Solar and Heat Pumps: The Winter Reality

The Question Everyone Asks

"If I install solar panels and a heat pump, will the solar run the heating in winter?"

The honest answer is no. Not even close. But that doesn't mean the combination doesn't make financial sense — it just means the savings come from the other nine months of the year, not December and January.

Source: All numbers from the hourly engine (8,760 timesteps/year). 5 kWp system, 10 MWh heat pump demand, SCOP 4.6. See methodology.

What a December Day Actually Looks Like

Let's start with the single most important number: what happens on a typical December day in Germany with a 5 kWp solar system and a heat pump?

Metric Value
Daylight hours 7.8 hours
Solar production (5 kWp) 2.90 kWh — the entire day
Heat pump electrical demand 14.80 kWh — running 24 hours
Other household consumption 6.85 kWh
Total daily demand 21.65 kWh
Solar covers 2.90 kWh (13.4% of total)
Of which heat pump gets ~2.3 kWh (19.6% of HP needs)
Grid supplies the rest 18.75 kWh (86.6%)

That 2.90 kWh of December solar — it's worth about €1.02 at German electricity prices. But the heat pump burns through €5.18 worth of grid electricity in the same day. Solar isn't "powering" winter heating. It's taking the edge off.

And that's on a sunny December day. On overcast days, production drops to near zero.

Why the Day-Night Cycle Kills Winter Solar

In January, 84% of solar production is concentrated into the midday band (4 hours around noon), because days are short. Meanwhile, a commuter household's consumption is spread across the whole day:

Time Band Solar Production (Jan) Household Consumption Match?
Morning (6-9) 7% 15% ❌ Solar too low
Midday (9-17) 84% 20% Partial match
Evening (17-22) 9% 40% ❌ No solar
Night (22-6) 0% 25% ❌ No solar

Even on a sunny January day, the heat pump runs all night and all morning on grid power. Solar only offsets a fraction of the midday load.

Winter Performance Across Europe

Country Dec Solar (5 kWp) Dec HP Demand Solar Covers Winter Solar Share
Germany 2.90 kWh/day 14.80 kWh/day 19.6% 13% of Dec load
Poland 3.62 kWh/day 14.80 kWh/day 24.5% 17% of Dec load
Hungary 3.23 kWh/day 14.80 kWh/day 21.8% 15% of Dec load
France 4.51 kWh/day 14.80 kWh/day 30.5% 21% of Dec load
Spain 4.71 kWh/day 14.80 kWh/day 31.8% 22% of Dec load
Portugal 5.58 kWh/day 14.80 kWh/day 37.7% 26% of Dec load

The pattern: Even in the best European location (Portugal), a 5 kWp system covers at most 38% of a December day's heat pump electricity — on sunny days. In Germany, it's 20%. Solar does not "power" winter heating anywhere in Europe at standard system sizes.

What About the Full Winter (Nov-Feb)?

Country Solar Produced HP Elec Needed Solar Covers Grid Needed
Germany 507 kWh 1,565 kWh 32.4% 1,880 kWh
Poland 633 kWh 1,565 kWh 40.5% 1,836 kWh
Hungary 564 kWh 1,565 kWh 36.0% 1,872 kWh
France 788 kWh 1,565 kWh 50.4% 1,755 kWh
Spain 823 kWh 1,565 kWh 52.6% 1,737 kWh
Portugal 975 kWh 1,565 kWh 62.3% 1,682 kWh

Over the full 4-month winter, even Portugal only covers 62% of heat pump electricity. Germany covers 32%. The grid supplies the majority of winter heating regardless of where you are.

Where Solar ACTUALLY Saves Money

The month-by-month breakdown for Germany tells the real story:

Month Solar Self Export Import Solar Share Bill
January 114 114 0 554 17% €194
February 172 147 24 384 28% €132
March 335 184 151 291 39% €90
April 470 220 250 157 58% €35
May 531 159 372 53 75% −€11
June 552 154 397 51 75% −€14
July 539 159 380 53 75% −€12
August 470 159 311 53 75% −€6
September 360 132 227 73 64% €7
October 237 136 101 250 35% €80
November 131 131 0 386 25% €135
December 90 90 0 581 13% €203

Notice the negative bills in May–August. That's the solar system exporting surplus at €0.08/kWh. These export revenues are what make the annual economics work.

Season Months Solar of Annual % of Annual Savings
Winter (Nov-Feb) 4 13% 21%
Summer (May-Aug) 4 52% 41%
Spring & Autumn 4 35% 38%

Winter provides only 21% of the annual savings. The other 79% comes from the other two-thirds of the year.

Payback: Winter-Only vs Full Year

What if we lived in perpetual winter? Here's how payback changes:

Country Full Year Payback Winter-Only Payback Difference
Portugal 7.2 years 10.9 years +3.7 years
Germany 8.7 years 13.7 years +5.0 years
Spain 10.1 years 15.4 years +5.3 years
France 12.7 years 18.8 years +6.1 years
Poland 17.5 years 32.0 years +14.5 years
Hungary 16.9 years 23.9 years +7.0 years

Without summer, solar payback in Germany jumps from 8.7 to 13.7 years. In Poland, it goes from 17.5 to 32 years — effectively never.

What This Means for Your Decision

If you're considering solar + heat pump

What you should know The reality
Solar covers winter heating No. 13–26% of December demand, 32–62% over the full winter. The grid supplies the rest.
The heat pump saves money Yes. Heat pumps are 3–5× more efficient than electric resistance, and cheaper than gas in every EU country.
Solar saves money overall Yes. The annual savings come from summer and shoulder seasons, not winter. Payback is 7–17 years depending on country.
Solar reduces winter bills Yes, marginally. A 5 kWp system in Germany saves ~€170 over the 4 winter months. Not nothing, but not transformative.

If you're only interested in winter heating

Solar panels are not the solution. Insulation is. Every kWh of heat you don't need is a kWh you don't have to generate or buy. See our Insulation First guide.

The Honest Bottom Line

A 5 kWp solar system in Germany produces 2.90 kWh on a December day. A heat pump heating a typical home needs 14.80 kWh. Solar covers 20% of the heat pump's daily demand.

That's not "powering winter heating." That's taking the edge off.

But over a full year, the same solar system produces 4,000 kWh — about 85% of what the heat pump needs annually. The mismatch is one of timing, not total quantity. Summer exports fund winter imports. The system works because the grid acts as a free seasonal battery.

If someone tells you their solar panels run their heat pump in winter, they either have a massively oversized system, live in Southern Europe, or are looking at annual averages instead of December reality. The physics doesn't lie: 7.8 hours of weak December sunlight cannot power 24 hours of heating.

The Waste Footprint: What You're Also Buying

Every solar installation creates a future waste liability. Here's what a typical 5 kWp system leaves behind:

Component Weight Material Recyclability
Solar panels (11 panels) 220 kg Glass, aluminum, silicon ~10% formally recycled in EU
Mounting/racking 60 kg Aluminum (rails, clamps) Highly recyclable (~95%)
Cabling (DC + AC) 20 kg Copper with PVC insulation ~50% copper recovery
Inverter (2 units over 25yr) 30 kg Electronics, aluminum, copper ~30% formally recycled
Battery (if 10 kWh) 120 kg LFP cells, steel, BMS ~50% recycled (loss-making)
Total without battery ~330 kg — —
Total with 10 kWh battery ~450 kg — —

Per €1,000 of annual savings: A 5 kWp system in Germany saves ~€802/yr and generates ~330 kg of waste → 411 kg of waste per €1,000 annual savings.

Per kWp: ~66 kg of hardware ends up on your roof for every kWp installed. After 25 years, every kilogram needs to go somewhere — landfill, recycling, or export. The cost of dealing with it (€300–500 for a 5 kWp system in present value) is rarely included in installer quotes.

See our Lifecycle Calculator for a full breakdown of your specific system. And the Environmental Lifecycle Guide for the complete carbon and waste analysis.

Last updated: May 2026