The 40 gallon solar collector is designed to produce about 40 gallons of heated water per day at a mid-latitude on the East Coast.
Depending on usage, and how hot the water is from the previous day, on a sunny day, the tank temperature can rise to 180 F or more. This is VERY, VERY hot and could cause scalding and serious personal injury if water that hot got to a faucet.
You MUST install an automatic thermal mixing valve in the hot water line after it leaves your inside hot water tank going towards faucets, showers, etc. The mixing valve has a dial on it which allows you to set the maximum temperature of the water coming out of the valve. If the water coming in is too hot, cold water is mixed with it to reduce the temperature until the output temperature is within the range you set - typically no hotter than 120 F. (48 C.)
A 3/4" MPT mixing valve comes with each system. You must install it, or one of comparable quality, for your safety. Lack of or improper installation of the thermal mixing valve voids the Suntern warranty.
Besides, you want a mixing valve. It increases your system efficiency by allowing your tank to store water hotter than the thermostat's setting (therefore, it doesn't turn on, saving you money), and mixing cold water with the super hot water makes your solar heated water go further.