Living off-grid – daily energy use and considerations

Smart ways to reduce your energy consumption

Smart ways to reduce your energy consumption

Living off-grid requires careful consideration when you design your system and purchase appliances, pumps etc. If done right you only have to pay little attention to your energy use on a daily basis.

As mentioned in an earlier post (https://modern-off-grid.com/2013/12/30/off-grid-solar-101/) the most costly piece of a off-grid system are the batteries. If the batteries are not fully charged for a prolonged period of time they slowly degrade. You really want to charge them up as quickly as possible every day to extend the life of these guys. On an average day I’ve the batteries fully charged around 12 noon and “free” energy all afternoon – that is otherwise wasted (since I can’t sell it back to the grid).  Any workload that can be moved to run in the “float zone” – that’s solar lingo for fully charged batteries – will extend the life of your batteries significantly.

PV Output - fully charged at noon

PV Output – fully charged at noon

Here is the high-level picture of my energy use, concurrent load and PV charge on a sunny day:

Theoretical max load  8,390  W
Outback Radian Inverter  8,000  W
Always-on load  2,990  W
Panels net charge per day  22,950  W
Consumption per day  11,705  W
Charge time per day  3  Hours

In the below table you’ll find my appliance and infrastructure work sheet I used when designing the house and the required infrastructure such as well-pumps, engineered septic system (now required by California building code) etc.  In the design you have to pay attention to a few important system variables:

  • Appliances that are difficult to control i.e always on but not always running. E.g. fridge, water-pressure pump etc.
  • Daily hours of use and how to control / minimize the usage.
  • Theoretical max load wattage for all appliances etc. vs. max load for the inverter
Appliance Workload Sheet Always-on watts Hours Per day W-Hours/Day Max load Watts
Well pump
Water pressure pump 1,320 1 1320 1320
Advantex Septic Recirculation 700 1 700 700
Radiant heat 200 8 1600 200
Low energy Fridge 100 12 1205 100
Washer 1500
Propane Dryer 0 500
Dishwasher 1700
House amplifier 70 24 1680 70
Samsung split A/C system 1200
Ambient usage 100 24 2400 200
Lights / Computers / TV 500 4 2000 500
Bathroom floor heating 400 2 800 400
Outdoor/Landscape night lights 100
Total 2,990  11,705 8,390

In the always-on column I calculated 3kW of load that would be hard to control. It is of course much lower in practice since few of these appliances are running at the same time. My max load has been 4kW which included running the washing machine so that it’s about right.

Hours of daily use turned out to be spot on. According to my table above I would use about 11.7kW-Hours per day. That’s very close to 100% accurate.

The theoretical max load is only slightly over the max load of Outback Radian 8kW inverter. Again it is highly unlikely that you will ever pull this much power concurrently unless you start all your appliances at once.

Battery SOC - state of charge

Battery SOC – state of charge over 24 hours

The most effective method to reduce the power consumption – other than buying ultra energy-efficient appliances – is to find ways to manage the loads. In the table below you’ll see that almost every component in the system is somehow managed to reduce power consumption without imposing any significant compromise for modern living standards.

Appliance Workload Sheet Managed load Method
Well pump Separate PV panels for well pump – Grundfoss SQ Flex / CU200 control
Water pressure pump Siemens slow start drive
Advantex Septic Recirculation Higher recirculation rate from 10a-4p
Radiant heat NEST Thermostat
Low energy Fridge Turning the default temp down
Washer Start Timer
Propane Dryer Start Timer
Dishwasher Start Timer
House amplifier Timer – turns off at midnight
Samsung split A/C system Separate room thermostats
Ambient usage
Lights / Computers / TV Auto off – motion detectors in every room
Bathroom floor heating Separate room thermostat/timer
Outdoor/Landscape night lights LEDs and Separate 12v solar system

On a daily basis the only real consideration is when to run your washing machine , dishwasher, vacuum etc. Of course you can run them at night if you’re in a pinch but if you can run all your loads in the float zone between noon and 5p it will have a very positive impact on the batteries lifespan.

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