Tariff shifting: could extra battery storage help you buy more electricity for less?

Your home needs electricity when life happens: breakfast before work, heating on a cold afternoon, dinner in the oven and the lights on after dark. Those hours will not always line up with the cheapest electricity prices.

Tariff shifting gives you a way to bridge that gap. With a suitable time-of-use tariff, your battery can charge when electricity costs less and supply your home later, when buying from the grid would be more expensive.

If your existing battery already does this, additional capacity could help you take the benefit further. It gives you more room to store lower-cost electricity and use it across a greater share of your day.

That makes battery extensions relevant throughout the year, including the colder months when your solar panels have less daylight to work with.

What is tariff shifting?

Tariff shifting means moving electricity purchases into cheaper periods, then using that stored energy later. A time-of-use tariff charges different prices at different times, creating an opportunity to plan when you buy power.

You might already move a dishwasher or washing-machine cycle into a cheaper window. A battery extends that principle to electricity you want to use at another time. You can prepare dinner at your usual hour while the battery supplies energy bought earlier.

The Energy Saving Trust's guide to smart time-of-use tariffs explains how shifting consumption can help households make use of different electricity prices. Storage provides another way to access that flexibility, without having to move every household activity into the charging window.

Your home still uses electricity and remains connected to the grid. The benefit comes from changing when some of that electricity is purchased and the rate you pay for it.

Why extra capacity can make a difference

A cheaper tariff window gives you an opportunity to buy lower-cost energy. Battery capacity determines how much you can keep for later.

Imagine your battery charges during a cheaper overnight period and then supplies the morning and part of the afternoon. By early evening, it reaches its minimum charge. The household still needs electricity, so imports resume at the rate applying at that time.

An extension could allow the system to carry more of that earlier, lower-cost electricity into the evening. The same principle applies to tariffs with several cheaper periods: extra capacity can help bridge the gaps between charging opportunities.

The useful question is how much additional higher-priced consumption the extension could cover. That is the extra benefit you are considering purchasing, on top of what your existing battery already achieves.

Our home battery storage service covers systems that store solar electricity, cheaper grid electricity or a combination of both.

A worked example: shifting another 6 kWh into cheaper hours

Consider a household that regularly needs another 6 kWh after its existing battery has reached its reserve. For this illustration, assume that those imports would cost 30p/kWh and that the household can charge additional storage at 8p/kWh.

We will also assume 90% round-trip efficiency. This allows for the energy lost across charging and discharging, so the calculation includes the extra electricity needed to supply those 6 kWh later.

How the additional electricity is supplied	Calculation	Energy cost
Buy 6 kWh when needed at the higher rate	6 × 30p	£1.80
Charge enough off-peak energy to deliver 6 kWh later	6 ÷ 0.90 × 8p	About £0.53
Gross energy-cost saving for that day	£1.80 minus about £0.53	About £1.27

If the extension made that additional contribution on 300 days, the illustrative annual gross energy-cost saving would be approximately £380.

The example uses assumed rates, efficiency and usage. It is not a current tariff quotation, a Sigenergy efficiency claim or a forecast for your home. The saving is before the cost of buying and installing the extension, finance, degradation and any additional ongoing costs. Standing charges remain payable.

What the example demonstrates is the value of regularly shifting a useful amount of electricity. Extra capacity can work alongside a favourable tariff to reduce the cost of energy your household would otherwise buy later.

How to read the price difference

The gap between the charging rate and the later import rate is often called the tariff spread. Conversion losses reduce the benefit slightly because you buy more charging energy than the battery subsequently delivers to your home.

For example, at an assumed 90% round-trip efficiency, electricity bought at 8p/kWh costs approximately 8.9p for each kWh later delivered from storage. If it replaces a 30p import, that is a gross energy-cost benefit of roughly 21.1p per kWh delivered.

This gives you a useful way to assess your own tariff: take the import price you would avoid and subtract the charging price divided by the efficiency assumption. Then consider how many additional kWh the extension would actually supply at that benefit.

You do not need to do the forecasting alone. Your tariff details and consumption data give YEYW the starting information to assess the opportunity for your system.

A useful winter role for your battery

During brighter months, solar generation may provide much of the energy you store. In winter, shorter days can leave more space in the battery while the household needs more electricity for lighting, indoor activities and, in some homes, heating.

Charging from a suitable cheaper tariff period gives that capacity another job. The energy comes from the grid and can be used later, when the household would otherwise pay a higher rate.

An extension can therefore support a different pattern across the seasons: storing surplus solar when it is available and holding cheaper grid electricity when that suits your tariff and demand.

The charging schedule needs to reflect the day ahead. If a bright day is forecast, leaving room for solar can be useful. If solar generation is expected to be low, a planned grid charge may cover more of the household's later needs. This is where control settings become part of the value of the installation.

Which type of tariff could support this?

Tariffs with predictable cheaper periods

Some tariffs have defined cheaper windows. These can make it straightforward to plan charging and estimate how much household demand the stored electricity could cover afterwards.

Compare the whole tariff, including the other unit rates, standing charge, any export arrangement and eligibility requirements. Some specialist products require an EV, heat pump or compatible equipment. A battery alone does not qualify a household for every offer.

Tariffs with changing prices

Dynamic tariffs vary with market conditions. They can create opportunities to charge at lower prices, with the timing and size of that opportunity changing from day to day.

Suitable controls can help schedule charging around those prices. The potential benefit depends on the actual rates available and the home's demand, rather than a guaranteed cheap period every day.

Octopus Energy's smart tariff overview illustrates the different approaches available for households with electric vehicles, heat pumps, solar and batteries. Check live supplier terms for your postcode and equipment before choosing a tariff. The right arrangement should work for the whole household bill, including the electricity used outside the battery's coverage.

Make the charging window count

Extra capacity needs enough time and available charging power to fill. The installer should consider the total expanded system, because the existing modules also need their share of the charging window.

As a simple illustration, putting 12 kWh into storage over four hours requires an average of 3 kW into the battery. Electricity drawn from the supply will be higher after charging losses, and other household loads may compete for available power. The actual limits depend on the installed equipment and supply.

A tariff with several cheaper windows creates a different pattern from one overnight charge. You may be able to top up between periods of demand, so the extension can be assessed around those gaps. This is one reason to share your tariff schedule before deciding how much extra capacity to add.

Let the controls support your routine

A well-configured system should help the battery follow the chosen energy strategy. The mySigen app provides monitoring and energy management features, with supported scheduling functions depending on the installation and tariff setup.

For tariff shifting, the practical priorities are that the system recognises the relevant charging periods, retains the agreed reserve and supplies household demand at the intended times. Monitoring then helps show how much electricity is still being bought outside the cheaper windows.

If you want ongoing help interpreting that information, YEYW's solar and battery support service includes app assistance, remote diagnostics where access is provided and performance reporting.

Could your existing battery storage system store more lower-cost electricity?

If your battery regularly reaches its reserve before the next cheaper charging window, there may be an opportunity for additional storage to cover more of the gap.

Send us your electricity tariff, postcode and a recent monitoring screenshot. We can review the higher-priced electricity your home still buys, check which expansion options your system supports and explain the appropriate next step.

Eligible Sigenergy battery extensions start from £2,800 installed. With current availability, suitable upgrades could be installed in less than a week, subject to compatibility, stock and installation availability.

By next week, your home could already be carrying more lower-cost electricity into the hours you need it.