Monthly Archives: October 2021

My Uninterruptable Power Supply (UPS) / Semi Energy Storage System (ESS)

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.

5kWh of LiFePO4 cells

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.

The first prototype on wheels

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.

Touch screen controller running Victron’s software – charging at the full 25A set

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!

New dashboard for my home monitoring

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!

My default dashboard showing commonly wanted information.

The acrylic laser cut tablet stand

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.

Real-Time Solar Energy Sign

The Solar / AEMO display

This is the perfect project for the energy conscious gadget geek homeowner or business. As we know energy efficient homes normally have solar panels installed. In Australia normal retail Feed In Tariffs (FIT) for solar are lower than your normal usage tariff so it is wise to try and use power generated from your own solar system first and limit power use from the grid.

If you want to change your habits and reduce your power bill and become more sustainable, you really need to know your generation in real time. That’s where this real-time energy display comes into play.

Built from 32×64 RGB matrix LED panels connected to a Raspberry Pi, it connects to your home network and grabs data directly from your inverter and AEMO’s website. AEMO is the Australian Energy Market Operator and controls the wholesale electricity costs in the NEM (Nation Electricity Market).

The top line shows the instantaneous power being generated followed by the daily generated energy (Right) for that day. These figures are very useful and come directly from your inverter.

The middle line is displaying the mains voltage and frequency at the inverter. The voltage is important as there is too much solar generation in some areas and this pushes up the voltage. If the voltage gets too high the inverter is programmed to reduce the power it is generating or in some cases, total stop generating until the voltage is reduced. It’s becoming a very common issue that I have during low demand months in Spring.

The bottom line is showing the spot wholesale electricity price and the total demand for the state. In this case both values are for South Australia. This data is pulled from AEMO in near real-time. Why is this important? Well some companies like Amber Electric now offer wholesale energy prices that change in each 30min internal. For switched on energy users, they can save lots of money but using electricity when prices are cheap or even negative (Yes, retailers can be paid for you to use electricity) and reduce their usage when prices are high.

First working prototype

The software is a simple custom python script that gets the data of interest and then uses a library called LED_Matrix written by Henner Zeller to display it. I can also display my import and export to grid data if required, however I show this on a Android Dashboard.

The hardware uses a Raspberry Pi 3B with a custom designed interface board for the display control. A red button can be used to shutdown the Raspberry Pi’s OS before removing power however this is not really needed.

This display can be reprogrammed to display anything from graphics to stock prices etc. If there is an API to get the data, it can normally be displayed. The possibilities are endless.

Specifications

Pixel Count32×128 pixels
Size670l x 185h x 90w
Power5V, 2A
Connectivity Wi-Fi or Ethernet
ProcessorRaspberry Pi 3B
Inverter compatibilityFronius

For more details or to place an order email info@embedtronics.com

Reconditioning Solar Garden Lights

We all have had garden lights where the solar panels are not really visible anymore (See photo below) The epoxy coating of the solar panel degrades in UV reducing the energy the solar panel can produce. Therefore they only run for a short time at night. Why put them into landfill, when you can easily clean them up to look like new?

A degraded solar panel giving poor run time at night.

Each year in spring, I spend a few hours cleaning the solar lights from spiders and cobwebs. At the same time I clean the surface of the solar panel and coat it with conformal coating to bring it up looking like new. Now I use conformal coating in a spray only because I normally have this around for Printed Circuit Boards. Any type of clear coat from an automotive or hardware store which is UV stable should work.


Conformal Coating in a aerosol can gives a nice uniform finish.
  1. Clean down the solar panel surface with water and detergent to remove all contamination like bird droppings. I will still have a white non-clear look, but the conformal coating will change that.
  2. Mask the area so spray will only go on the solar panel. Photo coming.
  3. Spray the area or use a paint brush to paint a layer onto the solar panel. I used a paint brush this time around as I had conformal coating in a standard container.
  4. Leave to dry.

About a month after recoating the solar panel.

If your garden light still does no work after a day of recharging in the sun check the battery connections and any switch. Normally the contacts just need to be cleaned.

Note: Try to buy higher quality garden lights with replaceable Lithium batteries as these should last longer than the older Nickel Hydride battery versions. Really this should be the case for all products, we seem to buy the cheapest and think that at this price, we just buy a 2nd when it fails. This is generating so much extra e-waste that then needs to be processed or put into landfill. Reduce, Recycle, Reuse!

These ‘higher’ quality garden lights run from Lithium batteries and are replaceable.

Flame effect lights after cleaning and coating the panel. Works and looks like new again.

These cheap gutter lights clean up very well. These are about 4-5 years old now and still working well.