Your solar panels might generate plenty of electricity in the middle of a bright afternoon. The thing is, for most of us, that’s when we’re out at work, doing the shopping or taking the kids to the park.
In fact, for most of us, it’s the evening when we use the most electricity. You get home, cook dinner, put the washing machine on, switch on the telly, charge your phone and perhaps even plug in an electric car or run the heating or air conditioning through a heat pump.
But by now, your solar panels are producing very little electricity, if anything.
A solar battery storage system is all about bridging that gap, ‘storing’ your solar energy so you keep some, or all, of it for later.
This doesn’t mean you get unlimited free electricity, and it doesn’t make your home completely independent from the grid. However, it does give you more control over your electricity use and helps you buy less electricity at higher-priced times.
And when combined with smart tariffs, smart batteries can even be used to make money. More on that below.
At Electrical Innovations, we help homeowners across the Midlands and beyond install full solar systems, including batteries. Learn more about how solar battery storage works on this page.
Solar battery storage in simple terms
Here’s how a standard battery storage system works. If your panels are producing more electricity than you need at any given moment during the day, the excess charges your battery, provided it’s set up to do that. Later, when your panels are producing less electricity than your home needs, the battery can discharge to help run your appliances.
The system’s inverter and monitoring equipment manage these decisions automatically. You can usually see what’s happening through an app, including how much electricity your panels are generating, how much your battery is storing and how much electricity your home is importing or exporting.
What happens over a normal day?
The easiest way to understand battery storage is to think about how your electricity use changes from morning to night:
Morning
Your solar panels begin generating electricity as daylight increases. Depending on the weather and how much power your home is using (i.e., how many times you boil the kettle and whether you need the heating), your panels may cover some or all of your morning demand.
If your household needs more electricity than the panels are producing, the difference comes from the battery or the grid.
Midday
This is often when solar panels generate the most electricity, especially on clear days.
If you’re out of the house and only have background demand from appliances like your fridge and freezer, internet equipment and devices on standby, your solar panels will likely produce more electricity than you’ll use. This might be a good time to charge your battery.
Evening
In a typical home, the evening is when battery storage becomes most useful. Solar generation falls as the day goes on, just as you begin using more electricity.
A charged battery can supply some or even all the electricity you need for cooking, lighting, entertainment, laundry and other evening use.
Without a battery, you’d usually import more of that electricity from the grid, and if you’re on a time-of-use tariff, that electricity is more expensive because of the time of day.
Overnight
Once your panels stop generating, your home can continue using stored electricity until the battery reaches its minimum reserve level or runs low.
After that, your home draws electricity from the grid as normal.
On shorter winter days, or during prolonged cloudy weather, there may be less surplus solar electricity available to store. A battery can still provide some help, but don’t expect it to run your entire home. It’s always best to look at your solar system’s overall annual performance.
What actually happens inside a solar battery system?
If you’re interested in a few more technical details, here they are.
Solar panels produce variable DC electricity, while household circuits use AC electricity. The inverter converts solar DC into AC and sends it to your consumer unit (fuse box). At the same time, a meter or CT clamp at the grid connection measures, moment by moment, how much electricity your home is using and whether power is being imported or exported.
The energy-management controls (usually spread across the entire system, not just the battery) then apply your chosen priorities. Normally, the home comes first. If your panels produce 3kW and your appliances need 2kW, the remaining 1kW can charge the battery. In an AC-coupled system, a battery inverter converts that spare AC electricity back into DC. In a DC-coupled system, solar DC charges the battery directly.
When solar output falls below household demand, the battery releases DC power and the inverter converts it back into AC. It does this only up to its maximum output and minimum reserve, so the grid covers any remaining demand.
If there’s still spare electricity after your home’s needs have been met and the battery settings allow it, it’s exported. By this point, the electricity is AC. It flows through your fuse box, past the import/export meter, and out through your main supply cable to the local grid. The inverter monitors this flow and limits export where required by your DNO agreement.
Can a solar battery charge from the grid?
Yes, most battery systems can charge from the grid as well as from solar panels.
This can be useful if you’re on a time-of-use electricity tariff, where electricity costs less during certain hours, often overnight. Your battery may be programmed to charge when electricity is cheaper and discharge later when electricity costs more.
This means a battery isn’t only useful during sunny weather. In fact, it can still be valuable even when your solar panels aren’t working. With the right setup and planning, you can minimise the cost of your imports (from the grid) without using less electricity.
Some smart tariffs take this a step further. Chat with an expert (such as Electrical Innovations) about how to set up compatible batteries to charge, discharge and export electricity at the most valuable times of day. In some cases, as well as minimising your bills, you could even make a little profit.
Can a solar battery earn money with a smart tariff?
Not always, and it’s not guaranteed, but in some cases, yes. We’ve installed systems that are capable of making, and do make, a small overall net income. Here’s how it works.
Some time-of-use tariffs (such as Octopus Flux) offer lower electricity prices overnight, when demand is lower, and higher import and export rates during the early evening peak. With a compatible battery, you may be able to charge it at the lower overnight rate, use your solar generation during the day, then either use or export the stored electricity, depending on which is more valuable.
This is sometimes called energy arbitrage. You’re buying electricity when it’s cheaper, then using or exporting it when it has greater value.
Your DNO export limit restricts how much electricity you can send to the grid at any one time. Even if your battery or solar panels could export more than your approved limit, the system will reduce output to stay within it. This does limit how much money you can make. For most households with a straightforward G98 connection, the standard export capacity is 3.68kW.
Battery capacity and battery power are not the same thing
If you’re thinking about getting a solar battery storage system, pay close attention to two ratings, capacity and power.
Capacity, measured in kilowatt-hours (kWh), tells you how much electricity the battery can store. You can think of this as the size of the tank.
Power, measured in kilowatts (kW), tells you how quickly the battery can supply electricity at one time. You can think of this as the flow rate of electricity filling or leaving that tank.
A large-capacity battery may store plenty of electricity, but its output still needs to be high enough for the appliances you want it to support.
For example, a battery may be perfectly capable of running lights, broadband equipment, televisions, fridge-freezers and other everyday appliances. These are relatively low-demand units. However, high-demand appliances such as electric showers, ovens, immersion heaters, heat pumps, air conditioning systems and EV chargers can draw a great deal of power.
That’s partly why it’s usually unrealistic to expect to become completely independent from the grid. Your installer should consider how much electricity you use, when you use it, how much solar electricity you’re likely to generate, and whether your demand may change in the future. That helps them recommend the most cost-effective, long-term solar battery storage system.
Will a solar battery keep my home running during a power cut?
To use solar and battery power during a power cut, your system needs to be specifically designed for backup operation. This may include additional control equipment and a carefully planned set of circuits that can continue operating while the grid is down.
It’s best to only back up essential items, such as lights, refrigeration, Wi-Fi, certain sockets, heating controls or a home office. Backing up every circuit in the property will require a larger, more expensive system.
If your system isn’t set up for backup operation, it will shut down during an outage for safety reasons, even if your battery is charged and the sun is shining.
Before accepting a quote, make sure you’re clear on the functions and limitations of your battery.
What happens when the battery is full?
Once your battery reaches its maximum charge level, it can’t store any more electricity.
At that point, your solar system will usually do one of three things with further surplus generation:
- Export it to the grid.
- Divert it to another compatible use, such as hot water heating.
- Use it to charge an electric vehicle, where suitable equipment and controls are in place.
If you export electricity, you may be able to receive payment through a Smart Export Guarantee tariff. Export rates vary between suppliers and tariffs.
In many cases, using your solar electricity yourself is worth more than exporting it. A battery gives you more opportunities to do that, particularly in the evening.
Can I add a battery to existing solar panels?
In many cases, yes. You don’t always need to install a battery at the same time as your solar panels.
If you already have a solar PV system, it may be possible to add battery storage later.
However, your installer will need to assess your existing inverter, consumer unit, generation capacity, monitoring equipment and grid connection. Some systems can be upgraded or rewired more simply than others, and some may need additional equipment to work safely and effectively.
Adding a battery later can be a sensible option if you want to spread the cost of your solar investment or have realised that you regularly export electricity during the day and import it again in the evening.
Solar battery storage systems we install
At Electrical Innovations, we install solar batteries to help you make better use of the electricity your panels generate. We can advise on a range of suitable systems, but most commonly recommend Sigenergy SigenStor and Tesla Powerwall 3.
Sigenergy SigenStor
Sigenergy SigenStor uses modular lithium-iron-phosphate battery units. The BAT 10.0 module provides 9.04kWh total capacity, 8.76kWh usable capacity, and 4.6kW maximum continuous charge or discharge power. Up to six modules can connect to one controller. The platform combines battery storage, inverter control, energy management, and optional DC EV charging.
Tesla Powerwall 3
Tesla Powerwall 3 has 13.5kWh nominal battery capacity, an integrated solar inverter, three solar inputs, and a system controller. It can provide up to 11.04kW of on-grid or backup power, depending on local conditions and configuration. Expansion units add 13.5kWh each. You need a Tesla Backup Gateway 2 to use the Powerwall 3 for backup during power cuts.
Make more of the electricity your solar panels generate
Solar panels work best when you can use the electricity they generate. A battery gives you more control over that electricity, helping you keep more of it for the times when your household actually needs it.
At Electrical Innovations, we pride ourselves on helping homeowners like you install the most cost-effective and useful battery storage system for your home. We’ll assess your solar generation, household electricity use, future plans, and available space to help you choose a battery system that makes practical sense for your lifestyle.
Get in touch with our Derby solar team to discuss solar battery storage, new solar installations, or adding a battery to an existing system.
