Agile and Time-of-Use Smart Tariffs Explained: Shifting EV, Hot Water and Washing to Cheap Windows

A time-of-use (TOU) tariff charges you different prices for electricity at different times of day. Shift your heavy loads — the EV, the hot water cylinder, the washing machine — into the cheap window, and your bill falls without you using a single kWh less. That's the pitch, and for the right household it genuinely works. But TOU tariffs aren't free money, and for some homes they'll cost more than a plain fixed rate. This guide explains how they work, who wins, and where the catch lives.

What a time-of-use tariff actually is

Instead of one flat unit rate all day, a TOU tariff splits the day into cheap and expensive periods. To be on one you need a smart meter (SMETS2) that records your usage half-hourly. The common UK options fall into three shapes:

• Fixed-window overnight tariffs — Economy 7 (the legacy version, roughly seven cheap overnight hours) and newer EV-focused plans like Intelligent Octopus Go, which offers around a 7p/kWh overnight window (verify the current rate). Great for storage heaters, battery charging and hot water.
• Load-tuned tariffs — Cosy Octopus sets its cheap windows around heat-pump running patterns.
• Fully variable — Agile Octopus re-prices every half hour, tracking the wholesale market. On windy or sunny days it can even go negative (you're paid to use power); on a cold, still evening the peak can spike hard.

Note that rates in your knowledge pack — like the ~7p Go window — are indicative and change with 30 days' notice. Always read the customer's actual bill before quoting a figure.

What to shift, and roughly what it's worth

The saving comes entirely from moving flexible loads into the cheap window. The Ofgem price cap implies a typical unit rate of around 24.67p/kWh (it resets every quarter and standing charges apply on top). If an overnight window is a fraction of that, the arithmetic on shiftable loads is compelling:

• EV charging — by far the biggest prize. An EV can add several thousand kWh a year; charging it overnight instead of on a flat rate is where most TOU savings are made.
• Hot water — heat the cylinder on the immersion (or via a heat pump) during the cheap window. A solar diverter that sends surplus PV to the cylinder is a cheap quick win worth flagging separately.
• Battery charging — fill a home battery overnight cheaply, then run the house off it through the expensive peak.
• Washing machine + dishwasher — smaller loads, but free savings if you can delay-start them.

The catch with variable pricing

Here's the honest beat. TOU only saves money if you can genuinely move your usage. If your life runs at peak time — cooking, heating and appliances all clustered around 4–7pm with nothing to defer — a TOU tariff can leave you paying peak rates on the bulk of your electricity and end up dearer than a flat fix.

Fully variable tariffs like Agile add a second layer of risk. The upside (negative prices) is real, but so is the downside: on a cold, still winter evening the half-hourly rate can climb well above the cap-implied flat rate. Agile suits engaged users who'll actually watch the prices and shift load; it's a poor fit for a set-and-forget household.

There's also the standing charge and the shape of the tariff to check. A headline-cheap overnight rate can be paired with a higher-than-cap daytime rate, so if you can't move much load overnight, you lose on the day rate what you'd hoped to save at night. Two other watch-outs:

• You need a working smart meter transmitting half-hourly reads — no smart meter, no TOU tariff.
• Some premium export tariffs (for solar) are separate again — for example Intelligent Octopus Flux is time-of-use and requires a battery. SEG export rates across the market currently span roughly 4 to 16.5p/kWh and are retailer-set and volatile, so confirm the current figure before relying on it. Your import and export supplier don't have to be the same company.

How to decide if TOU is right for you

Work through this honestly before switching:

• How much load can you actually shift? Add up EV miles, hot-water heating and deferrable appliances. If it's a small share of your total, the gains are modest.
• What's your current tariff? Read the bill for your unit rate (p/kWh), standing charge (p/day) and whether you're already on Economy 7 or a fix. Compare like-for-like against the TOU day and night rates — not just the headline cheap number.
• How engaged are you? Fixed-window tariffs reward simple habits (charge overnight, run the dishwasher on delay). Agile rewards active management. Be realistic about which you'll do.
• Do you have — or plan — a battery or heat pump? These transform the case, because they let you move far more load into the cheap window automatically.

For Northern Ireland, note the electricity market is separate and these specific tariffs may not apply — treat NI separately.

We don't sell tariffs, batteries, EV chargers or referrals, and no supplier or installer pays us a penny — even the "free" comparison sites earn a commission from whoever they send you to. Our only job is to model your actual usage against real windows and tell you plainly whether shifting your load pays, or whether a boring flat rate is quietly the better deal for you.

Figures in this guide are current at the date of publication and indicative only — SEG/export rates change with 30 days' notice, the Ofgem price cap resets quarterly, and grant terms change. Confirm the current numbers for your situation before you commit. This is general information, not personal financial advice.