Calculating Solar

[iFred]

I have been calculating the amount of power a single solar panel that I made produces.

These calculations are helping me determine how many batteries I will require, the correct inverter to use and the total load that can be safely applied.

Based on present information I have made panels with 28 cells, each cell produces ½ volt @3amps, 28 cells are wired in series to produce a single panel, this panel produces a calculated total of 14vdc, however for some strange reason, the entire panel delivers a true measured voltage of 15.5 -16 VDC. Since there is a descripency between the calculated values and the measured values, I am going simply average it and say the panel is fully capable of delivering 15.5vdc. With this number 15.5vdc x 3amps=46.5 watts per panel.

Each panel therefore has the capacity of 46.5 Watts.

Depending on your location, you will have specific hours in which the sun gives you maximum hours of light and maximum power. Solar Isolation is the technical name given to the these solar power maps. They are available from this link.

http://www.solar4power.com/solar-power-global-maps.html

What I find most interesting about these maps is that all the data presented is the worst case conditions. For Windsor, Ontario, Canada this is a 1.5 to 2.0 in winter, worst case on December 21 (when you really want to measure properly the lowest possible value do it on this date, this is when the sun is at it's lowest output, in regards again to my location)

Most collectors work optimum between +15 and -15 degrees with a direction of due south, it is this adjustment that must be done 4 times a year for each season to achieve maximum output. By doing a simple adjustment of 15 degrees once for each season you will gain output. This is what is done most with stationary collectors.

Note: The difference between an adjustable tracking motor driven collector and a stationary collector is a difference of about 5% output increase after rotation; it is questionable to spend the extra amount of time and money on an adjustable tracking system for a difference of this minute amount of extra energy unless it can be done cheap. I intend to use motors and gears from automatic glass door from cars to drive the system for tracking. I already got them and need just to build a controller and mounts for it. I think over time it may pay itself off for the extra 5% efficiency.

Back to power calculating...As stated, each panel can put out about 46.5 watts/per hour, if you multiply this times the hours of peak sun (my location is about 6 hours) from 10am to 4pm is the best window, you will get about 46.5x6= 279 watt hours per panel. This means that in one day it will produce a about a maximum of about 280 watts a day.

That's just one panel. Now I have 10 panels done, I am making a total of 20 panels when completed I should have about 1KW of solar power. Which works out to 6000 watt hours per day. However, as we move into spring and summer the hours change and with it the amount of hours per day.

In calculating loads, here are some web sites to help you.

Load calculator

http://www.altenergystore.com/cart/university/tools/load.html

And a nice web site on Solar Basics

http://www.solar4power.com/solar-power-basics.html

Back to the calculations again... Now that I had this info I used the above web site to calculate the total watt hours per hour, day, week and month and with this number I could determine my total batteries needed.

I hope this helps others that are going through the same things! As I find out more i'll post my findings. Good Luck!

[jimovonz]

Here is another link very helpful for calculating the amount of resource you have on your site (wind/solar):
http://www.fieldlines.com/story/2004/10/6/164945/703

[bob golding]

and here is another

http://www.anotherurl.com/therm/Default.htm

lots of good stuff on pv and solar heating.

bob golding

[stm]

Here's a link to a small piece of software, which does the calcolations for you based on the number of hours the sun shines each month. batteries, load and amount of panels :-)

Check it out it's well worth the time.

http://www.kerychip.dk/MatelMiniPV.zip  (the site is in danish, but the program was writen in english) - i'm using this myself

/steffen

[windstuffnow]

  Just to touch on a point here... You say your getting 15.5 volts at 3 amps or 46.5 watts per panel.  If your charging a 12 volt system you'll never see anything above 14.6 volts except when you equalize bringing the batteries to 15 volts.  If your using the batteries on a normal basis their most likely to vary from 12 to 14 volts.  So the most you could expect from your panels would be 36 to 42 watts and only for brief periods depending on the daily conditions and orientation.

  Prior to purchasing my panels I made the realization that even though their rated at 16.1 volts at 7 amps, no one ever brings their batteries to 16.1 volts so the best I could expect from them is 7 amps each at battery voltage.  But... they still charge you for what the panel could do... not necessarily what they will do ( cost per watt ).  

  One other thing to take note of, is line loss.  Your going to have to make sure your line losses are extreemly low.  If you loose 1volt through the line the best you can do is 14.5 volts and you'll have to equalize from another source periodically.

  I purchased 650 watts of panels to make sure I'd see at least 500 watts of charging.  The best I've seen from them was around 600 watts but only when I was equalizing.  Most of the time they run around 480 to 560 during peak sun. Averaging them out they make about 130 Ah daily or an average of 220 watts per hour.  I'm sure this could come up a bit with a tracker.  So when you calculating the overall output don't forget, if their stationary, to calculate the differences as the sun comes up to peak then falls off again to sunset.  Sizing the system would be quite dependant on a multitude of variations.

  All in all, put up more panels then you need (unfortunately), because your going to need more than you thought.

Have Fun

Windstuff Ed

[stm]

With your setup, you should consider the investment of a mppt charger.

Without a maximum power point charger you are loosing power equal to at least a few panels depending on the size of each panel in your setup.

A mppt tracker would also decrease the power lost if you choose one which takes an array of panels connected in series - ie 48-192 volt by lowering the amps which travels within your wires.

/Steffen

[Gary D]

Fred, if there's snow reflecting light onto your array, you're calculations could be a bit high. The mirror effect? Amps will drop slightly when the snow melts.. during cold weather, a little mirroring won't hurt due to cold temps tho... Gary D.

[iFred]

Hi Guys!

I should have mentioned it. I did in another post about a week ago or so. I am hooking my panels 2 in series and then everything in parallel. This produces 30vdc @3A. I wanted the higher voltage so that -no mattter what- the charging voltage would be met. I have a c-35 xantrex solar controller. The batteries I am using are sealed gel cell. Rating at  24ah, 12vdc.(got tons for free from a friend) They need a charge of 13.8 for 4 hours and then a trickle charge of 200-500ma thereafter, however I have been charging them with 14.8 for 4hours from the mill through a my controller and they seem fine.

 As far as line loss, I am using #2 wire from the batts/controller to the panels which is 100ft away. I calculated almost no copper line loss. I'll finnaly see what happens when I hook it all together.

[windstuffnow]

  iFred,

    My panels are about 100 ft away from my batteries also.  I started out with #2 wire when I installed the first 3 panels and all seemed fine.  I added 4 more 77 watt panels and the output seemed poor.  I wasn't getting the amps I thought I should.  I decided when I strung the 1/0 wire for the wind genny I'd string another set of 1/0 wire for the panels.  I'm very glad I did.  The output of the panels jumped considerably and I believe I have a little room for expansion should I decide to in the future.  I hate doing things over again, I was trying to "cheap" out in an area you simply cant or shouldn't.  I did however buy the cheaper wire that needs to be burried in PVC, the cost of the PVC and wire was far cheaper than the direct bury type although a bit more work.

  Just a few mistakes I made while setting up my panels... I'm fairly new to solar so I really didn't know what to expect from them.  Also I found when I had the first 3 up (340 watts) this was fine until I had a few bad days in a row where my batteries were getting low was there wasn't enough to bring them back in one day.  Thus adding the 4 others cured the problem.  

   I sized my battery bank for 5 days with no input, although, its uncommon to get nothing between the wind and solar over the period.  We commonly have several overcast days with one day of sun which I'm dependant on the wind as the primary charging system.  So far its working well although there are days I wish I had the time last year to get the second wind machine on the tower... it'll be up this summer.

   I wish I had your soldering skills, I'd like to attempt putting a few "home made" panels together just for fun... I still might try it but I'm still a little hesitant...

Have fun and keep up the great work!

Windstuff Ed

[ghurd]

Hi Fred,

I hate to come back to the 36 cell vs. 28 cells. The insolation tables assume 36 cells. When the sun is less than optimum, the voltage with 36 cells will still have output. 28 cells will not.

The charts will be including poor conditions where 36 cells will have a lower output for many hours, but 28 will not have any output at all.

I would suggest making a quicky panel with 8 cells, put it in series with a 28 cell panel, and compare the outputs into batteries on a typical overcast crappy

winter day.

The other day, 10v and no charge (0.357/cell) would have been 12.85v and maybe some charge.

The sealed batteries are not going to like that higher charge many times.

I usually tell people they will have more than they know what to do with in the summer, and not enough for anything in the winter. Deticated systems that ran for 3 or 4 years with no problem may need a gas charger every 2 weeks in the next winter.

G-

[iFred]

Soooo cold...Where in the hell is global warming when you need it? We should be outside with aerosol cans...LOL

The cells indicated the same power with and with out snow. Did'nt seem to matter, however as soon as we get a good glazing snow day, i'll check that theory!

[iFred]

How strange Ed? Your saying that you basically had to overcome a loss with more larger wire? You could have hooked more cells in series if that where the case, this would have increased your voltage and thus reduced the loss. Maybe something wrong with the wire??

I too am completely newbie to solar, but I'm learning quickly what's good and what's not. This is the first time I am playing with the stuff more seriously since I now have all the panels almost completed and ready for wiring and hookup. I know winter is the worst months to work with solar.. I would love to have more wind gennys up right now! Come this year starting spring, I am going to put up some good ones. No more playin around.. Time to get serious.

Ed, are you using a solar controller? If so what is it?

Got coffee, I'll be over and show you how to solder those cells together no problem, patients is the key, not really ability, that is learned. I bet if you sat down and played with just a pound of them, you would have it down in a week max. Move slowly, think everything out first, be fast on the soldering and slow on movement.  Use nice thin solder, works every time. If you want I can make a small video of how I did specific things, if you think it would help?

Good Luck!

[iFred]

G-

As stated, you can hook up the panels in series to produce more voltage. In this case I did experiments with 2 panels in series and get 30vdc at 3A. This then goes to a controller, which handles downconverting the voltage from 30volts to 12 volts. In doing so it increases the amprage from 3 amps x2  or about 5. As a result even a crappy day will produce more then 24 vdc, any less then 24 (which I have not yet seen in mid winter except at night) would be useless anyway because there is no current in any case. Try hooking more of your panels in series and see what I mean.  If your using a controller, then go the maxium voltage that you can input into it. it will convert it anyway and boost your amps, but can't do it if the voltage is less the charging voltage.

[ghurd]

I thought you were going for a 24v system!  My bad.

Your numbers will be skewed the other way, in your favor.

I've had good luck with any of the calculation sheets.  I personaly favor the ones using amp-hours instead of watt-hours. I think in amp-hours.

Snow on the PVs for a few days is usually the reason for any power shortages.

G-