PV management.

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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.
http://www.solarpowerportal.co.uk/news/ecobuild_fronius_embraces_energy_management9876

So you can set this up and go out to work. When the PV output meets the set
level it will switch on (and off).
Prevents inadvertent use of non PVpower.



Re: PV management.
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Its a strangely complex product for a very simple job.


NT

Re: PV management.
NT wrote:

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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.

http://chrisrudge.co.uk/immersion.htm

Both seem to have too simple an algorithm. They only look at
generation, not consumption.

The best arrangement should measure generation and consumption,
and only turn on <specified equipment> 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
--
Chris J Dixon  Nottingham UK
chris@cdixon.me.uk

We've slightly trimmed the long signature. Click to see the full one.
Re: PV management.
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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

Re: PV management.
On Thursday, 5 April 2012 15:15:10 UTC+1, NT  wrote:
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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

Re: PV management.
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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


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re right - you are always better off selling back to the grid than storing =
/ using at a later time.
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indeed

Re: PV management.
NT wrote:

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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.


Re: PV management.
wrote:

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What's at stake here, capital cost verses potential saving of what? If
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.
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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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