New solar water heater controller for school proje

When I moved to Edinburgh last year I set up an engineering group at a local secondary school. The kids are building solar water heater to my design for a children's retreat in Bulgaria. I have to say, they are doing a very neat job of it too, all galvanised sheet steel construction and flawless soldered pipe joints.

Obviously, since they are only 15 years old, its taking them a while to complete the work but they are well underway, and its great to see them developing as individuals and realising that they can achieve impressive results if they put their minds to it.

As its a bit beyond their current ability, I paid for and built the control unit myself, and this video shows its testing. Due to the radicly different system requirements of a Bulgarian retreat with no electrical supply Vs an urban Derby house with electricity, gas and internet, the whole system is significantly different (And simpler) as compared to the Mark 1. The future Mark 3 will be an amalgam of the two.

Reliability, simplicity and robustness are the keywords here. The main issue with the Raspberry Pi control system on the mark 1 was the boot-up time and the need to "Understand" the software. The mark 1 control system was vastly superior in terms of ability, adaptability and information presentation, but it is not suitable for a powerless croft in Bulgaria. A variation of it will defiantly be used on the future Mark 3.

This mark 2 system is all analog, based on simple LM324 Op amps. External controls are one switch - Off or On. There are three indicator lights. The whole is in a self contained IP67 box, with cable glands. Connections are by standard DIN terminals mounted on rails.

There are, in addition, some internal controls for setting the system up. Cut-in and hysteresis are adjustable, as is the dump load.

A small rechargeable battery keeps the circuits running when the PV panel is not working, and the PV panel charges the battery and operates the pump.

A big advantage of the Mark 1 system over any other controller I know is that it could vary the speed of the pump. The Mark 2 can also do this, but it does so passively - The varying voltage on the PV cell should vary the pump speed. This may take some setting up, but the theory is there.

Finally, I have gone for the less efficient closed loop glycol circulation system for this build, again for simplicity. Lack of computer control and power on site means its not feasible to use a drain down system as I did on the Mark 1. The students built a heat exchanger inside a water cylinder, and the plumbing is looking good.

I am proud of what the kids have achieved, and once they have finished, I will clear it with the teacher and get a video made up.

Any questions, let me know as ever!

Видео New solar water heater controller for school proje канала drawingboard82