Re: Solar PV ?

["Andy" <andywhitfield2002@xxxxxxxxxxx>]

Marcus,

It's the current and resistance of the cable you need to look at.

For example I was wiring up an inverter (UPS) to some external batteries.
The inverter was 5000va / 3750 watts max load.  And 48Vdc on the batteries.
The cable I have is 8 AWG which is 8.37mm2 and rated at 40+ amps depending
=
on the insulation.
It's resistance is 2.061 Ohms per Km.  These figures are from a table I
fou=
nd on the internet.
For my inverter, the max current is 3750watts / 48Vdc (from the batts) =3D
=
78 Amps.
I doubled up the cable to carry the max current.
So the resistance per metre (doubled up cable ) is..... 0.0010305 Ohms.
The voltage drop per meter at max current of 78 Amps is.....  0.0804 Volts.

I used very short cables on my inverter but if you have 15m then voltage
dr=
op is 15 x 0.0804 =3D 1.21Vdc
But that would be on the positive and negative cables from the batts.
So a total of 2.4Vdc drop.
If the batts were fully charged and in good condition and the inverter had
=
a max load then the batt voltage would start at about 48Vdc and the
inverte=
r would switch off at around the 42Vdc mark.
But in this example 2.4Vdc has been dropped across the cables.  So it
would=
reduce the run time noticeably.

Also at 1.2Vdc per 15m cable and 78 amps, you are wasting almost 94 watts
p=
er cable.

Of course I don't know what your figures are.
And this is just an example, but it is worth working it out with your
figur=
es.

BTW what is a micro inverter?

Regards
Andy the UPS Man

--- In ukha_d@xxxxxxx, Marcus Warrington <marcus.warrington@...> wr=
ote:
> Stewart,
>
> I looked at the micro inverters but the cost (for me) was prohibitive.
21=
panels each with its own micro inverter=20
> worked out around =A34000 , the cost of a single 3 string,
transformerles=
s SMA inverter was more like =A31600.  I was=20
> looking at the SolarPV as an investment so the bottom line was not how
ef=
ficient things would be but how much profit=20
> they would earn me over 25 years. I don't believe the micro inverters
cou=
ld ever earn me back enough in the 25 year=20
> period to pay for the cost differential. Of course if I was only
having a=
few panels then it may work out=20
> differentially, e.g a 1.2Kwh array of 240W panels would only need 5
micro=
inverters so may well even have a smaller=20
> capital cost than buying a single central inverter.
>
> Having said all that I guess it does depend a lot of the amount of
shadin=
g you have, I only have a small localised=20
> amount so can work around it by having the potentially shaded panels
on s=
eparate smaller string.
>
> Regarging the noise issue, I belive (and hope!) that this is an issue
wit=
h the ones that have a transformer in them=20
> and that the transformerless ones do not generate a noise (or at least
no=
where near as loud) as well as being slightly=20
> more efficient.
>
> Our fitting date is in two weeks, but I'm still undecided if I should
fit=
the inverter in the loft, where it will will=20
> get hot but have short DC cable runs, or have it in cellar where it
will =
be nice and cool (and easily accessable) but=20
> have a longer (~15M) DC cable run. The installer seems confident that
run=
ning 10mm DC cables will limit any=20
> ineffeciencies upto around 25M.
>
> Marcus
>
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of=
Stewart
> Sent: 11 July 2011 11:12
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Solar PV ?
>
>
>
> Kevin/Marcus,
>
> Had the chap from Sun Renewable here last week (thanks for the
> recommendation Mark and, YES, we did mention your name to Tom) and
we're
> looking at using Sharp panels and micro-inverters (1 per panel) made
by
> Enecsys. These micro-inverters fit directly onto the back of each
panel a=
nd
> solve the problem of one shaded panel bringing down the output of the
arr=
ay
> and also, as we were worried about the noise generated by a loft
mounted
> inverter, these will be mounted outside so noise won't be a problem
(we
> hope!).
>
> The micro-inverters are a recent development so there's no worthwhile
> reliability data yet, however, they do come with a 20 year warranty.
>
> regards
>
> Stewart
>
> From: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>=20
> [mailto:ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>]
On Behal=
f Of
> Marcus Warrington
> Sent: 16 May 2011 15:36
> To: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
> Subject: RE: [ukha_d] Solar PV ?
>
> Kevin,
>
> I think in theory it still does, but you can get panels with built in
byp=
ass
> diodes that should mean only those cells (or possibly string of cells)
> within the panel that are shaded get affected. I have another
installer
> coming tonight so I'll be quizzing him a little more about this :)
>
> Marcus
>
> From: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
<mailto:ukh=
a_d%40yahoogroups.com>
> [mailto:ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
<mailto:u=
kha_d%40yahoogroups.com> ] On Behalf
> Of Kevin Hawkins
> Sent: 14 May 2011 14:15
> To: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
<mailto:ukha_=
d%40yahoogroups.com>
> Subject: Re: [ukha_d] Solar PV ?
>
> If you had an array of panels but one of them was in shade , perhaps
> from a chimney stack , does this same situation occur ? I'm
> assuming not as it must be correctable via electronics but just
checking.=
..
>
> K
>
> On 13/05/2011 09:06, Marcus Warrington wrote:
> > Since I've now read that output of a string of panels is dictated
by th=
e
> lowest producing panel, that's means if I have a string of Sharp
panels a=
ll
> producing +10% but the last one produces -5% then its as though all
the
> panels are at -5%.
> > Marcus




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