Heating my greenhouse

Have a greenhouse 16'x 8'x7' (896 qf) I wish to use 3 solar panels @ 15w ea. (45W) through a charging regulator to a set of batteries @12v to power my 1000w continous MSW inverter to power a 1000 watt coil heater. I plan to use 4 deep cycle marine batteries giving me about 400 ah. the heater will have a thermostat set a 54 deg. and should be on about 7 to 9 hours (nights), will this setup work ? :confused:

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,329 ✭✭✭✭
    Re: Heating my greenhouse

    You are better off adding thermal mass wall to the back of the greenhouse to absorb day time radiation. I knew a guy in Colorado that used milk jugs with water in them.

    45 watts of solar panels will do nothing to run a 1000 watt inverter or charge 400ah of batteries. In a short time the batteries will be DOA.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Heating my greenhouse

    Welcome to the forum.

    If you want to see the math it looks a bit like this:

    45 Watts of panel * 4 hours of good sun / 2 = 90 Watt hours of AC power.
    That would run a 1000 Watt heater for about 5 minutes.

    The batteries could supply 200 Amp hours @ 12 Volts or 2400 Watt hours.
    That would run a 1000 Watt heater for about 2.4 hours.

    Neither includes the system efficiency losses.
    Electric heat is terribly inefficient. Solar Dave's suggestion of mass storage (and a bit of insulation) will work far better.

    And stay tuned, for next year I'm supposed to redesign a conventional "kit" greenhouse into something that will work in the Cariboo without suffering from the 50C daily temperature swings. Don't ask me how I'm going to do it, but she who must be obeyed commands it. :p
  • mike95490mike95490 Solar Expert Posts: 7,217 ✭✭✭✭
    Re: Heating my greenhouse
    .....
    And stay tuned, for next year I'm supposed to redesign a conventional "kit" greenhouse into something that will work in the Cariboo without suffering from the 50C daily temperature swings. Don't ask me how I'm going to do it, but she who must be obeyed commands it. :p

    I'm tracking this thread, as I also co-habit with a SWMBO.
    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 ,

  • solar_davesolar_dave Solar Expert Posts: 2,329 ✭✭✭✭
    Re: Heating my greenhouse
    mike90045 wrote: »
    I'm tracking this thread, as I also co-habit with a SWMBO.

    Ditto from me too! In fact this coming weekend is one of those!
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Heating my greenhouse

    Every year I say I'm going to build a lean-to greenhouse. Every year I put it off until too late and the plants take over the kitchen for the winter. Every year my wife complains when I move the plants inside. Every year she complains when I move them back outside in the spring because she has gotten used to them being in the kitchen.

    Some fights you just can't win.
  • System2System2 Posts: 6,290 admin
    Re: Heating my greenhouse

    Thank you for your input, it is something to think about. I wonder if having an abient temp. of about 65 - 70 deg. during a sunny day and a 1000w heater to heat the jugs.... how fast the heat from the jugs would take to drop from 65 or 70 deg. Do you by chance have a link to the Colorado man ?

    Thanks again
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Heating my greenhouse

    Haven't worked out the details, but the basic principal hinges on being able to control both the thermal gain and the thermal loss.

    So for gain it is best to have double-pane glass with a southerly exposure and good ventilation for when the temp starts to get too high.
    For controlling the loss you need good insulation on the non-solar surfaces and enough mass to heat up during the day and radiate back at night keeping the temp above "too cold" (which will vary according to the plants).

    Unfortunately the kit greenhouses fail on all of these counts, being basically aluminium (heat conductive) frames with single-sheet acrylic or polycarbonate sheets in-between for all surfaces.

    I see potential in adding R5 foam insulation (at least) between the frame pieces, Reflectix in some areas, additional solar-powered venting, and some ceramic tile floor mass at least.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse
    Electric heat is terribly inefficient. Solar Dave's suggestion of mass storage (and a bit of insulation) will work far better.

    Minor point of correction: electric heat is 100% efficient, you put one kilowatt of energy in, and get one kilowatt of heat out.....zero waste.

    The problem is the generation of electricity can be extremely inefficient....which I'm sure is what you meant.

    In this case, 45w probably won't even keep up the self discharge on that size battery bank, much less leave any to work with.

    Takingtime1 would do far better to do as ya'll have suggested, and build a well insulated greenhouse with lots of thermal mass to minimize the amount of heat needed to start with.....then use solar for direct heating of air or water, and store it for overnight/cloudy days.


    Hey...that's what I'm doing ! ;)


    When I first set up my PV system, I need a "power room" out as near to the arrays as possible to house the gear and batteries. So I benched out a place in the south facing side of the mountain, and built a combo solar room/greenhouse ( SWMBO got the greenhouse part ).

    Initial construction:

    The small 4x8 section on the front left side is my power room, the 12x20ish on the far end is her greenhouse.

    ry%3D480

    The back, far end and front wall are all earth bermed. The front is a permanent bed of strawberries outside now.

    ry%3D480

    Homemade rafter/trusses made of 2x6 treated lumber/plywood gussets, on 24 centers. You can see the trackers I built for my two initial arrays before the drive actuators or panels were installed.

    ry%3D480

    Same shot, taken from the house garage door.

    ry%3D480
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse

    Completed greenhouse, two arrays behind with actuators installed now.....my two helpers in the pic. The glazing is 16mm triple wall polycarbonate panels (4' wide, custom ordered for length). REALLY nice stuff to work with.

    ry%3D480

    Inside shot. Knee walls are 2x6 with fiberglass insulation, and 1" pink foam inside.

    ry%3D480

    Outside. Raised bed, gutter into water barrel.

    ry%3D480


    First year we did raise tomatoes, but even this design requires a lot of supplemental heat to keep the overnight temps up to where tomatoes will set fruit, so last couple years, she overwinters her deck flowers, and raises bedding plants for the garden to get a head start there.

    ry%3D480
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Heating my greenhouse

    TnAndy;

    That is some fine building!
    Unfortunately I shall have to delete the pictures to eliminate any possibility of my wife seeing them. :p
    (Just kidding, of course.)
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse

    Even in sub-zero weather, the greenhouse will stay above freezing, but only slightly. As I said, too low to work with warm weather crops like tomatoes w/o adding heat.

    ry%3D400

    But it CAN be done:

    ry%3D480

    This year, I rounded up some stainless steel 55gal drums off Craig's List, and plan to mount them under the benches for water storage. Also snagged a few water collectors ( parabolic reflector type ) that were used to heat water for a YMCA pool for many years, plan to mount them above the back top edge of the roof, and run a solar water heating system during sunny days and store the water in the drums, just letting it bleed heat off during the night. Let ya'll know next spring how that project worked out !
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse
    TnAndy;

    That is some fine building!
    Unfortunately I shall have to delete the pictures to eliminate any possibility of my wife seeing them. :p
    (Just kidding, of course.)


    I completely understand....a man's gotta do what a man's gotta do.....ahahahaaaa
  • BB.BB. Super Moderators Posts: 26,658 admin
    Re: Heating my greenhouse

    Note that Heat Pumps can be ~200% efficient (yes, for a 1,000 watts in, you get 2,000 watts of heating out).

    Pretty neat. Better than a simple (and cheap) electric heater.

    Heat pump systems are not cheap:cry:--but lay that over electric (or off grid) cost of power--They can have pretty nice savings/payback.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Heating my greenhouse

    You know, the concept of a solar hot water heater system to heat water mass inside the greenhouse is a good one. There is always a risk of freezing, of course, if things go wrong. But if you buried a big underground tank ... I believe someone on build-it solar http://www.builditsolar.com/ did just this to heat a shop or possibly a house.

    The temperature swings for the greenhouse in the Cariboo are psychotic: I have a thermometer in there that gives up at a high of 50C and on the same day it will record overnight temps below freezing.

    Like I said, everything about those kit units is wrong.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse

    Yeah, the fluid I'm planning to use will be a glycol-water mix. Scored some cases of vehicle anti freeze off CL, and plan to mix it for about a -20 situation.

    My next greenhouse project, I plan to go something like a 24x40 with a thermal mass wall on the north side, and use conventional tubing/double wall plastic on the overhead. Then I've got a BUNCH of pex heating tubing and a couple of zoning manifolds left from a project house that never happened, and I plan to get an outdoor wood boiler and sink the Pex in the ground under the bedding areas of the inside of the greenhouse.

    So many projects......so little time.....
  • mike95490mike95490 Solar Expert Posts: 7,217 ✭✭✭✭
    Re: Heating my greenhouse

    here's the solar water heating shed:
    http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
    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 ,

  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Heating my greenhouse

    Here is a house in Maine that uses solar heat in a big way (and solar PV, but not for heating). Click on the link on the left side. http://www.solarhouse.com/
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Heating my greenhouse

    How about a compost furnace? Gardens and greenhouses produce lots of biomass. Why not put it to work heating your greenhouse? I am yet to try it, but seriously considering the idea for our greenhouse-to-be. I have friend who's tried it in his greenhouse. He does employ multiple techniques (compost, insulation, thermal mass), but he manages to keep his greenhouse above freezing through Montana winters. Here is a link to one if his blog posts: http://montanawildlifegardener.blogspot.com/2009/01/heating-greenhouse.html
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭✭✭✭✭
    Re: Heating my greenhouse

    TnAndy- your pictures just made my wife drool! Very nice looking greenhouse you have, it's been on our list forever now and I think your posts just bumped it a bit higher up that list...
    Cheers!
  • SCharlesSCharles Solar Expert Posts: 123 ✭✭
    Re: Heating my greenhouse

    I fought the keep-it-warm-enough-in-winter thing for several years, refusing to consider gas or electricity. I gave up. Some vegetables are sensitive enough to temp' that even a few nights of cold will disrupt their growth/fruit set. Plus, as someone else alluded to, many plants, such as those in the tomato family, need a certain number of hours of light to set fruit or to produce fruit that is edible. Plus, that light must be of sufficient quality and strength. Lost of $$$ to set up some sort of light system and lots of electricity to run them. Not really useful for people of average financial resources and just growing for a household. Maybe ok if you are selling fresh produce to restaurants or whatever in winter and can charge a premium in a commercial operation, I suppose.

    I now let my plants go by about October and the greenhouse rests til spring. I can use it for germinating new plants from seed starting anywhere from January to March, though the earlier winter months are still dark and cool and the seeds are not as fast to germinate and the seedlings don't grow very fast. I've found, for my high Colorado area, starting seeds in the greenhouse is about as effective in March or April as January, they grow that much faster in the early spring anyway. Last year, I started some seeds in Jan. and some in May, to test this, and by the first of June, the plants were all the same size.....

    The heat-water thing, with solar water heaters or any other method, would probably lessen or eliminate the winter temp' swings in my greenhouse. However, enough volume of water will take up much space. I don't care how big the greenhouse is, before long you'll want even more room for growing. Dedicating room in the greenhouse to water storage must be planned and engineered carefully to prevent losing too much growing area. If outside the room, maybe better but not an option up here where I am.

    I do keep my herbs in pots so they can come into the house proper and live on windowsills during the winter months. The lower light/shorter days slow them way down, too, but I plan for that now and have many more pots of basil, etc., that I could ever use during the summer.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: Heating my greenhouse
    SCharles wrote: »
    The heat-water thing, with solar water heaters or any other method, would probably lessen or eliminate the winter temp' swings in my greenhouse. However, enough volume of water will take up much space. I don't care how big the greenhouse is, before long you'll want even more room for growing. Dedicating room in the greenhouse to water storage must be planned and engineered carefully to prevent losing too much growing area. If outside the room, maybe better but not an option up here where I am.

    Why can't you bury the tanks outside of the greenhouse? That's what I would do, free insulation and it wouldn't take up useable space.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • SCharlesSCharles Solar Expert Posts: 123 ✭✭
    Re: Heating my greenhouse

    Yes, burying would be an option some places. Not here. We sit on pretty much solid rock. It would take a major dynamite/drilling operation to get a hole. It could be done in an above-ground shed or something, then piped into the greenhouse. I don't have the room for it.

    Some friends of ours in a different area dug a huge hole next to their home and filled it with rock. They ran air through the rocks, air heated by panels on the surface. They had a way to blow air through the rock and into their basement through vents, then the air made its way through their upstairs and was exhausted to the outdoors. The idea was that the rocks, once heated up, would provide a fairly even source of heat even when the sun wasn't shining on them, a heat-sink to keep them warm around the clock and keep them warm on cloudy days. It was a pretty slick and technical set-up and you could stand next to the vents in the basement and feel warmish air coming out. But it was not hot air or even REAL warm air. After a few years of trying, they mothballed the system. It kept the house from freezing [protected the pipes if they were gone] but they were not warm enough for any comfort. They'd spent a lot of money on it, and perhaps a water system would have worked better. Maybe.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Heating my greenhouse

    Water is a far better storage medium.....about 2 to 3 times better than crushed rock ( depending on the % of void in the rock ), per unit of volume, as your friends found out.
  • TheBackRoadsTheBackRoads Solar Expert Posts: 274 ✭✭✭✭✭✭
    Re: Heating my greenhouse

    Just throwing out an idea, why couldn't you use a tank(s) as legs for a growing table. (set a wood table on top of a tank) Surely not everything sits on the floor....?
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