The solar panel tango

Submitted: Friday, Jun 03, 2016 at 22:12
ThreadID: 132637 Views:2780 Replies:7 FollowUps:8
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At campsites around the country we owners of PV panels can be seen dancing with them pointing to the sun.

Question is how much difference it makes to get them square on. Anyone done any measuring?
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Reply By: Peter_n_Margaret - Saturday, Jun 04, 2016 at 00:04

Saturday, Jun 04, 2016 at 00:04
Flat all day compared to perfect angle pointing north all day is about 20% I understand.
Chasing the sun east to west all day as well would be some extra.
Personally, an extra panel on the roof is much better value, I reckon.

Cheers,
Peter
OKA196 Motorhome
AnswerID: 600931

Follow Up By: Baz - The Landy - Saturday, Jun 04, 2016 at 13:07

Saturday, Jun 04, 2016 at 13:07
2 x 140 panels on the roof for me, and never give it a thought.

Mind you, I don't have substantial power requirements..

Cheers, Baz - The Landy
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Reply By: Member - Boobook - Saturday, Jun 04, 2016 at 06:48

Saturday, Jun 04, 2016 at 06:48
It makes a lot of difference in the Morning till about 10:00 then from about 3:00 in Winter and 9:00 till 5:00 in Summer. About double at those times,

The morning in particular it is important to face the sun as the air is cool, and the batteries low. That is when the efficiencies kick in, especially with a MPPT controllers.

If you move the panels a few times like above then you will get pretty close to the available power.

The big issue is that most people simply buy too little solar. 160w for example is good for a fridge and some extra power IN PERFECT conditions. If you had 320W then you could move the panels less and still get power on cloudy days.

As a guide if you lay the panels flat. At about Sydney, if its winter ( worst case).
at 9AM you get about 25% of the sun's power
at 10 AM you get about 45.
at 10:30AM you get about 60%
at 11AM you get about 75%
at Midday you get about 85%

In summer it might look like
at 8AM you get about 25% of the sun's power
at 9 AM you get about 50.
at 10:30AM you get about 70%
at 11AM you get about 85%
at Midday you get about 100%
AnswerID: 600934

Follow Up By: Sigmund - Saturday, Jun 04, 2016 at 07:06

Saturday, Jun 04, 2016 at 07:06
Thanks Boobook.

Is it true that output drops right off in the afternoon?
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Follow Up By: Member - Boobook - Saturday, Jun 04, 2016 at 07:32

Saturday, Jun 04, 2016 at 07:32
Oh sorry Sigmund, I was just being lazy. It drops off at the same rate as it increases in the morning. So for example at about 3PM in winter it will be the same as 9AM ( 3 hours from midday) - 50% approx.

The figures are rough but a good indication of the relative amount of power you can harvest.

I found a graph that demonstrates it better. I'm not sure where the location is but hopefully it shows the idea. The green and black lines are the ones to look at.
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Follow Up By: wombat100 - Saturday, Jun 04, 2016 at 10:45

Saturday, Jun 04, 2016 at 10:45
Hi Sigmund
Drops even lower at night !!
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Follow Up By: Peter_n_Margaret - Saturday, Jun 04, 2016 at 13:25

Saturday, Jun 04, 2016 at 13:25
This pics was taken at midnight at Nordcapp, the most northerly point in the world that it is possible to drive to (in Norway).
The panels were flat and there were almost no clouds (some more would help with reflection), but the sun does not go below the horizon.

Many solar panels here are mounted vertically to keep the snow off.





Cheers,
Peter
OKA196 Motorhome
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Follow Up By: Member - Boobook - Saturday, Jun 04, 2016 at 15:10

Saturday, Jun 04, 2016 at 15:10
Peter do you know how many watts of solar panel was there gathering that 0.3A. Also the voltage??

The meter reading by it's self doesn't mean much.
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Follow Up By: Peter_n_Margaret - Saturday, Jun 04, 2016 at 23:12

Saturday, Jun 04, 2016 at 23:12
It was 420W of nominal 12V panels.
Not much, but they were literally at 90 degrees to the sun, so anything was a surprise. It was better an hour earlier and an hour later, but I just had to get a pic at midnight.

We actually had no problem keeping the batteries topped up with cold temperatures, clear skys and 24 hour daylight. The compressor fridge was not working very hard although the inside of the van was warm due to the 50mm of urethane insulation in the walls, ceiling and floor.

Another midnight pic a bit further south.



Cheers,
Peter
OKA196 Motorhome
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Reply By: rumpig - Saturday, Jun 04, 2016 at 07:08

Saturday, Jun 04, 2016 at 07:08
We put a monitor on a mates 160W panel one day at camp and were surprised at it's low output reading for the size of his panel compared to one of my 80W panels I have which I'd just checked minutes earlier. We then tilted his panel back a touch more as it was standing abit to straight up and down I thought ( though was angled in full sun already), and straight away it's output doubled.
AnswerID: 600935

Reply By: pop2jocem - Saturday, Jun 04, 2016 at 10:53

Saturday, Jun 04, 2016 at 10:53
The other factor other than the panel's angle to the sun is the internal heat of the panel. As it gets past a certain point the output drops off considerably.
This is particularly noticable with panels mounted against a flat surface without a clearance being made to allow air circulation to allow cooling.
Personally I move my 80 watt free standing panel a few times during the day (without getting too anal about it) and this connected with an MPPT controller mounted close to the DC battery powers my Engel 40 lt fridge and puts enough extra into the battery to last through the night. The fridge doesn't get opened after around 8 or 9 pm though.

Cheers
Pop
AnswerID: 600945

Reply By: Member - Blue M - Saturday, Jun 04, 2016 at 12:36

Saturday, Jun 04, 2016 at 12:36
For the past week I have been holed up in a gravel pit between Meekatharra and Wiluna. I was parked pointing to the west. The best input I would get was 10.6 amps from my 420 watt panels mounted on the van roof.
I knew it should have been better and because for the past 1000k's have been dirt roads I thought dirty panels.
I got up and cleaned them up pretty good and the results were the same.
After the 4th day I moved the van to point to the North and the input rose from a maximum of 10.6 amps to a maximum of 17 amps.
These maximums didn't last very long during the day, probably from 11:00 to 14:00.
By 16:30 input was practically nil.
Whilst I was up on the ladder cleaning the panels I noticed that the air conditioner was shading a small portion of two panels when I parked pointing to the West.

Today I am sitting in a rest area, totally overcast day and charging at 6.5 amps at 10:30.
(Hopefully the generator haters will not park near me this afternoon as I feel I will have to give it a run later to top things up.)

Cheers

AnswerID: 600954

Follow Up By: LandCoaster - Sunday, Jun 05, 2016 at 11:20

Sunday, Jun 05, 2016 at 11:20
I spent two weeks in project with 420 watts on a mmpt... I would get 16 amps between 10 and 2, 10 amps on a one hour shoulder and 6 amps most anytime else. Parked east/west was best for me and I thought I should have gotten better as well..
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Reply By: Sigmund - Saturday, Jun 04, 2016 at 12:53

Saturday, Jun 04, 2016 at 12:53
Yeah, camped in the Bungles a few weeks back in the low 30s, 150 w of free-standing panels yielded about 6.5 amps max. PWM controller. Was doing the dance. Should be getting more?
AnswerID: 600958

Reply By: Member -Dodger - Saturday, Jun 04, 2016 at 15:46

Saturday, Jun 04, 2016 at 15:46
My son installs panels on houses, vans, house boats etc and when asked what panels are best he says the sun chaser variety.

Viz. Those of us that have portable solar.

I too have panels on the roof of the van but like to park where the hot afternoon sun is shaded from the van so that is when the sun chaser panels really do help.

Yep you can't have too much solar.
I used to have a handle on life, but it broke.

Cheers Dodg.

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