How the electricity price comparison is calculated

This page documents every assumption behind the electricity price comparison, so you can check the numbers and see when anything changed. It is written for people who want to audit the result, not to sell anything.

1. Which plan is priced for each supplier

Each supplier is represented by one plan: the headline plan a new customer on a standard 24-hour urban meter can sign up to today. Where a supplier offers a switching discount we use the discounted rate and record the discount in the plan name. Where a supplier lists no new-customer discount (Flogas at the time of writing) we use the standard variable rate and say so. Rates are inclusive of 9% VAT and are taken from the supplier's own tariff page, then cross-checked against two independent tariff datasets. The plan name, contract length, exit fee and payment conditions are shown with every result.

Verified 12 Sep 2026. Rural standing charges are higher and are not modelled yet.

2. Year-one cost formula

For each supplier the year-one cost is:

unit rate × imported kWh + standing charge + PSO levy − welcome credit − export income

• Announced price rises. If a change takes effect inside the next twelve months, the unit rate and standing charge are blended by the number of days on each price. A rise on 12 October counted from 12 September puts 30 days on the old rate and 335 on the new one.
• PSO levy. €19.10 a year until 1 Oct 2026, then €6.67 (both inclusive of VAT), blended the same way. Every supplier charges it, so it never changes the ranking, but it keeps the total honest.
• Welcome credits are deducted once, in year one only, exactly as the supplier applies them.
• Export income is exported kWh × the supplier's Clean Export Guarantee rate. It is only non-zero when you already have solar or in the solar what-if.
• Smart plans. With a smart meter, each verified smart plan is priced band by band: night 23:00 to 08:00, peak 17:00 to 19:00, day otherwise, plus any EV or evening window the plan defines. By default the usage pattern is priced as it is. Two optional shifts can be added: EV charging in kWh per day, placed in the plan's cheapest window; and grid-charging a battery overnight, which moves up to 90% of its capacity a day out of peak and then day rates into the cheap window at the cheap rate divided by the round-trip efficiency, applied only where that is cheaper than the rate it displaces. Where a supplier publishes gross rates with separate direct-debit, online-billing and plan discounts (Energia, SSE Airtricity) the combined discount is applied to the unit rates only.
• Not included: gas, dual-fuel bundles, weekend and free-day plans, dynamic (wholesale-linked) tariffs, cashback paid in later years, and the standard rate you revert to after 12 months.

3. Your usage

Annual kWh only. The figure is spread across the twelve months with a seasonal weighting (winter days carry about 20% more than summer days) and across the day with a typical Irish household shape: a low overnight base, a morning bump, a lull, and an evening peak between 5pm and 9pm, calibrated so the annual split matches the ESB Networks standard domestic smart profile (57% day, 32% night, 11% peak; 2,399 / 1,332 / 469 kWh for a 4,200 kWh home), the same split every CRU-accredited comparison uses. The default is the CRU typical usage of 4,200 kWh.

Bill upload. The photo or PDF is read once to extract the supplier, plan, unit rate, standing charge, kWh billed and the number of days. Usage is annualised as kWh ÷ days × 365, which over-states a winter bill and under-states a summer one, so the figure can be edited. Personal identifiers are never extracted or stored.

Smart meter file. The ESB Networks 30-minute file (kW or calculated kWh) is parsed in the browser. Timestamps mark the end of each interval and are shifted back to the start. The most recent 365 days are kept; each month's average hourly import is used, and any month with no readings is filled from the synthetic shape and flagged. Export readings, where present, are annualised and switch the calculator into "already have solar" mode.

4. Solar and battery model

• Annual generation = system kWp × the county yield in kWh per kWp from PVGIS for a south-facing roof at a typical pitch (Wexford 965, Dublin 915, Donegal 817; national fallback 880).
• Monthly split: Jan 3.0%, Feb 4.8%, Mar 8.3%, Apr 11.3%, May 13.3%, Jun 13.4%, Jul 12.7%, Aug 11.5%, Sep 9.1%, Oct 6.3%, Nov 3.7%, Dec 2.4%.
• Hourly shape: a cosine-squared bell centred on 1pm, spanning 7 hours of generation in December to 16.5 in June.
• Self-consumption is computed hour by hour: generation used directly = min(load, generation). Surplus goes to the battery if there is room, otherwise it is exported. A deficit draws from the battery first, then the grid. The battery uses a 87% round-trip efficiency, one representative day per month, run twice so the state of charge settles.
• Cost and payback: system cost uses the same per-kWp price tiers as the solar calculator, less the SEAI grant (€700 per kWp for the first 2 kWp, €200 per kWp for the next 2, capped at €1,800). Payback = net cost ÷ (cheapest bill without solar − cheapest bill with solar). Battery hardware is not included in the cost; degradation and inverter replacement are ignored.

With the default inputs the model lands on 40% self-consumption without a battery, the same figure used across the rest of this site, and about 70% with a 5 kWh battery.

5. What this comparison is not

It is not a CRU-accredited switching service and it cannot move your supply. It prices one plan per supplier, so a supplier may have a cheaper plan for your specific meter or bundle. Always confirm the live rate on the supplier's site before signing up.

6. Change history

• 12 Sep 2026: Version 1.2. Load shifting: EV charging (kWh per day) is priced in each plan's cheapest window (EV window if the plan has one, otherwise night); a battery can be charged from the grid overnight, moving up to 90% of its capacity per day out of peak (then day) rates into the cheap window at the cheap rate divided by the 87% round-trip efficiency, only where that is cheaper. PSO levy change date corrected to 1 October 2026 per the CRU, and the 2026/27 network charge increase (about €41 a year) added to the change log.
• 12 Sep 2026: Version 1.1. Smart-meter plans added: 19 day/night/peak, EV-window and single-rate smart plans from nine suppliers, every band rate read on the supplier's own tariff page, priced hour by hour on the usage profile with no load shifting. Toggle 'I have a smart meter' to include or exclude them.
• 12 Sep 2026: Version 1. Ten suppliers priced on their headline new-customer 24-hour urban plan. Announced rises for Pinergy (14 Sep), SSE Airtricity (5 Oct), Bord Gáis Energy (9 Oct) and Energia (12 Oct) weighted by days. PSO levy cut on 1 Oct modelled. Solar overlay with county PVGIS yields, monthly shares and an hourly bell curve; optional battery with 87% round-trip efficiency. Smart meter file parsing for the ESB Networks 30-minute HDF and supplier exports. Bill photo and PDF reading.