We all want to power our homes with as much of our self-produced, clean energy as possible, right? So why do we still draw energy from the grid when we have solar panels and a battery?
Knowing how your solar battery system works along with how external and system factors impact where you source energy from helps answer this question. And most importantly, it helps you understand how to limit the amount of energy you need from the grid. This allows you to make the most of your solar + battery system and save you even more.
All Plico solar systems are grid-connected. While you may be dismayed at seeing energy get imported from the grid, it is a necessary and important part of the system’s operation. The amount of grid energy you use compared to the solar energy you use for your home depends on a number of factors. These include your solar generation, the battery and inverter capacity, the energy demands of your appliance along with when and how you use energy.
Read on to find out why (and when) your household will draw energy from the grid.
Energy use exceeds supply
If your household energy use, or load, exceeds the energy your system generates and has stored in your battery, you will draw energy from the grid. This can occur on winter mornings after your battery has been depleted overnight. Alternatively, it may occur during the day when your energy demand exceeds what your panels are producing or what the inverter can provide to your home.
For example, during winter you may be producing 4.5 kW intermittently. It’s a cold day so you turn on the reverse cycle heating, which uses 4.5 kW to run. Add in other household appliances and your energy use is 5 kW. You are likely to draw the additional 0.5 kW from the grid to meet your household demand. Even if your battery has capacity, it may not meet the instant demand or it may be set to reserve capacity to discharge for later use.
When household demand exceeds solar production, you will draw energy from the grid.
Shading and cloud cover
The most obvious barrier to producing your own clean energy is the amount of shading on your solar panels. When the amount of sunlight reaching your solar panels reduces, so too does your solar generation. Shading caused by nearby trees, buildings and smaller items like aerials or satellites on your roof can impact your solar production. Similarly, thick cloud cover has a negative impact on how much energy you can produce. If shading reduces your solar generation to less than your household demand, you will draw energy from the grid.
The capacity of your battery significantly affects how much stored energy you can use in your home. A larger battery means you have more clean energy available for use. The size of your battery would have been selected based on your average household energy use, and any future energy considerations. Plico’s calculations take into account your power needs over course of an entire year, accounting for all four seasons. So while you might be waking up to an empty battery in winter, it’s likely to have plenty of charge on summer mornings – depending on your energy use overnight of course.
Once your battery has used up its stored energy and your panels are not producing, you will draw energy from the grid.
Another consideration with battery capacity is the depth of discharge (DoD) and state of charge (SoC). The DoD is the percentage of the battery that has been discharged relative to the overall capacity of the battery. Plico batteries have a DoD between 90% - 95%. An additional 5%-10% is included for blackout protection and to preserve the life of the battery. Setting your battery to its maximum DoD runs the risk of the battery drawing beyond this limit and shutting down for a short time. Including a small buffer prevents this from happening and provides additional energy during a blackout if your battery is depleted and your panels are not producing (think blackouts that occur in the middle of the night in winter). The SoC is the percentage of charge of a battery relative to its capacity. When you first have your battery installed, its maximum SoC will be 100% - 99%. This will drop gradually as your battery ages. Your battery’s minimum SoC is the lowest charge it will draw down to, as a percentage. For Plico systems this is usually 10% - 15%.
You can calculate the useable capacity of your battery by subtracting the minimum SoC as a percentage from the maximum capacity of your battery. If you have an older battery, you may want to include the maximum SoC in your calculations.
10.6 kWh battery – min SoC 15% = 10.6 x 0.85 = 9.01 kWh
10.6 kWh battery with 97% maximum SoC – min SoC 15% = 10.6 x 0.83 = 8.8 kWh
Once you know the useable capacity of your battery, you can work out how long it’s going to last you overnight before your panels start producing again. If you have appliances running on standby power only, you may only use 0.3 kW per hour. With this example, you can draw from your battery for 30 hours (9.01 kWh / 0.3 = 30.03 hours). If you have some appliances running overnight, your energy use may be 1 kW each hour. In this example you can draw from your battery for 9 hours. Or if you have heating and cooling running all night, your energy use may be double that, meaning you will only get 4.5 hours out of your battery. Note that from the time the sun goes down, energy use often fluctuates, as the TV goes on and off, the kettle is boiled, the oven is cooking and then cooling down – all in the first few hours after sunset.
The great thing with Plico is that all our systems come with an energy monitoring app, so you can see exactly how much energy your appliances are using and adjust them accordingly. Or you can set a timer to ensure you get the most out of your battery without having to draw from the grid overnight.
It’s also a good idea not to ramp up your energy use first thing in the morning, especially in winter. If your energy use spikes, it’s likely that you will need to draw from the grid.
High energy use appliances
As you can imagine – or perhaps you have confirmed by looking at your Plico energy monitoring app - some appliances need considerably more energy to operate than others. While most appliances can be run on solar power, some operate differently based on their energy demands. Think air-fryers, bore and pool pumps, hot water systems and ovens – these use a lot of energy, but often in short or irregular bursts.
While you may only run them for a short period, the amount of energy they require instantly cannot always be met by your solar + battery system. Batteries take longer to ‘ramp up’ than some high energy use appliances require, so your household will draw energy from the grid initially to meet this demand. But don’t worry, your battery will soon take over. Here is the process in a nutshell.
- The load occurs (appliance switched on).
- The system reads the load.
- The system sends the signal to the battery.
- The battery increases the amount of power it is delivering to the house.
You can see how this process isn’t as instantaneous as your hot water system might be. That’s where the grid provides a helping hand.
If you have on-site water or sewage pumps, electric hot water systems or boosters, or are charging an electric vehicle (EV), you can expect to have higher demands for electricity. Consider installing timers where you can, so that energy peaks are covered by your solar + battery system and not the grid.
In addition to high energy use appliances, many appliances also have switching loads. This is when they need to draw different amounts of energy at different times. For example, the element in a 2 kW oven needs to switch on and off regularly to maintain a constant temperature. Dishwashers, washing machines and tumble dryers will use different amounts of energy depending at which stage of the cycle they are at. There is often a delay in the battery (or panels) responding to this load shifting. Even your fridge, which you might expect to have a relatively constant energy demand, has switching loads. The compressor will turn on the motor briefly to maintain a constant temperature, and this motor can increase your fridge’s energy use eightfold.
As a result of switching loads, your home will draw energy from the grid to meet this extra demand before your solar + battery system can catch up with the load increase.
Just as our appliances cannot always access instantaneous energy from our solar panels and batteries, your energy monitoring app can also experience delays. The data from your inverter is sent to the cloud and then into the app on your phone or dashboard on your PC. Naturally, there are delays in this communication, which means that what you see on the app is not necessarily what is happening at that exact moment in time. Additionally, what appears to last five minutes on your app may only be a 10 second event. The communication system relies on your internet or phone service provider and the existing telecommunications network to send and receive these messages. So, just like your internet speed and phone coverage, it’s not always perfect.
Batteries are designed to charge and discharge on a regular cycle. If there were no interruptions to this flow, your battery would charge over the course of the morning until it was at maximum capacity. It would stay fully charged until the solar generation begins to drop in the evening, and gradually discharge overnight. This cycle helps protect the longevity and performance of the battery. If you have a solar + battery system, you’d know that not all days happen in that perfect sequence of charge and discharge. The clouds roll in, you turn on the heater first thing in the morning or the kids' school clothes are wet from the day before so into the dryer they go. When this happens, your battery will discharge if there are no schedules in place and it has the capacity to do so - but not all the time. The programming in the battery may force it to stay at its current state of charge, rather than discharging to the home. When that happens, you will draw more energy from the grid, but your battery will have more capacity to provide your home’s energy later in the day.
When we talk about the perfect battery cycle, it also applies to times when solar production is at its highest and providing almost all of your energy needs. If the battery is not being discharged regularly, it can impact its longevity and performance. So, once a week or fortnight in summer it’s a good idea to get your battery down to its minimum SoC. Leave the A/C on overnight or cook up a storm when the sun goes down. Your battery will thank you for it.
The amount of energy your solar + battery system can provide to your home at any one time is limited by the size of your inverter. The larger the solar inverter, the more electricity that can be converted from your solar panels and/or battery and provided to your home.
Inverters are usually rated in kilo-volt-amperes, or kVA. Like watts (W) and kilowatts (kW), kVA simply means 1000 volt-amperes (VA). And 1000 VA is a little less than 1000 W if you are matching your household energy needs with your inverter output.
For example, a 5 kVA inverter (Plico’s most popular inverter size) will be able to output around 5 kW to your home at any given time. Redback inverters are limited to 4.6 kW from the battery alone and Alphas can output 5 kW for solar and battery (unless you have a 3 kVA Alpha inverter of course). If your energy use exceeds this, you will draw the excess from the grid, no matter how much solar you are producing and how much capacity you have in your battery. Most household energy use can be met within the limit of 5 kW, however larger or 3-phase energy homes may require a larger inverter. The inverter limit applies only to the energy being sent to your home. Your panels can produce far more than this at any given time and the excess can be sent to your battery or the grid without impacting the amount your home receives.
Wouldn’t I be better off going off-grid?
Off-grid systems don’t draw any energy from the grid and are completely self-sufficient. There are many benefits to having an off-grid system, including complete energy independence, low running costs and being 100% renewable. If you live in an area with an unreliable network or without access to an electricity supply, then off-grid systems are highly beneficial. Their downfall, however, is that they require a significantly higher upfront financial layout because they need to be large enough to cover all your energy needs.
With a Plico system, you are connected to the grid as a back-up. So at times like those outlined above, you still have a reliable supply of electricity. If that supply lets you down, you have Plico’s blackout protection to keep the essentials going, even when the grid is down.
To learn more about going off-grid, read our blog to find out the pros and cons.
Load shifting / Scheduling battery charge and discharge
There are some instances when setting a schedule for your battery’s charging or discharging is beneficial. This may be because you are on a tariff that costs you more to draw from the grid at peak usage times or you may be preparing for an extended power outage. This is called load shifting and is possible with all Plico solar batteries. A word of caution, though. Unless you have a solid understanding of your system and how the battery operates, it’s best to seek advice from our friendly service team before you make changes to your battery’s operation. A small mistake could end up costing you more.
With load shifting, you can choose to purchase energy from the grid when it’s cheapest. This lets you keep your self-produced energy for later use, when the cost of energy is higher.
If you are considering switching tariffs to make the most of your solar + battery system, get in contact with us and we can set up a schedule for you, as well as monitor your system to see how it benefits you financially.
There are many factors affecting how much energy you will draw from the grid. The good news is that your solar + battery system will cover the vast majority of your energy needs, using the grid as a backup when required. Next time you’re drawing from the grid with a full battery or in the middle of a sunny day, come back to this list and you should find out why. Empowering yourself with this information will help you better understand your Plico system and allow you to get the most out of it.
If you’re ever concerned that your system is not performing as it should, we are here to help. As part of our service commitment, we can analyse your system’s data and identify any issues remotely. Please raise a service ticket and our friendly service team will be in touch.