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alfie:solar [2019/03/19 12:41]
jin
alfie:solar [2019/03/22 15:33] (current)
jin
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   * [[http://​solarbodge.blogspot.co.uk/​]]   * [[http://​solarbodge.blogspot.co.uk/​]]
  
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 +==== Unfinished Draft Rubbish... ====
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 +The problem I have with most charging systems / solar controllers is they don't really tell you what they'​re doing, even the really expensive ones, so I ended up with a cheap 10A MPPT eBay controller (but which at least has a display to show you what it's doing), a £30 intelligent split-charge relay from Furneaux Ridall, and called it good enough.
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 +Unless you're drawing loads of power you'll be fine with a 100W panel and basic controller. Also, if you're driving it around with any regularity (EG not parked up for a week) you're topping the battery off daily anyway at a far faster rate than any solar panel is going to.
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 +We ended up with 2x 100W panels and 2x MPPT controllers because we're restricted on battery size (due to not wanting to make major mods to the vehicle) and the fridge works hard for 5 days with zero engine running while we're parked up at LeMans - a 2nd panel and controller was cheaper than any of the alternatives and we already had the roof rack to sling it up there.
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 +We also spent "​extra"​ to get the most efficient fridge (Waeco CRX50) which means you need less battery and less solar. TBH it's been worth every penny, it will often freeze stuff unexpectedly even on the medium setting and it holds way more than you'd think as it's deeper than a 3-way fridge despite being physically smaller. Again, we didn't want to hack holes in the side needed to run a 3-way on gas 9the only efficient way to run one!) so the compromise was a flash 12v-only fridge.
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 +You can't put two panels into one controller - well, you *could* but they might fight each other, solar panels are weird...
 +I ended up running two sets of wires back to the battery terminal to prevent the controllers fighting each other.
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 +As I said, the problem with all this solar stuff is no-one tells you what any of it really does (and most of them don't know themselves) - the power claims for panels are total marketing optimism, the intelligence of controllers is vastly exaggerated and most of them are re-packaged so many times no-one remembers what the thing will actually do in any given situation. Ironically CTEK, the really expensive ones, tell you almost nothing useful either in the manual or on their display (usually the minimum number of LED's they can get away with).
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 +Given more time and enthusiasm I'd have made my own controller, and I might yet one day...
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 +For your purposes though, a single 100W panel + basic controller will be more than fine - adding battery capacity is far more efficient especially if the truck will be driven fairly regularly.
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 +The key to it all is working out how much power you need over an average 24h period, how much power the solar panel will be able to put back, and how much battery you need to sustain this.
 +There'​s no point having a big solar panel if your battery is "​full"​ after an hour of sunshine, as you're then throwing power away and not extending your "​range"​.
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 +For example - our average load over a day is maybe 2A/h (24W) - 1.2A/h for the fridge, 0.8A/h for everything else (lights, water pump, heater).
 +We have 200W of solar panels, which averages ~20W back into the system over 24h
 +So the battery has to cope with ~4W * 24h = 0.3A/h * 24 = 7.2AH of capacity lost per 24h
 +
 +Now, the elephant in the room is that the solar panels don't put out a nice even 20W of power 24 hours a day, they put out maybe 120W at midday and 0W overnight, and if the battery and fridge can't usefully absorb 120W, some gets wasted - which means that the battery has more to do when the sun's down and might average 10AH or more of lost capacity per day which the solar cannot fully replenish when the sun's up.
alfie/solar.txt · Last modified: 2019/03/22 15:33 by jin
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