Solar panel wattage

[R D S]

It's not a big issue, i'm just rigging up some LEDs at the back of the garden and it's only 20 quid but could this 40x20 cm panel possibly kick out 50w?

[Andy Burns]

unlikely

lower down it says 20 to 50W

lower down again, it says max 583mA @ 12V or about 7W

[R D S]

That's more like it i'd have thought.

[Martin Brown]

+1

Spec is a bit like Peak music power in the good old Dixon's days.

Incident solar energy is roughly 1kW/m^2 at normal incidence.

0.4 x 0.2 = 0.08m^2 ~ 80W incident.

Conversion to electricity ~30% best case so 24W if the thing is really well engineered. This looks a more promising one in the 30W class.

keyword "monocrystalline" gets you higher efficiency PV conversion.

[alan_m]

The descripti [quote] It needs to meet the conditions of a standard light intensity (1000W per square meter), the surface temperature of the solar panel is 25 degrees Celsius, and the sunlight is vertically irradiated to achieve sufficient power output. [/quote]

I'm not sure what they mean by a light intensity of 1kW per square meter but unless you are tracking the sun on a cloudless summers day and preventing the sun from heating up the panel I doubt if you will achieve anywhere near that for more than a limited number of hours per year.

Other Ebay retailers seem to be rating the same panel at 30W (MAXIMUM)

[Jeff Layman]

The generally accepted figure for solar radiation is 1kW/m^2 at the equator at noon. So a 40 x 20cm area would be 80W. But commercial solar panels are, at best about 20% efficient, so that panel could only provide 16W, and then only if mounted horizontally at noon on the equator.

Even then, impossibly optimistic.

[The Natural Philosopher]

Midday in June, definitely. Midnight in December, not so much

[The Natural Philosopher]

What they mean is solar insolation. That certainly can peak at over

1Kw/sq meter Assume 20% eff that gives you a *peak* output of 1000 x .2 x .4 x.2 which i make (but its late) 16W?

[The Natural Philosopher]

Or pointed directly at the noonday sun , when its shadow covers a much larger area than the panel is

[Brian Gaff]

Yes its not like its tracking the sun after all. Brian

[R D S]

And before I have a whinge at the seller, can anyone see in this description that this charge controller *cannot* be used with lithium batteries?

[Andy Burns]

What charge controller?

[alan_m]

No intelligent control over charging? The USB outputs could output

5V,1A (or over 12V, 0.5A) for 8 hours* irrespective of the charge in the battery.

What is to stop the battery overcharging? You either need something inbuilt to the battery or some other control circuit.

Big Clive has some advice

*Assuming a sunny day in mid summer

[Theo]

This is not a charge controller, it's a solar panel. The box marked 'solar charger' just converts the output to USB's 5v.

(since it says 5V 3A it rather belies the 50W claim - rather similar to the

16W true output)

You wouldn't connect a lithium (ion, iron phosphate?) battery to the panel directly, you'd connect it via a circuit that controls charging at the appropriate voltage. For example a USB powerbank containing a lithium cell and a managing circuit. Or a 12v lithium iron phosphate battery intended as a dropin for a lead acid. Both should have a management circuit inside that will regulate or cut off supply if the voltage goes too high or the cell is full.

Theo

[R D S]

Ooops...

[Theo]

I've got one of those. The battery type is set using a menu selecting from 'b01' to 'b07', as given in the instructions:

It'll do 4S and 5S lithium iron phosphate, and 3S and 4S lithium ion, but appears it won't do single cells, and the voltage thresholds can't be set manually. For single cells your best bet is the USB port on the panel.

Theo

[R D S]

Those instructions are different to mine.

[brian]

In message <tb8r0p$1jpik$ [e-mail], R D S [e-mail] writes

You'll get about 50W of Sunlight hitting it ( in the band that PV silicon responds to) - UK Solar flux is around 600W/m^2 at mid-day during the summer, including diffuse scatter. ( The oft quoted number of

1KW/m^2 beloved of solar panel salesmen , is for the entire solar band from UV to the Mid Infrared , much of which is outside the pass-band of silicon)

However, you only get about 20% of this converted to current because of the photo-electric effect. Although the quantum efficiency of Silicon is good between blue up to the beginning of the infrared (~1um), the number of photons/watt reduces with wavelength.

You might get about 10W of electricity.

Brian

[R D S]

Mini review, it's ####ing useless!

I wasn't expecting much but it can't give a battery enough power to light 10 LED garden lights (little hangy uppy things) for 5 hrs per evening.

[The Natural Philosopher]

You *were* warned.