Introduction: Going Off-Grid in the Aquaponic Geodesic Dome Greenhouse
I finally finished up the solar setup for the geodesic dome. It's amazing how you have to watch every watt you're consuming when you're not connected to the power company! This video details how it all went together. Enjoy!
Below is the transcript:
Large solar systems can produce current that can easily and quickly kill you. If you are not qualified to perform this kind of installation, please hire a licensed electrician that is experienced with photovoltaic solar systems.
In this video, I will show you how I sized and installed an off-grid solar system for my aquaponic geodesic dome greenhouse.
First I’ll start with a few calculations to figure out how large the system will be. It’s important to accurately find what the total wattage of all the equipment will be, including the electronics for the solar system. Since it is off-grid, there is no way to plug in the system if you run out of battery storage!
The average wattage of my equipment is 90 watts, so I increased it by 10%, just in case. For a 12 volt load, this calculates to 2400 watt-hours per day, or 200 amp-hours per day.
Each panel that I purchased is rated for 245 watts. This next part is important! The system has to be sized on the average amount of available sunlight during the winter. A visit to the National Renewal Energy Lab’s web site provides great information about the amount of sunlight that is available throughout the country.
The map for December shows that Connecticut gets about 2 hours of available light per day. This means I need to produce and store enough energy in 2 hours to run the pumps and electrics system for the entire day. During the summer, there will be a surplus that I can use for cooling the greenhouse.
Next is a percentage of lost light. Since this is a fixed mounted system and doesn’t have a solar tracker, it’s a 20% reduction of available sunlight, and then I added another 10% for trees and other obstructions. The calculation shows I need for 7 panels which I round up to 8 so I can evenly install four on each bank.
The deep-cycle batteries are rated for 325 amp-hours of storage with a depth-of-discharge of 50%. Based on the 100 watt load, I will need 1.2 batteries to store one day’s worth of power. Since these are 6 volt batteries, I need at least two in series to get 12 volts, but I purchased four which will give over four days of storage in the event the panels are covered in snow.
Now that everything is delivered, it’s time to get it installed!
The roof over the shed is a great location for the panels. It does angle to the north so it will need brackets installed to angle the panels to the south.
The brackets for the panels are attached to feet which are bolted into the roof rafters. The bolts must be anchored into the rafters to prevent the panels from ripping off in strong winds. To keep water from leaking through the shingles, the foot is covered with a special piece of flashing. A sealant is also used around some of the pieces to ensure water can’t get through the roof.
Once the first foot is installed, I can use a compass to orient the base bracket so the panels will face south. Now that the base bracket is oriented properly, I can anchor the remaining feet into the rafters. The top bracket temporarily rests on the roof so that the panels can attached to it.
The next step is to get the panels up on to the roof and fasten them to the mounting brackets.
The panels on the edges use a little clamp that slides into the bracket tracks and it then grabs to the inner lip of the solar panel. Between each panel, there’s a set of hold-down clamps.
The University of Oregon Solar Radiation Monitoring Lab has a nice program that can be used to calculate the solar elevation for your location. Just enter the zip code and it creates a chart showing the angle of the sun throughout the year. The average peak for here is about 47 degrees, but during the winter it’s all the way down 25 degrees. I set these panels to about 40 degrees. At some point, I may modify the legs so they can be adjusted depending on the season.
First I prop up the panels with temporary legs. Then I anchor a foot for each leg into the rafters below and attach the final leg.
The wiring on the panels have connectors molded into them with gaskets to keep water out. Any excess wire is just coiled up and attached to the brackets with cable ties.
To get the wires down through the roof, I installed a vent pipe. This allowed me to snake the wires with the molded connectors through a large hole. I then put a cap on it to prevent any rain from dripping through.
The electrical code now requires that photovoltaic systems have an earth ground. It’s always quite the challenge to pound an 8 foot rod through our New England soil.
All the electronics are mounted on a piece of cement fiber board. Even though all the controllers are in enclosures, it’s nice to have the extra insurance against a fire.
The power from the two sets of panels enters the building and comes to this circuit breaker box. This allows for the power to be disconnected from the entire system. Before doing any wiring, it’s important to make sure that the solar panels are disconnected up on the roof.
All of the circuit breakers have studs, so it’s necessary to put eye connectors on the wires. Not only do I crimp the connector on, but I also solder it so that it has a good bond with the wire and it will never fall off.
After the circuit breaker disconnect panel, each supply line goes into its own charge controller. The charge controllers are used to monitor and charge the battery bank at the proper voltages. This particular model has a lot of great features including data logging, battery temperature compensation, and networking.
The batteries are 6-volt flooded lead-acid. Two of them are needed to be connected in series to get to 12 volts. Then the first set is connected in parallel to the second set.
The power from the charge controllers goes through another circuit breaker disconnect and then to the battery bank. This disconnect panel is used to safely disconnect the batteries from rest of the system if it requires maintenance.
The power from the batteries goes back up through the disconnect panel, then into a load controller. This controller is used to monitor the battery voltage and disconnect the power between the batteries and the load in the event the voltage gets too low. After the load controller, the power goes into a circuit breaker panel, which is used to distribute the power to the various loads, which in my case are the pumps, fish feeder, and vent openers.
That’s the entire setup. If you enjoy these videos please don’t forget to subscribe to this channel and join us on Facebook. Thanks for watching!
Power comes in from the two solar panel sets through two 80 amp circuit breakers which are used as a power disconnect. Each line goes to a Midnite Solar classic 150 charge controller where the voltage is stepped down to provide the proper charging voltage and current. From the controller, each power line goes through a 100 amp circuit breaker panel which is used to disconnect the power from the batteries. A single line then goes from the batteries through a 40 amp disconnect breaker and through a Xantrex C35 load controller. Last the line goes into a circuit breaker panel which is used to distribute power to the various devices.
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