallel connection would lose the entire panel.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    catraveler,
    i agree with your statement of about 10% current gained by mppt on average, but can be dependent on the design of the system too for somebody using pvs with for example a vmp of 16.5v on a 12v battery in a high ambient temp area can see lower results. it can also be bumped up some, but to count on 30% or 40% all of the time would be wrong and those would be rare occurrences.

    i don't think he should get rid of his original pvs either as i advocated the addition of high wattage remote pvs to supplement what he already has.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Guys: Five years ago, when I did my research on panels, I determined that the only difference between lower wattage panels and higher wattage panels was the square footage of the panel. The watts per inch were nearly identical across all sizes and makes of panels.

    Is this still the same?

    Or have there been actual efficiency improvements in panels such that a new technology is actually producing more watts per one inch/foot/meter?
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    small efficiency improvements have been realized and won't be a vast difference for w per sq in or ft or whatever, but it is a moot point if the newer pvs get remotely ground mounted as a separate system to help charge his batteries. this would not be a permanent install to the ground and there are mounts (made for roofs with no holes made into the roof and i don't know if any of these are available from naws or not, but standard ground mounts can be adapted or modified) that with sand bags or something similar that can be placed on the ground you select aiming south and are adjustable too in some cases for the elevation angles. this is a better solution to me than changing out all of the pvs he has and then still not having enough while forced to park in the sun to collect the power.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: RV Solar Design Requested
    E350 4x4 wrote: »
    Guys: Five years ago, when I did my research on panels, I determined that the only difference between lower wattage panels and higher wattage panels was the square footage of the panel. The watts per inch were nearly identical across all sizes and makes of panels.

    Is this still the same?

    Or have there been actual efficiency improvements in panels such that a new technology is actually producing more watts per one inch/foot/meter?

    What I have heard (mostly in this forum) is that the market for higher watt, higher voltage panels for use with grid-tie systems gives them a production volume advantage over smaller panels, allowing for a lower price per watt even thought the technology used may not be any different. The market for smaller panels is, well, smaller. :-)
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested
    inetdog wrote: »
    What I have heard (mostly in this forum) is that the market for higher watt, higher voltage panels for use with grid-tie systems gives them a production volume advantage over smaller panels, allowing for a lower price per watt even thought the technology used may not be any different. The market for smaller panels is, well, smaller. :-)

    exactly so. now if e350 4x4 wants to change out the pvs on the roof then he can do so a few 200w+ pvs will certainly outperform what he has on the roof now, but laying flat will derate them just as badly as the present pvs and then what does he do with the present ones?

    now he has 4 80w pvs for 320w and after derating for efficiency and derating for being off angled he's very lucky to see 200w in winter. even one external ground mounted pv at 200w+ would deliver more than what he has on the roof. granted it's a pain to drag it out and set it up and reverse that before leaving, but it affords some flexibility as well as more power. of course the drawback is it will need another charge controller.
  • E350 4x4E350 4x4 Registered Users Posts: 8
    Re: RV Solar Design Requested

    Hey guys, could you suggest one or two makes/models of high wattage pvs for temporary angled ground set up? I have some thoughts in that regard.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: RV Solar Design Requested

    that won't be all that critical as you could just get the cheapest per watt. if you want it to be a tad smaller in size and weight you can opt for monocrystalline types (tad more $/w). these should be easier to store as well as set up and take down than a slightly bigger one. even if you got one under 200w you will certainly be improving on what you have.

    an example may be this 190w mono for $276.65 at this writing,
    http://www.solar-electric.com/as190wamosom.html
    it's 62.2" x 31.81" and 34.1lbs.

    now for about $12 more you can get this 240w polycrystalline pv,
    http://www.solar-electric.com/sosu240wamu.html
    it's 65.94" x 39.41" and 46.7 lbs.

    it's your money and you would be the one setting it up and tearing it down, in addition to finding room to store it inside.
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