Poll

is my writing style ok or am i too technical?

yeah, it makes sense, kinda
24 (66.7%)
eh? what choo hon aboot?
12 (33.3%)

Total Members Voted: 33

Voting closed: February 01, 2007, 11:09


Solar (photovoltaic) Electric Power

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Zak the Rabbit

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Solar (photovoltaic) Electric Power
« on: February 01, 2007, 11:09 »
Thought i would start a fresh thread to keep the solar and wind apart :?

Ok, so, i have just wired up my solar electric system to my weather satellite system.

The solar panel is a pair of 12v 4W amorphous silicon panels (thats like they use in calculators) rather than the more efficient poly or mono crystalline silicon. This is simply because its cheeper. They are mounted facing south at a 50degree angle towards the sun, in a homemade wood/plastic frame sealed with epoxy resin (fastglass). Both panels have 1N4001 silicon rectifier diodes as protection against reverse current flow (as what can happen when its dark)

The reservoir battery is a Yuasa 12v 7Ahr sealed lead acid. This is simply wired in parallel with the panels and the receiver (ie across the wires)

So, first tests - the weather sat receiver, in its 'standby' mode (not receiving a signal but sound on, scan enabled and squelch open (ie so i can hear the noise)) is drawing 80mA from the system. The solar panel, in bright winter sun is giving 20mA, thats a quarter of the current being taken by the receiver.

in this state, the panel will take 4 times as long to recharge the battery, as the receiver will operate for. Thats pretty good going for a charging system. The system voltage is steady at 13.4v

I was somewhat surprised when wiring it up to find the receiver managed to come on when connected only to the panel, with only a quarter of its required current :shock:  it behaved a little erratically, but shows that so long as the equipment being run isnt too ambitious, even a small renewable system is fine.

The next test of the system will be at 11:52, when the receiver activates for a pass by the NOAA-17 weather satellite.


sources - solar panels, bloke on ebay :)
              battery, half inched from works skip :wink:
(\__/)
(='.'=)
(")_(")
the rabbit of caerbannogg

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Ice

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Solar (photovoltaic) Electric Power
« Reply #1 on: February 01, 2007, 11:27 »
I understand what you are saying but only because I did physics and maths to a fairly high level many years ago.  Not sure the majority of people would understand, but apologies if I am wrong.

Would love it if you posted the occasional project that only required more everyday objects to assemble.  As long as you could use it in the garden or shed , of course  :lol:
Cheese makes everything better.

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Zak the Rabbit

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« Reply #2 on: February 01, 2007, 12:03 »
no problem, anything anyones unsure about just ask,

i will be posting info on how my chicken run is built, just as soon as i have the photos

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Zak the Rabbit

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« Reply #3 on: February 01, 2007, 12:17 »
ok, so the first full test has been done, and appart from the decoding software being all out of blooming step, so the images have a great big slant to them, it worked fine. The meter reading the voltage has dipped a bit but then steadied off at 12.9v, which is well inside the range at which everything will work ok.

well, ive just finished me garlicy fried spuds with cheese, beans and bacon, so im orf out again now to get on with painting the chicken house frames.

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muntjac

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« Reply #4 on: February 01, 2007, 13:57 »
im the one ,, wot ya ona bout voter ..  :roll:
still alive /............

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Zak the Rabbit

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« Reply #5 on: February 01, 2007, 15:43 »
cor, theres always one!  :D

i will try and do it with pictures, its usually better that way.

But not now, its like a spring evening out there, i only popped in to get the camera, so im off out to enjoy it :D

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shaun

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« Reply #6 on: February 01, 2007, 21:01 »
:?  :?  :?  :?  :?  :?
feed the soil not the plants
organicish
you learn gardening by making mistakes

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Gwiz

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« Reply #7 on: February 08, 2007, 17:27 »
Quote from: "muntjac"
im the one ,, wot ya ona bout voter ..  :roll:

not any more you`re not :lol:
i do kinda understand, but i always prefer the " janet and john " editions best :lol:  :wink:

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Zak the Rabbit

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« Reply #8 on: February 08, 2007, 18:53 »
it is a bit tricky to do the simple explanation when theres important technical ideas involved. I will try and make it all really simple :D

when i get round to it... :?

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Zak the Rabbit

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« Reply #9 on: February 09, 2007, 17:08 »
Ive just put the call out on a dozen or so freecycle sites, for broken or no longer wanted solar powered items, you know like those garden lights. The plan is to get a load of them, strip out the little solar panels, and wire em all together into a BIG solar panel :D

i'll let ya'll know how i gets on

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Annie

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« Reply #10 on: February 10, 2007, 00:18 »
I didn`t understand all of that but you usually are clear when I ask  some dumb question.

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Zak the Rabbit

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« Reply #11 on: February 10, 2007, 08:17 »
Its actually good practice for me, i want to teach science, so it helps me learn how to pitch the subject matter.


its quite simple really, big solar panels are made up of lots of little solar panels. The ones in the tops of solar garden lights have a voltage of about 2v and a current rating of about 10mA (in good sun)

the voltage is a measure of a power supplies ability to 'push' the current around the circuit. The current is a measure of how many electrons are moving and able to do work. Voltage is measured in volts (v), current in Amps (A), mA is milliamps, or thousanths of an amp, so 10mA is 0.01A

power is measured in Watts (W) and in a DC circuit like this, is worked out by ohms law  V x I = P, so these little panels are 2 x 0.01 = 0.02W, or 20mW

now, to be usefull the solar panel needs to give a voltage of 12v to charge a battery, so by wiring 6 of the 2v little panels in series (ie the + lead of one connects to the - lead of the next) we can make it a 12v panel (6x2=12). Trouble is, the current is still 10mA, even though we now have 6 panels. To increase the current, we wire in parallel (ie all + connect together, all - connect together). Lets say we want 100mA, we need 10 panels in parallel (10 x 10 =100), so what we end up with, is a grid comprising 10x6. ten lots of the 6 panel series wired units, wired in parallel.

so a reasonable panel that can charge a battery (albeit only trickle charge at this current) needs at least 60 of the small panels. It starts becoming easy to see why big solar panels are expensive!

Ok, so then we need to charge the battery. Now, lets assume we have a good commercial solar panel, rated 12v 1A (12W!), a typical lead acid battery has a rating of 20Ahr. That means you can take 20A in an hour, or 1A for 20h, before its flat. We also ideally charge the battery at 1/10th its capacity, so if its capacity is 20Ahr, we charge it at 2A for 10hours. So our panel of 1A will take 20hour in good sunlight to completely charge the battery. But! lets say the battery is only used for a light, but lets say for simplicity the light takes 1A at 12v(ie a 12w bulb!), we have the light on for 1hour a day, so the battery goes down 1A in that day, so we only need to charge it for as long as it takes to replace that energy. If it takes 20hour to replace 20A, it will only take an hour to replace the 1A we have used. So one hour of sunlight a day keeps the battery charged.

Of course this is very simplistic, ive assumed simple easy values and assumed good sunlight so the panel always gives its full rated output. In real life, the panel may often be giving lower output (poor sunlight/overcast days) or none at all for aprox half the day (ie at night). At other times the sunlight may be very strong and the panel exceed its ratings. This is where, if you have a big panel, a charge regulator becomes needed, to prevent overcharging the battery. As the sunlight increases in brightness, the voltage and current also increase. Its this increase in voltage above what the battery can handle that leads to overcharging. Current is more of an availability thing, the panel can supply 1A, but if nothing takes that 1A, it doesnt flow. Take as an example you mains electricity, your 100W bulb takes about 500mA, but your supply can give 100A! if all that was forced down your wires it would melt them very quickly!

Of course, if your light or whatever is a lower wattage on your solar setup, say a 5W 12v bulb, the current it takes in use is lower, the battery is less drained, and so it takes less time to restore it to full capacity.

This is why, except very rarely, a solar panel never directly powers anything, its output will tend to fluctuate, is not available at night, and is often too low. Its like drinking water, we get a constant supply from the tap despite the fact that rainfall and riverflow are not constant, due to the storage of water in reservoirs. The battery is your reservoir. And just as water systems have sluiches and valves to keep the reservoir form getting too full, thats what a charge regulator does!

OK, so, what panels are there? well, theres three basic technologies -

Amorphous silicon - brown, like in calculators, not very efficient, not good on overcast days, needs good light. But the cheapest!

polycrystalline and monocrystalline silicon - both blue colour, more efficient and able to keep a good output in poor light, disadvantage is they are more expensive.

My panel is made of a pair of 6"x6" (roughly) amorphous silicon panels.

The other essential is the Diode. This is a little semiconductor eletronic device (like a black cylinder with two wires sticking out) and acts as a one way valve to the flow of current. Each panel has one of these in its + lead, and it stops current flowing back through the panel from the battery or from any other panels its wired to, when the light is poor (which can damage the panel). They are cheep ( a 1N4001 diode is rated at 1A and cost about 3p if that) and small (3mm long ish), but have a slight disadvantage, the lose 0.6v across them. So a 2v panel will be a 1.4v panel on the other side of its protection diode. Because of this, a panel built of lots of smaller ones needs a few extra small panels to account for the loss. But thats preferable to breaking the panel!

for best results from a panel, it would follow the sun around, but such tracking is very expensive. For a simple setup, just get it facing south, at an angle where it will pick up most of the sunlight, say between 30-50degrees (45deg is good :wink: ) mines at about 50.

there we go, a quick introduction to the basic concepts of solar electricity, and a physics lesson thrown in free, gratis, AND fer nowt!, what more could ya want? :D  :D

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Annie

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« Reply #12 on: February 11, 2007, 00:43 »
Much clearer to my small female brain,yourfingers must beshorter tho`.

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MontyTom

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« Reply #13 on: February 16, 2007, 23:06 »
Quote from: "Zak the Rabbit"
Ive just put the call out on a dozen or so freecycle sites, for broken or no longer wanted solar powered items, you know like those garden lights. The plan is to get a load of them, strip out the little solar panels, and wire em all together into a BIG solar panel :D

i'll let ya'll know how i gets on


Did you get any free PV gear offered yet?  Just wondered how generous people are.

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Zak the Rabbit

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« Reply #14 on: February 17, 2007, 10:41 »
Sadly no, one chap had two of them but the distance was prohibitive to collecting them,

still, it was worth asking just to find out :)



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