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PV Inverter Question
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| GSLewis@gmail.com 2005-12-12, 1:21 am |
| I have had two Installers tell me two different things and am not sure
which is correct.
I want to put PV panels on a south and a western facing roof (25 deg
slope which is close to ideal.)
One installer said I would need a Sharp JH-3500U Inverter which is
really three separate inverters packaged as one. So each face of the
roof is optimized independently. She said that with other inverters,
all the strings must be in the same orientation.
A second installer said that I could use another inverter (a PV Powered
2000). He said this inverter optimizes the total power, but both
strings will be operating with the same parameters. He said since
voltage changes very little with light exposure, the loss is relatively
small.
The PV Powered inverter is cheaper, more efficient and has a 10 yr. vs
(5yr) guarantee.
I can't tell from the respective web sites who is correct?
Does someone know?
| |
| Windsun 2005-12-12, 3:21 am |
| What the second installer said is more correct, assuming that the panels on
the two different orientations are wired in parallel with each other.
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<GSLewis@gmail.com> wrote in message
news:1134363458.964979.157990@g44g2000cwa.googlegroups.com...
>I have had two Installers tell me two different things and am not sure
> which is correct.
>
> I want to put PV panels on a south and a western facing roof (25 deg
> slope which is close to ideal.)
>
> One installer said I would need a Sharp JH-3500U Inverter which is
> really three separate inverters packaged as one. So each face of the
> roof is optimized independently. She said that with other inverters,
> all the strings must be in the same orientation.
>
> A second installer said that I could use another inverter (a PV Powered
> 2000). He said this inverter optimizes the total power, but both
> strings will be operating with the same parameters. He said since
> voltage changes very little with light exposure, the loss is relatively
> small.
>
> The PV Powered inverter is cheaper, more efficient and has a 10 yr. vs
> (5yr) guarantee.
>
> I can't tell from the respective web sites who is correct?
>
> Does someone know?
>
| |
|
| In article <yi9nf.2121$n1.997@newsread2.news.pas.earthlink.net>,
"Windsun" <wind-sun@earthlink.net> wrote:
> What the second installer said is more correct, assuming that the panels on
> the two different orientations are wired in parallel with each other.
>
In my opinion both installers were selling, rather than consulting,
as inverters aren't the right equipment to be spec'd for this job.
Charge Controllers would be significantly more appropriate in this
example, and I would spec independant controllers for each array.
Me
| |
| Derek Broughton 2005-12-12, 4:21 pm |
| Me wrote:
> In article <yi9nf.2121$n1.997@newsread2.news.pas.earthlink.net>,
> "Windsun" <wind-sun@earthlink.net> wrote:
>
> In my opinion both installers were selling, rather than consulting,
> as inverters aren't the right equipment to be spec'd for this job.
> Charge Controllers would be significantly more appropriate in this
> example, and I would spec independant controllers for each array.
It did seem a little odd... So now that we're talking about the right
equipment, why would you spec independent controllers? I've wondered, on
and off, whether that wouldn't be a better idea than my existing system,
and I'm still undecided.
Redundancy is a good thing, especially considering that a second charge
controller now would cost me half (at most) what getting a controller
delivered within a week would cost if I waited for a failure.
otoh, the Trace documentation left me with the impression that their
controller wouldn't work optimally if there were other controllers in the
system.
--
derek
| |
| GSLewis@gmail.com 2005-12-12, 5:21 pm |
|
> "Windsun" <wind-sun@earthlink.net> wrote:
>
> [...] inverters aren't the right equipment to be spec'd for this job.
> Charge Controllers would be significantly more appropriate in this
> example, and I would spec independant controllers for each array.
This will be grid tied. Aren't Charge Controllers for batteries?
| |
| Steve Spence 2005-12-12, 8:21 pm |
| GSLewis@gmail.com wrote:
> I have had two Installers tell me two different things and am not sure
> which is correct.
>
> I want to put PV panels on a south and a western facing roof (25 deg
> slope which is close to ideal.)
>
> One installer said I would need a Sharp JH-3500U Inverter which is
> really three separate inverters packaged as one. So each face of the
> roof is optimized independently. She said that with other inverters,
> all the strings must be in the same orientation.
>
> A second installer said that I could use another inverter (a PV Powered
> 2000). He said this inverter optimizes the total power, but both
> strings will be operating with the same parameters. He said since
> voltage changes very little with light exposure, the loss is relatively
> small.
>
> The PV Powered inverter is cheaper, more efficient and has a 10 yr. vs
> (5yr) guarantee.
>
> I can't tell from the respective web sites who is correct?
>
> Does someone know?
>
unless these are grid tie units, you don't connect inverters to pv
panels. Don't bother putting pv facing west, just load up the south
facing roof.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
| |
| Steve Spence 2005-12-12, 9:21 pm |
| Derek Broughton wrote:
> Me wrote:
>
>
>
>
> It did seem a little odd... So now that we're talking about the right
> equipment, why would you spec independent controllers? I've wondered, on
> and off, whether that wouldn't be a better idea than my existing system,
> and I'm still undecided.
>
> Redundancy is a good thing, especially considering that a second charge
> controller now would cost me half (at most) what getting a controller
> delivered within a week would cost if I waited for a failure.
>
> otoh, the Trace documentation left me with the impression that their
> controller wouldn't work optimally if there were other controllers in the
> system.
I have a trace controller for the PV, and a separate controller for the
wind gen. They behave quite nicely.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
| |
| Steve Spence 2005-12-12, 9:21 pm |
| GSLewis@gmail.com wrote:
>
>
>
> This will be grid tied. Aren't Charge Controllers for batteries?
>
You didn't explain that. Yes, inverters are for pure grid tie, charge
controllers for battery or battery/grid tie. Shoot the "consultant" that
suggest west facing pv.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
| |
| Derek Broughton 2005-12-13, 10:21 am |
| Steve Spence wrote:
> Shoot the "consultant" that suggest west facing pv.
>
Not necessarily. I have a precise South-facing wall on which my PV panels
are mounted, but I have a huge expanse of West view over water that I would
like to take advantage of. My next PV purchase will be mounted
_vertically_ and facing approximately West. In summer, those South facing
panels are in full shadow long before the Sun sets, and in Winter the late
afternoon Sun is very oblique. I'd still get more total gain from
South-facing panels, but I'm out of Southern exposure.
--
derek
| |
| Derek Broughton 2005-12-13, 10:21 am |
| Steve Spence wrote:
> Derek Broughton wrote:
>
> I have a trace controller for the PV, and a separate controller for the
> wind gen. They behave quite nicely.
Which is the setup I have too, but I was a little uncomfortable about the
Wind generator because I read the Trace manual. That'll teach me :-)
Is there any real reason, besides redundancy or capacity, to have multiple
charge controllers for PV arrays?
--
derek
| |
| Steve Spence 2005-12-13, 11:22 am |
| Derek Broughton wrote:
> Steve Spence wrote:
>
>
>
>
>
>
> Which is the setup I have too, but I was a little uncomfortable about the
> Wind generator because I read the Trace manual. That'll teach me :-)
>
> Is there any real reason, besides redundancy or capacity, to have multiple
> charge controllers for PV arrays?
If your pv arrays are facing in different directions (west?), then yes,
put those on a different controller, or at least diode isolated from the
south facing ones. If I get more than 60 amps of PV, then I'll add an
additional controller.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
| |
| Harry Chickpea 2005-12-13, 12:21 pm |
| Derek Broughton <news@pointerstop.ca> wrote:
>Steve Spence wrote:
>
>Not necessarily. I have a precise South-facing wall on which my PV panels
>are mounted, but I have a huge expanse of West view over water that I would
>like to take advantage of. My next PV purchase will be mounted
>_vertically_ and facing approximately West. In summer, those South facing
>panels are in full shadow long before the Sun sets, and in Winter the late
>afternoon Sun is very oblique. I'd still get more total gain from
>South-facing panels, but I'm out of Southern exposure.
All this stuff is site specific. A lot of the time this area of FL
will start out with a clear day, and somewhere between noon and three
the clouds will build and block the sun. A fixed system pointing
slightly east might be a better choice here.
| |
|
| I like the idea of having a 2 or 3 mirrors on trackers to hit each
fixed west facing panel. Double power! If the mirrors get busted by
hail or hurricanes, they're cheap to replace. The PV panels are up
against the wall out of the hail, etc. See redrok.com for info on
heliostats
| |
|
| In article <43u273-srk.ln1@news.pointerstop.ca>,
Derek Broughton <news@pointerstop.ca> wrote:
> Steve Spence wrote:
>
>
>
> Which is the setup I have too, but I was a little uncomfortable about the
> Wind generator because I read the Trace manual. That'll teach me :-)
>
> Is there any real reason, besides redundancy or capacity, to have multiple
> charge controllers for PV arrays?
I would spec MPPT Controllers for each array, so that you get the most
out of each array. While the input energy of each array will vary due
to illumination, you will get the best available efficency from each
array indiviually, and not compromise one array, by having it limited by
the other arrays situation.
Me
| |
| Derek Broughton 2005-12-14, 9:21 am |
| Steve Spence wrote:
> Derek Broughton wrote:
>
> If your pv arrays are facing in different directions (west?), then yes,
> put those on a different controller, or at least diode isolated from the
> south facing ones. If I get more than 60 amps of PV, then I'll add an
> additional controller.
>
Ah! OK. All my PV panels are diode isolated from each other - which I
realized would be a requirement if they were oriented differently.
Thanks.
--
derek
| |
| Windsun 2005-12-14, 2:21 pm |
| Unless I missed something, the original post was about a grid tie system.
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"Me" <Me@shadow.orgs> wrote in message news:Me-
> In my opinion both installers were selling, rather than consulting,
> as inverters aren't the right equipment to be spec'd for this job.
> Charge Controllers would be significantly more appropriate in this
> example, and I would spec independant controllers for each array.
>
> Me
| |
| R.H. Allen 2005-12-14, 4:21 pm |
| Derek Broughton wrote:
> Steve Spence wrote:
>
>
>
> Which is the setup I have too, but I was a little uncomfortable about the
> Wind generator because I read the Trace manual. That'll teach me :-)
>
> Is there any real reason, besides redundancy or capacity, to have multiple
> charge controllers for PV arrays?
I have seen research indicating that in a grid-tie situation, multiple
inverters can increase the effective inverter efficiency. I'm not sure
whether the technique might transfer to charge controllers -- it all
depends on how the efficiency of the charge controller changes with
loading. My limited experience with them suggests that they maintain
high efficiency over a wider range of fractional loading than inverters
do, which, if true, would probably make this scheme less effective with
charge controllers.
The way it works is that multiple inverters are switched into and out of
the circuit so that the fractional loading on those in the circuit at
any given time is such that they operate near peak efficiency. For
example, a 4-kW system with four 1-kW inverters might use all four when
the system is producing 2.9 kW or more, three when it's producing
1.9-2.9 kW, two when it's producing 0.9-1.9 kW, and one when it's
producing less than 0.9 kW. (I have no idea whether those numbers are
realistic, they're just for illustration purposes.) Of course, a good
controller and control algorithm are needed, and the added cost may not
be worth the extra power output. And the final caveat is a big one:
AFAIK this scheme has only been illustrated in computer simulations, not
with actual inverters.
| |
| SolarFlare 2005-12-14, 8:21 pm |
| I have 6 facing 11:30 and 4 facing 2:30 on a hair
brained scheme that made sense at the time, before net
metering was legal here.
These panels, with the smallest amount of light put out
50-90 vdc each string and there is no problem with
feedback between the panels.
Think of it this way (they are all almost constant
current sources)
- You have a strong battery and a weak battery in
parallel and they are both being "pulled down" to 2/3
of their open voltage. The strong battery will supply
most of the current to the load "pulling the voltage
down". The weak battery contributes it part at that
voltage the best it can. There is no circulating
current as the weak battery is still tryng to keep it's
voltage higher than the "pulled down" or loaded
voltage. No diodes are needed as they never flow into
each other. If the voltage is left to swing wide open
(peak) ther could possibly be a slight circulating
current but who cares then? There is no waste power and
this could happen only when the inverter or load is
shutting down as it darkens. The panels don't have any
capacity then anyway.
Diodes are never necessary but fuses are. Why? When a
bunch of panels are paralleled the total capacity of
all the rest could cause a shorted or damged one to
handle the combined currents and cause a fire or
dangerous condition. So apanel capable of 6A could have
60Amps going through it from the ten others connected
to it.
"Derek Broughton" <news@pointerstop.ca> wrote in
message news:bag373-1c5.ln1@news.pointerstop.ca...
> Steve Spence wrote:
>
impression that their[color=darkred]
other controllers in[color=darkred]
separate controller for the[color=darkred]
uncomfortable about the[color=darkred]
That'll teach me :-)[color=darkred]
capacity, to have[color=darkred]
directions (west?), then yes,[color=darkred]
diode isolated from the[color=darkred]
PV, then I'll add an[color=darkred]
> Ah! OK. All my PV panels are diode isolated from
each other - which I
> realized would be a requirement if they were oriented
differently.
>
> Thanks.
> --
> derek
| |
|
| How about using a Maxwell Boostcap module inbetween the PV panels and
the grid tie inverters? They cant be overcharged. Just hook the panels
to it. Whats the input voltage range for the grid tie inverters?
| |
| Derek Broughton 2005-12-15, 9:21 am |
| SolarFlare wrote:
> Diodes are never necessary but fuses are. Why? When a
> bunch of panels are paralleled the total capacity of
> all the rest could cause a shorted or damged one to
> handle the combined currents and cause a fire or
> dangerous condition. So apanel capable of 6A could have
> 60Amps going through it from the ten others connected
> to it.
Don't the diodes prevent that situation? Almost all of my panels came with
the diodes already installed, so it's not like it's a big deal to have
them.
--
derek
| |
| SolarFlare 2005-12-15, 9:21 pm |
| If you are running a 12vdc system the losses incurred
are a huge percentage of your power available.
Yes, they do perform the same function as the fuses
until they blow. Diodes short out when the blow until
they explode with too much current, depending on
application. With a small lightning discharge one could
likely lose a solar panel and a diode could short
simultaneously.
Otherwise they are fine.
"Derek Broughton" <news@pointerstop.ca> wrote in
message news:7s1773-d47.ln1@news.pointerstop.ca...
> SolarFlare wrote:
>
a[color=darkred]
of[color=darkred]
have[color=darkred]
connected[color=darkred]
>
> Don't the diodes prevent that situation? Almost all
of my panels came with
> the diodes already installed, so it's not like it's a
big deal to have
> them.
> --
> derek
| |
| SolarFlare 2005-12-15, 9:21 pm |
| Ooops. Missed something here
The diodes your panels came with are most likely
"bypass diodes". This is not the same thing. Bypass
diodes are to prevent a panel (or sections thereof) in
series with another does not present a high resistance
to the series current the well light panels or sections
are trying to put out. Thus the diodes can "bypass" the
weaker sections or panels.
The ones I thought you would be using for this
application, of cross string power loss, would be
diodes in series with each string of panels. These
should be fuses, according to the manufacturers.
"SolarFlare" <sfl.are@hot.mail.invalid> wrote in
message news:ndudnSR99NEtlD_eRVn-rg@golden.net...
> If you are running a 12vdc system the losses incurred
> are a huge percentage of your power available.
>
> Yes, they do perform the same function as the fuses
> until they blow. Diodes short out when the blow until
> they explode with too much current, depending on
> application. With a small lightning discharge one
could
> likely lose a solar panel and a diode could short
> simultaneously.
>
> Otherwise they are fine.
>
>
> "Derek Broughton" <news@pointerstop.ca> wrote in
> message news:7s1773-d47.ln1@news.pointerstop.ca...
When[color=darkred]
> a
> of
to[color=darkred]
could[color=darkred]
> have
> connected
all[color=darkred]
> of my panels came with
a[color=darkred]
> big deal to have
>
>
| |
| Bill Kaszeta / Photovoltaic Resources 2005-12-15, 11:21 pm |
| On Wed, 14 Dec 2005 22:43:51 -0400, Derek Broughton <news@pointerstop.ca> wrote:
>SolarFlare wrote:
>
>
>Don't the diodes prevent that situation? Almost all of my panels came with
>the diodes already installed, so it's not like it's a big deal to have
>them.
>--
>derek
1. Diodes are not recognized under building codes as preventing excessive
(reverse) current in modules.
2. The UL listing of PV modules in the USA requires instructions with each
carton detailing the need for fuses.
3. Most of the diodes already installed in PV modules are bypass diodes,
they are across sections of the modules, not in series with the module.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
bill@pvri-removethis.biz
| |
| Derek Broughton 2005-12-16, 11:21 am |
| Bill Kaszeta / Photovoltaic Resources wrote:
Thanks both Bill & Flare, there's obviously been a gaping hole in my PV
education.
> 2. The UL listing of PV modules in the USA requires instructions with each
> carton detailing the need for fuses.
How long has this been required? I _do_ read the instructions that come
with my panels and have never seen anything indicating a need to fuse
panels _individually_. They're clear that there have to be fuses, but
right now all of my panels are paralleled, then fused.
--
derek
| |
| SolarFlare 2005-12-17, 1:21 am |
| I have three strings together and then two strings
together into separate breakers on my unit.
Not all of us follow the rules all the time....LOL
"Derek Broughton" <news@pointerstop.ca> wrote in
message news:q2va73-sfo.ln1@news.pointerstop.ca...
> Bill Kaszeta / Photovoltaic Resources wrote:
>
> Thanks both Bill & Flare, there's obviously been a
gaping hole in my PV
> education.
>
instructions with each[color=darkred]
>
> How long has this been required? I _do_ read the
instructions that come
> with my panels and have never seen anything
indicating a need to fuse
> panels _individually_. They're clear that there have
to be fuses, but
> right now all of my panels are paralleled, then
fused.
> --
> derek
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