Facts about the project

Builder/Owner/Planner: Erich Hormann
Photovoltaic output and orientation: 9.7 kWp East-West (since 2021)
4.5 kWp East-South (since 2022)
Inverter, battery storage: Storage 10 kWh since 2022 (BYD HVS Premium, 4x2,5 kWh)
Heat storage size (boiler or buffer tank): 300-liter hot water boiler (BS 301, Polyline S 100 RAL 9006)
Building type: Farmhouse with 3 residential units for heating
Year of construction and square meters: 1923, 340 m² (200 m² on the ground floor renovated in 2012)
my-PV product: AC ELWA-E (predecessor of the AC ELWA 2) for hot water preparation
System control: my-PV Power Meter (predecessor of the my-PV WiFi Meter)

A short explanation of the system

On a 100-year-old farmhouse in the district of Nienburg/Weser, Lower Saxony, Germany, there was plenty of unused roof space until 2021. This situation changed when it became evident that the wood chip heating system, which efficiently provides hot water and heating during the winter months, was significantly oversized for the hot water needs in summer. The wood chip heating system, a typical solution for farmhouses, was installed in 2017 and is a Fröling T4 with a capacity of 30 kW. While this capacity is necessary in winter due to the extensive space and high heat demand of a century-old farmhouse, it is completely oversized for hot water production in the warmer months.

To address this, a photovoltaic system was planned and installed in 2021, featuring an East-West orientation and a capacity of 9.7 kWp on one of the roof sections. In 2022, the system was expanded with an additional 4.5 kWp array facing East and South. This setup generates a sufficient surplus of electricity, as daily operations in the farmhouse do not consume all the available energy. Even after charging a 10 kWh battery storage system, added in 2022, there remains ample PV electricity available. This surplus can be efficiently utilized for what is known as photovoltaic heat.

Personal customer opinion and resumee

“The unit operates flawlessly, allowing the wood chip heating system to be turned off during the summer months. In the sunny months, from March to October, the AC ELWA-E consumes approximately 1,300 to 1,400 kWh. The AC ELWA-E works perfectly and significantly enhances the self-consumption of electricity from my own photovoltaic system,” summarizes Mr. Hormann, the owner of the historic farmhouse in Lower Saxony.

What to do with the surplus – the path to my-PV

To efficiently utilize surplus electricity, which is typically fed into the public grid at a low reimbursement rate, it is crucial to implement a linear controllable system. This ensures that electricity is not simultaneously drawn from the public grid or that surplus electricity is fed back into the grid when it could be used on-site. The importance of this is discussed in our article on inaccurate measurements in self-consumption optimizations.

With a linear controlled use of surplus electricity from his photovoltaic system, the owner of the farmhouse, Mr. Hormann, can support hot water preparation in winter and rely entirely on solar energy in summer. The AC ELWA-E, the predecessor product to the AC ELWA 2, has been chosen for this photovoltaic heat application. From May to October, it utilizes 100% of the electricity generated by the photovoltaic system to efficiently, cost-effectively, and environmentally friendly produce hot water.

Between November and April, the wood chip heating system is typically active to provide space heating for the farmhouse. During this time, the AC ELWA-E can only provide supplementary support, which is set up as follows: if surplus electricity is available during the less sunny months, it is used to assist heating. A timer controls the wood chip heating system to take over hot water preparation if the desired temperature is not reached by 4 PM using the photovoltaic system and the intelligent heating element from my-PV. “The AC ELWA-E works flawlessly, whether in summer or winter,” states owner Mr. Hormann.

Why solar thermal was not installed here?

“Solar collectors are too cumbersome to install, which is why I became aware of the products from my-PV during my online research,” explains Mr. Hormann from Lower Saxony regarding his decision. He aimed to increase the self-consumption of photovoltaic electricity, as every kilowatt-hour used during the day makes a kilowatt-hour from another energy source—such as gas, wood chips, or oil—obsolete in the evening, resulting in easily quantifiable economic benefits.

Good to know

If the reimbursement rates for feed-in continue to decrease, this can be easily offset against the heating costs incurred for gas, wood chips, oil, and so on.

Were there any obstacles or special features during the setup?

Fortunately, during the renovation in 2012, a LAN cable was already installed in the heating cellar. This significantly simplified the setup and commissioning of the AC ELWA-E, making the connection for surplus detection via the LAN cable very straightforward from the house connection point. The signal for this comes from the my-PV Power Meter, the predecessor of the my-PV WiFi Meter.

How many people in the household are covered by the hot water supply?

The farmhouse, with a total area of approximately 340 m², contains two residential units occupied by four people. Annually, there is a consumption of 60 m³ of hot water. Of this, about 40 m³—over 65%—is covered by the AC ELWA-E, which allows the hot water to be produced using surplus electricity rather than relying on a low feed-in tariff.

Hot water security is not activated during the months from April to October, as there is always sufficient surplus electricity available. In the remaining months, when less surplus electricity is likely to be available and grid power would have been needed for hot water security, the wood chip heating system is already in place to ensure a comfortable hot water temperature.

What makes this project special?

You can track the consumption data through our visualization in the demo version of the my-PV Cloud. Curious about the solar coverage rate? Want to see how much power the AC ELWA-E used each day for hot water production?

With just one click on the consumption data in the demo version of the my-PV Cloud, you can access real data from this reference project.

To the real-time data of this project in the my-PV Cloud

AC ELWA 2

the successor of AC ELWA-E

To maximize the self-consumption of your current PV system, AC ELWA 2 harnesses the system's surplus photovoltaic energy to heat your water. Increasing self-sufficiency simultaneously safeguards against unpredictable or rising operating costs.

More infos about AC ELWA 2

Back to overview

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