DIY solar for an apartment building.

Till Follow 02 Jan 2024
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A few months ago, we published the first part of an article on solar in apartment buildings (condominiums). The first part explained the basics of solar projects and possible implementation options using the example of a project in my own house. At the time, we were faced with a choice between the following types of providers:

  1. large companies (e.g. Swiss market leaders, or international providers)
  2. small local companies (SMEs)
  3. self-construction with the help of an energy turnaround self-construction cooperative (EWG) (often also called “Mitmach-PV”, “PV-Nachbarschaftshilfe” or “PV-Eigenbau”)
  4. Self-construction on your own initiative

As the title of this article suggests, we have decided to implement the project ourselves, with the support of a self-build cooperative (variant 3).

Decision to self-build with the help of an “EWG”

We obtained quotes (early/mid-2023) from a major supplier, two SMEs and one EWG. The costs varied between CHF 2600 and CHF 1600 per kWp, with the EWG self-construction offer being the cheapest.

The offers differed not only in price, but also in other factors, especially in the installed capacity between 30 kWp and 46 kWp! The big difference can be explained by the fact that our flat roof has a two-tiered surface and a slightly curved shape, as well as some superstructures and a permanently installed safety wire. The most “conservative” offers here only covered the minimum central area within the safety wires. The bids with more kWp attempted to make optimum use of the entire area.

Other points that are important when comparing the offers:

  • Are all the necessary services of an electrician included?
  • Is an energy manager and installation of self-consumption control (chargers, heat pump, etc.) included?
  • Is the roof covering (green roof substrate/gravel etc.) included?

It was sometimes quite complicated to understand what exactly was included in the offer and what was not, and it was necessary to ask the providers several times.

In the end, we opted for the offer from EWG Zürichsee with the largest and (especially thanks to self-construction) cheapest system (per kWp).

The idea to build our own system with EWG came from one of my neighbors. I was a bit skeptical at first, mainly because of the time required to build it (and the cost seemed a bit conservative to me), but I was also curious to install a system myself. It’s also a great neighborly project that helps people get to know each other better. As a reminder, when doing it yourself with the help of an EWG, the entire project management, ordering materials, connecting the systems etc. is done by the EWG, the buyers simply help with installing the panels and some other work.

Construction of the system

At the end of August, the time had come: the materials were delivered and a safety scaffold including stairs for easy roof access was installed by a scaffolding company.

In the next step, we cleaned the roof of weeds and laid a special fleece to prevent further weed growth. 1 The material (including panels) is then hoisted onto the roof by a crane.

After a few days break, the installation of the substructure (K2-Systems Dome 6) begins. Now the exact layout is measured and adjusted again on site. Incidentally, the substructure on the flat roof is not screwed to the roof, but fixed with weights (simple garden paving tiles).

After the substructure come the panels. Screwing on the substructure and the panels is quite simple and can be carried out by laymen after brief instructions. Even my 8-year old son helped with some of the works! The cable connections are made or checked by the EWG project manager, but here too they are simple plug-in connections.

The main work is completed in about a week, with at least two people from the house helping in addition to the project manager, often three or four. In the week before and after the installation, some people are also busy for several days with preparatory and supplementary work.

In our case, we decided to cover the fleece at the edge with normal gravel. This work turned out to be very time-consuming! A green roof with a substrate is therefore definitely an additional factor when installing solar.

After the actual installation of the panels, there was a break of around 3-4 weeks before the electrical installations were carried out. The original plan was 1-2 weeks due to vacations, but due to a combination of illness in the team and scheduling difficulties with the electrician, the system was not fully connected until the end of October.

The electrical installation is carried out up to the inverter (DC) by EWG, from the inverter (the AC part) by the electrician. It is also worth comparing the electrician’s quotes, we had cost differences of 100% in the quotes! Another important factor in the electrical installation is that in Switzerland a so-called external NA protection (grid and system protection) is mandatory from 30 kWp system size, the installation of which is quite expensive.

Billing of solar power consumption in an apartment building (ZEV)

Since we live in an apartment building, the question of billing the consumed solar power to the individual apartments arises. As already explained in the first article on our project, this is implemented in Switzerland with a so-called ZEV (association for self-consumption). (“Mieterstrom” in Germany, “Gemeinschaftliche Erzeugungsanlagen, GEA” in Austria).

For a ZEV in Switzerland you can work with a third-party software or with your local energy provider if they offer this service. We have opted for the latter option. With our local energy provider, the initial installation is quite cheap, but the billing costs are CHF 0.02 per kWh of self-consumed solar power. That’s not cheap, but according to my calculations it’s cheaper than typical third-party providers over the course of 20-25 years. In addition, we don’t have a long contract, we can switch at any time. Unfortunately, our energy provider is having difficulties procuring the necessary smart meters, so they won’t be installed until some time in Q1 2024. Until then, all the electricity generated will be fed into the grid. As soon as the solution is installed, billing will take place directly on our normal electricity bill for each party, meaning there will be no additional bills and no administrative work.

Energy management and self-consumption optimization

Of course, as co-founder of the Zerofy Home Energy Management System (HEMS) I am particularly interested in the topic of energy management and self-consumption optimization. In our case it was about:

  • Control of 3-4 electric cars or charging stations (Zaptec and Tesla)
  • Control of a Hoval heat pump (heating and domestic hot water boiler). If necessary, control of the boiler heating rod.
  • If necessary, control of a central dehumidification system in the basement

What amazed me in this area was how much time it took to discuss all the relevant information and options with the individual manufacturers. I will report on the exact control of the consumers and some data in a separate article.

The consumers, especially the heat pump, were connected at the beginning of December. In total, the project took a good 2.5 months.


The entire 46 kWp system cost us around CHF 72,000, i.e. around CHF 1560 / kWp before subsidies. The subsidies (Pronovo (national) + municipality) will be approx. 20k CHF, so the investment is reduced to approx. 1100 CHF / kWp after subsidies. And thus approx. CHF 0.05 / kWh electricity costs over 25 years.

It should be noted that we ordered the offers or panels at the beginning/mid 2023. The panel prices are very dynamic and have fallen again in the meantime. It is also important to note that EWG has a low margin on the panels and lists this transparently in the offer. Many suppliers have quite high margins on the panels and this is not directly visible to the layman.


In conclusion, I can definitely recommend the installation of a solar system by means of self-construction supported by an EWG, provided there are enough contributors to help during building.

  • The cooperation worked very well and strengthened neighborly cohesion
  • It is really fun to work on the project with your own hands
  • The cooperation with the EWG was relaxed and smooth

Some things that surprised me or that you should pay attention to:

  • It’s amazing to me how much every solar project is still just a “project” and just not a scaled product yet. There are a lot of details to clarify. In my opinion, as the owner, you have to read up a bit on the subject.
  • Depending on the size of the system, “a weekend’s work” is not enough, you have to allow for enough time and/or help.
  • There were various “pauses” in the course of the project, for various reasons.
  • The topic of solar self-consumption does not yet seem to be firmly anchored in the standard product range of many appliance manufacturers.

If this article was helpful to you and you are also interested in energy management in the home with solar, then take a look at our Zerofy app:

Download Zerofy on the App Store Download Zerofy on Google Play

Energy transition cooperatives in Switzerland (EWG)

Other Swiss solar cooperatives

Solar self-construction/neighborhood help in Germany

Report on Swiss television about self-construction

  1. This was necessary for us because we have a green roof with a substrate. There would be shade and moisture, especially under the panels, and the plants would grow particularly well. You have two options to prevent this: a special fleece (in our case DuPont Plantex Platinum Solar) or vacuum the substrate and replace it with gravel. The latter is quite expensive. On the other hand, one supplier also advised against using fleece due to poor or lacking long-term experience.