Many people hope to wipe out their power bill with solar and a battery. It is a fair goal. A well-designed system gets remarkably close. But it is worth being honest up front. The realistic answer shapes how a household should think about the investment. This guide explains how close a Perth home can actually get. It covers why a bill almost never reaches exactly zero. It shows how to push it as low as possible.
A good solar and battery system will not usually get a bill to exactly zero. The main reason is the fixed supply charge. However, it can realistically take most homes to around 80 to 95 percent self-sufficiency. That is a dramatic reduction. It is what a system should be designed to achieve.
Why a Bill Rarely Reaches Exactly Zero
An electricity bill has two parts. They behave very differently. The first is the usage charge. This is what a home pays for the energy it draws from the grid, measured in kilowatt hours. Solar and a battery attack this part directly. It can be reduced enormously. The second is the supply charge. This is a fixed daily fee for being connected to the grid at all. It is charged every day regardless of how much power a home uses. As long as a home stays connected to the grid, that charge remains.
This is the main reason a bill does not usually hit zero. A household could generate and store every kilowatt hour it needs. It would still see the daily supply charge on the bill. It is a small, fixed cost rather than a usage cost. It is simply the price of staying connected. For almost every home, staying connected is far more practical and less costly than going completely off-grid.
| Part of the bill | What it is | Can solar and a battery remove it? |
|---|---|---|
| Usage charge | The cost of energy drawn from the grid, per kilowatt hour | Yes, this is reduced dramatically |
| Supply charge | A fixed daily fee for staying connected to the grid | No, it remains while the home is grid-connected |
What 80 to 95 Percent Self-Sufficiency Looks Like
Self-sufficiency is the share of a home’s energy that comes from its own solar and battery. Rather than the grid. For most well-designed Perth systems, that lands somewhere between 80 and 95 percent. In practice, a household covers the large majority of its energy from its own roof. It buys only a little from the grid. This happens on the dullest winter days, during an unusually heavy load, or in the small hours if the battery runs down. The usage charge shrinks to a fraction of what it was. For many homes the remaining bill is mostly the supply charge plus a modest amount of imported power.
Reaching the very top of that range, or beyond it, is possible for some homes. But chasing the last few percent often means adding disproportionate amounts of panels and storage. The gain is small for a large investment. The sweet spot is the point where the system covers the great bulk of usage. It should not be oversized just for a number.
What Pushes a Bill as Low as Possible
Getting to the high end of self-sufficiency comes down to good design. Simply buying more equipment is not enough.
- A larger, well-sized array. Ensure enough generation, typically at least 8.8 to 9 kilowatts, to run the home and fully charge a battery, even in winter.
- A DC-coupled battery. Store the day’s surplus for the evening peak. It connects on the DC side for maximum efficiency. More of the solar becomes usable stored energy.
- Self-consumption habits. Run big loads like hot water, the dishwasher and pool pump during the day, on solar. Do this rather than at night.
- Electrifying efficiently. A heat pump for hot water and, where relevant, charging an electric vehicle on solar keep more energy on-site. This avoids importing it.
Should You Try to Go Completely Off-Grid?
If the supply charge stops a bill reaching zero, you might ask whether to disconnect from the grid. For the overwhelming majority of Perth homes the answer is no. Staying grid-connected means a household can draw power on rare occasions. This happens when its system cannot cover demand. Without staying connected, you would need an enormous, expensive system. It would be sized for the worst winter week. The grid acts as a reliable backup. The modest supply charge is far less costly than the extra storage that true independence would need. The smarter goal is very high self-sufficiency while staying connected. Total disconnection is not the answer.
How Positive Energy Solutions Can Help
Positive Energy Solutions designs systems to reach the high end of self-sufficiency. For the home in question, it sizes the array and DC-couples the battery. The household runs on its own energy for as much of the day as possible. The team is also straight about what is realistic. A household should expect a very small bill rather than a zero one. Every installation is completed by our accredited installers and signed off to Positive Energy’s completion standards. It is backed by a 10-year installation workmanship warranty and Positive Energy Protection. Positive Energy Protection is powered by Omnidian. The system is monitored to confirm it performs as designed.
Frequently Asked Questions
Can solar and a battery eliminate my power bill completely?
Not usually to exactly zero. Solar and a battery can wipe out most of the usage charge. But the fixed daily supply charge for staying connected to the grid remains. Most well-designed Perth systems reach around 80 to 95 percent self-sufficiency. This leaves a small bill made up mainly of the supply charge and a little imported power.
What is the supply charge?
The supply charge is a fixed daily fee for being connected to the grid. It is charged regardless of how much power a home uses. Because it is not a usage cost, solar and a battery do not remove it. This is the main reason a bill does not usually reach exactly zero while a home stays connected.
What does self-sufficiency mean?
Self-sufficiency is the share of a home’s energy that comes from its own solar and battery. Rather than the grid. A well-designed Perth system typically reaches 80 to 95 percent. The household covers the large majority of its energy itself. It buys only a little from the grid.
Should I disconnect from the grid to avoid the supply charge?
For almost all Perth homes, no. Going fully off-grid needs a much larger and more expensive system. It must cover the worst conditions. Staying connected lets the grid act as a low-cost backup. Very high self-sufficiency while remaining connected is more practical and better value. Total disconnection is not the answer.
Get Your Bill as Low as It Can Realistically Go
A power bill of nearly nothing is a realistic goal for a Perth home with the right system. Exactly zero is not the goal. Designing for the highest practical self-sufficiency is exactly what a Positive Energy Solutions consultation is for.
Talk to the local team about cutting your power bill: request your quote from Positive Energy
About the Author
Jason Wiktorowicz
Sales Manager, Positive Energy Solutions | Perth, WA
Jason has been at the centre of Western Australia’s energy transition for over a decade. He was Orchestration Lead on Project Symphony. Project Symphony is WA’s largest virtual power plant pilot. He was Stream Lead on Project Encore. He worked directly with AEMO, Western Power and Energy Policy WA. This work shaped how distributed energy resources connect and operate on the SWIS. That work included developing and rolling out CSIP-AUS. CSIP-AUS is now mandatory for all new WA grid connections. He also led Emergency Solar Management. This was the first program of its kind in WA. He led VPP for Schools, which provided direct market benefits through Supplementary Reserve Capacity. He led REBAR, the WA Residential Battery Rebate scheme.
At Positive Energy Solutions, Jason leads sales with a focus on system design accuracy and long-term performance. Positive Energy Solutions installs solar and battery systems, EV chargers and heat pumps. It holds partner accreditations with Fronius, SigEnergy, iStore and SunPower.
10-year installation workmanship warranty. Positive Energy Protection, powered by Omnidian, performance monitoring included on all systems.
