Does photovoltaics pay off for dialysis?

I would like to share a short report from our direct experience of the first few months with a photovoltaic system in dialysis on the roofs of our headquarters in Emsdetten. My name is Christian Meyer zu Altenschildesche. I've been on board since 1994 and am now Technical Director at Nephrologische Zentren Münsterland GbR, ÜBAG. It is a company with nine locations spread across the whole of Münsterland. It all began in 1975 in Emsdetten, when the first dialysis centre was founded here. It was the 23rd dialysis centre in Germany. Today, 13 medical partners, five salaried doctors and around 280 employees look after patients and carry out 110,000 dialysis treatments per year.

The Emsdetten site

The site in Emsdetten carries out 16,000 dialysis treatments a year. The headquarters for storage and logistics, technology and a laundry for all nine centres are located here. This gives us an annual electricity consumption of 165,000 kWh in Emsdetten alone. This figure is surprisingly stable over the last 10 years and allows us to predict our energy requirements for the future very well. With this in mind, we asked ourselves whether photovoltaics (PV) is worthwhile for a dialysis centre. And I would like to anticipate the answer right away:

For us at the Nephrology Centres Münsterland, it has long been clear that dialysis needs to become more sustainable. We have been implementing several measures for years, such as mixing concentrate on site or operating the dialysis machines in auto flow mode. Before we took the step of investing in photovoltaics, however, we had to clarify a number of issues:

1. How do I deal with surplus electricity?
2. How large should or must the system be?
3. Which orientation (south vs. east / west) makes sense for dialysis?
4. Costs: When does the system start to pay for itself?
5. How can I increase my own consumption and reduce feed-ins?

Freelancers are not permitted to earn commercial income. It is advisable to clarify the issue of surplus electricity in good time. As a freelancer, you are not allowed to earn commercial income. There is an exemption limit of €24,000 per year (at least this is the case in North Rhine-Westphalia), but this is not enshrined in law and therefore no legal entitlement can be derived from it.

Fig. 1 A bird's eye view of the roof of our dialysis centre in Emsdetten.

This limit is often already exhausted by inventory sales or cash-in payments. As a result, revenues from feeding surplus electricity into the grid could lead to problems even with low kWh prices paid out.

That's why we took the following route: We need legally binding information from our tax office stating that the PV electricity can be fed into the grid free of charge. We were then able to conclude a contract with the grid operator that allows us to feed in the surplus free of charge. If these bureaucratic hurdles are too high for you, you can also consider zero feed-in directly via the PV control system, although this is associated with somewhat higher costs.

PV system output at least 20 % above peak load

The next decision we had to make related to the size of the photovoltaic system. This question requires us to consider a few boundary conditions:

Fig. 2 Simulation of the south-facing orientation of a PV system on the roof of the Emsdetten dialysis centre

Fig. 3 Simulation of a PV system on the same roof of the Emsdetten dialysis centre with east-west orientation

• What is the maximum energy consumption for a fully occupied dialysis shift?
• How much space is available on the roof for such a system?
• How much more kWp (kilowatt peak = nominal output of a PV system under standard conditions) are you prepared to install than the maximum energy load you actually need per hour?

In our case, all these considerations led to the decision to install a system with 80 kWp with a peak load of 55 kWh. The original aim was to design the system in such a way that the PV peak output would be at least 20 % more than the peak load per hour (i.e. at least 66 kWp). However, as the photovoltaic modules are comparatively cheap in relation to the total installation per peak, we decided in favour of a slightly larger system (Fig. 1), especially as the roof area allowed it.

Which orientation makes sense for dialysis?

After the size, the question of orientation arose. Often there is no choice, but in the case of our flat roof, we were in the luxurious situation of being able to choose between two installation options: either south or east-west. Working with a good solar installer is highly recommended at this point. Our expert simulated both options based on our local conditions (Fig. 2 and Fig. 3).

The main decision criterion was the attempt to optimise self-consumption. The electricity consumption of a dialysis centre is distributed quite evenly throughout the day, and so the simulation was able to determine that the east-west orientation is more suitable for this load profile, as it allows us to use more energy from the PV system ourselves. This is reflected in the degree of self-sufficiency of 33 % (east-west) compared to 31 % (south), which corresponds to an absolute increase in self-consumption of 3,300 kWh.

Amortisation calculation based on real data even more attractive than simulation calculation

Before installing the photovoltaic system, there was of course another important point to clarify, namely when the system would be financially worthwhile or amortised.

With the knowledge of our annual electricity consumption (165,000 kWh), the targeted share of self-produced electricity of 33 % and an electricity price of € 0.32 / kWh, which we consider to be realistic, we were able to make a simple calculation (Fig. 4).

We compared the investment costs of € 110,000 for the system with the expected annual savings in electricity costs of € 17,424. As it can be assumed that such a system has low maintenance costs, these were disregarded in the analysis. We came to the conclusion that the purchase price should be recouped after just 6 years and 4 months.

Fig. 4 Amortisation calculation of the Emsdetten dialysis PV system with east-west orientation

Finally, the solar panels were installed on our roof in Emsdetten and the system went into operation in December 2022.

This now allows us to put the amortisation calculation (Fig. 4) to the test with real data (as at the beginning of May 2023) from the dialysis centre. As mentioned, the data we have collected on annual electricity consumption over the last few years has shown a high monthly reproducibility and amounted to the aforementioned ~165,000 kWh / year. Due to the war in Ukraine and the associated energy crisis, we have managed to reduce electricity consumption by ~2,000 kWh / month through targeted consumption optimisation. Extrapolated, this will lead to a consumption of only ~140,000 kWh / year from 2023.

Figure 5 shows the trend in reduced monthly electricity consumption (yellow bars). The green line shows how many fewer kWh we took from the public grid in the first quarter of 2023 after the photovoltaic system was put into operation.

The data from January up to and including April shows that we can cover almost 30 % of our electricity requirements ourselves at the centre in Emsdetten with the help of the new PV system even in the first months of the year, which tend to have little sunshine. No data is yet available for the usually sunny months of May to August. Nevertheless, I have taken the liberty of making a forecast for the whole of 2023 (Fig. 6), especially as our solar installer has calculated the yields amazingly well.

This means that we will probably be able to cover over 40 % of our annual electricity consumption with the PV system. With these new findings based on real data about the higher degree of self-sufficiency (41 % vs. 33 %) and the lower total consumption (140,000 kWh vs. 165,000 kWh), it is worth updating the amortisation analysis (Fig 7). In fact, it can be seen that the break-even point of the investment is now reached after 6 years, i.e. 4 months earlier than in the original theoretical calculation. If you now consider that a photovoltaic system can be in operation for a good 20 years, it quickly becomes clear that this is a very lucrative investment that will reliably reduce our operating costs from the seventh year onwards.

Fig. 5 Load profile with PV self-consumption for January - April 2023 with measured values

Fig. 6 Forecast for the whole of 2023 based on calculations and the measured values from January to April 2023

The area under the electricity feed-in curve (red) in Figure 6 totals an estimated 17,200 kWh over the year. As described at the beginning, this surplus electricity is fed into the local electricity grid at zero cost. On the one hand, this is a simple solution, as tax obstacles are avoided in advance. On the other hand, these 17,200 kWh have the potential to increase our own electricity consumption and thus our degree of self-sufficiency.

Initial considerations in this direction have two thrusts:

• Use of the electricity for surplus charging of centre-associated e-cars and
• the storage of energy for later consumption.

When it comes to e-mobility, we are currently examining how the vehicle fleet can be converted accordingly. Charging should of course take place when there is a surplus of electricity.

Fig. 7 Amortisation calculation of the Emsdetten dialysis PV system after commissioning with measured values

When it comes to storing energy, we have so far refrained from purchasing expensive battery storage systems. Instead, we are planning to use Cross-sector Integration to convert solar energy into process heat and store it temporarily as hot water, which can then be fed into the plant as soon as dialysis treatment begins.

With the initial results on photovoltaics in dialysis described here, it is clear to us at the Nephrology Centres Münsterland that we are on the right track. The next step will be to evaluate which other locations could also benefit from a photovoltaic system in the near future.