Smart Tariff Integration with Solar Batteries

Author: Steve Fairless
Published: 27th June 2026 · Updated: 2nd September 2026

A smart tariff can make a solar battery more useful, but only when the battery is controlled around the property's real load, solar forecast, tariff windows and export value. Cheap-rate charging is not automatically a saving, and exporting at a high rate is not automatically the best use of stored energy. The battery has losses, finite power, usable-capacity limits and a cycle cost that all need to be considered.

At Sustainable Energy Engineering, we design tariff strategy as part of the energy system rather than as an app setting added after commissioning. We want to know what the customer pays to import, what they receive to export, when those rates apply, how much solar is expected tomorrow and what the home is likely to need before the next charging opportunity.

Updated: 2nd September 2026.

What Is a Smart Time-of-Use Tariff?

Energy Saving Trust describes smart time-of-use tariffs as tariffs where the price changes according to when electricity is used. The aim is to encourage demand away from peak periods, when the grid is under greater pressure, and toward times when electricity is cheaper or more abundant.

Some tariffs use fixed cheap and expensive windows; others can change more frequently. The exact product terms are commercial and can change, so our energy-tariff guidance focuses on the underlying strategy rather than assuming one supplier or rate will remain best.

The Battery Gives You Control Over Time

Without storage, electricity has to be used when it is generated or imported when it is needed. A battery adds timing flexibility. It can capture surplus solar, charge from the grid in a low-price window and discharge later to avoid a higher import price.

That flexibility is the core value. The battery is not creating energy; it is moving energy through time. Every time it does that, some energy is lost in conversion and storage. A successful tariff strategy therefore needs enough price difference or avoided-import value to justify the movement.

Self-Consumption and Tariff Arbitrage Are Different Strategies

Solar self-consumption stores energy that the PV array would otherwise export and uses it later in the property. Tariff arbitrage deliberately buys electricity at a low rate, stores it and uses or exports it later when the value is higher.

A battery can do both, but the control priorities can conflict. If it fills to 100% from the grid at 5am and the sun produces a large surplus at noon, there may be nowhere to put that solar. If it stays empty waiting for solar and a cloudy day follows, the home may miss a cheap charging opportunity.

We therefore use seasonal settings, forecasts or simple conservative reserve rules depending on the equipment and customer. Complexity should earn its place.

A Simple Price-Spread Test

Suppose a battery charges 10 kWh from the grid at 10p/kWh. The energy cost is £1.00. If the complete charge-and-discharge pathway returns 90% of that energy to the property, around 9 kWh is available. Avoiding a later 30p/kWh import would then be worth £2.70, creating a gross spread of £1.70 before considering battery wear, standby use, tariff rules or other costs.

The same trade is much less attractive if the later rate is 14p/kWh. This is why we do not describe grid charging as free money. The spread has to be large enough, frequent enough and technically achievable through the battery's power and capacity limits.

Battery Power Can Be More Important Than Capacity

A tariff may have a two- or three-hour cheap window. A battery with plenty of kWh capacity but limited charge power may not be able to fill within that window. The same applies on discharge: if the home draws 7 kW during an expensive period and the battery can supply 3 kW, the grid will still provide the balance.

When we design solar battery storage, we therefore model both kWh and kW. A tariff strategy is only credible if the equipment can physically move the required energy in the time available.

What Happens on a Sunny Day?

Solar changes the economics because daytime charging can have a different opportunity cost from grid charging. If surplus solar would otherwise be exported, storing it means giving up the export payment in exchange for the later value of using it. If the later avoided import is much higher than the export rate, storage may create more value. If export is unusually valuable, sending the solar directly to the grid can sometimes be competitive.

Ofgem's Smart Export Guarantee framework requires participating suppliers to pay eligible generators for measured export, but suppliers set their own rates and terms. We do not assume the export value is fixed.

What Happens in Winter?

Winter often reverses the priorities. Solar surplus is lower, while household electricity demand may be higher. A battery that was mainly solar-charged in summer may become a tariff-shifting asset in winter. This is where time-of-use charging can keep the battery useful across the whole year.

Energy Saving Trust's battery guidance specifically notes that storage can be used with smart time-of-use tariffs to change when electricity is bought. That flexibility is valuable, but a year-round model still needs to allow for conversion losses and the battery's expected life.

Exporting From a Battery

Some tariffs allow customers to export stored energy when the export price is attractive. Whether this is worthwhile depends on the tariff terms, the source of the stored electricity, round-trip losses, battery warranty conditions and whether the home will then need to buy expensive electricity back later.

Ofgem also publishes guidance on co-locating storage with SEG and legacy generation arrangements. Where a system sits alongside older FIT metering, we review the scheme position instead of assuming modern tariff behaviour can be applied without consequence.

Backup Reserve Changes the Usable Capacity

If a customer wants 20% of the battery held back for outages, only the remaining portion is available for daily tariff shifting. That reserve can be commercially worthwhile because resilience has value, but it must be included honestly in the model.

The same applies to manufacturer minimum state-of-charge limits. We quote usable energy for the intended strategy, not just the largest number on the product label.

Automation Is Useful, but We Still Need Sensible Guardrails

Modern systems can use schedules, forecasts, dynamic prices and automatic modes. We like automation when it is transparent and controllable. We do not want a system repeatedly cycling for tiny price differences, filling before a sunny day or exporting reserve energy that the customer expected to keep for backup.

Our Recommendation: Design the Tariff and Battery Together

A battery can be a powerful energy-management tool, but the best settings are not universal. We want the storage to capture valuable solar, exploit genuinely useful cheap-rate periods, avoid expensive imports and still meet the owner's resilience requirements.

For existing systems, battery retrofitting can be designed around tariff control from the outset rather than added as an afterthought.