Feed In Tariffs(FIT) Announced.

zeupater

Cardew wrote: »

The irradiance is way higher in the South hence highr output

There are many maps like this which give solar output based on geographic location.

http://re.jrc.ec.europa.eu/pvgis/download/PVGIS-EuropeSolarPotential.pdf

You can see there is a large difference between NW Scotland and SW England. around 30%.

Taking two extremes the output from a 1kWp panel in Southern Spain is over 500% more than Northern Europe.

Hi

Agree and understand that the irradiance average is higher closer to the equator. My query was really based on the kWp production of panels within the UK only as a basis for the 4kWp threshold being set.

The link to the irradiance map provided (thanks, best irradiance map I've yet seen) is based on an average annual irradiance on opimally inclined panels which really proves that the annual gain is not only related to the sun hours and incidence at a given latitude, but also the prevailing local annual average weather's effect on the total solar gain available, else the irradiance map's colours would surely & logically form horizontal, parallel bands.

Surely for peak clear sky midday irradiance on optimally inclined panels there would be very little difference in the kWp capacity between any location within the UK and that would be the logical basis for setting the <4kWp banding for the FIT ?

Regards
Z

Cardew

zeupater wrote: »

Hi

Agree and understand that the irradiance average is higher closer to the equator. My query was really based on the kWp production of panels within the UK only as a basis for the 4kWp threshold being set.

The link to the irradiance map provided (thanks, best irradiance map I've yet seen) is based on an average annual irradiance on opimally inclined panels which really proves that the annual gain is not only related to the sun hours and incidence at a given latitude, but also the prevailing local annual average weather's effect on the total solar gain available, else the irradiance map's colours would surely & logically form horizontal, parallel bands.

Surely for peak clear sky midday irradiance on optimally inclined panels there would be very little difference in the kWp capacity between any location within the UK and that would be the logical basis for setting the <4kWp banding for the FIT ?

Regards
Z

Agree with your post, - except the last paragraph. However it comes to a different conclusion than this quote of yours:

As for the balance on arrays in more northerly latitudes not producing the same output as ones further south, isn't this the total kWh production which is related to the number of daylight hours and solar incidence, therefore if looking at kWp isn't it the case that an array, if installed at the appropriate angle, is capable of reaching approximately the same peak production in either location,

i.e. The lattitude does have a huge effect on peak production as the irradiance and temperature are lower further North.


My point was whatever level they fix the kWp output in panel size, 4kWp or greater, the Scottish array will produce a lower output than array in Cornwall.

So if they limited the kWh output that attracted FIT to 4,000kWh then someone in NW Scotland could fit, say, 6kWp of panels and if his output was 4,100kWh he would only get a subsidy for 4,000kWh.

John_Pierpoint

I have this strange feeling that in mid summer, given a cloud free sky, there is more solar radiation per day in the Arctic circle than there is at the Equator???
The point is that the former enjoys a 24 hour day and the latter only a 12 hour day.
Three flies in the ointment:
1. You would need tracking panels.
2. There is sweet FA radiation in the winter.
3. As anyone whoo has been to the tourist attraction called The North Cape knows, continuous sunshine is unusual in the Arctic.

Even still perhaps there are difficulties in the grid if too much electricity is pumped into it "backwards".

zeupater

Hi

Thanks for response ...

I don't really understand the following conclusion in the post though ....

Cardew wrote: »

Agree with your post, - except the last paragraph. However it comes to a different conclusion than this quote of yours:

..... as both clearly relate to peak production, which would be the maximum kW (not kWh) production attainable from the arrays.

Also, regarding .....

Cardew wrote: »

i.e. The lattitude does have a huge effect on peak production as the irradiance and temperature are lower further North.

.... although this is true for the irradiance on a level surface (say water), isn't it the case that this can be mainly allowed for by adjusting the angle of the array appropriately to allow for latitude .... remember, the point is a theoretical peak production, which although there would be an arguement for a reduction in the radiation reaching the panels from travelling through fractionally more atmosphere at a higher latitude on the theoretical peak production date/time. Also, if temperature differentials were actually significant in the UK, surely the cooler ambient temperature expected further north would actually increase the efficiency of the pv modules over those further south ?

Agree with the rest of the post regarding limiting the FIT to a nominal export capacity as it would actually stop the 'big players' concentrating and 'cherry picking' the larger arrays and would probably form a more level playing field delivering competitive cost advantages to the customer.

Regards
Z

Cardew

I am getting slightly confused here.

The further North you go, the lower the power of the sun and hence irradiance is lower and thus output in kWp is lower. So lattitude is a hugely important factor in the peak output.

The nominal output of a panel in kWp is based on a irradiance of 1,000Watts/m2

Power output in real conditions

The output of photovoltaic systems varies with the intensity of sunshine and other conditions. The more sun, the more power the PV module will generate. Losses will occur due to non-ideal alignment of the module in tilt and/or orientation, high temperature, module power mismatch, soiling and DC to AC conversion. Importantly the maximum power a module can generate can easily exceed the nominal power, anywhere where the intensity of sunlight exceeds 1000W/m2 (which corresponds roughly to midday in summer in Bavaria)

Dave_Fowler

Cardew wrote: »

I am getting slightly confused here.

The further North you go, the lower the power of the sun and hence irradiance is lower and thus output in kWp is lower. So lattitude is a hugely important factor in the peak output.

The nominal output of a panel in kWp is based on a irradiance of 1,000Watts/m2

The radiated power output from the sun per square meter (perpendicular to the source of radiation) is constant at a fixed distance from the sun. However the weather - ie the number of cloudy days - varies considerably for different parts of the UK. For a panel adjusted to face the sun at 90 degrees, the only reason I can think of that causes the received radiated power (on a clear day) to decease with latitude is the reduction in the radiation due to absorption in the earth's atmosphere. If panels could be fitted in space outside the earth's atmosphere there would be no difference in the radiation no matter where you were assuming a fixed distance from the sun. Is there anyone out there who can:-

1) Give figures for the effect on the radiation due to the distance the radiation travels through the atmosphere and also

2) Put some figures on the difference in the distance the radiation has to travel between the South of the UK and the North of the UK?

No doubt there will be some differences in the absorption due to the differences in the 'make up' of the atmosphere in different parts of the UK - more moisture content, pollution etc - even on a clear day.

Other factors which would reduce the heat gained from the the radiation would be losses due to the ambient temperature. This heat loss would not be of any consequence for PV systems, in fact it would help as the internal resistance would be lower.

Cardew

Dave_Fowler wrote: »

For a panel adjusted to face the sun at 90 degrees, the only reason I can think of that causes the received radiated power (on a clear day) to decease with latitude is the reduction in the radiation due to absorption in the earth's atmosphere.

Yes that is the reason and the relection of suns rays by the atmosphere.



It explains why it is warmer on a cloudless day in July than a cloudless day in December.

http://en.wikipedia.org/wiki/Effect_of_sun_angle_on_climate

Dave_Fowler

Cardew wrote: »

Yes that is the reason and the relection of suns rays by the atmosphere.



It explains why it is warmer on a cloudless day in July than a cloudless day in December.

http://en.wikipedia.org/wiki/Effect_of_sun_angle_on_climate

The link mainly refers to the effect of the sun shining at different angles to the horizontal. This is school-boy's stuff. The sun vertically overhead shines on half the area of the sun at 30 degrees and hence twice the power per square meter. Learned that fifty years ago.

I'm no mathematician; what's the difference between the sun's angle to vertical in the south compared with that in the north? What percentage is the reduction in radiation on a horizontal surface in the north compared with the south, purely due to the sun's angle? The UK is but a small island, surely the sun's angle difference can not account for the big reduction in power as one travels north.

Anyway, I was considering panels mounted at 90 degrees to the sun. The link does mention the effect of the atmosphere, but gives no calculation as to its effect.

The reduction in available heat has to be due to absorption in the atmosphere and, quite rightly as you say, reflection, along with ambient temperatures. Wind chill factors which are often quoted in the winter months make tens of degrees of difference between perceived and actual temperatures.

Cardew

Dave_Fowler wrote: »

The link mainly refers to the effect of the sun shining at different angles to the horizontal. This is school-boy's stuff. The sun vertically overhead shines on half the area of the sun at 30 degrees and hence twice the power per square meter. Learned that fifty years ago.

I'm no mathematician; what's the difference between the sun's angle to vertical in the south compared with that in the north? What percentage is the reduction in radiation on a horizontal surface in the north compared with the south, purely due to the sun's angle? The UK is but a small island, surely the sun's angle difference can not account for the big reduction in power as one travels north.

Anyway, I was considering panels mounted at 90 degrees to the sun. The link does mention the effect of the atmosphere, but gives no calculation as to its effect.

The reduction in available heat has to be due to absorption in the atmosphere and, quite rightly as you say, reflection, along with ambient temperatures. Wind chill factors which are often quoted in the winter months make tens of degrees of difference between perceived and actual temperatures.

The link does give a diagram in the top right corner the effect of the sun's rays having to travel much further through the Earth's atmosphere.

This is the standard map for UK that is used everywhere

zeupater

Hi

I agree with Dave's post above (#187). if you look at the variables involved all you have is the distance from the sun, the angle of the panels to the sun, the distance the radiation travels through the atmosphere, the current weather conditions, and the panel temperature.

I totally agree that over a period of time the amount of total power produced, as measured in kWh, will be lower at higher latitudes even for optimally inclined arrays, but logically this must be a result of the prevailing average weather conditions and the number of daylight hours available whilst the sky is clear more than anything else. It is on the average ground insolation which includes the affect of prevailing average local weather conditions that the insolation maps must logically be based.

If looking at the maximum peak production (kW) for a system, surely the couple of extra miles from the sun over the vast distance should be the first variable to be ignored. Second is the weather conditions, remember if we're talking 'peak possible power' then this must be measured on the 'best possible day', so on the assumption that the best days in the north of Scotland have skies as clear as those on the south coast, there should be no measurable impact from this variable. That really leaves the atmosphere and the mounting angle of the panels.

Looking at the angle of the panels, in order to correctly establish a peak output at the two locations, the panels must be positioned perpendicular to the sun in order to take the measurement, this not being the opitmal installation angle at each location because it is the momentary kW which is to be compared, not the total kWh over time.

That really just leaves the dilution effect of reflection, scattering and absorption in the atmosphere. Taking the difference in latitude between Inverness and Plymouth of 7.5 degrees as a basis for a rough calculation we find that at midday on 21st June the sun stands above the horizon at 55.5 degrees and 63 degrees respectively and a little trigonometry shows that the radiative transition through the atmosphere versus that at the Tropic if Cancer is 12.2% greater at Plymouth and 21.3% greater at Inverness, so a difference of around 8.1% (121.3/112.2) in absorption and scattering potential between the two locations. Now for simplicity lets assume that 1360W/m2 (solar constant) arrive at the top of the atmosphere and that translates to 1000W/m2 at the equator, then the atmosphere is absorbing 26.5% at the equator, so the absorption would likely be 32.1% at Inverness and 29.5% at Plymouth, describing a maximum difference between the two locations of 1-((100-32.1)/(100-29.5)) .. or 3.7%,, which although describing a difference is not substantial enough to warrant altering standard FIT bandings relative to latitude.

Regards
Z