Modern immersion heaters and well-insulated cylinders provide a simple and fast means to raise, and store hot water. Thermostat controls ensure the heater is cost-efficient to run.
If you have solar PV you can divert surplus solar electricity to an immersion circuit, rather than sell to the grid. This does NOT effect your 50% deemed export payment. Products such as immerSUN, Power Diverter and Solic 200 are well proven and widely available.
You can also use these devices to divert surplus solar electricity to your infrared panels, if they run on a dedicated circuit. This works best with up to 3kW of heater panels (assuming you have a 4kWp solar PV system installed).