Do I need a south facing roof for solar panels on my house?

The Optimal Solar PV Installation: Does Your Roof Need to Face South?

Solar Orientation Basics

One of the first questions people think of when initially looking into installing solar is: "Do I need to have a south-facing roof?"

This post intends to answer this query, including a brief look at solar energy generation and how it relates to your roof's orientation.

In short, the answer to this question is no, you do not need a south facing roof to have a solar installation, continue reading for more detail on this topic.

Common Assumptions

It's common knowledge that the sun rises in the east and sets in the west, suggesting a south-facing roof would maximise solar generation throughout the day due to its optimal positioning - this is correct.

This assumption is grounded in the idea that the sun is directly south (in the northern hemisphere) at solar noon, although this isn't entirely accurate for the purpose of this discussion, we will assume that the sun is roughly in its southernmost position around midday in the northern hemisphere. Therefore it is logical that a south-facing roof is the most beneficial for a solar photovoltaic (PV) system. In terms of pure generation, yes a south facing roof is the best, but it's not by any means a requirement and you could see better returns on your system if your orientation is not one of a purely southerly direction.

For individual homeowners, a decision to proceed varies depending on the objectives of your solar installation project and personal circumstances. For commercial installations aiming to maximise electricity production for net zero or carbon neutral goals, even north-facing roofs could be viable.

Roof Orientation and Solar Suitability

A general rule of thumb is that any roof orientation between east and west is suitable for a solar installation. Interestingly, some argue that having dual orientation—south east and south west—can be more advantageous than a south-facing roof, given certain living habits (being at home in the mornings and late afternoon/early evening) and optimising the use of the energy generated.

To provide a more comprehensive understanding, let's delve into the mathematics using the MCS criteria employed to calculate a system's typical generation capacity on a roof.

This calculation will take into account factors such as roof orientation, panel/roof angle, and geographic location in the UK. For example, Cornwall receives more sunlight than Cumbria.

For this analysis, we will assume a system installed at a 37-degree angle (typical for most domestic roofs is 30-degrees to 40-degrees, but 37-degrees is accepted as the peak angle) in the Midlands (Zone 6 on the MCS data tables). We will compare a south-facing roof to east-facing and southeast-facing ones (it's worth noting that southeast-facing and southwest-facing roofs would yield similar results).

Solar Output Comparison

A south-facing roof with a 37-degree incline in zone 6 (the East Midlands) will generate around 937kWh per kWp annually. Therefore, a 4kWp Solar PV system will generate approximately 3,748 kWh per year (4 x 937kWh’s).

Conversely, a southeast-facing roof of the same angle would generate around 882 kWh per kWp, or about 3,528 kWh per year for a 4 kWp system, a marginal difference of 220 kWh annually.

An east or west-facing roof will generate about 744 kWh per kWp annually, or roughly 2,967 kWh per year for a 4 kWp system. The below image is MCS’s irradiance dataset for Zone 6, which covers the majority of the midlands from Birmingham, Leicester and south Nottingham. This is where we have taken the data for the above calculations.

MCS Irradiance dataset for zone 6 (East Midlands)

Economic Considerations

To determine potential savings, you can multiply the kWh generated by the rate your energy provider charges. For example, at 28p per kWh, a 4kWp system would save you roughly £1,049 annually. We have a deeper dive into the mathematics of this in an article coming soon called ‘How are PV and Battery savings calculated’.

Daily Energy Consumption Patterns

An important factor to consider is the daily energy consumption pattern. Many of us use more energy in the morning and late afternoon or evening. Therefore, a system that generates more energy during these times could potentially offset any deficits caused by less optimal roof orientation. Additionally, during the peak summer months, south-facing roofs may over-generate and export excess energy to the grid. Although energy companies offer the Smart Export Guarantee (SEG), it's typically more cost-effective to utilise the energy directly.

The introduction of improving battery technologies adds a new dimension to the discussion. Excess energy generated in the middle of the day is of course stored for use in the afternoon. However, even with a battery, energy may still be exported to the grid as the battery can fill up quickly, particularly in the summer.

A roof facing southeast, southwest, or even east and west, could still fill your battery during the day, and you might want to take advantage of cheaper energy rates at night to recharge it. These complexities go beyond the scope of this article as they depend on various scenarios and individual energy consumption habits.

Conclusion

The crux of the matter remains: you do not need a south-facing roof for solar, but yes, a south facing roof will generate the highest amount of energy that you can from your particular roof (assuming there is no shading or other obstacles).

Southeast, southwest, and even east and west orientations are viable options, with most houses having better than mere east or west facing roofs.

Having an understanding of these nuances can help you interpret your solar survey results more accurately and ask your solar PV installation company more informed questions. At the Solar and Battery Company we are happy to answer any questions you have.