On Wednesday, 15 July 2015 14:27:53 UTC+1, David Paste wrote:
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

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.

And so surely I've done something wrong.

Thanks again.

I have a 4Kw setup.
I do an average of 4000Kwh/year.
(West Midlands in almost ideal situation.)

I think the figure you mention refers to the whole area of the solar farm not the actual panels. The rows have to be spaced to avoid shading.
A Kw is usually reckoned to need about 5 square meters of actual panel.
This is the peak output usually written as Kwp.

Efficiency is about 11-14% for silicon panels depending if they are mono crystaline or poly crystaline. (The crystal junctions cause losses.)

Apparently there are more efficient technologies in the pipeline.