More panels or better controller- or both

[Mike800966]

I presently have an 80w panel and 110Ah battery and we struggle a bit unlesss the sunshine is really good. I notice that the PWM controller isnt very good at low levels but as the current increases above about 1 amp, it works fine.
So if I want to worry less about battery voltage ( TV, water pump etc) what would give me the biggest step up, more panel- which seems to be cheapest, or more battery- I really dont want the extra weight in Lead acid?
Thanks in advance
Mike & Ann

 

[Mixyblob]

To be honest a 80w panel is a somewhat miniscule by todays standards. Swapping your PWR for a MPPT controller would increase the output efficiency of your panel. Adding another battery without doing anything else would be like getting a bigger bath but filling it with the same trickle of water.

 

[Raul]

A 150w solar with a 15A mppt controller will vastly improve your situation keeping the same battery.

 

[Mike800966]

Thanks Raul, that is my thought .
I am surprised at how panels have come down in price ( the 80w cost £400) in 2008!.
A second panel seems to be the cheapest way forward and a controller upgrade , but they do seem fancy prices.
Presume the two panels just connect in parallel ? Do the blocking diodes mean that voltages don't have to be identical?
Mike

 

[Lenny HB]

Unless you are only doing summer camping a second battery is the best first option followed by more solar together with a MPPT controller.

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[Raul]

To be honest, with the 110ah battery you could have as much as 315w of solar. That will give you a C/5 charge rate at the absorption voltage. Any more, then you could say you are over panelled, and more battery storage is needed. As it stands for the 110ah battery, a 150w solar will barely meet a modest C/10 rate in summer only.
If a minimum spend is priority, then upgrading the solar is most cost effective at this stage. Any further upgrades on storage, can be considered if solar proves to be not enough.

 

[the1andonly]

If a minimum spend is priority, then upgrading the solar is most cost effective at this stage. Any further upgrades on storage, can be considered if solar proves to be not enough.

I agree. But add
I once went against what was the favoured option , put up more panels. No room for more panels on a bongo so i changed controller for a cheap Chinese mppt (beware many advertised as mppt are not) there are YouTube videos that show you how to test then i could run my compressor fridge on 100w panel. Whereas with the pwm controller the battery was being hammered. The next step add another panel.
If min spending is not a priority and space is available look for a 250 to 350w domestic panel but this would require an upgrade to the mppt controller eg votronics or victron Due to voltage requirements (now at top end of game).
If you want to concider going down this route Raul knows his stuff. But youre now in the realms of whats another £100 for another battery. Its too easy to spend money solving a problem that might not be there.

 

[autorouter]

Presume the two panels just connect in parallel ? Do the blocking diodes mean that voltages don't have to be identical?

Connecting two panels in parallel will make the voltages identical - that's what parallel means. Ideally they would both have the same or very similar Peak Power Voltage - look for that in the spec sheet: Vmp, not Voc. The MPPT will maximise the power from the pair of them, but If they are not very similar, one or both of them will not be working at peak power.

 

[Abacist]

The base van and it’s wiring and your type of use will also have a bearing as if it has decent set up your split charge relay will also be charging when driving.

Abroad in full sun I don’t think you can go wrong with roughly the same wattage of solar panels as amp hours of batteries though in the UK you probably need 50% more solar.

VanBitz fitted us with 2 130 watt panels for our 2 110 amp batteries. I have since changed the batteries to 2 180 amp Varta sealed lead acid and that is fine abroad but I feel a bit under panelled at home.

 

[Mike800966]

Connecting two panels in parallel will make the voltages identical - that's what parallel means. Ideally they would both have the same or very similar Peak Power Voltage - look for that in the spec sheet: Vmp, not Voc. The MPPT will maximise the power from the pair of them, but If they are not very similar, one or both of them will not be working at peak power.

Thanks Autorouter, I imagined it might be like dissimilar batteries when they "chase " each other slowly downward. I dont know the spec for the existing panel.
How can I find out ?, can measure Voc easily but not V maxpwr?
No, I am not going to replace the old panel!
Thanks also to Raul, great advice
Mike

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[JJ]

Solar panels are like cold beers in the fridge...

...you can't have too many.


JJ

 

[autorouter]

How can I find out ?, can measure Voc easily but not V maxpwr?

The easiest way is to connect up an MPPT controller, put it in bright sunlight, and measure the voltage - either from the MPPT display or a meter.