A while back,someone brought up the problem of switching stuff on automatically only when the PV panel can meet the load. ie as weather conditions allow.
Answer is here, someone is making one.
Its a strangely complex product for a very simple job.
NT
one.http://www.solarpowerportal.co.uk/news/ecobuild_fronius_embraces_ener...>>>> So you can set this up and go out to work. When the PV output meets the set
Here is a much simpler solution, but look at the cost. You would take quite a while to recover £190 plus Part P installation. The calculation would also have to allow for the arrival of smart meters.
The best arrangement should measure generation and consumption, and only turn on if there is sufficient unused capacity.
Easily expressed, but not so easy to achieve in a manner that is both compliant and cost-effective.
Chris
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
Because the unFIT tariff means they're *not* better off doing that, they get paid for generating it, and (unless they have a smart meter) paid again on the assumption they export half of it, but the greedy sods want to use it all for their solar powered bog seat warmers or whatever.
). =A0You get a further 3.2p for every unit exported back to the grid.
so if you store rather than sell back, you have lost the opportunity of ear= ning 3.2p in order to save yourself 10p.
use before export: per unit: 21p generated use, export, use later: 21p +3.2p in, 10p out so on that basis youre right
e. =A0If 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.
and use it before it heads back to the grid.
indeed
NT
we have an array with peak output of 4kW and, say 3MWhr/annum before a smart meter is fitted then how much is actually consumed out of the
50% deemed to be consumed? Maximum potential cost of the deemed consumption is 15Mwhr @~10p. That's 150quid/annum. It gets better if a smart meter is fitted and one doesn't currently use much electricity in daylight hours.How would one start to do this. I for one would not value heat from an immersion element at the 10p/kWhr as my gas boiler probably only costs half that to do hot water.
The problem is also how would one predict having enough electricity to complete a task, after all a washing machine cycle will use 1kWhr to complete but it needs the peak power at set times. So even if the array delivers 1kWhr during daylight if the washing machine demands that during a cloudy period...
One could charge a large UPS and only switch the washing machine on when the UPS battery was above a set voltage??
How does one decide when the surplus is back fed to the grid, is it the phase change caused by the inverter over voltage into the grid impedance?
My A level physics suggests it's easier to measure V and A on the array DC bus to decide what is being generated.
AJH
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