solar thermal panels, series/series-parallel/parallel adjustable plumbing

[ben22]

i had an idea to use solenoid valves a temperature sensor and a microcontroller to cycle between different plumbing configurations for a solar thermal system

i.e from cold start have the 4 panels running in series, once a set temperature is reached (70-80 degC ?) the solenoid valves will switch to series-paralel then when the set temperature is reached again switch to all 4 panels running in parallel and the same in reverse with a lower set point as the temperature cools off




series - 1,2,3,7,8,9 closed 4,5,6 open

series parallel - 1,3,5,7,9 closed 2,4,6,8 open

parallel - 4,5,6 closed 1,2,3,7,8,9 open



does anyone know if this has been done before and if it will be worth while?

 

[robbob2112]

You can do it with contactors like these for not a lot of cash

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

Every time I have seen it discussed the conclusion is that it isn't worth it. Instead add an extra few panels and you get more power.

The other topic I've seen is using contactors to cut one panel out of a string when it gets cold and voltage goes up. In this case it generally ends with a conclusion of just wire different.

There have been a few discussions a month about it if you search.

 

[400bird]

That's a lot of solenoid valves and wiring. And a lot of money, time, and points of failure.

Seems like you be better off with a variable flow pump or to cycle the pump based on outlet temperature. If the sun can't heat the water hot enough on a single parallel pass, turn it off or down to let the water sit in the sun longer. However, I'm pretty sure you don't need to get to full temp in a single pass. Even if you only get 3c raise water temp raise from the panels in a single pass, you'll get an additional 3c on the next pass. It's not instant hot water, right? It's going to take time.

You can do it with contactors like these for not a lot of cash

Liquid, not electrons

 

[robbob2112]

I just realized... water...wet stuff... got it