In early August I convinced a friend that I was able to provide hydroponic grow beds for his greenhouse. We deciding the system must run off a solar panel because the power was too far away from the greenhouse. I had a solution already as I intended that the Growers’ Gizmos system would be solar powered. In fact, it has a solar battery charger built in. A 100 watt solar panel was chosen.
He had several grow bed containers. The first was a 4’x4’ bed. He filled it with ¾” inch stone. But I told him from my experience, that was too course. This application needs a smaller grow medium that will retain moisture. Pea stone works well. I have also used perlite (vermiculite). He replaced the medium with pea stone.
We installed 4 tubes in the corners to fill and drain the bed. We found the low spots and smoothed out the gravel. The tubes are attached to a 4 pump manifold.
All the pumps run in parallel. This pump panel provides redundancy and faster fill rate. At a lower electrical current than using a single larger pump. The pump panel is positioned below the grow bed in a nutrient container. The power comes from a 50 amp/hour AGM battery. A car battery in good shape will also work.
The Growers’ Gizmos controller is a cycle timer, solar charger, and water level sensor in one enclosure. The terminals are on a removable plug. The pumps have a resettable fuse for 5 amps.
After the initial tests of the smaller grow bed were successful, we decided to procedure with the other 4’x6’ grow beds. We ran 10 AWG cable , 2 conductor as a 12v bus from the solar panel to the controller and then to the battery. Then the cable runs from the battery trough the greenhouse.
For the 4’x6’ grow beds, the tubes were installed in 6 places. A 6 pump panel was connected to the tubes. This 6 pump panel draws only 3.2 amps at 12 volts. Each pump is 3.8 liters/minute for a total of 22.8 liters/minute. It fills and drains the bed at 6 points for even coverage.
The nutrient tank shown below needs a plastic liner for the water level senor to work properly. It is based on electrical capacitance. There is also a bed level sensor. Each controller will be powered from the same 12V battery through the 10AWG cable.
The 4’x4’ grow bed is about 226 liters in volume. But the pebbles take about 70% of that volume. So, that’s 67 liters of water volume. So, the bed fills in about 4.5 minutes. The 4’x6’ beds are about 340 liters or 102 liters of water. The 6 pump panel should fill the 4’x6’ beds in 4.5 minutes also. The 30% of volume remaining for water is the unknown. I suspect the water volume may be as low as 5%.
My friend plans to heat the greenhouse with a pellet stove, The wall will be double lined with an air blower. He hopes to achieve and R5 insulation value. The reason he is using hydroponics is that he can go more than a week without needing to water or fertilizer. I have gone as long as 3 weeks without maintenance.