This article is designed to help both the general public and solar installers understand the capabilities of solar battery storage systems, as well as an introduction to system sizing and the costs involved.
The huge leap forward in home battery storage technology has seen an immense amount of interest in people looking to go off-grid, store their own solar energy (self-use) and become energy independent. Although 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 or hybrid storage system is best?"
"What size system do I need to go off-grid?"
"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 simply because there is no one-size-fits-all solution. Every households energy needs are different and there are a huge 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.
How to size a Solar/battery system
This is not simple but in general the correct way to 'accurately' size a solar & battery system is by first monitoring your household energy consumption and using this to size a suitable solar array and battery. You can do this several ways, either by using energy meters or downloading your smart meter data (if you have one installed). Most smart meters log your energy consumption every 15 minutes and you can obtain this data for up to the last 2 years! The team at Clean Energy Reviews is developing a system to do this for you and you can join the free trial here.
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.
Why install a solar battery system?
For many people it is quite simple; to reduce energy consumption from the power grid and store solar energy for later use, but there are quite a number of good reasons listed below. However for people who are able to load shift (run appliances during the day) a common grid-tie solar system may be a more effective and viable option.
Reduce cost - save money by using less energy from the grid
Reduce emissions - reduce pollution from coal/nuclear/gas power generation
Be blackout safe - Have power available during a blackout or emergency
Become energy independent - operate off-grid where possible
Reduce peak demand - peak lopping and grid stability **
Depending on how you answer these will point you towards one of the 4 following systems. As expected they become progressively more expensive with the first option being the most affordable.
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 could be around 80% more due to the cost of additional solar panels and batteries - See the following sections for tips on how to reduce your energy usage.
The four common solar battery system types
Click on the options above to see full details, capabilities and cost breakdowns.
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. If you can obtain peak, shoulder and off-peak energy usage information or preferably a daily energy profile (using an energy monitor) will help you to accurately size a solar system to suit your needs.
There are many other ways to optimise solar use such as running electric hot water systems directly from your solar system during the day rather than using off-peak power as explained 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. For those who are at home during the day or work from 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 as it is being generated. 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. Many newer solar multi-mode inverters have inbuilt ‘demand management’ controls which can automatically switch on ‘smart’ appliances when there is excess solar energy rather than sending it to the grid for very little return. Also with the new generations AC batteries now available such as the SonnenBatterie and Tesla Powerwall a number of new grid-connect solar inverters are 'battery ready' so it will be easy to add battery storage to your home in the future.
By doing this you are effectively using your hot water as a battery, with the energy stored as heat.
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.
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 or interactive 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 full-time off-grid means that for most of year you can rely on your solar/wind generation but there will probably come a time when the weather turns sour 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 generator. In the 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 at least 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. Most advanced mult-mode or interactive inverters have in-built generator control systems to automatically start and run the backup generator.
This is a tricky one and a question I get asked very often is can I use a small scale wind generator instead of solar. The short answer is no, unless you live on top of a hill or by the ocean with consistent strong winds. Large scale winds turbines work extremely well and are located in area's which have been recorded to have consistent wind. Small scale residential turbines generally have poor performance due to the location. Many people assume the wind is well suited when in fact it is usually very turbulent and not efficient for a small scale turbine. In order to achieve full 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 600W turbine can easily cost $5K installed on a 15 meter pole. If you compare this to solar, for the same cost you could purchase 18 x 250W panels (4500W) 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