Solar....how much wattage is enough

[Alan de Enfield]

17 minutes ago, Richard10002 said:

I’m no expert  What would be a more reasonable assumption for estimating and specifying?

I seem to be fairly close with my 'estimations' of 

Spring 3 months 25% of rated for 8 hours per day

Summer 3 months 50% of rated for 12 hours per day

Autumn 3 months 25% of rated for 8 hours per day

Winter 5-10% of rated. 6 hours per day

 

Rain, clouds, trees /shadows, temperature, angles, etc all affect the output.

There are so many variables it is impossible to give definitive figures but my Controller's figure tend to be slightly higher than my estimates so I am on the 'safe-side'.

[Nightwatch]

Cheack lowenergysupermarket. (Whatever). 

I have 'finally' got some cable and connectors from Bimble. Took ages to get here and blow me, one of the connectors is broken. Superbly packed so may have been broken before despatch.

 

Bimble okay, but indeed not the best experience I have had.

 

martyn

Www.lowenergysupermarket.com

[MtB]

20 hours ago, Nightwatch said:

Cheack lowenergysupermarket. (Whatever). 

I have 'finally' got some cable and connectors from Bimble. Took ages to get here and blow me, one of the connectors is broken. Superbly packed so may have been broken before despatch.

 

Bimble okay, but indeed not the best experience I have had.

 

martyn

Www.lowenergysupermarket.com

 

I’ve found the same. Twice now I’ve bought panels described as coming with flyleads terminated with MC4 connectors, only to have them arrive with no flyleads at all. Not a big deal to me as I have a stock of cable and MC4 connectors but could have been REALLY inconvenient had I needed them to be plug and play. 

 

The second time I emailed complaining but got no reply. 

 

 

Edited May 20, 2018 by Mike the Boilerman
spellin'

[Nightwatch]

I was going to write and have a moan but when it took them ages to even send the goods, I wrote and didn't get a response.

[magictime]

I've just been looking at the Onboard Solar site, and part of their sales pitch is this:

 

"Importantly, these panels are rated at 165W with an output of 18V giving an output of 9.5 amps. Many suppliers use "domestic" spec panels. These are much bulkier and output typically 250W (which sounds much higher doesn't it?). However, they output at a much higher voltage - typically 48V so their actual current output is 5.2 amps. Be aware that in 12V or low voltage applications, AMPS are key not watts and AMPS are arrived at by taking WATTS and dividing by VOLTS."

 

Now if that's right - and somebody on here will soon pipe up if it's not! - that suggests that even asking the question in terms of watts is pretty misguided (because 500W of high-voltage panels, say, might actually do a poorer job of charging the batteries than 250W of low-voltage panels).

[Dr Bob]

24 minutes ago, magictime said:

I've just been looking at the Onboard Solar site, and part of their sales pitch is this:

 

"Importantly, these panels are rated at 165W with an output of 18V giving an output of 9.5 amps. Many suppliers use "domestic" spec panels. These are much bulkier and output typically 250W (which sounds much higher doesn't it?). However, they output at a much higher voltage - typically 48V so their actual current output is 5.2 amps. Be aware that in 12V or low voltage applications, AMPS are key not watts and AMPS are arrived at by taking WATTS and dividing by VOLTS."

 

Now if that's right - and somebody on here will soon pipe up if it's not! - that suggests that even asking the question in terms of watts is pretty misguided (because 500W of high-voltage panels, say, might actually do a poorer job of charging the batteries than 250W of low-voltage panels).

I read that as well when buying ours. Simple answer, just buy the 18-20V panels.

[rusty69]

2 minutes ago, Dr Bob said:

I read that as well when buying ours. Simple answer, just buy the 18-20V panels.

I read it too. Didn't understand its meaning 

Edited May 20, 2018 by rusty69

[Tony Brooks]

It probably has some validity if they are using a PWM controller but I can't see it now MPPT are so available. Either the site has not been updated or it could be a company to avoid because their expertise must be in question.

 

When adding to a existing array its probably better to try to match the panels maximum voltage to those you already have so mixing nominal 12V panels with domestic ones is probably not a recipe for maximising output.

[Sea Dog]

Hmm, so if the 250w panels operated at 5kV (theory chaps, theory!) there'd be negligible current hence they'd not be producing anything?  Someone tell the National Grid!  

[rusty69]

1 minute ago, Tony Brooks said:

It probably has some validity if they are using a PWM controller but I can't see it now MPPT are so available. Either the site has not been updated or it could be a company to avoid because their expertise must be in question.

 

When adding to a existing array its probably better to try to match the panels maximum voltage to those you already have so mixing nominal 12V panels with domestic ones is probably not a recipe for maximising output.

It could be. They seem to think mppt is not a typical system :

 

" We use the best available computer controlled MPPT controller. This allows panels to run at the full output voltage and thus boosts output further. We can get around a 30% uplift on a typical system" 

[rusty69]

6 minutes ago, Sea Dog said:

Hmm, so if the 250w panels operated at 5kV (theory chaps, theory!) there'd be negligible current hence they'd not be producing anything?  Someone tell the National Grid!  

Think how small the cable could be

[frahkn]

10 minutes ago, Tony Brooks said:

It probably has some validity if they are using a PWM controller but I can't see it now MPPT are so available. Either the site has not been updated or it could be a company to avoid because their expertise must be in question.

 

When adding to a existing array its probably better to try to match the panels maximum voltage to those you already have so mixing nominal 12V panels with domestic ones is probably not a recipe for maximising output.

They fitted some panels and an MPPT controller for me about 5 years ago. I've had no problems with the installation. The guy plays bass guitar but I don't hold that against him.

[magictime]

49 minutes ago, Dr Bob said:

I read that as well when buying ours. Simple answer, just buy the 18-20V panels.

Well, yes, that is the simple answer (and the point they're making), but if the issue hadn't been on the OP's radar it seemed worth raising. A quick Google does indeed reveal that even some of the flexible panels being marketed specifically for narrow boat roofs are indeed 46v.

 

45 minutes ago, Tony Brooks said:

It probably has some validity if they are using a PWM controller but I can't see it now MPPT are so available. Either the site has not been updated or it could be a company to avoid because their expertise must be in question.

 

When adding to a existing array its probably better to try to match the panels maximum voltage to those you already have so mixing nominal 12V panels with domestic ones is probably not a recipe for maximising output.

Excuse my ignorance, but could you offer a layman's explanation of how an MPPT controller negates the concern?

 

I'm not sure I'd question the company's expertise so much as their honesty in making out that something is an issue when they know that, with the right controller, it isn't.

[Alan de Enfield]

1 hour ago, magictime said:

"Importantly, these panels are rated at 165W with an output of 18V giving an output of 9.5 amps. Many suppliers use "domestic" spec panels. These are much bulkier and output typically 250W (which sounds much higher doesn't it?). However, they output at a much higher voltage - typically 48V so their actual current output is 5.2 amps. Be aware that in 12V or low voltage applications, AMPS are key not watts and AMPS are arrived at by taking WATTS and dividing by VOLTS."

But, but, but

Isn't the function of an MPPT controller to takes those "5.2 amps at 48v" and convert them to "20 amps at 12v" (number approximate for easy maths)

 

My 170w solar panel outputs (typically at 90-100 volts) so in 'theory' I should be getting 1.7amps - BUT I am getting 10.8 amps at 14.6 volts going into the batteries

That's what's important to me - a "smiley battery"

 

Sounds like a company with limited knowledge and one to avoid - maybe he should stick to playing guitar.

 

 

[MtB]

3 minutes ago, Alan de Enfield said:

ut, but, but

Isn't the function of an MPPT controller to takes those "5.2 amps at 48v" and convert them to "20 amps at 12v" (number approximate for easy maths)

 

 

Exactly right.

 

So the On Board Solar statement that current is the only panel specification that counts, is plain wrong. 

[rusty69]

4 minutes ago, magictime said:

A quick Google does indeed reveal that even some of the flexible panels being marketed specifically for narrow boat roofs are indeed 46v

Pretty sure my 4 x 250W non boaty panels(3 in series) are rated at 43V open circuit, so over 100V in series.

[Robbo]

1 hour ago, magictime said:

I've just been looking at the Onboard Solar site, and part of their sales pitch is this:

 

"Importantly, these panels are rated at 165W with an output of 18V giving an output of 9.5 amps. Many suppliers use "domestic" spec panels. These are much bulkier and output typically 250W (which sounds much higher doesn't it?). However, they output at a much higher voltage - typically 48V so their actual current output is 5.2 amps. Be aware that in 12V or low voltage applications, AMPS are key not watts and AMPS are arrived at by taking WATTS and dividing by VOLTS."

 

Now if that's right - and somebody on here will soon pipe up if it's not! - that suggests that even asking the question in terms of watts is pretty misguided (because 500W of high-voltage panels, say, might actually do a poorer job of charging the batteries than 250W of low-voltage panels).

This site explains it better; https://www.solar-electric.com/learning-center/batteries-and-charging/mppt-solar-charge-controllers.html

[MtB]

4 minutes ago, rusty69 said:

Pretty sure my 4 x 250W non boaty panels(3 in series) are rated at 43V open circuit, so over 100V in series.

 

And in poor light conditions e.g. winter, it is better to string your panels together in series as this adds together the (low) voltage each panel is giving, and sometimes you'll get more output than if they are in series. 

[reg]

16 minutes ago, Mike the Boilerman said:

 

And in poor light conditions e.g. winter, it is better to string your panels together in series as this adds together the (low) voltage each panel is giving, and sometimes you'll get more output than if they are in series. 

Perfect summary

I wire mine for winter usage ensuring they are wired for a high voltage and low amps through an mppt controller. that way I have a chance of obtaining a charging voltage in low light conditions. 

No point wiring for higher amps if you can't reach a charging voltage. 

Might only get an amp or 2 in winter but that beats no amps

 

Alan's picture ^^^ perfectly shows the advantage of an mppt controller 1.6a entering the controller and 10.8a going out. 

Edited May 20, 2018 by reg

[Alan de Enfield]

14 minutes ago, reg said:

Alan's picture ^^^ perfectly shows the advantage of an mppt controller 1.6a entering the controller and 10.8a going out. 

And another in slightly better focus :

This was 18/2/2018 

(0.5a 'in' and 3.3a 'out', worth having even for a short time)

Edited May 20, 2018 by Alan de Enfield

[MtB]

9 minutes ago, Alan de Enfield said:

This was 18/2/2018 

(0.5a 'in' and 3.3a 'out', worth having even for a short time)

 

Blimey was that on a sunny day? 

 

On a typical dull day in Feb my 560w all in series are more likely to deliver 0.2A or 0.3A out (into 24v).

 

Then when April arrives its like a switch. Wham, 15A until charged, then it starts equalising with the surplus power!

 

 

Edited May 20, 2018 by Mike the Boilerman

[Alan de Enfield]

2 minutes ago, Mike the Boilerman said:

Blimey was that on a sunny day? 

A sunny few minutes between rain and clouds - just happened to be looking and thought 'WOW' getting some juice in Feb !!!!

[reg]

Out of fairness Just been reading the on board solar site and can sort of understand what he is saying for the way he is supplying and installing his panels . He has chosen, for reasons he explains, to make up his systems by stringing together a number of smaller sized panels. 

My controller has a max of 150v (using rounded figures in this example) so I could use a max of 3 panels of my specification 38v and 4a

However he would be able to string together a max 8 panels at 9.5a 

So I can see his logic from his point of view and for his method of installation. 

In general I, as stated in previous post, chose to go the other route of high voltage lower amps. 

 

Complete aside

Any body else after first installing their system sat on the step  cup of coffee in hand (other drinks are available), just staring at the mt50 output? 

I didn't because I'm not that sad?

Edited May 20, 2018 by reg

[Alan de Enfield]

5 minutes ago, reg said:

Just been reading the on board solar site and can sort of understand what he is saying for the way he is supplying and installing his panels . He has chosen, for reasons he explains, to make up his systems by stringing together a number of smaller sized panels. 

My controller has a max of 150v (using rounded figures in this example) so I could use 3 panels of my specification 36v and 4a

However he would be able to string together 8 panels at 9.5a 

So I can see his logic from his point of view and for his method of installation. 

In general I, as stated in previous post, chose to go the other route of high voltage lower amps. 

There are several videos on you-tube explaining the pros & cons of connecting in series vs parallel.

 

[rusty69]

3 minutes ago, Alan de Enfield said:

There are several videos on you-tube explaining the pros & cons of connecting in series vs parallel.

 

Wot about series-parrallel?