solar powered pir led lights

[fred]

I'm looking at solar powered pir outdoor leds. Does the solar panel have to face the sun or is sky view sufficient. ( Id need to make up a bracket to allow the panel face south)

[Bob Minchin]

South facing would be highly desirable, 30-40 degrees up from horizontal ideally too. Don't expect much charge from now-ish until March.

[Chris Hogg]

Be aware that they're pretty useless in the winter months. Not enough sun to charge them up, and too much night-time darkness during which they run down.

[Martin Brown]

Apart from in midwinter when even professional grade solar powered devices die a horrible death wrecking the batteries - it doesn't matter too much whether you point a solar panel E,S or W. It must get direct sunlight to have a sensible efficiency but it isn't all that critical which way it points - a 30 degree pointing error loses about 15%.

[Brian Gaff]

They work better facing the sun, but in this country, you are not going to get much out of those i fancy. Brian

[Brian Gaff]

Stick em under a streetlight? :-) Brian

[Brian Gaff]

What about some kind of lens or something. I guess the moving and focussing electronics would use up any extra you gained. Brian

[harry]

You can get them with separate panels on a short wire so the panel can face South if necessary. You need to avoid shading too.

Some have a small night light + brighter PIR. In Winter packs in after a few hours due to lack of charging and this small night light.. But lasts longer the nearer to South pointing & least shading the panel has.

I have several. Only last about 5hrs in Winter and dull days. You only find out after you've bought them.

PIR alone might be better (ie without night light)

[John Rumm]

Let me guess, they are off! ;-)

Just position them near a bright halogen, and they will be fine.

Yup, pointing toward the sun will help a bit, but they are generally unsuited to UK winter operation IME.

[Martin Brown]

A lens doesn't work, but a trick that can be used at the risk of cooking the solar panel is to put the panel at the base of half a hexagonal prism with two mirrors either side reflecting light onto it. It roughly doubles the output for minimal extra weight. Sort of trick that some portable charging devices sometimes use - it can fold flat to carry.

ASCI Art sketch (sorry Brian - no help to you)

\_/

Solar panel at the base. Mirror either side. Doesn't work well for larger panels because of wind loading but OK on a small scale.

If you want to be fancy then a parabolic mirror curve on either side with its focus at the base of the opposite side will ensure any light ray that enters the front aperture will eventually hit the PV cell.

There are whole families of cunning non-focussing flux intensifiers mainly intended for high energy physics photomultipliers.

MOst of it is behind a paywall but this review article isn't. YOu want chapter 4 Compound Parabolic Concentrators.

[Martin Brown]

I have one of the PIR devices powered by 3x C cells over my front door. Been going nearly two years now on the same batteries. I fitted one outside the VH. I bring the solar PV garden lamps in for the winter.

The dank foggy weather and winter frosts destroys their batteries. We have plenty of solar powered "Please go round the (dangerous) bend" signs round here. They are great fun in mid-summer flashing away and for an hour after sunset in winter but completely dead in the water on a cold frosty winters morning when they might actually do some good.

[The Other Mike]

As insolation for a region is reasonably predictable on an annual basis, as is the 5:1 maximum summer to minimum winter seasonality for much of the UK, then some would conclude these 'professional grade' solar devices are anything but.

You can, space and windload permitting, over provide to meet winter demand requirements at the expense of more panel area and a means to dump excess in the summer. Any battery charge management is relatively easy too if you have a grip on the load profile and the predicted pv output and in my experience actual PV output really doesn't vary much from the predicted.

[tabbypurr]

professional means someone's making money out of it, hence the mickey mouse panels.

NT

[Martin Brown]

They are widely deployed by highways on remote rural roads to try and stop muppets speeding into tight corners when it is frosty. They work brilliantly in mid summer but last at most a couple of hours after dark on a typical dull mid winters day. Even less if it has been dull and foggy for a few days in a row.

It doesn't vary that much, but you have to be very very remote before it can compete with physically swapping a rechargeable battery. The big problem is that bad weather comes in periods of weeks in winter and at our high latitude the signs never get properly recharged again.

[charles]

The BBC built a tv relay in the west of Scotland which was powered by a combination of solar and wind. worked well. The IBA tried a similar one in Cornwall. A storm blew the blade off the wind turbine which, on its way down, smashed the solar panel