Answer
A dynamic electricity tariff charges the wholesale price for each hour or half hour, so a solar home with a battery can charge cheaply and discharge at the evening peak. The deciding factor is the price spread you can actually capture after battery losses and supplier fees. Without a smart meter and a flexible load, a dynamic tariff rarely pays.
Wholesale electricity prices swing by the hour, and a flat retail tariff hides that swing from you. A dynamic tariff passes it through. For a home with solar panels and a battery, that creates a simple question: can you buy power when it is cheap, use your own solar when it is free, and avoid the expensive evening hours?
This guide explains how three well-known dynamic tariffs price power, what the arbitrage maths looks like, and what to check before switching. It uses each supplier’s own published terms, and it leaves out price and savings figures that no primary source supports.
Last updated: November 2026
What you will find below:
- How Octopus Agile, Tibber and aWATTar publish their pricing
- A worked example of the aWATTar price formula
- The arbitrage formula, with clearly labelled hypothetical numbers
- Negative prices and spike risk, and how to limit both
- A short checklist for installers and homeowners before a switch
Model a battery on a dynamic tariff before you quote it
Put the roof, the load and the tariff structure into one financial model, so the battery case rests on your own numbers.
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What Is a Dynamic Electricity Tariff?
A dynamic electricity tariff is a retail contract where the price per kilowatt-hour follows a wholesale market and changes during the day. Day-ahead prices are published in advance, so you can see tomorrow’s prices today and plan when to run heavy loads.
A flat tariff charges one rate whatever the market does. A dynamic tariff passes the wholesale price through and adds the supplier’s fee. It is the reverse of a feed-in tariff: instead of being paid a fixed rate for export, you pay a variable rate for import.
Dynamic tariffs need interval data. In practice that means a smart meter that records usage in short intervals. In some markets this is the main barrier, so check it before anything else.
How Do Octopus Agile, Tibber and aWATTar Price Electricity?
Each supplier publishes its own pricing rule, and the rules differ in interval, fee and protection against spikes. The table below uses only what each company’s own site states, checked in November 2026.
| Feature | Octopus Agile (UK) | Tibber Smart Dynamic (Germany) | aWATTar Hourly (Austria) |
|---|---|---|---|
| Price interval | Half-hourly | Not stated on the tariff page | Hourly EPEX SPOT AT prices |
| Price publication | Updated daily, between 4pm and 8pm, usually nearer 4pm | Not stated on the tariff page | Not stated on the tariff page |
| Price rule | Tied to wholesale prices | Not stated on the tariff page | (EPEX SPOT AT price + 1.50 ct/kWh) plus 20% VAT |
| Fixed monthly fee | Not stated on the Agile page | Not stated for this tariff | 4.79 EUR net, 5.75 EUR gross |
| Price cap | 100p per kWh (Price Cap Protect) | Not stated | Not stated |
| Negative prices | Yes, can drop below zero (Plunge Pricing) | Not stated | Yes, the page shows a negative price example |
| Smart meter | SMETS2 or some SMETS1 | Required for Smart Dynamic | Check the supplier’s terms |
Sources: Octopus Agile page, Tibber tariff page and aWATTar Hourly page. Where a cell says “not stated”, the company’s own page does not publish that figure, so this guide does not fill it in.
Key Takeaway
The three tariffs are built differently. Agile is capped and half-hourly. aWATTar adds a flat 1.50 ct/kWh to the hourly market price. Tibber’s Smart Dynamic needs a smart meter. Compare the contract terms, not the headline name.
How aWATTar’s price formula works
aWATTar publishes a clear rule: the gross energy price equals the hourly EPEX SPOT AT price plus 1.50 ct/kWh, then 20% VAT. Its own example uses a spot price of 5.00 ct/kWh, which gives 7.80 ct/kWh gross. At a spot price of 0, the result is 1.80 ct/kWh. Network charges and levies are extra.
The chart applies that published formula to four spot prices. The 5 ct and 0 ct points are aWATTar’s own examples. The 10 ct and 20 ct points are our arithmetic on the same formula.
- Spot 0 ct/kWh1.8 ct
- Spot 5 ct/kWh7.8 ct
- Spot 10 ct/kWh13.8 ct
- Spot 20 ct/kWh25.8 ct
Source: aWATTar Hourly tariff page formula (spot + 1.50 ct, plus 20% VAT); 10 and 20 ct points calculated from it, checked November 2026.
What Does Battery Arbitrage Actually Earn?
Battery arbitrage is buying electricity when it is cheap, storing it, and using it when it is expensive. The result depends on the price spread you capture, the battery’s usable capacity, and how many days per year you complete a cycle.
A simple estimate is:
Annual value ≈ captured spread per kWh × usable kWh × cycles per year
Captured spread means the buy-sell gap after round-trip losses and fees. It is always smaller than the best-hour to worst-hour gap on a chart. Round-trip efficiency, the share of stored energy you get back, drives the loss side.
The table is a hypothetical example, not market data. It shows how sensitive the result is to the captured spread and the number of cycles, using a 10 kWh usable battery.
| Captured spread (net of losses) | 150 cycles per year | 250 cycles per year |
|---|---|---|
| 5 ct per kWh | 75 EUR | 125 EUR |
| 10 ct per kWh | 150 EUR | 250 EUR |
| 15 ct per kWh | 225 EUR | 375 EUR |
Replace the spread with a figure from your own meter history. The point is the shape: halve the spread and you halve the value.
Key Takeaway
Arbitrage value scales directly with captured spread and with cycles. A battery that cannot grid-charge on a schedule has a captured spread of zero, whatever the tariff says.
Why solar changes the calculation
When the battery charges from your own panels, the charging cost is the export income you give up, not the market price. The evening discharge then replaces peak-hour imports. Our post on battery arbitrage versus self-consumption works through how to value each source of benefit without counting the same kilowatt-hour twice.
Test the battery payback on your own tariff data
Run the same home through flat and dynamic tariff cases and compare long-term cash flow before the customer signs.
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What Happens When Octopus Agile Prices Go Negative?
When wholesale supply exceeds demand, prices can fall below zero, and Agile passes that through. Octopus’s Agile page says prices can drop below zero and that its Plunge Pricing lets customers get paid for the electricity they use during these slots. It also says customers receive alerts when this happens.
Negative slots are not a schedule you can count on. They follow wind, sun and demand. To benefit, you need something that can absorb energy at short notice: a battery with free capacity, an EV that is plugged in, or a hot water tank or heat pump.
Pro Tip
Set the battery to charge below a price threshold that you choose, not only at negative prices. Pick the threshold by looking at your last 12 months of half-hourly prices and how often each band occurred. Negative slots are rare. A low positive band is far more common.
How Risky Are Price Spikes?
A dynamic tariff passes spikes through as well as dips. Octopus states that Agile customers will never pay more than 100p per kWh, and that spikes up to that level can occur at any time. For Tibber Smart Dynamic and aWATTar Hourly, their tariff pages do not describe a hard price cap, so read the contract terms before you assume protection.
Two limits help on any dynamic tariff:
- Price-trigger automation. Switch off non-essential loads when the next price crosses a threshold you set.
- Battery reserve. Keep enough charge before known tight periods so the evening peak is covered by stored energy.
Also compare against the right alternative. In Great Britain, Ofgem sets its price cap level every three months, so the flat-tariff benchmark moves. Always run your comparison against the current cap or the tariff you could actually switch to today.
What Do You Need to Automate a Dynamic Tariff?
You need three things: interval prices, a controllable battery or load, and software that links them. Doing this by hand rarely works, because prices change every day.
- Home Assistant with Predbat. Predbat describes itself as home battery prediction and automatic charging for Home Assistant, supporting inverters such as Deye, Fox, GivEnergy, Huawei, Solis, Sunsynk and Tesla Powerwall. Its page does not list supported tariffs, so check its documentation for yours.
- evcc for EVs. evcc says it charges automatically in the cheapest hours on spot price tariffs and follows solar surplus. It lists Tibber and Octopus Energy among its integrations.
- Provider apps. Each supplier offers its own app. Check what it controls for your hardware before relying on it.
Can your inverter charge from the grid on a schedule?
Not every battery and inverter allows scheduled grid charging, and settings can differ by firmware. Read the inverter or battery manufacturer’s documentation for time-based or schedule-based grid charging before you quote any arbitrage value. Our guide to time-of-use battery scheduling shows how charge and discharge windows are set.
Pro Tip
Pull 12 months of half-hourly or hourly consumption from your smart meter. Price it on your current tariff and on the dynamic one, and compare the two totals. If the dynamic result is not clearly lower with realistic load shifting, do not switch.
Should You Switch? A Short Checklist
Work through these questions in order:
- Do you have a working smart meter that your chosen supplier can read?
- Do you have a battery, an EV, a heat pump or another load you can move?
- Can your inverter or charger accept scheduled grid charging?
- What do your export terms pay for solar you send to the grid? Octopus’s Agile page covers import pricing only, so check the export tariff separately.
- Has a backtest on your own data shown a clear gain over your current tariff?
If any answer is no, fix that first. For UK system design, see our battery solar system design guide. Installers can also run proposals through the generation and financial tool to compare flat and dynamic cases side by side.
What Is Changing in 2026 and After?
European day-ahead trading moved to 15-minute products on 1 October 2025, per EPEX SPOT market data. Customers whose meters and supplier contracts support 15-minute settlement can see finer price steps, while hourly contracts stay as they are. Check your supplier’s notice to see which applies to you.
Vehicle-to-home and vehicle-to-grid are also growing. Whether your car and charger support them depends on the manufacturer’s documentation, so verify the exact model. Our vehicle-to-grid design guide covers the design points.
Conclusion: Three Action Items
- Backtest your last 12 months of meter data on the dynamic tariff before you switch. Use the supplier’s published rule, such as aWATTar’s spot plus 1.50 ct plus VAT, to price each interval.
- Confirm in writing that your inverter supports scheduled grid charging, and that your smart meter works with the tariff.
- Set price-trigger rules for spikes before the first bill arrives.
Installers selling batteries on dynamic tariffs can show the flat versus dynamic comparison in a proposal. Book a demo to walk through a real project and see how a proposal presents the numbers.
Frequently Asked Questions
What is a dynamic electricity tariff for solar?
A dynamic electricity tariff prices each kilowatt-hour at a wholesale market rate that changes through the day. Octopus Agile updates every half hour, while aWATTar Hourly follows hourly EPEX SPOT prices. With solar and a battery you can charge when prices are low and use that energy in the evening peak.
Do I need a smart meter for Octopus Agile, Tibber or aWATTar?
Yes for Octopus Agile and for Tibber’s Smart Dynamic tariff. Octopus says it can connect to SMETS2 meters and some SMETS1 meters, and Tibber says Smart Dynamic is only available to households with a smart meter. Check the current terms of any supplier before you sign.
Can Octopus Agile prices go negative?
Yes. Octopus says Agile prices can fall below zero, and its Plunge Pricing feature lets customers get paid for the electricity they use during those slots. Negative slots depend on the wholesale market, so you cannot plan a fixed number per year.
What is the maximum price on Octopus Agile?
Octopus states that Agile is protected by Price Cap Protect, so you never pay more than 100p per kWh. That cap applies to Octopus Agile only. Check the published terms of Tibber or aWATTar for how they handle price spikes.
Is a dynamic tariff worth it without a battery?
Only if you can move real load into cheap hours. Without a battery, an EV, a heat pump or another flexible load, you mostly take the average wholesale price with no way to avoid the evening peak. Backtest your own meter data against your current tariff first.
How do I automate charging on a dynamic tariff?
Use software that reads day-ahead prices and schedules your battery or EV. Home Assistant with Predbat is a common UK choice for batteries, and evcc says it charges EVs automatically in the cheapest hours on spot price tariffs. First confirm your inverter allows scheduled grid charging.
Further Reading
Compare payback methods in the battery storage payback calculator guide.
Sources used: Octopus Agile, Tibber tariff page, aWATTar Hourly, Ofgem energy price cap, evcc, Predbat documentation and EPEX SPOT market data. All were checked in November 2026.
Where this fits
This article is part of SurgePV's Solar Business & Operations hub, which works through the topic from first principles to the decisions a project team actually has to make.
