No batteries, no wires, no worries

Energy efficiency, sustainability, smart building automation, flexibility, low system costs, connectivity - these are the main concerns for building owners. Public institutions and private corporations are becoming more dependent on smart technology innovations to improve this situation. One integral component to improve this situation is the energy harvesting light and shutter switch. The special feature is that these switches operate entirely wireless and battery-free and can be used as light or shutter pushbuttons. These smart pushbuttons are developed and produced by ZF Friedrichshafen AG. The principle is to create an intelligent and flexible room concept combined with high energy efficiency and low system costs.

No wire means flexibility

Whether for new buildings or retrofitted in existing buildings, wires require a detailed plan and an evaluation of project sites for suitable wire connections between several actuators, sensors, control units and receivers. Once complete, it is only possible to change the positions of these modules with an investment of effort. Adjustments can require a new planning phase, tear down, laying of the new wires and returning the building to its previous state. To gain a full picture of the budget required for an installation, it is not enough to consider only the initial costs – such as the wages bill for electricians, but also for the follow up costs if re-designs are required over time.

An alternative to cabling is RF communication between lights and pushbuttons. When it comes to the decision whether to use batteries or energy harvesting technology, the initial cost consideration is still a crucial factor for building owners.

Further criteria to evaluate are the additional maintenance of battery changing, cost of purchase and cost of disposal. Building managers need to understand the performance of battery-powered modules and have a detailed overview of the locations of the modules, while keeping track of when to change the batteries. For hotels, airports, production halls and company offices this would mean monitoring hundreds of light switches, which are located within a large building complex over several offices and floors. If it results in an operation failure due to an expired battery, the facility manager is required to replace the battery. This results in extra work and is time consuming. 

Further essential considerations are the costs of battery disposal and the waste of resources. Batteries are considered a hazardous waste. Depending on the type, they can consist of mercury, lead or cadmium, which have a detrimental impact on the environment and need to be disposed of responsibly which is often expensive. In Germany alone, more than 80,000 tons of batteries were used in 2019. As a consequence, complicated recycling procedures take place which require a high energy effort.

Figure 1: The two-way pushbutton KNX-RF ready and EnOcean 3.0-compatible module from ZF

Energy harvesting  

Energy harvesting has the opportunity to resolve the disadvantages that come from using wires and batteries. ZF’s technology for example is based on the inductive principle. A small generator can create mechanical energy typically around 330µW by manual actuation. This energy output is enough to reliably transmit RF commands to smart lighting applications or other smart home modules. These commands include on / off and dimming of lights. The communication range varies between the protocols used and achieves up to 30m indoors, using either the 865MHz or 915MHz frequency ranges. The main advantage is to reduce maintenance effort, due to the long lifetime of the energy harvesting generators. Up to 1,000,000 switching cycles can be achieved.

The RF light switch module from ZF is already available in two RF standards - KNX-RF and EnOcean3.0 (Figure 1).

In co-operation with ON Semiconductor, ZF has published a reference design for an energy harvesting Bluetooth low energy switch and a first demo light switch module. It is compatible with standard frames and can also be combined with customer-specific control and design panels.

Especially in changing building complexes, wireless light switch modules help to ensure flexible room design and rearrangement of light switches - without maintenance costs. In contrast to batteries, the self-sufficient radio variant protects the environment and resources. In addition, in a long-term perspective, the system costs decrease, since there are no internal expenses for purchasing new batteries, battery replacement and disposal.

Figure 2: ZF’s Bluetooth Low Energy 5.0 reference design for low-cost, low-energy applications

About the author:

Simon Ziegler is a junior product engineer at ZF Services