DC water heater.

Giantkiller said:

I had planned on using solar hydronic panels. But the cheapest are $900 all the way up to $2600.

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If you can wait and enjoy the hunt for a deal there's often all sorts of deals to be found on auctions sites like govdeals.com

Here's some thermal panels that sold in 2023. https://www.allsurplus.com/asset/936/9917

Here's 10kW of PV, ballasted racking and an inverter that's currently at $725. https://www.govdeals.com/asset/15/9276

mciholas said:

Geothermal (aka ground source) heat pumps are not like that. They work well in the winter. You can get water to water GSHP.


You want vertical wells if you can find the right driller. This is particularly true in northern climates where earth temperatures are cold even quite deep. My office building uses 32 wells, each 300 ft deep. My entering water temperature (EWT) is about 63 F year round.

This boils down to a simple equation, what gets you the most hot water for the system cost, a smaller PV array with a water to water GSHP, or a larger PV array with resistive heat? You need about a 4 to 1 ratio of PV array size for the equivalent performance.

I could easily see the larger PV array with resistive heat winning that race. For one thing, it will tolerate intermittent sunlight better than a GSHP.

I like the idea of DC direct couple to the heating elements. No inverter to buy or fail. You just need a good way to have the thermostat cut off the power so you don't have a melt down. Hence my idea of using an RSD device to avoid any mechanical contacts being involved. There are also SSR (solid state relays) that work on DC voltages if that would be better.

Mike C.

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Yes I know geothermal is not like that. I have one for my house. That I self installed. Works quite well. Here in Wisconsin 56ish degrees 6-7' down mine are 9-10' down. My horizontal (cheaper than vertical by far) loops cost me $5,000 6 years ago. Probably way more now. So figure $7,000 -$12,000 for vertical loops. Plus $6,000+ for the water to water unit Plus pumps. Best case $14,000 for geothermal. Plus cost of solar panels Plus inverter. Because I don't think there are DC geothermal units $20,000ish Vrs solar panels to DC inserts 2 large water heaters. $3,000ish

OzSolar said:

If you can wait and enjoy the hunt for a deal there's often all sorts of deals to be found on auctions sites like govdeals.com

Here's some thermal panels that sold in 2023. https://www.allsurplus.com/asset/936/9917

Here's 10kW of PV, ballasted racking and an inverter that's currently at $725. https://www.govdeals.com/asset/15/9276

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Wow. Thanks for the heads up. Didn't say if they were s shape or h with header pipes. Need h for drain back system. And I would need atleast 10 solar hydronic panels. But wow what a deal.

There are no DC thermostats. Those at MW&S will burn up. You need to keep panel voltage at power point to be efficient. Doing it electronically is so cheap and easy. I can't see why this isn't more popular here. Out of tens of thousands of people around the world it would seem there ought to be some here with talent. You can't do what you think you can't do.

Wow, impressive setup. I am also in a northern climate and have experience in not only Solar but also Solar hot water panels. I have found that the solar panels mounted on the roof do not produce electricity until all the snow melts. The solar panels I have in the yard require periodic maintenance by removing the snow off the panels, so they start to produce electricity again.

If you are hoping that the solar panels will provide electricity to melt the snow on your driveway then you may have a catch 22. It is almost like trading one chore for another one. Snow blowing a driveway vs removing snow from the panels. If you mount the panels on the roof then it just will not work until the sun melts the snow off the panels. If you mount your panels using a ground mount, as I have done, then it takes a while to suit up and clear a path to the panels and then remove the snow.

Solar hot water panels can be found at extremely good prices now. A lot of people are removing the hot water panels due to roof restoration and then replacing them with Solar panels. They produce more BTU's per sq foot than the equivalent Solar panels. They also eliminate all the issues with converting electricity into heating water. They also need to have the snow removed to produce heat.

My suggestion is to find some dirt cheap Solar hot water panels on Craigslist and then mount them in the yard somewhere and use them to heat your driveway. I have a number of them installed throughout my yard. Two of them are used to heat my domestic water tanks. The remainder are used to heat my swimming pool.

Giantkiller said:

Thanks for the idea. But. Heat pump water heater are great especially in southern climates. Since like all heat pumps they remove the heat from the air and put it into the tank. They in turn cool the air around them. Not really a great idea when up north. Especially when the only time I would be using it is in the middle of winter.

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You do realize 1 Kwh of electricity equals 3,412 btu's?

If you are planning on using PV direct to heat water for heating a house, driveway or other large heat loss object, the amount of Kwh needed is quite high. Missouri Wind and Solar put out this chart showing how many watts needed to raise water temp X number of degrees per hour. https://windandsolar.com/how-to-size-a-dc-water-heating-element/

I plan on using my heat pump water heater to supply domestic hot water in my house in the winter. Yes, it will draw some heat energy from the surrounding area if I use the heat pump. I can also use the 4500W heating element instead to heat water by simply changing the source on my phone from anywhere I have cell service. In winter, the heat pump water heater will be mainly a dump load that either will heat all the water or tempers it before the propane water heater.

I live in northern IA, about 20 miles south of MN border and west of WI about 80 miles. It gets cold here too.

Giantkiller said:

And It would be running constantly. During any day that the sun is shining. AC in an insulated area you want to keep as hot as possible. Heat pumps are awesome there efficiency is great. But it declines when trying to pull heat out of -20° air that's why they aren't used too much up nort der hey.

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My heat pump water heater is in my basement. It stays about 60°F there all winter even when it's -30°F here in Iowa there ey. I'm not concerned about the heat energy it will pull from the basement during winter, during extreme cold I heat with wood or the propane furnace.

Giantkiller said:

They do make northern climate heat pumps that can somehow pull heat out of really cold air. But again at major loss of efficiency and durability. Due to having to run constantly, during the winter.

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You are referring to outside units like air to air mini splits. I'm not putting my water heater outside, the heat loss would be quite large.

Giantkiller said:

Thats why I installed my geothermal. Heat pump that only has to take heat out of 56° water. And for that matter it gets to put heat into 56° water. During the summer. Way less work. That's why geothermal heat pumps can last 30- 40 years. They aren't trying to pull heat out of -20° air and trying to put heat into 90° to 100° air.

A geothermal heat pump would be the best to heat my driveway. But again lack of space in my yard for loops. And cost. I got 3 estimates for geothermal for my house/shop. All 3 had different ideas for equipment. And all 3 came back estimate of just over $45,000. Like they all got together and said lets tell him $45,000. I installed it myself for a little over $22,000. With Warmboard infloor heat upstairs. And that includes paying $5,000 to have the loops installed. It took me a month to figure it all out and still working 65+ hrs driving a forklift to pay for it. If I knew what I was doing. I probably could have installed it in a day maybe 2. So the geothermal guys where making $23,000 + for a couple of days work.

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You have geothermal which is what you should be using to heat the water as the electricity used with a COP of more than 4 (geothermal) would be more efficient than DC direct. Remember, one Kwh of electricity equals 3,412 btu's. A heat pump with a COP of 3 makes the 1 Kwh of electricity 10,236 btu's and a COP of 4 is 13,648 btu's.

Giantkiller said:

Sorry I got off on a rant.

Anyway thanks everyone for the information. It's greatly appreciated.

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If you want to drill wells, you need to be like Larry who I ran across one day on Youtube. Actually, you could simply use his method of extracting ground heat for your driveway clearing in winter, just pump closed loop water glycol from the ground which should be around 55°F and circulate it thru your driveway loops.


I would drill with a large hole and much faster using this method. Just pull the casing back up and run your loops down the hole like Larry. Four 40 foot deep wells would be 320 feet of loop.

Everyone I ever heard of in the Massachusetts area who had electric driveway heaters locked them off after the first power bill came in.

wpns said:

Everyone I ever heard of in the Massachusetts area who had electric driveway heaters locked them off after the first power bill came in.

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Yep like I said before. Those are heated to higher points. Because they want it to melt extremely fast. Due to liabilty.I generally just drive over it with my truck until it melts on it's own. I did have a friend plow my driveway this winter. After a Blizzard dropped a foot and a half on my driveway. I put my inslab inside the house so I figured I would do the same on the driveway. Before the concrete got poured. It will work no matter what way I do it. Because I really don't care how long it takes. If it takes a week of sunny days. To melt it. So what. Luckily. Global warming has made it so snow doesn't really stick around in Wisconsin any more. That's why I pulled the moter out of my rx1 sled to stick it. In my smart car. This is just an experiment. To see if I can get it to melt my snow faster than the Global warming does.

WindWizard said:

Wow, impressive setup. I am also in a northern climate and have experience in not only Solar but also Solar hot water panels. I have found that the solar panels mounted on the roof do not produce electricity until all the snow melts. The solar panels I have in the yard require periodic maintenance by removing the snow off the panels, so they start to produce electricity again.

If you are hoping that the solar panels will provide electricity to melt the snow on your driveway then you may have a catch 22. It is almost like trading one chore for another one. Snow blowing a driveway vs removing snow from the panels. If you mount the panels on the roof then it just will not work until the sun melts the snow off the panels. If you mount your panels using a ground mount, as I have done, then it takes a while to suit up and clear a path to the panels and then remove the snow.

Solar hot water panels can be found at extremely good prices now. A lot of people are removing the hot water panels due to roof restoration and then replacing them with Solar panels. They produce more BTU's per sq foot than the equivalent Solar panels. They also eliminate all the issues with converting electricity into heating water. They also need to have the snow removed to produce heat.

My suggestion is to find some dirt cheap Solar hot water panels on Craigslist and then mount them in the yard somewhere and use them to heat your driveway. I have a number of them installed throughout my yard. Two of them are used to heat my domestic water tanks. The remainder are used to heat my swimming pool.

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I original wanted to use solar thermal panels. But like I said the cheapest ones were $900. All the way up to $2600. I never really thought about looking for used ones. I have about 50' × 13' lean-to that I built on the south side of my house. So figured I would need 11 or so to fill it up. I'll have to take a look around. Maybe I'll get lucky.

Giantkiller said:

Those are heated to higher points. Because they want it to melt extremely fast.

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The faster you heat it, the less total energy it takes to melt your snow load. Higher power limits the lost heat to the environment and puts more of it into melting the snow.

At some lower power level, the energy is all lost and did no good. If you think going with less power will save energy, that is backwards for this use case.

This is why there are design guidelines to make a system that works. Residential target is 37 watts per SF. If you can't put in at least 15 watts per SF, it isn't worth trying, IMO. That's 30 KW for 2000 SF driveway. If you can have 3 zones, that's about 10 KW minimum power if you do each one in sequence.

Good luck.

Mike C.

When you break up what I said. It doesn't make sense. Yes I was talking about exterior. Heat pumps. And last I checked the manufacturers of heat pump hot water heaters recommended a minimum of 35° for them to function properly. I would be using mine in a small insulated area. In my exterior lean-to. Only in the winter. I had already checked into the heatpump water heater. Won't work for what I'm doing. That's pretty cool what Larry's doing. He said he was making 15' deep holes in sand and clay. And he had to dig down a couple of feet to put the lines to tie them all together below the frost line. More like 4' around here. And my Land is full of really big rocks. I know geothermal would be the best and would heat it really quick.
My geothermal heat pump has a water jacket around the compressor. That provides all my domestic hot water for free.
A picture of the rocks that I pulled out of about a 3rd of the small pile of dirt that came from excavating my very flat lot for my slab on grade house. So once again as I said geothermal to heat my driveway would be a minimum of $14,000

mciholas said:

The faster you heat it, the less total energy it takes to melt your snow load. Higher power limits the lost heat to the environment and puts more of it into melting the snow.

At some lower power level, the energy is all lost and did no good. If you think going with less power will save energy, that is backwards for this use case.

This is why there are design guidelines to make a system that works. Residential target is 37 watts per SF. If you can't put in at least 15 watts per SF, it isn't worth trying, IMO. That's 30 KW for 2000 SF driveway. If you can have 3 zones, that's about 10 KW minimum power if you do each one in sequence.

Good luck.

Mike C.

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Thanks for the information. Like I said I don't need it to melt it quickly. And I think the little bitte bit of heat that I can get out of 8000watts of heating elements will melt the snow on top of the concrete a little bit. Before it will go down through the 2" of foam under it to the ground. I really was just looking to find out how to run power from the 9,360watts of panels that I have room for. To 4 2000watt dc heating elements. Wich would cost about $4,000 all total.
Thanks for wishing me good luck.

WindWizard said:

Wow, impressive setup. I am also in a northern climate and have experience in not only Solar but also Solar hot water panels. I have found that the solar panels mounted on the roof do not produce electricity until all the snow melts. The solar panels I have in the yard require periodic maintenance by removing the snow off the panels, so they start to produce electricity again.

If you are hoping that the solar panels will provide electricity to melt the snow on your driveway then you may have a catch 22. It is almost like trading one chore for another one. Snow blowing a driveway vs removing snow from the panels. If you mount the panels on the roof then it just will not work until the sun melts the snow off the panels. If you mount your panels using a ground mount, as I have done, then it takes a while to suit up and clear a path to the panels and then remove the snow.

Solar hot water panels can be found at extremely good prices now. A lot of people are removing the hot water panels due to roof restoration and then replacing them with Solar panels. They produce more BTU's per sq foot than the equivalent Solar panels. They also eliminate all the issues with converting electricity into heating water. They also need to have the snow removed to produce heat.

My suggestion is to find some dirt cheap Solar hot water panels on Craigslist and then mount them in the yard somewhere and use them to heat your driveway. I have a number of them installed throughout my yard. Two of them are used to heat my domestic water tanks. The remainder are used to heat my swimming pool.

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Windwizard. The panels I have on my upper roof are steep enough that the snow that does stick to them. Only takes about half a day of sunshine to melt and slide off. Check out the picture of the lean-to I built it to the best angle for winter solstice. Not much Chance of snow sticking to it and 2 strings of panels is still about 14" above the concrete.

If I had a dollar for every time this subject comes up I could buy some of those cheap panels.

Hot water is something we all need. It takes tons of energy. If you really want a birds eye view of hot water needs vs wants, go off grid with a small budget. You will feel like a 1 hour hot shower is a mega luxury.

If you are just trying to save a few $$$ on your energy bill, well.....make sure your not tripping over dollars to pick up pennies.

Your best bet might be to add in a cheap charge controller so you can string up your panels and STAY in the voltage window of the element. I have always wanted to try it but found out I just don't need as much hot water as I thought I did. Its much easier to down size your life style vs trying to live like a king all the time.

Zwy said:

I think DC water heating will become a dinosaur. I recently installed a heat pump water heater and run it on heat pump mode although I could run it with the electric 4500W element if desired. I originally installed it as a dump load but found the heat pump water heater efficiency is pretty amazing. A COP of 3 to 4 will greatly increase the usable btu's per kwh.

Normal day we use 3 to 3.5 Kwh of power to heat the 50 gallon tank plus I have propane water in series after the heat pump water heater with the thermostat on the propane water heater turned down much lower than the heat pump water heater. All 100 gallons is heated by the heat pump water heater. I left the propane in place for increased water heater storage capacity and for times in winter with very minimal sun.

Granted there are some conversion losses by changing DC to AC to run the heat pump. The COP efficiency by far exceeds those losses.

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Combine the water heater heat pump with a fridge or freezer on the other end then you have a winner.

sunsurfer said:

Combine the water heater heat pump with a fridge or freezer on the other end then you have a winner.

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While I honestly believe people are genuinely trying to be helpful with the myriad of suggestions, I think one point is overlooked. You've put in a TON of work already and you're clearly doing this as an experiment and learning experience. I, for one, salute your tenacity and hard work. The result looks amazing and you've truly embraced the DIY spirit! Well done!

Giantkiller said:

So once again as I said geothermal to heat my driveway would be a minimum of $14,000

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Here's a Air to Water heat pump for cold climates. I seriously looked at it for my radiant into floor but I ended just regular water heater that I converted to allow both 5500 watt elements to run at the same time. For no more than I would need it here in Southern Missouri, coupled with I'm taking quite a bit of excess net metering credits I couldn't justify it. Yes, added a 2nd 30a circuit.

mciholas said:

I like the idea of DC direct couple to the heating elements. No inverter to buy or fail.

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I would like to see someone do this and report back. It would be good info. But........

I know this thread is going all over the place but I just want to add a concept that gets told over and over again. Heating elements are rated for a voltage and as your voltage drops or raises, the element output will change non linear to the voltage change.

Example; A 2400w 240v element will put out 600w at 120v. That is 1/4 the output. So make sure you match this. I'm using 4800w 240v elements at 120v(1200w).

Your panel voltage will change depending on light conditions/temperature and you will have a mismatch and may get very low output except on those perfect conditions.

If I was going to do this, I would pickup a cheap MPPT and make a string of panels. I would then build a circuit on a timer to turn on the charge controller in the morning(battery simulator) and then a switch to turn on the load. This would be clunky.

Someone started building a specific hot water controller but it never took off. I would buy one if someone made one less then $500.

Another option would be an PWM load diversion controller but that will require panels in parallel and similar voltage to elements. It would not work good in low light. I guess one could run an MPPT controller from the panels and just set a load diverter to a slightly lower charge voltage.

Of course some of these ideas goes into the lower voltage range 12v-48v which creates high amperage issues

Check out this Green boost for water heating

This might work? What do you think?