In an ELWA system, no power is fed into the grid. Any excess energy remains unused as in a solar thermal system. The main technical difference is that this does not result in any material fatigue compared to solar thermal energy.  In addition, the share of excess energy with ELWA is very low. Practically it is 5-8 percent. That would be about 100-150 kWh per year for a 2 kWp system, or at best 15 euros per year. If you need an inverter, an electricity meter with meter rental, a feed-in point and the grid connection, then the additional effort is not worth it at all.