I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).

--
Chris Green
·

Chris Green wrote:

I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

Andy Burns wrote:
Chris Green wrote:

I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above but a
simple "you'll get about 20% of the panel rating averaged over the
year" would be more useful. I want to know how much panel I need to
install to run a water pump, or how big a water pump I can reasonably
power from a 260 watt panel.

--
Chris Green
·

Chris Hogg wrote:
On Mon, 19 Aug 2019 19:59:04 +0100, Chris Green wrote:

I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).

I think Harry gets about 15%, and that's pretty good. He's about 10
miles SW of Worcester. The average for commercial solar farms in the
UK is about 9%, 20-25% in Summer, down to about 4% in Winter, IIRC.
South of England better than the north, obviously, but east versus
west probably makes little difference. Optimum orientation and lack of
shadowing more important. It's questionable whether solar panels in
Northern Europe actually produce more energy in their lifetimes as is
used in their manufacture. South of France, North Africa, California,
yes, fine there, but not in Northern Europe. Without subsidies, or
misleading claims by mfrs and installers, it's doubtful whether anyone
in the UK would install them.

Some links to individual records/comments/experience:
http://www.viridis.net/energy/solar-pv.html
http://tinyurl.com/q2993y9
http://www.jaharrison.me.uk/Misc/Solar/index.html

Thanks, *that's* the sort of stuff I wanted to know. So my 20-25%
figure is a summer figure. The winter figure means I can only run a
10 watt or so pump from a 260 watt panel and even that requires enough
battery storage to keep going for several days I would guess.

--
Chris Green
·

On 19/08/2019 19:59, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

One book which stems from the OPEC induced oil crisis of the 1970's is
called Sun power, by J.C. Mc Veigh, Pergamon Press 1977

https://www.amazon.co.uk/Sun-Power-I.../dp/0080208622

"Save It" campaign was way more active than anything of recent times.

I'd recommend avoiding the Kindle edition which is overpriced by about
an order of magnitude. I have a copy that was withdrawn from the library
system and sold off as scrap. You want table 2.4 which has experimental
monthly figures based on Kew data 1958-1968. It is in MJ/m^2.

There have been a few improvements since it was written but it isn't a
bad guide to DIY solar collectors 4 decades on from when it was written.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).

Better than that in summer and much much worse in winter. Peak summer to
worst winter ratio is about a factor of 9. Week by week is more extreme.

Solar powered devices where I live in North Yorkshire wreck their
batteries every winter. This is a shame since they work perfectly in
midsummer but fail to remind people that on frosty mornings entering a
tight bend too fast results in hitting a tree.

--
Regards,
Martin Brown

On 19/08/2019 21:47, Chris Green wrote:
Chris Hogg wrote:


I think Harry gets about 15%, and that's pretty good. He's about 10
miles SW of Worcester. The average for commercial solar farms in the
UK is about 9%, 20-25% in Summer, down to about 4% in Winter, IIRC.
South of England better than the north, obviously, but east versus
west probably makes little difference. Optimum orientation and lack of
shadowing more important. It's questionable whether solar panels in
Northern Europe actually produce more energy in their lifetimes as is
used in their manufacture. South of France, North Africa, California,
yes, fine there, but not in Northern Europe. Without subsidies, or
misleading claims by mfrs and installers, it's doubtful whether anyone
in the UK would install them.

Some links to individual records/comments/experience:
http://www.viridis.net/energy/solar-pv.html
http://tinyurl.com/q2993y9
http://www.jaharrison.me.uk/Misc/Solar/index.html

Thanks, *that's* the sort of stuff I wanted to know. So my 20-25%
figure is a summer figure. The winter figure means I can only run a
10 watt or so pump from a 260 watt panel and even that requires enough
battery storage to keep going for several days I would guess.

When I used to try to charge a leisure battery off a small panel to run
an intermittent stable light in the winter, the actual performance was
in the low single figures percentage, not actually worth doing. (Now I
just use a couple of camping lights with lithium batteries).

On Mon, 19 Aug 2019 22:53:32 +0100, newshound
wrote:

snip

When I used to try to charge a leisure battery off a small panel to run
an intermittent stable light in the winter, the actual performance was
in the low single figures percentage, not actually worth doing. (Now I
just use a couple of camping lights with lithium batteries).

We currently have a 5W panel trying to maintain charge on a small
sealed battery (~16Ah) to run an electric fence (~50mA) round
daughters rabbit hutch from dusk to dawn (managed by the PWM charge
controller).

TBF, the panel isn't optimally placed ATM (temporary / test setup) and
so only get's any real / direct sunlight in the mornings, the end
result is even with all the sun we have been getting recently, supply
can't keep up with demand.

As the days get shorter and less sunny this will only get worse and so
I've either got to reposition the panel, add another panel or run some
light SWA out to the rabbits store shed.

I *think* it's reducing the rate at which the batteries get discharged
but when adding the panel I also swapped batteries (from 22Ah to the
smaller one).

Cheers, T i m

Chris Green wrote:

Andy Burns wrote:

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above

well it's not difficult e.g assume you live in cambridge, a 1kW panel
would give you 863kWh/year, so a 250W panel a quarter of that is
215kWh/year or 0.6kWh/day, an average 25W

"Andy Burns" wrote in message
...
Chris Green wrote:

Andy Burns wrote:

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above

well it's not difficult e.g assume you live in cambridge, a 1kW panel
would give you 863kWh/year, so a 250W panel a quarter of that is
215kWh/year or 0.6kWh/day, an average 25W

But what matters to him is what happens on the worst days in winter and how
many of those you get in a row so that he doesnt get enough water moved.

Swer wrote:

Andy Burns wrote:

an average 25W

But what matters to him is what happens on the worst days in winter and how
many of those you get in a row so that he doesnt get enough water moved.

That may well be what matters, but what he actually asked for was

"the average output of (say) a 250 watt panel over the year"

On Tue, 20 Aug 2019 17:11:27 +1000, Sewer, better known as cantankerous
trolling senile geezer Rodent Speed, wrote:

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above

well it's not difficult e.g assume you live in cambridge, a 1kW panel
would give you 863kWh/year, so a 250W panel a quarter of that is
215kWh/year or 0.6kWh/day, an average 25W

But what matters to him is what happens on the worst days in winter and how
many of those you get in a row so that he doesn¢t get enough water moved.

He didn't say that, you pathological "all-knowing" trolling senile pest!

--
Website (from 2007) dedicated to the 85-year-old trolling senile
cretin from Oz:
https://www.pcreview.co.uk/threads/r...d-faq.2973853/

On 20/08/2019 07:27, Chris Hogg wrote:
On Mon, 19 Aug 2019 21:47:42 +0100, Chris Green wrote:

Chris Hogg wrote:
On Mon, 19 Aug 2019 19:59:04 +0100, Chris Green wrote:

I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).

I think Harry gets about 15%, and that's pretty good. He's about 10
miles SW of Worcester. The average for commercial solar farms in the
UK is about 9%, 20-25% in Summer, down to about 4% in Winter, IIRC.
South of England better than the north, obviously, but east versus
west probably makes little difference. Optimum orientation and lack of
shadowing more important. It's questionable whether solar panels in
Northern Europe actually produce more energy in their lifetimes as is
used in their manufacture. South of France, North Africa, California,
yes, fine there, but not in Northern Europe. Without subsidies, or
misleading claims by mfrs and installers, it's doubtful whether anyone
in the UK would install them.

Some links to individual records/comments/experience:
http://www.viridis.net/energy/solar-pv.html
http://tinyurl.com/q2993y9
http://www.jaharrison.me.uk/Misc/Solar/index.html

Thanks, *that's* the sort of stuff I wanted to know. So my 20-25%
figure is a summer figure. The winter figure means I can only run a
10 watt or so pump from a 260 watt panel and even that requires enough
battery storage to keep going for several days I would guess.

I think averages are a bit misleading in this context. On a sunny day
in mid-winter, the output might be quite high, but only for a few
hours, after which time you get next to nothing, and you get next to
nothing for the full 24 hours on dull cloudy winter days.

That is true - on a clear winters day the cold conditions mean that the
PV array runs at higher efficiency, but not by enough to make up for the
very low sun. To first order you can predict output in clear sun to vary
as cos of the angle between normal to the panel and the sun and derate
output by 0.3% for each degree C the unit is above 20C.

The other rough heuristic is that the flux arriving directly from the
sun and the diffuse scattered component averaged by month are roughly
equal provided you have the collector at a sensible azimuth and angle.

There is a slight advantage to pointing ESE or SE rather than due south
since fair weather clouds in summer afternoons can rob you of power.

That's the problem with any renewable power supply; they're
intermittent, and unless you have battery back-up of sufficient
capacity to tide you over the dull days and darkness, and sufficient
renewable power not only to supply what you're trying to run but also
to recharge those batteries, you're stuffed!

It is even more of a problem for such things like the radar activated
"please go round the dangerous bend" on remote hillsides. They work
brilliantly in midsummer but are stone dead two hours after sunset in
winter and *NEVER* working on those cold frosty mornings. The batteries
in them are ruined completely every winter without fail.

I note that most (all?) of those solar powered garden lights you see
in garden centres etc these days, are useless in winter. The
dullness/darkness is too long and the capacity of the photocell is
insufficient to recharge the battery in the few hours of sunshine you
might get once or twice per week, so the device never works.

Again you are better off switching them off and putting them in the
garage. The combination of hard frosts and the batteries being brutally
discharged for a long period does them no favours at all.

Incidentally most of them are not that hot at our high latitude either
since they come on too early in our long twilight. They work much better
at lower latitudes when sunset to darkness is much faster.

--
Regards,
Martin Brown

T i m wrote:
On Mon, 19 Aug 2019 22:53:32 +0100, newshound
wrote:

snip

When I used to try to charge a leisure battery off a small panel to run
an intermittent stable light in the winter, the actual performance was
in the low single figures percentage, not actually worth doing. (Now I
just use a couple of camping lights with lithium batteries).

We currently have a 5W panel trying to maintain charge on a small
sealed battery (~16Ah) to run an electric fence (~50mA) round
daughters rabbit hutch from dusk to dawn (managed by the PWM charge
controller).

TBF, the panel isn't optimally placed ATM (temporary / test setup) and
so only get's any real / direct sunlight in the mornings, the end
result is even with all the sun we have been getting recently, supply
can't keep up with demand.

As the days get shorter and less sunny this will only get worse and so
I've either got to reposition the panel, add another panel or run some
light SWA out to the rabbits store shed.

I *think* it's reducing the rate at which the batteries get discharged
but when adding the panel I also swapped batteries (from 22Ah to the
smaller one).

Yes (OP here), I can see very little use for small panels except maybe
for maintaining very low consumption devices like simple phones.

We have three 'full sized' (i.e. 260 watt) panels on our boat which is
only a small (10 metre) boat and they are OK in the summer, in France,
to run a domestic fridge plus lights etc. Through the winter they
maintain the batteries (which is handy since I can remove the shore
power connection and thus reduce the corrosion risk).

I'm coming to the conclusion that even a similar sized panel (i.e. 250
watt or so) panel isn't going to run much of a pump all the year
round. Since just the panel will cost about £100 that's not a sensible
economic proposition.

--
Chris Green
·

On 20/08/2019 05:10, Andy Burns wrote:
Chris Green wrote:

Andy Burns wrote:

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel.Â* I could work it out backwards from the above

well it's not difficult e.g assume you live in cambridge, a 1kW panel
would give you 863kWh/year, so a 250W panel a quarter of that is
215kWh/year or 0.6kWh/day, an average 25W

Average insolation is indeed about 10% of peak.

I get emails enthusing about how Gridwatch shows how great solar power
is. And why is coal still on the BIG dial

They are never posted at midnight Or in te winter.



--
"Women actually are capable of being far more than the feminists will
let them."

On 19/08/2019 21:42, Chris Green wrote:
Andy Burns wrote:
Chris Green wrote:

I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above but a
simple "you'll get about 20% of the panel rating averaged over the
year" would be more useful. I want to know how much panel I need to
install to run a water pump, or how big a water pump I can reasonably
power from a 260 watt panel.


With or without something to store energy?
The output from a panel will vary from zero to 260W so if you attach a
pump that uses a couple of hundred watts it isn't going to start on a
cloudy day.

So you really need a battery of some sort and then use the average to
size the pump.

Does it need to run on demand or will it be OK running one day in three
in summer and once a fortnight in winter?

On Tue, 20 Aug 2019 11:18:12 +0100, Chris Green wrote:

snip

I *think* it's reducing the rate at which the batteries get discharged
but when adding the panel I also swapped batteries (from 22Ah to the
smaller one).

Yes (OP here),

waves

I can see very little use for small panels except maybe
for maintaining very low consumption devices like simple phones.

It was handy to take one when cycle camping. We left it strapped to
the top of the trailer and it would charge batteries for the GPS or
torches whist we were on the road and again with the panel outside the
tent when pitched up. 'Luckily' we had a reasonably sunny week and
enough batteries to ensure we had some stock should it become overcast
too long. Not having power hookup for the week paid for the panel and
would have been overkill in a small tent in any case. ;-)

We have three 'full sized' (i.e. 260 watt) panels on our boat which is
only a small (10 metre) boat and they are OK in the summer, in France,
to run a domestic fridge plus lights etc.

We see plenty of big panels on the narrow boats near here but they are
often in the shade for at least one half of the day and dirty and not
optimally aligned etc. I question what use they are above maybe
keeping an alarm online?

Through the winter they
maintain the batteries (which is handy since I can remove the shore
power connection and thus reduce the corrosion risk).

When I took battery 'A' off the rabbit hutch electric fence solar
panel and put it on a smart charger indoors you could actually hear it
sigh from the pleasure of a real charge. ;-)

I'm coming to the conclusion that even a similar sized panel (i.e. 250
watt or so) panel isn't going to run much of a pump all the year
round. Since just the panel will cost about £100 that's not a sensible
economic proposition.

I think you can get these things doing what you want but you really do
need to go OTT on both the panels and batteries to *guarantee* enough
power when you want / need it.

It's like when you see places in the back of beyond living off grid
when there may be several pretty large solar arrays, wind turbines,
water wheel *and* a 'battery room' full of pretty big batteries
(sometimes Milk Float / Submarines sized setups).

Again, it's one of those things that if money was no object (and
assuming you had the space etc) I would probably have a large solar
setup, just because. What I wouldn't do though is expect other people
to pay for it ... ;-(

Cheers, T i m

On 19/08/2019 19:59, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).


Rule of thumb in Eastern England is average of 10% rated power over 1 year.
For example a 250W panel will yield an average output of 25W over the
year, giving a total yield of 220kWh.

On 20/08/2019 12:03, Andy Bennet wrote:
On 19/08/2019 19:59, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year.Â* There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.Â* I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this.Â* (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).


Rule of thumb in Eastern England is average of 10% rated power over 1 year.
For example a 250W panel will yield an average output of 25W over the
year, giving a total yield of 220kWh.

http://contemporaryenergy.co.uk/insolation-map/

is worth understanding.

peak to trough is a factor of about 9. And thats just the annual ...

Gridwatch is not definitive, because it never ever reaches the maximum
rated capacity on all te solar panels in the country at te same time but
this is what I get

mysql select avg(solar), max(solar) from day where timestamp like '2018%' ;
+-------------------+------------+
| avg(solar) | max(solar) |
+-------------------+------------+
| 1244.565825030031 | 9050 |
+-------------------+------------+
1 row in set, 1 warning (0.97 sec)

So in 2018 the average solar was 1.2GW and the max was 9GW
The min of course was no solar at all.

I believe green****s reckon there was well over 12GW of installed panels
during 2018

In winter - espoeciallcy December, its dire

select avg(solar), max(solar) from day where timestamp like '2018-12%';
+--------------------+------------+
| avg(solar) | max(solar) |
+--------------------+------------+
| 254.30559681425026 | 3130 |
+--------------------+------------+

So the average is a fifth of the annual average, and the peak is well
down too.


--
€œwhen things get difficult you just have to lie€�

€• Jean Claud Jüncker

On Monday, 19 August 2019 21:48:05 UTC+1, Chris Green wrote:
Andy Burns wrote:
Chris Green wrote:

I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel.

It's more comlex than you seem to appreciate.
Where abouts do you live I'm guessing a panel is scotland might be differnt from that in cornwall, then there's the angle, is it fixed or what direction does it face, or perhaps it'll be directional and controlled.
Then there's the panel itself, there's differtn types and they age too and depending on how hot they get that will also change it's effcicincy and useful life.

I've seen this with students they calcluate what they'll get from a 12V panel, which is normally spec'd for far higher light levels than we get in the UK, they bring it into the lab expecting 12V at say 3 amps and they end up with 6V and milliamps (because of indoor lighting too).



I could work it out backwards from the above but a
simple "you'll get about 20% of the panel rating averaged over the
year" would be more useful. I want to know how much panel I need to
install to run a water pump, or how big a water pump I can reasonably
power from a 260 watt panel.

Do you expect the water pump to run at night ?




--
Chris Green
·

Andy Bennet wrote:
On 19/08/2019 19:59, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).


Rule of thumb in Eastern England is average of 10% rated power over 1 year.
For example a 250W panel will yield an average output of 25W over the
year, giving a total yield of 220kWh.

Yes, that seems to be about it. The additional problem/downside being
that the average through the winter is going to be much less so,
unless you have *huge* batteries, you need to size your system to
provide your required average power through the middle of winter.

Thus a 250W panel will probably, just about, run a 10 watt pump (or
whatever) through the winter if you have battery capacity for several
days. Assuming 12 volts that means you need something in the hundreds
of amp-hours capacity to keep your 10 watt pump going.

(We have 3 x 100Ah batteries on the boat with 3 x 260 watt panels, as
I said, in France, that can handle a domestic fridge plus some lamps
while we're away from mains power)

--
Chris Green
·

On 20/08/2019 11:29, The Natural Philosopher wrote:
On 20/08/2019 05:10, Andy Burns wrote:
Chris Green wrote:

Andy Burns wrote:

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel.Â* I could work it out backwards from the above

well it's not difficult e.g assume you live in cambridge, a 1kW panel
would give you 863kWh/year, so a 250W panel a quarter of that is
215kWh/year or 0.6kWh/day, an average 25W

Average insolation is indeed about 10% of peak.

It is certainly a good working ballpark figure. Though it can be worse
than that if a part of the array is ever shaded at any time in low sun.

I get emails enthusing about how Gridwatch shows how great solar power
is. And why is coal still on the BIG dial

They are never posted at midnight Or in te winter.

BTW Do you have demand and load graphs available with 1 minute
resolution (or better) over the period of the recent grid SNAFU 9/8
16:52-16:57 ? The ofgem report is well hidden online at:

https://www.ofgem.gov.uk/system/file...ry_-_final.pdf

Looks very much to me like the wind farm at Hornsea was the instigator
of the problem that National Grid encountered. 737MW dropped off 230ms
after the lightning strike shorted out blue phase. Barford dropped off
within a second (their timestamps so far are only good to the second).

--
Regards,
Martin Brown

On Monday, 19 August 2019 20:03:05 UTC+1, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).

--
Chris Green
·

My 4Kw roof array does 4000Kwh/year approx. (W. Midlands.)
It has an almost perfect orientation, open aspect and no shading.

Weather has an effect. hrs of sunshine, air temp, etc.
They reckon to deteriorate 1%/year.
Newer ones do better I'm told as the technology has improved.

On Monday, 19 August 2019 20:03:05 UTC+1, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).


On a perfect day, my 4Kw array can generate 30Kwh.

On a bad day in Winter 0.3Kwh.
It might only be running at 50w peak.
I 'spect if there was thick frozen on snow, I'd get nothing at all.

A 4kW array in East Yorkshire spends days at a time generating sub 1kWh in mid winter and a few days around midsummer generating 27 kWh with progressive variation between these extremes as the seasons change.
Not much point expecting any useful work from the output in December/January