Solar panels make electricity from sunlight.
You can use some of this electricity in your home. Then, if you have a battery, you may be able to store some for later.
However, solar panels and batteries are two different things.
So, it helps to understand each one first.
How Do Solar Panels Work?
Solar PV panels turn sunlight into electricity.
PV means photovoltaic.
The panels first make a type of electricity called DC electricity.
However, your home mainly uses AC electricity.
So, an inverter changes the electricity into a form your home can use.
The basic journey is:
Sunlight → Solar panels → Inverter → Your home
What Happens to the Electricity?
Your solar panels make electricity during daylight hours.
If your home needs electricity at that time, some of the solar power can be used straight away.
Then, any extra electricity may be:
- stored in a battery
- sent to the electricity grid
So, when you use electricity matters.
If you are at home during the day, you may use more of your solar power as it is made.
However, if you use most of your electricity in the evening, a battery may help.
What Does a Battery Do?
A home battery stores electricity.
You can then use some of that electricity later.
For example, imagine your solar panels make plenty of electricity at lunchtime.
However, nobody is home.
Instead of sending all the extra electricity to the grid, some could be stored in the battery.
Then, when you come home in the evening, the battery could supply some of your electricity.
So, a battery can help move electricity from one part of the day to another.
Can a Battery Charge From the Grid?
Some battery systems can also charge from the electricity grid.
This can be useful with some electricity tariffs.
For example, a battery may be able to charge when electricity is cheaper.
Then, you may be able to use that stored electricity when grid electricity costs more.
However, this depends on:
- your battery
- your tariff
- when you use electricity
- the price difference
So, don’t assume that adding a battery will always save money.
What Do kW and kWh Mean?
You will often see kW and kWh when looking at solar panels and batteries.
They mean different things.
kW means power
This tells you how quickly electricity can be produced or used.
kWh means energy
This tells you how much electricity has been produced, stored or used over time.
For example, a battery might store 5 kWh of electricity.
So:
kW = how fast
kWh = how much
What Does kWp Mean?
Solar systems are often described using kWp.
This means kilowatt peak.
It is a standard way to describe the rated size of a solar PV system.
For example, you might see a solar system described as 4 kWp.
However, this does not mean it will produce 4 kW all day.
Actual solar power changes with conditions.
How Much Electricity Will Solar Panels Make?
This depends on several things.
For example:
- system size
- roof direction
- roof angle
- shade
- location
- weather
- time of year
So, two homes with the same number of panels may not make the same amount of electricity.
Also, solar panels normally make much more electricity at some times of year than others.
Therefore, look at the expected yearly generation, but also think about when that electricity will be made.
Does a South-Facing Roof Matter?
A suitable south-facing roof can work very well for solar panels in the UK.
However, it is not the only option.
Other roof directions may also work.
For example, an east-west system can spread solar generation across more of the day.
So, don’t rule out solar simply because your roof does not face due south.
Instead, get a proper estimate for your property.
What About Shade?
Shade can reduce the amount of electricity your panels make.
It may come from:
- trees
- chimneys
- nearby buildings
- other parts of the roof
However, the effect depends on where the shade falls and when it happens.
So, shading should be checked before you buy a system.
How Big Should the Solar System Be?
Bigger is not always better.
A larger system may make more electricity.
However, you also need to think about what happens to that electricity.
Ask:
- How much electricity do I use?
- When do I use it?
- How much could the panels make?
- How much could I use myself?
- How much might I export?
So, don’t choose a system only by counting how many panels will fit on the roof.
How Big Should the Battery Be?
Again, bigger is not always better.
A larger battery can store more electricity.
However, it will normally cost more.
Also, there is little benefit in paying for storage that you rarely use.
So, battery size should be linked to:
- your electricity use
- your solar generation
- when you use electricity
- your tariff
- how you plan to charge the battery
The aim is not simply to buy the biggest battery.
Instead, it is to choose one that suits how you use electricity.
Can You Sell Electricity?
Yes, you may be able to get paid for electricity that you send to the grid.
In Great Britain, eligible small-scale generators can receive payments through a Smart Export Guarantee, or SEG, tariff.
However, export tariffs and their terms can differ.
So, check the current options before choosing one.
Also, don’t assume that your export company must be the same company that supplies your electricity.
Is It Better to Use or Export Solar Power?
There is no single answer.
It depends on what you pay to buy electricity and what you receive for exporting it.
For example, using your own solar electricity may avoid buying electricity from the grid.
However, an export tariff may also pay you for electricity you send out.
So, compare the value of:
using it now
storing it for later
and
exporting it
The best choice can change with your tariff.
Do You Need a Battery?
No.
Solar panels can work without a battery.
Without one, you can use solar electricity while it is being made. Then, extra electricity can normally be exported.
A battery gives you another option because some electricity can be saved for later.
However, the battery adds to the cost of the system.
So, the important question is not:
“Would a battery be useful?”
It is:
“Would a battery be useful enough to justify its cost?”
How Long Will It Take to Pay Back?
There is no single payback time for solar panels or batteries.
It depends on factors such as:
- installation cost
- solar generation
- electricity prices
- how much solar power you use
- export payments
- battery use
- future costs
So, be careful with simple claims such as “this system pays for itself in X years.”
Instead, ask to see the figures and assumptions behind the estimate.
Then, compare them with how you actually use electricity.
Before You Buy
First, look at your electricity use.
Then, check when you use most of it.
Next, get an estimate of how much solar electricity your home could make.
Also, ask what is expected to happen to that electricity.
For example:
- How much might I use directly?
- How much might go into the battery?
- How much might I export?
- What happens when the battery is full?
- Can the battery charge from the grid?
- What happens during a power cut?
- What warranties apply?
Finally, compare the likely savings with the full cost of the system.
Key Points
- Solar PV panels make electricity from sunlight.
- Solar panels and batteries do different jobs. Panels make electricity, while a battery stores electricity for later.
- You can use solar electricity in your home while it is being made. Extra electricity may then be stored in a battery or exported to the grid.
- When you use electricity matters. Using more electricity during daylight hours may help you use more of your solar power directly.
- Some batteries can also charge from the grid. This may be useful with certain electricity tariffs, but it will not always save money.
- kW and kWh mean different things. kW tells you how quickly electricity can be produced or used, while kWh tells you how much energy is produced, stored or used.
- kWp describes the rated size of a solar PV system. It does not mean the system will produce that amount of power all the time.
- Solar generation changes throughout the day and year. Roof direction, angle, shade, location and weather can all affect how much electricity you produce.
- A south-facing roof is not essential. Other roof directions may also be suitable for solar panels.
- Bigger is not always better. Solar and battery sizes should match your home and the way you use electricity.
- You may be able to get paid for electricity you export to the grid. So, compare the value of using, storing and exporting your solar electricity.
- You don’t need a battery to have solar panels. A battery should provide enough extra benefit to justify its additional cost.
- There is no single payback time. Installation cost, energy use, solar generation, electricity prices, export payments and battery use can all affect the result.
- Check the assumptions behind savings and payback estimates before buying a system.
- Most importantly, match the solar panels and battery to when and how your home uses electricity.
Important Information
Energility provides general information to help you understand energy, household and business costs, services and ways to save money. It is not financial, legal, tax, technical or professional advice.
Prices, tariffs, grants, government schemes, regulations and other information can change. Costs, savings and calculator results are estimates and your actual results may be different.
Before making an important financial decision, signing a contract or carrying out significant work, check the latest information and consider getting advice from a suitably qualified professional where needed.
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