Why 60–90% Self-Consumption Claims Are Wrong
The Headline Every Installer Uses
"With a battery, you'll use 70–90% of your solar energy instead of exporting it!"
This number appears on installer websites, battery manufacturer brochures, and even government-approved calculation tools. It is not a lie — but it is not true for your house either.
Here's why the number is so high, and why your actual self-consumption will be much lower.
What Self-Consumption Actually Means
Self-consumption is the percentage of solar energy you use in your own home instead of sending it to the grid.
| What happens | Value per kWh |
|---|---|
| You use solar directly | Retail price (€0.10–0.40) — you avoid buying from the grid |
| You export solar | Feed-in tariff (€0.01–0.12) — the grid pays you wholesale |
| You store solar in battery, use later | Retail price minus feed-in tariff (€0.08–0.38) — the "spread" |
Higher self-consumption = better economics. So installers have every incentive to show you the highest possible number.
The Three Reasons Their Number Is Too High
1. They Assume No Heat Pump
This is the biggest one. The MCS UK certification standard MGD 003 — the official guideline British installers use to quote self-consumption — states explicitly:
"Additional self-consumption arising from non-typical domestic loads such as electric space heating, heat pumps, electricity power diverters, electric water heating and electric vehicles is not accounted for in the method."
The UK government HEM-TP-18 methodology derives its self-consumption formula from field data of UK dwellings that all had gas boilers. Heating demand was literally excluded from the dataset.
What this means: The 60–90% figures you see are for households using 3,000–5,000 kWh/year with gas heating. With a heat pump, you're at 8,000–15,000 kWh/year.
| Scenario | Annual Demand | 5 kWp Solar | Demand / Solar Ratio | Self-Consumption (no battery) |
|---|---|---|---|---|
| MCS "typical" home | 3,879 kWh | 4,059 kWh | 0.96 | 29–39% |
| Home with heat pump | 8,500 kWh | 5,000 kWh | 1.70 | 20–25% |
Wait — the MCS table shows 29–39%, but installers claim 60–90%. Where's the gap?
The gap comes from three hidden assumptions that stack on top of each other:
- "Home all day" profile — adds ~15 percentage points vs "away at work"
- Battery — adds another 10–20 points (but only in summer — see below)
- No heat pump — the biggest factor; adding one cuts self-consumption by half
Stack them all and 29% becomes 70% — but only for a very specific type of household: someone with no heat pump, who's home all day, with a battery that cycles every day. Change any one factor and the number drops.
2. They Ignore Winter Reality
In December, a 5 kWp system in Germany produces about 3 kWh/day. A heat pump heating a typical house needs 25–35 kWh/day of thermal output, which means 5–8 kWh/day of electricity at COP 4.6.
The math is brutal:
- Solar peaks at 0.3–0.9 kW in winter midday
- Heat pump runs 1.0–1.5 kW continuously
- Battery has nothing to charge from — every watt of solar goes straight to heating
Our calculator's hourly simulation shows 47 zero-charge days per year for a battery in a heat-pump household. In December, the battery charges an average of 0.06 kWh/day versus 5 kWh/day in May.
Important: the battery boost is seasonal. The "+10–20%" self-consumption improvement from a battery happens almost entirely in March–October. In November–February, the battery has nothing to charge because all solar is consumed at home immediately. See our 8 Battery Myths guide — particularly Myth #7 about batteries and heat pumps.
Most online calculators use monthly averages or simplified formulas that smooth over this winter gap. They assume the battery charges something every day. It doesn't.
See our Solar and Heat Pumps guide for the full winter analysis, including a month-by-month breakdown of a 5 kWp system in Germany.
3. They Use "Home All Day" Occupancy Profiles
The MCS lookup tables have two archetypes: "home all day" and "out half the day." The "home all day" profile gives much higher self-consumption because someone is always there to use solar directly.
But even then, their maximum realistic case is 72% grid independence — not 90% self-sufficiency. And that's for someone with no heat pump who never leaves the house.
Self-Consumption Is Seasonal
A single number like "35% self-consumption" hides enormous seasonal variation. Here's what a 5 kWp system in Germany with a heat pump actually does month by month (from our band-by-band engine):
| Month | Solar Produced | Self-Consumed | Export | Self-Consumption Rate |
|---|---|---|---|---|
| January | 114 kWh | 114 kWh | 0 kWh | 100% |
| April | 470 kWh | 220 kWh | 250 kWh | 47% |
| June | 552 kWh | 154 kWh | 397 kWh | 28% |
| August | 470 kWh | 159 kWh | 311 kWh | 34% |
| December | 90 kWh | 90 kWh | 0 kWh | 100% |
In winter, self-consumption is 100% — every watt is used at home. But there's almost no solar to consume. In summer, self-consumption drops to 28% — the system produces far more than the home can use.
The annual average (45% for this case) is a blend of these extremes. An installer quoting "45% self-consumption" is giving you a useful annual number, but it doesn't tell you that your December bill will be nearly the same as if you had no solar.
The battery paradox: In the months when self-consumption is lowest (May–August, 25–28%), a battery could help significantly. In the months when self-consumption is already 100% (November–February), a battery has nothing to do. This is why battery payback is so sensitive to climate and season — see our Battery Myths guide for the full analysis.
The Carbon Tension
Higher self-consumption sounds better — and financially, it is. But there's an environmental tension:
- Without a battery, excess solar exports to the grid and displaces fossil fuel generation
- With a battery, more solar is stored for later use — but the grid loses that clean energy
- The grid has to generate more power from fossil fuels to compensate
Maximising self-consumption is not the same as minimising carbon. A battery increases your self-consumption but may increase the grid's carbon intensity. The net effect depends on your grid's fuel mix, the battery's efficiency (85–95%), and the carbon cost of manufacturing the battery itself (~650 kg CO₂ for a 10 kWh LFP pack).
The greener choice: Exporting solar to the grid is better for the climate in most cases. A battery only makes environmental sense if it enables you to install more solar capacity than you otherwise could.
See our Environmental Lifecycle Guide for the full carbon analysis, and Myth #3 in our Battery Myths guide for why grid-connected batteries can increase your carbon footprint.
The European Commission JRC study (Quoilin et al., 2016) — the most cited academic paper on residential solar self-consumption — found:
"For an average European household, the self-sufficiency rate without battery varies between 30% and 37%." (Note: Quoilin et al. use "SSR" — self-sufficiency rate, defined as solar consumed on-site divided by total household demand. This is closely related to but not identical to self-consumption rate.) "Self-sufficiency cannot exceed 80% without excessively oversizing the system."
And that was for average households without heat pumps.
A 2023 Barnsley study by the UK National Energy Action monitored actual households with batteries:
"The self-consumption of the solar generation was typically between about 40% and 60% for the households with batteries that were on the heat network."
Only one outlier hit 80%, and that household had unusually high consumption. Most were in the 40–60% range — with batteries, without heat pumps.
What You Should Expect (Annual Averages)
Note: These are annual averages. Your December self-consumption will be higher (near 100%), your June self-consumption lower. See the seasonal table above for the monthly breakdown.
| Your Situation | Realistic Self-Consumption | With Battery |
|---|---|---|
| No heat pump, home all day | 45–60% | 55–70% |
| No heat pump, away at work | 30–45% | 40–55% |
| Heat pump, home all day | 25–40% | 35–50% |
| Heat pump, away at work | 20–30% | 30–40% |
These are our calculator's outputs, validated against hourly simulation. If another calculator shows you 80% for a heat-pump household, it is not modeling your household.
The Honest Test
Ask your installer or calculator:
- "Does your model include a heat pump?" If they say no, their 70% figure is irrelevant to you.
- "What is the hourly solar vs. demand profile for a winter week?" If they show monthly averages, they're hiding the winter gap.
- "What annual electricity demand do you assume?" If it's under 5,000 kWh, they're not modeling a real household with electric heating.
- "What real-world monitoring data backs up your claim?" If they cite the MCS tables, those explicitly exclude heat pumps.
Bottom Line
The 60–90% self-consumption claims are technically correct — for a narrow, unrealistic set of assumptions that exclude the very equipment (heat pumps) driving Europe's electrification.
Self-consumption is not a fixed number. It depends on:
- Your heating system — heat pump vs gas (largest factor)
- Your occupancy — home all day vs away at work
- The season — 100% in December vs 28% in June
- Your battery — helps in summer, does nothing in winter
- Your climate — Southern Europe has better winter self-consumption than the North
Our calculator is lower because it models your actual house: a heat pump running in winter, a battery that often has nothing to charge, and solar production that sometimes can't even cover heating demand.
The numbers are lower because reality is lower. Anyone promising 80% self-consumption for a heat-pump household is either using the wrong model or selling you something.
Want a more accurate number? Use our calculator which runs a 365-day hourly simulation, or see the Solar and Heat Pumps guide for monthly breakdowns by country.
Last updated: May 2026