Why Two Identical Houses Can Need Completely Different Solar Systems

When considering solar panel installation, it’s easy to assume that two houses of a similar size, with similar roofs and similar electricity consumption, will need almost identical solar systems. After all, if the properties are practically the same, surely the solar requirements should be too?

Not necessarily.

One of the most important factors when designing a solar PV system is not simply the size of the property or the number of people living in it. It’s when and how the household uses electricity.

Two neighbouring homes could have identical roofs, similar annual electricity consumption and the same number of occupants yet benefit from very different solar panel and battery storage configurations.

The reason comes down to something known as an electricity consumption profile, or load profile. Understanding this is essential when determining the right solar system size, battery capacity and overall system design.

At SolarTherm UK, we believe a successful solar installation should be designed around the household, not simply the available roof space.

Why Does Electricity Usage Matter When Choosing a Solar System?

Solar panels generate electricity during daylight hours, with generation generally increasing throughout the morning, reaching its peak around midday and then gradually reducing towards sunset.

However, most households don’t necessarily use electricity in line with this generation pattern.

Think about a typical household. The occupants might leave for work and school in the morning, leaving the property largely empty throughout the day. Electricity consumption could be relatively low between 9am and 5pm, before increasing significantly when everyone returns home.

Cooking dinner, switching on appliances, watching television, charging devices and running other household equipment can all contribute to a substantial evening electricity demand.

Now consider another household in an almost identical property.

Perhaps someone works from home, running appliances throughout the day, or is retired and spends most of their day at home. Their electricity consumption may be considerably higher during daylight hours.

Both properties could use exactly the same amount of electricity over a year, but their solar requirements could be very different. This is why annual electricity consumption alone isn’t enough to determine the most suitable solar system size.

Two Identical Houses, Two Different Solar Requirements

Let’s look at two hypothetical households to understand how this works in practice.

House A: The Daytime Electricity User

House A is occupied throughout much of the day. The occupants work from home and regularly use appliances such as washing machines, dishwashers, computers and cooking equipment during daylight hours.

When the solar panels are generating electricity much of that energy can be consumed immediately by the household. This is known as direct self-consumption.

For example, if the solar system is generating 3kW and the household is using 2kW at that moment, the property can use the majority of its solar generation without needing to draw electricity from the grid.

There may even still be some surplus electricity available to charge a battery or export to the grid through the Smart Export Guarantee (SEG), depending on the system configuration.

For this household, a suitably sized solar array may deliver excellent results even with a relatively modest battery, or potentially without a battery at all. The priority is to match solar generation with daytime electricity demand.

House B: The Evening Electricity User

House B has the same roof, similar annual electricity consumption and the same number of occupants. However, everyone leaves the property during the day.

Electricity usage is relatively low while the solar panels are generating, with demand increasing considerably after 5pm when the occupants return home.

This creates a different challenge.

The solar panels may generate plenty of electricity during the day, but much of it cannot be used immediately. Any surplus can be exported to the grid, but the household will still need to purchase electricity when demand increases in the evening.

This is where battery storage becomes particularly valuable.

A solar battery allows surplus electricity generated during daylight hours to be stored and used later, helping reduce reliance on the grid when the household needs electricity most.

For House B, a larger battery may offer greater benefits than it would for House A, depending on the amount of surplus generation available and the household’s evening consumption.

The crucial difference isn’t the property itself. It is the timing of its electricity demand.

How Battery Storage Changes Solar System Design

Battery storage has become an increasingly important part of residential solar installation, particularly for households that use most of their electricity outside daylight hours.

Rather than exporting surplus solar electricity during the day and buying electricity back from the grid in the evening, a battery can help move that energy to when it’s needed. However, choosing the right battery capacity is just as important as choosing the right solar panel system size.

A battery that’s too small may not provide enough stored energy to meet evening demand. Conversely, an unnecessarily large battery could increase the installation cost without delivering a proportionate financial benefit.

The aim is to find the right balance between:

• Solar panel generation capacity
• Household electricity consumption
• The amount of electricity used during daylight hours
• Evening and overnight electricity requirements
• Available battery storage capacity
• Electricity import and export tariffs

For example, a household that regularly uses 5kWh of electricity after sunset may benefit from a different battery configuration to one that uses 12kWh during the same period.

It’s also important to remember that battery capacity and usable battery capacity aren’t always identical. The usable energy available will depend on the battery’s specification and operating settings. A properly designed system considers all these factors rather than simply recommending the largest battery available.

What If You Have an Electric Vehicle?

Electric vehicle (EV) charging is another factor that can significantly influence the design of a solar PV system.

Consider House B again. The occupants are out during the day and return home in the evening. They also own an electric vehicle that needs regular charging. This introduces another potentially substantial electricity demand.

If the vehicle is charged during the evening, the household could find itself using considerably more electricity after sunset than the solar panels can generate directly.

There are several ways to approach this:

Option 1: Increase Battery Storage

A larger battery may allow more surplus solar generation to be stored during the day and used later, including to support EV charging. However, the battery needs to be sized according to the actual charging requirements and the amount of solar energy available to charge it.

Option 2: Charge the Vehicle During Daylight Hours

If the vehicle is at home during the day, it may be possible to charge it directly using solar generation. Smart EV chargers can help manage charging around available solar generation, depending on the charger and system configuration.

Option 3: Take Advantage of Off-Peak Electricity Tariffs

For households with an EV, an off-peak electricity tariff could provide an alternative to relying entirely on stored solar energy. Charging overnight when electricity rates are cheaper may be more cost-effective than using battery storage for every charging requirement.

In some circumstances, the most effective solution is a combination of solar generation, battery storage and intelligent overnight charging. The important thing is to consider EV charging as part of the overall solar system design, rather than treating it as an afterthought.

How Do You Work Out What Size Solar System You Need?

One of the most common questions homeowners ask when considering solar installation is:

‘How many solar panels do I actually need?’

The answer depends on several factors, and the size of your roof is only one of them. A professional solar assessment should consider the following:

1. Your Annual Electricity Consumption

Your annual electricity consumption provides an important starting point. Looking at your electricity bills can help establish how much electricity your household uses over a 12-month period. However, this figure doesn’t tell the whole story.

2. Your Half-Hourly Smart Meter Data

Your smart meter data can provide a much clearer picture of when electricity is being used. Half-hourly consumption data allows an installer to identify:

• When household electricity demand is highest
• How much electricity is used during daylight hours
• How much electricity is required in the evening
• Whether there are significant overnight electricity requirements
• Opportunities to shift electricity usage to cheaper tariff periods

This information can be particularly useful when deciding whether battery storage is worthwhile and determining the appropriate battery capacity. Rather than relying on assumptions about when a household uses electricity, the system can be designed around actual consumption.

3. Your Roof Space and Orientation

The available roof space determines how many solar panels can physically be installed. Roof orientation, pitch, shading and any obstructions can also affect how much electricity the panels generate.

South-facing roofs generally offer favourable generation conditions, but east- and west-facing roofs can also work very well. In some circumstances, installing solar panels across different roof orientations can help spread electricity generation throughout the day, potentially matching household demand more effectively.

4. Your Future Electricity Requirements

Your electricity consumption today might not reflect what you’ll need in five or ten years. Are you planning to purchase an electric vehicle? Will you be installing a heat pump? Are children growing up and becoming more independent, or are you expecting to spend more time working from home? These changes can all affect future electricity demand. A good solar installation should consider not only how your home operates today, but also how it might change in the future.

Why Your Neighbour’s Solar System Might Not Be Right For You

It’s natural to look at a neighbour’s solar installation and wonder whether the same system would work for your property. They might have a similar house, an identical roof and even a comparable electricity bill.

However, copying someone else’s solar system isn’t necessarily the best approach.

Your neighbour might:

• Work from home while you commute
• Have an electric vehicle while you don’t
• Use most of their electricity during the day
• Have significantly higher evening electricity consumption
• Prefer to maximise battery storage rather than export surplus electricity
• Be on a different electricity tariff

Even seemingly small differences can influence the ideal combination of solar panels, inverter capacity and battery storage.

This is why SolarTherm UK doesn’t believe in a one-size-fits-all approach to solar installation.

The right solar system should be determined by the property’s generation potential, actual electricity consumption and the homeowner’s future requirements.

Getting the Balance Right: Solar Panels, Battery Storage and Electricity Tariffs

A well-designed solar system isn’t simply about generating as much electricity as possible. It’s about making the best use of the electricity generated.

For some households, installing additional solar panels may be the most effective way to increase generation. For others, increasing battery storage could deliver greater benefits by allowing more of that generation to be used after sunset.

Electricity tariffs also play an important role. The Smart Export Guarantee (SEG) allows eligible homeowners to receive payments for surplus electricity exported to the grid, while certain time-of-use tariffs offer cheaper electricity at specific times of the day.

This means there may be opportunities to combine solar generation, battery charging and electricity imports strategically.

For example, a household could:

• Use solar electricity directly during daylight hours
• Store surplus generation in its battery
• Export excess electricity when the battery is full
• Charge the battery overnight using cheaper off-peak electricity when appropriate
• Use stored electricity during more expensive peak periods

The most suitable strategy depends on the tariff, battery system, household consumption and the export arrangements available. Getting these elements working together can make a considerable difference to the overall performance and financial value of a solar installation.

How SolarTherm UK Designs the Right Solar System for Your Home

At SolarTherm UK, we understand that every property and household has difference energy requirements. That’s why we look beyond the number of bedrooms, roof dimensions and annual electricity consumption when recommending a solar PV system.

Our approach considers the factors that influence real-world system performance, including:

• Electricity consumption: understanding how much electricity your household uses throughout the year
• Usage patterns: identifying when electricity is consumed and how this compares with solar generation
• Roof suitability: assessing available space, orientation, pitch and potential shading
• Solar generation: calculating the likely output of a proposed solar array
• Battery storage: determining the most appropriate battery capacity for your requirements
• Future energy needs: allowing for potential changes such as EV charging or additional electrical appliances

As an experienced solar installer, SolarTherm UK provides professionally designed solar and battery storage systems for homeowners across Essex, Kent, Suffolk, Hertfordshire and the wider South East and East Anglia.

We are an MCS Accredited and NICEIC Registered Installer, giving homeowners confidence that their installation is being carried out by appropriately accredited professionals.

With more than 16 years of industry experience, our team can help you understand the options available and recommend a solar system designed around your property and electricity requirements.

The best solar system isn’t necessarily the biggest one. It’s the one that’s designed to work for you.

Contact SolarTherm UK today for a free, no obligation quote and design, tailored to your property, usage and future energy needs. No hard sell, just honest, expert advice – and the time you need to make an informed decision.

Your home. Your energy. Your future.

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