What is the simplest way to heat 330 Gallon tanks with solar to warm greenhouse. DC thermal dump recommendations.

[Hieusays]

Hi,

So my friend has a greenhouse and wants to keep it warm during the winter. He already has multiple 330gal tanks and I was thinking we can heat the water to use as thermal mass that can release throughout the day/night.

Is there a DC thermal dump that you can directly connect to solar panels to generate heat? Trying to do this without any batteries as it would raise cost. A cheap inverter if necessary but we'd prefer to go without that either if possible.

 

[MisterSandals]

Search results for query: water heating element

diysolarforum.com

 

[wpns]

Hi,

So my friend has a greenhouse and wants to keep it warm during the winter. He already has multiple 330gal tanks and I was thinking we can heat the water to use as thermal mass that can release throughout the day/night.

Is there a DC thermal dump that you can directly connect to solar panels to generate heat? Trying to do this without any batteries as it would raise cost. A cheap inverter if necessary but we'd prefer to go without that either if possible.

I know they are falling out of favor, but if that's all he wants to do with solar, he might look at solar thermal, that's established technology and doesn't require anything but a circulator pump like

https://www.amazon.com/KOLERFLO-Circulating-3-Speed-Circulation-Heater/dp/B07D54THTT

a controller like
https://www.amazon.com/Differential-Temperature-Controller-Thermostat-Greenhouse/dp/B0C387DPZK
and some thermal panels. Look for hot water or pool heater kits.

Hot water directly from PV has a lot of issues, see @MisterSandals above.

 

[OzSolar]

I know they are falling out of favor, but if that's all he wants to do with solar, he might look at solar thermal, that's established technology and doesn't require anything but a circulator pump like

https://www.amazon.com/KOLERFLO-Circulating-3-Speed-Circulation-Heater/dp/B07D54THTT

a controller like
https://www.amazon.com/Differential-Temperature-Controller-Thermostat-Greenhouse/dp/B0C387DPZK
and some thermal panels. Look for hot water or pool heater kits.

Hot water directly from PV has a lot of issues, see @MisterSandals above.

**unless they are in a freezing climate, then the system has to be freeze proof.

I semi regularly watch the local used adds and it's not uncommon to see used solar thermal panels. That could be great way to go. They are big so you'd need a friend or two and truck.

One way to handle the freeze protection part is to mount the panels higher than the tanks (which may not be easy...) and make sure the piping all slopes down so when the pump shuts off it drains into the tanks.

In others words PV or thermal aren't going to be easy.

For some good reading check out Ed Mazria's Book.

 

[Hieusays]

**unless they are in a freezing climate, then the system has to be freeze proof.

I semi regularly watch the local used adds and it's not uncommon to see used solar thermal panels. That could be great way to go. They are big so you'd need a friend or two and truck.

One way to handle the freeze protection part is to mount the panels higher than the tanks (which may not be easy...) and make sure the piping all slopes down so when the pump shuts off it drains into the tanks.

In others words PV or thermal aren't going to be easy.

For some good reading check out Ed Mazria's Book.

View attachment 271801

Yeah, it sometimes gets below freezing, which is when it's the most needed. It's 5 degrees F today but sunny, which is why I was hoping to run solar panels. They're cheap, easy to find, and almost maintenance free vs the solar heaters that use a pump. All I would need is some electrical wire running into a tank that is inside the greenhouse. I saw someone was using a thermal dump for their windmill but I lost the thread.

 

[AntronX]

Do the math on how many solar panels you would need to make this work. To heat one 330 gal tank by 50 degrees C would take 70kWh of energy. Thats about 18kW of panels needed on a clear winter day assuming perfect Vmp match of panels to heating elements. Then you’d have no use for all these panels in the summer.

 

[wpns]

**unless they are in a freezing climate, then the system has to be freeze proof.

Or, if the tanks are just for thermal mass, add some antifreeze.

My solar thermal hot water system is still running on the original Taco circulator it started with 20 years ago. I replaced the tank and collectors recently, but the circulator and controller were still going strong. I think I replaced one or two sensors in that time. Now I have a new controller, a spare circulator, and a full set of sensors plus a flowmeter and some other bits sitting in the spares bin.

 

[xjaw4]

Does the greenhouse use 2 layers of plastic with a blower to inflate the space in between the layers? Do the side curtains inflate as well? How well sealed are the ends? Do they have row covers inside? We have a bender that makes 1/2" emt conduit into hoops for that purpose. Using row covers we have been able to grow/ over winter crops without any heat. Chard, carrots etc tomatoes and peppers would require more heat where we are. There are heat pumps that can run directly off pv but I have not seen one that also heats water. Do some math on how much energy will be required to reach your goal temp and or how much heat each solution can provide. Have you considered using compost for generating heat or a wood boiler?

 

[OzSolar]

Or, if the tanks are just for thermal mass, add some antifreeze.

My solar thermal hot water system is still running on the original Taco circulator it started with 20 years ago. I replaced the tank and collectors recently, but the circulator and controller were still going strong. I think I replaced one or two sensors in that time. Now I have a new controller, a spare circulator, and a full set of sensors plus a flowmeter and some other bits sitting in the spares bin.

That’s a lot of antifreeze. My suggestion was for a drain back system, no need for antifreeze.

The Grundfos “circulators” (technically they aren’t pumps) I’m using in my radiant in-floor heating system have been in near constant use since the late 70’s. They were 15 years old when I removed them from a SHW space systems I was contracted to decommission in the early 90's.

Whenever a customer calls and says their pump is bad it rarely is. Those things are tanks.

Do the math on how many solar panels you would need to make this work. To heat one 330 gal tank by 50 degrees C would take 70kWh of energy. Thats about 18kW of panels needed on a clear winter day assuming perfect Vmp match of panels to heating elements. Then you’d have no use for all these panels in the summer.

It's more like how many kWh for 5c? They aren't trying to do space heating, just keep thier plants from freezing.

 

[AntronX]

It's more like how many kWh for 5c?

Sure 5C = 7kWh or 1.8kW solar. But will such small temp difference do any meaningful heating?

 

[OzSolar]

Sure 5C = 7kWh or 1.8kW solar. But will such small temp difference do any meaningful heating?

Not much at all, but like I mentioned, just trying to keep the plants from freezing at night so they can survive the night and keeping growing the next day.

Even then it's a still nearly impossible task. Short, often cloudy days and long cold nights have been the demise of many of well thought out and very expensive space heating systems. It's come up before and not one person here has been able to point to a working system.

I removed dozens of Carter era systems all through the 90’s. Some we were tasked to try to make work, others they had long since given up on. Sorta broke my heart but at least it paid well.

 

[45North]

You want the simplest? Forget about solar electric.
Just heat the water directly. Called "solar thermal".
Often used for swimming pools etc..
Can be DIY'd with off-the-shelf black, heat absorbing, pipe. You just need to circulate the water and keep it from freezing.

 

[solarpowergood]

Hi,

So my friend has a greenhouse and wants to keep it warm during the winter. He already has multiple 330gal tanks and I was thinking we can heat the water to use as thermal mass that can release throughout the day/night.

Is there a DC thermal dump that you can directly connect to solar panels to generate heat? Trying to do this without any batteries as it would raise cost. A cheap inverter if necessary but we'd prefer to go without that either if possible.

Hello, I've been considering something similar. I'm looking at forcing solar heated air through a heat ex-changer in a water tank. I know, not the most efficient setup but the air is free, heats readily, flows easily AND it doesn't freeze! Plus the only energy required would be for a small 12v fan controlled by a thermostatic switch. I have all the components I need and hope to have a trial system up and running in a few weeks or so. I'll let you know how it goes.

 

[45North]

Hello, I've been considering something similar. I'm looking at forcing solar heated air through a heat ex-changer in a water tank. I know, not the most efficient setup but the air is free, flows easily and it doesn't freeze! Plus the only energy required would be for a small 12v fan controlled by a thermostatic switch. I have all the components I need and hope to have a trial system up and running in a few weeks or so. I'll let you know how it goes.

Suggest you do the math on that first: I suspect that air alone doesn't have the thermal density and will not be able to carry enough calories to make it worthwhile. But hey, that's just a guy feel; mebbe it'll work!

 

[solarpowergood]

Suggest you do the math on that first: I suspect that air alone doesn't have the thermal density and will not be able to carry enough calories to make it worthwhile. But hey, that's just a guy feel; mebbe it'll work!

Lol, "math"? Uh-uh, not this guy. However, I do know that if you place a hot air pipe up against a cold water pipe, the water inside that cold water pipe will heat up.

(Hope I didn't seem flippant here but, honestly, me and math never mixed very well.)

 

[sumpower]

My sons greenhouse is similiar to the ones at this link and he just uses the sun to heat the water in barrels. Year round growing at 5,000 feet in New mexico.

Greenhouses

Our passive solar greenhouses are 100% sustainable. They perform on their own year round with absolutely no fossil fuel, we don't even have to plug in a fan. Stored water, balanced design, double...

www.pennandcordsgarden.com

 

[solarpowergood]

My sons greenhouse is similiar to the ones at this link and he just uses the sun to heat the water in barrels. Year round growing at 5,000 feet in New mexico.

Greenhouses

Our passive solar greenhouses are 100% sustainable. They perform on their own year round with absolutely no fossil fuel, we don't even have to plug in a fan. Stored water, balanced design, double...

www.pennandcordsgarden.com

Checked out that link - very impressive.

 

[OzSolar]

My sons greenhouse is similiar to the ones at this link and he just uses the sun to heat the water in barrels. Year round growing at 5,000 feet in New mexico.

Greenhouses

Our passive solar greenhouses are 100% sustainable. They perform on their own year round with absolutely no fossil fuel, we don't even have to plug in a fan. Stored water, balanced design, double...

www.pennandcordsgarden.com

Very nice work. Looks a Trombe Wall to me. The book I suggested #4 digs into all sorts of things like that and it's not that hard to read.

 

[sumpower]

Very nice work. Looks a Trombe Wall to me. The book I suggested #4 digs into all sorts of things like that and it's not that hard to read.

I read this book cover to cover when it first came out in print.
Linked here: https://www.amazon.com/Passive-Solar-Energy-Book-Greenhouse/dp/0878572376

I utilized the knowledge gained from the book (and a couple others) in multiple builds during the 80's and they are still functioning today at virtually no cost in maintenance along the way. Passive solar doesn't get the accolades it deserves most of the time.

The physics (magic) of converting solar to electric with all the benefits of it is why we are all here. So more solar panels is the answer to heating that 330 gallon tank. Lots of solar panels!

 

[Hieusays]

I read this book cover to cover when it first came out in print.
Linked here: https://www.amazon.com/Passive-Solar-Energy-Book-Greenhouse/dp/0878572376

I utilized the knowledge gained from the book (and a couple others) in multiple builds during the 80's and they are still functioning today at virtually no cost in maintenance along the way. Passive solar doesn't get the accolades it deserves most of the time.

The physics (magic) of converting solar to electric with all the benefits of it is why we are all here. So more solar panels is the answer to heating that 330 gallon tank. Lots of solar panels!

That's the plan. Solar panels are cheap. What I'm mainly asking is what people are using as an electrical load dump. Can I just take a heating element from a defunct water heater and hook up the positive and negative and let it go to town? Or is there a more purpose-built device that can handle various different currents from solar panels and be maintenance free.

 

[wpns]

That's the plan. Solar panels are cheap. What I'm mainly asking is what people are using as an electrical load dump. Can I just take a heating element from a defunct water heater and hook up the positive and negative and let it go to town? Or is there a more purpose-built device that can handle various different currents from solar panels and be maintenance free.

The problem is that without a MPPT (or at the very least a current regulator that’ll hold the input voltage around Vmp) your harvest from the panels will be a fraction of Pmp, so it won’t work very well.

 

[Al Coppa]

Hi,

So my friend has a greenhouse and wants to keep it warm during the winter. He already has multiple 330gal tanks and I was thinking we can heat the water to use as thermal mass that can release throughout the day/night.

Is there a DC thermal dump that you can directly connect to solar panels to generate heat? Trying to do this without any batteries as it would raise cost. A cheap inverter if necessary but we'd prefer to go without that either if possible.

There is no way to heat the water using solar electric. I will explain why:
330 gallons of water will only give off heat to the surrounding area when its temperature is more than 70 degrees.
When you try to heat the water to 120 degrees then you are going from 70 to 120 and that is a gain of 50 degrees.
50 X 8.345 pounds per gallon X 330 gallons = 137,700 Btu's of heats.
Burning a gallon of propane equals 91,450 Btu's. That means that 137,700 / 91,450 = 1.5 gallons of propane to make that happen each night.
I know that normal people do not like to hear that and they do not believe it but that is the way that heating water works.
You can't use batteries because there is not enough space in the green house to put the batteries.
1 Kilowatt hour of electricity is equal to 3412 Btu's of heat. And a 1500 watt electric heater will produce 5100 Btu's of heat.
The numbers are not in your favor.
You would need a system that could produce 40 Kilowatt hours in one day. 40 X 3412 = 136,500 Btu's. The days are shorter in the winter.
You can heat the water inside a water heater because it is only 40 or 50 gallons and it is in an insulated tank.
Heating a green house is like trying to heat your house using electric heaters because you are not talking about heating 50 gallons of water.

 

[Tweak3r]

There is no way to heat the water using solar electric. I will explain why:
330 gallons of water will only give off heat to the surrounding area when its temperature is more than 70 degrees.
When you try to heat the water to 120 degrees then you are going from 70 to 120 and that is a gain of 50 degrees.
50 X 8.345 pounds per gallon X 330 gallons = 137,700 Btu's of heats.
Burning a gallon of propane equals 91,450 Btu's. That means that 137,700 / 91,450 = 1.5 gallons of propane to make that happen each night.
I know that normal people do not like to hear that and they do not believe it but that is the way that heating water works.
You can't use batteries because there is not enough space in the green house to put the batteries.
1 Kilowatt hour of electricity is equal to 3412 Btu's of heat. And a 1500 watt electric heater will produce 5100 Btu's of heat.
The numbers are not in your favor.
You would need a system that could produce 40 Kilowatt hours in one day. 40 X 3412 = 136,500 Btu's. The days are shorter in the winter.
You can heat the water inside a water heater because it is only 40 or 50 gallons and it is in an insulated tank.
Heating a green house is like trying to heat your house using electric heaters because you are not talking about heating 50 gallons of water.

Where are you pulling that water will only release heat over 70 degrees?

 

[Shawn Hayes]

Just two options depending on how you want to plumb them into the system?
Both have 1” NPT threads.
Both are DC powered with built in thermostats.

48 Volt 700 Watt DC Water Heating Element with Adjustable Thermostat

48 Volt 700 Watt 6 Inch DC Water Heating Element for Use with Solar Panels or Batteries - built-in adjustable thermostat for easy temperature control. Model Features: High standard electric terminal screws zinc plated with rubber gasket Ratings: (Ni-Chrome coils / High...

windandsolar.com

12 Volt 200 Watt Submersible DC Water Heating Element with Adjustable Thermostat

12 Volt DC Submersible Water Heating Element with built in adjustable thermostat for DC water heating only from Missouri Wind and Solar.

windandsolar.com

 

[solarpowergood]

Suggest you do the math on that first: I suspect that air alone doesn't have the thermal density and will not be able to carry enough calories to make it worthwhile. But hey, that's just a guy feel; mebbe it'll work!

Did some prelimary work and without getting into a bunch of detail, it looks like you're right. Didn't see the results I was hoping for. But not ready to give up on the idea, yet; the "idea" being that I have this nice 40 gallon Superstor heat exchanger/tank hanging around doing nothing. I'm hoping to use that to store solar preheated water all year long -- IF I can figure out how to make an antifreeze system on the cheap.