January 13, 2026
Watt a mess
What a year of solar and batteries saved us in 2025
Sunshine dreams, bill screams: Tesla vs BYD, DIY batteries, and usage shock
TLDR: A UK home logged a year of solar and battery use: about 20 MWh pulled from the grid, 6 MWh exported, and 3.2 MWh generated. Commenters battled over high usage, pricey Tesla vs cheaper BYD or DIY builds, and a U.S. tax-credit deadline that could flood eBay with used solar gear
A UK homeowner dropped a year of solar-and-battery receipts: 14 roof panels, 3 Tesla Powerwalls, smart charging via Octopus Energy, and a very British confession that the meters “align so poorly.” The numbers sparked instant popcorn: ~20.1 MWh imported, 6 MWh exported, 3.2 MWh generated, with export only paying real money (15p/kWh) from June. Cue the usage wars. One commenter said 21.6 MWh “seems too high,” triggering “are you heating a castle?” jokes and a grand debate about EVs, heating, and UK cloudiness. Then came the battery brawls: Tesla fans vs value hunters. BYD stans called Powerwalls a “fan tax,” waving bigger capacity for less cash; DIY heroes bragged about a €1600 15kWh pack from China, stitched together with Raspberry Pi magic and custom code—half the crowd cheered, the other half pictured kitchen fires. Across the pond, deal hunters eyed the IRS credit deadline and predicted a flood of used solar gear on eBay. Meanwhile, Octopus nerds flexed 30‑minute API graphs like energy Pokémon cards. The vibe? Admiration for clever off‑peak savings at 7p overnight, mixed with spicy doubts about high usage, Tesla pricing, and whether DIY or BYD is the real king of the garage
Key Points
- •Household’s 4.2 kWp solar array (14 Perlight panels managed by Enphase) produced 3.2 MWh in 2025.
- •Three Tesla Powerwall 2 batteries used for load shifting between peak (£0.28/kWh, 05:30–23:30) and off-peak (£0.07/kWh, 23:30–05:30) rates.
- •Grid import measured by three sources: supplier 20.1 MWh, Home Assistant 21.6 MWh, Tesla Gateway 21.0 MWh; supplier figure used for calculations.
- •Export tariff increased from ~£0.04/kWh to ~£0.15/kWh at end of May; practical exporting began in June, totaling 6.0 MWh for 2025.
- •Peak solar output recorded was 2.841 kW on July 8 at 13:00; production varied seasonally with higher output in summer.