"PV for idiots"

[pphilpot]

Hi wise ones

I've just purchased some solar 'security' lights to replace my halogen PIR lights, and it's made me more interested in (slowly) learning more about it.

I don't have the budget to have a 'dive right in' approach, but I'd like to learn about the practical ways that I could maybe start with 12v lighting in my house (3 bedroomed bungalow - so not much to light ).

Thereofore, is there an 'idiots guide to PV' that will set me along the path?

Cheers

Paul

[martin]

ahhhhhhhhhh! Like most things in renewables, it's probably not as simple as it looks......
The problem with 12 volts is amps - whereas half a dozen 18w energy saving bulbs are together using around half an amp at 220 volts, at 12volts, that's 9 amps.......meaning in simple terms, enormously larger cables and switches are needed....... Which is why a pragmatic solution is to isolate your lighting circuits from the mains, and run them off an inverter from your batteries..........that way you can safely use your existing lighting wiring and switching......

[pphilpot]

Thanks for the quick reply Martin. Using an inverter would stop me in my experimental tracks I guess, as I like the idea of doing a bit at a time.

OK, how's this as a project example - the kitchen has 6 GU10 downlighters, which currently have 7W CFLs  in each. Could 12V LED downlighter bulbs be used (powered by PV) instead (using mains wiring/switches)? Is it actually viable in terms of cost, or should I take my wife out for many more meals instead?

Cheers

Paul

[martin]

You can buy a perfectly good 150 watt pure sinewave inverter for around £50 - by the time you've sourced 12v versions of your current bulbs, and beefed up the wiring and switching, you'll be far worse off.....
Then we have the "run them off pv" statement - if I take it literally, when the sun is out, the lights are on, at night, when you need the lights.........
So you've got to store the power, which means you've got to get a controller (so you don't fry the battery), and a substantial battery, as well as the pv panel......
In other words, it isn't easy to do in "bits and pieces", you could do it in "stages", but you'll be best to undertake some careful planning first........

[pphilpot]

Kinda what I thought - I knew about the concept of charge controllers/quality battery etc. (from reading posts here), but wondered if it was possible to implement it slowly. I guess the answer is 'probably not'

I think there's a market for 'An idiots guide to solar PV' if you want to get writing

Cheers

Paul

[martin]

sounds like a plan.........

[Paulh_Boats]

Paul,

You could convert the entire lighting circuit to 12V using the existing wiring, as long as you stick to 6 amps which is the typical circuit breaker limit OR split the lighting circuit in two to keep within the current limit of the wire (might be 1mm or 1.5mm).

Then a 12V switched mode supply for LED lights can provide power from the mains, into a big switch to choose battery or mains. Start with a cheap gel battery from ScrewFix, being careful not to go past 50% discharge which really shortens its life.

To make a serious dent in the electric bill you will need several hundred Watts peak. 10 or 20 Watt panels will be a waste of time, you can learn a lot just by reading the Internet anyway.

Alternatively make your own 24V LED bulbs, to reduce current, they might be available for lorries that use 24V batteries.

-Paul

[billi]

here are some  24 Volt bulbs

http://www.phocos.com/datasheet_24v_cfl.html

billi

[tony.]

you are off to a good start with a bungalow, its easier to alter wiring rather than a 2 storey house.


regards

tony

[pphilpot]

I just worked out (a tad slow off of the block) that my six 7w CFLs are costing about £3 a year to run - it could be an expensive little project to convert to solar PV...

[wyleu]

I like the idea of a 12-24V (some said 42V some said 48V) bus.  http://www.navitron.org.uk/forum/index.php/topic,2527.0.html

There was a poll on this, but I can't find it now.

Take the time to consider what components you would need if you had no mains. Which areas would you consider for LED 'Emergency lighting'? Cos that might well be the best approach to use.
It might be sensible to bring 2.5mm twin and earth back to a central point, and if you are to have a central point where would it be? That way you can control your system from one location rather than distributed switches.
That way you can start to play with the system with a directly beneficial element. That central point would seem to be a sensible place to locate batteries or if you feel a mains infrastructure is more suitable then that can be implemented as a fail over as well as the existing house lighting. But please remember a 240 Volt infrastructure like this would require proper PArt P certification and as it is separately sourced then there are complications.

The objective is to move from one traditional 240 Volt system to a hybrid where,upon consideration you can turn off 240 Volt components was you come to turns with what you might require out of the standby system.

How you control the system becomes an important area of consideration but I wouldn't think it could be really properly considered until you've seen the low voltage system in context. Is it bright enough to provide safe movement in all areas of the house.

Switching might initially seem to be a lacking element but rather than go to all the domestic upheaval of wiring a separate switch system  with all the confusion if you use anything like the same style of switch, you might start to consider motion sensors as a suitable mechansim for switching your new system. The control of such in the low voltage world is at best dedicated and as such you are likely to be constructing certain elements yourself.
If you lay a screened twin pair of signal cable along with the 2.5mm twin and earth  then perhaps you could consider some degree of centralized control. ( He's going to say one-wire isn't he?) using something like one-wire. That way you could ( I don'd know of a specific PIR to one wire but i'm sure your new found skills would welcome that as a project component that will certainly get you considering some of the characteristics of such systems) take control with a once only visit for installation.

If I can't find my voltage poll I should be able to get by without being reminded of my 'Don't use one wire for control' post, but you should be able to get a low voltage system to be fairly noise immune, especially if part of your system design means it works when there isn't any mains. Thats probably a fairly cost effective solution. It also protects you from all the complexities of switching off the various mains devices that you might consider important when you have mains but less so when you don't.

What you will lack is standard components for this sort of thing. A trip to a proper truck stop will demonstrate a bewildering range of devices for 12 and 24 volt infrastructure and that probably a fair bit cheaper than approaching the sailing community, which tends to have a leisure based price tag attached. Personally I think it's going to be 42 Volts as cars are going to that voltage so components should get cheap, but thats just my view.
The excellent part of your approach is you are using the system to perform both a useful energy project as well as an excellent teaching toll.

Please tell us how you get on.

[pphilpot]

Thanks for this wyleu - I'm inspired to look into this further. Seeing that I'm thinking downlighters, I could easily have dual sets (not sure how this would look though) - one 24v (or 48v) and the other mains - being on separate circuits I could play without fearing the knock on the door from Building Control

you might start to consider motion sensors as a suitable mechansim for switching your new system

I'm liking that idea already.

Now, I just need to learn about the basics ;-)

Cheers

Paul

[wookey]

Martin is right in general about power distribution being better at high voltages, but for something like LED lighting the low-voltage case is worth a proper look. LEDs are intrinsically low-voltage so it makes sense to supply them like that rather than invert up to 240V and then convert back down again, losing between 5 and 25% each way. Yes, you need thick-enough wires, but for enough LED to equal your current lighting that's not going to be expensive.

6 x 7W CFLs is about 1800 lumens, which requires 20watts of latest Cree X-RE R2 LEDs, or 25W of older P4. That would need between 6 and 16 physical LEDs e.g. a max current of 4A at 12V (powering 4 strings of 3 LEDs). Wire for that will cost you about 25p/metre (speaker wire). Choosing best value number of LEDs/efficiency is a bit complicated as there is far too much choice, but something like 2 6-LED Q4 bin modules from cutter would be 50 quid, ( without any mounting hardware or lenses).

So LED lighting would let you approx halve your power consumption and let you run direct from a low-voltage source. You would need something to unsure suitable current control (which could be very simple if running from a stabilised source like a battery), and work out mounting/lenses/number of LEDs. It would cost you at least 50 quid to do this, which is proabbly at least 3 times as much as the CFLs cost, but not ridiculous. The cost of the wire is not going to be a big part of it.

I guess that's a pretty typical analysis for most home lighting situations at the moment.