Solar home owners in south Australia and also Australia are facing a problem where the energy they generate from solar that can’t be used during the day (and therefore exported to the grid) will be worthless soon. The problem we have are wholesale power prices during the day are so low and in some cases negative due to this oversupply in solar energy. Feed in Tariffs (FIT) have been dropping for the last few years from high prices of 50-60c to a low of 5c (AGL). Within a few years I expect export will be worthless.

The snapshot from last week, shows the electricity prices in South Australia was negative for most of the sunlight “solar generating” hours. This was a Saturday with mild weather which reduces demand therefore large negative periods.

Source: Opennem.org.au

If you have money to burn, you can install a Tesla Powerwall 2 or similar to storage energy generated during the day to use during the night. This technology is proven and all works, just the economics is not good. In my case and the case for many home owners the system would take 15+ years to payback.

I upgraded a small off-grid system months ago to new LiFePO4 cells. In the process of buying new batteries, I decided to double the order. This gives me a 2nd battery bank of 8x 200Ahr LiFePO4 cells or about 5kWh of storage capacity (4.2KWh useable) to play with.

Introducing my new UPS/ESS below. I wanted to design a simple plug in semi-portable system. Something that could be used by anyone owning their home or renting. I wanted to be able to charge up the battery using my own solar energy and then run loads at night or on cloudy days from the battery. The hardware is very simple, a Lithium battery bank (24V/200Ahr) with custom BMS wired into a Victron Multiplus Inverter. The Multiplus inverters are brilliant as they come with a inverter, battery charger, automatic transfer switch and more importantly, software controllable.

Out of the box, these Multiplus unit can be programmed as a UPS, but in my application the smarts are in the custom software on a controller. Just like a UPS it plugs into a powerpoint (GPO) for charging and then my loads (Computers and my whole electronics room) runs from the output. The unit is setup so it can’t export energy into the powerpoint which is a legal requirement, so really is just a programmable UPS.

This controller connects to my home automation system via Wi-Fi to read the data of how much power I’m importing or exporting. When the sun comes up and there is enough spare power generated from the solar to cover the connected loads, the battery charger kicks in and starts slowly charging the battery. As more power is generated by the solar, the charging rate (Amps) increases to use up any exported power just like a fixed home battery would.

Then at night, it switches to inverter mode and runs all my loads from the stored solar power I had generated that day. Also if there are cloud cover or a large load turned on in the house, the system can switch the connected load to battery to reduce the power imported. As always there are lots of extra smarts and protection to keep the batteries within a safe State of Charge (SOC) in case of a power blackout. This can be customised in software, just like a Tesla Powerwall.

This is just part of my demand management for my home. I’m also controlling non-critical loads like dehumidifiers and some lighting. The next goal is to control the air conditioning for the home.

So what does it all cost? Is it worth it? This will be covered in a following post!

I have been using the Open Energy Monitor’s content management system (emoncms) for at least the last 10 years to log and monitor various sensors around my house. The software is brilliant in my view, however Home assistant is slow taking over with all the new energy monitoring dashboards, etc. I think if I was to start again, I would run everything from Home Assistant. Currently I run home assistant mainly for control.

As a hardware person, I would always design and build my own sensors that would talk W-Fi directly to my local emoncms running on a beaglebone (Now a raspberry pi). I now have hundreds of data points coming in from all different types of resource monitoring and environmental sensors. Water, Electricity, Temperature, Humidity, Tank Levels, CO2, PM2.5, PM10 and much more as it’s always expanding. All the data can be displayed on the normal emoncms dashboards, however I wanted a basic real-time display in the kitchen that I could just look at.

As I can pull the data from emoncms via MQTT, you can download apps to make dashboards. That is all I have done here using MQTT Dash. The main screen displays Grid Power, Grid Voltage, Grid Import for today, Grid export for today, Mains Water Flow, Water usage for today, outside temperature and rain fall since 9am.

This is a great way for me to understand my electricity and water usage in real time. As a household with solar panels, I can save money by using my own energy directly from my solar panels during the day. The goal is bring the imported energy (Energy from the grid into your home) down to the lowest possible. I have now achieved very low imports with some smarts and automations throughout the house. Personal habits also help with using large items like vacuum cleaners, heating, cooling and the washing washing mostly only during the day. I still have to cook tea and live in comfort, but little changes can make big impacts over time!

During the day when I’m ready to run large usage items, I can look over to the display and check the grid power value. When the grid power value is negative, I’m exporting power to the grid and only getting a low Feed in Tariff (FIT) for it. This is when I can turn on items to use more of my own power. If the grid power value is positive like in the photo below, I’m importing power from the grid and therefore want to get this value as small as possible, so I can delay using electrical items.

I fitted a 6.6KW solar system a few years ago. This is much bigger than I need for a well insulated standard home, but the goal was to have a EV (Electric Vehicle) by now. This shouldn’t be long now!

The acrylic laser cut stand was made at the local makerspace in Adelaide. They have lots of cool equipment like 3D printers, laser cutting, CNC routers, woodworking, metal working. You simply sign up for membership and go in and use the equipment. Volunteers are onsite to help you with your project and how to use the equipment.

Battery Management

Tablet and laptop makers want to achieve the the longest battery run time. That’s a selling point and what people want, however this can reduce the battery life to only a few years in always on applications. Lithium batteries do not like to remain fully charged for long periods of time. To increase the battery life and reduce the chances of the lithium battery swelling, there are apps that allow you to control the battery charging profile with the goal to only charge to 80%, etc. On Android this requires that your tablet or phone has been rooted. Check out Battery Charge Limit. In my case this does not work on my Google Nexus 7 (2012) pictured above.