craig1410
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| posted on 7/1/24 at 09:13 PM |
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quote:
Originally posted by David Jenkins
I fitted house batteries just over 12 months ago - a major difference! Mine charge overnight using Octopus Go (which I have for our cars) so, most of
the time, we run appliances during the day at off-peak rates (less than 1/3 cost per unit). In sunnier months we don't take much energy
overnight as PV tops it up all day so little is required to get back to 100%. In these months we also charge our cars during the day - and we get
paid for all electricity that comes off the roof (under an old solar payment scheme) so we get paid to charge the house and car batteries! No longer
possible under current schemes though...
It's nice to sit watching TV in the evening, seeing the total house grid load on the smart meter display varying between 0 and 100W most of the
time (usually near 0W).
But I won't open the debate whether house batteries are economic if you include the installation cost... still not cheap to fit.
Yeah same here, I fitted house batteries and commissioned them on 29th Oct 2022, initially purely for energy arbitrage via Octopus Go, but since I
installed solar PV panels in June 2023 and subsequently got my export tariff despite no MCS certificate in late July, I now also export energy at
15p/kWh. I am currently on the Intelligent Octopus Go tariff which gives me 7.5p/kWh off -peak from 11:30pm until 5:30am and 29.96p/kWh at other
times. It also gives off-peak energy at other times when there is excess grid energy. Even better, by opting in to "Saving Sessions" you can
earn anything up to 400p (yes £4) per kWh by reducing consumption and maximising export during the session times. I made £71.88 from 5 of these
sessions which lasted 5 hours or so in total. Even the basic 15p/kWh is pretty comparable to many of the FIT tariffs of the past and it's likely
to increase further in time. I started with 0p since I had no MCS cert, then got 4.1p, then 8p and now 15p, all since the start of August.
I've stopped charging our EV from solar generation because I can earn 15p from exporting and it only costs 7.5p to charge the EV overnight.
Better to export to the max during the day and charge the EV at night. I know how the old FIT tariffs work so what you're doing probably works
better for you. In the summer we have more power than we know what to do with and even in the winter our battery capacity is enough to get us through
the day on cheap rate power. Should pay for itself in 5 years or so.
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Mr Whippy
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| posted on 8/1/24 at 07:46 AM |
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Amazing stuff 
Fame is when your old car is plastered all over the internet
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tegwin
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| posted on 8/1/24 at 12:22 PM |
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Really interesting thread, the prices are definitely at the point where its starting to make sense.
I had been eyeing up my garage roof as it would be easier to take the panels with me if I move. Its a gently sloping flat roof - I had thought about
using frames to give a good angle but how much difference would it make if the panels were basically flat?
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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craig1410
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| posted on 8/1/24 at 02:22 PM |
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quote:
Originally posted by tegwin
Really interesting thread, the prices are definitely at the point where its starting to make sense.
I had been eyeing up my garage roof as it would be easier to take the panels with me if I move. It's a gently sloping flat roof - I had thought
about using frames to give a good angle but how much difference would it make if the panels were basically flat?
Yeah I have been waiting a few years until the payback period became short enough for me to jump in but that point came over a year ago in my opinion
where the estimated payback dropped to around 5 years by my reckoning. A combination of high electricity prices and reducing PV and battery prices.
My garage roof where my panels are installed is only around 14 degrees slope and is 5 degrees west of due south. The optimal angle and direction would
be 41 degrees angle and 4 degrees west of south. What this means for annual generation for my system at my location is 5919.87 kWh / year vs 5488.16
kWh / year (optimum vs actual). That's 92.7% which isn't bad I think.
You can enter your own location and details into this tool to get a prediction: https://re.jrc.ec.europa.eu/pvg_tools/en/
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JoelP
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| posted on 8/1/24 at 06:16 PM |
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quote:
Originally posted by tegwin
Really interesting thread, the prices are definitely at the point where its starting to make sense.
I had been eyeing up my garage roof as it would be easier to take the panels with me if I move. Its a gently sloping flat roof - I had thought about
using frames to give a good angle but how much difference would it make if the panels were basically flat?
An easy approximation of the percentage efficiency is 100cos x, where x is the angle away from ideal. Presuming you're in the UK, 55 degrees from
horizontal is a start. Bearing in mind you'll have a huge surplus of power in summer, you could argue the panels should be optimised for winter,
and installed more vertically.
Beware! Bourettes is binfectious.
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craig1410
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| posted on 8/1/24 at 10:24 PM |
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quote:
Originally posted by JoelP
An easy approximation of the percentage efficiency is 100cos x, where x is the angle away from ideal. Presuming you're in the UK, 55 degrees from
horizontal is a start. Bearing in mind you'll have a huge surplus of power in summer, you could argue the panels should be optimised for winter,
and installed more vertically.
Something else to bear in mind is that, if you don't have a perfectly south facing roof then steeper panels exaggerate the reduction in
efficiency. To visualise this, consider a completely flat array (ie. 0 degrees elevation). An array like this doesn't matter which direction it
is facing because the sun can shine on it from any angle (assuming no shading of course). Now consider an array where the panels are mounted
vertically and you'll realise that it becomes much more sensitive to deviation from due south.
In addition, if you are considering mounting the panels on some sort of frame to increase the angle then this will have an impact on wind loading and
if the top row of panels are higher than the apex of the roof then you might have issues with planning permission.
My advice would be to keep the panels low to the roof to minimise wind loading and avoid planning issues. The reduction in efficiency really
isn't that much and if you have the space on the roof then you can probably just add another panel or two to compensate. I'm at 55.7
latitude and still managed to get 3136W peak today at 12:43pm from a 6800W array. Total generation was 5.8kWh for the day. Not bad for January 8th!
In other news, we had a nice surprise from our Intelligent Octopus Go tariff this evening. My wife plugged the EV in at around 5:30pm and Octopus
created a schedule to charge the EV starting at 7:30pm and running through to 6:30am tomorrow morning. That means that ALL consumption between those
times is at the off-peak 7.5p/kWh rate. So of course we have charged the home batteries and EV batteries up to 100% and ran the dishwasher and washing
machine. That's the longest "smart charge" session we have seen yet and basically means we can run from the grid until 6:30am and then
start to deplete the batteries. Tomorrow looks like another sunny day so should be able to export PV energy for a good 3-4 hours in the middle of the
day.
If anyone fancies switching to Octopus and sharing a £100 credit then use this referral link. https://share.octopus.energy/bold-foal-39
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Mr Whippy
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| posted on 9/1/24 at 07:42 AM |
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Fantastic information guys
That calculator is great too, it's amazing at how much power it predicts per month, a real eye opener. Looks a fantastic project to take on in
the spring. Thanks.
Fame is when your old car is plastered all over the internet
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jacko
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| posted on 12/1/24 at 07:11 PM |
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Don’t forget to fit netting to stop pigeons they love solar panels
G
555
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David Jenkins
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| posted on 14/1/24 at 11:54 AM |
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quote:
Originally posted by jacko
Don’t forget to fit netting to stop pigeons they love solar panels
G
Yep. I've just paid a bundle of money for a firm to clear out all the dove nests under my panels, and to fix wire mesh all around...
No way I was going to get on the roof to do it myself - I know my limitations!
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coyoteboy
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| posted on 15/1/24 at 10:46 AM |
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Mine are too close to the roof for them to get under.
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craig1410
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| posted on 17/1/24 at 06:43 PM |
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quote:
Originally posted by coyoteboy
Mine are too close to the roof for them to get under.
Same here - it's on a steel trapezoidal section roof so very minimal gap. Might still be a problem for smaller birds like swallows so might add
some bird protection before they start nesting but I doubt it'd be a problem.
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MarcV
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| posted on 23/1/24 at 08:44 PM |
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What is the slope of the roof?
For a flat roof you should consider that you'll generally end up with rows of panels. So you don't want too much slope on the panels as they
will stick up and cast a shadow over the next row. Especially in winter this is an issue and that is where you'll need the energy most.
As example I have just rotated a set of panels on our roof. Now I have one set facing SE, the other SW. Tilt is some 5 degrees, barely enough to keep
themselves clean. Anyway, when the sun is in SE, the SW panels make most energy as they don't have shadow of the other rows. In a little while
the sun will be high enough to make SE panels more efficient with SE sun.
Optimising for winter is hard on a flat roof. But depends on the area and orientation you have available. I wouldn't put panels any flatter than
5 degrees, water and dirt will remain on them.
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craig1410
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| posted on 24/1/24 at 12:51 PM |
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quote:
Originally posted by MarcV
What is the slope of the roof?
For a flat roof you should consider that you'll generally end up with rows of panels. So you don't want too much slope on the panels as they
will stick up and cast a shadow over the next row. Especially in winter this is an issue and that is where you'll need the energy most.
As example I have just rotated a set of panels on our roof. Now I have one set facing SE, the other SW. Tilt is some 5 degrees, barely enough to keep
themselves clean. Anyway, when the sun is in SE, the SW panels make most energy as they don't have shadow of the other rows. In a little while
the sun will be high enough to make SE panels more efficient with SE sun.
Optimising for winter is hard on a flat roof. But depends on the area and orientation you have available. I wouldn't put panels any flatter than
5 degrees, water and dirt will remain on them.
Hi, not sure if your question was directed at me but my roof is 14-15 degrees pitch so more than enough to keep the panels clean naturally. Here is a
photo:
 
PV Array
And one during the roof refurb (do you like our home made staircase to carry the 60Kg roof sheets into position  )
 
Description
I agree that tilting panels on a roof will require extra spacing between rows and this would certainly have caused me a problem since I didn't
have much spare room up the roof for that spacing. You need to stay away from the roof edges by 300-500mm to reduce wind loading and you don't
want your panels to be higher than the roof apex for planning permission reasons either.
I'm pretty lucky to have a due-south facing roof (actually it's 4 degrees west of south which is actually better according to the solar
prediction tool) and the pitch, although not idea, made the installation much easier than if it was a steeper pitch, and doesn't reduce
efficiency very much either. We didn't need to bother with scaffolding since as long as the roof was dry, it was pretty safe to walk around up
there as long as you take care near the edges and around the roof lights. My wife and I actually installed the entire roof on this building in the
summer last year as well as the solar panels so we're quite proud of ourselves! I was a bit nervous in recent days with the 70+MPH wind gusts
but so far all good. I did go around the bottom row of PV clamps with the torque wrench a few days ago just to check they were still tight (13NM)
which they were. I also used extra long screws (160mm) when installing the 80mm thick insulated roof panels, and added extra, "optional",
screws.
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