TL;DR
A UK household with a 4.2 kWp rooftop array and three Tesla Powerwall 2 units tracked a full year of data for 2025. Supplier meters show the house imported about 20.1 MWh, exported 6.0 MWh, produced 3.2 MWh of solar and ended the year with a net electricity cost of £557.37.
What happened
The homeowner monitored three independent data sources for 2025: supplier billing, a Home Assistant CT clamp, and the Tesla Gateway. The supplier's figures were used for calculations and show 20.1 MWh imported from the grid while the household exported 6.0 MWh after an export tariff change in late May/June. The roof is fitted with 14 Perlight panels (4.2 kWp), producing 3.2 MWh across the year; peak instantaneous output recorded was 2.841 kW. Energy storage comes from three Tesla Powerwall 2 units used primarily to shift load from peak (£0.28/kWh) to off-peak (£0.07/kWh) periods. After accounting for export payments (£886.49) and the standing charge, total billed electricity for 2025 was £1,608.11, yielding a net cost of £557.37—an effective rate around £0.03/kWh.
Why it matters
- Combining solar with batteries can substantially reduce energy bills by shifting consumption to lower-rate periods and exporting surplus generation.
- Accurate supplier metering matters: homeowner used supplier figures for final accounting because those determine billed amounts.
- Tariff design and export payments materially affect household economics; a mid-year export tariff change increased the value of exported energy.
- High household demand (EVs, home working, servers) can still be partly offset with appropriately sized storage and generation.
Key facts
- Solar array: 14 Perlight panels, 4.2 kWp capacity; annual production: 3.2 MWh.
- Battery storage: three Tesla Powerwall 2 units installed to enable load-shifting.
- Grid import (supplier): 20.1 MWh for 2025; Home Assistant measured 21.574.8 kWh total import, Tesla Gateway showed 21.0 MWh.
- Grid export: 6.0 MWh; export payments reported at £886.49 for the period where export tariff applied.
- Household energy consumption calculated at 17.3 MWh (imports + solar − exports).
- Tariff rates used in analysis: peak £0.28/kWh (05:30–23:30), off-peak £0.07/kWh (23:30–05:30), export tariff later set at £0.15/kWh (previously £0.04/kWh).
- Recorded peak solar instant output: 2.841 kW on 8 July at 13:00.
- Annual billed electricity before subtracting standing charge: £1,608.11; after standing charge adjustments and export payments, net electricity cost: £557.37.
- Effective electricity cost for the year calculated at about £0.03/kWh.
- Installation costs reported: Powerwalls #1 & #2 £17,580; solar array £13,940; Powerwall #3 £7,840; total £39,360.
What to watch next
- Long-term payback period for the combined purchase and install cost versus ongoing savings—not confirmed in the source.
- Future tariff and export rate changes that could alter the economic case for batteries and solar—not confirmed in the source.
- Battery degradation and replacement schedules which will affect lifetime savings—not confirmed in the source.
Quick glossary
- kWh: Kilowatt-hour, a measure of energy equal to one kilowatt of power used for one hour.
- kWp: Kilowatt-peak, a rating of the maximum power output of a solar array under standard test conditions.
- Load-shifting: Moving energy consumption from higher-cost periods to lower-cost periods, often using batteries or timed appliances.
- Export tariff: A rate paid by an electricity supplier to a customer for energy exported from the customer's system back to the grid.
- Powerwall: A brand of home battery storage that stores electricity for time-shifting, backup power, or grid services.
Reader FAQ
How much did the household save on electricity in 2025?
The author reports a year-over-year reduction of £3,078.49 versus a no-solar/no-battery scenario for 2025.
What was the net electricity bill for 2025?
Net electricity cost after export payments and standing charge adjustments was £557.37.
How much energy did the panels produce in 2025?
The solar array generated 3.2 MWh during 2025.
What did the installations cost in total?
Combined reported installation costs totalled £39,360.
What is the projected payback period?
not confirmed in the source
TESLA POWERWALL What a Year of Solar and Batteries Really Saved Us in 2025 Scott Helme Security researcher, entrepreneur and international speaker who specialises in web technologies. More posts by…
Sources
- What a year of solar and batteries saved us in 2025
- Before & After: How Solar Panel Installers Cut Your …
- UK announces plan to cut household energy bills by £150
- Solar Panels After the 2025 Budget: What Homeowners in …
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