Solar - hypothetical question...

[robtheplod]

Not sure if this is answerable, but if i had 1000W of solar (4 x 250w) made up of 4 panels lying flat what would be the most i could realistically expect from it?  im looking at controllers (Victron), but there is a huge difference in price so thought if i can find out real world figures, or roughly real world, then i might not need the larger one.......  hope that makes sense?   

thanks!

rob

[IanD]

8 minutes ago, robtheplod said:

Not sure if this is answerable, but if i had 1000W of solar (4 x 250w) made up of 4 panels lying flat what would be the most i could realistically expect from it?  im looking at controllers (Victron), but there is a huge difference in price so thought if i can find out real world figures, or roughly real world, then i might not need the larger one.......  hope that makes sense?   

thanks!

rob

About 3.5kWh/day average in midsummer, about 0.5kWh/day average in midwinter.

 

Go here and enter your information (use "off-grid"), it will tell you everything you need to know 🙂

 

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#api_5.2

 

You can also look at what happens if you have tilted panels (south-facing!) -- considerably more output in winter (maximum at about 60 degree tilt!), a bit more in summer (about 30 degree tilt), but only if the boat is moored E-W...

Edited December 6, 2022 by IanD

[rusty69]

Are you after the maximum current likely so that you can size an MPPT controller? 

 

I have 4 x 250W panels connected 2x2 in series through two separate 30A controllers. The panels are flat mounted . I reckon the biggest number I saw this year was 25 A into each, so 50A total, which is a bit disappointing for what should be achievable (more like 80A).

 

ETA. For clarity, this was in summer when the panels were at their warmest. I don't tend to monitor the output in the colder months.

Edited December 6, 2022 by rusty69

[Alan de Enfield]

Presumably you are looking at the highest current you can expect in order to buy a smaller / cheaper controller.

 

The worst day will be a sub-zero temperature, bright sunny cloudless day in February. 

 

It is best to work on the maximum you'll get rather than an 'average'

[nicknorman]

1 minute ago, rusty69 said:

Are you after the maximum current likely so that you can size an MPPT controller? 

 

I have 4 x 250W panels connected 2x2 in series through two separate 30A controllers. The panels are flat mounted . I reckon the biggest number I saw this year was 25 A into each, so 50A total, which is a bit disappointing for what should be achievable (more like 80A).

You say ”into”. Do you mean the current into the controller from the panels, or the current from the controllers into the batteries?

 

Back to the OP, the nature of the sun (how clear the atmosphere in the way is) and the temperature, make quite a big difference. Full sun with crystal clear skies on day with a cool airmass will give quite a bit more than blazing hot sun on a hot and hazy day. Under ideal conditions even in the UK I think you could get close to the full 1kw which would amount to around 70A, but then again ideal days don’t come around that often.

[robtheplod]

Yes, looking at Victron the Smart 100/50 was my first thought but the max wattage is 700w so allow 30% over (as they allow apparently?) thats 910w before damage?

[rusty69]

1 minute ago, nicknorman said:

You say ”into”. Do you mean the current into the controller from the panels, or the current from the controllers into the batteries?

 

Back to the OP, the nature of the sun (how clear the atmosphere in the way is) and the temperature, make quite a big difference. Full sun with crystal clear skies on day with a cool airmass will give quite a bit more than blazing hot sun on a hot and hazy day. Under ideal conditions even in the UK I think you could get close to the full 1kw which would amount to around 70A, but then again ideal days don’t come around that often.

Current into the batteries.

[Tony Brooks]

4 minutes ago, Alan de Enfield said:

Presumably you are looking at the highest current you can expect in order to buy a smaller / cheaper controller.

 

The worst day will be a sub-zero temperature, bright sunny cloudless day in February. 

 

It is best to work on the maximum you'll get rather than an 'average'

 

And a decent MPPT controller will just clip the maximum current to its rated maximum if the panels produce more. Just don't exceed the controller rated voltage.

[IanD]

6 minutes ago, robtheplod said:

Yes, looking at Victron the Smart 100/50 was my first thought but the max wattage is 700w so allow 30% over (as they allow apparently?) thats 910w before damage?

Be careful, it's usually the output current that sets the MPPT power limit, not the incoming power. If you want to be able to convert the entire output of a 1kWp panel in bright sun in midsummer, you need a big enough MPPT controller.

 

Try entering your panels here and see what MPPT is recommended:

 

https://www.victronenergy.com/mppt-calculator

 

For 2S2P 250W I suspect you'll need a BlueSolar or SmartSolar 150/60, which are not cheap...

Edited December 6, 2022 by IanD

[TheBiscuits]

11 minutes ago, rusty69 said:

I have 4 x 250W panels connected 2x2 in series through two separate 30A controllers. The panels are flat mounted . I reckon the biggest number I saw this year was 25 A into each, so 50A total, which is a bit disappointing for what should be achievable (more like 80A).

 

Why would you expect 80A from 2 x 30A controllers?  60A would be the maximum, shirley?

[rusty69]

Just now, TheBiscuits said:

 

Why would you expect 80A from 2 x 30A controllers?  60A would be the maximum, shirley?

Yes indeed. But as they never neared 60A, I was never gonna see 80A even if I had two 40A controllers.

[robtheplod]

9 minutes ago, IanD said:

Be careful, it's usually the output current that sets the MPPT power limit, not the incoming power. If you want to be able to convert the entire output of a 1kWp panel in bright sun in midsummer, you need a big enough MPPT controller.

 

Try entering your panels here and see what MPPT is recommended:

 

https://www.victronenergy.com/mppt-calculator

 

For 2S2P 250W I suspect you'll need a BlueSolar or SmartSolar 150/60, which are not cheap...

thanks, i did look at that and used their spreadsheet and came up with this result. i was a little concerned by exceeding the 30%...... but it still says valid, which then makes me think the controller might restrict things on a good day?

 

[IanD]

10 minutes ago, robtheplod said:

thanks, i did look at that and used their spreadsheet and came up with this result. i was a little concerned by exceeding the 30%...... but it still says valid, which then makes me think the controller might restrict things on a good day?

 

 

It just seems a false economy to me to undersize the MPPT controller, because especially in summer quite a lot of the total energy yield comes from the times when there's a lot of sun.

[nicknorman]

13 minutes ago, robtheplod said:

thanks, i did look at that and used their spreadsheet and came up with this result. i was a little concerned by exceeding the 30%...... but it still says valid, which then makes me think the controller might restrict things on a good day?

 

If you change the controller to a bigger one, it will show you the max possible current.

[robtheplod]

Going up in range (and price!)... the 60amp one:

 

and the 70amp one:

 

So it all seems to hinge on max output current of the controller?     is 60 or 70 nearer realistic figures or do both still restrict?  (Guessing as in yellow they may)..

Edited December 6, 2022 by robtheplod

[rusty69]

7 minutes ago, IanD said:

 

It just seems a false economy to me to undersize the MPPT controller, because especially in summer quite a lot of the total energy yield comes from the times when there's a lot of sun.

Works for me. As long as I have fully charged batteries by the end of the day, it makes little difference. They don't even need to be fully charged.Mine are charged by lunchtime most days anyway, and that's on solar alone. Chuck in some engine running, it would be even sooner. I do however have lithium batteries, so the situation may not be quite as good with lead acid batteries.

 

As for false economy, I suppose it depends how deep your pockets are. I guess it would be for you. Are you not the guy who has spent over 100K on a narrowboat?

[IanD]

4 minutes ago, rusty69 said:

Works for me. As long as I have fully charged batteries by the end of the day, it makes little difference. They don't even need to be fully charged.Mine are charged by lunchtime most days anyway, and that's on solar alone. Chuck in some engine running, it would be even sooner. I do however have lithium batteries, so the situation may not be quite as good with lead acid batteries.

 

As for false economy, I suppose it depends how deep your pockets are. I guess it would be for you. Are you not the guy who has spent over 100K on a narrowboat?

Yes, but I fail to see the relevance of this here -- and please leave out the personal digs, I'm getting fed up with them.

 

If you've spent money on buying and mounting 1000W of panels and install an MPPT controller that limits the output, you've wasted some of that money. That should bother anybody, regardless of how deep their pockets are.

 

If the panels are providing more output than the OP needs in summer, it could well be cheaper to use smaller panels and a bigger MPPT controller that doesn't limit the output. Most PV systems are designed this way for precisely that reason... 😉

Edited December 6, 2022 by IanD

[rusty69]

1 minute ago, IanD said:

Yes, but I fail to see the relevance of this here -- and please leave out the personal digs, I'm getting fed up with them.

 

If you've spent money on buying and mounting 1000W of panels and install an MPPT controller that limits the output, you've wasted some of that money. That should bother anybody, regardless of how deep their pockets are.

It was not a personal dig, it was a reference to your 'false economy' comment, but as this is the second time you have accused me of this, I shall bother you no more.

[robtheplod]

1 minute ago, IanD said:

If you've spent money on buying and mounting 1000W of panels and install an MPPT controller that limits the output, you've wasted some of that money. That should bother anybody, regardless of how deep their pockets are.

yes agree fully.. I'm trying to get the best controller for this setup but each model steps up in quite big steps so just see 'what i can get away with' basically..

[Alan de Enfield]

But - it is Winter time when you are potentially going to get the highest current (not Summer time). 

 

It is also Winter time when you need every amp you can get so why scrimp on equipment so it actually limits the current ?

 

Doesn't make sense.

[IanD]

5 minutes ago, rusty69 said:

It was not a personal dig, it was a reference to your 'false economy' comment, but as this is the second time you have accused me of this, I shall bother you no more.

"False economy" means doing something which you think will save money, but turns out not to -- according to the dictionary, not me 🙂

 

Bigger panels and an undersized MPPT controller is likely to be exactly that.

 

5 minutes ago, robtheplod said:

yes agree fully.. I'm trying to get the best controller for this setup but each model steps up in quite big steps so just see 'what i can get away with' basically..

An undersized controller will mean less output in sunny conditions -- if you're happy with this (e.g 1000W/3.5kWh/day is more than you need) then that's OK if you already have the panels.

 

If you're buying everything to build the system and have a fixed budget, the best solution is normally to have an MPPT controller that doesn't limit the maximum power.

Edited December 6, 2022 by IanD

[rusty69]

4 minutes ago, Alan de Enfield said:

But - it is Winter time when you are potentially going to get the highest current (not Summer time). 

 

It is also Winter time when you need every amp you can get so why scrimp on equipment so it actually limits the current ?

 

Doesn't make sense.

That would depend on whether you rely on the solar in the winter or not. Personally, I do not. Maybe the OP does.

[IanD]

6 minutes ago, Alan de Enfield said:

But - it is Winter time when you are potentially going to get the highest current (not Summer time). 

 

It is also Winter time when you need every amp you can get so why scrimp on equipment so it actually limits the current ?

 

Doesn't make sense.

The MPPT controller will never limit the output in winter because there isn't enough sunlight to get the panels anywhere near peak power, it'll only limit it in summer.

Edited December 6, 2022 by IanD

[robtheplod]

nothing is purchased. just trying to get opinions on what i can expect to get with 1000w solar, which Ian sorted thanks. Not looking to scrimp on the setup but no point getting anything bigger than required...  i have some Yorkshire in me!! 

 

the setup with be throughout the year, all going well but had a diagnosis which may scupper things..

[Alan de Enfield]

4 minutes ago, IanD said:

The MPPT controller will never limit the output in winter because there isn't enough sunlight to get the panels anywhere near peak power, it'll only limit it in summer.

 

 

Maybe in your theoretical world it won't but in the real world February is the only time I have ever had 100% output of my panels - allbeit for a short period.

If I had an undersized MPPT it would have capped the current.

My MPPT is matched to the panel 100% output so it allowed every amp into the batteries.