Solid state water heating element

[Netsua]

I have a few 55 gallon drums of water in my greenhouse for thermal mass. They help for sure, but in the dead of winter, there’s only so much they can do.

I was thinking I could use a spare panel connected directly to a metal element of some kind in a barrel. Nothing fancy - literally just something that would convert whatever sunlight is available to heat, which would be passed to the water.

Anyone have more knowledge on how this might work?

 

[robby]

There are Lots of videos on YouTube with details on doing this.

 

[sunshine_eggo]

solid state?

Heating elements are just resistors. Resistors are nearly 100% efficient in converting power to heat. The best solar panels are about 20% efficient in converting sunlight to electricity.

For the same surface area, a direct solar water heating system is likely much more effective.

 

[Frick]

I used old 60 cell 250 watt panels I bought cheap (40$ ea) and they will wire directly to a 36 v water heating element with the right resistance. There is a voltage drop with 1 , less with 2, and minimal with 4. I got 400 watts reliably from 2 parallel panels directly wired panel to heater without amy control circuit. In You case the only real danger is running the element dry.

solar water heaters are good, but requires a lot of set up and comtrol to work safely. tend to end up far more expensive.

that said, 400w of heat isnt a ton, amd greenhouses tend to lose heat very easily. Not sure the benefit.
there may be better answers, like this:

Reinventing the Greenhouse

Contrary to its fully glazed counterpart, a passive solar greenhouse is designed to retain as much warmth as possible.

solar.lowtechmagazine.com

others have heated greenhouses with a solid compost pile and you get roughly the same btu’s as burning that weight of wood. You also get CO2 which helps.

 

[Netsua]

solid state?

Heating elements are just resistors. Resistors are nearly 100% efficient in converting power to heat. The best solar panels are about 20% efficient in converting sunlight to electricity.

For the same surface area, a direct solar water heating system is likely much more effective.

Exactly. I just meant that I’m not looking for something with a thermostat or circuitry of any kind - basically a submersible resistor.

 

[Netsua]

I used old 60 cell 250 watt panels I bought cheap (40$ ea) and they will wire directly to a 36 v water heating element with the right resistance. There is a voltage drop with 1 , less with 2, and minimal with 4. I got 400 watts reliably from 2 parallel panels directly wired panel to heater without amy control circuit. In You case the only real danger is running the element dry.

solar water heaters are good, but requires a lot of set up and comtrol to work safely. tend to end up far more expensive.

that said, 400w of heat isnt a ton, amd greenhouses tend to lose heat very easily. Not sure the benefit.
there may be better answers, like this:

Reinventing the Greenhouse

Contrary to its fully glazed counterpart, a passive solar greenhouse is designed to retain as much warmth as possible.

solar.lowtechmagazine.com

others have heated greenhouses with a solid compost pile and you get roughly the same btu’s as burning that weight of wood. You also get CO2 which helps.

Thank you. That’s probably very similar to what I need. And my greenhouse is kind of similar to the one in the article - I’m just using water for the thermal mass instead of brick!

 

[efficientPV]

Your best bet is to choose a heating element with a resistance two to three times what you think is the ideal resistance. This will capture the power of the early and late sun much better. Here is data proving it. The far left data points are the ideal resistance, and you can see peak daily power is at much higher resistance. There are solid state heating elements for non-pressurized water tanks subject to getting low water levels.

 

[Netsua]

Your best bet is to choose a heating element with a resistance two to three times what you think is the ideal resistance. This will capture the power of the early and late sun much better. Here is data proving it. The far left data points are the ideal resistance, and you can see peak daily power is at much higher resistance. There are solid state heating elements for non-pressurized water tanks subject to getting low water levels.
View attachment 119638

Thank you! Any direction on where such a thing is sold?

 

[PVorBust]

Thank you! Any direction on where such a thing is sold?

Something like this will do the job. mount the drum on it's side with the big hole down.
Assemble the pipe fittings to seal the heater in place.
Fill with water, but leave the top hole open to prevent it pressurizing