1kW solar grid interactive - update

[Sylvia Else]

:Ross Herbert wrote:
:> On Sun, 17 May 2009 18:47:40 +1000, Sylvia Else <[email protected]>
:> wrote:
:>
:> :Ross Herbert wrote:
:> :> My Sharp/Fronius 1kW system has been pumping around 5kW/hr back into the
:> system
:> :> on a daily basis since it started running on the 5th May. Perth is
:> experiencing
:> :> an extended Autumn with sunny days in the mid 20's and no rain, so that is
:> quite
:> :> good performance. It should do a lot better in full Summer. Our 2 person
:> :> household averages a consumption of around 7kW/hr per day and it is now
down
:> to
:> :> 2kW/hr per day.
:> :>
:> :> Today's West Australian reported on the state budget released yesterday
and
:> this
:> :> sort of news
:> http://www.thewest.com.au/default.aspx?MenuID=77&ContentID=141680
:> :> makes me feel a whole lot happier still.
:> :>
:> :> In the budget it was also announced that WA would adopt a gross feed-in
:> tariff
:> :> of up to $0.60 per kW/hr for renewable energy sources so currently I stand
to
:> :> make a profit of about $2.60 per day. Of course, as the price of
electricity
:> :> increases, the profit margin will drop - unless the FiT also increases
(which
:> I
:> :> doubt). I am now considering increasing my PV array by 4 x 175W panels to
:> take
:> :> it to the maximum capacity for the existing inverter.
:> :
:> :Running the inverter at its design limit will reduce its reliability.
:> :
:> :Sylvia.
:>
:>
:> The latest model Fronius IG15 is nominally 1.5kW but rated for 2kW peak so I
am
:> certain it will handle the extra 4 panels without any loss of efficiency.
:
:I wasn't thinking about efficiency, but reliability. That is, how long
:it will work, on average, before you have to get it repaired or replaced.
:
:My guess would be that the peak is based on the thermal inertia of the
:heat sinks, and the nominal based on the dissipation rate from the heat
:sinks.

Efficiency is directly linked to the heat dissipated inside the inverter. If the
inverter were 100% efficient there would be absolutely no heat dissipated so
reliability would essentially be the same as if it were switched off. Now we all
know this is impossible to achieve, but a claimed efficiency of 94.2% for the
IG15 is pretty good. In addition, 10 x 175W panels = 1750W, and the rated peak
input for the IG15 is 2kW. The likely peak output of this sized array even with
high efficiency panels will most likely be in the order of 1600W so it is well
below the maximum rating in any case. Assuming 94% inverter efficiency with
1600W peak input we get an output of 1504W, ie. spot on with the rated output.

I don't know why you're giving me a lecture on basic physics. As I said,
the issue I see does not relate to efficiency, but reliability. It
doesn't matter what its ratings are, or how efficient it is - the higher
the power you run through it, the hotter it will run. Hotter usually
means less reliable.

Sylvia.

 

[Davo]

I don't know why you're giving me a lecture on basic physics. As I said,
the issue I see does not relate to efficiency, but reliability. It
doesn't matter what its ratings are, or how efficient it is - the higher
the power you run through it, the hotter it will run. Hotter usually
means less reliable.

Sylvia.

Someone gives you a statement based on fact and you reply with a
statement based on a generalisation. If you're going to be critical you
should at least put some factual data behind your argument.

 

[terryc]

Someone gives you a statement based on fact

Yep it was definitely the physicist/engineers view. Practically, I want
to hear from the techo that services these things.

 

[Adrian Jansen]

err, don't you mean the angle from the horizontal should be your latitude
PLUS 22.5% and orientated due north? (to peak winter output).

If you set the angle to peak winter output (latitude + 22.5), you will
get a 45 degree off axis angle in mid summer. That will reduce your
summer output to cos(45) = 0.71 of peak ( assuming cosine law holds ).
But if you set say 20 degrees higher than that ( ie a few degrees lower
than latitude), you will get an off peak of cos(20) in winter, and
cos(45-20) in summer, which is a much better compromise. Other values
are possible, depending on exactly what you think the winter/summer sun
ratio is, of course the cloud cover effects come into this too.

--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
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