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.
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|
|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|
|Water pressure pump||1,320||1||1320||1320|
|Advantex Septic Recirculation||700||1||700||700|
|Low energy Fridge||100||12||1205||100|
|Samsung split A/C system||1200|
|Lights / Computers / TV||500||4||2000||500|
|Bathroom floor heating||400||2||800||400|
|Outdoor/Landscape night lights||100|
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.
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|
|Propane Dryer||Start Timer|
|House amplifier||Timer – turns off at midnight|
|Samsung split A/C system||Separate room thermostats|
|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.