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Find out how well solar PV works in bad weather

Posted by Chris Jardine on 19 March 2013 at 9:11 am

Snow in March? Last summer was dreadful, and seemed to rain constantly. Seems like we’ve had bad weather for ages now, and a period of prolonged sunshine seems eons ago.  So we might expect the performance of solar PV systems to be equally poor over the same period of time.  But just how bad has it been?

To look at this in more detail I’ve looked at a long-term dataset of PV output (my house as it happens!) since February 2009 and looked at the variability in annual generation. The graph below shows annual variability in output compared to the overall average. Each point is the previous year’s generation, so the value on 1/2/2010 is the year’s output between 1/2/2009-1/2/2010 and so on.

We can see the variability in solar radiation over the last 3 years. In last March (remember that? It was really hot and sunny!) the year’s output between March 2011 and March 2012 was the highest we have seen - up 6% on the average.  However, after our dreadful summer last year, the period August 2011 to August 2012 was some 5% down on the average.

So we can see there is a spread of output, based on natural weather variability over the past three years. In fact, this spread is remarkably narrow; with the very best weather and very worst within plus or minus 6% from the average. Intuitively, it’s felt darker and more miserable than this over the last year, but this isn’t reflected in PV output. Which shows that what PV experts have been saying all along is true – even in cloudy weather there is still a substantial amount of solar energy that can be converted into electricity.

This actually makes solar PV output really rather constant – certainly more so than wind output. This is reassuring for householders purchasing systems – the worst case scenario is that your income is just 6% down on average. For developers of large scale projects, or if you are thinking of investing in a community-based solar scheme, a knowledge of this spread of output provides useful high/low scenarios for financial modelling.

So here’s hoping we get back to long term average weather over 2013.  Or, heaven forbid, above it. Either way we can be confident about the performance of PV systems.

More information about solar PV on YouGen

Video introduction to solar PV

Is solar PV suitable for my home?

10 tips for choosing a solar installer (with video)

Financial incentive for solar PV (feed-in tariff)

Find a local solar PV installer

Photo Credit: h080 via Compfight cc  

About the author: Chris Jardine is technical director of Joju Solar and teaches on the MSc course in Environmental Change and Management at Oxford University.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

3 comments - read them below or add one

RobertPalgrave

RobertPalgraveComment left on: 1 April 2013 at 10:13 am

Vanessa,

I did see a case on the recent BBC 2 TV programme (called I think 'The Planners') about a couple who got planning permission for solar PV on a building in a conservation area. The planning committee went against the recommendation of the planning officer who was arguing that panels would be really out of place in that setting. Not sure if the building was listed though.

My advice - talk to the council yourself, don't use an intermediary. I have seen the excessive fees charged by  some so-called planning consultants for their advice and their easy to copy letters. Our local Friends of the Earth group helped a lady defeat her council who had demanded she remove panels she had installed under permitted development rights. Council tried to insist planning permission was needed. She had spend what I considered to be a fortune with an ineffective planning consultant. You might find someone in a local FoE group or Transition group prepared to help free of charge.

You might get an easier ride if you can put panels on a roof which is not visible from the street. And if you have a big enough garden, you might consider a ground mounted installation?

 

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RobertPalgrave

RobertPalgraveComment left on: 1 April 2013 at 10:01 am

Chris,

My solar PV output for March just gone confirms that there has been a real shortage of sunshine. I have two systems -  from one, output in March 2013 was precisely half that of 2012. And I check the inverter every few days so am confident that there have been no faults. In any case, my other system also shows a near 50% reduction.

here are the numbers:

 

System 1 (1.4 kWp)

System 2 (1.9kWp)

Mar-09

133

 

Mar-10

105

 

Mar-11

113

 

Mar-12

128

148

Mar-13

67

74

If I recall, in March 2009 we had a lot of snow which shut my system down for a few days. This March, we had maybe one full day of snow cover. So that doesn't explain the low figures.

For me at least, March 2013 has been a remarkably low month. Yet my output in February this year was about average

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vanessa pooley

vanessa pooleyComment left on: 28 March 2013 at 10:40 pm

i would love to install solar PV

but live in a grade two listed building

love advice on whether its worth trying none the less

had an installer who wanted an effectively open cheque to research the possibility with my local lplanning debt... but was unable to say what the odds were

Advice????

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