calculating loses
David Lesher
So I have a demand of 1.6 KWh/day, and insolation is 5.5 kwh/M^2day.
If the world was perfect, I'd just divide to get panel area.
It's not, so I assume there are other factors I must
include; the panel efficiency of course, and some electrical
losses. [It's a DC pump motor, so that eliminates one,
conversion losses..]
Where do I go for more data on this aspect?
--
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Ron Rosenfeld
<wb8...@panix.com> wrote:
>
>So I have a demand of 1.6 KWh/day, and insolation is 5.5 kwh/M^2day.
>
>If the world was perfect, I'd just divide to get panel area.
>
>It's not, so I assume there are other factors I must
>include; the panel efficiency of course, and some electrical
>losses. [It's a DC pump motor, so that eliminates one,
>conversion losses..]
>
>Where do I go for more data on this aspect?
With regard to your panels:
Panel efficiency is one determinant of required "Area". However, you
need to know how the panel efficiency was determined. It should be
determined at some specified test condition (e.g. STC or PTC) which
may not be reflective of your real world conditions.
Then you may need to know the temperature coefficient of power,
depending on your environment. That data should be published with the
panel specifications. If not, you should contact the manufacturer.
If area is irrelevant, than you can just start with the panel output
ratings and ignore efficiency (but not the variation between the test
conditions and your real-world conditions).
You need to add in some factor for panel aging. Probably you can get
that from the warranty. e.g. If the panel is rated to produce at
least 80% of its nameplate output at 25 years, then 80% might be an
appropriate factor.
Wiring losses can be obtained from various sources -- they will vary
depending on wire run length and wire size. They may be insignificant
if the panels are close to the pump. They can be mitigated by using
an appropriately sized wire.
Will the pump be running 24/7? If so, you will need to factor in
losses from your electrical storage medium.
You should know that the solar insolation values are a multi-year
average. Depending on your requirements, you may have to take into
account worst-case scenarios. For example, an average annual (or
pumping season) insolation of 5.5 does not mean there will be 5.5
every day. There will be more on some days, and less on others.
If your pump needs to run 24/7, then you will need to include the
losses in your energy storage medium (usually batteries)
And there's more you need to be aware of in designing a system, but
the above should get you started.
David Lesher
>>So I have a demand of 1.6 KWh/day, and insolation is 5.5 kwh/M^2day.
>>
>>If the world was perfect, I'd just divide to get panel area.
>>
>>It's not, so I assume there are other factors I must
>>include; the panel efficiency of course, and some electrical
>>losses. [It's a DC pump motor, so that eliminates one,
>>conversion losses..]
>>
>>Where do I go for more data on this aspect?
>With regard to your panels:
{STC vs PTC, temp derate, aging}
Thanks. I was also hoping for some writeups on how much each
factor deserves, etc.
>Wiring losses can be obtained from various sources
...
And unlike one vender's bid: by keeping the supply voltage up.
[The SqFlex series will run from 30-300V, and run well above 120V.]
>Will the pump be running 24/7?
Nope, we're storing energy the rational way: Ug = mgh
No oxides of lead or such needed, and very low losses.
We shall all wear out before G*{m_1*m_2}/{r^2} does.
>You should know that the solar insolation values are a
>multi-year average. Depending on your requirements, you may
>have to take into account worst-case scenarios.
I figure we have 40-60 DAYS worth of water storage, so a few
cloudy days won't cause grief.
Further, there's some balancing factors. Rainy season has less
sun, but the well level will likely be 75-125 ft higher, using
less power. And the panels will be cooler.
>And there's more you need to be aware of in designing a system, but
>the above should get you started.
Well, I've got a handle on everything save the panel issues.
Thanks for your help.
Ron Rosenfeld
<wb8...@panix.com> wrote:
>Ron Rosenfeld <r...@nospam.net> writes:
>
>>With regard to your panels:
>
>{STC vs PTC, temp derate, aging}
>
>Thanks. I was also hoping for some writeups on how much each
>factor deserves, etc.
That is manufacturer specific, so you have to obtain that data from
the manufacturer. They should have it published on their data sheets;
but sometimes you have to contact them directly. If not available,
they probably haven't tested it and you're guessing.
For example, for their 165W panels (which I use), Sharp publishes both
STC and PTC ratings. They don't publish temperature coefficients but
I was able to obtain that from the mfg. They do publish both solar
cell and module efficiency, but since the size of the panel is also
published, I didn't really need to know that. I just counted up the
panels I needed and determined the area, making sure they would fit in
the available space.
So far as a factor for aging, I use 80% from their warranty (% rated
power output at 25 years).
>
>>Wiring losses can be obtained from various sources
By that I mean charts or equations to compute wire loss vs current and
wire size. For the same current, larger wires = less losses.
For the same kW output, higher voltage --> lower currents --> less
losses.
>...
>And unlike one vender's bid: by keeping the supply voltage up.
>[The SqFlex series will run from 30-300V, and run well above 120V.]
>
>>Will the pump be running 24/7?
>
>Nope, we're storing energy the rational way: Ug = mgh
>No oxides of lead or such needed, and very low losses.
>We shall all wear out before G*{m_1*m_2}/{r^2} does.
>
>>You should know that the solar insolation values are a
>>multi-year average. Depending on your requirements, you may
>>have to take into account worst-case scenarios.
>
>I figure we have 40-60 DAYS worth of water storage, so a few
>cloudy days won't cause grief.
>
>Further, there's some balancing factors. Rainy season has less
>sun, but the well level will likely be 75-125 ft higher, using
>less power. And the panels will be cooler.
>
>>And there's more you need to be aware of in designing a system, but
>>the above should get you started.
>
>Well, I've got a handle on everything save the panel issues.
>Thanks for your help.
As I alluded to above, since you will have the power output rating of
the panels, efficiency only comes into play if space available is
limited.
Martin Riddle
"Ron Rosenfeld" <r...@nospam.net> wrote in message
news:5n8346p1tsvjggurd...@4ax.com...
Include Panel dust too.
I believe the efficiency turns out to be somwhere around 75% of the
advertised panel power.
72% if you want to be exact for a grid tie.
I think someone here , with the same question, was seeing values in this
range.
cheers
stevey
Generally, according to NREL-Colorado the nominal performance when
new, within first two years, 77% is good. However, dust is ever
present,
and usually account for 5% of loss; unless you get rain often, and
have
a good tilt angle, or that you wash it down often.
May the Sun always warm your face and your panels!
-Steve
Martin Riddle
"Ron Rosenfeld" <r...@nospam.net> wrote in message
news:5n8346p1tsvjggurd...@4ax.com...
Include Panel dust too.
Ron Rosenfeld
<marti...@verizon.net> wrote:
>
>Include Panel dust too.
>
>I believe the efficiency turns out to be somwhere around 75% of the
>advertised panel power.
>72% if you want to be exact for a grid tie.
>
>I think someone here , with the same question, was seeing values in this
>range.
I wonder if the "advertised panel power" is using STC or PTC, and
whether the calculations first compensated for temperature.
For design purposes, I usually use 80% of PTC to account for aging,
and I do use temperature compensation.
I haven't added anything for dust, but my panels, when there's no snow
or frost on them, seem to put out at least their rated STC power from
time to time.
Unfortunately, I have no way of measuring independently what the sun
is doing at the time, so it's certainly possible that there is more
than the assumed kW/M^2 falling on the panels.
From an NREL database, the highest incident solar at my site is 1.22
kW/M^2, and values over 1 only occur for 138 hrs/yr; but that's based
on a 20-30 yr average.
Martin Riddle
"Ron Rosenfeld" <r...@nospam.net> wrote in message
news:0veo469g89bv7d1i7...@4ax.com...
Panel dust and atmospheric dust (eg dirt, smog) has an effect. Depends
upon location as to the amount. I have some info somewhere, if I
remember correctly its in the 3% range.
Something associated with Global Dimming ;) 1Kwm some think is
unrealistic. And conservativly use 800wm instead.
I have some info somewhere, I'll try to dig it up tonight, got something
to do before this heavy wall of rain hits NY.
Cheers
Martin Riddle
"Martin Riddle" <marti...@verizon.net> wrote in message
news:i2hvj5$859$1...@news.eternal-september.org...
I have notes that indicate 900wm^2 is a realistic value to use in
calculations.
Inverter effeciency 94%
Wiring loss 2%
Dust and wire connections 10% loss.
.9 x .94 x. 98 x .9 = 74.6% system efficiency.
Cheers
Ron Rosenfeld
<marti...@verizon.net> wrote:
>I have notes that indicate 900wm^2 is a realistic value to use in
>calculations.
>Inverter effeciency 94%
>Wiring loss 2%
>Dust and wire connections 10% loss.
>
>.9 x .94 x. 98 x .9 = 74.6% system efficiency.
>
>Cheers
What system are you using for rating the panels?
What is the source of your "notes"?
Martin Riddle
"Ron Rosenfeld" <r...@nospam.net> wrote in message
news:4uvp46h78uaun79na...@4ax.com...
The PVwatts system is a good system, heres a list of derating factors.
<http://www.nrel.gov/rredc/pvwatts/changing_parameters.html>
Dust, or Soiling (as it is listed) Does vary with location.
But generally, the system efficiency is ~75%
Cheers
Ron Rosenfeld
<marti...@verizon.net> wrote:
>
>
>"Ron Rosenfeld" <r...@nospam.net> wrote in message
>news:4uvp46h78uaun79na...@4ax.com...
>> On Sun, 25 Jul 2010 23:05:01 -0400, "Martin Riddle"
>> <marti...@verizon.net> wrote:
>>
>>>I have notes that indicate 900wm^2 is a realistic value to use in
>>>calculations.
>>>Inverter effeciency 94%
>>>Wiring loss 2%
>>>Dust and wire connections 10% loss.
>>>
>>>.9 x .94 x. 98 x .9 = 74.6% system efficiency.
>>>
>>>Cheers
>>
>> What system are you using for rating the panels?
>> What is the source of your "notes"?
>
>The PVwatts system is a good system, heres a list of derating factors.
><http://www.nrel.gov/rredc/pvwatts/changing_parameters.html>
>
>Dust, or Soiling (as it is listed) Does vary with location.
>
>But generally, the system efficiency is ~75%
>
>Cheers
>
I would agree with their derating system, but note that they start
with STC nameplate values. And there are site specific issues
including not only dust, but also snow; shading, and so forth.