Number of solar panels to aim for with this roof setup?

looking_ahead2

Hi All,

Been following the various solar posts on here for a while and looking more closely into taking the plunge on an install.

Have a got a few quotes in and they seem to follow a 10 panel + battery standard (this is before any site visits so understand it would be quite general), but before refining it a bit more I wanted to check a good number of panels to target. I've seen on a few posts that a chunk of the cost is getting the scaffolding up and the install, and it might not add a huge amount to the costs to increase panels at that point?

From some quick measurements, I make the length of the roof about 6m, and the width about 7m (though pitch down the middle so more like 3.5m halves). I think roof pitch is about 30 degrees, on a 60s build semi detached. Orientation wise, if north is 0degrees then our roof is about 70-80 degrees, i.e. pretty much east-west facing. So about two areas of 21m^2 give or take (all a bit rough working!)

I'm assuming the 10 panel quotes are aiming just to put the panels on one half of the pitched side of the roof. Do things get more complicated splitting that over the pitch sides, with extra panels? Less efficient when the suns moved over come the afternoon? I'm assuming things like extra weight doesn't come into it massively but maybe i'm wrong there.

Usage is around 9000kwh a year so I suspect the extra generation would come in handy, so long as it doesn't drive the cost up too much or through losses isn't worth it?

Thanks for any advice!

pcgtron

The usual advice is to put as many panels up as the roof can take, from a space point of view, but it also depends on the orientation of your roof. I have an E/W array, so I've got panels on both pitches of the roof. If you have a North/South facing house, putting panels on the north side might not be as cost affective, depends on generation reports. 
I'm afraid I have no idea about how many panels you could expect to get on a roof your size however. 

When I was costing up mine, the first quote was for 10 panels east, and 5 panels west (The most the west side could take) 
I reduced this down to 5 on each aspect, due to cost pressures, and not really needing the larger generation that a 10/5 split would give me. Yes, I could sell the excess back to the grid, but at the end of the day, I doubled the size of the battery (Which made sense for my usage) and the price was still cheaper than a 10/5 split with half the battery. This will be the first summer that we have the panels (Installed in November) but yesterday was the first day that we exported any energy back to the grid since panel install. 
For context, the house uses approx 5000kw a year (With the electric car using the other 5000kw) I did not size the installation to utilise electric car charging, as the car is not parked at the house for the majority of the time the sun is out, so would have been a waste. We charge on off peak power anyway

Screwdriva

As many panels that can fit on a South or Western roof aspect usually proves the most lucrative, followed by the Eastern aspect. With your usage, a battery is a sensible investment. 

For panels, I recommend: REC/ SHARP/ Hyundai/ Solarwatt or Panasonic panels (~£3K for 10 panels)
For battery + inverters, I recommend: MyEnergi Libbi (£9K for 10 kW), Tesla Powerwall (£12K for 13 kW) or GiveEnergy 2 inverter/ battery (£6.5K for 10.4 kW) 

Always chose brands with the best reputation(s) you can afford. 

looking_ahead2

Thanks very much both, that's food for thought.

I'll struggle to stretch the budget out to include a battery right now, but it sounds like adding a few more panels on to the western roof might be worth it, depending on the cost impact. Will run a few scenarios through a spreadsheet and see how it looks.

EcoScruples

Don't forget if you buy a battery at the same time as your panels then its zero VAT (unsure if the prices Screwdriver quoted include VAT or not) which is a nice chunk off you outlay.

70sbudgie

I also have an E-W pitched roof. My original quote had been for 5 panels on each pitch, but when they came to do the site survey, we discovered that the E pitch had an extra row of roof tiles and therefore with a different configuration of panels could fit an extra two. Those two panels only increased the total cost by £500 (2 years ago), so I went for it. 

I am of the opinion that putting as many panels on the roof as you can fit is a good idea. With an E-W orientation, I find the winter generation is lower than those with S facing panels and the peak generation in summer is not as high. But the daily peak is flatter and lasts a couple hours in summer and I have a longer period of generation - about 10-12 hours usuable generation with perhaps an hour or two of dregs either side. 

If you've been reading this board a while, you'll probably know to have a look at PVGIS to see how much your panels could produce. I did each pitch sepearately and then added them together.

yp70479

If you have a bit of spare time and fancy a play - try https://easy-pv.co.uk/home. As you already know the size, pitch and orientation of your roof you can try out different sizes  and orientations of panels to see how many you can fit on. The site is linked to Midsummer wholesale, so it only shows the panels they sell, but it can give a good idea of how many you could fit on. You do have to register, but you don't have to pay anything. The diagrams will automatically put a 30cm outline on your roof layout - this is because panels should not be closer than 30cm to the gutters or ridges. You can also put in any vents, windows  and chimneys to see how this may affect the layout. Get your optimum layout and the use PVGIS to see how much it will generate.