I got a thermostat from Missiouri Wind and Solar for DC water heating. I put 3 275w panels on my pool house and wired them directly to the 120v heating element. Gave me one tank of water per day. DO NOT use the normal t-stat that comes with a water heater. DC will weld the contacts every single time.
Water heating with solar
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efficientPV
Solar Wizard
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Not anymore than the one you got from MW&S, they don't have a good reputation. Are your panels in series?
12v or 48v with built in thermostat $100. Panel wires directly to it.
windandsolar.com
DC Water Heater Elements | Missouri Wind and Solar
Choose from a wide variety of submersible DC water heating elements for direct connection to your batteries or solar panels. Great for RVs, heating stock tanks, or converting your AC water heater. Don't forget to add a thermostat.
windandsolar.com
dougbert
Solar Wizard
I heat 2 50 gallon electric water headers (in series) with my excess PV power AFTER my battery is full
I heat them to 125deg F and it usually is complete by 2-3pm
I use 3000 watt 240v coils in both, upper and lower heaters. All cascaded
here are the 2 links in my build thread
theory
implementation
works great, very little nat gas is used in the summer in the tankless water heater - majority of the water coming in is higher than the tankless is set for
I also have dial mixing valve to ensure the water is not too hot going to the facuets
I heat them to 125deg F and it usually is complete by 2-3pm
I use 3000 watt 240v coils in both, upper and lower heaters. All cascaded
here are the 2 links in my build thread
theory
implementation
works great, very little nat gas is used in the summer in the tankless water heater - majority of the water coming in is higher than the tankless is set for
I also have dial mixing valve to ensure the water is not too hot going to the facuets
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Yes three panels in series. They float at 120vdc and pull down to 95v when under the 1000w load of the water heater element. A person doing this should not bypass the safety emergency pop off thermostat on the water heater just in case. But my MW&S thermostat has never given me any problems.
I have built a circuit (based on the design of @efficientPV) that heats water directly from my 4kW (4s2p) solar panels (2 heating elements 220v x 3500W). It sucks the energy right from the panels and never makes it past the SCC and thus never cycles the batteries. It was relatively cheap to manufacture (like 50USD all in). It uses a version of power point (i.e., turns on when the voltage of solar panels is above Vmp) that just uses whatever current available until voltage drops below Vmp. I have it wired in parallel with my Victron SmartSolar controller -- its been running for a week and works great. It's designed to handle upwards of 30 amps at 170V DC.
Here is a picture -- I can provide circuit diagram to whoever wants it. I suggest watching @efficientPV videos on Youtube to get a better idea of how this works -- its quite ingenious as it doesn't use a microcontroller (just analog electrical components -- ressitors, capacitors, MOSFETs, etc).
Here is a picture -- I can provide circuit diagram to whoever wants it. I suggest watching @efficientPV videos on Youtube to get a better idea of how this works -- its quite ingenious as it doesn't use a microcontroller (just analog electrical components -- ressitors, capacitors, MOSFETs, etc).
Interesting. I would like to see the schematics.
I can do pcb layout and board manufacture
Daddy Tanuki
Emperor Of Solar
when you say it sucks it prior to the SCC can you be a little more specific or descriptive? IE: so when it sees xx.xx volts it turns on and takes anything above that voltage and directs it to the heating elements, and then anything below that it shuts off and allows the SCC to send it to the battery? or does it sit there and cycle back and forth as it draws power off? seems to me you would need a PWM SCC and not an MPPT or the MPPT would endlessly cycle attempting to match the available power.
efficientPV
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It pulses from the capacitor bank proportionately and only draws enough current to bring the PV array voltage down to the natural power point. That can be from a couple watts to over hundreds. Here is a graph of it responding to clouds for a half hour period. Response is very fast to capture any excess. Not shown in schematic is a power diode that must ve between array and capacitor bank when used in parallel with MPPT charge controller to allow for proper tracking.
Daddy Tanuki
Emperor Of Solar
how many amps can it handle? so I have panels that at 55 volts output roughly 110 amps, (3 controllers) now normally they run less than that and obviously drop off as the batteries voltage rise, so what happens when the SCC slow down their output to match their setpoints? does this board continue to pull as much as is available? if so how many amps can it handle safely?
efficientPV
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It is natural to latch onto the first hot water controller you see. There are dozens of designs that will work. Controllers are like children. They are all the same, but everyone is different. This IR2153 design has an alternating output, note Heater1 & Heater2. In his application they will be tied together and there is no mechanical thermostat in series with the heater element. The unique feature of this design is that #1 has priority and all power will go to that first. Think of a tank with upper and lower heating elements. The top heats first, typically panels are off axis and power is lower. Approach mid day and any extra power goes to the lower element. Upper element shuts off and all power goes to the lower element. This end of the day power from the array is likely less than half power. Since outputs are alternating at low frequency (on period is never more than 10ms), there is natural arc interrupt and standard AC relays and thermostats can be used.
The preferred output FET has a TO-247 package which has lower thermal resistance. Boards should have this package. Standard connectors will fit in these holes and you can have replaceable FET with just a screwdriver.
This control only needs 15ma and resistor voltage dropping is practical and provides best spike protection. For convenience a small 12V switching supply eliminates voltage resistance calculations. I found one supply which works from hundreds dowh to 20V. Isolate this with a 47ohm resistor on the high side and a capacitor for protection from lightning. Provide +12 and common terminals on board to provide external power.
Thermostat control can be provided with a 4.7K resistor to pin #1 of opto to external contact to common. Another 4.7K would go to +12V. Contacts opening short out timing capacitor and turn off the IR2153. He is using this board in a system with computer control. He has the option of controlling the set voltage to make it more aggressive depending on battery state.
There are FAKE IR2153 which do not have the shutdown feature. These will actually force output on. In a board they will semi work and drive you crazy.
The first engines were single cylinder. We don't drive cars which are one cylinder today. While you could do high amps a low voltage, it is a bit insane from a design standpoint. You go for higher voltage first on elements. Then add in heating elements connected directly as a function of current. Then you use the board to trim the additional current.
The preferred output FET has a TO-247 package which has lower thermal resistance. Boards should have this package. Standard connectors will fit in these holes and you can have replaceable FET with just a screwdriver.
This control only needs 15ma and resistor voltage dropping is practical and provides best spike protection. For convenience a small 12V switching supply eliminates voltage resistance calculations. I found one supply which works from hundreds dowh to 20V. Isolate this with a 47ohm resistor on the high side and a capacitor for protection from lightning. Provide +12 and common terminals on board to provide external power.
Thermostat control can be provided with a 4.7K resistor to pin #1 of opto to external contact to common. Another 4.7K would go to +12V. Contacts opening short out timing capacitor and turn off the IR2153. He is using this board in a system with computer control. He has the option of controlling the set voltage to make it more aggressive depending on battery state.
There are FAKE IR2153 which do not have the shutdown feature. These will actually force output on. In a board they will semi work and drive you crazy.
The first engines were single cylinder. We don't drive cars which are one cylinder today. While you could do high amps a low voltage, it is a bit insane from a design standpoint. You go for higher voltage first on elements. Then add in heating elements connected directly as a function of current. Then you use the board to trim the additional current.
Daddy Tanuki
Emperor Of Solar
understood, but if my system is making over 100 amps at 55 or 56 volts then at 240 it still should be making 25 amps or more i would think. my system is not a high voltage system to begin with but I have access to some other panels to play with and am curious to see what this is capable of.
I just installed a heat pump water heater. Certainly more $ than these options, but I didn't want to run heavy gauge wiring plus DC across my basement. I wanted to keep it simple. It is amazing how much hot water you get from 2 kwh on these. I have the 120V model so I just ran 12ga romex across basement to a new receptacle. Its plug and play. The 240V would have been less feasible given I only have one multiplus.
efficientPV
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I promote good design in heating water. I'm not limited t promoting any one circuit. Looking at PV array voltage is a good way to determining when excess power is available. Diverting from the array is efficient and cost effective. This method is very cheap and avoids using the resources of charge controller, inverter and battery. Nobody thinks they do, but every successful solar system has excess power which is free for the taking. This is a picture of my camp from the south, see any solar panels? I run a camp and heat water with the excess. I have three water tanks and one is just for laundry. All cycles use hot water. If you can't heat water, "Don't blame Desenex."
Here is a shot I took this morning, it is totally overcast and will rain today. Everyone is impressed with big numbers. Look at all those YT videos of the "bucket people", they stick an element in a bucket and connect it to a panel. It is bright and sunny and everything works fine. They never show you the rest of the day when it drops to nothing when the mismatch kills the power. They have no idea that the power is a function of the square of the current. I find this shot impressive, you probably won't.
I run three water heaters and they all can be operating at the same time. Each has a set priority based on voltage. I test my board at 30A and it has half the capacitors. The board shown I think he will be trying 4KW. I designed a microprocessor for a guy in Canada that had a converted oil tank with five elements. Four were switched in and one had variable power. Dacian "matrix man" and I can't think of the board has a switched element system to match the array. Great idea, just about impossible to implement because factory heating elements don't exist in the values needed or your tank only has two. This is where a proportional system works out better.
Here is a shot I took this morning, it is totally overcast and will rain today. Everyone is impressed with big numbers. Look at all those YT videos of the "bucket people", they stick an element in a bucket and connect it to a panel. It is bright and sunny and everything works fine. They never show you the rest of the day when it drops to nothing when the mismatch kills the power. They have no idea that the power is a function of the square of the current. I find this shot impressive, you probably won't.
I run three water heaters and they all can be operating at the same time. Each has a set priority based on voltage. I test my board at 30A and it has half the capacitors. The board shown I think he will be trying 4KW. I designed a microprocessor for a guy in Canada that had a converted oil tank with five elements. Four were switched in and one had variable power. Dacian "matrix man" and I can't think of the board has a switched element system to match the array. Great idea, just about impossible to implement because factory heating elements don't exist in the values needed or your tank only has two. This is where a proportional system works out better.Here is the basic theory. Let's start at the panel current vs. voltage curve. The maximum powerpoint is when the voltage is highest and current is highest. With no load on panel, the voltage goes torward open circuit voltage. When a load current is applied, the voltage drops. A good assumption is that when panel voltage is above maximum power point voltage (Vmp) there is excess solar to be harvested.
This is how the circuit works: it monitors the panel voltage and when it goes above Vmp it turns on the heating elements. If the solar charger is also trying to get some energy the panel voltage will drop below Vmp and the heating element turns off and the charge controller uses MPPT to find the optimal power point. The heating element circuit is just responding to solar availability and current charge controller consumption. Of course the chosen voltage to toggle the heating element is going to be a little dynamic because of panel temperature coefficient, etc. A toggle voltage slightly above Vmp seems to work well for me.
I designed my version to handle my panels (above Victron VRM screenshot) which operate at a Vmp of ~168V. I am running two 220V x 3500W heater elements in parallel. The resistance of the each element is ~15.4ohm or ~8ohms total in parallel. At 168V that is putting through ~21 amps and 3500W of heating power. I will be using this to heat a cypress hot tub in southern Chilean Patagonia (currently in testing in the US).
I chose this design to not cycle by LiFePO4 battery bank (no water heater power goes through the charge controller or the inverter). Also as @efficientPV points out you get the efficiency from the high voltage. 48V heating elements are totally useless.
I have 4000W of solar panels, a Victron MPPT Solar Charger (250/100), Cerbo GX and REC BMS connected to a 15kW battery bank (48v). We have so much solar in summer that we use an electric oven with no problems.
This is how the circuit works: it monitors the panel voltage and when it goes above Vmp it turns on the heating elements. If the solar charger is also trying to get some energy the panel voltage will drop below Vmp and the heating element turns off and the charge controller uses MPPT to find the optimal power point. The heating element circuit is just responding to solar availability and current charge controller consumption. Of course the chosen voltage to toggle the heating element is going to be a little dynamic because of panel temperature coefficient, etc. A toggle voltage slightly above Vmp seems to work well for me.
I designed my version to handle my panels (above Victron VRM screenshot) which operate at a Vmp of ~168V. I am running two 220V x 3500W heater elements in parallel. The resistance of the each element is ~15.4ohm or ~8ohms total in parallel. At 168V that is putting through ~21 amps and 3500W of heating power. I will be using this to heat a cypress hot tub in southern Chilean Patagonia (currently in testing in the US).
I chose this design to not cycle by LiFePO4 battery bank (no water heater power goes through the charge controller or the inverter). Also as @efficientPV points out you get the efficiency from the high voltage. 48V heating elements are totally useless.
I have 4000W of solar panels, a Victron MPPT Solar Charger (250/100), Cerbo GX and REC BMS connected to a 15kW battery bank (48v). We have so much solar in summer that we use an electric oven with no problems.
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efficientPV
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This graph compares the voltage on the array compared to what is sent to the heating element. Off times the capacitor bank charges. On times panel current and capacitor bank current are added together until lower set point voltage is reached. If delta V is kept small the conversion is very efficient.
ksmithaz1
Solar / EV Junkie
30A circuit breaker. Generally 4KWish 18-20A
ksmithaz1
Solar / EV Junkie
I'm telling you OZ is on point. Dedicating panels to a specific purpose makes the provided output unavailable for other purposes. If it's for a silly fun one-shot proof project, that's fine, but general sanity dictates the most efficient use of your solar panels is to get them all on the same job, hooked to AIO's or MPPT's on the back side of an AC power plant that produces power you can send around to wherever the demand is via AC, or divert to storage (battery) for use later by the inverter.
You can use simple timers or relays from the AIO, or even sensors to activate loads based on demand. I started this way, then just scaled up. I'll be pulling all but one ATS (the one that feeds the EV charging) next re-work. It was fairly easy and not expensive.
You can use simple timers or relays from the AIO, or even sensors to activate loads based on demand. I started this way, then just scaled up. I'll be pulling all but one ATS (the one that feeds the EV charging) next re-work. It was fairly easy and not expensive.
It appears you're confused on the theory and your approach is very inefficient. The power is always available, its just takes what is not consumed in the moment (ie., no loads, batteries charged).
There are losses in the charge controller, the inverter and what do you do when you don't have more battery storage? Also, power transmission is efficient at high voltage -- most inverters/controllers max out at 48V and power is P = VI or P=I2R.
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SolarShed23
New Member
Have you considered going to a heatpump water heater?
That would be a good option for him. Mine uses 100-120kwh a month.
Im also putting in a 40 gallon pre heater tank for it with a couple of old unused panels i have direct wired to a dc heating element with a thermostat.
Im betting it will cut its current kwh usage in half during the summer time.
ksmithaz1
Solar / EV Junkie
I'm rather well versed in Ohms law. Starts out as E=I*R, transposes to I=E/R. Much discussion around 'R' above to keep I sane. If you are talking about diverting output directly from a panel string away from an MPPT into a water heater based on SOC in some batteries, it would be demonstrably more efficient for the time it is needed for that particular load. Unfortunately, then useless for anything else once the need is fulfilled. Losses are real but my hwh has cut on 6 times in the last 24 hours, I keep it at ~145F (40 gal). A 10% conversion loss is just not significant enough to justify diverting output to a specific appliance. The reason demand HWH's save money is they soak power while on, then shut off, but reality is hot water heaters, don't really use that much power in the grand scheme.
I would heat the water normally when demand is low, and batteries are 'almost' charged, say above 90%. Divert the extra effort and money into more batteries.
gary_lankford
New Member
Not exactly "dedicated", as it's a secondary use case, but I have 4x 300w panels 2s2p (about 70 vdc) that I use to run my solar direct well pump through its controller. It doesn't take much energy to keep that low producing well pumped dry, so I have excess solar available from that array...
I have a 110vac receptacle, that I can switch from the pump to the receptacle in a breaker box, wired directly to the pv panel output, so 70vdc at the receptacle. I have a 5 gal single element water heater that I sometimes run off that array. (I can't remember if I used a 1000w 48v or 110v element, but I think 110v as I can also just plug that WH into the grid.) When the sun is good, the water heats up in a few hours. The WH has a standard WH thermostat, so it shuts off at the set temp.
I have a 110vac receptacle, that I can switch from the pump to the receptacle in a breaker box, wired directly to the pv panel output, so 70vdc at the receptacle. I have a 5 gal single element water heater that I sometimes run off that array. (I can't remember if I used a 1000w 48v or 110v element, but I think 110v as I can also just plug that WH into the grid.) When the sun is good, the water heats up in a few hours. The WH has a standard WH thermostat, so it shuts off at the set temp.
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