Your DIY tech to perfect the off-grid living experience

[ozdw]

I thought it might be interesting and enlightening to share the DIY tech that helps us all live our best off-grid lives. If you have a PV array that can produce 100 kWh in the depths of winter, this might not be the topic for you. For those of us who have to pay attention to the solar energy forecast and juggle our EV charging (or pool heater, etc.) around it, let's chat about what you've invented or deployed to make it easier to get close to (or better than) an on-grid day to day experience.

I'll start.

We're in southwest Victoria, Australia, within earshot of the Southern Ocean at -38.7 degrees latitude. We're 70km from town and off-grid for electricity and water, with propane deliveries for cooktop, hot water and slab hydronic heating. We have 23 kW of roof-top PV, 60 kWh of DIY LiFePO4 batteries supported by a full Victron setup and a 10 kVA genny (used maybe twice a year). Our primary loads comprise a Tesla Model Y, two large heat pumps, two ovens, a washer, heat-pump dryer and dishwasher. Rooftop rainwater is stored in a 120K litre tank and we have a 6K litre tank fed from the river for watering the garden.

Challenges:
1. Make it easy to charge the car without having to pay attention to the house battery SOC
2. Ensure the house water tank doesn't empty due to a burst hose or tap left on
3. Ensure the garden water tank is full in summer

I solved #1 with a combination of Node Red, the Tesla BLE proxy running in a Raspberry pi, the Solcast API, Home Assistant and mqtt to integrate it all. It took me some time and many iterations to determine how I wanted this to work. In summary, Node Red is the mastermind. If I plug in the EV, it will start charging under Node Red control of the supplied current. It considers the current house battery SOC, the forecast PV (by hour) for the next 24 hours and the forecast power usage (by hour, based on yesterday's). In automatic mode, the house battery will get enough power to hit 95% before nightfall, with the car being given the excess (calculated every 20 seconds). If I've forgotten to charge the car and there's surplus PV, it'll start charging the car in auto mode. It'll protect the house battery from unacceptable discharge by reducing or stopping charging.

I can set manual mode on an HA dashboard if I want to set a specific car charging rate. If it calculates that the house SOC will be below a given value within the next 12 hours, it will enter automatic mode to vary EV charging based on available PV or stop it if the SOC is forecast below threshold.

All of this info is available on the HA dashboard, with the key data being the forecast minimum SOC over the coming 12 and 24 hours and when next we'll hit 100%.

Much easier was solving #2, with a solar-powered Arduino and an ultrasonic transducer on our tank. This measures the water level and sends data via LORA radio to a LORA-MQTT gateway. There's a wifi smart plug (Shelly) on the house water pump that allows it to be controlled and to report on/off. Node Red picks up these data and will alert me via Telegram or Pushover if the tank is draining rapidly. This saved us once when a hose burst while we were away.

The answer to #3 is a solar powered pump from Aliexpress 100m down the hill. It pumps from our river-fed stock water system up to the house, controlled by another Arduino and an ultrasonic transducer on the garden tank, but this time communicating via LORA to an Arduino on the pump. The pump is on until the sun isn't or the tank is full. A similar setup controls pumping of river water into our main stock tank.

All of these elements send data that winds up in InfluxDB and is visualised with Grafana. Victron has very flexible options for DIY automation and I've chosen to use the mqtt broker running in the Victron Cerbo GX. Solcast is one external (cloud-based) dependency and the Tesla API is the other. The BLE proxy allows me to locally control the car charging with as many API calls as I want, whereas the Tesla API is severely rate-limited. I now only use that api to determine the car's state of charge for display on the dashboard, but I could live without it.

Two dashboard screenshots are attached. Note that power used for car charging is excluded from the forecast, as it's too variable. The forecast is updated hourly.

Over to you! Share what you've cooked up to make your life easier.

Tesla ble proxy: https://github.com/wimaha/TeslaBleHttpProxy
Solcast: https://toolkit.solcast.com.au/
Node Red: https://nodered.org/
Arduino w/LORA: https://lowpowerlab.com/
LORA mqtt gateway: https://github.com/1technophile/OpenMQTTGateway

 

[Spartan]

My strategy was to reduce as much electricity usage as possible, then install the largest capacity system that I could (within reason) and live a happy life by interacting with my system as little as possible. For about 8 months of the year, I give little thought to the fact that I’m off-grid.

When winter arrives up here in the U.S. Pacific Northwest (latitude 42), It’s just a matter of sunshine and battery state of charge. When practical, we just wait for a sunny day to use energy hungry devices. Sometimes for efficiency’s sake, you can schedule when to do certain things based on if sunshine is forecast or not.

Other times in the winter, we just know that the generator is going to soon kick in no matter what and that also opens an opportunity to do energy hungry tasks. With the generator is running to charge batteries, we can run energy hungry devices at the same time.

The only energy intensive task I have complete control over is running the well pump. Since we have 6,000 gallons (22,700 liters) of water in storage for residential use, we can easily go a month with that amount. I have yet to have a winter where I could not find one sunny day to top off the storage tanks within a 30-day period. In summer, the well pump automatically comes on whenever the storage tanks drop below 90% full. In the winter, I switch to manual activation and top off the tanks only when the sun is out.

We’ve been off grid 7 years now. The only thing I think I will do different in the future is to go with a larger capacity Lithium-Iron battery bank when the present lead-acid battery bank reaches the end of its service life.

 

[ozdw]

Waiting for a sunny day in winter isn't in the plan here. It's too variable and we can go weeks without a sunny day. In summer, I can produce 120 kWh. The worst days in winter are 8 kWh, though luckily they are not frequent. On principle, I don't want the genny to run, ever. It only runs if I make a mistake or the solar forecast is way off.

If we didn't have an EV and if we had a well that could replenish our water supply, I wouldn't bother so much with these details, as our 60 kWh battery can carry us for a few days of weak solar production. But we have an EV with a larger battery than our house and we are dependent on rain for our house water supply.

Not wanting to start a discussion on new batteries, but have you checked out the price of LiFEPO4 cells these days? They are crazy cheap-- I just replaced our old lithium batts with MB31 cells from EVE for roughly $8K AUD, including new cables, BMS's, etc. I recommend you have a look if you are even occasionally annoyed by your lead acid bank.

 

[Spartan]

…Not wanting to start a discussion on new batteries, but have you checked out the price of LiFePO4 cells these days? They are crazy cheap-- I just replaced our old lithium batts with MB31 cells from EVE for roughly $8K AUD, including new cables, BMS's, etc. I recommend you have a look if you are even occasionally annoyed by your lead acid bank.

Interestingly, when I started on this journey building an off-grid home, all of the new battery chemistries were more expensive than lead acid. There was also no clear winner as to which new battery chemistry was the superior for off-grid living. I reasoned, at the time, that the prudent thing to do was go with tried and true lead-acid and wait to see what happens with the other battery technologies.

Within just a few years of setting up my system with lead-acid, LiFePO4 quickly gained in prominence and prices subsequently dropped quite rapidly. So now I’m just waiting out my lead-acid battery’s service life and then I’ll jump in on LiFePO4. I’m looking forward to that as I can get quite a lot more amp-hours than I have presently for less money than I paid for my original battery bank. Battery maintenance workload also goes away so there’s that to look forward to as well.

…been to Australia a couple times; beautiful Country, awesome people!