Author Topic: PV hot water  (Read 783 times)

DEinME

  • Jr. Member
  • **
  • Posts: 58
Re: PV hot water
« Reply #15 on: April 02, 2019, 12:50:20 AM »
DEinME,

NOT!

10 ohms at 120 volts is not the same current as 10 ohms at 240 volts!  Total power will be 4 times as much at 240 volts.......simple math......at a given resistance twice the current will flow at twice the voltage and twice the current at twice the voltage is four times the power!   Basic ohm's law!

David
My post said "When they're both running on 120V . . . "

What I meant was that a 10 ohm coil will put out the same heat at 120V no matter if that 10-ohm coil is made for 120V or 240V. I just wrote a different version of that in the earlier post, but my post was correct.

So why not get a 240V coil?

Yeah I reread your post - you do say when they are both running on 120v but that is easy to mix up with the rest of the statement.
I see your point was that the wire may different in a 120v manufactured  heating coil compared to a 240v heating coil.
People had no trouble reading it for a month.

I suspect that people who read the whole discussion would follow what the discussion was about and not just take part of a sentence out of context and pile on with criticism.
4800W PV in 2 circuits of 96V & 50A each after the Midnight combiner. Two Midnight Classic 200. MagnaSine 4448 split phase inverter on a Midnight e-panel. 700Ah or 900Ah FLA @ 48V. Birdhouse,WBjr, etc. Replaces 16-year-old off-grid full-time 408W PV & 300W Morningstar inverter.

ClassicCrazy

  • Hero Member
  • *****
  • Posts: 2201
Re: PV hot water
« Reply #16 on: April 02, 2019, 01:33:12 AM »
Oh well - it was an easy mix up - the eyes play tricks on meaning sometimes especially when reading a post fast or if someone is reading on a tiny screened phone.  I had to read it twice after it was pointed out to get it all straight in context.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

DEinME

  • Jr. Member
  • **
  • Posts: 58
Re: PV hot water
« Reply #17 on: April 02, 2019, 02:45:23 AM »
Oh well - it was an easy mix up - the eyes play tricks on meaning sometimes especially when reading a post fast or if someone is reading on a tiny screened phone.  I had to read it twice after it was pointed out to get it all straight in context.

Larry
At this point people won't need to read any of my posts at all to decide that I'm wrong.

The most recent correction quoted my 4-sentence post that included this sentence: "What I meant was that a 10 ohm coil will put out the same heat at 120V no matter if that 10-ohm coil is made for 120V or 240V."

I don't think they read it at all.
4800W PV in 2 circuits of 96V & 50A each after the Midnight combiner. Two Midnight Classic 200. MagnaSine 4448 split phase inverter on a Midnight e-panel. 700Ah or 900Ah FLA @ 48V. Birdhouse,WBjr, etc. Replaces 16-year-old off-grid full-time 408W PV & 300W Morningstar inverter.

RossW

  • Sr. Member
  • ****
  • Posts: 365
Re: PV hot water
« Reply #18 on: April 02, 2019, 05:24:52 PM »
What I meant was that a 10 ohm coil will put out the same heat at 120V no matter if that 10-ohm coil is made for 120V or 240V. I just wrote a different version of that in the earlier post, but my post was correct.

Might be easier to refer to the coils by their nominal wattage.
A "240V/5.7kW element" will have a resistance of 10 ohms, but if run on 120V will only draw 1.2kW
A "120V/1.2kW element" will ALSO have a resistance of 10 ohms, and will also draw 1.2kW on 120V.

The difference is that a 120V/1.2kW element will be made of much lighter wire, and probably a much lighter general construction than a 240V/5.7kW element. One would expect, therefore, the 5.7kW element would have a far longer service life because you're running it way below it's rated capacity.

A bit like the old "RS" (Rough Service) light globes. I believe they were designed for a higher voltage so they were being run under full load and therefore lasted much longer.
3600W on 6 tracking arrays.
7200W on 2 fixed array.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
Selectronics SP-PRO 481 5kW inverter
Fronius 6kW AC coupled inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

tecnodave

  • Hero Member
  • *****
  • Posts: 734
  • Learn something new every day
Re: PV hot water
« Reply #19 on: April 02, 2019, 08:10:12 PM »
RossW,

Rough service bulbs are rated at 130 volts, traffic light bulbs too, last longer because they are not run at full brightness.......downside....they are less efficient......less lumens per watt.

david
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

ClassicCrazy

  • Hero Member
  • *****
  • Posts: 2201
Re: PV hot water
« Reply #20 on: April 02, 2019, 08:32:38 PM »
Interesting fact for you warm weather climate dwellers . The old inefficient light bulbs in stop and go signals used to melt the snow off from the heat generated.  One city near here replaced with new efficient LED fixtures and we had a very windy sticky snow and it covered all the stop and go lights . The city had to sweep them off because it wasn't melting. Not sure if there have been any design changes since then to help alleviate that winter problem.

Larry 
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

tecnodave

  • Hero Member
  • *****
  • Posts: 734
  • Learn something new every day
Re: PV hot water
« Reply #21 on: April 02, 2019, 08:36:22 PM »
Larry,

I don't miss the snow, ...really.  So what is less expensive, LED lights or snow sweepers....lol

David
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

bee88man

  • Jr. Member
  • **
  • Posts: 62
Re: PV hot water
« Reply #22 on: April 19, 2019, 08:42:17 AM »
As for the Titled subject matter... for PV hot water I set up a modified modulating tankless electric water heater and small circulating pump to store up to 200 gallon of hot water stricly from diverted power destined to go to the grid...beautifull sight when meter stands still from early till late day and hot water is all sourced from PV.
Concidering adding a 'heat dump' to avoid the rare event of maxed out storage and dumping kW to the grid...I'm not sharing...