solar heater for cold frame

I was wondering if anybody ever made a solar-powered heater that could be used in a cold frame. What I am looking for is this: Something to kick on when it gets 27 or 28 and raise the cold frame a degree or two. It could do this two or three times in the night and I'd be happy. I was wondering if a 15W solar panel could do it?

I haven't done what you describe.

What you describe would require some sort of battery to store power generated during the day and then power a heater at night--maybe even just a few light bulbs.  Not sure about specifics there, interesting if anyone has done this.

If interested, I posted this about my cold frame last March.  I don't use my cold frame all year--only late winter/spring for getting things started.  My cold frame is above ground, on my deck along a south facing wall of the house.  It sits on extruded polystyrene (pink foam board) and I made a pink foam board shell (covered with a tarp) I put on it at night.  The cold frame is lined with water filled milk jugs that were spray painted black.  It did a good job down to nights in the upper single digits last March--but it is very dependent on the amount of sunshine the day before.

A cold frame actually within the Earth would do better on its own and this approach may be enough to get you over the top (the black jug part, as I'm guessing you're not wanting to cover/uncover something out in the yard all winter). Just a thought.

(oops, late to the gate. +1 for what jmsieglaff said)

I've never made one; I'm just thinking out loud:

A basic system: A solar panel would charge a battery that, controlled by a thermostat and relay, would power a DC heater or light bulb.  

Without even sizing out the components needed, the dollars are adding up fast to a point that in my mind makes the idea not economically practical.  

You'd be better off looking into passive solar heat storage ie heating a mass within the cold frame during the day that would release the heat after dark.  Water containers, concrete, and rocks are frequently used for that purpose.

Any cool season veggie should be OK at 27-28 degrees inside a cold frame.

Dave had a muse on this  thread .
 
I love tinkering as my main trade was electro mechanical engineer who worked in industrial electronic testing & servicing  for a while many many moons ago .


My conclusions are :-

Perhaps think along the lines of a small PV solar panel charging  a single  12 volt 100 Ampere hour lead acid battery (  tested & working well  ..off a truck out of a breakers yard perhaps )  or even several 12 volt batteries wired in parallel.
 
You can get 12 volt DC time clocks nowadays ( online off eBay ??) for those that live off the grid who want to run central heating switches etc. but don't have regular mains power supply wire to them .
  
So it would be relatively easy to wire up two 10 watt bulbs in parallel and set the time clock to bring them on say once every 30 min for 10 min and use them as warmers .

 The plants would also enjoy the few extra meagre beneficial radiation/ light  rays that the incandescent lamps give off . 

 Or 

 Perhaps even more a simple ....get hold of bi metallic adjustable thermostat that only needs cold/ heat  to get it to operate on and off.
 

The best thing about PV panels is that they don't need real bright sun to get maximum voltage /current output .. thy work well on quite grey days. so long as there is reasonable light to see by


 Though you would do well to check out just how low or high  a temperature the panels can  effectively generate electricity at and select the  type best for you . Electronics in most normal electronic devices need heater resistors to keep things warm if the temp drops below about minus 20 oC . The PV panels have an electronic processor controlled charging regulator associated or integral with them to charge the batteries .

That has given me an idea. I think for starters, I will insulate the inside of the cold frame with that pink foam insulation, maybe 3/4 inch. The cold weather earlier this month, zapped the lettuce when it got below 21 or 22 degrees.

cyclonegardener wrote:That has given me an idea. I think for starters, I will insulate the inside of the cold frame with that pink foam insulation, maybe 3/4 inch. The cold weather earlier this month, zapped the lettuce when it got below 21 or 22 degrees.

I bought a wonderful book this fall called, "Backyard Winter Gardening," by Caleb Warnock. One of the most valuable things in the book is his list of cold weather tested seed types.  He also sells his own seeds and I have purchased quite a few from him.  He is quite involved in finding, growing and saving old heritage seed types and is an entertaining writer.

His website is calebwarnock.blogspot.com


Lettuce is one of the things I'm growing the most in my winter garden.  We live 50 miles from most shopping so having fresh lettuce is our most cost effective money saver we can grow (not so much for the cost but for the time/money/effort saved in making fewer trips down the mountain).