Keep in mind that it takes 5.5kWh to heat your concrete slab by 1 degree. So 14 panels in winter weather will not be effective at all. You are better off just running 3kW 240V heater (since you have 20A circuit in the shop already) from grid power. It will take 230 kWh or 3 days to bring up your slab temp to 70F.
Dumb heating element and water pump
- Thread starter fatjay
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I don't need 70, it would just be nice to not be working on a 20f slab, 40f is much warmer. I have a 110k kerosene bullet heater I use there now but it's loud and I go through $30 of kerosene in about 6 hours, to hit 50f. I want to take the chill out of things, not run around naked.
And at current grid rates, 230kwh is $43. I'm trying to reduce consumption as much as possible, adding a new thing on the grid is going in the wrong direction.
And at current grid rates, 230kwh is $43. I'm trying to reduce consumption as much as possible, adding a new thing on the grid is going in the wrong direction.
Getting up to 40F will take 110 kWh and less energy per day to offset thermal loss to maintain that temp. Where are you located? If you are up north then solar will not help you keep your shop warm in winter. You really have to insulate first then measure energy required to maintain desired temp inside. Then you can decide which heating strategy will be most cost effective.
Hedges
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Do some math and design it before you buy it or try it.
Resistive heating elements work the same at 240VDC as at 240Vrms AC.
Thermostats and over-temperature safety switches do not; they will fail with high voltage DC. They could be used for "pilot duty" at 24VDC to control a relay or SSR rated for the DC voltage. But as long as you have a non-pressurized tank and element remains underwater (automatic fill valve?) no hazards. Use a suitable DC rated switch to shut off.
Look up the specs of the heating element, 120V or 240V. If it is rated 4800W at 240V, that is 4800W/240v = 20A. 240V/20A = 12 ohms.
With that, you can calculate how much current it would draw at Vmp of your PV string, and how many watts it would deliver.
Probably don't configure series string of PV panels such that Vmp exceeds the 240VAC rating of heating element, to avoid damage.
See if you can make an array 240 Vmp able to deliver around the 20A (if using 4800W element).
$0.19/kWh.
PV panels can be had for $0.005/kWh amortized over 20 years, give or take. So 6 months payback compared to using electric grid for heating, if mounting hardware and the rest was free and you wanted the heat year round. 1 year if heating 6 months. Depending on how well you scrounge materials, maybe a few years payback
I'm in eastern PA, it definitely gets cold. I'm going to be building out a better system next summer, I was just hoping to get some relief this winter with a system i could reuse the components of when i build something bigger.
Around here 240w panels are $30-60. I have 18 sitting in the shop waiting on an application.
It'll be a closed system, I was going to find an old hot water tank and use that. Circulation pump off the top port pulling water from the system and pushing it into the tank where it would be warmed and then out to the the manifold. Tanks typically have 2 heating elements.
If memory serves the panels are 31Vmp and 37Voc. 240/31 is 7.7 panels or 7. 7 panels is peaking at 1680 watts for a 3kw element, so I should be able to get 2 strings of 7? Or 6 to be safe?
It's been a long time since my electronic principals course, volts and watts and amps are easy but ohms is resistance, heating elements have resistance, that's how they produce heat. But I'm not sure why the panels have resistance. Or is it their ability to overcome impedence?
If it is reduced efficency, wouldn't it be better to get a small mppt to convert that to a solid 48v output with varying amps and get a 48v dc heating element to match? Or won't it be much different?
Around here 240w panels are $30-60. I have 18 sitting in the shop waiting on an application.
It'll be a closed system, I was going to find an old hot water tank and use that. Circulation pump off the top port pulling water from the system and pushing it into the tank where it would be warmed and then out to the the manifold. Tanks typically have 2 heating elements.
If memory serves the panels are 31Vmp and 37Voc. 240/31 is 7.7 panels or 7. 7 panels is peaking at 1680 watts for a 3kw element, so I should be able to get 2 strings of 7? Or 6 to be safe?
It's been a long time since my electronic principals course, volts and watts and amps are easy but ohms is resistance, heating elements have resistance, that's how they produce heat. But I'm not sure why the panels have resistance. Or is it their ability to overcome impedence?
If it is reduced efficency, wouldn't it be better to get a small mppt to convert that to a solid 48v output with varying amps and get a 48v dc heating element to match? Or won't it be much different?
Hedges
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7s2p or 6s2p should work fine.
But it will only put out that power at Noon, or whatever orientation the panels. Other times, they get less than full sun.
Since you have 18, try 6s3p, oriented SE, S, SW. Maybe all oriented S and tilted for winter sun, one string rotated E and the other W on that axis to catch morning and afternoon sun.
But it will only put out that power at Noon, or whatever orientation the panels. Other times, they get less than full sun.
Since you have 18, try 6s3p, oriented SE, S, SW. Maybe all oriented S and tilted for winter sun, one string rotated E and the other W on that axis to catch morning and afternoon sun.
Be careful not to contaminate your radiant floor loop with gunk from old water heater. You really don't need it. Just get a pipe, weld on threaded fittings on the sides, cap the end and weld on threaded adapter on top to fit heater element threads. A DIY tankless water heater.
Panels have a sweet spot where they will make peak power provided that load impedance (resistance) is just right. MPPT controller acts as variable load impedance tuner to present panels with optimal load they need in order to transfer max power available. You can manually pick a load vs. panels combo to get them as close to their ideal load as reasonable. Since you have 18 panels you can try 6 in series and 3 strings in parallel and not worry too much about getting it perfect right now. During winter you will not get 1000w/m^2 sun anyway.
efficientPV
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Not a bad idea though, i have metal buckets. what's the worst that can happen.
What is the best that can happen? Not much. You can stick two wires into a dead chicken and heat water, it doesn't prove anything. If you don't have numbers to backup what was done it is absolutely worthless. Heating water isn't rocket science, almost all the information is already available. A solar calculator will tell you what energy is available. With direct connect you will at best get half of that. Solar panels do not work well into fixed resistance. Heating is a function of squares and a small drop in current dramatically reduces the actual heating. That is the reason that the calculated ideal resistance can be almost doubled and still produce more daily heating. At least four heating elements are needed to sequence in as sun intensity increases and decreases thru the day. If you want an education, buy a power meter and connect it between the panels and the element. It will soon become apparent that direct connect is a pipe dream. Hydronic heating is total folly unless the floor can be brought up to temperature and maintained. The mass that has to be heated is too large to increase any significant amount. Go with radiant electric. Heat pump would be best. However, that is a major investment in solar equipment.
What is the best that can happen? Not much. You can stick two wires into a dead chicken and heat water, it doesn't prove anything. If you don't have numbers to backup what was done it is absolutely worthless. Heating water isn't rocket science, almost all the information is already available. A solar calculator will tell you what energy is available. With direct connect you will at best get half of that. Solar panels do not work well into fixed resistance. Heating is a function of squares and a small drop in current dramatically reduces the actual heating. That is the reason that the calculated ideal resistance can be almost doubled and still produce more daily heating. At least four heating elements are needed to sequence in as sun intensity increases and decreases thru the day. If you want an education, buy a power meter and connect it between the panels and the element. It will soon become apparent that direct connect is a pipe dream. Hydronic heating is total folly unless the floor can be brought up to temperature and maintained. The mass that has to be heated is too large to increase any significant amount. Go with radiant electric. Heat pump would be best. However, that is a major investment in solar equipment.
MisterSandals
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efficientPV
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No, sticking a heating element in a bucket connected to a panel is stupid without getting any data.
A great heating element nobody knows about is the HE90240. This is a single phase 9KW 240V element for on demand water heaters which is 6.5 ohms. It is physically the same size as a standard 5500W found in many tanks.
A great heating element nobody knows about is the HE90240. This is a single phase 9KW 240V element for on demand water heaters which is 6.5 ohms. It is physically the same size as a standard 5500W found in many tanks.
Its $40. But here is idea fop OP to use tankless water heater instead of tank. Just make sure to wire PV direct to heaters bypassing temp switches.
I know this thread is about dumb heating elements and water pumps for concrete heating but you should probably also consider mini split heat pumps. In heat mode, they run like an AC in reverse (cool outside, heat inside). They are commonly 3x more efficient per watt-hour than pure resistive heating. They are also not super expensive (you don't need the hyper heat stuff since it is for shop heating). Maybe something like this: https://www.pioneerminisplit.com/co...lit-air-conditioner-heat-pump-system-full-set. You'd use the mini split during typical operation and if it's super cold and you need to be in the shop, supplement with kerosene/propane (if it's super cold, they'll be running as basically pure resistive heating anyways).
Do you have anything for the floor heat now? Pumps, heater anything.
Reason I ask is if you could hook it up to a generator you already own, or could borrow you will get a real world estimate on just how long it is going to take your floor to get up to temp. Personally I think it is going to take longer then you think it will. The concrete is a great deal of mass, I don't think it is going to be an on, and 5 hours later it will be nice in there, I have a feeling the floor will still be ice cold to the touch. Naturally the farther from the heater the less you are going to feel it.
I really think a test is in order before you go too far down this road.
Folk I know with this system leave it on all the time. This way the water is not ice water coming back requiring more energy to get it up to temp. They never turn it off. I don't know what their power bills are however.
Just my two bits. And yes I agree with you a cold floor no matter how good your boots are will get to your feet sooner or later.
Reason I ask is if you could hook it up to a generator you already own, or could borrow you will get a real world estimate on just how long it is going to take your floor to get up to temp. Personally I think it is going to take longer then you think it will. The concrete is a great deal of mass, I don't think it is going to be an on, and 5 hours later it will be nice in there, I have a feeling the floor will still be ice cold to the touch. Naturally the farther from the heater the less you are going to feel it.
I really think a test is in order before you go too far down this road.
Folk I know with this system leave it on all the time. This way the water is not ice water coming back requiring more energy to get it up to temp. They never turn it off. I don't know what their power bills are however.
Just my two bits. And yes I agree with you a cold floor no matter how good your boots are will get to your feet sooner or later.
Right now it's just the manifold capped off holding pressure. I can rig up a pump pretty easily to circulate water, just the main problem is making it warm.
You have a point, I should just experiment with ac power first. But it's not good for the long term. Even if a 1000w heating element is running 24/7 that's ~9a or 24kwh per day, for 30 days, at $0.19/kwh that's $136.8/mo. That's a lot of juice.
1000w is also fairly low, which is why I was thinking 2-3 strings of panels each being 1200w each that will blast it with heat. Like I said I am not looking for a balmy 70f, I just don't want my feet to be freezing on an ice cold concrete floor.
You have a point, I should just experiment with ac power first. But it's not good for the long term. Even if a 1000w heating element is running 24/7 that's ~9a or 24kwh per day, for 30 days, at $0.19/kwh that's $136.8/mo. That's a lot of juice.
1000w is also fairly low, which is why I was thinking 2-3 strings of panels each being 1200w each that will blast it with heat. Like I said I am not looking for a balmy 70f, I just don't want my feet to be freezing on an ice cold concrete floor.
I see where you are going, I will tell you about the two folk I know with the systems. Now I don't know their bills, or time to get "warm" but I do know a little bit about two systems on each end of the extreme.
Guy one lives in northern ID almost Canada. His system in in a VERY nice hanger, like airplane hanger. This guy has all kind of cool toys, those $40 four person side by side hot rods, naturally airplanes. I think he lights cigars with $100 bills. His system in commercial, and only has it off for a few months in the spring-fall. When outside temps are in the 50's it is getting cold at night. His runs all the time, and the floor is "warm" to the touch. It is not "hot", and warm is not the best word. Lets say you put your hand on the wood kitchen table in your house, thats it.
The other guy is a "home made" setup using a big hot water heater. I think he said he has 3-4 different "loops", not sure if that is a thing, I really don't know much about it.
When he cranks his up again around this time of year here in middle MO. He has it set to pretty hot. You don't want to hold your hand under the water hot. he says that will warm up the slab quicker. I never asked how quick. Then he will turn it down to what I would call lukewarm. Personally I think the floor is still cool to the touch, much cooler then guy 1, but it is warmer then my floor, when on a 50f day and you open the shop it is flat cold in there, and if you leave a bottle of water on the floor it is the same temp as you take it out of the fridge. His is on 24x7 in the winter. Everything he has is electric. I don't know what the bill did after he hooked that up, that would be tacky to ask. You don't ask if bills go up, but you do ask if bills go down....solar people tend to like to talk about that.
I think it would have to, I have never seen the light on the water heater off, but I don't look every time I am over there. And that pump is always running, you can hear that in one part of his shop. He is a big time wood worker with vac hoses in the floor and this big fancy dust collection deal he setup. Stuff to keep the wood in storage nice, humidity,heat, cool all that jazz.
I also admit I am not sold on it for my use. I am out in my shop darn near every day, at least 4 hours after work, and usually most weekends. It is my man cave. I just have normal heat. Up stairs it gets quite warm with the heat running that you need to turn it off even with two fans moving stuff around. I thought about heating the slab, but not sure if my use would warrant it.
Peco is the power company.
Yes, it's a 50/50 mix with water and RV anti-freeze, water is just a bit of an oversimplification.
I heat my house with wood. It's a bit of a pain. Felling tree's, cutting them up, splitting the wood, seasoning the wood. I'm looking for less maintenance and less reliance on outside elements.
I know a guy in nebraska that heats his shop with radiant floor heat with electric hot water for between $40-60/mo. However, he has massive amounts of insulation. Which I will have eventually. But not yet. My walls are 8" thick which means I can get R27 in there, and R40-50 in the roof. The garage doors and man doors are insulated as well. The idea is once there's heat there, it'll stay.
Yes, it's a 50/50 mix with water and RV anti-freeze, water is just a bit of an oversimplification.
I heat my house with wood. It's a bit of a pain. Felling tree's, cutting them up, splitting the wood, seasoning the wood. I'm looking for less maintenance and less reliance on outside elements.
I know a guy in nebraska that heats his shop with radiant floor heat with electric hot water for between $40-60/mo. However, he has massive amounts of insulation. Which I will have eventually. But not yet. My walls are 8" thick which means I can get R27 in there, and R40-50 in the roof. The garage doors and man doors are insulated as well. The idea is once there's heat there, it'll stay.
orangezero
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One idea that isn't mentioned much is to hook up solar panels outside and wire them up to solar panels inside. Panels are basically just large surface area diodes that can dissipate heat, and you can more easily keep them near the max power point of the outside panel and get a bit more energy than just directly hooking up a heating element to a solar panel. You could also use diodes in series to dissipate heat, but you already have panels.
The guy I heard about this from used two outdoor panels to run into 2/3rds of an indoor panel, and it heats his internal panel up to a good temp, but less than a typical solar panel may get on a hot roof in summer. Dacian from electrodacus.com has pictures on his forum/website in the gmail section. Not everyone wants solar panels in their homes, but for this case it could do some good without spending a lot of money.
The guy I heard about this from used two outdoor panels to run into 2/3rds of an indoor panel, and it heats his internal panel up to a good temp, but less than a typical solar panel may get on a hot roof in summer. Dacian from electrodacus.com has pictures on his forum/website in the gmail section. Not everyone wants solar panels in their homes, but for this case it could do some good without spending a lot of money.
ruralsolar
New Member
Lots of math about how much energy to heat the slab to a certain temp. What is really missing to help size the system is the temp the slab needs to be at to keep the air temp at a certain point (if that is something desired beyond warming up the floor some for when doing work). Siegenthaler has some excellent webinars and blogs about low temp hydronics, more specifically in this case, the math to figure out what surface temp a floor needs to be at to maintain a certain room temp assuming you know the BTU load of the space.
www.pmmag.com
John Siegenthaler: Radiant panel systems
Radiant floors don’t necessarily have to feel warm to work properly.
www.pmmag.com
They offer residential heating TOU rates. Try their cost savings estimate: https://www.peco.com/smart-energy/innovation-technology/time-of-use-pricing
That is interesting, I didn't know that existed. Thanks.
Whats-n-Watts
New Member
Water Heating Calculator for Time, Energy, and Power
The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.
DC submersible water heater element for 12 24 and 48 volt heating
DC submersible water heater elements for 12 24 and 48 volt heating. a great alternative to AC and sumplimenting solar hot water systems
www.hurricanewindpower.com
A 4500w 240v element can be used but a true DC would perform much better. 240v will only give you around 900w or so water heating power at 48v. I read something to the effect of each time the ac element voltage is reduced by half the output is 25% of the sticker ratings or something like that. Unless you use an inverter stick to the DC element. Missouri Wind and Solar have the reputation of selling AC elements for DC but I have no experience with them so I can't say for sure.
You could throw a small battery in, wire as a normal small system and just leave the inverter out if the mix. You could power one off the battery and the top element off the LVD. A decent scc should supply the rated Amps of the controller. I'm going to do some experiments with a dump load fed into a MPPT battery input so the controller has voltage to power it from a separate system and throw a panel or two on the second scc and set them so that when the LVD from controller #1 drops off the other #2 still has power coming in. Of course I will fuse and diode between the two controllers to prevent back feeding. Will it work? I don't know but there is one way to find out. Try it.
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