I am interested in going off grid. Unfortunately, I live in a very hot and humid region, and going without a/c is not a viable option for me. Therefore, I've considered some configurations that might make it practical. The biggest problem seems to be the size of the battery bank required. Both the short and long term costs of batteries seem to be the bane of off grid PV systems. The scenario is to use a small highly insulated enclosure to contain a thermal mass cooled by conventional vapor compression a/c units. A small battery system is provided to act primarily as a voltage regulator. Air is circulated through the enclosure and then through the home using a small fan on a thermostat. NOTE: I am considering here a very small well-insulated home.
The simplest approach I've considered would be to use water as the thermal mass, and use multiple small window a/c units. These are not particularly efficient, but they are readily available and inexpensive. Furthermore, I like the redundancy that this configuration provides (i.e. multiple small units), and it's a better fit for a small battery system. What I've considered is that it must be possible to design the system such that the units power on and off sequentially. It seems this can be devised by using battery voltage as an input. I have no formal electrical training. Yet it seems that this could be configured using solenoid switches. Could a load diversion charge controller (i.e. shunt regulator) be used to energize the solenoid circuit with the primary contacts used for the compressor motor? Could several solenoid switches be made to operate motors sequentially by placing rheostats in the solenoid circuits (to effectively adjust set points)? The idea is that battery voltage rises as it's charged from the PV array, and above a certain setpoint some current is shunted to a secondary circuit that contains multiple solenoids wired in parallel and each with a separate reheostat. When one solenoid is energized the compressor motor is energized off the inverter that's placed on the battery. This would draw down the battery voltage. If the PV array output is high enough, then battery voltage would continue to rise until one or more units come on line. Conversely, the units would power down sequentially in a similar fashion.
Any engineers out there please chime in with your thoughts as to why this is (or is not) a viable idea. If not, then please suggest a way to make it so.
Mark
The simplest approach I've considered would be to use water as the thermal mass, and use multiple small window a/c units. These are not particularly efficient, but they are readily available and inexpensive. Furthermore, I like the redundancy that this configuration provides (i.e. multiple small units), and it's a better fit for a small battery system. What I've considered is that it must be possible to design the system such that the units power on and off sequentially. It seems this can be devised by using battery voltage as an input. I have no formal electrical training. Yet it seems that this could be configured using solenoid switches. Could a load diversion charge controller (i.e. shunt regulator) be used to energize the solenoid circuit with the primary contacts used for the compressor motor? Could several solenoid switches be made to operate motors sequentially by placing rheostats in the solenoid circuits (to effectively adjust set points)? The idea is that battery voltage rises as it's charged from the PV array, and above a certain setpoint some current is shunted to a secondary circuit that contains multiple solenoids wired in parallel and each with a separate reheostat. When one solenoid is energized the compressor motor is energized off the inverter that's placed on the battery. This would draw down the battery voltage. If the PV array output is high enough, then battery voltage would continue to rise until one or more units come on line. Conversely, the units would power down sequentially in a similar fashion.
Any engineers out there please chime in with your thoughts as to why this is (or is not) a viable idea. If not, then please suggest a way to make it so.
Mark
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