PV Hot water and heat at a small camp

[OperaHouse]

Batteries Not Included.......

https://www.youtube.com/watch?v=eKiCRogzjjA

This is an interesting video.  650W of panels at a small camp in Minesota in the winter providing 6 gallons of hot water and when that is up to temperature, excess power goes to a space heater. This system operates in parallel with charge controller off array DC voltage. Panels are kept at power point voltage for efficient transfer of power to heating element.  Standard heater mechanical thermostat with arc interrupt so no damage to contacts.  Thermostat (only one in this tank) was switched with an upper type and when temp is reached, power is sent to a 1500W space heater.

Camp is heated with propane to prevent pipes freezing.  PV heating will save some of this expense.  Diversion is proportional and when more camp items are turned on, less energy is diverted.  This camp has a 12V lithium battery which never supplies power for heating and is always kept at full charge.  Wall switch is a three way. In one direction it goes to the water heater and automatic diversion to space heater.  Or in other position it only goes to space heater.   

[kitestrings]

Clever.  Thanks for sharing.

The thermostats are switching DC from the panels, but at or near their nominal voltage, using the MPPT controller?  Do I have that right?

[OperaHouse]

No, the heating element is PWM from a capacitor bank.  The duty cycle keeps the array just above power point voltage so a charge controller doesn't notice it. The DC can not be on longer than 10ms, similar to 50Hz.  Then it turns off for an arc quenching period. That only happens at near full power.  Other times the on cycle is less than 10ms and off times are significantly longer.  This allows AC contacts to be used. Video is of a fairly low voltage system, ideally the board runs from  90-140V array voltage which allows standard elements to be used.

[kitestrings]

That's very cool.  Is the circuit board/cap bank a design of yours OpH?

The only thing I don't like is the proximity of all the plumbing to the (some open) electrical goings on.  Hopefully no leaks.  It appears space is at a premium.  I assume that is why.

[OperaHouse]

Yes, it is my design.  it can track the panels with optional temperature sensor, but in most cases just a seasonal adjustment in MPP voltage is good enough.  Once it is out of your hands there is not much you can do about the installation.  I prefer it to be in a metal case in case anything goes wrong. Especially in an enclosed space made of wood. Typically, power is 1K to 1.5K which could easily create some burning.

At my summer home I have a 50L tank for the house which is enough for the showers and dishwasher.  Keep that at 60C. A 40 gallon tank for the garage laundry provides enough so that all cycles use hot water.  This only heats when all house needs are fully filled.  The LG washer operates off panels with no battery. so laundry is totally free.  This is the only water heater you will see with jumper cables.  I use the pulsing DC to desulfate batteries I pick up at town recycling.  Can't save many, just a science project.