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Dumb heating element and water pump

fatjay

Solar Enthusiast
Joined
Oct 31, 2022
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In my shop I have radiant floor heat, except I never hooked it up. It's a hot water system. Due to complications of inflation, I still don't have the 400' of 0-4 wire run to the shop from the house, so my electric hot water and circulation pump system has not come to pass at this point.

That got me thinking, I have a lot of roof space and it's an east/west roof. What if I put 1000w of panels on each side, and some how wired them into a heating element inside 20 gallon "bucket" of water, then put 250w of panels on each side and somehow tied it to a circulation pump. Then, as the sun rises in the morning, heating element starts slowly, circulation pump starts slowly, by ~11am it's heating and pumping and circulating and at around 3-4pm it slows down, but the heat is then in the concrete which should last me a couple hours. I typically hit the shop around 1pm anyway and am there until about 8pm.

I built this shop by hand, so I know everything about it. It's currently uninsulated, but I haven't got $10k to insulate it yet. I'm not looking for a balmy 70f, but it would be nice if it wasn't 25f. But from my googlings, I am not sure I can find a heating element or circulation pump that will handle partial draws. My idea is to come strait off the panels, maybe 2 strings, which 37voc is ~185v for 5 panels, 2 strings of 5 panels. I have spare panels laying around, it might be nice to be able to utilize them and get my shop warmer.
 
Ok from what I can tell, I need an MPPT, and heating element from the looks of things.


That says 48v 20a output.


That's 48v 1000w heating element.

I string 5x 240w panels together, go to the pv input of the victron, then wire hte load to the heating element, and it should get hot if the sun is up and panals are producing?

The shop is big, it's a lot of concrete, so I'm guessing I'll need 2-3 sets of these to even hope to make a difference.

Assuming that all works, i need a way to pump water.
 
Ok from what I can tell, I need an MPPT, and heating element from the looks of things.
No, an MPPT is for charging batteries.

The solution might be as simple as connecting your 1000W of panels to a ~2000W water heating element in a 55 gallon drum (they make kits with all the fittings for heater).

A DC motor could be powered directly from a panel with roughly the right voltage. It would need to be a small RV pump or similar other wise it might not overcome surge/startup amps.

Let me look for the discussion on this.
 
I thought that might work, but someone told me that the heating element wouldn't work right unless because the panel voltage vary widely, and panels didn't work like I think they work.

For the record I have lots of 240w panels laying around. They're 37voc. But I would like to send amps to the heating element even if they were not optimal.

The mppt I linked has load terminals, and a fella on youtube shows that it does output to do things like power a dc kettle. So I'm just trying to make sure I'm getting as much power out of the panels as possible. Because it will be probably closer to 3-4 heating elements and 3-4 sets of 1000w's of panels.

 
The mppt I linked has load terminals,
The load terminals on SCCs are intended for small loads, like a light or a solenoid.
I thought that might work, but someone told me that the heating element wouldn't work right unless because the panel voltage vary widely, and panels didn't work like I think they work.
I don't think a heating element is overly picky about voltage. I agree a big heating element might drag the voltage down but it would be pulling a bunch of amps. I look at how many watts i am applying to a dumb heating element and expect to get a reasonable amount of those watts as heat on the element.
 
Good to hear. I'm debating just buying a heating element for $13, applying random dc voltage, and seeing what happens. I've played with this stuff all my life, but never tried to use it for anything other than it's intended use. In my mind, a heating element is just a wire with resistance that heats up when amps are applied because current is resisted.
 
In my shop I have radiant floor heat, except I never hooked it up. It's a hot water system. Due to complications of inflation, I still don't have the 400' of 0-4 wire run to the shop from the house, so my electric hot water and circulation pump system has not come to pass at this point.

That got me thinking, I have a lot of roof space and it's an east/west roof. What if I put 1000w of panels on each side, and some how wired them into a heating element inside 20 gallon "bucket" of water, then put 250w of panels on each side and somehow tied it to a circulation pump. Then, as the sun rises in the morning, heating element starts slowly, circulation pump starts slowly, by ~11am it's heating and pumping and circulating and at around 3-4pm it slows down, but the heat is then in the concrete which should last me a couple hours. I typically hit the shop around 1pm anyway and am there until about 8pm.

Radiant floor heat is not a quick turn on and you get heat. It takes time.

1000W of panels on each side won't go far. Take a look at this chart https://windandsolar.com/how-to-siz...How many watts does it,one degree in one hour.

10 gallons of water with a temp rise of 40F takes 1000W for 1 hour. The radiant heating system is probably at least 50 gallons of water so 1000W raising the temp 40F will last about 12 minutes. It won't heat the concrete that fast but you need to get the water warm and circulate it to get heat transfer to the concrete. My gas condensing boiler runs the output temp at around 120F to 140F with a primary/secondary loop system.

I built this shop by hand, so I know everything about it. It's currently uninsulated, but I haven't got $10k to insulate it yet.

Insulate it first before moving to any solar system. What type of building, size and type of insulation? I did 3 inches of spray foam on the walls. The walls are 11 inches thick, 8 inch poles and a 1.5 inch girt on inside and outside. I filled the rest of the wall cavity with cellulose before installing the ceiling. If I was to do it over again, I would have just done the cellulose. My ceiling followed the knee braces in the top corner and this allows for a cheap energy truss as insulation will be a few feet deep at the top corner. If the wall cellulose settles, there is plenty at the top corner to still keep the corner well insulated. If you have a steel truss building then spray foam is really the best choice. I've been in shops with steel trusses, the problem is where the liner meets the truss. Always a gap at that point, one shop I was at they told me they can feel the breeze from that gap.

I'm not looking for a balmy 70f, but it would be nice if it wasn't 25f. But from my googlings, I am not sure I can find a heating element or circulation pump that will handle partial draws. My idea is to come strait off the panels, maybe 2 strings, which 37voc is ~185v for 5 panels, 2 strings of 5 panels. I have spare panels laying around, it might be nice to be able to utilize them and get my shop warmer.
You will need to mix water with glycol so your system doesn't freeze. That isn't cheap.
 
Use one of the many heat loss calculators on the web to figure out how many btu per hour you need for your building. Then convert btu to watts. I think you will find you will need much more power than you think.
 
Build some solar thermal water heating stuff. HD says 0000 is $1200 for 500 feet. I'm assuming need 3x that due to L1, L2, neutral. + some extra for ground (not as big a wire). That's $4000 you could use to do solar thermal heating.


Of course you'll still need electricity eventually but if you greatly reduce the heating needs, you can downsize your wire.

I frankly do not understand why you'd want to use electricity for in floor heating. The whole concept of in floor heating is that you don't need a high temp to put out a good amount of heat, so the temp delta is lower, which is more efficient if using a boiler/heat pump. Electricity has no such temperature delta adjustment so it's just as expensive per BTU output regardless of the temp.
 
The building is 1056 sq ft and 25' tall. The slab is 8" thick and there's 1600' of pex tubing which has an interior volume of 16 gallons. The slab is sitting on 2" foam insulation with insulation along the sides. I have a single 20a circuit available, so there is some power available. It's steel over plywood over 2x8 walls. Eventually I'll stick R27 in those walls, but not until I've finished electrical and plumbing. I'll be using a mix of water and RV antifreeze in the radiant floor heat system, the total capacity of the hoses is ~16 gallons plus about a 15-20 gallon heating tank.
 
I finally found the solar water heating product site i was thinking about.

I saw that, I don't think it gets very warm though, and doesn't take much power. 12v and 200w is more like something that just keeps water from freezing.
 
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When building it, I had the trusses engineered to take 6000lb of panels. It's steel siding on top of plywood wrapped with tyvek on 2x8" walls.

The complication is the roof is very far away from the slab, so much more than a couple wires is going to be a real pain. Also it's facing north, so the sides are east/west. The pitch is shallow but I can get AM and PM panels up there.
 
1056 sqft x (8 inches / 12) = 704 cubic feet of concrete
133 lbs per cu ft *704 *.2 = 18,726 BTU to raise the temp of the floor 1 deg F (ignoring losses to the ground, air, etc)


1 kwh electric power = 3412 BTU/h

so if we had 2 KWh of electric heat that would be 6824 btu per hr

2 kw of electric power would be enough to run a 12,000 BTU heat pump possibly 24,000 btu

see also trombe wall
If the back wall without the garage doors faces south and it was a solar thermal collector .... 24' wide x 25' high = 600 sqft sun at 300 btu / sq ft * 50% efficient solar thermal collector = 90,000 btu / hr
 
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Ok i'm tossing all preconceived knowledge out and starting from scratch.

I have solar panels. I want a heating element that can make hot water. I do not want batteries. Can I connect panels directly to heating elements? If not, is there some controller that will let me do that.

This is a temporary system that will get scrapped and the panels will be used elsewhere. I do not want to spend much money on this for components I won't reuse later.

What are my options? Panels to make water hot with as few additional components as possible? There must be a way I haven't figured out. Can I connect a heating element to the battery port of an mppt controller?
 
Can I connect panels directly to heating elements?
Yes
If not, is there some controller that will let me do that.
A thermostat
Can I connect a heating element to the battery port of an mppt controller?
No

You can get a $10 hot water heater element from a hardware store, connect a panel and stick it in a bucket of water (i'd use a metal bucket if the hot element cannot be kept away from the bucket itself).
See how it works, add panels to get more mower. I cannot think of a strategy as whether its best to add in series, parallel or some combination.
 
Yes

A thermostat

No

You can get a $10 hot water heater element from a hardware store, connect a panel and stick it in a bucket of water (i'd use a metal bucket if the hot element cannot be kept away from the bucket itself).
See how it works, add panels to get more mower. I cannot think of a strategy as whether its best to add in series, parallel or some combination.
Standard heating elements are AC though, where panels produce DC. I know they're just resistors that get warm, but I wasn't sure what would happen if i connect dc to the element designed for ac. Not a bad idea though, i have metal buckets. what's the worst that can happen. I'm just hoping I don't damage the panel in some way.
 
I'm just hoping I don't damage the panel in some way.
A resistive load pulling as much power as it can is exactly what an MPPT charge controller is designed to do.

Get a heating element that will handle the number of watts for the panels you intend to use. Like a 2000W element for 2000W of solar.
 
Get 240V heater without thermostat. For example this one is 3kW 240V for $7. Calculate heater resistance: 240^2 / 3000 = 19.2 ohms. Calculate solar panel impedance: 28 Vmp / 7Amp = 4 ohms. 19.2 / 4 = 4.8 or ~5 panels needed in series to have their max power point match this heater element. That's it, theres nothing else you need. Use 15A 240V plug and socket as PV disconnect. No need for thermostat because 1000W of panels are unlikely to boil your radiant floor water loop.
 
If you want 2 strings of panels in parallel and maintain impedance you would have to go with 4500w heater. You can do 7 series 2 parallel or 14 panels with that element for 2400w total PV heating power.
 
Thanks for the info.

What if the panel impedance is lower than the heater? Such as times when the panels aren't operating at 100%? Early mornings, late afternoons, cloudy days?
 
They still produce power but at less efficiency. They will produce max current they can but at mismatched voltage because at low solar irradiance their effective impedance will go up.
 

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