Solar Self-Sufficiency Is Feasible, Even in Moderate?Climates

Solar self-sufficiency for modern single-family homes is feasible, even with electric cars in moderate climates such as Switzerland

Why Bother With Self-Sufficiency?

In 2021, Switzerland consumed 58 billion kWh of electricity, of which 33% were consumed in private households, and 8% for transportation (mainly railways). Whilst tackling climate change and renewable energy supply won’t work in one big step, it seems worthwhile to address a sector that’s responsible for a third of the entire electricity consumption?—?private households.

While renewable energy can also be produced centrally using dams, large-scale solar installations, or wind farms, decentralized production of renewable energy has the additional advantage of insuring against power outages. More and more, these occur during heat waves when electricity demands for air conditioning surge?—?even in “cold” places like Switzerland.

In this article, I will take you through the solar power setup I am using in my own house?—?well knowing that my house won’t save the world, but it could nevertheless serve as a demonstrator for further developments.

The Setup

We built our home on the green field back in 2012, paying close attention to energy efficiency. The house has a Drexel+Weiss Aerosmart X2 combined heating/ventilation system with a ground heat pump since the first day, which has helped us keep energy consumption for heating very low (when running on full power on a cold winter day, the consumption of the heating system is around 1.2 kW).

After living in the house for some years and learning about our energy consumption, we added the following systems step-by-step:

• 8 kWp east-west solar panels on the carport
• 14 kWp east-west solar panels on the house
• 12 kWh Fronius Solar Battery
• 2 Tesla Model 3 with a 75 kWh battery each

A Loxone building control system is controlling the large power consumers (cars, washing machine, heating), taking into account solar power availability, charging levels of the batteries, and the seasons.

Self-Sufficiency over the?Year

So, what self-sufficiency levels did we reach since 2017 with the installation mentioned above? First of all, let’s look at the annual consumption values:

Average self-sufficiency levels over the years have been above 70% for the whole year?—?this is with two electric cars!

Drilling down to the months (I am using 2020 as an example), self-sufficiency is pretty much 100% between mid-February and mid-October. We have seen quite some variations in the second half of February and the first half of October?—?the weather in these periods can be anything from foggy all day to bright sunshine all day.

The period of mid-October to mid-February typically yields 20–30% self-sufficiency only?—?again, self-sufficiency levels vary greatly based on weather and temperature.

Self-sufficiency is only half the equation. When we have around 8 months in the year with around 100% self-sufficiency, then there must be some surplus energy production in the summer months. Again using 2020 as an example, the energy surplus is depicted in grey in the below graphic:

In Switzerland, surplus energy can be fed back into the grid and sold to the local utility company. Balancing of supply and demand occurs through our many pumped storage plants in the mountains, such as the Limmern pumped storage plant.

The Role of The Building Control?System

The on-demand society has forgotten how to hold back their needs even for only a few hours. This is exactly what can be done with a building control system.

Given the patterns of usage, the charge state of all the batteries, and the current solar production, you can switch on and off large consumers such as cars, washing machine, or the heating/ventilation system without the loss of any comfort.

Of course, fine-tuning the building control system takes some time to learn about your habits, and the burning desire to optimize energy consumption all the time.

To illustrate this, below is a sample production chart of an autumn day (September 30, 2021):

The building control system automatically stopped the charging of the cars, to charge the battery in the house. In this way, there was enough energy available throughout the night for all other consumers in the house.

Recent Improvements

Just like the building control system needs constant improvement, so does the entire energy setup of a single-family home.

In late 2021, we exchanged our Tesla Model X and S for two Model 3, with one of the main reasons being energy efficiency. Whilst reducing the battery capacity from 90 kWh to 75 kWh, ranges increased from almost 400 km to almost 500 km. This translates into an efficiency improvement of around 30–35% for our EV mobility.

More important, it reduced electricity consumption in Q1/2022 by roughly 400 kWh against electricity consumption in Q1/2022, translating into an increase in Q1 self-sufficiency from 51% to 66%.

Future Improvements

The dark and windy winter months we typically see in Switzerland don’t help solar self-sufficiency. Also, snow on the solar panels doesn’t boost solar power production.

Here is what I intend to do to further increase winter self-sufficiency:

• This fall, I will get the vertical panels lining parts of the facade. Installing an additional 4.9 kWp will yield an additional 2'500 kWh per year?—?also in winter when the sun is flat and the roof is covered in snow. Using historic data since 2017 as well as an accurate solar calculator predict that the vertical panels will increase overall self-sufficiency from 70% to 80% throughout the year.
• Wind power generally complements solar power. A small commercial-off-the-shelf wind turbine for use in residential areas yields around 1 kW?—?together with the solar panels and the house battery, this would be enough to power our heating system. Unfortunately, communal politics have prevented us from installing a couple of such turbines for the time being.

As mentioned in the beginning, I don’t think that our installation will save the world, but it could catalyze further developments:

• Running a brand-new house on very little energy is feasible with today’s building technologies. However, retrofitting older houses with solar installations will require significantly larger installations to achieve the same self-sufficiency levels as we do. Again, communal and national politics need to come up with sensible regulations to modernize older houses in terms of insulation and heating systems. If this can be done, the setup I have described in this article can also be transferred to older houses with the same results.
• Making a single-family home self-sufficient is only the first step. More and more people live in large compounds, and it makes a difference if you need to charge 2 or 200 electric cars on solar power. To catch the surplus energy in the summer months at a large scale and use it to charge large numbers of cars at night or power entire suburbs through the winter, seasonal storage is required. The efficiency of such storage systems is still very limited?—?for example, hydrogen catalysis and fuel cells still have a very low round-trip efficiency of around 25%. Efficiencies and costs typically improve when the scale of an installation is increased, which is why seasonal storage should rather be implemented on a communal than on a private level.

Last but not least?—?I hope you noticed that I am an engineer. I burn for creating and improving solutions, thereby contributing to solving the large problems in this world. Let’s train more engineers and scientists in the future, they are enablers for future technology breakthroughs!

Further Reading

Solar Self-Sufficiency: Optimizing Winter Car Charging Patterns for Geopolitics

Solar Self-Sufficiency: The Dollars Behind

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