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Matching Water Heater Elements to Solar PV Panels
#1
Since this has been the topic of discussion a few times, I figured I'd share this. This David explains this issue pretty straight forward and simple, with added humor.


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#2
Wouldn't it be more efficient with a MPPT buck converter?

Because the MPP will change when the brightness changes. The given MPP (VMPP and IMPP) represents the MPP at 1000W/m2 and not at any brightness.

A chart from Wikipedia showing the different MPP's at different brightnesses pretty well:


The different colors are different brightnesses, the inclining grey line represents the Maximum Poer Point (MPP).
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#3
Of course an MPPT would be better. But that's not what the video was about. It's about sizing heating to your panels. I know that the charge controller is to be factored in, but that doesn't negate the math to get the right elements.
Regardless if using straight connection or pwm or mppt, the numbers and math required to size correctly is the same. It's based on the Vmpp and Impp of the panels.

Granted, if he'd used mppt controller, the water would of heated faster as the usable wattage would be available far longer.
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#4
(02-17-2019, 01:22 PM)LEDSchlucker Wrote: Wouldn't it be more efficient with a MPPT buck converter?

Yes, direct connection of a resistive load to PV is a wasted resource, you might gain more enlightening and factual correctness by viewing Daciens content, specifically his MPPT thermal controller presentation.

https://electrodacus.com
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#5
Quote:Water can usually be considered free so the cost in this case is related to storage and I selected in this example a very common 206 Litres (55 Gallon) HDPE barrel than can be had
new for about 60 USD or used/recycled for much less.
The water has the highest heat capacity of any liquid and is 4185.5 J/(kg⋅K) where 1 Joule is actually 1Watt-second to transform this in Watt-hour you just need to divide this by 3600
the number of seconds in one hour. So heat capacity of water is about 1.16Wh/(kg⋅K) and since water density is about 1 then 1kg of water is the same as 1 litre of water and a delta of 1
Kelvin is the same as a delta of 1 Celsius the calculation of amount of energy stored in that barrel of water is quite simple.
Say that usable temperature range in that HDPE barrel is 20°C to 55°C so usable temperature delta is 55°C-20°C = 35°C then
206 litre * 35°C * 1.16Wh/(litre⋅°C) = 8363.6Wh = 8.364 kWh this is a large storage capacity for a small cost and almost infinite cycle life so I hope this shows why thermal storage is
so important in a solar setup

I think the guy in the video explained it a lot better, imho. He explained it in such a way that "anyone" can understand it. Not saying that the guy from Electrodacus didn't do a good job, just not in everyday language that most people could understand.
Plus, the guy in video presented it in an entertaining manner instead of reading a pdf Tongue
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#6
I guess some are happy with just the entertainment, whereas others want plain simple facts and figures, and have the ability to comprehend.
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#7
I do believe that the math the guy in the video presented was actual facts and figures. He explained the delta Temps and what to look for. Then he presented a spreadsheet that would allow you to input your solar panel figures to find out which heating element would be best matched with the panels. I think that calls for Facts, Figures, AND ability to comprehend.
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