Mobile Solar

SystemSystem Posts: 2,511 admin
As I work to put together my small system, I am a little concerned about theft. Since I will only be at my property for weekends (and maybe not every one) things would be unattended. I have heard about mobile solar mounted in trailers. Does anyone have any experience in how well the various components handle rough washboard type roads? The mobile solution sounds appealing but I worry about things getting beat to death. Thanks for the input.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Mobile Solar

    You are probably between a rock and a hard place here... The risk from theft vs damage of packing and unpacking a trailer weekly, and the chance of a wind storm blowing the panels way if you can't get them properly tied down (or put away) in time is probably roughly equal.

    Motion capture video, IR, and a cell phone based alarm may not be worth the costs or get somebody there in time to stop the thieves. Putting panels on a roof (or 2nd story roof, or high structure) may help.

    But any determine thieves with enough privacy and time will not stop until you are stripped clean to the foundation (or just party out and destroy anything of value):

    Who stole my house? - Thieves pillage family's remote vacation spot

    It was never recovered:

    EL DORADO COUNTY - Family's happy reunion at site of stolen cottage - Donor erects new one -- theft still unsolved

    But he has installed a steel shipping container to put his valuable tools in it (and keep the temptation down).

    In the end, the above event is very rare (one time event, 2003, in the US?).

    Keeping the the visible items of value minimized (not too large array, installed on roof facing away from the road, or on the ground behind the cabin), don't keep irreplaceable objects at the cabin, a watchful neighbor, and having good insurance is about the best you can hope for.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mobile Solar

    record your serial numbers at the very least. as said a determined thief will get what he wants, but all you can do is try to slow him down. you could use special hardware that won't take normal tools such as http://store.solar-electric.com/mohasebo.html
  • catkincatkin Registered Users Posts: 19
    Re: Mobile Solar

    We drill holes through all the module frames, run a multi-strand wire rope through the holes and swage the ends together.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: Mobile Solar
    catkin wrote: »
    We drill holes through all the module frames, run a multi-strand wire rope through the holes and swage the ends together.

    Thats pointless, a standard bolt cutter will snip that in 2 seconds
  • System2System2 Posts: 6,290 admin
    Re: Mobile Solar

    Thanks to all for their input. I don't think anyone addressed if they thought keeping the charge controller, inverter, batteries, combiner box (if needed) and so on, permenantly mounted in a small enclosed trailer would be damaged by rougher roads. I have see some examples of bigger setups people have put on wheels. Any experience with these? Thanks much!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mobile Solar

    i can comment on some things, but i'm not an over the road type guy.

    most pwm controllers will be fine. just buy one that will suit your needs now and in the future that has a battery temperature sensor (bts).

    same with the inverters, but be sure that items you have to run that are sensitive to modsines would be either on dc or a sinewave inverter.

    batteries on the go i'll say hands down for agms. these are sealed so no spillage or gassing with a good controller and bts. maybe enclose them in a box with some room at the top and allow cushioning with say a foam sheet under wood or thick plywood that the battery(s) will sit upon. some of that foam on the sides of the box may also be a good idea for temperature stability, but be careful if it has any foil on it that it will not be able to come into contact with any wires or terminals. it can be pealed away if need be.

    a combiner will depend on what you have in pvs and as some controllers may accomodate more wires or some in series(i don't recommend series for mobile), but i recommend the ability to switch things off and protected from shorts with fuses or good dc circuit breakers preferably.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Mobile Solar

    Very simply... Figure out how many panels you will need, and then design something to hold 1/8" 66"x33" 34 lb each tempered glass sheets with a 2" aluminum rail around the edge (like aluminum frame windows) that can open, close, survive a trailer and high winds. BP (205 watt panel example) uses 50 pounds per square foot for wind and 113 PSF for snow loading.

    Just wind loading would give you 756 lbs per panel that the structure would have to withstand. If you are doing 2-4 panels--may be OK to do... Larger folding/portable system would be very difficult.

    For batteries, just figure out how many amp*hours you want, and go to the Wind-Sun store and see how big and how much they would weigh.

    A small system (which will not supply much standby power), will not be too heavy... A large one--will be difficult and expensive to two. If the trailer has some sort of suspension (required for the glass panels), the batteries, if well mounted so the wires don't pull, will probably be just fine (like car batteries take the vibration OK too).

    Honestly, if you are going to just need a few hours of power per day, for weekends, a small $1,000 Honda eu2000i generator (1,600 Watt, 4 hours on 1.1 gallons of gas or 400 watts for 15 hours on 1.1 gallons of gas) and a few gallons of gasoline will be much easier to use and probably cost you less to run than just the fuel for towing the trailer.

    -Bill

    You could also build your own hybrid system... Put the batteries in a locked box/cellar and use the generator to charge them while you are there (plus a small solar panel for trickle charging), then add solar panels later when you are there much more and the price/security justify the added costs.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SavingEnergySavingEnergy Registered Users Posts: 9
    Re: Mobile Solar

    5ohSteve,

    Your idea of the enclosed trailer should work fine. I've done this for years on a recreational vehicle. I have four 60w panels that are about 17 years old. They're actually on their second RV now, an enclosed trailer I converted into a toy hauler. Two standard lead acid batteries are mounted on the tongue, and a Morningstar controller is in an upper cabinet. I don't know how large of a system you are considering, but I've seen a motorhome with 24 panels and two wind generators on the roof.

    A Honda generator is a viable alternative, but I personally despise the noise.

    John
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mobile Solar

    "but I've seen a motorhome with 24 panels and two wind generators on the roof."

    holy sh*t, really? you should have taken some pics of that.:cool:
  • System2System2 Posts: 6,290 admin
    Re: Mobile Solar

    Interesting idea on using the generator to charge the batteries while there to make up for usage. I have a 5000w gas generator with DC connections but I have no idea how that would be wired to the batteries. Does it need to go through a different sort of charge controller? My batteries are 4 L16, 420 ah planning on wiring them series/parallel. Roughly how long would you expect the generator to have to run in the AM? Thanks for the idea and thank you to the other posters for their valuable information.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Mobile Solar

    You should take a look at the Wind-Sun's battery FAQ to understand how best to charge your battery bank...
    Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.
    Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.
    Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.
    Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.
    Assuming you have flooded cell batteries, you can adjust your generator to output at least 14.2 volts (remember temperature correction, colder than ~77F, the voltage will need to go up) and charge until see or hear the batteries begin to bubble (or use a battery monitor) for most weekends. Then once in a while (once or twice a month), crank the voltage up to 15.5 volts or so and equalize charge them.
    Flooded battery life can be extended if an equalizing charge is applied every 10 to 40 days. This is a charge that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. This makes sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. If the liquid in standard wet cells is not mixed, the electrolyte becomes "stratified". You can have very strong solution at the top, and very weak at the bottom of the cell. With stratification, you can test a battery with a hydrometer and get readings that are quite a ways off. If you cannot equalize for some reason, you should let the battery sit for at least 24 hours and then use the hydrometer. AGM and gelled should be equalized 2-4 times a year at most - check the manufacturers recommendations, especially on gelled.
    So, for example, Say you have 3 days of store power--and you discharge down to 60%, for a C/10 (1/10 battery rating as charge current), it would take you 4 hours to recharge with the generator set.

    You have a 500watt generator with DC connections--is that a 500 watt DC generator or a 500 watt generator with 10 amp 12 VDC connections (120 watt)?

    Ideally, you would like the output of your DC generator (or your AC generator with DC charge controller) to output about C/10 rating of your battery bank (more current than C/10, and you could over heat your batteries, less current that C/33 and you will not be able equalize your batteries--plus it will take you 3+ times longer run time to charge your bank).

    Then, for trickle charging your battery bank while you are not there, you could get enough solar panels such that they would be somewhere between C/33 to ~C/80 with charge controller that you can adjust (to float voltage) or a several stage charge controller (to finish up the charging of your battery, then switch to float).

    A MPPT (Maximum Power Point Tracking) charge controller is wonderful, but for small arrays (typically less than 400 watts), a full sized MX 60 (60 amp) charge controller ends up being less efficient than the less expensive PWM type controllers (there are some new, smaller MPPT units intended for RV/cabins that might work well on a smaller panel set).

    Read through the FAQ and look closely at the battery charger / generator... Not all are equal and for an AC charger on a generator, depending on the charger, you may need to oversize the generator by 2-3 times the charger rating because of the "poor power factor" of many AC chargers.

    You will probably want to oversize the generator anyway--use it in the morning to charge your batteries and run the vacuum, do the wash, make coffee, etc. Don't make the generator too large, they tend to waste fuel when running with light loads (some less than 50% load, other brands/models with less than 25% load).

    My personal choice for a small, very quiet, fuel efficient generator is the Honda eu2000i. Between 25% and 100% load (400 watt to 1,600 watts) the fuel flow is very linear with load (1,600 watts, 1.1 gallons of gas, 4 hours. 400 watts, 1.1 gallons of fuel, 15 hours). It does this because it has an internal inverter that allows the engine to throttle back (slow down) when the loads are light.

    If you have really light loads, you could also look at the eu1000i).

    A regular 5kW $400 genset will use many times the amount of fuel when running at light loads). I would stay the heck away from one of these... $500 price difference (vs eu2000i) is about 120 gallons of gasoline--it may take as little as 10-40 days of use to "drink through" your savings (depending on how long you run it at low power). Plus they tend to be obcenly noisy when used in quite locations. The Honda eu family, you can hold a normal conversation right next to it.

    If this where a full time home with larger loads, then a real "prime mover" type generator running off of propane or diesel would be a better pick. And looking at RV generators might be an intermediate solution (quite, automatic start, pretty fuel efficient). However, I tend to find that almost all of these other solutions are way to large for my needs... I can live with an eu2000i quite nicely even for my 3 bedroom home (would have to watch my power use or stop using a microwave and toaster oven)--The prime mover types seem to be 10-20 kWatt for a small one. Way too much power (and cost) for me.

    Anyway, that is how I would approach the problem. Some others may have other generator suggestion (especially for the mid to large size units).

    -Bill

    PS: For your 4x 6 volt L16 batteries--assume 12 vdc @ 420 amp*hours...

    Battery bank @ 12 volts=840 AH rating
    Battery Charger: 84 amps, or 1,302 watts
    Solar Panels C/33 to C/80= 25 amps to 10.5 amps (or ~425 to 178.5 watts of panels)...

    If you go with a 1,300 watt battery charger, you may need to go with a larger Honda eu3000i generator (with electric start)...

    Solar panel sizing is based on 17 volt rating, and a C/33 sized system (~3%) may even let you get away with skipping the generator if your cabin loads are very light and you don't draw down the batteries much (say, no generator when you are there alone and spending most of your time fishing--and fire up the genset when the family is there playing video games, have the fan on, and using a lot of well water for showers during cloudy weather).

    Sizings are approximate and you can certainly go up or down on many of the suggestions.

    -BB

    PPS: Sorry, I missed that was a 5,000 watt genset, not 500... Just substitute your numbers...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • catkincatkin Registered Users Posts: 19
    Re: Mobile Solar
    Thats pointless, a standard bolt cutter will snip that in 2 seconds
    True, a standard bolt cutter will snip it but I don't agree that it's pointless. There's no such thing as absolute security. Opportunistic thieves don't carry bolt cutters and well-organised thieves pick easy targets. It's a probablistic cost-benefit analysis game and I reckon steel wire's a good bet, not -- of course -- a cert.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mobile Solar

    i'm afraid i'll have to agree with sg on this as anybody who is going on a roof to steal pvs, they would anticipate the possible need for a bolt cutter. 1 cut and all are free of the wire, but the use of off standard hardware may thwart them better as they may need to use a drill on each pv and they know time isn't on their side so it's less likely they'd either go through with it or they'd take fewer pvs.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Mobile Solar
    5ohSteve wrote: »
    ...I have a 5000w gas generator with DC connections...

    Sorry, I first read that as a 500 watt generator--not 5,000 watt.

    Anyway, if you want to use that generator a larger battery charger would be more fuel efficient (or using other large appliances, like a well pump and coffee maker + charging with a ~1,300 watt charger would be more fuel efficient).

    Running a 1,300 watt charger on a 5kW genset will probably suck fuel like now tomorrow... But you can run your own test... Fill tank, run for twenty minutes with known load (get a kill-a-watt meter set for kWhours and you can measure anything up to 15 amp 120 VAC loads). And figure out your fuel flow...

    Say you get 0.5kWh * 1/0.25 gallons used = 2.0kWhrs / gallon of fuel (made up numbers).

    Or 1,500 watts * 20min/60min (1/3 hour for actual power produced) * 1/0.25 gal = 2,000 watt*hours/gal or 2.0kWhr/gal

    If it is near 400 watt * 15 hours / 1.1 gal of fuel = 5.45 kWhrs per gallon of fuel (Honda eu2000i specs.) then you have a reasonably fuel efficient portable generator. (1,600w*4hr/1.1gal=5.8 kWhr/gal at rated power for Honda eu2000i).

    By the way, the Honda's have a "ECO Throttle" switch on them--set to ECO most of the time, but if you have big starting loads you may need to switch to off (motor runs at full RPM) to start large loads like an A/C.

    From numbers I have seen, even the inexpensive generators are pretty efficient near full power (possibly even more efficient than the Honda eu family). However hardly anyone runs their generators at nameplate rating.

    Most of us run at quite a bit lower loads and only use the name plate ratings to start motors (well pumps, fridge, freezer, washer, heater, etc.).

    You can't run a well pump at genset capacity--the generator would probably not be able to start the pump unless it is 2x-3x the pump rating (unless it is a sump or low pressure pump).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • catkincatkin Registered Users Posts: 19
    Re: Mobile Solar
    niel wrote: »
    i'm afraid i'll have to agree with sg on this as anybody who is going on a roof to steal pvs, they would anticipate the possible need for a bolt cutter. 1 cut and all are free of the wire, but the use of off standard hardware may thwart them better as they may need to use a drill on each pv and they know time isn't on their side so it's less likely they'd either go through with it or they'd take fewer pvs.
    Thanks, I'm persuaded. Another remedial task joins the list :cry:
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Mobile Solar

    Well, somebody is thinking of the ultimate mobile solar:

    Solarial solar blimp concept:
    rom time to time, an idea pops up which causes you to say, "Why didn't I think of that?" Often, these concepts seem to make so much sense that they absolutely must be implemented as soon as possible. Andrew Leinonen's concept for a floating solar-powered power station may just be one such idea. Using a lighter-than-air vessel, like a blimp, which can be maneuvered pretty much over anyplace in the world, power could be granted to disaster areas and other needy places using solar cells embedded all over the blimp which would turn the suns rays into electricity. It's possible that a vessel such as this could be tethered to the ground using "power boxes" which would be deployed from the airship using long power-carrying cables. The concept features twelve one-hundred-twenty volt outlets along with two two-hundred-forty volt outlets which would be able to offer power where it's needed most.

    An Industrial Design undergrad thesis.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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