Hot Water by Solar Electric direct via MPPT ?

[neweclipse]

Yes, because I'm not allowed to export to the grid. The power company will not accept any. I been trying to figure out what to do without going to a large battery packs. I've looked into the Outback Radian but on Gridzero that constantly cycles the batteries, does not a good solution to me. Any suggestion?

I do exactly this by 'load diversion'. I have 200 gallon of DHW storage between 2 separate tanks. So far, on a good sunny day I can max them both out at 125*F. I am currently looking at a means to 'dump' any excess PV production beyond my storage capacity, as a last resort.

Using standard factory tank electric immersion elements and thermo-switches, only mod to DHW heater for me was to make elements independent circuits, others may find that unnecessary in their situation.

Using this 'load diverter' , popular in Europe, can literally holds the electric meter at a 'dead stand still' while diverting and can self-regulate even with moment by moment changing household loads.
Control is by an electronic PCB with Atmega328 8-bit microcontroller running a SSR or triac switching at zero-crossing referenced to surplus load available as measured 60 times per second.

All this is easily found at 'openenergymonitor.org'...that's how I got all my info. Cheers
Note: Europe does use 230 VAC @ 50Hz, so that needs factored in to make this work for NA 240 VAC @ 60Hz
Sorry, No, does Not work off-grid and batteries...Only Grid-Tied.

[bcroe]

David Poz does demonstrate the kind of results that can be expected when things are thrown together without any
careful design. All you need are a few basic equations, like ohms law, P = Vsquared /R, etc. and your 4 function
calculator. Get a better visual on it with a load line like this.

So now enlightened Dave will solve your problem with his spreadsheet? Am I to just TRUST this so recent
improvement, to do it all? Can nobody actually do, or is too lazy to do, or is too impatient for gratification, to do
the most simple design and calculations for themselves any more? I did that phase with a slide rule.

Anyway Dave has ignored the fuse requirements for 3 paralleled panels, and there is
no mention of the type thermostat capable of DC operation. good luck, Bruce Roe

PVLdLn.jpg

[PNPmacnab]

Having a quick list of available elements is handy. Selecting the ideal resistance only guarantees that the resistance is not way less than the panel can support in the best two hours of the day. A slightly higher resistance may perform overall better daily in a direct connect without some power point control. In a half light condition the current is half, but the power is 1/4 and rapidly going down hill from there. For most of the day your heating will be in the toilet with direct connect. Panels are cheap. Solar is the only thing I know where the people are so happy if it even works at all. David will soon be demonstrating MPPT heating.

[travissand]

I saw a handy spread sheet calculator at https://www.davidpoz.com/
I will attach the file here that I added current prices with hawaii shipping to.
He said he will be making a better version so be sure to check his we page not just use the file i upload here.
Put in your solar panel specs and it shows what hot water heater element is a good match.
He even has links to buy them.
Here is a link to his youtube about it.

https://www.youtube.com/watch?v=kVaxAfXQPDU

Do you guys think his math is correct?

[PNPmacnab]

Don't know what your point is. I've seen MPPT controllers not operating at the real power point voltage, but lower. A MPPT water heater controller may operate at MPPT during on cycle, but not have enough capacitance to store all the energy of the off cycle. Hunting and algorithms can also reduce real output over a time interval.

[J.P.M.]

Just from what little I've read, the German unit is better and cheaper. However it uses a thermal sensor to switch off. The techluck uses a fixed dead time and don't think the capacitor bank is sufficient to store all that energy during it. Real efficiency is not power in vs power out. It is using all the power that is available. A MPPT charge controller can not be connected stand alone to a heater.

Measuring efficiency involves power out/power in. That's a quotient and different than finding the most efficient use of the input for a desired output. That involves minimizing that quotient for the process.

[inetdog]

The heating element will not care whether the applied voltage is AC or DC, but the thermostat, if one is used, certainly will. Any thermostat, switch, or relay will generally have a lower interrupting voltage and/or current compared to its AC rating.

[PNPmacnab]

Just from what little I've read, the German unit is better and cheaper. However it uses a thermal sensor to switch off. The techluck uses a fixed dead time and don't think the capacitor bank is sufficient to store all that energy during it. Real efficiency is not power in vs power out. It is using all the power that is available. A MPPT charge controller can not be connected stand alone to a heater.

[cretch]

This is why the guy at TechLuck recommends higher voltage and the standard AC element. You said it yourself, power is proportional to voltage squared;
I'd love to hear feedback about that German controller since the online doc's are sorely lacking; it's unclear to me what DC voltage is going to the heating element.

As for TechLuck:
If you have 1000W of PV (say 4-250W panels at ~28VDC each) on a 4500W AC element (~12.8 ohm), that's: (28x4)^2 / 12.8 = 980W, full use of your PV!
Problem is switching 120VDC without arcing, supposedly TechLuck solved this but I haven't tried one yet.

Thanks, I didn't realize Techluck controller could put through 100 volts, this solves a lot of problems. Most Mppt controller out put at 60 volts max.

[psablo]

Do you actually have 1KW panel overage to put into a heater. 250W seems like a good match for two panels. I have one of those oil filled heaters. It has two elements and is capable of 1,500W. I can dump 300 some watts into it at 60V and you can't put your hand on it. This is just used to take the chill off at a comfortable ambient. If below freezing it could take the full watts.

I am planning to do the same thing with 2-300W PV panels at 32.6Vmpp each but I am concerned about the internal AC switches of the oil filled radiator handling 65.2VDC.
Sounds like you've had no issues with arcing?

[psablo]

Definitely change the heating element. A potential problem with any direct input DC system is the ability of the resistance element to generate heat. A 4500-watt element designed to run on 240 volts is only going to put out 280 watts with 60 volts and significantly less with 48 volts. This would waste a large amount of the solar power if you had 750 watts of possible power. The Missouri wind & solar element above looks like a good bet. If you have 1000 watts of power you need to be able to put that somewhere. The heating element doesn't care whether it is AC or DC, but the voltage does matter. If cut the voltage in half then your heat output will be one quarter of what it was.

This is why the guy at TechLuck recommends higher voltage and the standard AC element. You said it yourself, power is proportional to voltage squared;
I'd love to hear feedback about that German controller since the online doc's are sorely lacking; it's unclear to me what DC voltage is going to the heating element.

As for TechLuck:
If you have 1000W of PV (say 4-250W panels at ~28VDC each) on a 4500W AC element (~12.8 ohm), that's: (28x4)^2 / 12.8 = 980W, full use of your PV!
Problem is switching 120VDC without arcing, supposedly TechLuck solved this but I haven't tried one yet.

[cretch]

Yes, because I'm not allowed to export to the grid. The power company will not accept any. I been trying to figure out what to do without going to a large battery packs. I've looked into the Outback Radian but on Gridzero that constantly cycles the batteries, does not a good solution to me. Any suggestion?

[PNPmacnab]

Do you actually have 1KW panel overage to put into a heater. 250W seems like a good match for two panels. I have one of those oil filled heaters. It has two elements and is capable of 1,500W. I can dump 300 some watts into it at 60V and you can't put your hand on it. This is just used to take the chill off at a comfortable ambient. If below freezing it could take the full watts.

[cretch]

Does anyone know of a high resistance baseboard heater? The best I could find is a 120v 1000 watt strip. ( https://www.homedepot.com/p/KING-KP-...1210/307675585 ) which would only put out 250 watts at 60V DC. At that rate it would cost almost $500 to absorb 1 KW.

[cretch]

Definitely change the heating element. A potential problem with any direct input DC system is the ability of the resistance element to generate heat. A 4500-watt element designed to run on 240 volts is only going to put out 280 watts with 60 volts and significantly less with 48 volts. This would waste a large amount of the solar power if you had 750 watts of possible power. The Missouri wind & solar element above looks like a good bet. If you have 1000 watts of power you need to be able to put that somewhere. The heating element doesn't care whether it is AC or DC, but the voltage does matter. If cut the voltage in half then your heat output will be one quarter of what it was.