Photo of Terence Eden. He has a beard and is smiling.

Comparing Solar Panel Generation - East/West split

· 19 comments · 350 words · Viewed ~3,638 times.

We have just installed solar panels on our house in London. We also had panels on our old house in Oxford. How do they compare?

Oxford London
Latitude 51.753738 51.486880
Panel Size 4000 Watts 5040 Watts
Orientation South East/West Split

Obviously, it's hard to compare exact weather conditions - lower temperature makes for more efficient generation - but I've picked a date in April where both sets of panels seemed to have an unblemished view of the sky.

This is the South-facing panels in Oxford generating 24.28kWh. Solar generation graph.

And here's the E/W split in London generating 18.59kWh. Solar graph of London.

London - despite the disadvantageous placement of the panels - generated 75% of the electricity that Oxford did! That's much more impressive than I was expecting. True, the panels have 25% more potential, and are slightly further South, but I was expecting the split to make things much worse.

I've written some code to graph how the different sides of the roof perform. This means I can see how East compares to West. Naïvely, I assumed that the panels not directly illuminated by sunlight would be basically useless. But nothing could be further from the truth!

Here's the split of the above graph.

A graph of two solar generators. Both are fairly even.

Wow! Both East and West generated about the same amount of power - 9kWh.

Given the average UK household uses ~10kWh per day, I could have completely offset my energy use with half the panels!

There are some caveats. Spring is perfect solar weather - long days, cool temperatures, and little tree coverage. Cloud coverage can ruin the generation.

If you're thinking about getting solar panels, but are worried about your roof's layout - I hope this provides some useful information.

You can follow my solar panels on Twitter.

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19 thoughts on “Comparing Solar Panel Generation - East/West split”

  3. says:

    One of the advantages I can see here is that it also helps to draw out the generation early in the morning and into the evening, we've got all out panels facing almost perfectly south but one of our peak loads is cooking dinner around 7pm, having some westerly panels would help to provide more PV output when its needed. The battery storage helps with this but I don't like running the battery down when it's still quite light out. The extra morning energy is probably less useful unless you're a big cooked breakfast person 🙂
    Reply

  7. said on twitter.com:

    East and west should (and are, other than timign) be similar. You want to compare to North (idiots!) and South (hurray!) But the point is you make decent energy even with sub-optimal directions. Wish they got incorporated by default into new builds. Don’t like the stick-on-tops.
    Reply | Reply to original comment on twitter.com

  9. Chris says:

    The only issue with E/W (and I actually can't believe it isn't highlighted more!), is that your generation in the winter months in far less than a S facing array. It's probably 40-50% less. Overall, it is between 15 and 20% less output generally.
    Reply

    1. @edent says:

      Based on my data so far - it doesn't seem that much worse in winter. You can check all the records at https://twitter.com/edent_solar But, the main thing is, you can't change the orientation of your house! So what I'm trying to say is that even if you're on a disadvantageous orientation, you can still make use of solar panels.
      Reply

    2. Micky.b says:

      Hmm…. OK but if your entire roof is E/W split… could you not fit twice as many panels… Just a thought….. and some great info here btw.
      Reply

    3. peter mc nally says:

      I agree, the drop in output in winter is rarely mentioned. Mid-winter months produce almost nothing. Also agree that overall losses are 25% and over a south-facing array are 15% at least.
      Reply

  10. Richard Burke says:

    Thanks for this great post, my house has an East West aspect so I'm glad to see your date here. My terrace has a chimney on the south end of the roof, I'm concerned about the effect of the shadowing in winter, could you share your thoughts on this? Appreciate the effort bloggers like you put in to help the rest of us, thank you!
    Reply

    1. @edent says:

      We don't have a chimney, so I can't give you any data about that. But shade that close to a panel will degrade performance. I'd suggest either movong the chimney or plotting out the areas it shades and moving the panels away from there.
      Reply

    2. Micky.b says:

      Hi Richard, I am no expert but from what I have picked up on so far... firstly ensure you have 2 solar inputs on your inverter. one for south and also for west. the shading from chimney will only affect 1 side AM and the other PM so you will still get a fair output. there are shading calculators online and you can adjust day, month and time of year to see how shadow is cast. If you can work out which panels will be mostly affected then you could purchase optimisers for each of those panels (approx £45 each) so if one panel is shaded it will not affect the entire array (a shaded panel is a bottleneck for the whole array on that input). I did my own calculations on a fag packet and this produced a better output than removing panels from shaded areas. HTH.
      Reply

  11. Gary says:

    Are you east and west panels tied onto the same string or do you use micro inverters, so east and west have their own inverter?
    Reply

  12. Roger says:

    As we all know, south facing produces the most. East and west produces the longest. What about combining the two into one ? Take 2 rows of panels, sitting side by side on a south roof. Like 2 playing cards sitting side by side and touching. Now take the cards where their touching and raise them to form them into a inverted v /. Now take several sets of rows and do the same thing. /\/\/\ Calculate the angles to be 15 degrees. Take 2 68" panels sitting end to end, left panel, left side on the roof, right side 17.6" high. second panel, left side 17.6" high, right side on the roof. Both 17.6" connected together to form center. 0 / 17.6 \ 0 Two right triangles back to back.
    Reply

  13. Micky.b says:

    You can already buy this kind of setup and the panels come in pairs but more designed for flat roofs plus the advantage of fitting more panels per sqm. During peak summer months with a south facing roof the entire array would be shaded before approx 09:00 as this is when the sun is due east. My east array can yield >4kwh by that time and same for west during dusk so they wold probably not be taking full advantage of the long summer days…. You would need to fit lower to the ridge of the roof and also have a triangle plate for wind buffering…..
    Reply

What links here from around this blog?

  1. Solar panels on our roof. Happy Solstice from @edent_solar
  2. A generation meter showing 4,165kWh. 1 year of @edent_solar. We are 100% offset!
  3. Graph showing the difference between east and west panels. Which generates more electricity - East- or West-facing solar panels?

What are your reckons?

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