Building a self-sufficient home with Tesla batteries

A few days ago, several members of the Slow Studio team watched Leonardo DiCaprio and National Geographic’s documentary on climate change, Before the flood.

It is a highly recommendable documentary for all those who have a certain concern for an ecological and sustainable lifestyle and who think that change is truly possible and that we all have our part of responsibility in it.

Although at times it is discouraging and you feel that it is very difficult for us to get out of this, there is a positive background or intention to motivate change, and among other stories of change promoters, DiCaprio visits Elon Musk, co-founder and main public face of Tesla Motors.

Tesla is a pioneering company in the manufacturing of electric cars that is also positioning itself in the domestic battery sector and aims to revolutionize the way we produce and consume energy.

DiCaprio’s visit to the first Tesla mega-factory and the interview with its founder Elon Musk did not leave us indifferent; as an architect, you truly believe this is a full-fledged revolution.

And the thing is, if you could understand how frustrated we feel about the approval of laws in our country that penalize self-consumption, specifically the controversial Sun Tax that penalizes domestic photovoltaic energy generation installations to the point that the profitability of installing them in a private home is questioned, you would get an idea of the hopes we have in this type of domestic energy storage systems.

But why is it so important to be able to store electrical energy?

Precisely for that reason, because until today it has not been possible on a domestic scale to store energy at an affordable cost for a standard family. If we could store the energy we produce with photovoltaic panels, we could consume it when we need it, that is, when we arrive home at night, when there is no longer sun.

This would make us truly self-sufficient, in the sense that we could live on the energy that the sun sends us.

Today, at the moment we generate energy (during the day), we are usually out of the house working and therefore we must feed it into the electrical grid, and at night when we come home and want to take a shower, cook, and watch TV is when our panels do not generate energy and then we must consume electricity from the grid. Until a few years ago, this system was subsidized and the electricity companies had to pay you as a producer for feeding energy in.

Well, with the approval of the Sun Tax, not only do they not pay us for the energy fed into the grid, but to be fair and supportive we must pay for using the grid for every kW we feed in, in addition to paying a fixed fee as an energy factory.

Storing solar energy in a battery

The sun is the quintessential renewable and free source. In terms of power, the sun sends us in just 14.5 seconds the same energy that the human species consumes on Earth in a year.

For this reason, today we want to leap into the future and explain to you what a self-sufficient home with Tesla batteries will be like.

Although Tesla is a brand and we could simply talk about batteries—and we promise you that Tesla does not sponsor this article—it is true that the investment and firm commitment of this particular company to self-consumption in homes through domestic batteries have made it the best positioned worldwide at this moment to make energy storage viable at the domestic level at a price affordable for the vast majority of people.

For this reason, we declare ourselves absolute fans of Tesla, and although it is not our usual practice, we are writing a post mentioning specific brands and systems.

How does a home with Tesla batteries work?

At the domestic level, there are basically two ways to obtain electricity effectively. The first is through wind turbines—which work with the wind—and the second is with photovoltaic panels—which generate electricity from solar radiation.

Each system has its advantages and disadvantages, and it will be necessary to evaluate which system is more efficient in each particular case.

Wind turbines

A wind turbine is an electrical device with a turbine that converts the kinetic energy of the wind—the energy of motion—into electrical energy.

Simply explained, a wind turbine consists of one or more small-scale windmills that can be installed in a home and that automatically orient themselves based on a built-in weather vane. In addition, they have a safety system to prevent damage.

A Bornay wind turbine, for example, starts operating from a wind speed of 3.5 meters per second –12.6 km/h-. With strong winds exceeding 14 m/s, the blades change their position and the turbine brakes to avoid excessive stress.

Photovoltaic panels

Photovoltaic panels are the most commonly used system for generating electricity and also the most suitable for building a self-sufficient home with Tesla batteries.

First of all, it is important to remember that photovoltaic panels should not be confused with solar thermal panels. The latter are surely the most common, but they do not generate electricity, but rather hot water. This water is stored in tanks or used directly for DHW—domestic hot water—or for heating systems such as underfloor heating.

Photovoltaic panels, on the other hand, are capable of generating an electric current from the solar rays that reach them. Of course, the number of panels, their position, and their orientation will have great importance in their efficiency.

With photovoltaic panels we can also store energy in water. Although it is a little-used system, it can be useful when the demand for electrical energy is not very high. In this case, the electricity captured by the panels is sent directly to a heat pump or an aerothermal machine that heats the water.

How do photovoltaic panels work?

The operation of photovoltaic panels is based on the conversion of solar radiation into electrical energy.

The panels are made up of one or more sheets of a semiconductor material that is coated with glass to reduce heat loss.

Most cells are silicon and have efficiencies between 14% and 17%. There are also cheaper ‘second-generation cells’ but with lower efficiencies from 10% to 12%, and recently work is being done on systems with efficiencies between 25% and 30% but still at quite high prices.

Sunlight is composed of photons—a particle present in all radiations—that strike the photovoltaic cells of the panels. When this happens, the photons interact with the electrons in the panels, and in this way the electrons are released and circulate through the material. This movement is what generates electrical energy.

The more intense the light, the greater the amount of electricity generated. Furthermore, direct radiation is not necessary, since on cloudy days the panels also work.

The Sun Tax

In 2015, the Government of Spain approved the “Sun Law”. It establishes that those homes with photovoltaic panels that are connected to the grid must pay a tax based on the kilowatts they generate.

Specifically, the Government established that one would have to pay 9 euros per year per kW of generated power plus a variable amount based on the energy fed into or consumed from the electrical grid, to which we must be connected if we do not have an energy storage system via batteries to cover demand during the hours when we do not have sun, that is, during the night.

According to the executive that approved the law, it is a solidarity toll for using energy from the grid at times when the panels do not generate energy, and since we are using the electrical grid, we must contribute to its maintenance.

However, the surplus energy generated in a home is fed into the general grid for free, without the producer receiving anything in return for it.

In this way, a home with photovoltaic panels connected to the grid must pay for the energy it consumes from the electricity companies, plus the sun tax, but receives nothing for the electricity it feeds into the grid, as was the case before the approval of the Sun Tax.

Due to the controversy generated by this tax, there is now a proposal in parliament to repeal this law and not harm homes that want to generate their own energy, although it remains to be seen whether it will ultimately go ahead in the short term since not all opposition parties are united; as always in political matters, common sense and the common good do not usually prevail, but rather the particular interests of each political party and internal pacts to gain more or less support.

In any case, European directives are heading in the completely opposite direction to the Spanish Government, and let’s hope it is not many years before the European authorities start to raise objections, if not fines and penalties, to Spanish regulations regarding self-consumption and production of clean and free energy such as solar energy.

Now, what does all this have to do with building a self-sufficient home with Tesla batteries?

Well, it must be remembered that the sun tax applies whenever electricity is fed into the grid. If we want to build a self-sufficient home with Tesla batteries, we can completely disconnect from the general grid and be self-sufficient, and in this sense, we will be exempt from paying this tax.

Storing energy with batteries

When building a self-sufficient home with Tesla batteries, storing energy will be the second step to achieving self-sufficiency.

The number of batteries needed in a home depends on the size and energy needs of the dwelling. In most homes, one or two batteries are enough to supply the entire house.

There are several companies that manufacture domestic batteries, among them, Tesla, Nissan, and Solar Rocket are some of the pioneering brands in the sector.

In this sense, today’s article is focused on Tesla batteries, and although we are not in favor of mentioning commercial brands in our posts, the reality is that Tesla is stepping up and positioning itself as a leading company in the sustainable revolution with the introduction of electric vehicles and batteries at affordable prices for the standard consumer.

For this reason, we bet on this company and dedicate a post to tell you how homes with this type of batteries will work, which, if nothing new arises, will arrive in Europe during this same year.

A home with Tesla batteries

Although Tesla batteries can be applied to different systems, even from non-renewable energy sources, they are designed to work together with a photovoltaic panel installation.
Tesla’s idea is that its battery becomes just another appliance in the home, but instead of washing dishes or keeping food cold, it stores the energy we generate.

The Tesla Powerwall 2 battery

Powerwall 2 is the latest battery model that Tesla plans to bring to market, and the first units are expected to arrive in Europe by the end of the year.

The Powerball 2 battery can store twice the energy as the first model Powerball 1 and can power a two-bedroom home for an entire day. It is a compact, stackable battery with a built-in inverter, a feature we will explain later.

Specifically, it measures 77.5 cm wide, 115 cm high, and 15.5 cm thick, dimensions that allow it to be installed hanging on a wall.

The Powerwall 2 is designed to connect with photovoltaic solar panels and allows using this energy and storing the surplus so that it can be consumed during the night, when we have no possibility of generating energy and precisely when we need it most, which is when we get home and want to turn on the lights, cook, or turn on the television.

Installation

Installing a Tesla battery is simple due to its dimensions. It can be placed both indoors and outdoors and requires no maintenance. Additionally, it works with a fully automatic system that can be controlled from a computer or a smartphone.

Economic savings

Of course, when installing photovoltaic panels, one must evaluate the economic and energy savings they would entail.

Perhaps it is best to evaluate it through a real example, published a few days ago in Ecohabitar Magazine.

Let’s take an average single-family home with 3 bedrooms and 100 m² that consumes 3,000 kWh each year, so an installation of 2 kW is recommended; this has an approximate cost of 7,000–8,000 euros depending on the area and the company we consider.

This type of installation represents an approximate saving of between 25% and 30% on the electricity bill. In the case that we do not have batteries in which to store the energy surplus, 60% of the energy that our panels produce is fed into the grid for free, according to current law.

However, it is possible to build a self-sufficient home with batteries and store this unused energy. This makes it possible to live without being connected to the electrical grid, so that in the same home the energy that we will later consume during the night is generated and stored.

In this case, the installation of an energy production and battery storage system is around 12,000–14,000 euros. With this type of installation, however, we manage to save around 95% of the energy –and economic– expenditure of a home.

The total cost of the installation can be amortized over approximately 10 years, and if we consider that the minimum useful life of photovoltaic panels is estimated at around 30 years, that results in 20 years in which we will not spend a single cent on electrical energy.

Building a self-sufficient home with batteries is possible today. There already exist in Spain self-sufficient homes that are not connected to any grid, water, electricity, or gas, that do not have to pay bills.