A very basic 12 volt PV system for emergency lighting.

[adam2]

I have now received the lamps refered to above.

The 3 watt cold cathode lamps are smaller than most 12 volt CCFLs, being smaller than a mains GLS lamp.
The light output was very impressive for 3 watts, so impressive that doubts began to form in my cynical mind !

The measured current was

at 13.7 volts----- 0.38 amps (5.2 watts)
at 12.4 volts-----0.36 amps (4.4 watts)
at 11.7 volts-----0.35 amps (4.1 watts)
It would therefore appear that these "3 watt" lamps are in fact over 4 watts.
They appear well made, and the light output is still good for 4 watts, certainly well worth consideration, despite the possibly misleading wattage.

I then tried the 7 watt CCFL,
current used at 12.8 volts was 0.62 amps (7.9watts)
current used at 11.9 volts was 0.60 amps (7.1 watts)
These are therefore marginly over the stated wattage, but the difference is unlikely to be significant, and could be instrument error.
Also appear well made, and more compact than competitive products.

Both the 3 watt and the 7 watt lamps light instantly, but only very dimly, they take a minute or two to reach full brightness.

I then tried the 20 watt lamp, this is of the conventional hot cathode design.
It lights instantly, not at full output, but probably about 50%, as with mains voltage CFLs.
The internal ballast does not appear to preheat the tube ends, therefore I would predict a short life if very frequently switched.
The measured current was only 1 amp, almost exactly one amp and did not alter much from 11.8 volts to 13 volts supply voltage.
This lamp is therefore only about 12 watts.
Good light output for 12 watts though, and again well worth considering, certainly budget priced.

All three lamp types all cool white, stated to be 4000K.

They arrived promptly, well packaged.

I have only used these lamps for a few hours, so the durability is unknown.

NOTE the supplier of these lamps is part of the "taras choice" group, who sell a variety of "adult" goods.
Something to be aware of if ordering on a joint bank account !

DISCLAIMER the test instruments used are only cheap ones, and have not been formally calibrated, though I have no reason to doubt the accuracy.

[rightee]

I'm really keen on building something like this as a little project. Would be good to charge phones and have a light or two from solar.

Adam do you have any news on your lamp trials?

Also has the price of the solar modules come down in the last few years and/or are there any improvements to your original post.

How long could the cable from the solar to the battery be? Mine might have to be quite long 20-30 metres as our flat isn't in direct sun so panel would have to go on the roof.

[adam2]

The 12 volt 7 watt lamps refered to above have now been in use for over a year, all night every night, approx 5,000 hours use so far and still working fine.

The 3 watt lamps have only been used briefly so the durability is still unknown.

The price of PV modules varies somwhat, but does not appear to have generally declined.
Demand is substantial and it would appear to be a sellers market at present.

In the case of a large PV system then the battery should be close to the array or exceedingly thick and expensive cable will be needed.

For a smaller system 20/30M should be fine.
You will probably need 2.5mm cable though, the 1.5mm that I suggested at the begining of the thread is only suitable for short runs.EDIT the above 12 volt 7 watt CCFLs have now been replaced on a planned maintenance basis, not because they had failed. Still working fine at about 6,000 hours