One Year in a Passivhaus Plus Home: 11,929 kWh Generated and €332 in Energy Bills
First-year measured data from Can Naiades, a Passivhaus Plus home near Barcelona: 11,929 kWh generated, 85% self-sufficient, €332 of electricity bills.
One Year in a Passivhaus Plus Home: 11,929 kWh Generated and €332 in Energy Bills
I’ve learnt that the first few months after moving into a house you have built yourself are probably more stressful than the whole construction process. There are bills still to pay and no money in the account. Your business has suffered because you gave so much of your time to the project. Aches and pains surface in odd parts of your body from too many hours hunched over a cost-control spreadsheet.
And then there is a point where you close the spreadsheet, decide never to open it again, and actually begin enjoying the wonders of living in a decent house — one that is genuinely comfortable, has great air quality, and is remarkably cheap to run.
That was a year ago. We now have twelve full months of measured data from Can Naiades, our certified Passivhaus Plus home in Sant Julià d’Alfou, 40 km north-east of Barcelona. This is what the first year in a Passivhaus Plus home actually looks like, in kilowatt hours and in euros.
A quick recap of the house
Can Naiades is a two-storey, four-bedroom family home of 127 m² treated floor area, built on a prefabricated lightweight timber frame. The envelope is insulated with recycled glass wool — 250 mm in the walls and 350 mm in the roof — with triple-glazed timber-aluminium windows at Uw 0.81 W/(m²K) as installed, and an airtightness of 0.44 air changes per hour at 50 Pa. Every window has an external venetian blind. If you want the full build story, we set it out in the fifteen steps we took towards a comfortable, healthy, resilient and efficient home.
There is no conventional central heating system. A heat pump with a single ducted split unit, sized for the cooling load, also provides occasional heating; the rest is handled by small towel radiators in the bathrooms and an underfloor loop in the ground-floor bathroom. Fresh air comes from a balanced mechanical ventilation unit with heat and moisture recovery, running continuously. On the roof sit 21 photovoltaic panels totalling 8.5 kWp, paired with a 13.8 kWh battery.
Here is the finished house in a minute, before we get to the numbers.
How we calibrated the PHPP model
Comparing measured data against a design model is only meaningful if the model has been told the truth about the year that actually happened. So before making any comparison, we calibrated the PHPP certification model in two ways.
First, we replaced the standard climate data set with outdoor air temperature and relative humidity recorded at a local meteorological station over the monitoring period. Second, we adjusted the occupancy assumptions to match the household as it really is — three adults and two young children — rather than the standard occupancy the certification method assumes.
That matters. Without those two corrections you are comparing a real house in a real year against a generic house in an average year, and any agreement — or disagreement — between the two tells you very little.
What the house generated, and what it used
Over the twelve months from 1 September 2025 to 31 August 2026, the photovoltaic array generated 11,929 kWh. Total consumption across the same period was 7,835 kWh, of which 898 kWh went into charging a plug-in hybrid car — roughly 4,000 km of electric running. Strip the car out and the house itself used 6,937 kWh.
So the house generated 52% more electricity than everything in it consumed, car included. Against the building alone, generation was 72% higher than consumption.
The agreement with the calibrated model is the part we find most satisfying. PHPP predicted 11,139 kWh of generation; the array delivered 11,929 kWh, 7% ahead. PHPP predicted 7,052 kWh of household consumption; the meters recorded 6,937 kWh, 1.6% below. For a whole-building energy model to land within a couple of per cent of reality over a full year is about as good as this work gets.
Of the 11,929 kWh generated, 6,697 kWh was used directly in the house — a self-consumption rate of 56%, helped considerably by the battery. The remaining 4,964 kWh went to the grid. Over the year the house drew just 1,149 kWh back from the grid, which means 85% of everything it consumed was covered on site, and it exported 3,815 kWh more than it imported. Averaged out, that is 32.7 kWh generated and 21.5 kWh consumed per day, with only 3.1 kWh a day coming off the grid.
Consumption, month by month
The annual totals agree almost exactly, but the monthly pattern varies. From December to May the house used more than the model predicted, most noticeably in January at around 30% above. From June to September the reverse held, with measured consumption comfortably below the model — particularly in July and August, where PHPP expected over a megawatt hour a month and the house used considerably less. Our first summer article covers how the house is kept cool: the blinds, natural night ventilation where possible, and a small amount of active cooling from the single split unit.
So PHPP overestimated our summer cooling energy and underestimated our winter and shoulder-season electricity use, and the two discrepancies very nearly cancel out across the year. That is consistent with the caveats in EN ISO 13790 — since superseded by EN ISO 52016 — on which PHPP’s monthly energy demand calculations are based: the monthly method is reliable for the annual total but not necessarily for individual months, and relative errors can be large at the start and end of the heating or cooling season.
Solar generation, month by month
The array beat the model in nine months out of twelve, with the largest gains in April and June. Three came in below prediction: January and December, both marginal, and September, where measured output of 650 kWh fell well short of the 990 kWh predicted. September stands out against every other month, explained by cloudier weather than usual and less solar radiation.
The energy bills
Across twelve months the total electricity bill for the house came to €332 — an average of €28 a month. That is the whole bill: heating, cooling, hot water, ventilation, lighting, appliances and PHEV car charging, for a household of three adults and two young children.
The shape of it matters as much as the total. June, July and August cost nothing at all, because generation and export credits covered everything the house drew. April and May came in at €2 and €1. The bills only become visible in the depths of winter, peaking at €95 in January and €94 in December, when generation falls to roughly a third of its summer level and the house draws more from the grid. Even then, a €95 winter electricity bill for an all-electric four-bedroom house is not a number most people are used to seeing.
What a year of living here has taught us
Three things stand out.
The first is that a well-calibrated model is worth the effort. Landing within 2% on consumption over a full year is not luck; it is what happens when the climate data and the occupancy reflect reality. It also means we can now trust the model when it tells us something about a future year, or about a design change we are considering.
The second is that the building fabric does the heavy lifting, and the systems stay small. There is no boiler and no combustion anywhere in the house. There is one split unit, a couple of towel rails, and a ventilation unit that runs quietly in the background — and how the ventilation unit has actually performed is a story in its own right. The comfort does not come from the kit; it comes from insulation, airtightness, glazing and shading getting the conditions close to right before any system is asked to do anything.
The third is that the numbers only tell part of it. Stable temperatures, no draughts, no radiators taking up wall space, quiet rooms and air that stays fresh are things you notice daily and stop being able to measure. We wrote about that in more detail after our first winter.
The short version
- 11,929 kWh generated over the year, against 7,835 kWh consumed including PHEV charging — 52% more produced than used
- 85% of all consumption covered on site by solar PV and battery storage, with just 1,149 kWh drawn from the grid
- 3,815 kWh net exported to the grid
- €332 of electricity for the whole year, averaging €28 a month, with three months at zero
- Measured consumption within 1.6% of the calibrated PHPP prediction, and generation 7% ahead of it
A Passivhaus Plus home is not a theoretical proposition. This one has now run for a year, and the meters agree with the design.
Can Naiades is certified Passivhaus Plus and Near Zero CO₂. Praxis Resilient Buildings delivered the Passivhaus design, site supervision, preliminary Blower Door testing, thermal bridge calculations, dynamic hygrothermal modelling with WUFI and the HVAC system design.
