When do panels start producing?

pHredd9mm

If a solar panel array is pointed south (northern hemisphere) and is set an an appropriate angle from vertical for the time of year, when does the array start producing power after sunrise and when does it stop producing heading towards sunset. Or in other words, at what side-angles does the sunlight become enough for the panels to produce power as the sun rises towards noon and then late afternoon stop producing? Assuming no shading.

jagec

Re: When do panels start producing?

It starts producing a TINY amount of power pretty soon after the sun rises, but the serious power is pretty much all being produced during the 4-6 hours of "peak sun" each day.

Check the blue line:

solarix

Re: When do panels start producing?

You'll be amazed at how soon in the morning a few watts start to flow. At dawn, even before the sun comes up, you should see a admittedly small amount of power. The variation in solar "gain" is tremendous throughout a day - It is only because of the miracle of our marvelous eyesight that it seems kind of constant through the day. Even with a fairly heavy cloudcover, a lot of sunlight is till hitting your array.

pHredd9mm

Re: When do panels start producing?

My reason for asking was to design a set of arrays with the main section pointed true south and a small section pointed southeast and a small section pointed southwest to gain that early morning and late afternoon sunshine without having to use an electro-mechanical tracking device.

Cariboocoot

Re: When do panels start producing?

pHredd9mm wrote: »

My reason for asking was to design a set of arrays with the main section pointed true south and a small section pointed southeast and a small section pointed southwest to gain that early morning and late afternoon sunshine without having to use an electro-mechanical tracking device.

In practical terms it will make a difference what latitude you are at. Also the time of year will vary the results, as will the type of panel.

When you're far North like I am, the solar arc is quite extreme. The closer to the Equator, the less variation.

I'd suggest making some observation of how early light falls on the proposed "main" section area and how long it stays there. If there are truly no shadows or obstructions you probably will not gain much from having three different arrays.

And that is another point: for the plan to work best it should be three separate arrays on three separate controllers; one for 'morning', one for 'midday', and a third for 'early evening'. I have considered adding a 'morning' array to my system due to the slight off-South orientation of the main array and the positioning of trees which keep light off the panels until about 10:00 AM at certain times of the year. Mid-Summer it isn't a problem.

Blackcherry04

Re: When do panels start producing?

Here is something that might help. You can use the satellite view if want to find your house. There are others out there also.

http://suncalc.net/#/38.2527,-85.7585,10/2011.10.26/13:27

BB.

Re: When do panels start producing?

Yes, another is PV Watts and it is pretty easy to use.

It will do fixed, one and two axis arrays. And, if you wish, you can get a detailed output that shows output every hour over a 24 hour period 65 days a year.

Also, PV Watts takes ~ 20 year average into account... So if you have summer afternoon thunder showers, it will show more power output in summer if you point the fixed array southeast, etc.

-Bill

Cariboocoot

Re: When do panels start producing?

One other plan for "extending the day" is to have two arrays: a larger one pointed somewhat South-East to generate the major charging power morning-on for Bilk & Absorb stages and a smaller one oriented South-West to maintain Float until the sun goes down.

But everyone's site is different, so you really have to get some observations and numbers (including charge/usage pattern) for yours to determine what sort of configuration would work best for you.

waynefromnscanada

Re: When do panels start producing?

Re when they start producing in the morning: Where I am in NE Nova Scotia (Canada), I tilt my panels to the vertical for winter, which reminds me I've got to do that today as wet snow is forecast next couple of days. In late fall/early winter here, the sun is way south of it's spring/summer position and with my panels mounted vertically, when the sun pokes it's head up over the south-eastern horizon in the clear morning air, it's just seconds until I'm getting probably 75% of full power, especially if there's reflective snow on the ground. Unfortunately I don't get the same output pre-sunset, as some trees on neighbors property cuts me off an hour early. Furthermore, the pre-sunset atmosphere is seldom as clean and clear as it was at sun-up.

ggunn

Re: When do panels start producing?

Cariboocoot wrote: »

In practical terms it will make a difference what latitude you are at. Also the time of year will vary the results, as will the type of panel.

When you're far North like I am, the solar arc is quite extreme. The closer to the Equator, the less variation.

The difference in altitude of the sun at solar noon between the winter and summer solstices is 47 degrees no matter where you are on the planet. On the equator the center of the variation is directly overhead and at the poles the center is on the horizon, but the variation is the same (2X the tilt of the earth's axis from its orbital plane) and the center of the variation is your latitude, setting zero degrees at directly overhead.

The difference in the strength of the insolation between winter and summer solstices is more extreme the farther from the equator you are until you get to the arctic or antarctic circle.

Cariboocoot

Re: When do panels start producing?

"Twist theory and fact a lot doth lack."

Read Wayne's post.

Here in the Great White North the sun pops up for a brief visit in Winter, rolling up and down in its low arc with barely any East-West trajectory. In Summer it rises behind the cabin and makes a great wide arc across the sky. Usable sun in Winter: 2 hours out of 6. Usable sun in Summer: 12 hours out of 16. Changes in panel angle between the seasons means the Spring/Fall production gets hit with the sun needing to "round the corner" of the panels, causing significant loss of potential harvest.

It's not as simple as "47 degrees everywhere" and the people who teach that are the same idiots who think daylight savings time is a good idea. Welcome to planet Earth: it's round in both directions.

And yes I do know the sun doesn't revolve around the Earth.

jagec

Re: When do panels start producing?

Here are some more detailed charts that I made for my location:





In the integrated production chart, the steep section of the line is where all of the real power is being made. It's a fair bit longer in the summer months. In the winter, the party is pretty much over at 3 PM for my array.

Want to make your own charts for your location and array? Download the attached PDF, CHANGE THE EXTENSION TO .xlsx (No, it's not really a pdf), import hourly data for your system from PV-Watts, and replace my data with yours.

ggunn

Re: When do panels start producing?

Cariboocoot wrote: »

It's not as simple as "47 degrees everywhere" and the people who teach that are the same idiots who think daylight savings time is a good idea. Welcome to planet Earth: it's round in both directions.

And yes I do know the sun doesn't revolve around the Earth.

The difference in the apparent altitude of the sun at solar noon is 47 degrees different from solstice to solstice no matter where you are on the planet; that is a fact.

The points on the horizon where the sun rises and sets is a different (though connected, of course) issue, and it is why tracking systems work better at higher latitudes. At the north pole you'd want one that revolves continuously.

Daylight savings time is a great idea for me, personally; I like not having to drive to work in the dark in the winter and I like having lots of daylight hours after work in the summer. That's another thing that is different for higher latitudes; winter days are shorter so you are probably driving both to and from work in the dark anyway, and summer days are longer so you have plenty of daylight hours at both ends of the work day. If you don't have a job where 8AM and 5PM are significant times for you then it probably doesn't mean as much to you no matter where you live.

YMMV, but please don't categorize me as an idiot. I'm not and I have papers to prove it.

jaggedben

Re: When do panels start producing?

Cariboocoot wrote: »

One other plan for "extending the day" is to have two arrays: a larger one pointed somewhat South-East to generate the major charging power morning-on for Bilk & Absorb stages and a smaller one oriented South-West to maintain Float until the sun goes down.

If he's designing an off-grid system -- he didn't say -- then that might work. For a grid-tie system what he is proposing does not make much sense.

Cariboocoot

Re: When do panels start producing?

ggunn ol' friend I think we got lost in the posts.
The original query was about when (time of day) panels start/stop producing. This involves both the Summer/Winter difference (47 degrees) and the latitude difference (total daylight hours). Heck if we're going to factor in everything local topography can play a big role; you should drive through the canyon here and watch how you go in and out of darkness for the way those mountains block the light! The poor folk on the south side of our lake are sun challenged even in July.

And before anyone else gets too confused, the 47 degrees we're talking about will be about the difference between you best Winter angle and your best Summer angle anywhere in the northern hemisphere just like ggun said. But it does not address the sunrise/sunset time differences for latitude and their effect on panel production (East-West solar arc and how it relates to insolation of panels) like I said.

Just a couple of resource reposts for anyone trying to follow this:
Macslab panel angles: http://www.macslab.com/optsolar.html
Latitude/Longitude finder: http://www.satsig.net/maps/lat-long-finder.htm
Sunrise/sunset table: http://aa.usno.navy.mil/data/docs/RS_OneYear.php
Build-it Solar's methods of finding solar South: http://www.builditsolar.com/SiteSurvey/FindingSouth.htm

ggunn; I am not an idiot either, although many seem to think I am. Where do you get those papers?

niel

Re: When do panels start producing?

let's try the simple approach to the question. pvs will start to produce anytime there is direct insolation on the pvs with an incidence angle less than 90 degrees to the sun. sometimes there is also production when the diffuse sky radiation is strong enough or the light has been reflected from some other area. some of these less than optimal conditions will not produce much current, but they can still produce.

Cariboocoot

Re: When do panels start producing?

jaggedben wrote: »

If he's designing an off-grid system -- he didn't say -- then that might work. For a grid-tie system what he is proposing does not make much sense.

I always think in terms of off-grid. Everybody knows that by now!

pHredd9mm

Re: When do panels start producing?

As the OP, I was thinking of the possibility of off-grid. But that doesn't make a difference to my original question: An array is sited so it points true south.... assume the panels are tilted at the optimum angle for the season and distance from equator.... At what SIDE angle does the panel start producing power.

Using SunCalc, use a zipcode of 98584 and Sept 21st as an example, gives a sun arc of about 180 degrees. Again, array pointing true south, at what point, time wise, or sun's azimuth, do the panels start producing power?

At this point this is an intellectual study as we look at several properties for purchase for future build. Might be grid-tie, good possibility will be off-grid. We are looking at a full range of properties with potential building sites from flat fields to hilly with trees. Having an idea before hand of how much cleared area will be needed will make us better land shoppers.

Thx.

Cariboocoot

Re: When do panels start producing?

If you distill down all the posts you come to:

Niel's response; the panels start producing power the moment there's any light on them. If you think of the panels as being flat in respect to a theoretical horizon, the moment the sun's angle rises above zero degrees the panels will begin to produce power. At this point it will be very small amount of power, not even enough to set a controller to charging. As the sun rises higher the power increases. When it's directly above the panels the power will be at maximum. As it sets the reverse will happen. You will get Voc as long as there's any illumination in the sky, but that does not equate to producing usable power. "Usable" is the caveat here.

In addition, relating this to time of day will change with season and latitude. A fairly reliable rule-of-thumb is that you will have "X" hours of "equivalent good sun" per day maximum. The "X" here will vary according to latitude and time of year. This number can be divided up between AM and PM thus: 4 hours of equivalent good sun = usable power production from 10:00 AM to 2:00 PM. In reality it is a non-linear curve; some of the power production will occur before and after those hours, with the percentage of that contribution varying due to the aforementioned factors.

Sorry the answer isn't straightforward, but it is a complex issue. Panels don't just turn on at "so much" sun on them and start producing their full power. Too many promoters out there give that impression.

Speaking as someone who does squeeze power out of the sun off-grid, I can tell you that the future obstructions of any kind that you have East or West or South will be better. It is also often advantageous to favour slightly East or sometimes slightly West of solar South: the easterly orientation can give you full charging power earlier to recharge batteries quicker after overnight use, the westerly orientation can make sure the batteries are fully charged as late as possible giving you full potential for overnight use.

Much depends on your pattern of use and site-specific factors like obstructions or recurrent weather patterns (marine layer, morning fog, afternoon thunderstorms).

You should also know that you won't be able to make use of the panels' full power potential much of the time: once the batteries are full, any additional power potential is wasted because there's no place for it to go (no further storage capacity). The solution to this is to adjust usage patterns so you have things to turn on once the batteries achieve Float, for example. I select that time to run the water and septic pump, which are two big power hogs.

There's only so much you can do towards picking a site for its solar value; some of the design work goes the other way - adjusting the solar to meet the site specifics.

BB.

Re: When do panels start producing?

My array will produce power with no direct sun--just back-scatter from the sky (my array faces south east a bit, so the setting sun is well behind the array).

However, 50 watts from a 3.5 kW array is not very much and can pretty much be ignored (Grid Tied system).

-Bill

pHredd9mm

Re: When do panels start producing?

Thanks for all of the good info. Gives me lots to ponder.

-Ed- (OP)

mike95490

Re: When do panels start producing?

here's a graph of my GT array (fixed, west facing roof), over the course of a day.

http://www.mike-burgess.org/images/MB_May-3-2007.htm
(tabs way at the bottom for more fun looking at it)

Picture is worth a thousand words

My 3Kw off grid array produces 200-300w in cloudy weather.

ggunn

Re: When do panels start producing?

Cariboocoot wrote: »

And before anyone else gets too confused, the 47 degrees we're talking about will be about the difference between you best Winter angle and your best Summer angle anywhere in the northern hemisphere...

In the southern hemisphere, too, but actually if you are up for splitting a hair or two, one might argue that the best winter angle is about 12 degrees down from latitude tilt and the best summer angle is about 12 degrees up from latitude tilt, i.e., halfway between the median and the extreme.

Cariboocoot wrote: »

ggunn; I am not an idiot either, although many seem to think I am. Where do you get those papers?

I was extensively tested for IQ when I was a kid and I scored very well. I have annihilated many brain cells since then, though, so I may not be the towering intellect that I once was.:p

Cariboocoot

Re: When do panels start producing?

ggunn wrote: »

I was extensively tested for IQ when I was a kid and I scored very well. I have annihilated many brain cells since then, though, so I may not be the towering intellect that I once was.:p

Completely understand. Couple of strokes have punched some serious holes in my brain. Regrettably this is far more noticeable at times than I'd like it to be.

garlic

Re: When do panels start producing?

BB. wrote: »

My array will produce power with no direct sun--just back-scatter from the sky (my array faces south east a bit, so the setting sun is well behind the array).

However, 50 watts from a 3.5 kW array is not very much and can pretty much be ignored (Grid Tied system).

-Bill

I experience the same thing on a smaller scale .With 600 watts and MPPT I get

a whopping 4 watts a half hour before the sun comes up.

ggunn

Re: When do panels start producing?

Cariboocoot wrote: »

Completely understand. Couple of strokes have punched some serious holes in my brain. Regrettably this is far more noticeable at times than I'd like it to be.

Oh, man, I apologize for the flippancy of my remarks. My cerebral deterioration, such as it is, is self-inflicted.