Energy Matters Forums

[Gordon-Loomberah]

I've been living on off-grid solar and wind power well out of town here at Loomberah (35km SE of Tamworth NSW) for 18 years. With my partner Hether we have a large vegie garden, a few chooks, and lots of cherry and other fruit trees.
I've gradually built up my collection of solar panels, and currently have 2.77kW worth of them on 2 trackers. Here they are, along with a 200W WTG in the 2009 Spring Equinox dust storm:
The trackers are great for getting the most out of the panels all year round, and even in cloudy weather we dont need to run a backup generator... just as well, since we dont have one On sunny days we have enough power to weld, there was lots of welding in that big tracker, or run the electric concrete mixer for quite large pours. This time of year we are busy netting and bagging the cherry and apricot trees to protect the fruit from birds and fruit flies, we do everything organically, and most of the block is devoted to regenerating bush, so we have lots of wildlife.

Gordon

[MadMax]

That's a great pic Gordon ... looks like you're living on Mars.

[Gordon-Loomberah]

Thanks Max, yes it sure was a bit like Mars that day! ... and not too different again today with another dust storm, although it was mostly greyish dust this time, and not quite as thick, but it was enough to stop me from heading out for a 125km mountain bike ride I had planned all week
Here are the panels in action on a clear day :

http://astro.gunagulla.com/images/Tracking-Panels20090925.wmv

Gordon

[Lyngarin]

Hello Gordon, very interesting set of panels. I know Loomberah area, I go to Rob Halings place on the Loomberah road, to buy and collect Lucerne Hay. What size are your panels? also how do you determine the Kilowatt rating of a system. I have 8 x 80 watt panels 12 volt.

[Gordon-Loomberah]

I'm further out, a fair way out past the end of Loomberah Rd. I've got a total of 2.77kW of panels, made up of several different sized panels accumulated over a few years. and each array runs through its own MPPT regulator.

Your system's rating would be 640W, or 0.64kW. Its just a matter or multiplying the rating of each panel by the number of panels. Keep in mind that those ratings are measured at 1000W/m^2 and 25C, which isnt realistic for what they encounter out in the sun. 800W/m^2 and 50C is much more like real conditions. You can occasionally see higher than an array's rating on a cool day when the sun is illuminating the edge of a cloud near its line of sight to your panels. Mornings are best for seeing peak outputs, since the panels are generally cooler then. Its a bit like having another sun in the sky- oddly shaped and dimmer, but still increasing the amount of light hitting your panels. My larger array's rating is 1830W, but 'i have seen 2130W out of it briefly. On a sunny afternoon like today they more typically produce ~1.4kW

I'd guess you would see something like 40A out of your panels on a day like today during bulk charging when they are facing the sun.

Gordon

[kdawson]

Hi Gordon,
I'm curious how you came to the figure of 40 Amps from a days charging from a 640watt system. I've got 3 x 130 watt panels (360watt total) and on a nice day like today I've used 112 Amps according to the Plasmatronics regulator.

2009-09-29_165859.png (11.05 KiB) Viewed 8242 times

Regards,

Karl

[MadMax]

Assuming:
0.64kWp of PV
4.9kWh/m2/day of solar irradiation
0.8 approx. overall system efficiency (battery charging)

According to my calculations, for battery charging applications in Loomberah you should get about:

0.64 * 4.9 * 0.8 = 2.5kWh /day average (obviously more in summer and less in winter)

To convert to Ah:

208 Ah @ 12V
104 Ah @ 24V
52 Ah @ 48V

I think Gordon may have been referring to instantaneous Amps (A) and Karl is referring to Energy measured in Amp hours (Ah)

Nice graph by the way ... are you using the Plasmatronics software to generate it?

regards,

Max

[kdawson]

Hi Max,

Yes, it's from the Plasmatronics remote control software. It'd be nice if it was possible to have it show it in watts, but unfortunately you can't.

Regards,
Karl

[MadMax]

Hi Karl,

I don't want to go off topic, but you can convert most units that appear in solar calculations using ohms law:

http://www.csgnetwork.com/ohmslaw2.html

Watts = volts x Amps

Max

[Lyngarin]

Good Evening Gordon, Thank you so much explained very well. Your career obviously gives you some knowledge of solar systems. Also throwing in some learned electrics. Yes my panels do achieve 40 amps sometimes, I have actually seen a charge of 43 amps, I guess every thing was solar lined up perfectly. I was very annoyed that on cloudy days etc I would need the generator on to watch TV otherwise my batteries would flatten off too much ( bellow 80%) I have a 780 amp/hour bank of 6 x 2 volt batteries. I spent some time devising a means of assisting my powersupply. I now have two 110 A/H 12 volt batteries parralleled, they run a small freezer through a second 1700 watt inverter. When going to bed I change my house to the secondary batteries. Which leaves no load on the primary. To charge the secondary I parrallel them to the primary set and the solar panel system does the charging, when no sun I disconnect the secondary. Does this system sound a reasonable way of getting more use of batteries. It has certainly saved me from using the generator by about 70 %. Naturally sun is the final deciding factor. My worry was that I may be over taxing the primary batteries. Sorry for this long message, but you seem to have enough nouse to advise me. Regards Gary.