Direct to water heating.

[efficientPV]

The picture of the board in the middle, that guy connects it to his dryer and when operating it switches from the water heater to the dryer element. I can't imagine that heat exchanger working very long from my experience with lint buildup in dryer vents. I'm waiting for those new dehumidifier dryers to start breaking. They won't be able to afford to get them fixed. I got my LG washer that way for $150 delivered. It was only two years old from the sale tag stuck on it from Lowes. Guy said he stored it for a year and when he went to use it the machine wouldn't go into any cycle. Evidently, something was stored on top of it bending the case. A piece of plastic held in one button and the computer stuck there. Few swipes of a file fixed it. Repair people are no longer affordable. It is a throw away society.

 

[copec]

He is using the core to a heat recovery ventilator, but I just want to seal a radiator around the back of a drier for the inlet air and circulate hot water through it, while still venting to outside. It is far cheaper to store the energy in hot water than in a battery to be used by the drier.

 

[efficientPV]

Going back, dryers don't cycle on and off based on temperature. The heater chamber has a thermostat for over temp and many have an adjustable duty cycle timer to control temperature. Some also sense moisture and once it goes down to a certain conductive level the timer then starts to adjust level of dryness. Adding extra heat may not change electrical use unless duty cycle is turned down.

 

[copec]

Going back, dryers don't cycle on and off based on temperature. The heater chamber has a thermostat for over temp and many have an adjustable duty cycle timer to control temperature. Some also sense moisture and once it goes down to a certain conductive level the timer then starts to adjust level of dryness. Adding extra heat may not change electrical use unless duty cycle is turned down.

Good to know, sounds like I need to get an old drier and make my own controller for it. An easy "hack" would be just to use an air-dry mode when the air is being externally heated. I know my modern LG drier does use a fraction of power in the summer where I'm at (outside of Vegas), when I close off the laundry room and let it pull the outside air through a window. It will use about ~2kw/h per load versus ~7kw/h during the non-summer seasons.

Sorry for OT, but I figure on-topic enough because I'm talking about uses of direct heating water with PV.

 

[Roswell Bob]

He is using the core to a heat recovery ventilator, but I just want to seal a radiator around the back of a drier for the inlet air and circulate hot water through it, while still venting to outside. It is far cheaper to store the energy in hot water than in a battery to be used by the drier.

Are you trying to preheat the air going into the dryer with hot water in a radiator? I think this is interesting but not sure it will work well.

 

[copec]

Are you trying to preheat the air going into the dryer with hot water in a radiator? I think this is interesting but not sure it will work well.

That's the idea. I'll have an 80 gallon tank that could reach ~140F. I would seal off the inlet on the back to pull through a coil like this: https://www.mbtek.com/collections/h...coil-12-x-12-80000-btu?variant=12990377230379 where I would circulate the water from the hot of the tank back into the cold with a circulation pump rated to those temps.

Except I would do it on a shoestring budget with salvaged stuff

 

[curiouscarbon]

nice ideas here, appreciate the thermal humidity brainstorming!

neat that @copec linked that heat sink/radiator, found a very similar one from this vendor https://www.amazon.com/stores/AB/AB/page/7BC63985-3048-4881-AB37-A29D0EBE1C08

this page used to have in stock multiple sizes of copper core aluminum fins radiator https://www.amazon.com/Water-Exchanger-Copper-Forced-Heating/dp/B07BB3TLCF but right now it appears out of stock for all sizes.

i got two of the 22x24” radiators for a heat recovery project. brazing the copper is somewhat intimidating lol. probably just need to get a blowtorch and watch some youtube tutorials and ensure wearing proper protective equipment or something while outside.

the fittings is a challenge for me, but the raw thermal conducting capacity of these radiators is no joke. copper is ~400W/m•K and aluminum ~200W/m•K vs water of ~4W/m•K ~0.6W/m•K (doh mixed up specific heat capacity and thermal conductivity)

cool ideas, i think there’s merit in the peripheral water heating topic discussion! heat recovery and redirecting is just neat!

 

[Roswell Bob]

That's the idea. I'll have an 80 gallon tank that could reach ~140F. I would seal off the inlet on the back to pull through a coil like this: https://www.mbtek.com/collections/h...coil-12-x-12-80000-btu?variant=12990377230379 where I would circulate the water from the hot of the tank back into the cold with a circulation pump rated to those temps.

Except I would do it on a shoestring budget with salvaged stuff

The radiator that you are going to pull air through is going to add a lot of back pressure to the system. The air flow through the dryer is going to be restricted. The dryer needs a LOT of air. If the air is reduced you are likely to suffer thermal shut down of dryer as the heating elements will overheat.

Given the quantity of air that you need to dry cloths the velocity going through the radiator will be a few hundred feet per minute. The temperature difference between the air on each side of the radiator will only be a degree or so.

 

[Hedges]

We have a Bosch heat exchanger condensing dryer in a rental condo (because no vent to the outside.) It has been there a couple years, no complaints from tenants. I bought it for them because they didn't like the ugly old full-size one on the patio, which was wired to a 120V outlet. The cross-flow air heat exchanger is a cartridge that can be pulled out.

Heat exchanger on outside of a standard dryer is something I've thought about but not implemented. I have gas and electric dryers on hand, and sufficient electric surplus at this time to not reduce usage. One issue with the heat exchanger is if effective you get condensation, need to catch and dispose of that. My laundry is outside (small house), and I had the idea of concentric pipe heat exchanger, sloped down so condensation drains out the end. Obviously more baffles can improve efficiency, increases problem of clogging.

I see copec's link reports a project done a decade ago. Standard dryers are an obvious inefficiency. Those measurements reported put preheated air at 10 to 30 degrees below discharge air. Ambient wasn't quoted, but assuming 70 degrees, for a rise of 40 to 50 degrees. Something between 50% and 80% recovery.

He is using the core to a heat recovery ventilator, but I just want to seal a radiator around the back of a drier for the inlet air and circulate hot water through it, while still venting to outside. It is far cheaper to store the energy in hot water than in a battery to be used by the drier.

That should work.
But why not just dry the clothes on a line while the sun shines, instead of storing energy?

Going back, dryers don't cycle on and off based on temperature. The heater chamber has a thermostat for over temp and many have an adjustable duty cycle timer to control temperature. Some also sense moisture and once it goes down to a certain conductive level the timer then starts to adjust level of dryness. Adding extra heat may not change electrical use unless duty cycle is turned down.

Here's a simple dryer circuit diagram. It has an over-temp thermostat, also high/low thermostats switch selectable.

https://i.pinimg.com/originals/dc/07/fc/dc07fc656c8502f441264f757f1b7295.png

The radiator that you are going to pull air through is going to add a lot of back pressure to the system. The air flow through the dryer is going to be restricted. The dryer needs a LOT of air. If the air is reduced you are likely to suffer thermal shut down of dryer as the heating elements will overheat.

Given the quantity of air that you need to dry cloths the velocity going through the radiator will be a few hundred feet per minute. The temperature difference between the air on each side of the radiator will only be a degree or so.

Could set dryer to low or no heat, so hot water is only source. Might not be hot enough to be very effective, unless high temperature water in radiator (like from an engine, around 200F).
But if I'm correct on thermostat switching heating element, drying temperature would be regulated. Same as if hot vs. cold ambient air.

You're right, though, that restricted air could be a problem. Filaments run a dull red, and air inlet temperature won't affect them that much, but low air flow would cause them to run hotter and could fail sooner. If the over-temp thermostat is by the element (rather than in discharge air like high/low), then it would cut out.

I think an automobile size radiator could handle the airflow of a dryer, which doesn't have all that large of a fan. Extra fan on radiator could help with the backpressure.

 

[Hedges]

i got two of the 22x24” radiators for a heat recovery project. brazing the copper is somewhat intimidating lol. probably just need to get a blowtorch and watch some youtube tutorials and ensure wearing proper protective equipment or something while outside.

Brazing would be a whole 'nother story. I use oxy/acetylene for that.
Copper pipes I usually solder with a propane torch. Lead-free solder for drinking water applications.

But compression fittings are another way to go. Avoids applying heat to anything with solder or plastic. Avoids problem of turning trapped water to steam, which keeps joint from ever getting hot enough. Good for last connection, e.g. to replace a shower valve, I re-plumbed the four pipes so all were parallel & same direction, then slid on a new valve plumbed to match.

 

[copec]

Their site has selectable size, but selecting the drop down didn’t change the link although from what I’m reading 12”x12” would still probably be sufficient as it has much more effective area than the 4” exhaust piping, but yeah, I would test and not limit the flow. I measured the flow of mine at ~200CFM.

The reason I’m looking at this is the water heaters share the other side of the wall with my laundry room, and I have 7 people in my household, we have a lot of laundry and a dryer is so convenient. Now I have a lot of PV but not a lot of battery, but hate the idea of a huge battery to just power a dryer and am going to have like 30kw/h a day I can dump into a storage tank on average.

I seem to have a hard time training people to use the dryer when the sun is out without making it into a fight :-D

I already have the PV in place with an inverter and battery, PV oversized to handle everything if we use the energy when the sun is out, but if I can figure out how to use it to make everything the same and as convenient unlimited grid, that would be a super win.

 

[curiouscarbon]

h2o much cheaper than lifepo4 for equivalent capacity of thermal storage

 

[efficientPV]

I had a dryer element burn out and I had a new resistive element I had picked up at an auction. Put it in and wife said the cloths were,t dry after an hour. It was a 2,000W element and I was supposed to cut it down to make a 4,000W element. I added a 50% duty cycle timer in series with the dryers 1 hour timer to double the range. My buddy puts only 2,500W into his dryer from solar.

 

[Honuz]

What voltage is safe? People used to die with 32V Delco generators if they were sweaty. I admit I was a little anxious when I climbed into a shower in Europe and there was a 230V instant heater there with me. There has to be a current path. Ground makes a local safe area. Even with low voltage elements you have the potential to creating a current path with the panels. I use 60V which is relatively safe in most cases. You are already courting death with 200V so you must have some comfort with it. It sounds like you are currently using this as a system and are interested in paralleling that with the water heater.

A 2,000W power supply is not cheap. You likely only need 600W so four small power supplies are a cheap option. There are dozens of ways to do this. An arduino is an easy way to control these power supplies, multiple elements or pulse the element. All can be used to keep the array at near power point. If a current MPPT system exists, you can not put another in parallel that calculates power point with current and voltage calculations. My system uses a calculated NATURAL power point using temperature to predict that voltage. If a panel is rated at 60V standard conditions, if it reads 62V in the sun it is obvious it has power not being used by a charging system. My array can easily climb to 66V during the day when power point is at 56V. I just draw off enough heater power to bring the voltage down to something reasonable. I have multiple parallel arrays due to intense shading. I don't bother using temperature tracking as this can be adjusted seasonably. I have no problem heating all the water I need with my size array.

I do have a board and my stock of parts does not allow 200V. Shipping to Europe is also too expensive. Of all the boards I have sold in the last year, not one person has even gotten around to putting them in operation. I am no longer interested in selling boards. Many around the world have built these systems from scratch. None are interested in making a video due to controversy surrounding this method. Do it yourself apperars to be too technical for most in solar. I would suggest looking at the ACTii AC7391 which is made in Poland as an off the shelf solution.

Here is a picture of a 1300W system someone made in Lithuania. He had no technical background and even made his own circuit board. He followed one of my designs and heats water for floor heating. A little overkill because of the parts that were available. I was extremely impressed with the build for so someone with no electronics experience. The next is a guy in Florida who designed his own board. last is mine.

Point taken, 200V now seems too risky to play with for the heater, i mean with a direct connection (lack of proper diferential breaker mainly and the very low fatal current at this voltage)

I got 10 new panels so i can chain them how i want, i"m planning to use 200V cause there is 30m between panels and the house. (2 strings of 5 panels = 2x(5x40 Voc / 10A max) )

I understand your concerns about selling board and people not doing anything with them or even being unhappy cause it's not a ready to use device; i got you and i understand.

I looked at the Polish device, it seems good for my use but it use the same voltage on the output then on the input... the risk is still here, and i still can't use a differential breaker.

Now, let's say i'm not good with electronics but i can partially fix that with an Arduino (Programming is .. i mean... was my job for many years).
What would i need to build this system .. ?

1 - A voltmeter module (150-250V roughly) to get the string voltage
2 - A Shunt to get the current entering the System
3 - A Buck converter circuit (input 250V DC Max and output 48V DC (pretty safe to use)

Now for what i understood of what you said, i got to control the duty cycle of the Buck Converter depending on the available voltage on the input (Are PV over their MPP voltage, or under ?).

I could make something that learn the impact of the variation of the duty cycle on the decrease of the PV voltage... ( perhaps with a pilot panel and the power used by the inverter. That would make the seasonal changes on the limit pv voltage to cut the buck converter... automatic.
Now... did i got most of it .. or ... m i completly in the woods ..? :D

For info, my heater is coming and is a 200 gallons one, it's what we call here a "dead water" tank, the water inside is always the same, it's in a closed circuit, i just use an exchanger to heat my shower water.
There is also a second exchanger lower in the tank, that i will use it to heat the house too. By saying that i meant that i need to harvest every little watt instead of wasting them.

 

[Honuz]

Yes, and they are available for AC.
The link you provided for one was also AC. Do you have a link for DC?

"

Fréquence	50 Hz
Tension nominale	230 V~

"

We had been concerned about switching DC for a water heater, because thermostat and over-temperature cutout are made for AC, would fail at moderately high voltage DC. You brought up the issue of ground fault, which is a valid concern too. Your 30 mA whole-house GFCI in Europe would shut off if water heater element started leaking current to ground. In the U.S., we generally only have our 5 mA GFCI on outlets outside, kitchen and bath, and now garage. Water heater would not trip the the GFCI, so only its ground wire would prevent a shock hazard.

You mentioned Arduino. Water heater as a dump load would ideally consume exactly the surplus power available. It could be toggled on and off, like PWM. On AC side this would cycle battery as inverter drew more power than PV provided. DC from battery would be similar. PWM from PV to heating element would draw no more than the power PV could supply into its resistance, so not has large a load during times of less sun.

A dimmer circuit on the AC side could be used to adjust power from zero to full rating of element. The waveform might be difficult for inverter to supply, with a multi-kW load as compared to small lights/motors. A separate square-wave or MSW inverter might be good for this.

The more ideal on AC side is a high-frequency switcher with variable width pulses to draw current in proportion to voltage, synthesizing sine wave current.

As an alternate to power electronics, on AC side, a Variac with its shaft servo-controlled would produce variable amplitude AC to the heater.

On battery or PV DC side, high frequency PWM could draw reduced average current. With an inductor (filter), current draw could be smoothed, reducing high frequencies that might confuse SCC.

Hello,
Sorry, i took time to respond.
Yes, i got your point guys and i agree, High voltage DC to the heater is .. BAD. About ground wire, i've read that even if grounded we still can get an electric shock from the tank if there is a current leak... reason we use 30mA differentials.
But what about a buck converter that would convert the 200 VDC to let's say .. 48 or 60 VDC, still need something like 50Amp to get a decent amount of energy dumped into the heater (2500W) when it's possible. But 50Amp is acceptable if the heater is not far from the buck converter.

I agree, the heater should idealy consume ALL surplus. Agreed... it's bad on the AC side for all reasons you reviewed and certainly some more like wear on the inverter. A dimmer could generate noise on the AC line where other devices like computers are used ... so .. not amazing neither.

Yes i though of a second inverter but i only know of chinese all in one that start without battery others need a battery... and those all in one batteryless inverters need some time to start up... so .. no go since the systeme got to react fast on a 10 mins nice sun window.
My conclusion is that the best way is the PWM in parrallel to the actual inverter to take advantage of the surplus.

But .. as i said .. i 'm not in electronics... so .. my point of view is just by analysing some various logic points.

 

[efficientPV]

The devil is always in the details. Most switching power supplies will not run with DC over a certain wattage because they do voltage doubling of the primary voltage so you will be limited to multiple 12V power supplies in series. You could turn on each power supply as the voltage increases, 4 or 5 steps. Modifying power supplies is not for the novice. I just can't tell you a simple way to do it. I don't have any interest in an inappropriate design. Just why is your array 200V.

 

[Honuz]

The devil is always in the details. Most switching power supplies will not run with DC over a certain wattage because they do voltage doubling of the primary voltage so you will be limited to multiple 12V power supplies in series. You could turn on each power supply as the voltage increases, 4 or 5 steps. Modifying power supplies is not for the novice. I just can't tell you a simple way to do it. I don't have any interest in an inappropriate design. Just why is your array 200V.

My panels are 30m from the inverter, running too many amps need big cables, reason i'm running 200V.
Why the inverter is in the house and not under the PVs ? Cause i want the batteries to be in a safe and cool place (in the house) and cause i got a DC circuit in house to power pumps, lights, computer charger .... in case the inverter fail.

 

[efficientPV]

I think everyone should watch Mike Holt's videos on grounding and bonding. Especially the swimming pool video to understand the principals of bonding. Power can short to the pumps frame and still the pool is safe. It is a lot to take in and can be confusing. Even Mike tells you not to do something and in another video he will do just that. If you feel a heating element can be a danger in your house then no metal in your house is safe to touch. Your inverter provides exactly the same 200V DC path as the water heater element would. An isolated power supply wouldn't really provide extra isolation.

2,000W would be expensive using a power supply. I have had Europeans asking to design a boost technology for their single element 2,000W 230V heater element on 120V DC systems. Boosting that with a power supply would be practical. Older MSW inverters would be a practical way to produce AC for a phase triggered system. The inefficient boost inverter section can easily be bypassed and the HV DC can be feed in directly with a triac changing duty cycle. A capacitor bank and isolating diode will still be needed to make it efficient. Energy must be stored in the capacitor bank during the off cycles. With solar panels you have to use the energy or loose it forever.

 

[Pierre]

Power Optimal Elon 100 Solar PV Geyser Controller - ERA Energy Tech

Most efficient way to convert and store solar energy Converts solar PV energy into heat energy in geyser Using solar energy saves on electricity bill – up to 40% No inverter or batteries required Both AC mains and PV compatible Tested and approved to IEC / SANS standards Easy installation...

www.era-energytech.com

I have 5 x 420w PV panels feeding about 210v DC to the water heater controller in the link above.
The heating element is rated at 230v AC , 3kW. The controller switches the DC to the heating element and the thermostat only tells the controller when to turn off. In the past 3 months I only had to use grid energy 3 times due to overcast conditions.

 

[copec]

I know this has already been cited, and it is expensive, but I love what http://www.cyboenergy.com/products/offgridHmodeloverview.html does in that they simply vary the AC voltage according to the actual solar output. Someone should really contact one of these Chinese inverter manufacturers and suggest they make an option in their firmware to do the same thing, then eventually a bunch of them would be on the market for cheap.