Solar PV Panels

don0301

maths flawed, update soon

don0301

maths flawed, update soon

don0301

hope this is more accurate:

I just did some calculations regarding my fairly steep roof, 49 degrees, and how the Sun's height in the sky will affect depending on time of year.
Dec 21 - 14.5 degrees off perpendicular
Mar 7 - perpendicular (optimum)
Jun 21 - 24.5 degrees off perpendicular
could anyone point me to where i could get the information off how much % performance you lose from solar panels by relative angle to the sun.
ie perpendicular then 100% performance
20% off perpendicular then X% performance.
thanks
　
from my extensive scientific research (google search )
the optimum roof pitch for my latitude (51 degrees North,Essex) is 42 degrees for best all year round performance.
solar panel loss (in relation to roof angle to sun) at 15 degrees off optimum is 3%?
cannot find panel losses due to different angles during the year
I wonder if anyone knows a website that can tell you overall % performance for a roof angle, at a certain latitude (in relation to roof angle and optimum roof angle at that latitude)
hope that makes sense :P

Martyn1981

Don, have you tried this site

http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#

You can put in roof angle and consider the different results.

Mart.

don0301

oh, i knew about that site

but hadnt thought to use it in that way

thanks for the idea

I'll have a play about


according to that site theres very little difference in annual output!

30 degrees - 3940kWh
42 degrees - 3980kWh optimum
49 degrees - 3940kWh my roof
45 degrees - 3970kWh my neighbour

will be interesting to see how it turns out

Martyn1981

Don, just read backwards, before I repeated anything, and it worked. Cardew spotted and explained the logic of the 'undersized' inverter, which when reading or chatting with others with PV does seem to be a sensible idea. That and panel angle explains those pretty damn high figures you quote for Dec - I'm very jealous.

My system is quite young (August), but due to complexities I get to compare and contrast as it's technically 2 systems.

Phase1 2.4kWp at 30deg ESE on a SMA 2500, and
Phase2 1.2kWp at 20deg ESE on a SMA 1200

Already noticed several differences,
1. the smaller inverter comes on earlier and goes off later, only running maybe 5 to 10w but shows that it takes less to get going,
2. P2 in August was producing 50% of P1 - as you'd expect, but now with shallow sun angle it's down to 30% or less.

Will be interested to see if P2 outperforms P1 (ie greater than 50%) in May to July when sun is higher.

Regarding peaks, wait till you get full sun and cold panels, that'll blow your mind. On a sunny day in August, after a cloud had gone over and cooled the panels, P1 for nearly 5 mins not only exceeded 2,400w but it actually hit 2,580w. Once hot the panels seem to sit steady at about 90%, so your 3.5kW inverter sounds perfect. Been told that a traditional April with sunny showers can give even higher, short term, performance.

Last thought, I too tried one of those energy monitors, but found it useless below 200w. So I got a current cost ENViR (E-bay) and a current cost optismart that sits over the red flashing light on the TGM. Instant readout of exactly what the TGM is recording.

Beware however, the optismart is no good on the main meter if you have PV as it gets confused when the solid red light stays on to warn of RED (reverse energy detection), and fails.

Mart

don0301

Martyn, thanks for the replies

like you, i find this topic very interesting (especially now ive invested in a PV system )

ive kept records since my system went online on 30/11/11

in December i made 161.7kWh, my best day was 13kWh

and to date i have made 232.3kWh

whats interesting for me is i have a neighbour with roughly the same system as me, but he is 2 story, i am 3 story. also same direction south.his roof is 45 degrees, mine is 49. but this time of year he has 3 trees that partially shadow his panels.

on good days im making 6-7 times his output!

we do compare production, and it will be interesting to see how it pans out over a full year and beyond.

i have seen peaks of 3.7kW on my owl monitor but i understand its 5% inaccurate?

i just use the owl as a bit of fun, as at night it constantly reads 113W which makes any stats from it useless, which is a shame. although its very useful in the day to work out what i can use for free

i quite often so far have seen a steady 2.5-3kW on a sunny day.

im very happy with my investment. i guess ill be jealous of your readings come summer hehe :j

Martyn1981

Don, sorry to bore you again, but 161 in December, are you serious! I'm staggered. Is that in line with PVGIS?

I was pleased with 54, PVGIS was 53.

I was outperforming PVGIS, till I was told to lower the system losses from 14% to 9%. Since then everything has been very close (a little over or a little under).

Can't back this up, but something is nagging in the back of my mind, that all of the 'oh my god' generating numbers I've seen / read / heard about have involved undersized inverters.

Another thought I had, was that whilst your system may be a winter optimised, it will mean more even generation, and a better chance of using more generation yourself, improving savings on domestic bill.

Best of luck mate.

Mart.

don0301

you dont bore me at all. its all good

ive been putting in 11% for other losses. sure i read that somewhere.

on that basis my Dec should have been 150 (153 for 9% losses). so i beat it yeah.

was doing really well until the middle of the month onwards. second half of the month i had only one decent day :cool: (112.6 to the 15th, so only 49.1 16-31st)

yeah, agreed about the winter optimized. it seems from playing around with the link you gave me, that overall annual output varies little with pitch of roof (who would have thunk that), but with having a steep roof i am getting more relative performance in the winter months.

im retired now, so plenty of opportunity to use washing machine or dishwasher when the sun comes out

my electric consumption (that i will pay for) has dropped quite dramatically so far :T

im sure come high summer you will be making me jealous

Martyn1981

Don, now I know you're taking the mick!

49.1kWh's for the weeks straddling the winter solstice. Bah, humbug! My breakdown would be roughly 30 / 20.

If you're generating enough, consistently, then you could could consider supplementing your heating during the day. But be careful not to trade high quality fuel (leccy) for low quality gas. There should be a bit of heart v's head on what is best.

I don't generate enough, nor consistently enough to consider this properly. However, I've found that with the addition of a pair of ski socks and fleece top over my regular clothes, that I've managed to leave the heating off when the wife is out, with this mild winter, and just keep the room I'm in warm with a 400w oil filled radiator. Rad runs about 50% (on 10 mins off 10 mins with thermostat), so 200w. Tried to do the maths compared to gas, but ran out of talent. So assumed, better to heat one room than most of the house, particularly kitchen, hall and landing with GCH when the wife is out.

You might want to look up a device called 'EMMA', google emma + energy. Expensive, so questionable returns, but might be of interest to you, given your system.

Mart.