Author Topic: PV Space Heater  (Read 443 times)

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PV Space Heater
« on: September 19, 2017, 04:03:24 PM »
I bought a $2 oil filled space heater at a garage sale and of course that prompted me to get 4 new 280W Trina solar panels, got a good price.   The heater is 120V and 1200W, of course it measures less than that.  I was wanting to take the chill out of one room at the camp.  Just raising the temp 3 degrees makes a lot of difference.  The panels were actually purchased to provide more supplemental power to the existing 36V array on those really bad rainy days so I don't have to buy a bigger battery.  On other days it might as well heat the house.

The heater has a dual heating element 0f 15  and 25 ohms.  Much like a three way light these gave three different power levels.  With both connected in parallel this gives about 400W at 60V, the power point of the panels.  I was pretty surprised at this low a power level the heating fins are two hot to touch.  I can't imagine how hot this would be at 1200W.  The intention is to eventually get another.  I have often seen these cheap at garage sales.  Cheaply made, the connectors and switches go bad.

The control system is similar to my water heating program and very close to the ontfarmer program except the voltage is fixed.  A capacitor bank stores energy at the panels power point voltage and PWM dumps that into the heater elements.  A simple up down counter is used to set the PWM.  If the voltage is over the set point it counts up each loop. The UNO and NANO have six PWM outputs so up to six heater elements could be connected.  The capacitor bank doesn't have to be that large, about 2,000uF, since only one heating element is pulsed at a time.  The other elements are either fully on or off at any time.

The actual use of this is very close to a GHURD controller.  At present O have to use this to prevent actual voltage from going over 60V.  The rest of my system has a power point of about 52V and with 60V FETs it would be destroyed if the voltage got to 80V of the grid tie panels.  Temporarily I feed to the system 52V buss through a 3 ohm resistor and diode.  That limits it to a couple amps for that extra boost in the morning.  A FET switches it off when the voltage goes over 52.5V.  I will also be using this for dishwasher heating.  Will have a better ide of what I actually want the control system like next yer.