Switch a load when PV panels are active.

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Jack-Tar Sam
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JoinedCOLON Fri Nov 01, 2013 4:25 pm

Switch a load when PV panels are active.

Postby Jack-Tar Sam » Sat Nov 02, 2013 4:10 pm

:idea: I suspect this may already have been done by someone, but here goes anyway.

I am interested in producing an automatic load switch which will allow a load of up to 3 kW to be switched in when a PV array becomes sufficiently active in daylight hours.

As I can see, this can be done in 2 ways.
1. You could tap on to the PV panel array to gain a dc voltage signal (this can be up to 300v dc - so care is needed!) from the input to the 'inverter' which you know will correspond to a 3 kW output being available for use from it. Or
2. Have an independent smaller PV panel mounted facing the sun, which will allow you to compare its voltage output and allow that to mimic your roof PV array, using the signal here to switch a relay to which the load is attached. In this case, the relay could work a load switch coupled into a power extension cable leading to the load. I envisage the setting that operates the switch being varied by a rheostat to suit the actual size of the load that is connected.

The intention is for the 'load switch' to switch the load in and out, depending on there being sufficient solar activity to produce the power. No point having the load powered up after switching when the sun has gone in as the power consumed then comes from the grid.

Buying such an item commercially costs an 'arm and leg' for what is a relatively simple and cheap circuit to design. My trouble is that I can't design such an item, but can certainly build it. Anyone able to assist?

Sam :idea:

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Re: Switch a load when PV panels are active.

Postby Rich » Wed Jan 29, 2014 10:34 pm

Sounds like you need a Schmitt trigger to quickly bring in and out the relay. Street lamps have them so they come on suddenly.
Look in to Zener diodes too they, when reversed biased, at a certain specified voltage level will suddenly start to conduct.

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