Heating hot water with photovoltaic panels

Photovoltaic water heating is a new way of using solar energy that is competitive thanks to new technologies and the falling prices of photovoltaic panels. A well-designed PV system and quality equipment will bring cost savings associated with water heating during the year. It is a maintenance-free system with easy installation that is reliable and efficient.

Principle of operation

The current trend is clear and relentless. The benefits of photovoltaic water heating are winning out over standard solar water heating systems with conventional thermal collectors. PV water heating is a relatively simple technical matter. The energy from the PV panels is fed through two thin rubber cables to a control unit located near the boiler. The control unit directly feeds the electric coil in your boiler. Thus, you heat water from the photovoltaic system, not from the grid.

Compared to photothermal systems, there is a significantly simpler installation of the wiring and de facto zero operating and service costs; moreover, in the event of surplus energy, the system does not stagnate, but the resulting surplus can be utilised via the DC output. Currently, a PV system is cheaper (than traditional water heating using photothermal), including installation.
The requirement for efficient operation of a PV system is to ensure the optimum operating point- i.e. continuous operation of the PV generator at the point of maximum output. In the case of PV power plants, the inverter takes over this function; in the case of a water heating system, this function must be ensured by means of a controller.

This can either control the size of the load (e.g. switching the heating coil taps in several stages) or, ideally, continuously regulate the power to the load by means of electronic control. It turns out that a system without this regulation is only able to deliver a maximum of about 77% of the energy (in practice 60% - 70%), with the highest extra losses on days when the solar intensity is low and therefore the energy is most needed.

Photovoltaic panels work even in reduced solar intensity, so they produce energy even in winter when photothermal has difficulties. At the same time, in summer it is possible to manage larger surpluses by sizing the system, or to use the energy for example to power the air conditioning.

Main advantages of PV water heating:
- connection of PV panels directly to the boiler, no inverter needed!
- easy installation without the need for approval of the distribution company (it is an island system)
- simple control
- significant savings in electricity or gas costs
- low heat loss of the system
- easy and simple regulation
- possibility to use an existing boiler
- no operating fluids are needed, no circulating pump or pipe insulation
- no overheating of the system, even in summer
- no need for antifreeze and no risk of freezing in winter.

More information about Dražice heaters