RV Solar & Genset Off-grid Setup Ep. 1 (Planning)

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SOLAR POWER! The sun’s energy has intrigued me since I was a child. In 6th grade, I wanted to build a solar powered battery bank to power my Gameboy on long road trips. A few years later and they were out on the market!

I was going to go to college for alternative energy. Wind turbines were all the rage in Indiana, 2010. I never ended up going, but absorbed the gist of it over time.

Right! So. RV Power needs. I have 120VAC, 30A input. My greatest power needs are the 13,500 BTU Air Conditioner. 2800-3000W starting, 1500-2000W running. Heat is provided by a propane furnace, the fridge can run on propane as well (although, can also run on electric, it’s dual fuel). 600W starting, 180W running.

RV Power Needs (Luxury loads, mostly 120VAC):

  • 2000W A/C unit (full load, on HOT day)
  • 180W Refrigerator (on electric, can be Propane)
  • 87W Laptop (full load)
  • 1500W Electric heater (Fireplace or Portable)
  • 1440W Electric Water Heater (can be run on Propane)
  • 1100W Microwave
  • 650W Coffee Maker
  • 1200W Toaster Oven/Griddle (Combo unit)

RV Power Needs (General loads, mostly on 12VDC):

  • 60W Water Pump
  • 1200W Furnace Fan 1/3HP (propane, but 12V circulation fan)
  • 10W LED Lighting
  • Slide/Jack motors
  • Radio
  • Range fan/light
  • Water heater (propane mode)

I’m not going to spend too much time detailing my loads. “The first step is to calculate how many amps you use daily.  To do this, you must go through meticulously and calculate amp usage by hours used.”

But, I’m lazy. Here’s a good site with common draw items, all calculated out for you: http://trailertraveler.net/calculate-rv-amp-usage/

The Solar System

A relatively modest 800W panel setup on a 60A controller will be tasked with charging a 12V, 400AH battery. Considering I only wish to discharge (DoD) the bank to 25-50% (the lower the better for cycle count longevity), I’ll be outputting 1.2kWh-2.4Wh to discharge, while providing 2.526kWh charge (600W~ solar output, 4.21 average hours of peak sunlight).

Ideally, I’d want to expand my battery bank in the future to 800Ah to run a 25% DoD for 200Ah of storage to store, use the full 2.526kWh charge.

The difference between a 50% DoD and 25% DoD is cost beneficial. My batteries would last more than two times longer at a lower discharge.

For now though, it gives me flexibility considering my panels will be static on the roof (non-tiltable), provides charge capacity while cloudy, and will help absorb parasitic, running loads anyway (1.326kWh on a perfectly sunny day) while still charging the battery.

The Generator System

A 3500W inverter generator with remote start will be absorbing high load items and providing bulk battery charge duties. When the battery bank reaches my configured DoD, the generator will kick on until the batteries are at a 90% charge, all the while powering high load items. It’s the same theory of operation as a Pruis, pretty cool, eh?

The Control System

The hardest part, as it involves a custom controller to build automation into the system. The controller will need to:

  • Monitor battery bank state DoD
  • User configurable to either turn off the 120VAC inverter, or start the generator
  • (Maybe) Monitor amperage usage and kick on the generator for high current draws (such as the A/C, electric water heater, etc) – but the 25% DoD will kick it on, or turn off high load items anyway
  • Be smart enough to keep in sync with end user switch toggling (such as, if the inverter off, generator on state is toggled, turn on the genny if needed, or vice versa)
  • Control the generator’s wireless remote control to start/stop unit
  • Control the inverter’s power switch (while keeping in mind that the inverter remote panel setting can conflict with the on inverter switches) – thankfully the priority and override logic is documented in the manual, meaning they thought about it

I’d be running a BMS to monitor DoD and it has an RS 232 protocol which will interface with an Arduino or Pi. If I use a Pi, I have a 7″ touchscreen to play with, but I’d need to design a UI and write more code.

Long story short, I’d be developing an App in Python, or simple logic in Arduino.

But first! Do all the things manually! May be a better idea than burning down the RV due to a software bug 😀

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