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Yes ,we all have this problem when the days get darker and we need more power . Having researched a bit i m begining to wonder if we are all fitting the appropriate panels to best do the job and suit our needs in a motorhome....
Technology undoubtably moves on , yet we still fit the 12v panels we started with in yesteryear and i m wondering why as they dont meet our needs for reasons above....
I ve noticed some of the 30a auto12v /24v solar regulators now have a 50v input for the solar panels....
I take it from that , i can couple up to a 50v panel and the regulator drops the voltage to charge at the correct voltage for 12v and also does all the usual charging features....
I m wondering if there would be an advantage to using the higher voltage panels to solve the low light level charge ?
Basically if you feed in a 36v panel to a charge regulator that can deal with it (as above) and everything works well in bright sunlight... when the days dull and the voltage produced and fed in drops by 20%.... you still have a voltage entering the regulator of 29v that will produce a charge ....
It's not about volts, it's about power. The solar technology dictates how much power you can get from sunlight.
If you do use a higher voltage panel (and I know nothing about them), it means that the regulator will have to work harder to reduce the voltage down to 12V, which means you'll be wasting a lot of the power you get in heat in the regulator.
Yep, i can go with the amps being the driving force, but these regulators are the same physical size as normal ones and i doubt they develop any more heat than normal as theres nothing physical to suggest its a problem ...
i suppose what i m asking is, if the regulator drops the voltage from 36v to charge the battery at 12v (keeping figures simple) and the wattage of the pannel is 200w produced at that time...
200w divided by 36v = 5.5 a
does this become
200w divided by 12v = 16.6a less losses in in regulator after passing through it...
Spatz1 - what you appear to be describing is an MPPT regulator and it will do exactly as you describe without loss of power - the system becomes more efficient.
They gain their efficiency by maintaining the panels at their most efficient voltage where possible ( for a 12 volt panel this is usually around 16 volts) while supplying the correct voltage for the battery.
However MPPT regulators are expensive, and in the past at least, you would have needed a fair sized system (panels rated at 1Kw or so) to be worthwhile (I'm talking about a system for a house off-grid.
However they must be getting cheaper so may be option at some point.
If it's low light you seek amorphous panels are best not quite so efficient in full sun but better in low light. Coupled with an MPPT controller that would be the bees knees however they are not normally sold in panels but in sticky backed strips most suitable for a narrow boat.
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Surely, to get to the kind of voltage you are talking about, you will need an array of panels - something over 400W perhaps?
It was my understanding (having just had a 135W Kyocera panel fitted) that MPPT controllers really come into their own in large, multi-panel array installations, but the extra harvest benefit available from a typical motorhome installation is unlikely to provide a worthwhile gain over a decent PWM regulator.
The following quote is taken from a Morningstar information leaflet:
Low power (specifically low current) charging applications may have equal or better energy harvest with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency regardless of the size of the system (all things being equal, efficiency will be the same whether using a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting efficiencies (relative to their peak efficiency) when used in low power applications.
I'm no expert, but when I queried the value of a MPPT controller in my recent installation I was advised that the benefit would be minimal and probably not worth the additional cost. In the event I chose the Schaudt PWM dual battery controller as it integrated into the existing system.
There's obviously something I'm missing here. From the website:
Your panel puts out 7.4 amps. Your battery is setting at 12 volts under charge: 7.4 amps times 12 volts = 88.8 watts.
But doesn't Newton or someone say that you can't create or destroy energy. Therefore, power in = power out X efficiency. Therefore, although your output voltage is lower, your current is higher? A bit like a transformer?
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