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  • solar power for greenhouse

    Hello SunEagle, I am new to the site and have read some of your post. I would like to ask you a question but cannot figure out how to navigate to do that. I tried to tag onto an existing post yesterday but im not sure how effective that is going to be so I thought I would try this. the following is the post I sent yesterday, any help on this would be greatly appreciated.

    Hello, I am new to solar and don't have a background in electricity. I just built a greenhouse and thought it would be a fun project to add solar power to run a pump (.5V) and fan also .5V. My solar panels produce 100 watts at peak and i am using a group 27 deep cycle battery with 180 ah. My pump runs 2 hours each day and the fan has been averaging about 4 hours. The problem is that my charge controller keeps giving me a low voltage alarm by the end of the day. I'm pretty sure I either need another battery in parallel or possibly more panels? Can anyone please suggest the best solution. Thanks in advance.

  • #2
    Originally posted by jeffsgreenhouse View Post
    Hello SunEagle, I am new to the site and have read some of your post. I would like to ask you a question but cannot figure out how to navigate to do that. I tried to tag onto an existing post yesterday but im not sure how effective that is going to be so I thought I would try this. the following is the post I sent yesterday, any help on this would be greatly appreciated.

    Hello, I am new to solar and don't have a background in electricity. I just built a greenhouse and thought it would be a fun project to add solar power to run a pump (.5V) and fan also .5V. My solar panels produce 100 watts at peak and i am using a group 27 deep cycle battery with 180 ah. My pump runs 2 hours each day and the fan has been averaging about 4 hours. The problem is that my charge controller keeps giving me a low voltage alarm by the end of the day. I'm pretty sure I either need another battery in parallel or possibly more panels? Can anyone please suggest the best solution. Thanks in advance.
    Hello jeffsgreenhouse.

    Do you know that wattage rating of the pump and fan? That (.5v) you stated does not make sense to me and it is hard to calculate the number of watt hours your loads will run in a day.

    A 180Ah 12v battery should be able to safely deliver about 540 watt hours a day. ( 180Ah x 12V x .25% = 540wh) So unless the pump and fan use more than that you should have no problem.

    I will say that a 100w panel can provide at best about 5.5amps of charging which is pretty low for a 180Ah battery. You really need somewhere between 15 and 22 amps to keep it fully charged at the correct rate. My guess is that you are slowly depleting the battery each day and the 100w solar panel is not putting back what you take out.

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    • #3

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      • #4
        This is the pump. It says .5 amps at

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        • #5
          After re-reading the manual that came with the solar panel system (harbor freight) I think I might not have the charge controller on the right mode to charge the battery. However, it sounds like you are saying I could use more panels to increase the amps? again, thanks for your help.

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          • #6
            I moved all of the posts to your this thread instead of being in 2 places.

            I still do not know which fan you are talking about. Please provide me with the model number and voltage.

            Also is that pump running at 12V DC or 120V AC?

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            • #7
              the fan is ILG8SF10V. I have the battery connected to a 1000W power inverter and the fan and pump are plugged into it.

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              • #8
                Originally posted by jeffsgreenhouse View Post
                the fan is ILG8SF10V. I have the battery connected to a 1000W power inverter and the fan and pump are plugged into it.
                Ok. That fan draws 0.55A at 120V which calculates out to about 66 watts.

                If the pump also draws 0.5A at 120v that also comes to 60 watts.

                With 4 hours for the fan that calcs to (66w x 4h = 264wh) and the pump at 2 hours comes to 120wh.

                So your total daily load is roughly 384wh. With losses that could easily increase to 450 wh which is less than what I calculated for that 180Ah battery.

                Now I see two issues.
                1st - that HF 100W system probably does not even get you 5 amps of charging and it will degrade a lot over the next 2 years.
                2nd - that 1000w inverter is probably consuming 5% of its rating all day long, which calculates to about 1200wh (1000w x 5% x 24h = 1200wh. Add that to your 2 loads and you are draining your battery almost down to nothing each day. You will never put back into the battery what you use to run your loads and inverter with only 100watt of panels.

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                • #9
                  would a 400w inverter help?

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                  • #10
                    Originally posted by jeffsgreenhouse View Post
                    would a 400w inverter help?
                    Yes. Depending on the type and how it is used will save you a lot in watt hour usage. Look at the inverter specs and see what they rate it for "losses". That value is in either watts or a % of the inverter watt rating. Now if you leave the inverter on all the time it will continue to use those wasted watts. If you plan on only running the loads during specific times of day it can be turned off during the other times which again reduces your watt hour usage.

                    The biggest issue you have is just not enough charging amps to put back into the battery what you take out each day. Over usage will shorten the number of cycles requiring a new battery much sooner then you had figured.

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                    • #11
                      Thanks, I really appreciate your help and patients. I think i will switch to a 400w and only power it on during the day. i will also invest in another 100w panel.

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                      • #12
                        I also have a greenhouse with a solar system. I have a fan similar to what you have. The plate on the side of the motor says 1/20 hp. If you work that out it should be 37 watts. Long story short, a kill-a-watt meter says it draws 106 watts when running. You might want to verify what your actual loads are with one of those before buying more equipment. I have a 300w inverter with outlets and simply plugged the kill-a-watt meter into the inverter outlet and then the extension cord into that (everything in the greenhouse is powered off that extension cord). Bottom line is that I learned my actual loads were higher than I thought they were.

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                        • #13
                          Thanks, I will look into it. can you tell me how many watts your solar panel put out and what type of battery you are using.

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                          • #14
                            One more thing to watch for, cheap $130 400w inverters, are often Mod-Sine inverters and will cause motors to consume 20% more power than spec'd. You should run motors off of a Pure-Sine inverter (costs more)
                            Powerfab top of pole PV mount (2) | 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

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                            • #15
                              Originally posted by jeffsgreenhouse View Post
                              Thanks, I will look into it. can you tell me how many watts your solar panel put out and what type of battery you are using.
                              I have a ventilation fan (the one that says 1/20 hp, but draws 106 watts) which is on a thermostat. It only runs when the greenhouse is getting too hot and that only happens when the sun is shining brightly. I also have a circulation fan that is on a timer than uses about 40 watts. That runs about 4-5 hours per day. The timer runs constantly and draws about 1.5 watts. There is also a radio that is on when I'm in there and has a minimal draw. I figure the 300w inverter uses around 15 watts and is on constantly.

                              I have two 190 watt solar panels that face due south and are tilted about half of what would be optimum for my latitude (61* north). The battery bank is four 6 volt Costco golf cart batteries wired in series for 24 volts. The greenhouse is in operation from mid-April through the end of September.

                              In sunny weather the solar system easily keeps up with everything. The highest draw item, the ventilation fan, only runs when it is sunny and doesn't draw on the batteries at all. The circulation fan runs early morning and is powered almost solely off the batteries. If it is a sunny day, the batteries are usually fully charged before the ventilation fan comes on. However, in late summer we can go a week or more without any sunshine and the batteries may start to fall behind. When that happens I'll usually cut back the time the ventilation fan runs, charge the batteries from another source, or just shut the inverter off until the batteries are fully charged again.

                              Hope that helps.

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