West Midlands - 10 kWp (Oct '25)

Overview

Spirit Energy was commissioned to upgrade a legacy 2011 Feed-in Tariff (FIT) solar PV system that had reached fifteen years of operation with no component failures and minimal degradation. The homeowners had recently installed a heat pump and wanted to expand their solar capacity, add battery storage and maximise self consumption without jeopardising their highly valuable FIT payments.

The final design combined a new 10 kWp bifacial array with a Tesla Powerwall 3, while retaining the original FIT-registered inverter and meter arrangement.

Existing System

Original installation: 3.5 kWp (19 panels, 14 percent efficiency)
Commissioned: 2011 under the FIT scheme
Inverter: Original string inverter still in service
Performance:
~3,000 kWh annual generation
Output still at or above the original estimate of 2,858 kWh
No panel failures or maintenance required

Over fifteen years the system generated more than £23,000 in FIT income. With over 74 p per kWh paid for generation, preserving the FIT arrangement was essential.

Reasons for Upgrading

The homeowners had three main drivers:

Increased electrical demand due to a newly installed heat pump.
Opportunity to expand generation by replacing early-generation panels with modern 500 W bifacial modules.
Desire for storage to reduce grid reliance, support the heat pump and make better use of off peak tariffs.

The roof area that once held a 3.5 kWp system could now support approximately 10 kWp thanks to higher efficiency panels.

Technical Design

The upgrade required careful engineering to comply with FIT rules. The existing inverter had to remain in place and could not be replaced with a higher rated unit. The new design consisted of two electrically distinct systems:

1. FIT System (retained)

7 new panels connected to the original inverter
Same inverter rating
Same generation meter
FIT payments unaffected

2. New System (added)

13 bifacial panels feeding a Tesla Powerwall 3
13.5 kWh usable storage
Up to 20 kW DC solar input
Integrated hybrid inverter
Tesla Gateway providing whole home backup

This arrangement allowed the battery to capture excess solar from both the new array and the FIT array without breaching FIT rules, as export under FIT is deemed rather than metered.

Expected Performance

The upgraded system is projected to deliver:

£1,781 annual savings from solar self consumption, battery discharge, off peak charging and export under a modern SEG tariff
FIT income continuing separately, expected to remain above £2,200 per year at current generation rates
Significant reduction in peak-time grid import due to battery support for the heat pump

The homeowners opted for one Powerwall 3 initially to ensure frequent full cycling and stronger economics. A second unit can be added later if required.

Outcome

The project demonstrates how a legacy FIT system can be expanded and modernised without compromising tariff eligibility. By isolating the FIT system and integrating a separate hybrid inverter and battery, the homeowners now benefit from: