Solar Panel Basics.....

Weakestlinks

Hi
So I'd like to gather a few basics before I venture into the PV world. I hope some experts can help - apologies now for the newbee approach.

I live in South East England about 10 miles north of Hastings in a detached bungalow with a South facing roof and no shade. It's not a massive roof (about 3.5m x 8.5m) and about a 40 degree slope. From what I've read that sounds a reasonable start.
There is someone home pretty much all day and over the last few weeks I've been monitoring our power use (using an OWL monitor) and between about 9am until 8pm we use about 12KW of power - typically we have washing machines and dishwashers running most days. Peak never really rises above 3.5Kw at any given time unless the kettle goes on when we're already got the washing\oven etc.

So is my understanding correct that a 4KW solar system should be able to sustain a 3.5KW draw from the applainces without me having to draw from the grid? Or is that only under ideal conditions (no cloud, no wind and when there's an R in the month)?
On a generally 'overcast' day can I expect a 10% or 50% or perhaps lower reduction in what the solar panels can provide

Next - These things seem to be about 1000mm x 1600mm in size and I need to leave a bit around the edge of the roof. So a rough calculation tells me I may be able to get 13 panels configured as a row of 8 in portrait orientation with a row of 5 in landscape either above or below these - can these panels be laid out with different orientations or must they all be the same way?

to get 4KWh system from 13 panels I was looking at the SunPower 327w panels which will be (13 x 327w) = 4.251KWh (I think BenQ also do some). If my consumption is generally around 3.5KW/h and there is only a small reduction in efficiency during cloudy days then would any more panels just be a waste of money buying extra panels I don't need?

For anyone who has read this far - I'm grateful and will not bore you any further..... I haven't even started on SolarEdge\iBoost and inverters yet.... that's be for another post perhaps.

Finally - Any idea on price for these more expensive panels (I do plan to get it installed by an MCS installer)..... should I be looking at sub £8k if I get a good inverter and iBoost?

Anyone know a good reputable installer in East Sussex\West Kent areas?

Thanks

Fruit_and_Nut_Case

Welcome to MSE :wave:

Weakestlinks wrote: »

...between about 9am until 8pm we use about 12KW of power...

I think you mean 12kWh.

Weakestlinks wrote: »

On a generally 'overcast' day can I expect a 10% or 50% or perhaps lower reduction in what the solar panels can provide...?

Yes

Weakestlinks wrote: »

...can these panels be laid out with different orientations...?

No problem.

Weakestlinks wrote: »

I do plan to get it installed by an MCS installer

You'll have to if you want to register for FiT.

Weakestlinks

Thanks for the fast reply - you've answered a couple of the questions but confused me in others....

You're right about the 12KWh thing - I was never one for physics.....
It's the panels that are measured in KW isn't it? not the energy I use from them.

Your next bit confused me a bit - I wanted to get a feel for how cloud might affect output and so was asking if cloud cover would perhaps reduce the output by 10% or 50% or perhaps even more.... when you say 'Yes' to that question are you talking about the density of cloud could mean all three are possibilities? - in which case I think that's a whole new world of physics I will never understand.......

Good news on the orientation thing - which I assume also means you agree on my sizing that I can get 13 panels on a 3.5m x 8.5m. I wasn't sure on how much edge gap I would perhaps need.

....and I can see you're from Devon so perhaps not best positioned to recommend any fitters in my area -

Thanks again for the reply - I appreciate your time.

tunnel

Bear in mind that by going over the 4kWp system size then you'll be going into the next FiT rate, ie..4-10kWp rate. Might be better to stick at 12 panels and 3.92kWp system size.

Weakestlinks

Ah - Thanks
Didn't know that....so 12 panels it will be. I guess the FiT is based on what the panels can potentially supply rather than what is actually delivered due to shading.

Are you able to shed any light (seriously bad pun!) on the cloud cover question.
I did speak to a solar panel sales rep who said that its now UV that's important and not sunlight so any daylight will be effective.
I think what he meant to say was that cloud cover will probably reduce the output by over 50% - as I have been recently reading.

Dave_Fowler

Weakestlinks wrote: »

Ah - Thanks
Didn't know that....so 12 panels it will be. I guess the FiT is based on what the panels can potentially supply rather than what is actually delivered due to shading.

Are you able to shed any light (seriously bad pun!) on the cloud cover question.
I did speak to a solar panel sales rep who said that its now UV that's important and not sunlight so any daylight will be effective.
I think what he meant to say was that cloud cover will probably reduce the output by over 50% - as I have been recently reading.

On an 'average' cloudy day, at mid-day, you may expect 10% to 30% of the peak power output. On a seriously cloudy day, the whole thing will just shut down and you'll get nothing. At the moment it's hazy sunshine here - no distinct shadows but the sun's disc can be seen. I'm getting 0.64kW from my 3kWp system.

Dave F

Weakestlinks

That's great info - thanks Dave
It's good to get some real world figures and descriptive weather conditions I can use as a tangible yardstick

cheers

rogerblack

Weakestlinks wrote: »

I did speak to a solar panel sales rep who said that its now UV that's important and not sunlight so any daylight will be effective.

This very closely approaches a flat-out lie.
I would certainly be making a complaint to the company, and the certification body about this if I was told this.

It seriously misrepresents the truth.
Yes, panels can make some power from non-visible light, even in overcast conditions.
Visible light dominates.
The amount of power from overcast conditions where the average person would say there is no sun is at best 30%, often much lower.

groovyf

Have a look at one of my better days... well it was until the cloud came along, which is pretty evident from the drop in performance just after 3.45pm on the graph:
http://pvoutput.org/intraday.jsp?id=29935&sid=27404&dt=20140701

theboylard

Evening all!

If you've not seen it before, then have a butcher's at pvoutput.org

A bit of digging suggests that looking at systems in your area may give you a better insight into your local weather and possible performance of a pv install.

http://pvoutput.org/listmap.jsp?sid=5257

You may have to register with the site to see the above, takes less than a minute and not at all intrusive!
But if you're serious about setting what solar can do in your area, then it's a great resource.

Good luck!

mac2008

Yes, just to back this up further, my rule of thumb is a heavily overcast day will reduce output by 90% - ie i budget on getting a tenth of their peak power rating.