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Solar Hot Water ...
#11
(06-09-2019, 11:43 PM)completelycharged Wrote: Hot water should really be direct thermal, going DC is way less efficient and then becomes a spill battery in a way.

Agreed, however, if the batteries are topped off and solar is still generating lots of power, then even if it's only 10% efficient, you're still using more than 100% more power than what would of been wasted anyways Wink
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#12
I'm hoping it'll work well from the batteries, seems it's useless off one 36v 250w panel (but pannel might have issues lol one cell on the solar panel is WAY hotter than the rest
   


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#13
You'll need to get the load (ie the element) & the number of panels matched so that the panels can be operating near their max power point.
Eg you'll probably have to add multiple panels in parallel so that with the element connected, in full sun, the voltage on the panels ends up near 30V (ie approx Vmp for typical 36V VoC 60 cells panels). Otherwise you won't end up getting the expected amount of energy collected into the HWS.
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#14
Would it not be simpler and more efficient to use AC power from the inverter? The MPPT tracker optimizes power output of the PV panels, and no need to modify the boiler, which can safely be switched with a standard zero cross SSR or a relay.
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#15
(06-10-2019, 06:03 AM)Redpacket Wrote: You'll need to get the load (ie the element) & the number of panels matched so that the panels can be operating near their max power point.
Eg you'll probably have to add multiple panels in parallel so that with the element connected, in full sun, the voltage on the panels ends up near 30V (ie approx Vmp for typical 36V VoC 60 cells panels). Otherwise you won't end up getting the expected amount of energy collected into the HWS.
Yep working on this - the key is understanding it, and I learn by doing ... well sometimes Smile 
(06-10-2019, 06:13 AM)ajw22 Wrote: Would it not be simpler and more efficient to use AC power from the inverter?  The MPPT tracker optimizes power output of the PV panels, and no need to modify the boiler, which can safely be switched with a standard zero cross SSR or a relay.
IT sure would but this isn't going to be used anywhere near a power pole and budget is limited & we need an effective dumpload for the lithium cells, Patreon members have already had a sneak peek at where this will be heading Smile
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#16
One panel was dumb! lolz but we knew that right ?


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#17
Some discussion for you re the videos:
- the element is 600W at 24V so it's normal running current is is I = P/V = 600/24 = 25A
The element's resistance is R = V/I = 24/25 = 0.96 Ohms
- With one panel you measured approx 7.7V & 7.8A, so P-= V x I = 7.7 x 7.8 = approx 60W
- 60W is going to take quite a while to raise the water temp much!
- with three panels in parallel at approx 7A each = 21A that's be about 20V on the element & so about 20 x 21 = 420W going in.
at 420W, the 50L tank would take about 83 mins to rise 10 degC
- with 4 panels, it'd be approx 28A & 26.9V so approx 752W going in (you'd be pushing the element hard!)
at 752W, the 50L tank would take about 46.5 mins to rise 10 degC

If you got 600W going in, it would take about 4.85 hrs to raise 50L of 10 degC water to 60 degC

This calculator helps with the temp calcs:
http://processheatingservices.com/water-...alculator/

Basically, for your 50L tank & 60W input, it would take almost 1 hour to get just 1 degC rise!
With 600W going in, you'd see a 10 degC rise in approx an hour.
Yes there's some assumptions there...
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#18
(06-10-2019, 09:38 AM)Redpacket Wrote: Some discussion for you re the videos:
- the element is 600W at 24V so it's normal running current is is I = P/V = 600/24 = 25A
The element's resistance is R = V/I = 24/25 = 0.96 Ohms
- With one panel you measured approx 7.7V & 7.8A, so P-= V x I = 7.7 x 7.8 = approx 60W
- 60W is going to take quite a while to raise the water temp much!
- with three panels in parallel at approx 7A each = 21A that's be about 20V on the element & so about 20 x 21 = 420W going in.
at 420W, the 50L tank would take about 83 mins to rise 10 degC
- with 4 panels, it'd be approx 28A & 26.9V so approx 752W going in (you'd be pushing the element hard!)
at 752W, the 50L tank would take about 46.5 mins to rise 10 degC

If you got 600W going in, it would take about 4.85 hrs to raise 50L of 10 degC water to 60 degC

This calculator helps with the temp calcs:
http://processheatingservices.com/water-...alculator/

Basically, for your 50L tank & 60W input, it would take almost 1 hour to get just 1 degC rise!
With 600W going in, you'd see a 10 degC rise in approx an hour.
Yes there's some assumptions there...

Assumptions & math!! but I'm grateful for the effort - I can't wait to do tomorows test with more panels then the big final install running from batteries but that video will take a while to compete. And time isn't on my side.
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#19
Last one I'll be doing direct from solar but chuffed that with community input it's all working quite well and it's not even that expensive


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#20
Looking better there Pete :-)
Getting the panels to right angles to the sun will help.
Re the control voltage for the SSR, if the thermostat opens, the panels will go to Voc, which is likely to be > than the SSR's max voltage.
Maybe try using a Zener diode + a resistor eg 27V 1W type across the control terminals with a 1k ohm 1W resistor going to the panels. That way, the 36V Voc will get safely limited to about 27V & the SSR won't get damaged.
So it'd be wired like this:
 

You could do this with a MOSFET too...
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