Solar energy systems are a key feature in improving a property’s energy efficiency. However, not all solar technologies are treated equally in Energy Performance Certificate (EPC) assessments. While Photovoltaic (PV) panels that generate electricity are well-understood by EPC software, solar thermal systems—which provide hot water—are often assessed differently, sometimes undervaluing their contribution to a home’s overall efficiency rating.
In this article, we explore how solar thermal systems influence EPC scores compared to PV panels and why understanding these differences is crucial for homeowners.
The Difference Between Solar PV and Solar Thermal Systems
Solar PV Panels: Convert sunlight directly into electricity for household use or export to the grid.
Solar Thermal Systems: Use solar energy to heat water, reducing reliance on traditional water heating systems like gas boilers or electric heaters.
Both systems reduce a home’s dependency on external energy sources, but their impact on EPC ratings is calculated through different pathways.
How Solar PV Panels Affect Your EPC Rating
Solar PV panels typically have a strong positive impact on EPC ratings because:
They reduce the demand for grid-supplied electricity.
EPC software can accurately model PV generation based on panel size, orientation, and shading factors.
The energy offset is directly applied to the property’s calculated electricity consumption, often leading to improved EPC scores.
How Solar Thermal Systems Are Treated Differently in EPC Assessments
Solar thermal systems face unique challenges in EPC assessments:
Hot Water Contribution Only
Unlike PV panels, solar thermal systems impact only the domestic hot water calculation. They do not reduce heating demand, which is typically the largest energy load in a home.
Limited Seasonal Efficiency Credits
EPC software applies a ‘solar fraction’—the percentage of hot water needs met by solar energy. However, this fraction can be conservative, especially in the UK climate, limiting the system’s perceived efficiency.
Interaction with Main Heating System
If the primary water heater (e.g., an old boiler) is inefficient, the gains from solar thermal may be offset in the overall EPC calculation, reducing the perceived benefit.
System Documentation Required
If the solar thermal system lacks proper documentation (e.g., system performance details, installation certificates), default values are used, which often underrepresent the system’s actual efficiency.
Why Solar PV Often Yields a Higher EPC Impact
Because EPC assessments heavily weight electricity consumption, and solar PV panels offset this directly, they often yield a more noticeable improvement in the EPC rating. In contrast, solar thermal systems, despite being highly efficient for hot water production, influence only a smaller part of the overall energy demand.
Maximizing EPC Gains with Solar Thermal Systems
To ensure your solar thermal installation is fairly reflected in your EPC:
Provide system documentation, including collector efficiency, cylinder size, and installation details.
Pair solar thermal systems with a high-efficiency boiler or heat pump to enhance the overall EPC outcome.
Consider supplementary measures like high-performance insulation to offset heating demands, amplifying the impact of your solar thermal system.
EPCrate: Expert EPC Assessments for Solar-Equipped Homes
At EPCrate, we specialize in detailed EPC assessments for homes with renewable energy systems. Whether you have solar PV panels, solar thermal systems, or both, our EPC assessment services ensure that your property’s energy-saving features are fully accounted for in your certificate.
Check our pricing options and book an expert assessment via our online booking platform.
Book Your EPC Assessment Today
Don’t let your solar investment go under-recognized. Contact EPCrate for an EPC assessment that accurately reflects your home’s solar energy efficiency.
