Off-grid greenhouse

dwaller
dwaller Registered Users Posts: 18
I am attempting to design an off-grid greenhouse that will consist of a small aquaponics setup to start. I'll have a 2'x8' grow bed with a 150 gallon fish tank. The design will be flood and drain, so I will need a pump to move water from the fish tank into the grow beds twice an hour, and the water will recycle itself back into the fish tank via gravity. I'd like to design a 12v system to control the water pump (6w/h @ 12VDC), air pump (10w/h @ 120VAC). The air pump will likely need to be AC, so I'll have to use an inverter for that. Here's what I have on my list at the moment for what I'll need to recover my usage each day (~400wh @ 12VDC):

2 - 135W Kyocera 12v panel
1 - Morningstar ProStar 30A Charge Controller

I'm undecided about the batteries, my original thought was to do two 12v 220ah batteries in parallel, but I'm open to suggestions.

I also was thinking about using solar collectors for in-floor radiant heat for heating the greenhouse in the winter, is this feasible?

This project is in the beginning phases, and nothing has been purchased. I've read a few of the other threads here, and while in the beginning it seems that they have been well thought out and planned, I've seen too many times where things fall apart in the middle of the project and it comes together kind of half-arsed. I'd like to avoid that and spend my money in the right place the first time around to avoid having to do a redesign in the middle.

Please let me know if you would like more information regarding any part of this project. Thanks.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    With solar PV--the system is expensive and depends on local weather conditions for how much power it outputs... So, to design a cost effective system we need to know a lot both about your exact power needs and where you are located.

    For your power needs, assuming your 400 Watt*Hours at 12 volts is going to be used during winter (since you asked about heating)... If you have not measured your power accurately--You can use a Kill-a-Watt meter for 120 VAC plug in equipment (also great to use around house for conservation). And/or for DC power here are a couple Amp*Hour / Watt*Hour meters.

    Your IP Address suggest that you are from the Minnesota area... Lets start with Duluth using the PV Watts Webset. Use 1 kW of solar panels (even number, and smallest array supported by PV watts). Use Derating = 0.52 (battery + off-grid inverter for end-end efficiency number). Defaults for rest:
    "Station Identification"
    "City:","Duluth"
    "State:","Minnesota"
    "Lat (deg N):", 46.83
    "Long (deg W):", 92.18
    "Elev (m): ", 432
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 46.8"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.9 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.29, 58, 4.58
    2, 4.27, 67, 5.29
    3, 5.41, 90, 7.11
    4, 4.99, 76, 6.00
    5, 5.42, 80, 6.32
    6, 5.51, 77, 6.08
    7, 5.36, 76, 6.00
    8, 5.26, 76, 6.00
    9, 4.48, 65, 5.13
    10, 3.85, 59, 4.66
    11, 2.61, 40, 3.16
    12, 2.61, 44, 3.48
    "Year", 4.42, 807, 63.75

    November is the lowest production at 40 kWhrs per month. To figure out how much your panel will produce per day:
    • 40,000 Wh per mnth * 1/1,000 watt of panels * 1/30 days per month * 2 panels * 135 watts = 360 WH per day
    So--as planned--for December, you are running a net negative amount of power for your usage. You will either need a back up energy source (genset+charger) and/or not use so much power during winter.

    First, you will have to decide on your power usage--Second, solar should have a back power source anyway--as you only will be storing 2-3 day of of backup power in your battery bank anyway--a week of no sun will require alternate power use (or drastically reduced power use) during poor weather (depends on your location).

    Regarding the battery bank, generally, we recommend to start with 3 days of no-sun backup and 50% maximum discharge for longer battery life:
    • 400 WH per day * 1/12 volt bank * 3 days * 1/0.50 batt dischrg * 1/0.85 inverter efficiency = 235 Amp*Hours (at 12 volts)
    So your 220 AH is a good start... You are looking at deep cycle (not marine/car batteries) and will keep them "warm" (above freezing--battery capacity drops when very cold).

    MorningStar makes very solid charge controllers. PWM controllers are less expensive. There are MPPT type charge controllers which can be used for larger solar arrays (longer wire runs from panels to battery shed, a big more power collection possible)--but may be overkill for your setup.

    All About Charge Controllers
    Read this page about power tracking controllers

    You should monitor your batteries to make sure you recharge them when below 50% capacity and you never want to get them below 20% capacity (or a weak cell can be reversed charged--will kill a battery immediately). Measuring battery voltage is only accurate if batteries have been rested for 3 or more hours (no charging/no load--need to compensate for temperature if you are not near 77F). An accurate hydrometer (for flooded cell batteries) with thermometer is a good investment. And I like a battery monitor (cumulative Amp*Hour meter) as you can read them any time (you can probably use the AH meter in my previous link--a true battery monitor is 2-4x the cost of the ones above). Read through the Battery FAQ's as mistreating a battery will quickly kill them (undercharging for weeks/months at a time will kill them).

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    Note that if this is "automated"--you may need some way to cut your loads before you flatten your battery bank. This adds complexity and costs to your system.

    Regarding winter heating--From the PV Watts output, it gives "average Full Sun Hours per day" by month... Deep winter is 2.61 hours of sun per average... You can figure out how much heat you can get from XX sqft/sqmeter of thermal collector...

    However, the green house is a solar collector itself... So, placing a couple 30 - 55 gallon black painted drums full of water may give you some freeze protection (use them to support your "table"?--just a wild suggestion--I don't have any experience with green houses in cold climates). If your panels are small with respect to the size of green house--you won't get much more heat from solar thermal panels. Also, you will need some sort of freeze protection for your solar thermal panels (anti-freeze, drain back, etc.) which add cost and complexity too.

    If you want to research further into solar thermal heating--check the first post for various solar thermal links from the "Working Thread for Solar Beginner Post/FAQ" (random thoughts/projects thread).

    Questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    Wow, thanks for the great reply. I'll post the answers to your questions below.

    I am in MN as my IP suggests, however, I am located 25 miles west of Minneapolis, which I believe is zone 4 vs. Duluth's zone 3 rating.

    For my power needs, I'll be using the following water/air pumps:

    Shurflo Bilge 500 (15 minutes out of every hour)
    Tetra Whisper Aquarium Air Pump 300 (liberal estimate of 24x7 operation)

    I'm not sure which inverter to go with, I was hoping to get suggestions related to my output here. Also related to my output, I'll probably have a single light bulb populated with an HCFL 60W equivalent bulb in case I need to do anything in there during the dark.

    I re-ran the PVWatts calculator and the following results were displayed:
    "Station Identification"
    "City:","Minneapolis"
    "State:","Minnesota"
    "Lat (deg N):", 44.88
    "Long (deg W):", 93.22
    "Elev (m): ", 255
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 44.9"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.9 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.85, 67, 5.29
    2, 4.72, 72, 5.69
    3, 4.97, 80, 6.32
    4, 4.91, 72, 5.69
    5, 5.74, 84, 6.64
    6, 5.91, 81, 6.40
    7, 5.89, 83, 6.56
    8, 5.64, 80, 6.32
    9, 5.21, 74, 5.85
    10, 4.28, 65, 5.13
    11, 2.95, 44, 3.48
    12, 2.85, 48, 3.79
    "Year", 4.74, 849, 67.07

    Using your formula, November also followed as the month with the least production and beat out Duluth by 4kWh. Here are the calcuations:

    Output per day (2 - 135W panels)
    44,000 * .001 * .033 * 2 * 135 = 395.60Wh

    Output per day (3 - 135W panels)
    44,000 * .001 * .033 * 3 * 135 = 588.06Wh

    Reading the charge controller link that you posted, it says the following
    Nearly all PV panels rated over 135 watts are NOT standard 12 volt panels...

    I'm wondering if I should go with a couple of larger panels right off the bat, as well as an MPPT controller to maximize the charge capacity of my batteries with such a small array. Is my thinking here correct?

    If so, are there any recommendations on an MPPT charge controller for a setup of my size, as well as a recommendation for larger panels?

    I'm still studying the battery situation, but I'm glad to see that at least one thing I've been working on has calculated correctly :) I'm going to have to think about the solar heating too, it might be easier to just do a couple of 50 gallon barrels painted black to keep it above freezing in the house.

    Thanks again for the detailed reply, I hope I answered all of your questions.

    -Darrick
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    Darrick,

    You are very welcome.
    dwaller wrote: »
    Shurflo Bilge 500 (15 minutes out of every hour)
    Tetra Whisper Aquarium Air Pump 300 (liberal estimate of 24x7 operation)
    You really need to measure the pump in operation in your setup... Centrifugal pumps tend to use more power with high flow, and less power at low flow--So depending on the elevation of the output and if you have any valves to slow the flow down--it may use less power. Also--is this is a 24x7 or do you cut back on usage at night?

    Regarding the air pump--(and water pump)--you need to measure their power usage in your application... For the most part, name plate ratings tend to be relatively high compared to actual use--but not always.

    And with solar PV off-grid power costing around $1-$2 per kWhr (or more)--it might be cheaper and more convenient in the long run to trench an AC cable from your home to the green house (if power is available).
    I'm not sure which inverter to go with, I was hoping to get suggestions related to my output here. Also related to my output, I'll probably have a single light bulb populated with an HCFL 60W equivalent bulb in case I need to do anything in there during the dark.

    The Morngstar 300 watt 12 volt true sine wave inverter is a really nice unit. However, for your 7.5 watt load--you will have to look very closely at the various inverters--many have 6-8 watts of load just running with no load (including the Morningstar). So, you will probably have to assume that your AC air pump load will be the 7.5 watts of the pump plus 8 watts of the inverter minimum load.
    Using your formula, November also followed as the month with the least production and beat out Duluth by 4kWh. Here are the calculations:

    Looks good to me... Yes, more power is appropriate... Depending on local weather, you will have variations over time (more storms, less clouds, etc.). If your output is within 10% of predicted--you are doing very well (or it is an accident). 2x the expected about of power is not unreasonable.

    In the "physical world" (engineering wise)--you could possibly do things like run the inverter/air pump with a 50% duty cycle and probably not see a difference in your plant growth (again, engineering wise, less than a factor of 2--things are almost the same. Things that are 10x or more difference--you can pretty much ignore the smaller contributor). The SureSine inverter has a digital "inhibit" input--that you could connect to a cycle timer very easily.
    Reading the charge controller link that you posted, it says the following :
    • Nearly all PV panels rated over 135 watts are NOT standard 12 volt panels...

    Pretty much true... Big panels are generally designed for large installations and Grid Tied use--both which use MPPT type controllers. Evergreen does make "12 volt panels" (18 volt Vmp)--You may have to look/call around to find some (very popular).

    To a degree--it will be a $$$ of panel vs $$$ of controller to figure out which would be the best price/performance for you needs.
    I'm wondering if I should go with a couple of larger panels right off the bat, as well as an MPPT controller to maximize the charge capacity of my batteries with such a small array. Is my thinking here correct?

    The minimum battery bank AH rating rule of thumb is based on several underlying reasons... In the end, you could go with a smaller bank--but you will have few days reserve to cover cloudy weather.. And, roughly, if you have 1/2 the amount of battery capacity, the bank will, last about 1/2 the number of charge/discharge cycles--so the physical cost of the batteries over time will be roughly the same (1/2 the mount of batteries or 2x the amount of batteries)--assuming you don't violate any major rules (boil dry, run dead, store for days-week at less than 75% capacity).

    Cost wise for solar panels--you could go 2-2.5 times larger without damaging the battery bank--and have more power available (bad weather, extra power for some lighting at night, etc.). Any more panels and the batteries will just not accept much more current (waste of panel energy and your money).
    If so, are there any recommendations on an MPPT charge controller for a setup of my size, as well as a recommendation for larger panels?

    The Xantrex XW MPPT charge controller is nice. The new Morning Star MPPT Charge Controllers are very nice (PWM and MPPT from both are good quality). The Rogue 30 amp MPPT controller is a solid performer too. (I am not in the solar business or connected with our host--just feedback from the board--do your own research).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • arkieoscar
    arkieoscar Solar Expert Posts: 101 ✭✭
    Re: Off-grid greenhouse

    There are several 12v air pumps on the market. They are mostly designed for aerating bait tanks for fishermen. That may save you the cost and losses of the inverter.
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse
    arkieoscar wrote: »
    There are several 12v air pumps on the market. They are mostly designed for aerating bait tanks for fishermen. That may save you the cost and losses of the inverter.

    Interesting. I didn't think to look for bait aerators. The only ones I'm seeing are quite expensive though. My other thought is to purchase a second 500GPH water pump, and rig it so that it pumps straight up into a U which sends it right back into the water; anyone familiar with aeration techniques know if this will provide sufficient oxygen in the water in a 150 gallon tank, as well as what my run time would need to be?
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse
    wrote:
    You really need to measure the pump in operation in your setup... Centrifugal pumps tend to use more power with high flow, and less power at low flow--So depending on the elevation of the output and if you have any valves to slow the flow down--it may use less power. Also--is this is a 24x7 or do you cut back on usage at night?

    Regarding the air pump--(and water pump)--you need to measure their power usage in your application... For the most part, name plate ratings tend to be relatively high compared to actual use--but not always.

    And with solar PV off-grid power costing around $1-$2 per kWhr (or more)--it might be cheaper and more convenient in the long run to trench an AC cable from your home to the green house (if power is available).

    I am fine with estimating high at the risk of spending a little more money on the front side of this project to make sure that I am covering all my needs with leftover capacity for those "just in case" times. I have it locked in that the water pump will run an average of 15 minutes per hour, which provides me with a pretty solid usage number. The aerator is another subject, and I think I may have some other ideas for it.

    From what I've read, I believe I can run the AC aerator I posted before @ 50% duty and supply a sufficient amount of oxygen to the fish, besides for the water cycling back into the tank via gravity. I still need to figure out just how loud the aerator is, and if having that pump cycling on and off every 30 minutes would stress the fish to the point of growth problems or even kill issues.

    But, like I said, I think I'd rather have more capacity to work with on the front end rather than getting everything setup and then realize that I need an additional panel to supply what I need. Running a cable really isn't an option at this point, as this will be completely off-grid and away from any housing (at least that's the plan right now).
    The Morngstar 300 watt 12 volt true sine wave inverter is a really nice unit. However, for your 7.5 watt load--you will have to look very closely at the various inverters--many have 6-8 watts of load just running with no load (including the Morningstar). So, you will probably have to assume that your AC air pump load will be the 7.5 watts of the pump plus 8 watts of the inverter minimum load.

    Wow, I guess I figured a smallish inverter would be a little less expensive. Admittedly it's something I haven't looked into fully yet. I would have liked to keep my system pure 12VDC, but the more I look at it, the more it seems that having AC ability is a necessary evil. It's a bummer that most inverters draw 6-8W idle, but again, one of the expenses of having the convenience of AC in the building.
    Looks good to me... Yes, more power is appropriate... Depending on local weather, you will have variations over time (more storms, less clouds, etc.). If your output is within 10% of predicted--you are doing very well (or it is an accident). 2x the expected about of power is not unreasonable.

    In the "physical world" (engineering wise)--you could possibly do things like run the inverter/air pump with a 50% duty cycle and probably not see a difference in your plant growth (again, engineering wise, less than a factor of 2--things are almost the same. Things that are 10x or more difference--you can pretty much ignore the smaller contributor). The SureSine inverter has a digital "inhibit" input--that you could connect to a cycle timer very easily.

    Pretty much true... Big panels are generally designed for large installations and Grid Tied use--both which use MPPT type controllers. Evergreen does make "12 volt panels" (18 volt Vmp)--You may have to look/call around to find some (very popular).

    To a degree--it will be a $$$ of panel vs $$$ of controller to figure out which would be the best price/performance for you needs.

    I'm really liking the price point on those Kyocera panels, and the 25 year warranty isn't all bad either. The panels are rated at 17.7Vmpp and 22.1Voc. If I decide to go with 3 or 4 of these panels, would it be best to go with an MPPT controller to make sure that I'm getting the most out of the panels that I can? My take on the previous link on charge controllers that you sent me, was that even with a true 12V panel and 12V charge controller, there is loss that can be regained using an MPPT controller (I know, that was kind of simple terms for what the article laid out..); is that a valid statement?
    The minimum battery bank AH rating rule of thumb is based on several underlying reasons... In the end, you could go with a smaller bank--but you will have few days reserve to cover cloudy weather.. And, roughly, if you have 1/2 the amount of battery capacity, the bank will, last about 1/2 the number of charge/discharge cycles--so the physical cost of the batteries over time will be roughly the same (1/2 the mount of batteries or 2x the amount of batteries)--assuming you don't violate any major rules (boil dry, run dead, store for days-week at less than 75% capacity).

    Do I need sets of 2 batteries to run in parallel, or can I run 3 batteries in parallel? My thought on this, is if I can get 3 12V, 220ah (or similar) batteries and run them in parallel, that will give me plenty of backup battery capacity in case I get more days than expected with little charge time, as well as a large enough bank to take advantage of the solar panels in peak production on a low charge. I've also read that a good solution is to run two sets of 6V batteries in series, and then parallel those two sets of batteries. As with anything, it is probably 50 cents of one or a half dollar of the other on what the best method is to get your desired end result.
    Cost wise for solar panels--you could go 2-2.5 times larger without damaging the battery bank--and have more power available (bad weather, extra power for some lighting at night, etc.). Any more panels and the batteries will just not accept much more current (waste of panel energy and your money).

    The thing I liked about the Morningstar charge controller I had originally decided to go with, is that it had a feature that wouldn't allow the batteries to be overcharged, as well as a configurable limit to how far the batteries could be run down in charge. It would pain me to see that my panels were charging my batteries in half the time I thought, but on the same hand, I could augment my battery array to allow for additional charging capacity.

    Thanks again for your responses, they are really helping me understand more about what is going on, as well as everything that needs to be taken into account before purchasing a system such as this.

    -Darrick
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    Perhaps a Powerhead to mix/aerate your tank... Past that point--you probably will need to talk with the experts. If you have schooling fish--you probably want water movement. If you have still water fish, too much water movement will hurt them.

    From the little that I could find--a powerhead will use a bit more power than an aerator but much less than pumping for a spray bar...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    I am not a big believer in running battery banks in parallel... When you run in parallel, you need to balance wire length/resistance so that the parallel strings properly share current. And each string should have its own large fuse for safety (more wire, more hardware, more money and issues).

    2-3 strings in parallel is very doable--I would go with a larger battery cell with higher current rating and a single string. But 2-3 maximum parallel strings does work for most people.

    MPPT controllers work on the principle of Pmax=Imax*Vmax --- And in cold weather, solar panels tend to have higher Vmp (voltage maximum power). So--the MPPT controller can, typically, harvest 10-15% more power +/- in very cold weather vs a PWM controller.

    The other very nice thing about MPPT controllers is you can put the solar array a 100' away from the battery shed and send the power over at up to ~100 volts DC and the MPPT can drop the voltage to 48-12 volts (depending on battery bank voltage) like a DC version of a transformer.

    The high voltage solar panel string can use much smaller copper wire (saves money) and less sensitive to voltage drop (farther distances supported) vs PWM controllers.

    For any controller--make sure you get the Remote Battery Temperature Sensor option--helps ensure batteries are quickly and properly charged (charging voltage drops as battery temperature rises).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Off-grid greenhouse

    Maybe areate the water as it goes to the plants? Maybe invest in disolved O2 meter, you may not even need areation, except in hot weather.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    Re: Off-grid greenhouse

    You do not generally need additional aeration in flood and drain systems, the action of the flood> drain pumping + exposing the roots to air give`s plenty, To add a little, You can try to make the fall back into the tank quite "splashy"

    Have a good one
    Tim
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    That is great to get some feedback on that. I have some ideas that I can use to provide more aeration for the water using the same pump that I'm using to flood my grow beds. The pump will have a main line exiting the tank to fill the grow beds, with a Y connection off of the main line into a smaller pipe with a U shaped spout to direct the water back into the fish tank with the flow being controlled by a ball valve. It would only run while the pump was filling the grow beds, but would eliminate the need for an additional pump as well as an inverter as the entire system would be able to be powered by DC. Here's an HD rendering of my idea:

    aeration.jpg

    Is the best solution for batteries to have 2 6V batteries in series to give me my 12V output? If I could find some 300-350Ah 6V batteries, I think this would be a good fit for the system. Something I need to do more research on I guess.

    If I ended up going with the 135W Kyocera panels, would it be best to run them in series into an MPPT controller, the use that to scale back the voltage to charge my 12V system? I'm having to wrap my head around a lot of stuff at the same time, but I think that would be the best solution for maximizing the output potential of my panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    Yes--you are understanding the MPPT charge controller correctly--it is sort of acting like a DC step down transformer for you.

    Regarding the "fish tank"--is it a tank full of fish or not?

    If "no fish", just let the drain back from the hydroponic table "fall" into the tank? I would assume that fish use much more oxygen than the decaying plant matter (in a fish tank, the fish take about 80% of the oxygen exchange).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    Alright, I'm finally starting to understand some of this stuff!

    Yes, it will be a fish tank. I haven't decided what species or how many as of yet, but there will be fish in there. Ideally they would be a species that would have enough meat to be eaten.

    -Darrick
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    What are some good tools to use for measuring what kind of production I would be able to get in the area that I'm going to be placing the panels? The PVwatts calculations are a good place to start, but I'd like to make sure I have a good idea of what kind of production I can expect before putting money down.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Off-grid greenhouse

    You might try http://www.green-trust.org/ they've had some articles about fish/hydroponics, recently, they setup a greenhouse and did a writeup of it.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    Darrick,

    From another thread, Jeff Fedison posted a link to his small company's web site to show how you can build or buy his version of a 5% accuracy solar irradiance meter--basically a small shunt resistor and DVM panel instrument--(I have never done anything with this website--but somebody else here said that they are good to work with).

    If you are looking for longer term automated measurement--They also have a battery powered data logger for, what seems to be, a nice price.

    The real question is are you going to do the measurements for 1 year or more to characterize the local weather conditions? I guess you could do, for example, 1 month and compare to PV Watts' monthly or hourly estimates.

    The issue with "measuring" your own solar is that local daily weather conditions affect the amount of sun you will receive. Looking at the "old fashion data" (charges and graphs), for Minneapolis (PDF), it looks like over a 30 year period, you have highly variable weather (cloud cover)--In the winter you may see a monthly average sun variation of 1.8 to 3.8 hours of sun in December (2.5 hours average) and 4-6 hours for July (5.6 hours average).

    So, will this year's measurement represent average, peak, minimum, or somewhere in between? In the end, extreme accuracy in measurement of a highly variable event is always going to be self limiting.

    Or are you looking to see how shade will affect your solar production... Poster "Nerdz" posted this Solar PathFinder report that his city (Burbank CA?) has as a requirement solar. I believe that Solar PathFinder software is still going to use a PV Watts like database for the average solar irradiation data.

    And--are you going to design for average or minimum monthly solar radiation--or just bite the bullet and use a generator to make up for the variability of solar collection (or accept that you will have to cut back on power consumption during stretches of bad weather which exceed your battery storage capacity anyway).

    If you need to use the power--regardless of sun--A generator and AC charger is going to pretty much be mandatory. I am a big believer that the generator+charger need to match the load requirements (typically charging requirements for your battery bank).

    Problem is that small systems need small, fuel efficient, generator sets. For manual start/stop--the Honda eu2000i, eu1000i, and eu3000i are some of the best (quiet, fuel efficient, not cheap). Yamaha makes some similar units, and there are knockoffs (of questionable quality). A Honda eu2000i will cost around $1,000 (Wise Sales or Mayberry are a couple suggestions) and a nice quality Iota battery charger another $130-$150 for a 30-45 amp battery charger.

    The Hondas, if setup correctly, could probably run your system (without solar) for five days (really rough guesstimate) on one gallon of gasoline (charge the battery bank every two-three days--hybrid generation system). Obviously, when the sun is out--then you would not need to run the generator.

    For larger systems--you can find gas/propane/diesel units in the 6kW +/- range from wrecked RV's for less than $1,000 (from what I have heard--your mileage will vary--diesel are probably more expensive). But these larger units will consume much more fuel if lightly loaded vs an euX000i version...

    Which comes back to my original question---Are you going solar because there is no utility grid option (too expensive), or are you doing this to learn, or "go green"...

    Off grid solar with battery backed power is never a cheap solution... It will cost ~10x or more per kWhr vs utility power (when you take capital and ongoing maintenance costs of batteries into account over a 20 year system life).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    Thank you again for the well thought out and informative post.

    I'll answer your last question first:

    I am doing this to learn about and become more familiar with solar power. I figured that since I was going to setup a greenhouse for housing my aquaponics setup, I would make it self sustainable (to a degree) while I was at it. I do realize that in the long run, solar is more expensive than being grid connected, but at the same time, I am mostly in control for when my building does or does not have power in a solar situation. Part of it is also "going green". There has been considerable discussion on this forum of what going green consists of. From a money perspective, this will definitely be more expensive, and I realize that up front.

    I hadn't fully thought through the testing idea. I likely will not be doing a year of testing, as I would like to have this project started when the snow clears this spring.

    As far as the design, I'd like to end up with excess, even if it adds extra cost, just to make sure I have all my bases covered. I am finding that without needing an inverter or air pump to start with, my requirements will not be as great as I originally thought. However, as I've seen explained many times on this forum, under estimating usage and over estimating production are two of the main faults when designing a system; I'd like to take the opposite approach if possible.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Off-grid greenhouse

    For my 2 cents--going green really starts with conservation and minimum usage/wasting of power--sounds like you are heading the right direction in your project.

    If you are looking for a "greener" solution--probably a Grid Tied system on your home and run a cable to the green house (if possible/practical). The nice thing about Grid Tied--You can pretty much use 100% of your power--either in your home, or even if you generate "too much" -- its still is used in your neighborhood (assuming 1 year net metering)... The issues with city/utility permits and approvals are not to be minimized--in may locals--Grid tied systems are really not even possible for many reasons (local codes, utilities that don't allow grid tied, poor financial return on GT systems, shade from trees/buildings, home owner associations, etc.).

    A pure GT system is the best bang for the buck--But it does not offer any emergency power support--If you have lots of power outages--a generator or hybrid GT/Off-Grid system may be worth it for you.

    The hybrids are nice... You have a battery bank--but it sits just a float voltage most of the time while the Hybrid inverter converts your solar power to power your home/utility. If there is a power failure, the Hybrid inverter has an internal transfer switch that can take your home (or part of it) off grid and supply power from your batteries, solar panels, and standby genset--basically a whole house UPS.

    If you can go with GT for your primary system--you will probably get a 4x return on the dollar vs off-grid for your capital costs over time (plus GT you can get various tax credits and breaks, and off-grid frequently does not).

    Not trying to change your direction--it sounds like you have the greenhouse loads down to a very reasonable amount--so the costs of an Off-Grid system are easier to justify for the learning experience.

    Very best wishes on your project!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwaller
    dwaller Registered Users Posts: 18
    Re: Off-grid greenhouse

    Well, my hopes to do this project this year have been dashed. The property that I thought I was going to be able to set this up on is now not an option, and I don't have room on my city lot to set this up.

    Instead, I will be doing a small indoor setup to gain more knowledge on the hydroponics aspect and once I get a handle on that, I will possibly introduce fish into the system. I really do appreciate all the help and knowledge sharing that I received from this site; hopefully I will be able to act on my plans in the near future.

    -Darrick