Sunday, 8 January 2012

Comparing Solar Generation Output.

I've always been interested in the efficiency of my system (14 Schuco 190W panels) rated at 2.66kWh in comparison with other peoples. I've detailed my thoughts on how all of us can make meaningful comparisons Link to details.

The beauty of the formulae means that you can compare your system whatever the size, orientation, etc. For those of you who have Sunny Beam or similar bluetooth monitors it's easy to see the comparison for every day of the month, but even if you provide a single figure (the total months generation) it still generates a comparison percentage.



The spreadsheet below compares an approximate 4 kWp system in Mid Norfolk with my 2.66 kwp system in Leicester. His system has been marginally more efficient than mine in December.




The graph below is interesting as it shows the the weather was moving from East to West during the month. You can see that the peaks and troughs are approximately 24 hours apart.





The only thing you are required to do is supply me with your "Standard" output figure for the month. I will collate the information and publish the anonymous comparisons each month.


Contact me if you need any additional information. I hope to hear from you soon.





Icarus


P.S. I now twitter on a daily basis regarding solar and satirical swipes at the establishment.@solaricarus

4 comments:

  1. As I see it the problem with the standard measure here, as used by the Government's Standard Assessment Procedure for Energy Rating of Dwellings (SAP 2009) CalcV2_0 and Encraft for example, (my own standard figure comes out at 3365 kWh/year) is that it makes no allowance for the intensity and duration of sunlight received at different points in the UK. We get a lot less sun in Manchester than you do in Leicester and even more so those that live in Southampton. So a geographical index also needs to apply - and I still don't know what the 0.8 part of the calculation refers to.

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    Replies
    1. I'm not sure how the UK government came up with the 0.8 figure?
      The official response is:0.8 = Reducing factor (Solar energy the UK receives = 800W/meter for every 1000W/meter transmitted)

      I used to be an analyst,it's difficult....In fairness to whoever was responsible it HAD to be a generic figure. You couldn't have an industry trying to apply specific figures for every household. However scientifically they arrived at the ratio it will be skewed by weather factors which are changing constantly.

      It least we have some means of assessing efficiency.

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  2. How Do I Calculate Sun Hours?
    Within the performance calculations, peak sun hours are also one consideration. Peak sun hours are directly related to another factor known as insolation, used by installation experts.

    Peak Sun Hours
    This figure relies on Met Office data. Peak sun hours relate to the intensity of the sunlight or solar energy. To the experts, peak sun hours are less important than the insolation factor, which is able to take other factors into account and give a more accurate figure of the amount of sunlight received at the Earth's surface. The location of the UK in the Northern hemisphere leads to a lower sun hours figure.

    To estimate a rough daily output for a solar system use the following equation:
    Peak sun hours per day x PV systems rated output (Watts) x 0.85 = Estimated daily output in Watts per day. The figure of 0.85 allows for the fact that it will not absorb peak sun at 1000W/m2, but around about 0.85 or 85% of that.

    Insolation
    Insolation (incident solar radiation) is a measure of the actual amount of sunlight or solar energy that strikes the surface of the earth (or the panel), and are a more accurate figure to use. The figures vary quite a lot across the UK. An accurate solar irradiance calculator by UK location is available online at
    www.solarelectricityhandbook.com/solar-irradiance.html

    Using that calculator:

    Bolton (nearer than Manchester to me)
    Average Solar Insolation figures
    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    0.66 1.32 2.30 3.63 4.92 5.00
    Jul Aug Sep Oct Nov Dec
    4.88 3.98 2.73 1.53 0.79 0.50

    Multiply this irradiance figure by the wattage of your photovoltaic panels to give you an average daily amount of energy you can expect to generate with your system, measured in watt-hours.

    Dec
    0.5 x 3.92 = 1.96kW per day
    June
    5.0x3.92 = 19.6kWh per day


    Norwich
    Average Solar Insolation figures
    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    0.72 1.35 2.37 3.60 4.68 4.90
    Jul Aug Sep Oct Nov Dec
    4.86 4.20 2.82 1.64 0.91 0.57

    Dec
    0.57 x 3.92 = 2.23kW per day
    June
    5.0x3.92 = 19.2kWh per day


    Leicester
    Average Solar Insolation figures
    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    0.71 1.36 2.28 3.47 4.51 4.68
    Jul Aug Sep Oct Nov Dec
    4.69 4.04 2.70 1.65 0.90 0.57

    Dec
    0.57 x 3.92 = 2.23kW per day.
    July
    4.69x3.92=18.4kWh per day


    Southampton
    Average Solar Insolation figures
    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    0.88 1.62 2.67 4.19 5.38 5.66
    Jul Aug Sep Oct Nov Dec
    5.58 4.76 3.24 1.90 1.06 0.67

    Dec
    0.67 x 3.92 = 2.63kW per day.
    June
    5.66x3.92=22.2kWh per day


    So some big differences! The amount of insolation, irradiation (or whatever) is ten times in June what one can expect in December.

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    Replies
    1. Wow. Impressive presentation. I thought "Isolation" was a bad thing. Now I want more of it.

      Good work Chris.

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