Maximizing self-consumption with AC ELWA 2
A backup for the heat pump
After experiencing three failures of their heat pump, the owners of a single-family home installed a PV heating element.
Facts about the project
- Owner
- Photovoltaic output and orientation
- Inverter, battery storage
- Thermal storage size (boiler or buffer tank)
- Building type
- Year of construction and square meters
- my-PV product
- System control
)
Ideal conditions for photovoltaic heating
A beautiful single-family home in Ternberg, Upper Austria, equipped with a 5 kWp photovoltaic system, provides excellent conditions for maximizing self-generated photovoltaic electricity. Completed in 2012, the house, home to four residents, features a 300-liter Vaillant boiler and a heat pump with surface collectors, also from Vaillant. Since 2012, the heat pump has failed three times, each for 3-5 days, leaving the house without hot water. In response, the owner sought a heating element and discovered my-PV solutions through a personal contact. These solutions offer more than just a standard heating element.
my-PV, an Austrian expert in photovoltaic heat solutions, provides products that maximize self-consumption by using the household's own solar energy. For over a decade, they have offered adjustable products that modulate based on the surplus electricity from the photovoltaic system. The perfect solution for Mr. Szekeres’ home was found with the AC ELWA 2. It supports maximum self-consumption by linearly controlling from 0 to 3.5 kW, depending on the photovoltaic system's output. Additionally, the AC ELWA 2 can serve as a backup heater during heat pump outages, ensuring an adjustable water temperature with power from the grid.
Personal customer opinion and resumee
“Although the heat pump consumes only a fraction of the power compared to the AC ELWA 2, that energy often isn’t from the sun and additional electricity must be purchased,” notes the homeowner. Feed-in tariffs for PV electricity have significantly dropped in Austria and Germany, making self-consumption optimization essential.
“My AC ELWA 2 has been in operation since early September 2024, and I’m happy to promote it among friends because it basically runs for free on my PV electricity,” Alexander Szekeres concludes enthusiastically.
Implementation challenges
The home’s existing 300-liter Vaillant boiler, installed since 2012, did not have a standard heating element connection (G 1 ½ inch), complicating the retrofit with the AC ELWA 2. Although the product is supplied in two parts (separate heating element and electronic unit), it requires a suitable connection to the boiler. To overcome this, the owner, convinced by my-PV’s solutions, took an alternative approach.
There was no standard maintenance cover with threading for an easy retrofit. To address this, the owner custom-designed a flange with a bolt circle and threading, which was fabricated by a local workshop. Images of the modification can be seen in the project documentation.
While retrofitting the boiler or buffer tank is often straightforward in other reference projects featured on our website, this project demonstrates that adapting to photovoltaic heating can be challenging yet achievable.
“The Vaillant 300-liter boiler allowed for the addition of a second temperature sensor for the AC ELWA 2, which I installed alongside the original Vaillant sensor in the temperature sensor pocket,” explains the homeowner from Upper Austria.
)
)
)
)
)
How is hot water supplied?
The four-person household primarily relies on the heat pump for hot water, which is set to operate twice daily – at noon and in the evening when sunlight is not available.
Although the heat pump operates at a better efficiency rate, it often uses grid electricity except on very sunny days. With a modulating heating element, sufficient surplus energy from the photovoltaic system would be available to heat the water using solar electricity, even at a lower efficiency rate. my-PV solutions ensure exclusive use of PV-generated electricity, with grid electricity only serving as a backup if manually configured.
The installed heat pump can only heat water to a maximum of 50°C. For legionella prevention, higher temperatures of 60–70°C are recommended at least once a week. While the heat pump cannot reach these temperatures, the AC ELWA 2 can heat the water up to 95°C, ensuring legionella protection.
This setup not only provides hot water during potential heat pump downtimes but also ensures safe, germ-free drinking water.
Benefits of switching to photovoltaic heating
“The clear advantage of the AC ELWA 2 is increasing the self-consumption of PV energy. Currently, feed-in tariffs are already low, and if they turn negative or are eliminated, feeding energy into the grid becomes even less profitable. I'd rather make better use of my PV electricity for heating,” says Alexander Szekeres.
Additionally, the AC ELWA 2 acts as a secondary heating system, ensuring the family doesn't go without hot water if the heat pump fails.
The main benefit, however, is reducing the heat pump’s workload in the summer, which effectively doubles its lifespan by minimizing its operating hours during sunny months, preserving the significant investment in the heating system. “This way, I make the most of my PV electricity while extending the life of my primary heating system – a win-win situation,” adds the homeowner.
)
)
)
)
)
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.
More infos about AC ELWA 2More Reference Projects
)
Refurbishment and PV heat as a blackout precaution
A resourceful Upper Bavarian benefits from the renovation of his house and implements PV heat as blackout precaution.
Read more...)
Masonry stove and photovoltaic heat instead of a heat pump
The newly built single-family home impresses with environmentally friendly construction and innovative heating technology.
Read more...)
AC•THOR 9s and the Polish PV market
A Polish homeowner is responding to the conditions on the Polish PV market with the AC•THOR 9s.
Read more...