On Thursday, 5 April 2012 15:15:10 UTC+1, NT wrote:
In the case of offgrid solar pv, the solution is rather simple:
monitor battery bank V and turn on a relay when V is high enough. High
enough means power to spare from the panels.

With grid tied pv, as you say it means monitoring production and
consumption, but its not too demanding a bit of circuit design.

But more to the point, why would one do it with a grid tied system,
when you're better off exporting electricity then using it when the
sun's gone down.


NT

Huh? You get 21p for every unit generated (whether you use it or not). You get a further 3.2p for every unit exported back to the grid.

But in the evening, a typical tarrif will cost you about 10p per unit, so if you store rather than sell back, you have lost the opportunity of earning 3.2p in order to save yourself 10p.

I am, of course, assuming that you've got the battery / storage for free. If there is a cost per unit 6.8p (which I think there is) then you're right - you are always better off selling back to the grid than storing / using at a later time.

Of course, the most effective thing you can do is generate electricity and use it before it heads back to the grid.

Matt