On 23/10/2018 21:48, The Other Mike wrote:
On Tue, 23 Oct 2018 13:00:08 +0100, Martin Brown
wrote:

On 23/10/2018 12:46, fred wrote:
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)

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%.

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.

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.

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.

https://pvwatts.nrel.gov/pvwatts.php

http://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#PVP

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.

--
Regards,
Martin Brown