You're probably thinking to yourself "Hey, isn't EVERY greenhouse solar powered?" To which you'd be correct. The greenhouse I've created is in fact a DOUBLE solar powered greenhouse in that it uses sunlight both day and night to help plants grow.
I live in Wisconsin, which is usually rather nice. Unfortunately Winter has been going full blast for months and shows no signs of letting up. For a mammal like myself, this kind of weather is annoying but not overly harmful. For my various house plants, however, this weather is quite deadly. Especially to the very small plants I'm trying to cultivate on my kitchen table.
To help my plants get a leg up on this weather I decided to build a greenhouse. The only problem is that a greenhouse only works part of the day when the sun is up. To give my plants a boost up, I'd have to throw on some grow lights which gets expensive and are overkill for my very small plants.
What I needed was a lighting system that turned on only at night. Not a tough task to accomplish so I decided to mix it up a bit and add an element of solar power to it. What I ended up with is a little acrylic plant incubator that runs night time lights powered by solar energy. (Just like the plants.)
Double Green Energy.
Step 1: What You Need
If you need some solar cells you can grab the one I used at my educational electronics website BrownDogGadgets.com. Otherwise all these parts can be found at local Radio Shacks or Maker Spaces.
2N3906 PNP Transistor
5K Ohm Resistor
2 AA Holder
2 Rechargeable AA Batteries
Solar Cell (I'm using a 5.5V 320mA Solar Cell)
Optional: Perf Boards to solder everything onto
(Or the super simple route of grabbing an old solar garden light and gutting it.)
Acrylic Cut Case
(Or going the super simple route of using a 2 Liter Soda Bottle cut in half.)
Step 2: Theory
There is nothing like natural sunlight. Pure, natural, solar power has more nourishment than anything people can create. Luckily we can produce a decent alternative every now and then.
During the Space Race different governments experimented on plants to determine what light wavelengths helped plants grow the best. When it came down to it, Red and Blue wavelengths produced the best growing results. These types of experiments are common in junior high and high schools as students can easily use colored glass or other materials to filter natural sunlight and then record plant growth. (Above image is from Wikipedia and shows NASA using red LEDs for growing. We're doing something similar)
It also goes without saying that the longer the length of time a plant gets sunlight each day the faster it will grow. This is how Alaska is able to grow various plants so quickly during the summer. Instead of having a long growing season with normal daylight hours, their plants just get a short growing season with very long daylight hours.
In this project I've taken both of those ideas and combined it with a very simple solar dark detecting circuit. During the daytime the solar cell recharges the batteries. At night the LEDs turn on via the batteries to help the plants grow. I'm using a bank of Red LEDs, though you may wish to try a combination of red and blue LEDs.
Step 3: The Super Simple Budget Version
Like many guides on Instructables, I'm going to completely nerd out and go overboard. My version required me to have access to a laser cutter and a stash of electrical parts. Easy to come by if you're at a college or Maker Space, not so easy to come by in most people's basements. This project doesn't have to be difficult or expensive which is why I'm first going to show you the super simple 10 minute budget version.
1) Grab a 2 Liter Soda bottle and cut it in half. Invert the top half into the bottom half. Put a plastic container on top. Greenhouse in two minutes.
2) Grab an old solar garden light. (Or find a super cheap one. Never spend more than $2 on one of these things.)
Take it apart. Put a red piece of clear plastic over the LED.
Or, if you want to be a tiny bit fancy, you can remove the white LED and wire in several Red LEDs. Just wire them up in Parallel. You could even slip a blue LED in there. If you're going this route, replace the AAA battery with a AA rechargeable battery. Check out this guide on how to replace/ add on more LEDs to a garden light.
3) Now combine the two together. Bingo. Solar powered LED greenhouse for the cost of a soda bottle and a garden light. (And possibly some Red LEDs.)
See, told you it wasn't tough. Now if you're wanting to make a really really powerful version….
Step 4: Wire Up The Circuit Board
Shown above is a very simple Dark Detecting circuit. It's quite similar to the one found in every day solar garden lights. It uses the solar cell and a PNP Transistor as it's dark detecting sensor.
(After completing this project I wished I would have gone with a Joule Thief setup. You can find many guides on Instructables for making a simple Joule Thief, and even a dark detecting Joule Thief. It's probably in your best interest to go that route if you can.)
I'm using a simple perf board to hold all the parts together. You could easily freehand this, but I had some boards handy and decided to use them.
Before you get going, try this out on a Breadboard. Seriously. Even though I've made this circuit 100 times, I STILL managed to put the transistor in backwards! (Which, not to everyone reading this, the TRANSISTOR IS IN BACKWARD in all of my photos until the end.)
First, place your parts on the perf board. Give yourself plenty of room. I started with the diode, resistor, and transistor. (Which is in backwards in my pictures.)
Second, solder the parts into place. Use their legs to connect them to each other.
Third, solder in the AA battery holder. It may be helpful to cut off some of the wire leads. I also like to thread my wires through a perf board's screw holes. This relieves tension and prevents the wires from breaking.
Fourth, solder some six inch wire strips to your solar cell. (I'm using red and yellow. Red for positive, yellow for negative.)
Fifth, if you'd like, you can solder the solar cell wires to the board or wait until later. At this point we're done.
I've written several notes on the photographs which may be of interest, so read up!
Step 5: Wire Up The LEDs
I used 12 big 10mm red diffused LEDs, and obviously the more LEDs the better. They're all connected in Parallel which means all of the positive legs are touching each other and all of the negative legs are touching each other. (You would probably have better luck using clear LEDs instead of diffused. That way more light reaches the plants.)
Now there are plenty of ways to do this, but I found it most simple to just use another piece of perf board.
I decided to place one LED on at a time, soldering it into place. I then connected each LED's legs to the next LED I laid down.
To make things super simple I made sure that the long leg on each LED (which is the positive leg) was always facing outward. This way I wouldn't get any of the legs mixed up.
After I soldered on all 12 LEDs, I cut two very long wires, stripped one end, and connected them. The yellow wire was soldered to the Negative row of legs while the red wire was soldered to the positive row of legs. I then tested them out using a battery.
Now my method of hooking up LEDs was not pretty, but it was functional. You could easily use some cardboard to hold them all together if you'd like.
Step 6: Connecting Everything
Before connecting everything up, make sure you thread your wires through the top of your "greenhouse" otherwise you'll have to cut your wires in order to get the LED board in.
At this point, all you'll need to do is solder the two long wires off your LED board to the Transistor Board.
Hook the positive wire to the unused Transistor Leg.
Hook the negative wire to the solar/ battery pack negative wires.
Your circuit is done.
I then used some foam tape to mount both the board and the battery pack to the rear of the solar cell.
*** In the final photo on this step you can see where I cut out the "backwards" transistor and just wired a new one in. This is why I always leave myself space.
Step 7: The Enclosure
I'm a member of the Milwaukee Maker Space and thus have access to a laser cutter. I cut some clear acrylic to form two boxes that fit on top of each other. This way I could lift the top off and water the plants. I also cut some little "leaves" into the acrylic for air vents. They ended up looking like birds.
*** You could easily make something similar to this on your own using clear plastic container. Just look around for some simple greenhouse designs. ***
To hold the entire setup together I used some water proof aquarium sealer I had from another project.
First I put the boxes together and used rubber bands to hold them right.
I then laid lines of sealer everywhere. That was difficult and annoying. (Regular white glue would work, I was just worried because of the moisture that would be around this thing.
The sealer takes 48 hours to cure. After waiting 48 hours it seemed dry but just to be safe I'm going to leave the rubber bands on for another 24 hours.
I made the enclosure large enough to fit 4 egg carton slots as I often use egg cartons to germinate seeds. You could make yours any size it just depends on what you're growing.
I also drilled in some drainage holes on the bottom. Just on the off chance I want to put a larger plant in there later on and I have water spillage.
I attached the LEDs to the top using Foam Tape. (You could use hot glue to fix them into place as well.)
Step 8: Add Plants and Enjoy
Just add your plants in and start the growing!
I think this project would work really well for germinating seedlings or for giving extra love to a plant that's not doing well. You could easily scale this project up and use it with larger plants. This would also make a nice science fair project as well.
Thanks for reading this guide. Let me know your thoughts on this project as well as ways you might improve the design!