8,725 kWh
Approximate annual household electricity consumption.
Real solar design case study · Central Scotland
Designing solar for a home with a heat pump, EV and high electricity demand.
This anonymised four-bedroom detached home used around 8,725 kWh of electricity a year and already had significant electrical demand from an 8 kW heat pump, electric hot water and an electric vehicle.
8,725 kWh annual demand
Heat pump + EV
20-panel design
The property
A highly electrified home changes the solar calculation.
The property was a four-bedroom detached home in Central Scotland. For privacy, the customer name, exact town, street and postcode have been deliberately omitted.
Annual electricity consumption was approximately 8,725 kWh — substantially higher than many homes because several major energy requirements had already been electrified.
✓ 8 kW air-source heat pump
✓ Electric hot-water immersion
✓ Electric vehicle
✓ High annual electricity consumption
✓ Four-bedroom detached property
Key design data
The numbers behind the proposed system.
20 solar panels
A 9.0 kWp array using twenty 450 W panels.
18.8 kWh storage
Two 9.4 kWh home batteries were proposed to provide substantial storage capacity for the high-demand household.
7 kW hybrid inverter
A larger hybrid inverter was selected rather than designing the system around a standard 3.68 kW G98-sized output.
34° roof pitch
Roof pitch was approximately 34 degrees.
Two roof orientations
The proposed array used both north-east and south-west roof areas.
Panel layout
8 panels north-east. 12 panels south-west.
The available roof space did not present one single ideal south-facing plane.
Instead, the proposed twenty-panel array was divided across two roof orientations:
✓ 8 × 450 W panels facing north-east
✓ 12 × 450 W panels facing south-west
✓ 20 panels total
✓ 9.0 kWp total nominal solar capacity
A split-orientation array can spread generation across a broader part of the day rather than concentrating all production around one peak period.
The important question was therefore not simply which roof direction was theoretically best, but how the available roof could be used sensibly alongside the home's unusually high electrical demand.
Battery strategy
Why nearly 19 kWh of battery storage was reasonable here.
Large batteries are not automatically good system design. Storage capacity needs a reason.
In this home, however, annual electricity consumption was already approximately 8,725 kWh and demand included space heating, hot water and vehicle charging.
Two 9.4 kWh batteries provided a combined nominal storage capacity of 18.8 kWh.
That created substantially more opportunity to retain daytime solar generation for later household use and to make use of lower-cost electricity periods where suitable tariffs were available.
The battery decision therefore followed the demand profile rather than being added simply because larger storage looked attractive on a quotation.
Heat pump demand
Electrified heating makes household demand much more important to solar design.
The property used an approximately 8 kW air-source heat pump for heating.
That does not mean the heat pump continuously consumes 8 kW of electricity, but it does mean heating forms a significant part of the home's wider electrical-energy strategy.
Heat-pump households can have substantial winter electricity demand at precisely the time of year when solar production is lowest.
Solar and battery proposals for these homes therefore need to be considered against annual demand and seasonal behaviour rather than assuming summer solar output represents the whole year.
Electric vehicle
An EV can turn surplus generation into useful household energy demand.
The presence of an electric vehicle added another significant and flexible electricity load.
Where the vehicle is at home during solar-generation periods, excess electricity that might otherwise be exported can potentially be used for charging.
That creates a different design question from a low-demand property: rather than asking only how much solar the house itself can consume immediately, the vehicle may provide another useful destination for daytime generation.
Charging patterns, tariffs and vehicle availability still matter, but the EV was an important part of the demand picture.
Inverter decision
The inverter was sized around the larger system rather than forcing the design into G98.
A common domestic solar threshold is 3.68 kW per phase under the standard G98 connection process.
This property had a 9.0 kWp proposed array and high household demand, so designing the system around a 3.68 kW inverter purely to remain within that simpler threshold would have imposed a significant limitation on the proposed installation.
A 7 kW hybrid inverter was therefore specified as part of the design.
That meant the grid-connection requirements needed to be considered through the G99 process rather than assuming a standard G98 notification would be sufficient.
G99
Grid approval was part of the design problem, not an afterthought.
Larger inverter capacities can require approval from the local distribution network operator before unrestricted operation or export is permitted.
For this system, the 7 kW inverter meant the proposed installation required G99 consideration.
That matters because an attractive solar design on paper is not complete until the network-connection position is understood.
Grid limitations can affect inverter settings, export capacity and, in some cases, whether the proposed design needs to be altered.
What this case demonstrates
High-demand homes need to be designed as energy systems, not just solar arrays.
Demand matters
A household using 8,725 kWh a year has a very different energy profile from a low-consumption home.
Roof direction is only one variable
The array used both north-east and south-west roof areas because system design involves the usable property as a whole.
Storage needs justification
The 18.8 kWh battery capacity was supported by substantial household electricity demand rather than being chosen in isolation.
Heating changes the picture
Heat pumps increase the importance of annual and seasonal electricity demand when judging solar and battery performance.
EVs provide flexible demand
Vehicle charging can create another productive use for solar electricity when the car is available during generation periods.
Grid connection matters
A larger inverter may make G99 approval part of the system-design process before installation can proceed as proposed.
The wider lesson
There was no single number that could design this system properly.
Twenty panels alone do not explain the design.
Neither does a 7 kW inverter, an 18.8 kWh battery bank or the presence of a heat pump.
The design only starts to make sense when those factors are considered together:
✓ Property and usable roof
✓ 8,725 kWh annual electricity demand
✓ Heat-pump heating
✓ Electric hot water
✓ Electric vehicle
✓ Two roof orientations
✓ Battery-storage opportunity
✓ Inverter capacity
✓ G99 requirements
That is why Tom Solar's starting point is the property and its energy demand rather than a predetermined package of equipment.
Considering solar?
Start by understanding what your own home actually needs.
Your home may need a much smaller system than this example — or it may have similarly high electricity demand.
The useful question is not whether this particular design should be copied. It is why each part of the design was chosen for this particular property.
An independent survey provides the evidence needed to answer the same questions for your own home.
Privacy note: This case study uses genuine system-design information from a real residential solar assessment. Customer-identifying information, including the name, exact location, street and postcode, has been deliberately omitted.