Solar & Battery Energy Guide

Introduction

Once your home has got solar panels, the nature of your household’s energy use will change. You’re now an energy generator as well as a consumer! This means that in addition to a normal energy bill that allows you to consume electricity, you’ll also want to get set up with an agreement that lets you sell any solar energy that you don’t consume yourself.

If you’re extra smart and then decide to add a battery to go with your solar panels, your behaviour as a consumer of energy becomes more complex again. You’re now faced with decisions such as whether you want to charge up the battery exclusively from solar panels, or whether you want to sell your stored battery energy back to the grid at a nice profit. At first glance, navigating your way around these questions can seem devilishly tricky. However, at its core are some very simple principles that everybody can understand.

At Renewables Marketplace, our number one goal is to help you find your cheapest energy bill in the shortest time possible. And if you’re an energy nerd like us, you’re also in the right place! Our educational content starts with some easy principles that everyone can understand and builds towards the more complex topics for those of you want to do the deep dive. You can hop off whenever you’ve learned enough.

What Are Import & Export Tariffs?

If you’re used to a standard energy bill, you might not have come across the terms “import” and “export” before. They’re straightforward once you know what they mean, and they’re fundamental to understanding how solar homes are billed for energy.

What is an import tariff?

An import tariff is the rate you pay for electricity you draw from the grid. This is the same as a normal energy tariff — the rate on your bill that everyone pays whether they have solar or not. When the sun goes down and your solar panels stop generating, your home will pull electricity from the grid to keep the lights on, and your import tariff determines the cost of that electricity.

What is an export tariff?

An export tariff is the rate you earn for electricity you send back to the grid. This is where things get interesting for solar owners. On a sunny day, your solar panels might generate more electricity than your home needs at that moment. Rather than wasting that surplus, you can sell it back to the grid and earn money for every unit you export.

Do I need separate suppliers for import and export?

Not necessarily. Some suppliers offer bundled deals that include both import and export on a single plan. Others require you to sign up for import and export separately, and you can even have your import with one supplier and your export with another. Our comparison tool tests every valid import and export combination to find the cheapest overall pairing for your setup.

The Smart Export Guarantee (SEG)

In the UK, all electricity suppliers with more than 150,000 customers are required by law to offer a Smart Export Guarantee tariff. This means they must pay you for the electricity you export to the grid, provided you have an MCS-certified installation and a smart meter. Export rates vary between suppliers, so it pays to shop around — some are significantly more generous than others.

How Is Electricity Priced?

To understand why different tariffs exist and why prices vary, it helps to know the difference between the wholesale electricity market and the retail price you pay at home.

What is the wholesale electricity price?

Wholesale electricity is bought and sold on trading markets, much like stocks or commodities. Power generators — from gas plants to wind farms — sell electricity to suppliers at a wholesale price. This price fluctuates throughout the day based on supply and demand. When demand is high and supply is tight (such as a cold winter evening), wholesale prices spike. When there’s plenty of generation and low demand (such as a windy night), prices can drop very low or even turn negative.

What is the retail price?

The retail price is what you actually pay on your energy bill. Your supplier buys electricity wholesale, adds their operating costs, network charges, environmental levies, and a margin, then charges you the retail rate. This is why your energy bill is always higher than the raw wholesale price — it reflects the full cost of getting electricity to your home.

The Ofgem Price Cap

In the UK, Ofgem sets a quarterly price cap that limits the maximum unit rate and standing charge that suppliers can charge on their default variable tariffs. The cap adjusts every quarter based on wholesale costs, network charges, and other factors. Fixed tariffs sit outside the price cap — suppliers can set whatever rate they like on a fixed deal, which is why some fixed tariffs are priced above the cap and others below it. Understanding the price cap helps you judge whether a fixed deal is good value compared to staying on a variable rate.

Single Rate or Time of Use?

Not all tariffs charge you the same rate throughout the day. Understanding the difference between flat rate and time of use pricing is one of the most important concepts for getting the best deal on your solar and battery setup.

What is a flat rate tariff?

A flat rate tariff charges you the same price per unit of electricity no matter when you use it. Whether you run your washing machine at 3am or 6pm, you pay the same rate. This is the simplest tariff structure and the one most people in the UK are on. It’s predictable and easy to understand, but it doesn’t reward you for shifting your energy usage to cheaper periods.

What is a time of use (ToU) tariff?

A time of use tariff charges different rates depending on when you use electricity. Typically, you’ll pay more during “peak” hours (usually late afternoon and early evening when demand is highest) and less during “off-peak” hours (overnight or during the middle of the day). Some tariffs have two bands (peak and off-peak), while others have three or more.

Dynamic tariffs

Dynamic tariffs take the time of use concept further. Instead of fixed peak and off-peak bands, the rate changes every 30 minutes based on actual wholesale market prices. Octopus Agile is the best-known example in the UK. The rate for each half-hour slot is published the evening before, so you can plan your energy use in advance. Prices tend to be cheapest overnight and in the early afternoon (when solar generation pushes wholesale prices down) and most expensive between 4pm and 7pm.

Dynamic tariffs offer the greatest potential savings for solar and battery households, but they require a bit more engagement. If you have a smart battery system that can be programmed to charge and discharge at the right times, a dynamic tariff can be extremely cost-effective. Our comparison tool models every half-hour of the day to calculate exactly how much you’d save.

Should You Fix or Stay Variable?

Beyond how your rate is structured (flat or time of use), you also need to decide whether you want a fixed or variable contract. This is about price certainty versus flexibility.

What is a variable contract?

On a variable contract, your unit rate can change over time. Most variable tariffs track the Ofgem price cap, which adjusts every quarter. When wholesale energy costs fall, the cap drops and your bill should follow. When costs rise, so does the cap and your rate. Variable tariffs give you no price certainty, but they do mean you automatically benefit when prices fall — and you’re never locked in.

What is a fixed contract?

A fixed contract locks in your unit rate for a set period, typically 12 months. No matter what happens to wholesale prices or the Ofgem cap during that time, your rate stays the same. This gives you certainty and protection against price rises. However, if prices fall significantly, you’ll be stuck paying the higher rate unless you pay an exit fee to leave early.

How does this apply to export tariffs?

Export tariffs work the same way. A fixed export rate guarantees how much you’ll earn per unit for the contract period. A variable export rate can go up or down. Since export rates are generally much lower than import rates, the stakes are smaller — but it’s still worth paying attention, especially if you export a lot of solar electricity.

How Should You Use Your Battery?

If you have a home battery alongside your solar panels, the way you choose to charge and discharge it has a big impact on your overall energy costs. There isn’t a single “best” strategy — it depends on your tariff, your solar generation, and your household’s consumption pattern.

Strategy 1: Solar self-consumption

This is the simplest approach. Your battery charges from excess solar generation during the day and discharges in the evening when the sun goes down. You’re maximising the use of your own free solar electricity and minimising what you buy from the grid. This strategy works well on any tariff type and doesn’t require a smart battery or time of use rates.

Strategy 2: Overnight grid charging

On a time of use tariff with cheap overnight rates, you can charge your battery from the grid during the off-peak window (typically midnight to 5am or similar). Your battery starts each day full, even in winter when solar generation is low. You then use the stored cheap electricity during peak hours when import rates are highest. This strategy works best on tariffs with a big difference between peak and off-peak rates.

Strategy 3: Peak export

If your export tariff pays well during peak hours, you can use your battery to maximise what you sell back to the grid. You charge the battery from solar during the day and then export the stored energy during the evening peak (typically 4pm to 7pm) when export rates on some tariffs are at their highest. This is an aggressive strategy that works best on dynamic or time-banded export tariffs.

Strategy 4: Combined optimisation

The most advanced approach combines elements of the above. You might charge from cheap overnight rates, top up from solar during the day, use stored energy during the peak period, and export any remaining surplus at the best available rate. This requires a smart battery with automated scheduling and works best on dynamic tariffs where the price varies throughout the day.

What Is the Best Energy Deal for My Battery System?

This is the question we hear more than any other. If you’ve invested in solar panels and a home battery, you want to make sure you’re on the tariff that squeezes maximum value out of your setup. The short answer is: it depends on your specific situation. The long answer is below.

Why battery owners need a different kind of comparison

Standard energy comparison sites compare tariffs based on a simple annual consumption figure. That works fine for most households, but it completely misses the picture if you have solar panels and a battery.

When you own a battery, your energy costs depend on when you use electricity, not just how much. A tariff with cheap overnight rates lets you charge your battery for a fraction of the daytime price. A tariff with premium peak export rates lets you sell stored energy back to the grid at a profit. The cheapest flat rate tariff for a normal home could easily be the most expensive option for a battery home.

That’s why we built Renewables Marketplace. Our comparison tool models your solar generation, battery capacity, and consumption pattern hour by hour to find the actual cheapest combination of import and export tariffs for your specific setup.

What makes a good battery tariff?

The best energy deal for a battery system typically has three qualities:

Cheap overnight import rates. Time of use tariffs offer reduced rates during off-peak hours, typically between midnight and 5am. This is when you charge your battery from the grid at the lowest possible cost. Tariffs like Octopus Go and Intelligent Octopus are specifically designed for this pattern, offering rates as low as 7p/kWh overnight compared to 24p+ during the day.

Premium peak export rates. Some tariffs pay more for electricity you export during peak demand hours (usually 4pm–7pm). If your battery is fully charged by late afternoon, you can sell stored energy at the highest available rate. Octopus Flux, for example, pays a higher export rate during peak hours than at other times.

The right battery strategy. How you program your battery matters as much as which tariff you’re on. There are four main strategies: solar self-consumption, overnight grid charging, peak export, and combined optimisation. The best strategy depends on your tariff structure, battery size, and solar generation. Our tool models all four strategies for every tariff combination and tells you which one saves you the most.

Which tariffs work best with batteries?

Based on our modelling across thousands of configurations, these tariff types consistently perform well for battery owners:

Time of use tariffs. Tariffs with distinct cheap and expensive periods are ideal for batteries. The bigger the gap between off-peak and peak rates, the more your battery can save you. Examples include Octopus Go, Intelligent Octopus, and Octopus Cosy.

Dynamic tariffs. Octopus Agile changes its rate every 30 minutes based on wholesale prices. Prices are often very cheap (or even negative) during low-demand periods and high during the evening peak. With a smart battery, you can automatically buy cheap and sell dear. This offers the highest potential savings but requires more active management.

Bundled import and export deals. Some suppliers offer paired import and export tariffs designed to work together. Octopus Flux is the most well-known, combining time of use import rates with premium peak export rates. Bundled deals simplify billing and are often optimised for battery homes.

Frequently asked questions

What is the best energy deal for my battery system?
The best deal depends on your battery size, solar panel output, location, and how much electricity you use. Time of use tariffs with cheap overnight rates and peak export windows tend to save the most. Use our free comparison tool to find the cheapest combination for your specific setup.

Which tariff is best for solar panels and a battery?
For most solar and battery homes, time of use tariffs like Octopus Flux, Octopus Go, or Intelligent Octopus offer the best value. These have cheap overnight rates for charging and, in some cases, premium export rates during peak hours. The best choice depends on your specific setup — battery size, solar generation, and consumption pattern all matter.

How much can I save with a battery on a time of use tariff?
A typical UK home with solar panels and a 5–10 kWh battery can save between £200 and £600 per year by switching to the right tariff and battery strategy. Savings depend on your solar generation, battery capacity, and how much electricity you use during peak hours.

Should I charge my battery from the grid or from solar?
Both strategies have their place. Charging from solar is free but limited by weather and season. Charging from the grid overnight on a cheap off-peak rate ensures your battery starts each day full, even in winter. Many battery owners combine both for the lowest annual cost.

Do I need a separate export tariff for my battery?
Yes. To earn money from electricity your battery exports to the grid, you need an export tariff. Some suppliers bundle import and export together, while others require separate sign-ups. The export rate varies significantly between suppliers, so comparing your options can make a real difference to your annual earnings.