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Solar PV panels on a garage roof - what area do they need to cover?


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Hi

I'm just recovering from the shock of my new renewal quote and feel it has greatly improved the economics of solar cells.  My main house roof is east/west but i have a well  placed flat garage roof. Has anyone  experience of installing pannels on a garage roof? What sort of area do I need for a typical three bed bungalow with retired occupants?

 

Thanks

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Best answer by MadArgy 16 August 2022, 08:37

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If you have space on your house roof an East/west solar array might serve your needs better than a South facing array. While each panel won't generate as much electricity you will start generating earlier in the morning and still be generating in the evening when a South facing array has stopped. This means you should use more of your generated electricity, which will save you money.

 

It's difficult to say what size of array would suit you. Most people simply fit as many panels as they can. A decent solar PV company will be able to tell you how many panels you can fit and should also provide information on the different options.

 

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Interesting. Not the answer I was expecting.  Will need to look in more detail how the sun moves around here.  I am very aware that our west facing room gets very hot after about 3pm in the summer. Unlike the south facing rooms that get the sun when it is much higher in the sky, the lower angle of the sun means the projected area is much greater.  I guess it will be affected by the slope of the roof. After loking at neighbours panels I'm not sure I have enough area on the garage roof.

Thanks for the advice

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Yeh I liked reading that response from M.isterW, never thought about it that way. 

 

We’ve got new forum members here with solar that I’d like to tag just in case they enjoy sharing their own expertise. What’s your opinion on solar positioning for south vs east/west? @Hello @leaf trials @Rishtonleaf @AndrewL @MadArgy @Ferring21 @Larissa @waiwurrie @simonL @Lucy P @Cate2404 

 

 

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Hi, the only side of the roof we could fit our solar panels was on was on a west facing roof. Whilst they don't generate as much as a friend's down the road (which is fully south facing) we're still very pleased with the generation results.

If you're looking at putting them on a flat roof or garage I think you'll also have to be comfortable that your flat roof will not need renewing/repairing for a good many years otherwise you may get the hastle/cost of having to take the panels down to carry out any repairs to the roof before putting them back up again.

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There are a couple of online formula solutions for calculating solar output, given location and orientation. The Energy Savings Trust one is accurate in my experience and gave a similar result to the professional software used by my installer. 
My panels are installed 8 East facing and 6 west facing. West facing gives a very long sustained daily output as long as not obstructed, because the sun sets very late in the west, throughout the summer months. I get power up till 9pm in three peak months and power up till 8 pm for a couple more months each side. 
South usually gives highest peak power but doesn’t last as long daily as west facing. 
East is worth adding extra panels to maximise the morning only output. 

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If you have space on your house roof an East/west solar array might serve your needs better than a South facing array. While each panel won't generate as much electricity you will start generating earlier in the morning and still be generating in the evening when a South facing array has stopped. This means you should use more of your generated electricity, which will save you money.

 

It's difficult to say what size of array would suit you. Most people simply fit as many panels as they can. A decent solar PV company will be able to tell you how many panels you can fit and should also provide information on the different options.

 

 

What’s your opinion on solar positioning for south vs east/west?

 

The companies that sell and install solar panels will do a suitability check of your roof, including efficiency based on the facing direction and how many panels you can fit, as part of the estimate of what it would cost to install them. Leave it to the experts… it’s free…

 

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After spending a couple of hours looking at my electricity consumption on an hourly basis via the Ovo app, I can see I use much more after lunch than before. The issue is to maximise  the useable,  not total power.  Thus the west facing roof has a clear benefit.  I’m now fitting some metered sockets to monitor my personal usage on an hourly basis.  No brainers will be to do the washing run tumble dryer after lunch.  I will also investigate the effect of a time switch on the freezer so i can shift the main consumption from overnight/morning to the afternoon.

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Keep us updated, @Beanbag112233 - you’re probably doing what hundreds more are thinking of doing. If they search online they may find this thread and see the advice. So keep us updated and best of luck! 

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Yeh I liked reading that response from M.isterW, never thought about it that way. 

 

We’ve got new forum members here with solar that I’d like to tag just in case they enjoy sharing their own expertise. What’s your opinion on solar positioning for south vs east/west?@Hello @leaf trials @Rishtonleaf @AndrewL @MadArgy @Ferring21 @Larissa @waiwurrie @simonL @Lucy P @Cate2404 

The companies that sell and install solar panels will do a suitability check of your roof, including efficiency based on the facing direction and how many panels you can fit, as part of the estimate of what it would cost to install them. Leave it to the experts… it’s free…

 

I feel that it really does depend upon the company you get! I would not call them all experts.

In our case we are in a bit of a hole as the company who installed our solar PV and solar thermal panels has gone out of business, the monitoring hardware we have now sends our data to a server that no longer exists and so we cannot get at the data or monitor it. Our system has Panasonic panels with micro-inverters on each so work really efficiently but as I say we cannot monitor them. And finding a company to help is to say the least proving difficult. Maybe there is some truth in the rumours that many of the solar panel installers were ex-double glazing installers!

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The fact that the company that installed your panels went bust, doesn’t make them less experts in solar installation.

A large percentage of the solar companies went bust, as their business model relied on the continued high volume of customers that the government incentives (FIT) were driving….

When the incentives programme was canned, their customer base shrunk a lot, as the payback for the panels became too long to be attractive. The recent increase in electricity prices and reduction in cost of the panels are making them more attractive again, so I wouldn’t be shocked to see a lot of new solar panel installers popping up. 

IMHO, the double glazing rumour must be just that, as solar panel installers have to be certified sparkies (at least one in each installer team), and it’s unlikely that so many ex double glazing installers became electricians… 

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I agree that an E/W split can work well - it is what we have (installed late July).  To date we consume 60% of what we have generated. I expect this to increase as we move into winter which I expect to increase as a percentage as we move towards winter which is why we don’t have a battery.  Our tree shaded Easterly set of panels have been kicking in around 6.30 am and  our Westerly facing panels knocking off around 7:30pm. Yes the peak power produced is less than the max possible for that number of panels but that is not the objective. At the moment OVO would give me 4p for every kWh I export but I would be paying 10 times that from October for every kWh I buy from them.

 

You can get more detailed modelling help from

https://joint-research-centre.ec.europa.eu/pvgis-photovoltaic-geographical-information-system_en

and a fb group

Solar & battery UK (including any other renewable energy source/storage)

 

and of course your selected installer

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I have found

https://loop.homes/loop-smart-meter-app/

who have app and web site that ties my actual consumption and roof orientation to interactive display showing effect of solar-panels and battery storage on daily basis.

 

Also been making detailed energy inventory on my standby load. Surprised by how bad appliences like my washing machine are. Seems to be worst for appliences over 10 years old. Just saved about 100kwh per year by turning them to off position.


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