This is the unmodified home installation.
I will explain it graphically.
This is the typical installation to consume the water heated by an auxiliary heater (gas or electricity)
This installation passes the solar water (the one that comes hot from the DHW installation) through the heater.
It really gives you the possibility to increase the temperature of the water that is already hot or warm from the solar tank.
It is a very good option when there is little sun or in a period of scarcity of solar radiation.
The drawback in this type of installation is that gas heaters have a very narrow coil, and this can reduce the pressure and flow of our tank if it lacks good pressure or is an inertia/gravity tank.
This installation should not be applied to an electric heater, or at least it would not be logical from a functional point of view since an electric heater is not a passage heater.
However, an electric heater CAN benefit from a warm water inlet, thus deriving a direct benefit from not having to heat the new water inlet, but this would obviously be a totally different point of view.
Connection of the solar heater, with a 3-way tap to switch the passage to the heater or directly to the taps.
It is a very good simplified installation option.
We can use this 3-way faucet to switch and temporarily override the heater (for sunny days), or we can make the faucet pass the solar water through the heater (when the solar water is only warm or cold)
It would be ideal to automate this switching.
If we cannot get the 3-way stopcock, we can also mount it with 2 normal stopcocks, opening and closing each one according to the desired use case. (As described in the following title)
This installation can be perfectly applied with an electric water heater with the same functionality.
It has the same functionality as the previous case, but using normal stopcocks instead of 3-way valves.
The "S" key represents the stopcock for the water that comes from the solar or DHW installation. (Tank outlet)
The key "C" represents the stopcock of the heater outlet.
The key "B1" represents the stopcock that acts as a bypass or bridge to communicate or isolate the solar thermal installation with the house
The key "B2 represents the stopcock that acts as a bypass or bridge to communicate or isolate the auxiliary heater with the house.
The bypass tap or bridge will be used to facilitate direct passage of water bypassing the auxiliary heater.
Quick and easy explanation.
We are in the middle of summer where we don't need the use of the auxiliary heater at all.
Open keys: S, B2.
This combination causes the hot water supply to come directly from the solar heater reservoir, without entering or leaving the auxiliary heater.
Our solar installation does not contain hot water, either because it is stopped, under construction, or simply a storm has not contributed to it.
We close key S, open key C, and close key B.
With this combination of faucets we make the hot water supply circulate only and exclusively through the auxiliary heater.
We are in a situation where the water in the solar installation reservoir is hot, but not hot enough for our comfort point.
This situation can perfectly occur on some days of storms or late winter or early spring.
We open keys S and C, but we close keys B.
This peculiar combination means that the hot water supply comes from the solar heater's tank, enters the auxiliary heater, and in this combined way reaches our taps.
Or in other words, it is a mixed configuration where the water is heated 2 times, by the sun, and by the auxiliary energy.