On 01/08/15 01:51, bm wrote:
"David Paste" wrote in message
...
According to:

http://www.fwi.co.uk/business/hampsh...ks-largest.htm

48 MW solar farm is being built.

No info on that page, as expected. Look at:

http://renewables-map.co.uk/details....Solar %20Farm

for more details:

Solar Panels: 50000
Capacity: 40 MW
Acreage: 200

More info:

200 acres = 80.9 hectares = 809,371.284 square metres.

40 MW from 809,371.284 square metres.

40,000,000 / 809,371.284 = 49.42 watts per square metre.

I am aware that this will be the avaerage over day and night, and over the
year. I am aware that solar insolation is very variable. But 49 watts per
square metre? Can that really be right? Is the 200 acres the site size, or
the combined size of all the panels?

I assume I have calculated something wrong. Can any one help?

Thanks in advance,

David Paste.



Background:

A not-particularly-technologically-minded friend was pondering whether or
not an electric train covered in PV panels would be viable. I said no,
assuming an easy to calculate figure of 10 MW for a Eurostar (wikipedia has
values ranging from 3.4 MW to 12.2 MW). I was assuming that the *avaerage*
yearly insolation for the UK was 1kW per square metre, garnered from:

https://en.wikipedia.org/wiki/Insolation

That graph and that figure is in fact WRONG.


I suspect its in Kwh per sq m per day not kw per sq m.

"The UK's annual insolation is in the range of 750€“1,100 kilowatt-hours
per square metre (kWh/m²). London receives 0.52 and 4.74 kWh/m² per day
in December and July, respectively."

If you divide 1000 kWh per year by 365 x 24 you get an average of around
110W/m which is about what the average insolation is given that its dark
and night and in winter.

PEAK midday midsummer insolation is about 1kW/sq meter.

Now the theoretical PV efficiency limit is 67% or thereabouts: In fact
IIRC they do around 20%, so the average output of a solar farm is
something of the order of 22w/sq m.

Contrast a wind farm at maybe 2W/sq m and biofuel at 0.1W /sq m.



so for 10 MW, you'd need (10,000,000/1,000 = 10,000 square metres = 1
hectare = 2.47 acres of panels for one train.

A rough estimation for BR Class 373 on the Eurostar gives about 1,000 square
metres of roof on a 20 car set. Or 1 MW at theoretical maximum. But it won't
be, will it. Curved roof, adverse weather, panel efficiency, all of that.

I know that PV panels are not 100% efficient at converting light into leccy,
but I was still staggered to see that 49 watts per square metre was the
average figure used for that solar farm.


That is in fact pretty close to the likely figure,


And so surely I've done something wrong.


Nope. renewable energy is for people who can't do sums.

For example, one onshore wind farm that is capable of delivering the
same average output as Fukushima did would permenently render an area of
land greater than the current exclusions zone *permanently
uninhabitable* on H & S grounds, It would be a desert covered in nothing
but windmills the size of greater london, and then some.

And it would STILL need a thwacking big coal or gas power station to
keep to working when the wind dropped.

Thanks again.

Wodney will be along shortly.




--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
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