Water heating with solar

[sun walker]

That adds new meaning to the term boom box.

How does the inverter like the TRIAC. I saw one commercial diverter that would rectify the AC on one side and PWM the sinewave. It was designed for use with PV inverters to give a better load. They must have done that for some reason. I only do PWM DC diversion. I don't know what it is like to have an inverter.

Are you then powering your washing machine/appliances etc directly from your pv via a PWM (no batteries or inverter)?

 

[efficientPV]

I use an old 2,000W Harbor Freight converter, 1,000W now because I just removed half the FET which were shorted. Interesting fact is the high voltage H bridge section will work with any voltage to make AC. If panel voltage drops it will still keep working down to zero volts. My 120V DC array just feeds the high voltage section directly. If a cloud passed over the washer would stop with a low voltage alarm. After it passed, I would just restart it. It was a LG front loader which would remember where it left off. I would always be working out in the garage when doing laundry and it wasn't a problem.

I ran for three years this way till a bad summer with just too many clouds and smoke from Canada. It was just stopping too much. So, I reactivated one of the seven 12V boost inverters to add up to 200W of additional power to supplement 900W of solar. 12V inverter section was adjusted to just below array Vmp voltage. The 12V battery only has about 9AH as it was grabbed from town recycling. The 12V boost converter of the inverter is normally off. When array voltage drops due to load and limited sun it will blend 1 to 200W of power to the array. Just a fun project to experiment with blending. I only use MSW inverters at my house even though I have a stack of pure sine wave inverters, I buy them when they are broken and cheap. My whole house runs pretty much only when the sun shines, even the fridge.

In the lower right of power panel is a transfer switch. The house charge controller runs on 60V array. When laundry is on the four garage panels are put in series for 120V by throwing a switch. 12V battery is kept charged on float at 13.5V from a 12V LED power supply (left). I bought more than a dozen of these blue inverters and use them for everything.

 

[Daddy Tanuki]

I use an old 2,000W Harbor Freight converter, 1,000W now because I just removed half the FET which were shorted. Interesting fact is the high voltage H bridge section will work with any voltage to make AC. If panel voltage drops it will still keep working down to zero volts. My 120V DC array just feeds the high voltage section directly. If a cloud passed over the washer would stop with a low voltage alarm. After it passed, I would just restart it. It was a LG front loader which would remember where it left off. I would always be working out in the garage when doing laundry and it wasn't a problem.

I ran for three years this way till a bad summer with just too many clouds and smoke from Canada. It was just stopping too much. So, I reactivated one of the seven 12V boost inverters to add up to 200W of additional power to supplement 900W of solar. 12V inverter section was adjusted to just below array Vmp voltage. The 12V battery only has about 9AH as it was grabbed from town recycling. The 12V boost converter of the inverter is normally off. When array voltage drops due to load and limited sun it will blend 1 to 200W of power to the array. Just a fun project to experiment with blending. I only use MSW inverters at my house even though I have a stack of pure sine wave inverters, I buy them when they are broken and cheap. My whole house runs pretty much only when the sun shines, even the fridge.

In the lower right of power panel is a transfer switch. The house charge controller runs on 60V array. When laundry is on the four garage panels are put in series for 120V by throwing a switch. 12V battery is kept charged on float at 13.5V from a 12V LED power supply (left). I bought more than a dozen of these blue inverters and use them for everything.View attachment 286173

this screams I have ample insurance and would love to have a fire.

 

[ksmithaz1]

this screams I have ample insurance and would love to have a fire.

To me it screams, why would you do this?

 

[Daddy Tanuki]

To me it screams, why would you do this?

something to play around with in a small shed outback is one thing... anywhere near the main residence... yeah count me out.

 

[sun walker]

To me it screams, why would you do this?

Why not?
With decent fusing.
PV's are cheap, batteries in S. Hem 2-3x the price your paying.
As most of my loads are day use, it makes good sense to go direct, not sure re fridge, but I was planing on adding a daylight relay to the pcb of the auto-defrost, big batt. draw.
This way I can meet all my needs with a 100Ah batt.
But keen to read any downsides.

 

[sun walker]

I only use MSW inverters at my house even though I have a stack of pure sine wave inverters

So I guess the appliances run ok on MSW? I thought modified caused poor performance.
Curious as to where your buying the used inverters from, online would make for expensive postal fees.

I quick look at AliX brings up a few pcbs "High power pure sine wave inverter drive board, H-bridge front and rear stage drive board module" not sure at this stage if any would be suitable.

 

[efficientPV]

It seems to me that in the digital age, why are we still using antique sine waves. MSW inverters have a design flaw that presents an issue with motors starting. Under high load like startup, the duty cycle increases which is exactly the opposite of what should be done. I modified my refrigerator MSW inverter to be a fixed duty cycle and shorter than normal. That reduced startup current in half and slightly lowered run current. So, the fact that it is square isn't an issue. It is a function of duty cycle and voltage. The LG inverter washer doesn't care as it just gets rectified. Only the pump and solenoids need AC.

The garage washer is an example of what can be done efficiently and cheap. The four solar panels, water heater tank, heater controller, washer inverter, battery and even the LG washer cost a total of $500. Not bad for free laundry with all cycles using hot water. But, this array even supplies a good portion of house power. For me it isn't about cost, it is about pushing the limits of technology (actually this is all kiddie table electronics that doesn't require much skill). I pay $4K a year to have grass cut I don't even see. I'm sure I could outspend most people here in solar.

 

[sun walker]

Hooked up 3pv in s. ~1200w 13A 105v directly (fused etc) to an old cu tank ~1.1m high & 1/2m across zinc metal case, with a 240v element with a measured 16 ohm resistance. Just stuff lying around, haven't done the math yet, & still have a lot more of threads like this to read.
12 hr Autumn sun, day temps ~20c, pv's on ~20 degree angle. Took all of the cloudy day to go from 16c to 43c. Guessing a sunny day would get it to 60c (standard tank temp).

 

[Daddy Tanuki]

I pay $4K a year to have grass cut I don't even see. I'm sure I could outspend most people here in solar.

not after the cheap labor disappears.

 

[sun walker]

Hooked up 3pv in s. ~1200w 13A 105v directly (fused etc) to an old cu tank ~1.1m high & 1/2m across zinc metal case, with a 240v element with a measured 16 ohm resistance. Just stuff lying around, still have a lot more of threads like this to read.
12 hr Autumn sun, day temps ~20c, pv's on ~20 degree angle. Took all of the cloudy day to go from 16c to 43c. Next day light overcast all day got to almost 60c (if I remember right 60c is the sweet spot, hot but not scolding & kills most bacteria).


So if my element is 3.5KW, I guess I should try more ohms maybe 1- 2 KW would heat faster?
If my math is correct?
Not at all sure if I need to go for a smaller element? As I'd assume bigger is better?
any help appreciated!

4000W/240v = 16.6A
240v/16.6A = 14.4ohms
105v/14.4ohms = 7.3A
105v x 7.3A = 766W

3000W/240v = 12.5A
240v/12.5A = 19.2ohms
105v/19.2ohms = 5.4A
105v x 5.4A = 574W

2000W/240v = 8.3Amps
240v/8.3A = 29 ohms
105v/29 ohms = 3.6A
105v x 3.6A = 378W

1000W/240v = 4.2A
240v/4.2A = 57ohms
105v/57ohms = 1.8A
105v x 1.8A = 189W

 

[efficientPV]

You failed to provide the most important data, the voltage on the element under the present condition. With the voltage you could see how far you are from the optimum voltage and calculate the matching resistance. It may need such a high resistance with clouds that it would be impractical for overall use. The current element would typically be a good match in direct connect (2X IDEAL RESISTANCE) for daily production. Below is a chart demonstrating dramatic resistance change with low sun. A 10A 100V array was used in this calculation.

% Rated,,,,,,,,,, Increase over ,,,,,,,,, Voltage with ,,,,, Power with ,,,,,,, Power with ,,,,,,,, Ideal
Panel Amp,,,,,,,,, Direct Connect ,,,,,,,,, 10 ohm ,,,,,,,,,, 10A panel ,,,,,,,, Direct Connect 10 ohm ,,,,,, Resistance

100% 0% 100V 1,000W 1,000W 10
90% 11% 90V 810W 900W 11.1
80% 25% 80V 640W 800W 12.5
70% 43% 70V 490W 700W 14.3
60% 67% 60V 360W 600W 16.7
50% 100% 50V 250W 500W 20
40% 250% 40V 160W 400W 25
30% 333% 30V 90W 300W 33.3
20% 500% 20V 40W 200W 50
10% 1000% 10V 10W 100W 100

The editor here turns everything to crap, need to do screen capture.

 

[sun walker]

the most important data, the voltage on the element under the present condition.

Still overcast, from (~1200w 13A) 105v pv output the measured v. with the element on was 48v & 3.4A.
So 48v/3.4A = 14.11 ohms (163W), not far from the "240v element with a measured 16 ohm resistance,"
& that's the best element for the job you reckon?

Tank will need more insulation, its been running continuously, pv direct only (no water used) & hovers 50c - 60c.
It will be interesting to see how it goes under full sun.

 

[efficientPV]

That should be 105V / 3.4A = 31 ohms element resistance for 357W vs 48V X 3.4A with 163W. With 29 ohm element the maximum power would be 378W. I have 6 gallon point of use water heaters and have no problem heating water with less than 400W.

 

[sun walker]

All day sunny, measured 96v 6.5A midday going into tank so 16.15 ohms, so 682.5W. Still it took all day from ~40c to get to ~60c, probably an ~18 gallon tank.
That's ok. Day temp 25c, no need for a relay or thermostat as its unlikely to get to 100c boiling, maybe during the hotter longer summer days, but maybe not if the water is being used, it will only bleed out the top anyway.
I think the best bet would be to add & subtract the pv panels, adjust the input wattage for the season, still have plenty of excess pv I can add, although the wet back on the wood burner covers my hot water winter use, separate tank.
But that seems the simplest no fuss solution, direct connection, nothing but the element to breakdown.

 

[sun walker]

My whole house runs pretty much only when the sun shines, even the fridge.

How does your refrigerator keep cool at night?

 

[efficientPV]

I usually keep a large mass of liquids like drinks in the bottom. Supplemented with plastic rectangle shipping blocks I get from my neighbor who is a doctor that the ship with medicines to keep them cold. It has worked for years overnight. Current 7cf freezer fridge has coils in the bottom and is so segmented I have to use a fan. Even so, ice develops on the bottom and never melts till we leave. A prior 5cf had coils in the top which worked much better. NEVER BUY A FREEZER WITH COILS ON THE BOTTOM.

 

[sun walker]

I usually keep a large mass of liquids like drinks in the bottom. Supplemented with plastic rectangle shipping blocks I get from my neighbor who is a doctor that the ship with medicines to keep them cold. It has worked for years overnight. Current 7cf freezer fridge has coils in the bottom and is so segmented I have to use a fan. Even so, ice develops on the bottom and never melts till we leave. A prior 5cf had coils in the top which worked much better. NEVER BUY A FREEZER WITH COILS ON THE BOTTOM.

Yeah I thought something like that would work, I have a f/f side by side, the coil is in the freezer lower wall with a fan to push the cool air to the fridge, so by filling the freezer with ice mass it should cool the fridge ok.
I did think about using direct connect to the 300W defrost element & a timer (like the hot water tank), as the f/f is getting old & starting to ice up (low refrigerant sign) gives me more control, & a smaller Watt inverter for the compressor.

 

[Ai4px]

Not anymore than the one you got from MW&S, they don't have a good reputation. Are your panels in series?

sorry for late reply.. just saw your question. Yes, 3 panels in series. They pull down to about 95v when under a load.