AC ELWA 2 in heritage-protected building
Climate protection award for a heritage-protected multi-family house with PV heat
Solar-powered heating works in heritage buildings! A 150-year-old house is designed for maximum energy self-sufficiency.
Facts about the project
- Planner/Installer/Owner
- Location
- Photovoltaic output and orientation
- Inverter, battery storage
- Heat storage size
- Building type
- Year of construction
- my-PV product
- System control
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Photovoltaic-powered heating is possible even in heritage-protected buildings: A 150-year-old multi-family house has been designed to be as energy self-sufficient as possible – and has been awarded a Climate Protection Prize for its innovative approach.
What challenges did heritage protection present?
“Making a heritage-protected building future-proof with renewable energy.” This was the title of the submission for the Climate Protection Award of the Konstanz district. The multi-family house (built between 1876 and 1879) impressed the jury with a wide range of measures. Due to its historical significance, the nearly 300 m² building is under heritage protection. As a result, installing a photovoltaic system or making significant structural changes was unthinkable during the renovation planned between 2015 and 2017. So how was it still possible to win a Climate Protection Award?
The entire system – comprising a photovoltaic installation, battery storage, PV heating elements, stratified buffer tanks with a fresh water station, and a central hybrid pellet-wood log heating system – was designed to achieve the highest possible level of energy self-sufficiency. And all this in a heritage-protected multi-family house with three residential units, each home to two to three residents. Extensive planning and determination were necessary to retrofit the 150-year-old building for a sustainable and future-proof energy supply.
Personal customer opinion and resumee
"We could have installed a heat pump, but in our case, it wasn’t economically viable. Instead, using a system with two AC ELWA 2 photovoltaic heating rods from my-PV, each costing under €1,000, is a completely different story in terms of price," says Patrick Reißner. "Additionally, the seamless power adjustment, which optimally adapts to the output of the photovoltaic system and directs heat into the two large stratified buffer tanks, combined with the prioritization of the battery storage, is simply unbeatable."
"We first determined the maximum possible area for the photovoltaic system that would be approved by the heritage protection authority. We achieved this by installing a PV canopy over a detached prefabricated garage (built in 1980, approx. 15 m²), creating a photovoltaic-covered area of around 40 m²," explains Patrick Reißner, describing the challenges of integrating a PV system. This 9.8 kWp system was thus installed on an already sealed surface without violating heritage protection regulations and was commissioned in July 2023. Due to shading, each PV module was equipped with a power optimizer from SolarEdge. The generated solar power is first fed into the general household electricity supply.
Integration of Photovoltaic Heating Elements
In October 2023, the system was expanded to include photovoltaic-powered heating elements – heating rods that linearly control surplus solar energy into heat.
"We came across the PV heating rods from my-PV while searching for an intelligent and integrable system in this area. Since a heat pump was not economically viable in our case, the AC ELWA 2 from my-PV became our preferred choice for photovoltaic heating," explains the owner of the multi-family house.
Thanks to the two linearly controlled PV heating elements, with a regulation range from 0 to 3.5 kW, solar energy can be directed into the two stratified buffer tanks (each with a capacity of 850 liters) during the day, instead of feeding excess electricity into the public grid at an unprofitable rate. Even in a renovated historic building, a considerable amount of energy is required for heating and hot water – so every kilowatt-hour of solar energy is a valuable contribution.
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How is the battery storage prioritized?
A BYD battery storage system with a capacity of 12 kWh, installed later in July 2024, is naturally prioritized for charging. This is easily achieved thanks to the system’s open architecture. The surplus energy detection is handled by a SolarEdge Home Energy Meter – SolarEdge being a compatibility partner of my-PV.
The management of PV modules, including power optimizers, battery storage, energy flow, and the control of PV heating rods, is handled by the SolarEdge inverter in combination with the SolarEdge Home Energy Meter – demonstrating true system openness.
Is all hot water heated with photovoltaic power?
Of course, a large system with 1,700 liters of heating water plus a fresh water station cannot rely solely on solar energy. For the dark winter months, an ETA hybrid central heating system using firewood and pellets is available. This system was also commissioned in October 2023 and reliably heats the water via the heating system from November to March. If surplus photovoltaic energy is generated on winter days, it can be used to support temperature maintenance in the buffer storage tanks via the two AC ELWA 2 PV heating rods.
In addition to the PV heating elements, a solar thermal system is also installed, contributing to heat supply. The overall management of heat generation is handled by the control system of the central heating unit. "This allows for either a direct or indirect interplay of all renewable energy sources," explains the owner.
From March to November, hot water – and, during transitional periods, also heating water – is generated in the stratified buffer tanks using the two AC ELWA 2 heating elements powered by photovoltaic electricity. If unexpected cold spells occur, especially in spring or autumn, the pellet component of the heating system compensates.
During the summer months, if there is still excess solar energy that cannot be used for heating, it is first utilized for household electricity, then to charge the battery storage, and finally for heating applications. Any remaining energy is then fed into the public power grid.
What are the Advantages of Photovoltaic Heating?
The biggest advantage is cost-effectiveness. "We could have installed a heat pump, but in our case, it wasn’t economically viable. Instead, using a system with two AC ELWA 2 photovoltaic heating rods from my-PV, each costing under €1,000, is a completely different story in terms of price," says Patrick Reißner."Additionally, the seamless power adjustment, which optimally adapts to the output of the photovoltaic system and directs heat into the two large stratified buffer tanks, combined with the prioritization of the battery storage, is simply unbeatable."
What would he wish for in the future?
"I would love for the ETA heating system to integrate better with photovoltaic heating—perhaps with a seasonal program that allows for detailed adjustments and coordination," says the homeowner in Konstanz.
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AC ELWA 2
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.
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