Re: Solar PV ?

["Andy" <andywhitfield2002@xxxxxxxxxxx>]

You need to find out the max amps from the solar string.
6mm cable is between AWG 10 and AWG 9 cable.
You might find AWG and a number printed on your cable.
AWG 10 is rated at 30 amps and has a resistance of 0.003277 Ohms / metre.

So 15 metres of cable at 0.003277 Ohms per metre is 0.049 Ohms.
At 10amps you'll drop 0.49 volts.
At 20amps you'll drop 0.98 volts.
At 30amps you'll drop 1.47 volts.

That will be on both the positive and negative cables.

I have UPSs that can be used as inverters.

Andy the UPS and Inverter Man.

--- In ukha_d@xxxxxxx, Marcus Warrington <marcus.warrington@...> wr=
ote:
>
> Andy,
>=20
> Thanks for the info.. I must confess most of it went straight over my
hea=
d and I'll need to sit down and ready it again slowly :)
>=20
> I do have to say I misquoted the cable diameter.. its 6mm they will be
fi=
tting, no idea where I got 10mm from !
>=20
> I think the voltage output of the solar string is also much higher
than y=
our 48Vdc batteries, something more like 150Vdc per string so the amps
will=
be lower?
>=20
> Marcus
>=20
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of=
Andy
> Sent: 13 July 2011 11:08
> To: ukha_d@xxxxxxx
> Subject: [ukha_d] Re: Solar PV ?
>=20
>=20
>=20
> Marcus,
>=20
> It's the current and resistance of the cable you need to look at.
>=20
> 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
dependin=
g on the insulation.
> It's resistance is 2.061 Ohms per Km. These figures are from a table I
fo=
und 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=
.
>=20
> I used very short cables on my inverter but if you have 15m then
voltage =
drop 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
ha=
d a max load then the batt voltage would start at about 48Vdc and the
inver=
ter would switch off at around the 42Vdc mark.
> But in this example 2.4Vdc has been dropped across the cables. So it
woul=
d reduce the run time noticeably.
>=20
> Also at 1.2Vdc per 15m cable and 78 amps, you are wasting almost 94
watts=
per cable.
>=20
> 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
fig=
ures.
>=20
> BTW what is a micro inverter?
>=20
> Regards
> Andy the UPS Man
>=20
> --- In ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>,
Marcus Wa=
rrington <marcus.warrington@> wrote:
> > Stewart,
> >
> > I looked at the micro inverters but the cost (for me) was
prohibitive. =
21 panels each with its own micro inverter
> > worked out around =A34000 , the cost of a single 3 string,
transformerl=
ess SMA inverter was more like =A31600. I was
> > looking at the SolarPV as an investment so the bottom line was
not how =
efficient things would be but how much profit
> > they would earn me over 25 years. I don't believe the micro
inverters c=
ould ever earn me back enough in the 25 year
> > period to pay for the cost differential. Of course if I was only
having=
a few panels then it may work out
> > differentially, e.g a 1.2Kwh array of 240W panels would only need
5 mic=
ro inverters so may well even have a smaller
> > capital cost than buying a single central inverter.
> >
> > Having said all that I guess it does depend a lot of the amount
of shad=
ing you have, I only have a small localised
> > amount so can work around it by having the potentially shaded
panels on=
separate smaller string.
> >
> > Regarging the noise issue, I belive (and hope!) that this is an
issue w=
ith the ones that have a transformer in them
> > and that the transformerless ones do not generate a noise (or at
least =
nowhere near as loud) as well as being slightly
> > more efficient.
> >
> > Our fitting date is in two weeks, but I'm still undecided if I
should f=
it the inverter in the loft, where it will will
> > get hot but have short DC cable runs, or have it in cellar where
it wil=
l be nice and cool (and easily accessable) but
> > have a longer (~15M) DC cable run. The installer seems confident
that r=
unning 10mm DC cables will limit any
> > ineffeciencies upto around 25M.
> >
> > Marcus
> >
> > From: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
[mailto:u=
kha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>]
On Behalf Of Stewar=
t
> > Sent: 11 July 2011 11:12
> > To: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com>
> > 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'r=
e
> > 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=
and
> > solve the problem of one shaded panel bringing down the output of
the a=
rray
> > and also, as we were worried about the noise generated by a loft
mounte=
d
> > 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><mailto:uk=
ha_d%40yahoogroups.com>
> > [mailto:ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com><mailto:=
ukha_d%40yahoogroups.com>] On Behalf Of
> > Marcus Warrington
> > Sent: 16 May 2011 15:36
> > To: ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com><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 b=
ypass
> > 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:uk=
ha_d%40yahoogroups.com> <mailto:ukha_d%40yahoogroups.com>
> > [mailto:ukha_d@xxxxxxx<mailto:ukha_d%40yahoogroups.com><mailto:=
ukha_d%40yahoogroups.com> <mailto:ukha_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> <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
checkin=
g...
> >
> > 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 =
the
> > lowest producing panel, that's means if I have a string of Sharp
panels=
all
> > producing +10% but the last one produces -5% then its as though
all the
> > panels are at -5%.
> > > Marcus
>=20
>=20
>=20
> [Non-text portions of this message have been removed]
>




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