Solar Panels?

[Ambleton]

Tbh the whole this is baffling. The cost and price guarantee really doesn't seem to add up.

Here's January for example....



Even if you average it all out. £111.64/266.6kWh= =41.87p/kWh

The day standing rate is about 4p/day cheaper than the max, but it still doesn't add up

Edited by Ambleton on Saturday 18th February 08:56

[AW10]

It's almost as though you don't use enough night time electricity to bring the average rate paid per kWh down to the level of the cap?

Looking at the table at https://octopus.energy/blog/energy-price-cap-oct-2... they seem to use a roughly 60% day/40% night ratio to get to the weighted average figure whereas your use is more like 80/20.

Your night use is quite low - not sure why you're on that type of tariff?

[Flooble]

Ambleton said:

gazapc said:

You can use this tool to estimate your monthly production.
https://re.jrc.ec.europa.eu/pvg_tools/en/

I'm probably being dumb, is Azimuth essentially the direction the solar panels will be facing?

IE, the roof surface has a bearing of 109.7degs SSE.

If yes, then 180 should yeild the best result, but it appears that zero does, hence my confusion.

I ticked "optimise Azimuth" and it came out as -5 ...

I thought Azimuth would be the angle along the horizon, so same as you, starting from North would have thought 180 degrees, but I can't see how that can be the case given my result. Come to think of it, -5 doesn't make sense as a compass direction at all, it has to be from a reference point. So I think we'd need to know from where they are taking the Azimuth reference point (North or South?). This is probably obvious to an astronomer but has me confused. I'm guess about their Azimuth starts from North or South and is then the degrees from that point, so 180 and 0 point to the same place - just starting from a different point.

I could be totally wrong but that seems the only logical answer to me?

[Ambleton]

AW10 said:

It's almost as though you don't use enough night time electricity to bring the average rate paid per kWh down to the level of the cap?

Looking at the table at https://octopus.energy/blog/energy-price-cap-oct-2... they seem to use a roughly 60% day/40% night ratio to get to the weighted average figure whereas your use is more like 80/20.

Your night use is quite low - not sure why you're on that type of tariff?

I agree with you and last time I spoke to them they said that I was on the most economical tarriff according to my usage. Think it might be time to shop around...

[dmsims]

I use a two rate tariff and average unit rate was 19.3p for January

[Ambleton]

If I amortise the whole lot out

266.6kWh (total usage) × 34p (price cap) = 9064.4
31 days × 46p (standing rate cap) = 1426
Total bill should be = £104.90 (before tax)

This equates to an amortised cost of 39.348p/kWh

Octopus have actually charged £111.64, so the amortised cost per kWh is 41.875kWh

Which means, as you've spotted, it's actually costing us more on the dual rate tarriff.

[Jambo85]

Flooble said:

I ticked "optimise Azimuth" and it came out as -5 ...

I thought Azimuth would be the angle along the horizon, so same as you, starting from North would have thought 180 degrees, but I can't see how that can be the case given my result. Come to think of it, -5 doesn't make sense as a compass direction at all, it has to be from a reference point. So I think we'd need to know from where they are taking the Azimuth reference point (North or South?). This is probably obvious to an astronomer but has me confused. I'm guess about their Azimuth starts from North or South and is then the degrees from that point, so 180 and 0 point to the same place - just starting from a different point.

I could be totally wrong but that seems the only logical answer to me?

360 degrees in a circle though innit, so 0, 360 and -180 are the same.

That calculator is odd, south seems to be their zero which is unconventional to say the least.

[AW10]

Jambo85 said:

360 degrees in a circle though innit, so 0, 360 and -180 are the same.

That calculator is odd, south seems to be their zero which is unconventional to say the least.

??

0 and 360 are the same and 180 and -180 are the same?

If you click on azimuth the site tells you "The azimuth, or orientation, is the angle of the PV modules relative to the direction due South. -90° is East, 0° is South and 90° is West."

Edited by AW10 on Saturday 18th February 11:53

[gazapc]

Jambo85 said:

Flooble said:

I ticked "optimise Azimuth" and it came out as -5 ...

I thought Azimuth would be the angle along the horizon, so same as you, starting from North would have thought 180 degrees, but I can't see how that can be the case given my result. Come to think of it, -5 doesn't make sense as a compass direction at all, it has to be from a reference point. So I think we'd need to know from where they are taking the Azimuth reference point (North or South?). This is probably obvious to an astronomer but has me confused. I'm guess about their Azimuth starts from North or South and is then the degrees from that point, so 180 and 0 point to the same place - just starting from a different point.

I could be totally wrong but that seems the only logical answer to me?

360 degrees in a circle though innit, so 0, 360 and -180 are the same.

That calculator is odd, south seems to be their zero which is unconventional to say the least.

Having azimuth = 0 = south is common in PV software.
If you click 'Azimuth' it explains the definition.

The optimum azimuth not being south is explained because the sun does not reach its highest point at exactly south facing, it is slightly off.
You can check your location here https://www.sunearthtools.com/dp/tools/pos_sun.php...

Worth noting though azimuth makes very little difference to overall production at modest angles.
You can test this in the PVGIS tool as an example 4 kW system in Birmingham will produce only a few kWh more over an entire year at the supposed optimum -4 vs 0 degrees azimuth. So not worth worrying about.

Edited by gazapc on Saturday 18th February 13:14

[Ambleton]

Thanks all.

I've run the numbers on a spreadsheet properly this time.

Essentially in my location, on my roof, the panels would produce.

Month	actual usage in kWh	projected generated in kWh	delta in kWh
Jan	273	90	-183
Feb	273	130	-143
Mar	251	250	-1
Apr	238	350	+112
May	225	400	+175
Jun	217	400	+183
Jul	225	410	+185
Aug	238	360	+122
Sept	238	280	+42
Oct	260	180	-80
Nov	269	100	-169
Dec	282	75	-207
Totals	2990	3025	+35

Because of the timings. It means that I'd have to BUY ~783kWh FROM the grid and SELL ~818kWh TO the grid.

If I was to stay without solar panels then I'd change to a single rate electric. Currently that's 34p/kWh. So totalling £1016/annum.

If I was to get solar panels I'd stay on Economy7 with cheap overnight electric. This is 44p/kWh during the day and 17p/kWh at night. The feed in is about 15p/kWh.

If I sold my 818kWh to the grid at 15p/kWh that would net me about £123 over the year. If I bought 783kWh of energy from the grid say on a 50/50 split of day/night rates, the 783kWh would cost me circa £238.

This means the total annual cost of electric would be circa £116. Saving me £900/yr on my electricity bill. (At current prices)

Cost of the system is ~£10500/£900= 11.7yrs before it breaks even.





Now. That's assuming it all stays at the same prices. It doesn't take a huge amount for that to swing massively one way or the other.

For example IF energy went to 50p/kWh average on a flat rate
And 60p&20p on a day/night rate with a 20p feed in. Suddenly that break even point becomes less than 8yrs.

[OutInTheShed]

Ambleton said:

Thanks all.

I've run the numbers on a spreadsheet properly this time.

Essentially in my location, on my roof, the panels would produce.

Month	actual usage in kWh	projected generated in kWh	delta in kWh
Jan	273	90	-183
Feb	273	130	-143
Mar	251	250	-1
Apr	238	350	+112
May	225	400	+175
Jun	217	400	+183
Jul	225	410	+185
Aug	238	360	+122
Sept	238	280	+42
Oct	260	180	-80
Nov	269	100	-169
Dec	282	75	-207
Totals	2990	3025	+35

Because of the timings. It means that I'd have to BUY ~783kWh FROM the grid and SELL ~818kWh TO the grid.

If I was to stay without solar panels then I'd change to a single rate electric. Currently that's 34p/kWh. So totalling £1016/annum.

If I was to get solar panels I'd stay on Economy7 with cheap overnight electric. This is 44p/kWh during the day and 17p/kWh at night. The feed in is about 15p/kWh.

If I sold my 818kWh to the grid at 15p/kWh that would net me about £123 over the year. If I bought 783kWh of energy from the grid say on a 50/50 split of day/night rates, the 783kWh would cost me circa £238.

This means the total annual cost of electric would be circa £116. Saving me £900/yr on my electricity bill. (At current prices)

Cost of the system is ~£10500/£900= 11.7yrs before it breaks even.





Now. That's assuming it all stays at the same prices. It doesn't take a huge amount for that to swing massively one way or the other.

For example IF energy went to 50p/kWh average on a flat rate
And 60p&20p on a day/night rate with a 20p feed in. Suddenly that break even point becomes less than 8yrs.

I think you have to look in more detail.

Even in Summer, you will need electricity from the grid, to run your fridge at night.
You can avoid that with a battery.

But even with a battery, there will be months where you both import and export, because you get a few cloudy days followed by a few rainy days.
with a bigger battery, you might reduce that.

[Jambo85]

AW10 said:

Jambo85 said:

360 degrees in a circle though innit, so 0, 360 and -180 are the same.

That calculator is odd, south seems to be their zero which is unconventional to say the least.

??

0 and 360 are the same and 180 and -180 are the same?

If you click on azimuth the site tells you "The azimuth, or orientation, is the angle of the PV modules relative to the direction due South. -90° is East, 0° is South and 90° is West."

Edited by AW10 on Saturday 18th February 11:53

Right you are, I think that is what I was trying to write.

Using south as zero is baffling, you’d be looking for a new job if you did that in my line of work.

[pingu393]

Ambleton said:

Currently my electricity is...

44.17p/kWh daytime rate
16.61p/kWh night time rate
Octopus Outgoing is 15p/kWh on fixed at the moment.

Edited by Ambleton on Saturday 18th February 08:39

Unless >47% of your consumption is at night, you should get off E7 and onto the "normal" rate.

Also, I suggest that you join the queue for Octopus Tracker.

[pingu393]

There are other things. Like boiling a kettle. Even on a very bright day, you cannot boil a normal kettle for free, as the solar won't produce 2200W. You will probably be importing >500W during the boil. I bought a cheap 850W kettle. It takes about three to four times longer to boil the water, but it is free.

You actually want to minimise the amount that you export to the grid. You want to use all the power that your panels generate, but you can't unless you have a battery.


Imagine your panels are generating 1200W (not unreasonable for a bright winter's day) and you run a 2200W tumble dryer on a 120 minute cycle. You will import 1000W for two hours at 34p per kWh. That cost 68p.

If you exported during the sunshine and run the tumble dryer at night, you would have exported 1200W for two hours and been paid 36p. Running the tumble dryer when it's dark will cost £1.50. It costs £1.14 to dry your clothes at night, or 68p to dry them during the day.

No matter the numbers. As long as your panels are generating, you should be using the power, not selling it. Ideally, you should only sell what you CANNOT use.

[OutInTheShed]

pingu393 said:

There are other things. Like boiling a kettle. Even on a very bright day, you cannot boil a normal kettle for free, as the solar won't produce 2200W. You will probably be importing >500W during the boil. I bought a cheap 850W kettle. It takes about three to four times longer to boil the water, but it is free.

You actually want to minimise the amount that you export to the grid. You want to use all the power that your panels generate, but you can't unless you have a battery.


Imagine your panels are generating 1200W (not unreasonable for a bright winter's day) and you run a 2200W tumble dryer on a 120 minute cycle. You will import 1000W for two hours at 34p per kWh. That cost 68p.

If you exported during the sunshine and run the tumble dryer at night, you would have exported 1200W for two hours and been paid 36p. Running the tumble dryer when it's dark will cost £1.50. It costs £1.14 to dry your clothes at night, or 68p to dry them during the day.

No matter the numbers. As long as your panels are generating, you should be using the power, not selling it. Ideally, you should only sell what you CANNOT use.

I've known people get too obsessed with 'using everything they generate'.

You should dry your clothes when it's convenient and go and do something nice on a sunny day.
Or, if you're at home on a sunny day, put your washing on the line!

[jrb43]

OutInTheShed said:

I've known people get too obsessed with 'using everything they generate'.

You should dry your clothes when it's convenient and go and do something nice on a sunny day.
Or, if you're at home on a sunny day, put your washing on the line!

This. Otherwise we've regressed as a civilisation to the point just before fire was invented and all daily activities were governed by the position of the sun?

[TriumphStag3.0V8]

pingu393 said:

I was told that if you get a battery that isn't a Tesla, you will only be able to store energy. You won't be able to export to the grid. Any excess will just be wasted. Tesla batteries cost almost twice other batteries, and have a 12 month lead time.

You were told wrong. With a battery (any battery) you store the electricity that would otherwise have been exported to the grid. Once the battery is full, if the electricity will then go to the grid unless it has somewhere else to go:
For example - mine sends any excess production to the battery, then to an electric car charger (I don't have an EV but did have the charge point installed for future use), and then to an immersion heater controller, so once the battery is full, and the car is full, and the hot water is at temperature, then it will export to the grid.

One thing the Tesla powerwall does permit (at least certain models of it) is for the house to remain powered in the event of a power cut - the electricity companies do not like people putting 240v back down the wires whilst engineers might be working on them (!). So most systems cut off if the house power goes. The Tesla has a switching capability built in which allows the house to be isolated from the grid to stay live. I believe this type of system needs specific notification/approvals.

[pingu393]

TriumphStag3.0V8 said:

pingu393 said:

I was told that if you get a battery that isn't a Tesla, you will only be able to store energy. You won't be able to export to the grid. Any excess will just be wasted. Tesla batteries cost almost twice other batteries, and have a 12 month lead time.

You were told wrong. With a battery (any battery) you store the electricity that would otherwise have been exported to the grid. Once the battery is full, if the electricity will then go to the grid unless it has somewhere else to go:
For example - mine sends any excess production to the battery, then to an electric car charger (I don't have an EV but did have the charge point installed for future use), and then to an immersion heater controller, so once the battery is full, and the car is full, and the hot water is at temperature, then it will export to the grid.

One thing the Tesla powerwall does permit (at least certain models of it) is for the house to remain powered in the event of a power cut - the electricity companies do not like people putting 240v back down the wires whilst engineers might be working on them (!). So most systems cut off if the house power goes. The Tesla has a switching capability built in which allows the house to be isolated from the grid to stay live. I believe this type of system needs specific notification/approvals.

The alternatives that I was given were Solax or Tesla. I was told that Solax couldn't export to the grid. I may have misunderstood.

[Jambo85]

pingu393 said:

TriumphStag3.0V8 said:

pingu393 said:

I was told that if you get a battery that isn't a Tesla, you will only be able to store energy. You won't be able to export to the grid. Any excess will just be wasted. Tesla batteries cost almost twice other batteries, and have a 12 month lead time.

You were told wrong. With a battery (any battery) you store the electricity that would otherwise have been exported to the grid. Once the battery is full, if the electricity will then go to the grid unless it has somewhere else to go:
For example - mine sends any excess production to the battery, then to an electric car charger (I don't have an EV but did have the charge point installed for future use), and then to an immersion heater controller, so once the battery is full, and the car is full, and the hot water is at temperature, then it will export to the grid.

One thing the Tesla powerwall does permit (at least certain models of it) is for the house to remain powered in the event of a power cut - the electricity companies do not like people putting 240v back down the wires whilst engineers might be working on them (!). So most systems cut off if the house power goes. The Tesla has a switching capability built in which allows the house to be isolated from the grid to stay live. I believe this type of system needs specific notification/approvals.

The alternatives that I was given were Solax or Tesla. I was told that Solax couldn't export to the grid. I may have misunderstood.

I think TS misunderstood your post.

[TriumphStag3.0V8]

Deleted as subsequent discussion on here rendered it moot

Edited by TriumphStag3.0V8 on Saturday 18th February 19:23