SolarQuotes customer Louise Potgieter invested in a home battery system expecting to cut her bills down to size. She went on holiday, only to return to an unpleasantly large bill. She’s written about what happened, what to look out for, and how the right inverter paired with a 3 free hours of power plan solved the predicament.
Louise’s Story:
“The bill before our battery installation was $670 for the quarter. We bought an average of 17.62 kWh per day from the grid, and exported an average of 20.48 kWh per day.
When we first spoke with our installer, he asked if we needed the pool and shed backed up, but we decided backing up the house was enough. We picked the brand, 15kW inverter, 24kWh battery and to keep our legacy panels. We really didn’t discuss anything else other than timing.
Our system went into the garage, our installer made sure we had visibility on the monitoring app, then we left to go overseas. While friends were house-sitting for us, we watched the power consumption on the app from Mexico. Most days appeared self-sufficient, and on bad days, we imported <5 kWh from the grid. We were expecting the next quarterly bill would be low.
Imagine our shock, when the next account arrived virtually unchanged from the previous $670 bill.
Red Energy had us buying 1287 kWh and exporting 714 kWh, yet the solar monitoring reported 261 kWh purchased from the grid and 958 kWh exported over the same period.
In other words a 1000kWh understatement. Clearly something was amiss. After much forensic analysis and help from Community Groups and SolarQuotes, we found the installer had messed up the metering.
He installed the system so that it only saw the house demand, and not the pool or the shed. The footprint controlled by the power system as originally installed is shown by the yellow rectangle on the site plan below.”
Only the house is visible to the power system.
“As initially set up, the only time the pool ran on excess solar was when all the house loads were covered, and the battery approached 100%. This might be after lunchtime, when the pump had already been running for hours, or there could be days when the battery soaked up all available solar.
Clearly, this wasn’t right, so the temporary fix was to feed the pump via an extension cord from the house, so the pool demand was factored into the HEMS.
The permanent fix was to move the gateway and monitor the incoming/outgoing power at the MSB. Fortunately we found a data cable that already ran from the shed to the garage saving a huge expense in trenching. Had we not found this, there may have been a wireless option to measure the mains supply, but the shed wouldn’t be backed up in an outage.
Now our system has the footprint below, and aligns perfectly with the utility billing app.”
Now, everything is not just measured, but backed up too.
“Problems arise if the technology can’t ‘see’ all the power flowing to and from the grid.
This energy flow is measured by your inverter, either internally, with an external consumption meter/CT coil or often using a proprietary switchboard called a gateway. This is also where, during an outage, your system isolates the mains, so the lights stay on downstream of this point, but you aren’t trying to power the whole district upstream.
In most cases the inverter or gateway device will be right next to the Main Switch Board (MSB) where the utility meters are.
Be sure to ask your installer how they will measure power, at the MSB or wherever your existing solar inverter is. If they can’t explain how it works, you might find you’re one of the unsuspecting public having no idea why their systems don’t work. We were once there, too.”
Three Hours Of Free Power
“If, when we started this process, we knew what we know now, we would probably have put in bigger batteries to take advantage of the federal government rebate.
As it happens, the new Globird Zero Hero plan with its 3-hour free charging window has been our saviour, giving us full batteries at 2 pm every day. With this plan, we discharge our battery to 60% at 8 pm each day, which generally gives us enough power to get through to 11 am and the free charging window the next day. With this strategy, our average power cost is coming in at <$0.5/day, and so the payback on a bigger battery wouldn’t be there.
ZeroHero also pays a Feed in Tariff (FiT) of $0.15c/kWh for the first 10 kWh feed to the grid between 18.00 and 20.00, so sizing your batteries up to 10 kWh larger than your day to day demand, enables you to get a decent FiT whilst providing insurance for you to not have to pay peak rates when buying from the grid at times of high consumption.”
Inverter Size Is Crucial
“Like batteries, nobody complains their inverter is too big – it means faster charge and discharge to the grid.
Small inverter size limits the household load you can draw from the battery at any instant- anything more comes from the grid.
So if you have a single-phase 5 kW inverter and your household load is 10 kW, 5 kW will come from the grid, even if there is plenty of power in your battery to supply a big load. If you are on three-phase, the maximum load on any one phase is a third of the inverter capacity.
Which leads us to the surge rating. A motor such as a rainwater pump might use 0.4kW, but getting it started could demand up to 3.2kW ! On a single-phase 10kW inverter, this is no problem, but a 10kW three-phase inverter may struggle, which can be very disappointing.
Make sure you document with your installer exactly what you want reliably backed up.
Our installer recommended we install a 10 kW inverter, as he said this would be plenty to get the DC production from our solar panels into the battery. As we are on three phase, we sensibly upsized to 15 KW, to give us 5 kW/phase, at an incremental cost less than $1,200.
On days our battery is really depleted, we are able to fully charge to 24 kWh and satisfy our household load in two hours, leaving us an hour of the Zero Hero window unutilised. This will be helpful if we upgrade our batteries or add an electric car. If we had gone with a 10 kW inverter, it would have taken the full three hours to charge 30 kWh, and if our load was high, we would not have had full batteries at 2 pm.”
The Inverter Lets You See What’s Happening
“Systems installed today are so much more than the dumb inverters of yore. At the heart of your Home Eenergy Management System, the algorithm in the inverter manages solar and imported energy from the grid, when to export to the grid, when to draw from the battery and when to fill the battery.
The inverter talks to an app, so that any time, from anywhere in the world, you can see how your power is being managed. You could fill your batteries by downloading from the grid during “free” or “off peak” windows, and sell back to the grid during peak, and it’s the app which gives you the power to both see what’s going on, then change behaviour or the charging priorities to suit your preference.
Whether it’s incorporated inside the inverter or not, the gateway is the sentry to your property. It’s usually located at the MSB, and measures the power crossing your property boundary. During an outage, the gateway will isolate your property and provide backup power to preselected circuits for as long as the battery lasts.”
Retail Plans Come And Go
“Look at the retail plans and think about how you want to operate your system. Retail deals come and go, so aim for maximum flexibility with your system. Some people just want to set and forget, others treat energy trading as a new hobby.
Do you intend to use Amber to pay off their system in just a few years? Or join LocalVolts and sell power to your Mum for nothing? Join Facebook and Reddit community groups if you think trading power might be for you. You will need to size your batteries and inverter accordingly.”
From July 1, every energy retailer will be required to offer a 3 free hours of power plan in NSW, SA and SE Queensland, with Victoria to follow. If you’re planning to make the most of a plan like this by charging up a home battery, do your homework on what inverter to get with our deep dive guide to inverters, including recommended brands.
About Anthony Bennett
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