The best way to test a solar hot water system for leaks before filling it is to use compressed air. Before you fill a new solar installation with fluid use compressed air to check the system for leaks first. This concept was spelled out by the Godfather of solar hot water, Tom Lane.
“Glycol antifreeze systems that are pressurized and drainback systems absolutely require testing with air pressure. You will discover some leaks with air that will not show up with water” - Tom Lane
This is the best practice because most of the time, you can hear an air leak. Then you either tighten the fitting or re-solder the connection. The piping remains dry so that it can easily be soldered and you do not run the risk of damaging a clients property with water.
The best way to accomplish this is to adapt your fill pump with a Schraeder valve so that you can attach it to an air compressor. Then you connect the fill hose to the fill valve as usual except you add air instead of water. Glycol systems have a pressure gauge that you can monitor. Bring the pressure up to 30 - 40 psi for 30 minutes. If there is a leak you will usually notice right away that the gauge is falling.
You will save valuable time and effort by testing a system with air before charging it. If you have any questions about solar hot water please call Metro Solar in Atlanta at 404-409-7435.