Hot water with the ELWA

3 photovoltaic modules for hot water

Even a small PV system with 1.4 kWp prepares hot water in the summer with ELWA and thus saves 1 cubic meter of gas every day.

Datos sobre el proyecto

Photovoltaic power and orientation
Heat storage size (boiler or buffer storage)
Building type
Year of construction and number of square meters
my-PV product in use

How is the system set up with the ELWA?

"To cut to the chase, I am completely satisfied and the DC heating element from my-PV, the ELWA, reliably performs its job and helps me to save gas and costs, not only relieving my wallet but also the environment," summarizes owner Thomas Eckardt his experiences.

The ELWA is installed in a single-family house with 120 m² in western Thuringia. The off-grid photovoltaic system with 1.4 kWp is smaller than recommended, but for a simple reason: The small roof in the garden, which protects some gardening tools, was not larger. The roof of the house may be used for a grid-connected photovoltaic system in the future, so no more power could be installed on the small roof. Even with the yield of the small system, which the linearly controlled ELWA directly converts into heat, enough gas is saved.

How was the journey to my-PV?

As part of the heating system renovation, a stratified storage tank was planned. This entailed additional coverage in the garden – the homeowner installed the photovoltaic modules on the small roof in the garden. The pipes leading directly from the modules are laid in a small protective casing across the garden to reach the ELWA via a main switch in the basement - the cables are directly plugged into the ELWA.

Opinión personal del cliente y resumen

"Of course, those who have the opportunity should use the maximum number of modules to be able to benefit from the savings effect even far from the summer. In my case, I wanted to keep the house roof free for a future PV system. Nevertheless, the yield of the small PV system pays off fully due to the linear control of the ELWA – between May and September 2023, I save almost 1 cubic meter of gas every day!" Thomas Eckardt expresses his delight. "Continue to bring such great products to the market and ensure that the energy transition continues to gain momentum and benefits both people and the environment," was the homeowner's feedback to my-PV.

The stratified of the modernized Solvis heating system ensures that every watt of solar energy is transferred to the water. The domestic hot water in the Solvis Max is decoupled from the stratified storage tank via a heat exchanger as a so-called fresh water system. "I then treated myself to a data logger and occasionally read out the performance data, which I document in Excel," says the owner from Thuringia.

Through a heating engineer who has installed the ELWA privately in his own house as well, the last hurdle was also overcome, as the installation situation in the Solvis heating system seems very tight, and thus concerns about whether the ELWA can even be integrated into it were dispelled.

Initial yield data from the year 2023

From mid-May to mid-September 2023, the room heating was turned off, and thus the ELWA was solely responsible for domestic hot water. "The device mastered this task brilliantly, and I only consumed an incredible 4 cubic meters of gas because there were some cooler and cloudier days in the summer when the gas heater took over the hot water supply. On six summer days, the ELWA turned off during the day because the set maximum temperature in the stratified storage tank was reached," summarizes owner Thomas Eckardt the yields from the summer months of 2023.

Saving 1 cubic meter of gas every day

The ELWA delivered its highest daily output of around 9 kWh from the 1.4 kWp photovoltaic system at the end of May. Over the summer months, an average of about 6 kWh reaches the layered storage tank.

Before the modernization of the heating system and the associated construction of the photovoltaic system including the commissioning of the ELWA, the Thuringian homeowner also required approximately 1 cubic meter of gas daily for domestic hot water heating during the summer – outside the heating period. This amount of gas can be saved through photovoltaic heat with the ELWA. Thus, hot water in the summer can be prepared for the 4-person household in an environmentally friendly and cost-effective manner using the power of the sun – despite the small PV-system!

Future expansion to a hybrid heating system with a heat pump

In the future, the Solvis heating system will be expanded to a hybrid heating system with a heat pump. The homeowner also intends to cover the entire, previously unused house roof with a PV system and expand the household with a home storage. Nevertheless, in all expansion plans, the grid-independent ELWA will transform solar energy into heat as an island system – in the summer for domestic hot water, and in the winter for heating support. "Currently, the ELWA is readily available again, and the prices for PV modules have fallen sharply. This makes the entire package even more financially attractive," summarizes Thomas Eckardt the advantages due to the market situation.

ELWA Seitenansicht


in use

ELWA is a 2 kW photovoltaic water heating device. Direct current from photovoltaic modules is transferred directly to the built-in heating element and immediately converted into heat without loss.

More infos about ELWA

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