mobile solar array shipping container

edpotx
edpotx Registered Users Posts: 9
I am attempting to build a mobile office that can be powered by solar panels.

the office will have to house my server and be cooled by AC/ fans.
The office will be constructed out of a shipping container and for the most part be in storage . I think i will be able to power the system only on solar but will have the ability to grid-tie for when i need it. I will not be selling power back to the utility company.

I am wondering what happens to the power that i generate that can not be storred on batteries? will it be shot into a ground?

any thoughts?

thanks for your help

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: mobile solar array shipping container

    Welcome to the forum.

    You essentially will have an off-grid system with the ability to use grid or generator power when available. This is quite normal. As such any power the panels are capable of but which is not utilized either by charging batteries or powering loads is simply not realized: PV's are a current source, and if there's no resistance connected to them (battery or load demand) they produce nothing. This is why off-gridders try to take advantage of "full batteries + sunshine" situations with opportunity loads like water pumps and heaters.

    The very first thing you will have to do to plan your system is determine the power usage of all the equipment you want to run. You mention a server and A/C to keep things cool. These are two big power consumers, so beware. The server may draw hundreds of Watts constantly, and the A/C unit will have big start-up demand and hefty cyclical consumption. We on the forum have tested quite a few A/C units, btw, and found quite some advantage using the mini-split design. You can find lots of threads about power usage under Energy Use and Conservation.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    I am wondering what happens to the power that i generate that can not be storred on batteries? will it be shot into a ground?

    The 'extra' energy is just wasted, solar PV doesn't need a dump load...

    Really, do NOT recommend a Shipping container for this use. Being big and heavy the loading and unloading and setting up will all be major head aches, I'd look into building a custom building on wheels, from a heavy trailer. If you won't need A/C, you could even look into a camper with a cooler just for the server and perhaps the batteries, Your looking at a lot of array and batteries even for a custom use built trailer for standard server, might look into customizing a low wattage computer into a 'server'...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mobile solar array shipping container

    Here are a few threads talking about a shipping container office + A/C:

    Alternative Air Conditioner -- Your Ingenuity Required

    Design help needed for off grid air conditioner
    And Now which Inverter??

    Regarding unused power generated... For Solar panels, they are fine with being turned on and off--And that is exactly what a typical solar charge controller does--just turns on and off the panel to keep the average voltage/current flow to the battery "regulated".

    For Wind and Hydro turbines, it is a bit more complex. For the most part, these turbines need to be loaded all the time or they will over-speed and self destruct. So, what is used is a "shut/diversion/dump" type charge controller. When the battery bank is full, the controller turns on and dumps excess current a "load bank" (basically a set of resistors to heat the air or make hot water).

    In the end, it is all about the power you use and ensuring you use it as efficiently as possible. Utility power is pretty cheap vs off grid solar/battery supplied power, and any amount of conservation (most efficient appliances/computers you can find, turning stuff off when not in use, etc.) is critical to an off grid power application.

    Using a Kill-a-Watt type meter to measure each of your loads and making a spread sheet to add it all up is your first requirement. Then conservation. And finally it is a matter of "running the numbers" for ZZZZ amount of solar panels on a YYY Battery bank for X days of solar power with a W backup genset.

    Just to give you an idea... A "small off grid system" of 500 watts of panels can generate around 1 kWH per day (small cabin). A 1,500 watt array may generate around 3.3 kWH per day (enough for a very energy efficient home with fridge, laptop, lights, well pump, washing machine). A very efficient grid connected home (using natural gas) may be around 8-10 kWH per day.

    It is the 24x7 loads that kill off grid power systems. Say you want a desktop server + Monitor + network, and some lighting. Call it 300 watts * 24 hours per day:
    • 300 watts * 24 hours per day = 7,200 Watt*Hours = 7.2 kWH per day -- Not a small system.

    Assume that you get 4 hours of sun around 9 months of the year:
    • 7,200 Watt*Hours per day * 1/0.52 system efficiency * 1/4 hours of sun = 3,462 Watt Solar Array minimum

    And a battery bank... Assume a balanced design of 2 days of "no sun" and 50% maximum discharge (longer battery life):
    • 7,200 Watt*Hours per day * 2 days of backup * 1/0.50 maximum discharge * 1/0.85 inverter efficiency * 1/48 volt battery bank = 706 AH @ 48 volt battery bank

    Or, roughly 16-24 "golf cart" sized batteries (just to give you an idea of size of the battery bank.

    And we have not even started with A/C or other loads... Computers, A/C, and Refrigerators are among some of the most difficult off grid loads to support.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    thanks for the comments

    the shipping container is a must have. I see the benifits to using a trailer but right now I'm restricted to using a containers.

    I will have the panels stored in the container and hook them up when they are needed. has anyone seen a folding stand that can bolt to a panel.

    the server and the AC are really the only things that will be powered but you are correct BB they suck the juice.

    thanks everyone.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    I will have the panels stored in the container and hook them up when they are needed. has anyone seen a folding stand that can bolt to a panel.

    I've seen them for small panels and stake out is a common way for larger panels, pretty much extending the sides down with aluminum and pushing into the ground like a stake, with 1 or 2 stakes from the top or sides into the ground, often done at energy fairs.

    Your likely talking about a largish system of 3000 watt array or more and 800lbs+ of batteries... I guess you understand this? at least to A/C a whole container.

    How much will you try to A/C? you can just use processor chillers and perhaps be OK. You might even stick the whole server into a Chest freezer running lines for input and out put and look at running it at fridge temps. There are threads on refrigerator conversions here. If you try to A/C a whole container, even a 20 foot one, you will need lots of insulation and a large solar system.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: mobile solar array shipping container

    Is it an insulated container? 20 feet? or 40?
     
    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
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    it will be used for mobile office as well, so the container will be insulated and cooled with a 14000 btu portable A/C vented out.

    For the most part the server will be the only thing in the container and I was going to seal off the ac and server together and when the office space was not needed could just chill the smaller area with just the server and A/C. yes I do understand the number of batteries that I need is large. everything will be secured for travel should it need to be i.e. strapped down batteries, bolted to solid steel.

    right now ive tested my server and its pulling about 192- 300 watts . A/C is about 1200 w.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    right now ive tested my server and its pulling about 192- 300 watts . A/C is about 1200 w.

    The server will be constant when on, so if that's 24 hours a day best figure on 6kW hours for that alone.

    The A/C will cycle, and there's no way of predicting how much! If it's 50% that will be a nasty 14kW hours.

    This totals a massive 20kW hours per day. On a 48 Volt system that's 417 Amp hours for a minimum 834 Amp hour battery bank. Now you are into the realm of maxed out largest size MPPT controller (80 Amps) and about 5kW of array to feed it.

    You can see how important it is to get accurate usage numbers and to minimize the power use as much as possible.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    I am attempting to build a mobile office that can be powered by solar panels.
    <snip>
    I think i will be able to power the system only on solar but will have the ability to grid-tie for when i need it. I will not be selling power back to the utility company.
    Why on earth do you want to build a battery based off grid system when you have the grid available? --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    this is a off grid solution for when the grid is not available.

    the system will be mostly in standby mode because the primary server will be used. The mobile server will be redundant for if the primary goes down it can take over.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mobile solar array shipping container

    How long do you plan on running off grid during a power outage? Days or a couple weeks? Then a genset+fuel supply is probably the better deal. If you are looking for many/multiple weeks/months without power, then solar may be an interesting choice.

    What about communciations links? Those can take a fair amount of power too... But then, if there are working com links (depending if local, wide area, full blown nation wide networking), then a "cloud service" of some sort would be interesting--and change the local server into a communications only hub.

    Having a local off grid server--Are you going to have data duplication issues (keep server data fresh/sync'ed)? Which then implies that there will be some sort of non-trivial daily loads too even when not deployed/in use.

    Will the cube be parked in a lot (with grid power, and possibly Internet/private networking connections) except during deployment?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: mobile solar array shipping container

    If you want to have a solar office and have plenty of money to burn then great, go at it. Just realize that for 99% of applications, a generator and a battery bank is going to be a order of magnitude less. The telecom folks do this all the time for cell towers. If you do go with the generator battery bank option, you can add solar panels to stretch the period between running the generator. The battery bank inverter combination will isolate the computers from the generator operation.
  • Sulfur
    Sulfur Solar Expert Posts: 62 ✭✭
    Re: mobile solar array shipping container
    Photowhit wrote: »
    I've seen them for small panels and stake out is a common way for larger panels, pretty much extending the sides down with aluminum and pushing into the ground like a stake, with 1 or 2 stakes from the top or sides into the ground, often done at energy fairs.

    Your likely talking about a largish system of 3000 watt array or more and 800lbs+ of batteries... I guess you understand this? at least to A/C a whole container.

    How much will you try to A/C? you can just use processor chillers and perhaps be OK. You might even stick the whole server into a Chest freezer running lines for input and out put and look at running it at fridge temps. There are threads on refrigerator conversions here. If you try to A/C a whole container, even a 20 foot one, you will need lots of insulation and a large solar system.


    A chest freezer does not have enough cooling capacity for a desktop PC, especially a server, which often draw more power than a desktop. I tried it:)
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    the com-link will be a staged set up ( wifi, 4g, satlink) depending on the available grid and location for the set up.
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    the deployment could be extended weeks or months.

    I'm trying to mount most the panels on the roof of the container this should maintain the server. I don't think i have enough real estate on the roof to mount all.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    the deployment could be extended weeks or months.

    I'm trying to mount most the panels on the roof of the container this should maintain the server. I don't think i have enough real estate on the roof to mount all.

    Flat or angled? With mobile deployment you may not always have ideal insolation angle.

    It may be possible to attach some to the side(s) at the top and raise them to the best angle when in position.
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    hadnt though of side mounting.

    how is the ' power rating' on a panel measured? (voltage* open current)
    If i combine panels differently i.e 6 sets of 2 in series. I'm looking at 12 400w panels ( link below). if i did my calculations correct i should get about 8 kw from the 48v panel.

    it looks like i need about a 5000w system

    http://www.thesolarbiz.com/Helios-9T2-400W-Mono-Solar-Panel_
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: mobile solar array shipping container

    Power rating of a panel is Vmp * Imp, and rarely occurs in the real world.
    The Voc rating is meaningless for power, but necessary for determining maximum input to a charge controller or GT inverter (in combination with temperature coefficient).

    The panels you link to have a Vmp of 48.43, Imp of 8.26 which makes the rated 400 Watts.
    The Voc is 59.8, so two in series would be 119.6. You need at least two in series to make sufficient Vmp for a 48 Volt system (>70 Volts) and with more than two the Voc would exceed the input max of most charge controllers (179.4 vs. 150 max in) other than the MidNite 200, 250 or Xantrex 600.

    Twelve 400 Watt panels is 4800 Watts. This will average an output around 3696 Watts and provide nearly 15 kW hours DC in a 4 hour day. With batteries and the standard over-all system losses it would yield roughly 12kW hours AC in a 5 hour day. Your actual yield will vary with insolation, temperature, hours of sun, and particular system efficiency.
  • edpotx
    edpotx Registered Users Posts: 9
    Re: mobile solar array shipping container

    so i can not expect any more power by combining panels in different ways. the rating is the max?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: mobile solar array shipping container

    Usable panel wattage is really Vmp*Imp*0.77 panel+controller deratings... Voc is Voltage Open Circuit--Which means no current is flowing and you have zero useful energy.

    Lets say you have 12*400 watt panels fixed mounted at latitude near Norfolk Virginia. using PV Watts we find that such an array will get this many hours of "noon time equivalent" sun per day over a 12 month average (this is a long term average of 20+ years or so, and can vary by +/-10% or more for shorter term averages, and can be 5% or less on days with thick clouds/stormy weather--So a generator+fuel is probably still required if you need 24x7 power):
    Month    Solar Radiation (kWh/m 2/day)
    1      3.84     
    2      4.53     
    3      4.69     
    4      5.47     
    5      5.40     
    6      5.69     
    7      5.44     
    8      5.61     
    9      5.02     
    10      4.95     
    11      4.04     
    12      3.37     
    Year      4.84      
    

    So, I toss the bottom three months and assume you will have to make up the difference with a genset+fuel (still should have enough power during sunny stretches of weather (note that PV Watts has "real" hour by hour data so you can see what "typical" days may look like). That gives us February with 4.53 hours of sun per day average:
    • 12*400 watt panels * 0.52 typical end to end efficiency * 4.53 hours per day = 11,307 WH = 11.3 kWH per day (off grid February average)

    Of course, during non-summer months, you will hopefully need less power because of no/little AC needs (possible dehumidification though).

    Nominally, for long battery life we recommend 1-3 days of storage and 50% maximum discharge. 2 days usually ends up with a pretty well balanced system. So, the size of battery bank that would be suggested by 11.3 kWH AC power would be:
    • 11,300 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volts = 1,108 AH battery bank.

    Just to double check, a battery bank should have 5% to 13% rate of charge:
    • 1,108 AH * 58 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 4,173 Watt array minimum
    • 1,108 AH * 58 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 8,346 Watt array nominal
    • 1,108 AH * 58 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 10,850 Watt array "cost effective" maximum

    So, based on the above guesstimates, your 4,800 watt array would meet your minimum rate of charge--But given that you are using a lot of energy during the day--You should double check your day time loads + minimum battery charging current (5-13%) to ensure that your daytime loads do not prevent the batteries from being properly recharged.

    Notice that everything is interrelated... A lot of power requires a big battery bank. And a lot of power requires a large solar array. And a larger battery bank also requires a larger array.

    Just to finish this off--A pair of 24 volt fork lift batteries (just for example--this is a high end battery bank): Crown Industrial Battery - 24 Volts, 1125 Amp-hours will cost around $10,000 and weigh ~3,480 lbs. Say your solar array (panels+mounts) weigh another 2,000 lbs... And you are upwards of 5,500 lbs just for solar power.

    Just to look at it via a generator solution... 11,300 WH per day is an average power of (divide by 24 hours per day=) 471 Watts average load 24x7.

    I will suggest a Honda eu2000i genset running on gasoline (propane conversions are available) will go about 9.6 hours on 1.1 gallons of fuel at 1/4 rated load (400 watts). Or:
    • 400 watts * 9.6 hours * 1/1.1 gallons per tank = 3,491 WH per gallon of gasoline.
    • 11,300 WH per day * 1/3,491 WH per Gallon = 3.2 gallons per day of fuel

    Say gasoline weighs around 6lbs per gallon and assume 1 lb per gallon for fuel tank structure. And that you want 1 month of fuel storage:
    • 30 days * 3.2 gallons per day (solar equivalent power in February) * 7 lbs per gallon of fuel+structure = 672 lbs of "fuel" per month

    So, with a simple (cheap) genset (~50 lbs) plus fuel would be ~722 lbs of weight (of course, there are oil changes and I would get 1-2 spare gensets for backup)... Compare that to a 5,500 lb solar power system (would still need backup genset anyway):
    • 5,500 lbs "solar" / 722 lbs of "generator" per month = 7.6 months "break even" based on weight
    • 3.2 gallons of fuel * 30 days per month * 7.6 months of equivalent weight = 730 gallons of gasoline
    • 730 gallons * $4.00 per gallon = $2,920 of fuel
    • Get 3 Honda gensets for ~$1,000 each = $3,000 worth of generators
    • Vs $20,000-$25,000 (or more) just for the batteries and solar array

    Anyway--Not trying to tell you this is the ideal design for your needs--Just trying to show how I would do the trade-offs. Propane or Diesel may be other options (propane does not "go bad" but less btu per gallon, diesel is more BTU's per gallon of fuel, diesels are more efficient, but it is very difficult to find small/fuel efficient generators).

    Batteries will require charging at least once per month and servicing (water, monitor, etc.).

    A "hybrid" power system makes lots of sense if the loads vary greatly over the day (high afternoon/evening loads for A/C + lights, and low loads off peak), but if you have pretty constant power (computer server + limited A/C / dehumidification, a few LED lights, networks, etc.), then a generator "sized to the loads" usually makes more sense.

    Adding solar to an emergency power system looks nice--But solar really only "makes sense" if it is used 9+ months out of the year. For a few weeks (or months or two) at a time, a large solar system is largely wasted--Plus remember those batteries will age out over time (3-5 years for "golf cart batteries" and perhaps 15-20 years for fork lift batteries--But in any case, batteries designed for "cycling" need cycling for longer life. Just keeping them on float will usually result in less life.

    I will stop here--Tell us what your thoughts are.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: mobile solar array shipping container
    edpotx wrote: »
    so i can not expect any more power by combining panels in different ways. the rating is the max?

    Yes. It does not matter how the Volts and Amps are arranged, they multiply out to the same Watts - with very small variations based on efficiency and losses. For example higher Voltage leads to less power loss through a given wire size (due to lower Voltage drop through the resistance) but also higher array Voltage converts less efficiently to lower system Voltage. But we are not talking about significant differences here. And the total power available at (and from) the batteries will always be less than the combined panel ratings.