The huge leap forward in battery storage technology has seen an surge in interest from people looking to go off-grid, store their own solar energy (self-use) or become energy independent. However, the rapid pace of technology development has resulted in some confusion over what is achievable and which system is best suited to an individual’s needs. While trained solar installers offer very good advice, much of the public and media have little understanding of the various solar / battery storage system capabilities and limitations.
Which battery storage or off-grid system is best?
What battery capacity do I need?
How many solar panels do I need?
These might seem like straight forward questions, but they are not easy to answer because there is no one-size-fits-all solution. Every household energy needs are different and there are a wide variety of hybrid and battery systems available. I have found one very effective way to answer these questions, especially for those not well informed is to describe several scenario’s which would apply to the modern ‘efficient’ Australian home. For those who want to skip the explanation and jump straight into learning about the best batteries and off-grid solar systems, see the best solar battery and best off-grid solar articles.
How much does a solar battery or off-grid system cost?
Clean Energy Reviews have developed an free tool to help those looking to purchase solar and batteries understand what size is best suited to your energy requirements and an estimated cost. Enter the solar and battery simulator.
Basic battery price guide
Battery storage is measured in kilowatt hours (kWh) and typically cost from $700 to $1000 per kWh, plus installation and inverter costs. Therefore, a moderately sized 6kWh battery will cost around $6000 including the cost of a compatible hybrid battery inverter and installation. Solar panels on the other hand are relatively cheap with an average size 6kW solar array (roughly 18 panels) costing around $5000 to $8000 installed. Off-grid solar systems are much more expensive due the large battery systems and powerful off-grid inverters required. See the detailed guide to battery storage systems.
The four common solar battery system types and prices *
Click on the options above to see full details, capabilities and cost breakdowns.
* Note: prices are in Australian dollars and are estimates only - including all parts and labour for a hybrid solar installation on a efficient 3-bedroom home with average energy consumption of 12kWh per day. If your energy use is higher, for example double this (24kWh per day) then the cost would be 60-80% higher due to the cost of additional solar panels and batteries - See the following sections for tips on how to reduce your energy usage.
How to size a Solar/battery system
The correct way to 'accurately' size a solar & battery system is by first monitoring your household electricity consumption and using this data to size a suitable solar array and battery. You can get this data in several ways, either by using an aftermarket energy meter or by downloading your smart meter data (if you have one installed). Below we explain how to obtain smart meter data.
Use Your Smart Meter Data
Most modern electricity ‘smart’ meters log your electricity consumption every 15 minutes and you can obtain this data for up to the last 2 years from your local electricity network operator. Do not confuse this with your electricity retailer who sends you your bills. The network operators own the poles, wires and meters. There are many network operators around Australia. In Victoria alone there are 4 main operators shown below.
Click the links below to sign up and get your smart meter data in Australia.
United Energy (VIC)
If you are building a new home then you will have to estimate your energy consumption based on a load table. A load table lists all your major appliances and approximate energy used per appliance to determine the total electricity uses per day in kWh. A professional solar installer can help with this process.
If your solar array is undersized and your battery capacity is oversized you risk not generating enough solar energy to charge your battery, especially during the shorter winter days. Or if your household consumption is high during the day you may directly use all your solar energy and not require a battery at all.
Before we describe the various options, it is important to determine exactly what you want to get out of a solar or hybrid battery system. For those not familiar with hybrid solar and home energy storage read this first. Also you can learn more about the many different hybrid/off-grid inverters and batteries here.
The amount of energy your home consumes per day is measured in kilowatt hours (kWh) and will be listed on your electricity bill. Creating an more efficient home may mean you can achieve more savings by using a standard grid-connect solar system rather than installing a more expensive hybrid battery system.
Unfortunately most Australian homes are very inefficient and on average use around 20kWh of electricity per day. Naturally if you create a more efficient home which consumes less electricity your costs will be lower. Simple things like adding extra/improved insulation, LED lighting and solar boosted hot water can make a huge difference. The amount of energy your home consumes per day (measured in kilowatt hours / kWh) will be listed on your electricity bill. The more information you have about your energy use the better.
There are many other ways to optimise your use of solar. A good example is running electric hot water systems directly from a solar PV system during the day rather than using off-peak power (explained in more detail below). Creating an more efficient home may mean you can achieve more savings by using a standard grid-connect solar system rather than installing a more expensive battery system on an inefficient home - Refer next section.
For information about how you can reduce your energy use and create a more efficient home refer to this article on our companion site - Go off-grid/hybrid.
It is often worthwhile investing in new, more efficient appliances like fridges, freezers, heat pumps and solar hot water systems to reduce your total energy use and in turn reduce the size and cost of a solar / battery system to power your home.
You don't need batteries to take full advantage of solar
For many people, the cost of a battery system is simply too high, but this doesn’t mean you can’t make the most out of installing solar on your home. Generally installing only solar can reduce your electricity cost by 50-60%.
For those who are at home during the day or work at home, it is generally far more cost-effective to install a common grid-connected solar system (approx $6,000 for a 5kW system) and use the solar energy directly. For example, it is possible to run energy-intensive appliances such dishwashers, air-conditioners and washing machines (not all at the same time) for free using your solar energy during the day. Also, there are now many ‘smart’ appliances which can be remotely turned on or activated using timers to operate when there is excess solar energy, rather than sending it to the grid for very little return.
Also, you can easily add a battery later using an AC battery system available such as the SonnenBatterie and Tesla Powerwall 2. Many new grid-connect solar inverters are ‘battery ready’ hybrid inverters, which makes it easy to add battery storage in the future.
Using hot water as a battery!
Electric hot water systems are extremely energy intensive and often account for around a third of annual energy costs (unless you have gas hot water). Electric element hot water systems are usually set to heat your water using cheaper off-peak electricity but a grid-tie solar system together with a clever device called a solar diverter to divert your excess solar energy to your hot water system can maximise your solar consumption, saving you money. By doing this you are effectively using your hot water as a battery, with the energy stored as heat. There are several well known solar diverters available such as those from Catch power, ImmerSun and AWS SunMate.
How can home batteries prevent grid wide blackouts?
It is not well known that multiple small home batteries have the ability to stabilize the grid by selling power back during peak times (such as during heatwaves) thus eliminating the need for expensive gas backup power stations used only several days a year. This works by having a 'remote' control system which can feed energy back into the grid from hundreds or even thousands of home and commercial battery systems simultaneously. The Australian startup 'Reposit Power' are already using this model and the German battery manufacturer 'Sonnen' is also setting up a similar system.
Off-grid Solar Systems
To answer the common question about taking your home off-grid, I generally say to most people "if you already have the grid connected to your home then it makes no sense to go completely off-grid because the cost is too high; you will need a very large battery system to store energy for 3-5 days of bad weather along with a auto-start back-up generator for the winter months (in colder area's)". There is also the cost of fuel to run a back-up generator, maintenance, etc. so for most people it just doesn't make economic sense. Why not use the grid as your back-up power source and feed your excess solar energy into the grid for some return?
Still want to stick it the man and go off-grid anyway? If you are determined to become energy independent or you are planning on building an off-grid home we have a building off-grid homes guide on a companion site - Go hybrid/off-grid
Best off-grid solar system review - Click image below
If you are living or have built a standard home in an off-grid location then I would recommend an advanced multi-mode inverter system. There are many cheaper hybrid systems available which can operate off-grid but most are only suitable for smaller cabins and summer use. Read more information and reviews about the advanced off-grid systems here.
Living off-grid full-time means that for most of year you can rely on your solar/wind generation, but there will come a time when the weather turns sour for a prolonged period and you just don't have enough juice left in the battery. Also, at some stage there may be a fault or repair needed in the system so you will usually need some kind of back-up power source such as a generator. In temperate, colder climates where the winter days are much shorter (depending on your energy use), you will generally need to run a back-up generator once a week to top up the batteries during the few winter months. If you have continuous bad weather for a longer period of time, then the generator will have to run for longer. To help make this a seamless experience, most advanced off-grid multi-mode inverters have in-built generator control systems to automatically start and run the backup generator.
Typically with a correctly sized solar and battery system, the backup generator will only be used for 5% or less or your electricity needs. In most locations without severe shading issues, a solar array will cover 95% to 98% of the electricity consumption.
A question I get asked very often is ‘can I use a small scale wind generator instead of solar?’ This is a tricky one and generally the answer is no. This might sound surprising but there is a good reason why small scale turbines are much less effective than solar. Let me explain…
Large scale winds turbines used on wind farms work extremely well and are generally located in area's which have been recorded to have consistent wind. These tall turbines are high enough to capture the ‘clean’ or non-turbulent air-flow which makes them very reliable and efficient. The very long blades used (up to 75m long) have a huge ‘swept area’ and capture a large amount of energy.
Small scale residential wind turbines on the other hand, generally have poor performance due to the small size and location. Many people assume wind is well suited for their location, but the reality is the wind it is usually very turbulent and not efficient for a small scale turbine. In order to achieve full power output from a turbine, it needs to be installed at twice the height of the surrounding trees and buildings. Then there is the cost, a small 1000W turbine can easily cost $6K installed on a 15 meter pole. If you compare this to solar, for the same cost you could purchase 20 x 300W panels (6000W) installed on a tilt system. Plus solar panels have no moving parts and virtually no maintenance, so the numbers speak for themselves. Although, there are situations where a combination of wind and solar will work extremely well.
Learn more about hybrid solar systems and battery technology here