How to read a solar battery quote, line by line

Start with usable capacity, not the number on the box

Every battery has two capacity figures. Nominal capacity is the most energy the battery can hold at full charge, and it is usually the number on the label. Usable capacity is the energy it can actually deliver to your house. The government's own example: a battery with 10 kWh nominal capacity and a 90 percent depth of discharge has 9 kWh usable.

Usable is the figure to compare, for two reasons. It is the energy that runs your house after dark. And it is the figure the federal battery discount is calculated on: the certificates a battery creates are worked out from its usable capacity, and only the first 50 kWh of usable capacity counts. Nominal capacity still matters for eligibility, because the system has to be between 5 and 100 kWh nominal, but it does not size your discount.

So the first thing I look for on any quote is both numbers, written down. If a quote shows only one, ask which one it is. If one quote leads with nominal and another leads with usable, the battery that looks smaller on paper may be the bigger one in your garage.

You can check the figures yourself. The nominal and usable capacity of listed batteries are published on the Clean Energy Council's approved battery list.

The battery line: model, modules, and the list it has to be on

The battery line should name the exact model, not just a brand and a size. On a stackable battery it should also give the number of modules, because the capacity comes from the stack, and the discount rules look at the finished configuration: the stacked system as installed has to be on the approved list.

The list. To attract the discount under the Cheaper Home Batteries Program, the battery has to be on the Clean Energy Council approved battery list at the time it is installed. The Clean Energy Council maintains that list. The Clean Energy Regulator administers the scheme and can declare products ineligible. Lists change, so what counts is the listing on your installation date, not the day you read the brochure.

VPP capable. On a grid connected home, the inverter the battery connects to has to be technically capable of taking part in a virtual power plant. You do not have to join one. The rule is about capability, and whether you ever sign up to a VPP stays your decision. An existing solar inverter elsewhere on the site does not need to be VPP capable; the inverter the battery connects to does.

New, and installed in one job. The battery has to be new, not previously installed or claimed, and installed in a single job, including a group of batteries connected to operate as one.

A quote that just says "13 kWh battery" gives you nothing to check. Ask for the model and the module count, then look them up.

The inverter line: size, phase, and which kind of retrofit

The inverter line should give the model, its rating in kilowatts or kVA, and whether it is single phase or three phase. Those facts decide how much the system can run at once, whether it fits your connection, and what Energex will approve.

On a single phase home in the Energex area, a standard fixed connection is limited to 10 kVA of inverter capacity in total, solar and battery together. A dynamic connection on single phase can allow up to 10 kVA of solar inverter plus 10 kVA of battery inverter, but where a hybrid inverter is used on that dynamic single phase connection, the total is still 10 kVA. If a quote puts a battery inverter beside a large existing solar inverter, check the combined figure against those limits.

If you already have solar, the quote should also say which of the two retrofit designs it is: a hybrid inverter replacing your existing solar inverter, or an AC coupled battery added beside it. Both qualify for the discount. They behave differently in a blackout and use your connection allowance differently, and I go through both in hybrid inverter or AC coupled retrofit. If the quote does not say which one it is, ask why that design was chosen for your house.

Three phase homes have more headroom and their own tradeoffs, covered in three phase homes and batteries.

Backup: none, some circuits, or the whole house

Backup is the line most often implied and least often written down. A battery on its own does not keep your lights on in a blackout. Backup is a design choice with its own hardware and its own switchboard work, and the quote should say which of three things you are buying.

No backup. The system shuts down when the grid does, just as ordinary solar does. That is a perfectly legitimate choice if outages are not your concern, but the quote should say so, so nobody assumes otherwise.

Essential circuits. Named circuits, typically the fridge, some lights, the internet and a few power points, are wired to the backup output. The quote should list which circuits, not just say "essential loads".

Whole home. Most or all of the switchboard stays live. That usually means more hardware and more board work, and often the biggest loads are managed so they cannot flatten the battery. Whole home backup vs essential circuit backup goes through the tradeoffs.

Whichever it is, the quote should name the extra hardware, say how much the system can run in backup mode, and state the changeover time in milliseconds or seconds. Some systems switch over fast enough that nothing in the house notices. Others take long enough that a desktop computer will restart. Either can be the right system, as long as you know which one you are getting. "Includes backup" with no number is not an answer.

The switchboard is where two quotes really differ

When two quotes for the same battery are far apart, the difference is rarely the battery. It is usually the switchboard.

Adding a battery means new circuit protection, isolation and labelling at the board, and Energex itself notes that connecting a battery to an existing solar system needs some rewiring of your switchboard. On a modern board with room to spare that is a modest part of the job. On an older, full board it can mean real work before the battery can be connected, and backup adds more again.

So the switchboard work should be itemised, not folded into one installation figure: what is being added, whether any board upgrade is included, and what happens if the board needs more than expected once the cover is off. A low quote that says nothing about your board has not priced your board. What a switchboard upgrade costs on the Sunshine Coast explains what drives that line.

If you are not sure what state your board is in, our $199 electrical safety check will tell you before the battery quotes arrive, and the $199 is credited back if you go ahead with a solar or battery installation within 30 days of the check.

The discount line: how it should be shown, and what sets it

The federal discount comes from small scale technology certificates that your battery creates. Most people assign them to the installer in return for an upfront discount; you can also keep them and sell them yourself. Where the installer applies the discount, the department's guidance is that it must be clearly displayed against the price of the system, and it notes the installer may include administration fees or charges.

So a good quote shows three things in order: the full installed price, the discount as its own line, and the net amount you pay. Ask how the discount was worked out: the usable capacity it was based on, and which period's certificate factor it assumes. I do not put a dollar figure on the discount in articles, because the factor changes and certificate prices move with the market.

Energex: the connection application and your export limit

Before a battery is installed, an application has to go to Energex. Your installer normally lodges it through Energex's Electrical Partners Portal, and the quote should say that it is included. Connecting a battery to existing solar needs a new application before the work happens.

Two outcomes of that application affect you, so the quote should talk about both. The first is the export limit. Any alteration to an existing system triggers a fresh network assessment. Where the local network is constrained, Energex can approve a smaller system, approve a reduced export of 1.5 kW, or offer a dynamic connection instead of a fixed limit. If the assessment comes back lower than what you export today, Energex says you can keep your existing agreement and export limit, or go ahead with the alteration and accept the revised limit. The retailer also has to give you information about feed in tariffs and export limits in writing before installation.

The second is the connection type. A dynamic connection lets your export limit rise and fall with network conditions. It relies on your home internet, and if that link keeps dropping out, the system is held to the lower fixed export amount, typically 1.5 kW, until it is reestablished. Energex says it aims to make a connection offer on a dynamic application within 65 business days, which is worth knowing if timing matters to you.

If you are still on the original 44 cent feed in tariff, Energex notes you cannot export from a battery and keep that tariff. The rest of that story is in the hybrid versus AC coupled article.

Warranties: three limits and a registration step

A battery's manufacturer warranty is rarely just a number of years. It usually has three parts, and cover finishes when the first limit is reached: a term in years, an energy throughput figure in megawatt hours, which is the total energy the battery is warranted to deliver, and an end of warranty capacity, the share of original capacity it is guaranteed to keep, expressed as a percentage such as 60 or 70 percent at ten years.

The quote should state all three for the exact model quoted, or attach the warranty document. A household that cycles its battery hard can reach the throughput figure before the years are up, which is why the years alone do not tell you much.

Read the conditions as well. Some manufacturers make registration at commissioning a precondition of the warranty, some start the warranty from the date the product is activated and registered, and some require the system to stay connected to the internet. Once the job is finished, ask your installer to confirm in writing that the system has been registered.

The manufacturer warranty covers the hardware. The workmanship warranty covers the installation, and it comes from the installer, not the manufacturer. Ours is a lifetime workmanship warranty (conditions apply), explained in what a lifetime workmanship warranty actually means. Whoever you choose, the quote should say how long theirs lasts and what it covers.

Monitoring, and what depends on your internet

Almost every modern battery is set up and watched through an app, and more of the system leans on your home internet than most quotes mention. Three things can depend on it: a dynamic export connection, which falls back to the lower fixed export if the link keeps dropping; taking part in a virtual power plant, which needs an ongoing internet connection; and, with some manufacturers, the warranty itself.

So the quote should say how the system connects to your internet, who sets up the monitoring, and whether you get your own login to see what the battery is doing. If your router is at the far end of the house from where the battery will go, raise it before install day, not after.

One practical point from Energex: changing your wifi password, modem or router can break a dynamic connection's link. If you change internet provider, put the battery on the list of things to reconnect.

Where the battery goes: the location rules

A battery cannot go wherever there is a gap on a wall. Home battery installations have to comply with AS/NZS 5139, and compliance with it is also a condition of the federal discount.

In plain English, the standard's restricted locations include inside a habitable room such as a bedroom, living room, kitchen or study; in ceiling spaces and wall cavities; under stairways and access walkways; and in an evacuation or escape route. There are required clearances around exits, around windows or vents that serve habitable rooms, and around appliances that are not part of the battery system, such as hot water units and air conditioners. Where a battery is mounted on a wall with a habitable room on the other side, that wall has to act as a noncombustible barrier, or one has to be added.

The standard has been amended, and Queensland's electrical safety regulator says the amendment clarifies location and spacing requirements, what is permitted inside the restricted zones, and that barriers to habitable rooms must be at least 6 mm thick. The detail is the installer's job. Your job is to check that the quote says where the battery will go, and whether any barrier or wall lining that location needs is included. A quote that has not decided where the battery goes has not finished pricing it.

Exclusions, variations, deposits, dates and your rights

The last page of a quote is where the surprises live, so read it as carefully as the first.

Exclusions. Look for anything left out that your job could plausibly need: switchboard upgrades, long cable runs, a barrier to meet the location rules, backup hardware. An exclusion is not a red flag on its own. An exclusion that covers the likely expensive part of your job is.

Variations. Find out what would change the price after you accept, how that change would be priced, and whether you get to agree before the extra work goes ahead.

Deposits and the payment schedule. Know how much is due at acceptance, what the remaining payments are tied to, and what happens to your deposit if Energex approves the connection with conditions you do not accept.

The validity date. A quote can hold the installer's price for a set period. It cannot hold the discount, because the discount follows the install date. If the system is certified on or after 1 January 2027, the discount steps down to the new factor, even on a quote that is still inside its validity date.

Door knocks and cold calls. If the sale was negotiated by a salesperson who came to your door or phoned you without being invited, it is an unsolicited consumer agreement under the Australian Consumer Law. You have 10 business days to cancel, and during that cooling off period the seller cannot supply services or take or ask for payment. Inviting a business to come and quote does not invite it to sell: if the salesperson negotiates the sale on that quoting visit, it can still be unsolicited. If they leave the quote with you and you come back to accept it, it is not.

The rights you cannot sign away. Whatever the warranty says, the consumer guarantees under the Australian Consumer Law apply automatically. Products have to be of acceptable quality and fit for purpose, services have to be provided with due care and skill and within a reasonable time, and a business cannot exclude those guarantees.

The one number to compare: price per usable kWh after the discount

Once every quote has been read this way, one number makes them comparable.

Take the net price after the discount and divide it by the usable capacity in kWh. The answer is what you are paying for each kilowatt hour your battery can actually deliver to your house.

Three rules keep the number honest. Use usable capacity for every quote, never nominal, and check it against the approved list. Make sure every quote's discount assumes the same install timing, so one is not built on a factor another cannot deliver. And compare only the same scope: if one quote includes backup and switchboard work and another leaves both out, get the second installer to price the missing work, and add it, before you divide.

An illustrative example, not a real job. Quote A is for a battery with 10 kWh nominal and 9 kWh usable. Quote B is for a battery that sounds bigger at 12 kWh nominal, with 10 kWh usable. Same scope, same install month. If B's net price is more than about 11 percent higher than A's, A is the cheaper battery per usable kWh, even though B has the bigger number on the box.

The number does not tell you everything. A longer warranty, a higher throughput figure, or backup that suits your house can be worth paying more per kWh for, and a battery much bigger than your evenings will not earn its extra kilowatt hours at any price. But it strips the marketing out, and it turns a pile of quotes into a real comparison.

If you would like a quote from us to put beside the others, ask for it line by line and hold it to the same standard. If you want the system designed for your house first, that is the $299 solar and battery design visit: your board and any existing system checked on site, and a written design you keep and a locked in fixed price within 3 business days, credited back in full off the installation if you go ahead within 30 days of the visit.

Common questions