DIY thermal differential controller (solar hot water pump controller)

GaryGary · 09-12-09, 07:01 PM

Hi Tim,
Just learned today that the Goldline differential controller is no more. This was (to my knowledge) the cheapest controller out there at about $130. It did not have a lot of bells and whistles, but very solid. Surprised to see them decide to stop making them -- they had been around for many years.

On the direct PV power of the pump where the PV panel acts as the power and controller.

- Its difficult for some systems. For example, drain back systems where the collector is quite a lift above the tank need a pump with high starting head, and these tend to be AC pumps with fairly high power demand -- expensive to do with PV.

- Its nice to have a controller that knows what the tank temperature is. On days when the tank starts out cool, it can start the pump earlier in the day -- as soon as the collector can produce water hotter than the tank water. When the tank starts out fairly hot already, a controller that knows the tank temperature will wait until the collector is getting enough sun to actually heat the water in the tank. The PV panel has no knowledge of the tank temp.

- The efficiency of a PV panel and a thermal collector opposite dependencies on ambient temperature. So, on a very cold morning the the PV panel will make enough electricity to start the pump earlier than usual, but the water heating collector would ideally like to be started up later than usual, because it has higher losses and is less efficient.

All that said, a lot of people use the direct PV successfully, and it has a very appealing simplicity to it.

Gary

09-12-09, 07:01 PM	#11
GaryGary Apprentice EcoRenovator Join Date: Nov 2008 Location: SW Montana Posts: 139 Thanks: 1 Thanked 21 Times in 15 Posts	Hi Tim, Just learned today that the Goldline differential controller is no more. This was (to my knowledge) the cheapest controller out there at about $130. It did not have a lot of bells and whistles, but very solid. Surprised to see them decide to stop making them -- they had been around for many years. On the direct PV power of the pump where the PV panel acts as the power and controller. - Its difficult for some systems. For example, drain back systems where the collector is quite a lift above the tank need a pump with high starting head, and these tend to be AC pumps with fairly high power demand -- expensive to do with PV. - Its nice to have a controller that knows what the tank temperature is. On days when the tank starts out cool, it can start the pump earlier in the day -- as soon as the collector can produce water hotter than the tank water. When the tank starts out fairly hot already, a controller that knows the tank temperature will wait until the collector is getting enough sun to actually heat the water in the tank. The PV panel has no knowledge of the tank temp. - The efficiency of a PV panel and a thermal collector opposite dependencies on ambient temperature. So, on a very cold morning the the PV panel will make enough electricity to start the pump earlier than usual, but the water heating collector would ideally like to be started up later than usual, because it has higher losses and is less efficient. All that said, a lot of people use the direct PV successfully, and it has a very appealing simplicity to it. Gary