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%.
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.
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.
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.
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
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
On Tuesday, 23 October 2018 12:47:00 UTC+1, fred wrote:
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)
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.
Not possible to give an absolute answer, it depends
on the design, the area of the panel and the power
consumption of the system, and how often it is triggered.
Plenty of the commercial ones don’t work right thru
the night so it works first thing in the morning when
its still dark, even with the panel facing south etc.
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