Help with finding panels with proper dimensions or other ideas?

sunnysidesunnyside Registered Users Posts: 11
Great forum, I have been lurking for a few days. I am currently involved in installing a solar system on a Sprinter van and would like to ask some questions.

My plans are 2-4 Deka GC45 batterys 255 ah to 510 ah

Morningstar MPPT 45

Magnum inverter MS1000 or MS2012 I have been questioned on the over kill of the MS2012 but a occasional use of a power tool ect would be nice

The panel dilema is I have 84''X42'' area to install panels. I have found the perfect sized panels from Grape Solar, TS-100 but the cost is 277.00 each
and I would like to have 400 watts, so four panels are needed. I need panels that are 21''X40-43'' I Have found many other less expensive options if I can get by
300 Watts. The GS panels @ 2.77 per watt seem expensive. I am looking for alternatives

Any help with sourcing panels would be appreciated.

I will be living in the van for a couple weeks at a time and will not be driving much.

Needs are running a espar heater,12v fridge, 24hrs per day. lights, laptop,TV, Max air fan, Microwave, intermittently.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Help with finding panels with proper dimensions or other ideas?

    Welcome to the forum SunnySide.

    Would also like to know what time of the year, where you will be dry camping, etc... You can get from 3- hours to 6+ per day of "noon time equivalent sun" per day depending on lots of factors. Also, especially if winter use, will you be able to tilt the arrays?

    I think you load expectations are too high for a smaller array. And I would suggest that you measure your loads with a kill-a-watt type meter before you starting laying out any cash.

    But, we can help with some assumptions... Assume a 400 watt array and 4 hours of equivalent sun per day (~9 months a year). We recommend 5% to 13% rate of charge, but lets use 10% rate of charge--That is a healthy Array to Battery Bank ratio for an off grid power system with use during day and during night:
    • 400 watt * 1/14.5 volts charging * 0.77 panel+controller deratings * 1/0.10 rate of charge = 212 AH @ 12 volt battery bank

    So, that would point to the 2x 6 volt @ 255 AH batteries or a 12 volt @ 255 AH battery bank.

    How much energy would a 400 watt array produce? Assuming you are in/around Utah and using PV Watts for Solar Lake City, a fixed array mounted flat to the roof top:
    Month    Solar Radiation (kWh/m 2/day)
    1      2.00     
    2      2.96     
    3      4.05     
    4      5.29     
    5      6.84     
    6      7.32     
    7      7.47     
    8      6.72     
    9      5.24     
    10      3.78     
    11      2.35     
    12      1.64     
    Year      4.65      
    

    Tossing out the bottom 4 months gives us March at 4.05 hours (long term average) per day of usable sun. Or:
    • 400 watts * 0.52 AC off grid system efficiency * 4.05 hours of sun per day = 842 Watt*Hours of AC power per day

    If you can tilt the array to latitude (~41 degrees from horizontal), you would get:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.32     
    2      4.50     
    3      5.17     
    4      5.60     
    5      6.50     
    6      6.47     
    7      6.86     
    8      6.96     
    9      6.45     
    10      5.61     
    11      3.97     
    12      2.73     
    Year      5.35      
    

    Notice that winter available energy goes up, but summer goes down. And if you tilt to ~56 degrees from horizontal (winter setting):
    Month    Solar Radiation (kWh/m 2/day)
    1      3.53     
    2      4.63     
    3      5.08     
    4      5.17     
    5      5.74     
    6      5.56     
    7      5.95     
    8      6.32     
    9      6.22     
    10      5.70     
    11      4.18     
    12      2.89     
    Year      5.08      
    

    You can get some pretty decent numbers deeper into winter (if you get reflections from snow on the ground, you can even get better).

    How you mount the panels is going to be a big question for you... Tilting certainly makes the installation more complex and you have to design it to withstand high winds (both traveling and when parked on open lands during thunderstorms, etc.). But if you want the solar power, it may be a requirement for you.

    Some other options to think about... Conservation. Always the first place to start. Off Grid power is expensive--Think in the $1-$2 per kWH our rage (or 10-20x your utility power costs)--So "extreme conservation" almost is always the best investment.

    For your van, may not be astetically pleasing, but I have seen a few large motor homes/trailers that top hing the solar panels as a swing-out awning on the side of the vehicle. This allows you to have both shading from the sun in summer, and to tilt the panels to 45-90 degrees for better winter sun collection (on a van with right side doors, you probably would mount on the left).

    Finally, do not overlook the lowly genset... A Honda eu2000i is ~50 lbs, very quiet, and will generate 900 Watt*Hours on less than 1/3rd of a gallon of gasoline. Plus, you can support larger loads when needed (will run a skill saw pretty well) without carrying around 100's of lbs of additional batteries and over-sized AC inverter (that you don't have enough solar to recharge).

    Loads are tricky... And loads that run "24x7" will surprise you at how much they consume. For example, compare a laptop+modem+network+printer+small light to a microwave oven:
    • "office" at 50 watts * 12 hours per day = 600 WH per day for "office"
    • Microwave at 1,500 watts for 0.25 hours per day = 375 WH per day for "microwave at 15 minutes per day"

    The problem with large/surgy loads is that they require good sized battery banks to support. Lets take your 12 volt @ 255 AH and see what "typical" maximum loads would be... Again, these are very rough suggestions as a starting point:
    • 12 volts * 255 AH * 1/8 hour discharge rate * 0.85 inverter efficiency = 325 Watt "nice" maximum continuous load (will kill battery bank in less than 8 hours of use)
    • 12 volts * 255 AH * 1/2.5 hour discharge rate for surge * 0.85 inverter efficiency = 1,040 Watt maximum surge (10's of seconds to minute or so)

    So, with a 2x 6 volt 255 AH battery bank, you are looking at a 300 to 500 watt (with 2x maximum surge rating) for the example battery bank. Any larger inverter would be a "waste".

    Remember too, that we suggest you don't discharge a battery bank below 50% state of charge for longer battery life... Note that RV use, you can go lower and just plan on the batteries dieing in 3-5 years from deeper cycles instead of dieing in 3-5 years from old age.

    But, again, we recommend that you have 1-3 days of storage + 50% maximum discharge -- Or around 2 days of storage @ 50% maximum discharge would be 25% discharge per (no sun) day:
    • 12 volts * 255 AH * 0.25 discharge * 0.85 inverter efficiency = 650 Watt*Hours of "comfortable" battery energy per day (for two days)

    Or just enough to run the "office" with no other loads (lots of guessing here).

    Again, these numbers are just rules of thumbs and anything withing ~10% is "close enough" for solar work... (battery sizing, array sizing, etc.).

    Questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Help with finding panels with proper dimensions or other ideas?

    you will have trouble running the fridge and microwave on a small system
    suggest you use propane for the fridge , as it is far more efficient, hope it is a 3 way fridge for rec vehicle,
    look into larger 250w panels as they are much cheaper per watt
    look at our sponsors store for supplies. http://www.solar-electric.com/
    You also need to do a good evaluation of your loads in order to see just what size of system you really need for this project.

    cheers
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • sunnysidesunnyside Registered Users Posts: 11
    Re: Help with finding panels with proper dimensions or other ideas?

    Alot of info there, thanks. My absolute necessary consumption looks like this

    Espar = .6 to 3.3 amps hopeful 15 amp hrs
    Engel = .7 to 3.6 amps hopeful 48 amp hrs
    Maxair=.2 to 4.0 amps hopeful 24 amp hrs
    interior lights hopeful 5 amp hrs

    You have completely talked me out of the MS2012 I will use the save cash to buy a EU2000. I still think I will need a 1000W inverter as per a member on another forum could not run his 700W microwave on his 1000W inverter, and had to buy a 600W thats ok I can buy a 600w microwave but really need to run it without the generator.

    What is a shunt and do I need it?
    255ah battery banks sounds good per your info with 400 watts solar. I guess I might have to pony up for the Grape SolarTS 100's since there the only panels that will fit to get 400 Watts.

    I will need to mount my panels flat so ultimate efficiency will never be achieved.

    I do not want a propane fridge. I dont want to cut holes in my van or carry tanks.

    Any more help would be great. Great guess I do live in Utah
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Help with finding panels with proper dimensions or other ideas?
    sunnyside wrote: »
    Alot of info there, thanks. My absolute necessary consumption looks like this

    Espar = .6 to 3.3 amps hopeful 15 amp hrs
    Engel = .7 to 3.6 amps hopeful 48 amp hrs
    Maxair=.2 to 4.0 amps hopeful 24 amp hrs
    interior lights hopeful 5 amp hrs

    If these are real--then you are looking at 92 AH per day. With a flat mount array and assuming 5 hours ("summer time" use), your minimum array would look like:
    • 92 Amp*Hours * 12 volts = 1,104 Watt*Hours per day
    • 1,104 WH * 1/0.77 panel+controller losses * 1/0.80 battery eff * 1/5 hours per day summer sun = 358 Watt Array Minimum

    So--your ~400 Watt Array would barely squeak by with the loads you have listed, in the summer, in a good sun area like Utah. If your estimates are "off"--Then who knows.
    You have completely talked me out of the MS2012 I will use the save cash to buy a EU2000. I still think I will need a 1000W inverter as per a member on another forum could not run his 700W microwave on his 1000W inverter, and had to buy a 600W thats ok I can buy a 600w microwave but really need to run it without the generator.

    For a small system, the MorningStar 300 Watt (600 watt for 10 minutes) TSW AC 12 volt Inverter is just about the best unit you can find for the size (efficient, remote on/off, search mode to reduce standby losses, etc.). You will not find another inverter for ~$240 that will come close to the functions in this guy. Has also been proven to be very reliable too.
    What is a shunt and do I need it?

    A "shunt" is just a jumper wire. But we have "current shunts" which are high power (high current) precisoin resistors that are (usually) placed in the negative lead to the battery bank. A meter is connected to the shunt and measures the voltage drop (typically around 0.050 to 0.100 volts maximum) across the "shunt" and lets you accurately measure the current flowing into or out of the battery bank.


    wind-sun_2263_17213176
    You can purchase a "Battery Monitor" (Victron is another good brand) which measures the current (and battery voltage) over time to give you a display of the present state of charge (estimate) of the battery bank without having to measure specific gravity and such.


    Here is a nice thread with video from Kevin in Calgary Canada that shows designing and installing solar PV in a small RV trailer.

    Poster Robert "2ManyToyz" has created a web page about the installation and use of his Link Pro Battery Monitor. How to install instructions and youtube video included.
    255ah battery banks sounds good per your info with 400 watts solar. I guess I might have to pony up for the Grape SolarTS 100's since there the only panels that will fit to get 400 Watts.

    I would look around for >200 watt panels that may fit your available area--But sometimes you are stuck with what you can get. You might also call around--Many vendors have old stock (few panels left in the warehouse) that they don't bother listing on their website.
    I will need to mount my panels flat so ultimate efficiency will never be achieved.

    If your use is primarily in the summer, then you are OK--If it goes into the other 6 months of the year (towards winter), then you may be really hurt.

    Another option, if you are "fixed" camping--You might think of getting a couple extra panels to mount on the ground directly (staked/guyed to prevent wind storms and thieves from letting them walk). A pair of 230 watt panels will over double your available power if staked next to the camper van. Note that these are single weight tempered glass and any hard knocks or scratches in the glass will cause them to shatter and the panels will be scrape--or modern art).
    I do not want a propane fridge. I dont want to cut holes in my van or carry tanks.

    It is a choice... But you can get upwards of a month from a 20 lb cylinder with a small RV Fridge... Add cooking (or a multi-fuel camp stove)--anything to reduce your loads on the solar array/battery bank, is probably going to be helpful.

    Off grid solar power is difficult... Most people under estimate their loads and over estimate how much power a solar array/battery bank can supply.

    The old way to get "more power" was to add more batteries. Almost always a mistake. In the old'en days, batteries were "cheap" and solar panels were expensive. These days solar panels are "cheap" and batteries are expensive. Excessive battery bank size (vs solar array) can be supported with more generator use--Your choice.

    Some other options... The Honda eu1000i gensets are also very nice (smaller/lighter--still quiet and reliable). Also, if you have need for power tools, you might look at a larger MSW inverter (they are dirt cheap these days). Could run corded saws/drills pretty easily. I would avoid MSW if you can justify using TSW for your day to day loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sunnysidesunnyside Registered Users Posts: 11
    Re: Help with finding panels with proper dimensions or other ideas?

    Great info, say I have to run the Honda eu2000 for 30 to 45 min per day to use a 120v water heater couldn't it also supplement battery charging during that time through an inverter charger?
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Help with finding panels with proper dimensions or other ideas?

    Assuming you have a 10 Amp charger, in 1 hour your will charge 10 Ahr, out of the 92Ahr Bill mentioned. so about a 10% charge at a 10A rate, The higher the rate the more Ahrs you will get but you don't want to go much higher than 20 A... (~20% of battery Capacity rate)
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • sunnysidesunnyside Registered Users Posts: 11
    Re: Help with finding panels with proper dimensions or other ideas?

    Has anyone had any direct experience using one of these, MorningStar 300 Watt (600 watt for 10 minutes) TSW AC 12 volt Inverter running a 600W micro wave?
  • Dragonlady5Dragonlady5 Registered Users Posts: 19 ✭✭
    Re: Help with finding panels with proper dimensions or other ideas?

    It is generally recommended that an inverter powering a microwave be rated (continuous rating) at 2 times the cooking Watts. So would recommend a 1200 Watt or greater be used for a 600 Watt microwave. Typically its a bit less than 2 times but better to be safe than blow an inverter.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Help with finding panels with proper dimensions or other ideas?

    There are 12 VDC microwave ovens out there. So, there is the option of supplying 70 amps @ 12 VDC directly (that is still a lot of current for a 12 volt @ 255 amps):

    70/255 = 27% of battery bank rating

    Since microwaves are cheap, and they do sort of work on MSW inverters--You might get a 1,200 watt MSW "cheap" inverter and microwave and see how it works.

    You probably would need to add a DC power switch on the MSW inverter so you can turn it off when not being used. (inverters run from 6-20+ watts when DC power is applied).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Help with finding panels with proper dimensions or other ideas?

    Sunny side,

    Welcome to the forum,

    You hve come to the right place, from the Sprinter Forum.

    Good luck with your project.

    Tony
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