Are solar panels worth it with my roof and sloping direction?

[MrTWales]

Hi all, appologies if this kind of post isn't allowed but I've been pondering whether it's worth (*) getting solar panels installed and possibly a battery. The house was built in 2003 so the roof is in good condition.

 

(*) I know it's probably going to amount to a net cost over a reasonable number of years, but I'm OK with this for the greater good if it's not too dramatic a cost.

 

If I'm managed to do it correctly an image of my roof is attached. This is from Google Maps, with north upwards (so the front roof faces south east and the side roof faces south west). It would all be a decent size perhaps but for the dorma things taking some space (and I guess you can't have a panel on each facing south west?). I added a measurement line in white. 

 

In addition, I have a recent garden build that's about 20 feet by 15 feet (it's a games room). This is a flat roof, sloped slightly (for drainage) south west, with a fibreglass top. The wooden beams were solid and it was a proper build, even though it was a permitted development (so building regs didn't apply). It's only about 2m high so the height restrictions shouldn't be an issue. It does have an electric feed and it's own fuse box, but I've no idea what it would mean to electricity from there to the house. Every time I try Googling I confuse the hell out of myself! 

 

The other issue is where to store a batter as I don't have a shed. If it wasn't huge then maybe it could go in the games room I guess, but I think the attic would be too hot even with fans etc?

 

Anyway, and comments about the potential would be appreciated!

 

 

 

Edited May 7, 2022 by MrTWales
Two pics by mistake!

[MikeSharp01]

16 minutes ago, MrTWales said:

appologies if this kind of post isn't allowed but I've been pondering whether it's worth (*) getting solar panels installed and possibly a battery. The house was built in 2003 so the roof is in good condition.

Why would it not be allowed - it is and welcome to the forum.

 

PV is all about area, angle and shading. If you can max out a South ish facing slope at about 35 degrees with no shading for the vast majority of the days then you can generate well. You then have the challenge of using it. A battery helps and with associated controls you can then run appliances and if the battery is full perhaps some can go into the immersion heater or, worst case, be exported to the grid. 

 

There is loads on here about how much you can expect to generate and that's may be your starting point. 

[MrTWales]

Thanks a lot. I guess I should get some quotes but looking around it's not always that easy and I want to know exactly what to ask and be ready to just go if I am happy with a quote, rather than waste anyone's time.

 

There isn't any shading on the south east front facing roof and hardly any on the south west (though the chimney may not help, or that of my neighbour). I just wonder how many they could cram up there, and whether the flat roof would help a lot too. 

 

It's such a shame that batteries are so freaking big and expensive right now!

[Iceverge]

Welcome to the forum.I am hoping to get some PV too at some stage and am learning also.

 

In the depth of winter generation will be small. 

 

In the middle of summer the sun is higher so orientation is less critical. 

 

It's the shoulder months that having a good orientation and lack of shading helps out hugely. 

 

Most panels are 350-450w and take up an area 1m*2m. So your house roof looks limited on the SE facing pitch to maybe 6 panels?? Hard to tell. This would be 2-2.5 kW so a useful contribution. 

 

Theres a website PVGIS.eu 

 

https://re.jrc.ec.europa.eu/pvg_tools/en/

 

You can play with this to see you annual generation.  I reckon it would be about 2000 kWh and peak at roughly 9kWh per day. 

 

Our DHW demand is 10kWh/day so assuming you have similar usage and choose to install a diverter to an immersion you could use all your spare PV on heating water. A battery would be unnecessary. 

 

If you look at midsummer solar and creat an account you can draw your roof and it'll auto generate a package. 

 

 

[MrTWales]

Thanks, looks like you are a little further down the path than me!

 

Interesting points about the battery - I do work from home so could put the dishwashers, clothes washer etc on during the day, and the hot water tank is pretty new (it's like a giant thermos flask) with an emersion heater option so if that was linked somehow it would also help. Thinking about it, the oven is electric and we have two electric hobs so could use those rather than the gas hobs in the day. Nevertheless, I like the thought of at least some storage for the evenings. Whether or not it's worth it though, I'm not sure.

 

I had a look on Gloogle Maps and got my ruler out last night, and I thought that maybe 11/12 panels or so could fit on the two south-ish facing roofs. That maybe optimistic but it's funny how some installs go close to the edges and some don't, and not all panels seem the same size (maybe newer ones can be smaller?). Some are just a rectangle, but others have some panels in landscape and some in portrait to use the space. I have the thought that so many costs are fixed so the more panels fitted the better, and any extra costs are probably worth it unless you just don't use much energy. Maybe that doesn't apply to panels on my garden flat roof though, not sure. It's not that far to the electricity meter so maybe that helps.

 

I really should work out how much electricity we tend to use as you have, but I'm guessing that the 10kWh/day figure won't be far off. Maybe it's a bit more as there is basically always someone in.

[SteamyTea]

6 minutes ago, MrTWales said:

really should work out how much electricity we tend to use as you have, but I'm guessing that the 10kWh/day figure won't be far off.

Not just the total amount, it is how the power is delivered.

If evenings are just a light or two and a TV. Hardly worth getting £3k of storage for a 100W load.

 

[MrTWales]

Thanks. We don't have a smart meter (so I guess I can't check use by time) but a lot of cooking goes on in the evenings, and there are four people in the house. 

 

Interesting thoughts though. I kind of thought that most instals now have a battery but it's more of a consideration than I thought (and that's before the space issue).

[Iceverge]

If you can shift your usage to midday is almost certainly not worth getting a battery.

 

Our total electricity usage is about 18kWh/day excluding space heating. 

 

If you want to get a battery you may as well buy a second hand EV. £3500 buys you a new 5kWh battery. £4500 buys a 24kWh battery with a high miler Nissan Leaf attached. Even if you only use it on local trips it will reduce your energy usage dramatically.

 

My pretty efficient Skoda 1.6d does equivalent 60kWh/100km. 

An electric runabout would do about 15kWh/100km.  

 

[MrTWales]

Thanks - to be honest, my main take away from this thread is the battery issue. I was kind of assuming that you'd get a battery unless there was a good reason not to (eg nowhere to put it) but now I'm thinking that it's more a case of needing a good reason to get one. Plus, I suppose it would be possible to add one at a later date? I wonder if any part of an install can make it easier in the future to do this. I'm not up on the technology, but what little common sense I have tells me that with so much focus on electric cars, as well as solar, we may see improvements in decent sized batteries in the next 5/10 years.

 

We have a very efficient car (78 mpg is my personal best for a trip!), and don't do much milage, but our next car will 100% be electric and I can see that if you have this then it's going to use anything that you get from the panels that you don't use in the day.

 

Geeze, 15kWh of power can get you that far with a small EV? That's nuts. I'd never have guessed that.

[SteamyTea]

9 hours ago, Iceverge said:

My pretty efficient Skoda 1.6d does equivalent 60kWh/100km. 

An electric runabout would do about 15kWh/100km.  

My best has been 73 MPG, think that is 3.9 lt/100km.  Takes forever to get places though.

So about 38 kWh/100km

I filed up today at £1.724/litre, so £6.72/100km or 11p/mile.  300 miles journey in the morning.

If an EV uses 300Wh/mile and electricity is costing 30p/kWh, costs 10p/mile.  7.5p/mile at 15 kWh/100km.

So at todays prices, not much different.

Now I know someone that has just traded their 3 year old Jaguar iPace in for a Ford Mach-E.  The jag, which had only been charged on a granny lead, had lost about 40 miles of range (220 to 180 miles, can't get to Exeter and back in it).  Now I have no idea if this is normal, or they were unlucky, may heavy footed (or even if they worked it out correctly), does seem a high price to pay though.

Edited May 7, 2022 by SteamyTea

[Nickfromwales]

12 hours ago, SteamyTea said:

Not just the total amount, it is how the power is delivered.

If evenings are just a light or two and a TV. Hardly worth getting £3k of storage for a 100W load.

 

They don’t live with you  

The actual loads will be the vampire loads of a typical house. Stuff that you cannot be bothered to unplug, or switch off, or put into ‘power-saving’ mode. So a £3k system in my house would probably pay back its capital investment 3x over in its useful lifetime.

[Nickfromwales]

12 hours ago, Iceverge said:

If you want to get a battery you may as well buy a second hand EV. £3500 buys you a new 5kWh battery. £4500 buys a 24kWh battery with a high miler Nissan Leaf attached. Even if you only use it on local trips it will reduce your energy usage dramatically.

 

My pretty efficient Skoda 1.6d does equivalent 60kWh/100km. 

An electric runabout would do about 15kWh/100km.  

 

Elementary, my dear kW’stson.

The car can only charge at a certain rate of knots. To absorb sporadic pockets of excess solar PV the charger needs to be in ‘eco’ mode, and the car tethered whilst this is happening.

A domestic battery is fixed, and is dedicated to absorbing these ‘opportunities’, and will be the simplest and best option if capturing solar PV revenue is the remit. Most people will be wanting to drive places during the hours of daylight…. 

 

12 hours ago, Iceverge said:

If you can shift your usage to midday is almost certainly not worth getting a battery.

 

100% sound advice.

[SteamyTea]

4 hours ago, Nickfromwales said:

The car can only charge at a certain rate of knots. To absorb sporadic pockets of excess solar PV the charger needs to be in ‘eco’ mode, and the car tethered whilst this is happening.

A domestic battery is fixed, and is dedicated to absorbing these ‘opportunities’, and will be the simplest and best option if capturing solar PV revenue is the remit.

Does anyone know how quickly a BMS reacts to a burst of PV power.  Seem to remember someone mentioning there system was still exporting because the battery did not turn off the instant the load was removed i.e. it saw the grid as a load.  Wonder if it has the same time delay to a charge.

[Radian]

10 hours ago, Nickfromwales said:

The car can only charge at a certain rate of knots.

Expecting @SteamyTea to point out that one knot is 0.51 meter/second and that we can convert between kilogram-force meter/second and joule/second - but we would need to know the mass of something relevant to work out how many joules/second (Watts) that represented...

[SteamyTea]

23 minutes ago, Radian said:

we would need to know the mass of something relevant to work out how many joules/second (Watts) that represented...

About 2000 kg.

[MrTWales]

Oh feck. An installer just called and looked up the roof on their system and reckoned that, as you can't go anywhere near the edges, it probably wouldn't be worth installing panels on the front and side roof due to the dormas. 

 

Dammit 😞

[Pocster]

On 07/05/2022 at 23:59, Nickfromwales said:

Elementary, my dear kW’stson.

The car can only charge at a certain rate of knots. To absorb sporadic pockets of excess solar PV the charger needs to be in ‘eco’ mode, and the car tethered whilst this is happening.

A domestic battery is fixed, and is dedicated to absorbing these ‘opportunities’, and will be the simplest and best option if capturing solar PV revenue is the remit. Most people will be wanting to drive places during the hours of daylight…. 

 

100% sound advice.

The other benefit of a battery ( be it EV or home ) is you can fill yer boots at off peak rate . This is the best option during winter months when PV is negligible. A battery isn’t just for summer - it’s for winter also 😁

[Radian]

3 hours ago, MrTWales said:

Oh feck. An installer just called and looked up the roof on their system and reckoned that, as you can't go anywhere near the edges, it probably wouldn't be worth installing panels on the front and side roof due to the dormas. 

 

Dammit 😞

I would love to see how this magic 'distance to edge of roof' comes about.

[SteamyTea]

1 hour ago, Radian said:

I would love to see how this magic 'distance to edge of roof' comes about.

Comes about from the MCS rules.

If I remember correctly, 200mm from top and sides, 100mm from bottom.  But may be more as the rules change.

Wind and snow loading calculations should be done as well.

Should be something on the MCS website.

[Nickfromwales]

1 hour ago, Radian said:

I would love to see how this magic 'distance to edge of roof' comes about.

Not magic, maths and sense. 

[Pocster]

30 minutes ago, Nickfromwales said:

Not magic, maths and sense. 

Exactly the philosophy I apply on my build 🙄

[Radian]

1 hour ago, SteamyTea said:

Comes about from the MCS rules.

If I remember correctly, 200mm from top and sides, 100mm from bottom.  But may be more as the rules change.

Wind and snow loading calculations should be done as well.

Should be something on the MCS website.

 

 From the mcscertified.com PV Book :

 

Quote

Unless specifically designed to do so, systems should be kept away from the roof perimeter. For a domestic roof, a suitable minimum clearance zone is around 40-50cm. The requirement to keep an arrays away from a the edge of a roof is suggested because: wind loads are higher in the edge zones; keeping edge zones clear facilitates better access for maintenance and fire services; taking arrays close to the roof edge may adversely affect rain drainage routes; and when retrofitting systems, there is the potential for damage to ridge, hip, valley or eaves details. Note – on many roofs a 50cm gap from the edge will still mean that PV modules are fitted in the “Edge Zone” as defined in BS EN 1991-1 where higher pressure coefficients need to be implemented due to the higher imposed wind loads.

 

I've seen other, smaller, numbers like the ones you quote. But as you say, rules change. Of course in reality, the actual calculations will be complicated and highly dependent on the specific local topology - and probably completely useless if climate change means maximum wind speeds increase as they are expected to do. My point is, it's mostly hand-wavy guesswork that runs the risk of erring on the overly cautious side.

 

1 hour ago, Nickfromwales said:

Not magic, maths and sense. 

 

You mean Navier–Stokes? Just say it man!

[MrTWales]

I can understand not wanting to go close to a top or side edge if the risk of the wind weakinging the roof is greater there, but I got the impression that they wouldn't want to go near the top of the dormers dormers. Not sure why that would be to be honest.

[Radian]

Some research shows that panels mounted close to roof edges can actually mitigate problems with wind uplift damage to roofs. The panel manufacturers seem pretty confident in the panels themselves withstanding extreme winds. Having seen the typical lag screws used to secure the brackets to rafters I'm not concerned with them being unable to resist wind forces on the panels.

 

I could say that you don't see many reports of modules causing problems - but then we've got rules in place making sure of that.🙄

[MrTWales]

It's not obvious to be how it works to be honest, but Google Maps shows me that some panels are certainly very close to the edge!