The Nurgakivi story of a Pärnu home

More solar panels are not always better.

Solar panel sales tend to focus on big numbers. More panels, more kilowatts, higher output, a bigger battery. When the number is bigger, the solution can easily seem automatically better.

Then comes the talk about buying and selling electricity at the right time, arbitrage, flexibility markets, energy balancing and opportunities to make money on the energy market. Sometimes it can even sound as if all you need to do is install solar panels — or simply buy a battery system — and from then on, the system will start making money for you.

All of this is technically possible. But for most homeowners, it is not really the most important question.

After all, you do not build a home to become an electricity trader or to influence the energy market.

In much the same way, an ordinary homeowner with a greenhouse in the garden does not grow cucumbers and tomatoes to influence their price at the local market — let alone the global vegetable market. Most people grow and preserve cucumbers and tomatoes so that their own family can enjoy them.

The same logic applies to home energy.

The question should not be how to influence the electricity market with a small residential solar system, but how to cover as much of your home’s energy demand as possible, make that demand more stable, and keep your energy costs under control.

A home is meant to be a good place to live.

Every home uses energy — for lighting, household appliances, hot water, heating, and increasingly for cooling or charging an electric car.

How much electricity a home needs depends on its size, heated floor area, the number of people living there, and the technical systems operating in the building. In the Estonian climate, the heating system plays a particularly important role. Ventilation, cooling, a sauna, swimming pool, electric car, or other major energy consumers can also significantly increase a home’s energy demand.

That is why, for this Pärnu home, the most important question was not:
“How much money can we make from the electricity market with our roof?”

A much more practical question was:
“How much of our home’s electricity can we produce ourselves, and how much less electricity will we need to buy as a result?”

That distinction matters.

The electricity market price is only one part of what a homeowner ultimately pays. Getting electricity to your home also involves grid charges, taxes, and other fees. Even when the market price falls to zero or becomes negative for a few hours, that does not mean the electricity delivered to your home is free.

This is why electricity produced and consumed directly at home is particularly valuable to a homeowner. The best kilowatt-hour is not necessarily the one you manage to sell back to the grid at the highest price.

Quite often, the most valuable kilowatt-hour is simply the one you do not have to buy from the grid.

What is baseload, and why is it worth understanding?

Every home uses electricity even when no one is cooking, heating the sauna, or charging an electric car.

This is known as baseload. Baseload comes from appliances and systems that operate continuously or for a large part of the day: refrigerators, ventilation systems, circulation pumps, pool equipment, network devices, security systems, and other equipment.

For example, a building might have a baseload of around 0.75 kW. At first, 0.75 kW does not sound like a particularly large number. But if that load is present around the clock, it adds up to approximately 18 kWh of electricity per day. Over a full year, that is already around 6,700 kWh.

If a home is continuously consuming 500, 700, or 1,000 watts, it is worth understanding what is using that electricity. There may be perfectly good reasons for it. The ventilation system needs to run. The refrigerator needs to stay cold. The pool pump needs to keep the water circulating.

But if there is an old pump running somewhere, unnecessary circulation, or equipment that does not actually need to operate all the time, the cheapest energy saving may be found right there.

For example, if a home’s continuous load were reduced from 0.75 kW to 0.50 kW, annual electricity consumption would fall by approximately 2,200 kWh. No additional solar panels on the roof and no larger battery in the garage would be needed.

Sometimes the cheapest kilowatt-hour is simply the one you do not need to use.

At the same time, the relatively high baseload of this home is also very good news for the solar roof. When the sun is producing electricity around midday, there is almost always something in the home ready to use that energy.

Can electricity really be free?

Energy market news often talks about hours when Nord Pool electricity prices are extremely low, zero, or even negative. At first glance, this can create the impression that electricity from the grid is free during those hours — or that you are even being paid to use it.

For a homeowner, it does not quite work like that.

The electricity market price is only one part of the final electricity bill. As the chart below shows, the cost of the electricity itself makes up only part of the total. The rest comes from grid transmission charges, fixed fees, taxes, excise duties, and other related costs.

That means that even if the Nord Pool market price is €0/MWh during a sunny hour, the electricity you take from the grid is still not free. You still pay for getting that electricity delivered to your home.

The same applies when the market price is negative. A negative wholesale price does not automatically mean that your total electricity bill becomes negative. Grid fees, taxes, and other charges still remain.

In simple terms: a zero market price does not mean free electricity at home.

And that is exactly why electricity produced on your own roof and used directly on site can be so valuable. If you generate the electricity yourself and use it in the same building, you do not need to buy that kilowatt-hour from the grid or pay to have it delivered to your home.

The cheapest electricity is not always the electricity with a zero market price. Often, the most valuable electricity is the electricity you produce yourself and use directly.

A roof can do more.

Every building needs a roof anyway.

When building a new home, a roof has to be built. When renovating an existing home, the old roof will eventually need to be replaced. If that investment has to be made anyway, why should the new roof spend the next few decades doing nothing more than protecting the house from rain, snow, and wind?

With a SOLARSTONE solar roof, an additional layer of conventional solar panels is not installed on top of the finished roofing material. Instead, the solar energy solution is integrated into the roof itself.

The roof protects the home from the elements while also generating electricity that the household uses every day.

This also changes the way we should think about payback. With a conventional roof, we do not usually ask: “When will the roof pay for itself?”

Likewise, we do not judge a new heating system only by how many years it takes to recover every additional euro invested. A new heating system may be quieter, smarter, more efficient, and more comfortable — it is simply part of how a modern home works.

So, with a solar roof, a more useful question is:
“How much greater is the investment compared with a conventional roof, and what will that additional investment do to my home’s energy costs over the coming years?”

And that brings us to the real numbers from the Pärnu home.

A real home. Real bills. Real production & consumption.

For the Pärnu home featured on Nurgakivi, we did not base our analysis on a record-breaking day of solar production in July or the most impressive graph displayed in a smartphone app.

We looked at a much longer period.

The analysis covers 19 months, from 1 January 2025 to 31 July 2026. It includes 19 electricity bills from Alexela/Elektrilevi, approximately 52,000 electricity meter readings, data from the solar roof and battery system, as well as Nord Pool’s 15-minute electricity prices.

Together, this gives us a very good picture of what a solar roof can achieve in Estonian conditions — and what it cannot.

The simplest way to assess the impact of the solar roof is to look at what ultimately matters most to the homeowner:

how much they actually paid for electricity, and how much they would likely have paid without the solar roof.

Over the 19-month period analysed, the owners of the Pärnu home paid approximately €4,891 for electricity. According to the model, the same property, with the same energy consumption and the same electricity prices, would have cost approximately €10,293 without the solar solution.

That is a difference of approximately €5,402, or 52%.

This does not mean that every Estonian home would automatically save €5,000 with a 25 kWp solar roof.

This Pärnu home is not an average Estonian home. In addition to the main house, electricity is used by an outbuilding, an outdoor swimming pool and hot tub, as well as for hot water, heating, and cooling. As a result, the energy demand of the entire property is significantly higher than that of a typical detached home.

But that is exactly what makes this example so useful. When a home genuinely needs a lot of energy, it becomes much easier to see whether the solar electricity being produced can actually be used on site.

In spring and summer, the home needs very little electricity from the grid.

The impact of the solar roof is easiest to see in spring and summer. In April 2026, for example, the home bought an average of only around 10 kWh of electricity per day from the grid. In May, it bought just 143 kWh from the grid for the entire month, resulting in an electricity bill of approximately €43.

This does not mean that the home suddenly stopped using energy in May. The swimming pool is running. The ventilation system is running. Hot water is being produced. Household appliances are being used. The sauna is still enjoyed.

It simply means that during this period, a large share of the electricity the home needs is produced by its own roof, with some of that energy also passing through the battery.

The same pattern can be seen across the year: as solar roof production increases, the amount of electricity that needs to be purchased from the grid decreases.

You cannot eliminate the Estonian winter.

This brings us to the most important reality check in the entire story.

The problem with a solar roof is not that it suddenly stops working in January. The problem is that in Estonia, January is January — there is little sunlight and snow can cover the roof. At the same time, the home needs the most energy. Heating demand increases, it is cold outside, and the days are short.

The solar roof still does exactly what it is supposed to do in winter: it produces electricity whenever the sun shines. But even the best solar roof cannot make the sun shine seven hours longer in January.

The numbers from this Pärnu home illustrate this very clearly. In December, January, and February, the property bought a total of 14,607 kWh of electricity from the grid, costing approximately €2,769. Those three months alone accounted for 57% of the total electricity cost over the entire 19-month period.

The contrast with summer is striking. In May 2026, the total electricity bill was approximately €43. In January 2026, it was nearly €799.

Same home. Same solar roof. Same battery. What changes most are two things: how much sunlight is available and how much energy the home needs at the same time.

Why does winter energy consumption increase so much?

The metering data helps us understand this a little better.

While the home’s typical baseload is approximately 0.75 kW, during the night-time hours in January and February, the continuous load rises to around 3.5 kW. This means that during the colder months, roughly 2.7 kW of additional continuous load is added on top of the home’s normal consumption, most likely related to heating and other systems operating during cold weather.

Again, 2.7 kW does not sound like an enormous number. But if that additional load runs around the clock, it adds up to approximately 65 kWh of extra electricity consumption every day. This makes it easier to understand how electricity consumption during a cold January can reach nearly 4,000 kWh in a single month.

And that is important, because it leads us to the next question.

Couldn’t we simply add more solar panels?

At first, that seems logical. If there is not enough electricity in January, we clear the snow from the roof and add more panels. But additional solar production does not appear only in January. More panels produce most of their additional energy when there is already more sunlight — in spring and summer.

According to the analysis, this home’s 25 kWp solar roof could produce approximately 23,900 kWh of electricity per year. The property’s adjusted annual energy consumption is around 31,600 kWh. This means that the roof’s annual production corresponds to approximately 76% of the home’s annual energy demand, while around 67% of the electricity produced is used on site.

That already represents a solution that is well matched to the needs of this property. Adding even more panels would generate most of the additional electricity at times when the home already has sufficient energy. It would not solve the winter problem to the same extent.

This brings us back to the point made at the beginning of the article:
a bigger number does not automatically mean a better solution.

A good energy solution needs to balance three things:
how much energy the home needs, when it needs it, and when the roof is able to produce that energy.

What does a 40 kWh battery actually do?

A 40 kWh battery system was added to this home in 2025.

There is one very simple thing worth remembering about batteries: a battery does not produce electricity.

It can only change when electricity is used. When energy is plentiful or cheaper to buy, the battery can store it. Later, when the home needs electricity, that stored energy can be used.

The data from the Pärnu home shows that in February and March 2026, a large share of the electricity purchased from the grid was concentrated in the night-time hours, while during the day, grid consumption sometimes fell almost to zero.

In simple terms, the battery helps shift the home’s energy use from one time to another. It is a little like storing water in a tank. The tank does not create more water, but it allows you to use the water later, when you need it.

The principle is the same with a battery.

Why does it make sense to use your own solar electricity?

Over the 19-month period, the property exported 12,363 kWh of electricity to the grid. The total net revenue from that electricity was only around €270.

That number tells us quite a lot. If the same energy can instead be used on site — for example, to heat water, heat the swimming pool, power the home, or charge the battery — its value to the homeowner can be significantly greater than simply selling it back to the grid.

This does not mean that exporting electricity to the grid is a bad thing. When there is surplus energy, it is perfectly natural for it to flow into the grid. But the goal when designing a solar roof for a private home should not be to maximise its ability to export electricity.

The goal should be for as much as possible of the energy the home needs anyway to come from its own roof.

Just like in our greenhouse example. If the family eats its own cucumbers and tomatoes, there is no need to worry about whether the price of cucumbers at the market went up or down today.

What does this Pärnu home actually teach us?

This home does not prove that every Estonian household needs a 25 kWp solar roof or a 40 kWh battery.

Quite the opposite.

It shows why every solution should be designed around the specific home. This Pärnu property has high energy demand, which is why a large solar roof makes sense here. A significant share of the electricity produced is consumed on site, and from spring through autumn, the amount of electricity that needs to be purchased from the grid can become very small.

In winter, however, the picture changes.

The main question is no longer how to fit even more generation capacity onto the roof. What becomes more important is what is consuming energy in the home, how efficient those systems are, and how the available energy can be managed more effectively.

That is the main conclusion of the entire story:
a solar roof should not be designed to be as large as possible. It should be designed to match the specific home as well as possible.

And finally, back to the roof

We started with a simple idea: every home needs a roof anyway.

The 19 months of data from the Pärnu home show what happens when that same roof takes on another job. It protects the home from rain, snow, and wind — while also generating the electricity the household needs every day.

So the question is not simply when a solar roof will “pay for itself”.

A much better question is:
If I need to build a roof anyway, what else could that roof do for my family over the next few decades?

The roof you build today must work for tomorrow.
ROOF. DESIGN. POWER.