About Wattcalc

Our mission

Australia is in the middle of one of the most significant residential energy transitions of the last century. Rooftop solar now generates more than 12% of the country's electricity, EVs cleared 10% of new car sales in 2025, and a federal Cheaper Home Batteries rebate worth up to $258 per kWh has put battery payback within reach for the average household. The decisions households face — bigger system or smaller? Battery now or wait? EV or hybrid? — are genuinely complicated, the rebate landscape changes every few months, and the loudest voices in the conversation are often the people trying to sell you something.

Wattcalc exists to give Australians a clean, fast, independent way to run the numbers themselves. No sales pitch. No referral incentives. No watered-down maths. Just the inputs that matter, the formulas that produce a defensible answer, and short articles that explain what the result actually means in 2025–26 conditions.

What we do

We build calculators and supporting articles for the highest-stakes Australian energy and sustainability decisions:

• Solar payback — model system size, daily usage, self-consumption rate, retail tariff and feed-in tariff against installed cost (after STCs) over a 25-year system life.
• Home battery payback — model the federal Cheaper Home Batteries rebate (May 2026 program, $258/$155/$39 per kWh tiered), evening usage shift and FiT arbitrage to see whether a battery actually pays back, or just feels like it should.
• Heat-pump hot water — see what a heat-pump system costs to install (after STCs and state rebates like Victorian Energy Upgrades and NSW ESS) and run, vs gas or electric resistive.
• EV vs petrol — full cost of ownership including fuel/electricity, servicing, registration and depreciation, with home and public charging blended in.
• EV home charger install cost — typical 2026 ranges for 7 kW and 22 kW installs, plus the meter-board and switchboard upgrades that catch most homeowners by surprise.
• Articles — plain-English explainers and decision guides that connect the calculator outputs to the rebate, tariff and product landscape they sit inside.

How our maths works

Every calculator is built from the ground up against publicly available Australian data. We use:

• Default Market Offers published by the Australian Energy Regulator for retail electricity rates in NSW, SE Queensland and South Australia, the Victorian Default Offer set by the Essential Services Commission for Victoria, and OTTER pricing for Tasmania.
• STC zone ratings and deeming periods from the Clean Energy Regulator's Small-scale Renewable Energy Scheme.
• System performance assumptions drawn from ARENA residential solar studies and Clean Energy Council installer guidance.
• EV running-cost conventions consistent with ATO logbook methodology for fairness across petrol, hybrid and EV comparisons.
• Federal Cheaper Home Batteries program rebate tiers ($258/$155/$39 per kWh) as published on DCCEEW.

We deliberately use simple, transparent models over black-box optimisation. Every calculator shows the inputs it's using and the assumption it's making about anything you didn't enter. The goal is a defensible first-pass answer — not a quote.

Editorial principles

Wattcalc is published by the Wattcalc Editorial Team — a small group of Australian-based writers and engineers with backgrounds in energy systems, residential solar, EVs and consumer finance journalism. Every calculator and article is reviewed monthly against the original government and regulator sources. When a rebate ends, a tariff zone is redrawn, or a federal program changes its tiers, the affected pages are updated and the "last reviewed" date is bumped.

We commit to:

• Citing primary sources — every numerical claim links to ARENA, AEMO, AER, ATO, CER, Clean Energy Council, DCCEEW, or the relevant state energy department, not to second-hand summaries.
• Being explicit about assumptions — every calculator names the figures it defaults to and where they come from. There are no hidden constants and no commercial "adjustments".
• Refusing affiliate revenue from the products we model — no installer, retailer, dealer or manufacturer pays us, ever. Display advertising is the entire business model.
• Plain English over jargon — kWh is explained, FiT is explained, NMI is explained, 'self-consumption' is explained. We assume readers are smart but new to the topic.
• Updating content when reality changes — a monthly automated audit checks 11 key sources (federal rebates, STC pricing, AER and ESC retail tariffs, state schemes, ATO brackets, AIP fuel data) and flags drift for editorial review.

Read our full disclaimer and our privacy policy.

How we make money

Wattcalc is funded by display advertising delivered through Google AdSense. We do not sell solar systems, EVs, batteries, hot water systems, electricity plans or any other product. We do not earn referral fees, lead-generation commissions or affiliate revenue from any installer, dealer, retailer or manufacturer mentioned anywhere on this site. We do not sell or share visitor data with third parties beyond what AdSense and Google Analytics require to deliver the service.

Our independence is the entire point of the site. The numbers you see are not influenced by who pays us, because no commercial party in the energy or vehicle supply chain is paying us. If that ever changes — for example, if we run a sponsored calculator or a paid placement — we will label it explicitly on every affected page.

For independent retail electricity plan comparison, the federal government's Energy Made Easy (and Victoria's Victorian Energy Compare) is the only authoritative comparison service in Australia and is free.

Important: this is not advice

The calculators on Wattcalc provide general estimates only. They are not financial advice, energy advice or product recommendations, and they don't consider your specific roof orientation and shading, vehicle model and trim, tariff structure, network area, household occupancy pattern or any other circumstance unique to your situation. The output is a useful starting point for further conversation — not a quote, not a recommendation, and not a substitute for professional advice. Please read our full disclaimer, get written quotes from at least three Clean Energy Council-accredited installers for any solar or battery purchase, and speak to a licensed financial adviser before making any major energy or vehicle decision.

Get in touch

If you have feedback, spot an error in a calculator, want to suggest a new tool, or are an Australian energy researcher with primary data we should be modelling against, please email hello@wattcalc.com.au or visit our contact page. We read every message and aim to reply within two business days.