Solar Panel Guide Discussion

Dave_Fowler

orrery wrote: »

I agree, but what units were you expecting to see the answer in? A percentage was a good choice, as this removes any assumptions about system scaling.

The question you should have been asking was why the answers only went up to 80%. Hence my question 'When should I expect to see 100%?'. Presumably zeupater had a 100% in mind when he quoted the figures that he did.

I think Zeupater was putting 100% as the best figure attainable by a complete system, after making allowances for the inverter and cable losses.

The set of panels on the roof is rated at xkWp where x = (number of panels) * (panel output rating). The 'output rating' assumes the panels are at 25C and are receiving 1000W/square meter. Most panels are rated at y Watts -0%+5% so typically the output of a new panel could be more than that specified, but the panels will lose efficiency over time and by 10 years will have reduced by the 5% or more.

The xkWp figure will never be achieved under normal circumstances for a complete system.

Even assuming the panels are at 25C and receiving the 1000W/m2 radiation, the complete system will still have losses. The inverter typically loses 5%, the wiring a further 5%. If you add in the real factors where the panels are running hot due to the sun - I'd expect around 55C could be a very conservative estimate - then a further loss of 0.4%/degC is to be expected. This would be another 12%. So a total loss of over 20% would not be unusual.

As you will see, the panel losses due to temperature can be the greatest part of the overall loss.

There are times when the panel losses even under full sun are less - on a cold windy day and also when the sun comes out from behind a cloud but the panels have not had time to heat up. I would use the output figure at this time as the 100% figure for a system and base my cloudy day, rainy day etc output forecasts based on this.

Dave F

orrery

Dave_Fowler wrote: »

The xkWp figure will never be achieved under normal circumstances for a complete system.

OK, but I have heard of people getting over the xkWp capacity (locations Bedford and Derby) so not south coast by any means but certainly south of Sheffield.

Dave_Fowler

orrery wrote: »

OK, but I have heard of people getting over the xkWp capacity (locations Bedford and Derby) so not south coast by any means but certainly south of Sheffield.

I await the day where my system approaches 100% capacity! And I've been up and running well over a year now. The best I've managed is 2.7kW from my 2.96kWp system. I suppose if the radiation were 1200W/m2 (i.e. 20% above the standard figure used for calculations) and the inverter could produce the power, it would be possible to exceed the rated output.

The trouble is most systems are fitted with inverters which struggle to produce 100%; most are rated just below the maximum because the system designers never expect a figure of over 100% to be produced when all the system losses are taken into consideration.

Dave F

zeupater

orrery wrote: »

OK, but I have heard of people getting over the xkWp capacity (locations Bedford and Derby) so not south coast by any means but certainly south of Sheffield.

Hi

This will probably be a temporary reading from the inverter or remote monitor display as opposed to recorded generation history from the inverter.

It could be possible to have have a single time slice of data (or a very few consecutive timeslices !) which would record the nominal peak from the system, but this would probably need the combination of two things .... firstly, the panel pack received would need to be towards the top of the manufacturing performance tolerance range, and secondly you would need an inverter which would be capable of recording data for smaller than 'normal' time intervals ... my inverter does so in 5 minute timeslices, which is enough time for the cloud edge effect to drop and the panels to warm in full sun ...

HTH
Z

digitaltoast

Now it's starting to get interesting...
http://www.dailymail.co.uk/news/article-2055039/Is-sun-set-solar-power--leaked-document-reveals-government-planning-50-cuts-subsidies.html

Two things to remember.
1: It's in the Daily Mail. But...
2: Just because it's in the Daily Mail doesn't necessarily mean it's not true. Here's a quote:

Industry experts believe that if the new tariffs are introduced it could put dozens of firms out of business and cost as many as 25,000 jobs.

Shaun Taylor, managing director of Buckinghamshire-based SolarTech, posted on the ClickGreen website: 'If this leak proves accurate then the Government will be condemning tens of thousands of residents in social housing to continued fuel poverty as there is no way that 'free PV' schemes will now be financially viable.

'The impact on employment will also be enormous as the industry had forecast 20,000 to 30,000 jobs would be created in this sector.

Right - so "industry experts" is just a bloke who owns a company. Which must make me an "industry expert" in ranting on forums.

And "cost as many as 25,000 jobs" would suggest that these are existing jobs. Whereas "the industry had forecast 20,000 to 30,000 jobs would be created in this sector" sounds a rather different proposition.

Gordon Brown forecast "no return to boom and bust". Doesn't mean either of them know what they're talking about...

In particular, I dislike Shaun's emotive use of language in the following:

If this leak proves accurate then the Government will be condemning tens of thousands of residents in social housing to continued fuel poverty as there is no way that 'free PV' schemes will now be financially viable.

Eh?! How does that work then? In that it's people in social housing and fuel poverty who pay for this scheme and are LEAST likely to benefit from the enormous solar subsidies, how is this going to "condemn tens of thousands" of them?

Sorry, solar PV industry, but the gravy train has hit the buffers.

That's my 2p worth - what do the rest of us reckon?

Edit: Ooops, just seen this:

sly_dog_jonah wrote: »

EST 'draft' docs leaked today, parliament announcement expected Monday:

http://www.moneysavingexpert.com/news/utilities/2011/10/solar-subsidy-to-be-slashed

So I'll carry this on in the other more relevant discussion thread.

zeupater

digitaltoast wrote: »

Now it's starting to get interesting...
http://www.dailymail.co.uk/news/article-2055039/Is-sun-set-solar-power--leaked-document-reveals-government-planning-50-cuts-subsidies.html

Two things to remember.
1: It's in the Daily Mail. But...
2: Just because it's in the Daily Mail doesn't necessarily mean it's not true. Here's a quote:



Right - so "industry experts" is just a bloke who owns a company. Which must make me an "industry expert" in ranting on forums.

And "cost as many as 25,000 jobs" would suggest that these are existing jobs. Whereas "the industry had forecast 20,000 to 30,000 jobs would be created in this sector" sounds a rather different proposition.

Gordon Brown forecast "no return to boom and bust". Doesn't mean either of them know what they're talking about...

In particular, I dislike Shaun's emotive use of language in the following:



Eh?! How does that work then? In that it's people in social housing and fuel poverty who pay for this scheme and are LEAST likely to benefit from the enormous solar subsidies, how is this going to "condemn tens of thousands" of them?

Sorry, solar PV industry, but the gravy train has hit the buffers.

That's my 2p worth - what do the rest of us reckon?

Hi

I pretty much agree ..... I think that the industry will moan like anything for a while, then simply pull their socks up and become a little more efficient (there are still some taking 3 days to install a system !), and then reduce prices as required. Twelve months ago installed prices in Germany were around/lower than UK prices are today and the equipment prices have fallen considerably since, so there's plenty of fat in the system to cushion the industry against any claims of armageddon ....

Looks like the margins available as a result of the law of supply and demand will just be rebalanced towards the customer for a time whilst the supply side of the equation provides the necessary adjustments ..... all will be well for most in the long run, especially the providers of the funding for the FiT scheme, namely .... us

Z

orrery

zeupater wrote: »

...firstly, the panel pack received would need to be towards the top of the manufacturing performance tolerance range ...
...enough time for the cloud edge effect to drop and the panels to warm in full sun ...

Mine are quoted as -0 +3%, so 4kWp or higher (subject to all the riders about what kWp indicates in this context).

The cloud edge effect may be a good explanation as both '100%+' readings were obtained with clip-on displays, so mains-side and near instantaneous.

sly_dog_jonah

albyota wrote: »

What Inverter do you have?

We've got an Enfinity 3680-TL inverter. Sorry for slow response I'd forgotten to subscribe.

Nang

Well...

Looks like Fits may be ending sooner than expected.

Check out :-

http://www.bbc.co.uk/news/business-15507750

....

Dave_Fowler

Nang wrote: »

Well...

Looks like Fits may be ending sooner than expected.

Check out :-

http://www.bbc.co.uk/news/business-15507750

....

The Solar Power Portal http://www.solarpowerportal.co.uk/news/fit_cuts_2011_decc_proposes_21p_rate_december_deadline_5478/ gives a reasonably full account of what is proposed and when everything takes effect.

Dave F