A Simple Guide to Generating and Storing Electricity at Home

Solar panels allow you to generate electricity from sunlight.

However, the electricity they produce does not always arrive when you need it most.

You might generate plenty during the middle of the day, for example. Yet your highest electricity use could be in the evening.

This is where battery storage can help.

In simple terms:

Solar PV generates electricity.

A battery stores electricity for later.

Let’s follow the journey and see how they work together.

What Does Solar PV Mean?

PV stands for photovoltaic.

Solar photovoltaic panels contain cells that convert energy from sunlight into electricity.

Therefore:

Sunlight → Solar cells → Electricity

This is different from solar thermal.

Solar PV generates electricity, while solar thermal uses energy from the sun to help heat water.

We will look at solar thermal later in this section.

How Do Solar Panels Produce Electricity?

When sunlight reaches a solar cell, energy from the light causes electrical activity within the material.

This is known as the photovoltaic effect.

The result is an electrical current.

However, the electricity produced by solar panels is direct current, known as DC.

Your home normally uses alternating current, or AC.

Therefore, the electricity needs to be converted.

What Does an Inverter Do?

The inverter converts the DC electricity from your solar panels into AC electricity that your home can use.

So, the journey becomes:

Sunlight → Solar panels → DC → Inverter → AC → Home

Your appliances can then use this electricity.

Many modern inverters also provide monitoring through a screen, website or phone app.

As a result, you may be able to see how much electricity your panels are producing throughout the day.

What Happens to the Electricity?

Imagine your solar panels are producing electricity while your washing machine is running.

Some of that solar electricity can be used directly by your home.

However, your panels may sometimes generate more than you need.

The surplus can potentially be:

• Exported to the electricity grid
• Stored in a battery
• Used by another suitable appliance or system

At other times, your panels may not produce enough electricity for the home.

You then need electricity from the grid or, where available, a battery.

This means electricity can move in several directions depending on what is happening.

Understanding kW, kWh and kWp

Three terms appear regularly when discussing solar.

Fortunately, the difference is quite simple.

kW — Power

Kilowatts tell us how much power is being produced or used at a particular moment.

For example, a kettle might use around:

3 kW

kWh — Energy

Kilowatt-hours tell us how much energy is used or generated over time.

If a 3 kW appliance ran continuously for one hour:

3 kW × 1 hour = 3 kWh

Therefore:

Power × Time = Energy

Your electricity bill normally measures electricity use in kWh.

kWp — Solar Panel Rating

Solar PV systems are commonly described in kilowatt-peak, or kWp.

For example:

4 kWp solar PV system

This is the system’s rated peak power under standard test conditions.

However, a 4 kWp system does not continuously produce 4 kW.

Actual output changes constantly.

Why Does Solar Generation Change?

Solar panels depend on the amount of solar energy reaching them.

Therefore, generation can be affected by:

• Time of day
• Season
• Weather
• Roof direction
• Roof angle
• Shading

Panels can still generate electricity on cloudy days.

However, output will usually be lower than under stronger sunlight.

At night, solar generation stops.

This creates an important challenge.

The time you generate electricity may not be the time you need it.

Why Timing Matters

Imagine your panels are producing plenty of electricity around lunchtime.

However, nobody is home.

Later, everyone returns.

You cook dinner, switch on lights and use appliances.

By then, solar generation may have fallen considerably.

Without a battery, surplus daytime electricity may be exported to the grid.

Later, you may import electricity again when you need it.

A battery can change this pattern.

How Does a Home Battery Work?

A battery stores electrical energy so it can be used later.

For example:

During the day

Solar panels → Home → Battery

Then, later:

In the evening

Battery → Home

This can allow you to use more of the electricity your solar panels generate.

However, batteries can also be used in other ways.

Some can charge from the electricity grid when electricity is cheaper and discharge later.

This can be particularly useful with some smart tariffs.

Battery Capacity: kWh

Battery capacity is normally measured in kWh.

Suppose a battery has:

5 kWh usable capacity

That tells us approximately how much usable electrical energy it can store.

However, it does not tell us how quickly the battery can deliver that energy.

For that, we need kW again.

Battery Power: kW

A battery also has a maximum charge and discharge power.

Suppose a battery can store:

5 kWh

and discharge at:

2.5 kW

The first figure tells us how much energy it can store.

The second tells us how quickly it can deliver it.

A simple way to remember this is:

kWh = how much

kW = how fast

A Simple Battery Calculation

Suppose a battery contains 5 kWh of usable energy.

Your home is using a steady 1 kW.

Ignoring losses:

5 kWh ÷ 1 kW = 5 hours

If the home were using 2 kW:

5 kWh ÷ 2 kW = 2.5 hours

Real battery performance is more complicated.

However, this simple calculation helps explain the relationship between power, energy and time.

Batteries Lose Some Energy

Batteries are not perfectly efficient.

Some energy is lost while electricity is:

• Stored
• Converted
• Released again

For example, putting 5 kWh into a battery does not necessarily mean you will later get the full 5 kWh back.

This is why battery specifications sometimes refer to round-trip efficiency.

It tells you how much of the stored electricity can be recovered after losses.

Do You Need a Battery With Solar Panels?

No.

Solar PV can work perfectly well without battery storage.

You can use solar electricity while it is being generated and export surplus electricity.

A battery simply gives you another option.

Whether one makes sense depends on factors such as:

• When you use electricity
• How much solar electricity you generate
• How much you export
• Your electricity tariff
• Battery cost

Therefore, a battery should solve a problem rather than simply be added because one is available.

Solar and Smart Tariffs

Battery storage becomes particularly interesting when combined with smart tariffs.

Some tariffs offer cheaper electricity at certain times.

A compatible battery may be able to charge during those cheaper periods.

The stored electricity can then be used later.

Likewise, solar electricity can charge the battery when generation exceeds household demand.

This creates a more flexible system:

Solar + Battery + Smart Meter + Smart Tariff

However, the best arrangement depends on the household.

Use Monitoring to Understand Your System

Many modern solar and battery systems provide phone apps.

These can make energy flows much easier to understand.

Depending on the system, you may see:

• Solar generation
• Household electricity use
• Battery charge
• Grid imports
• Grid exports

For example, an app might show that your panels are generating more electricity than the home needs.

You can then see the surplus charging the battery.

Later, you may see the battery supplying the home as solar generation falls.

This turns something quite technical into something you can actually watch happening.

What About Winter?

Solar panels generate electricity throughout the year.

However, generation varies considerably by season.

UK solar generation is generally much stronger during the brighter months than during winter.

This matters if you also use electricity for heating.

Your heating demand is normally highest when solar generation is lower.

Therefore, you should not assume that a large annual solar generation figure means solar will meet the same proportion of your electricity needs every month.

Annual totals are useful. Timing matters too.

Bigger Is Not Always Better

A larger solar system can generate more electricity.

Likewise, a larger battery can store more.

However, bigger does not automatically mean better value.

The important questions are:

How much electricity will you generate?

When will you generate it?

When do you use electricity?

What will happen to the surplus?

Those questions matter more than simply buying the largest system possible.

In Short

Solar PV converts sunlight into electricity.

The panels produce DC electricity, which an inverter converts into AC electricity for your home.

Some electricity can be used immediately.

Surplus electricity may be exported or stored in a battery.

A battery then allows some electricity to be used later.

The important numbers are straightforward:

kW = power

kWh = energy

kWp = solar system rated peak power

Once you understand those three ideas, solar PV and battery storage become much easier to understand.

Most importantly, solar is not simply about how much electricity you generate.

It is also about when you generate it and when you use it.

That relationship determines how useful solar and battery storage can be for your home.

Next: How Air Source Heat Pumps Work →

Energility

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