Sensors Expo 2018: Solar Power for Indoor Sensor Systems


It seems that everywhere you go these days people are talking about IoT. Whether it’s smart light bulbs that respond to your voice or sensors that transmit data, these devices are everywhere. While IoT growth is staggering it will undoubtedly run into some future issues.


One of the major barriers to mass deployment of wireless IoT sensors is battery lifetime. Depending on power requirements, a primary battery will last a few months to a few years.  Short battery life adds significant cost to a system over its lifetime. The batteries themselves may be inexpensive, but labor and repeated replacements can add significant costs over a product’s lifecycle.


For example, a Bluetooth light/temperature sensor for HVAC/occupancy monitoring that sends data about once per second will consume about 1.5 mWh of power each day. If a common CR2032 battery (225 mAh, 675 mWh) is used to power the system, then the system will operate for about 14 months. This assumes that the battery will supply the full rated capacity, which will probably not be the case since the battery is rated at a 0.2 mA continuous discharge and the peak radio transmit current is over 10 mA.


This high current pulse over the life of the system will result in approximately a 10% decrease in capacity, so a year is probably a more realistic operation time. The batteries cost less than $0.30, so not a major cost, however the labor to replace the batteries will be greater than $10 per hour. If the sensors are deployed on a large campus, there could easily be a thousand rooms to monitor. Assume that battery replacement times average 10 minutes per sensor. It would take an employee 166 hours or just over 4 weeks per year to replace the batteries. Therefore, annual sensor maintenance would cost about $2,000.


This figure is very conservative and assumes an employee working for slightly above minimum wage with no benefits and no consideration for cost of sourcing and inventorying batteries.  Also, labor time could be significantly higher depending on the amount of time it takes to travel to the location of each sensor.


One solution to this problem is the integration of a solar panel into the system. Solar panels can harvest light energy both indoors and outdoors providing a source of consistent power and increasing the lifetime of your product while simultaneously decreasing the total cost to your customer. Solar is capable of harvesting significantly more power than many other sources including: electrodynamic switches, piezoelectrics, ambient RF, and small temperature differential thermoelectrics.


During my talk at the Sensor Expo, I will discuss solar energy harvesting in indoor environments. You will learn about the amount of energy available for collection using various commercially available solar technologies in common lighting environments and things to consider when choosing a solar technology.


Beyond solar, I will also talk about storage elements and how to properly size a storage element for your application based on peak current draw and average power consumption. Then, I will discuss commercially available energy harvest ICs and the feature sets they offer. Finally, I will walk through the steps to specify the correct battery and amount of solar to power a Bluetooth sensor system.


Please join me at the Sensors Expo & Conference in San Jose, CA at the McEnery Convention Center on June 27 at 11:00am to learn about using solar to make your IoT sensing device self-sustaining and eliminate battery and maintenance costs during my session, “Solar Power for Indoor Sensor Systems”.  Use coupon code 338L for $100 off conference passes when you register.


Dan Stieler, President, PowerFilm Inc.


Dan Stieler received his PhD in Electrical Engineering from Iowa State University in 2008. After graduation he started working for PowerFilm, Inc as a Senior Physicist. Currently Dan is the President of PowerFilm, Inc. He does research on both solar material and the electronics that are paired with the solar. His materials research includes improvement of roll-to-roll deposited thin film electronic materials, deposition techniques, and in situ monitoring. He has also lead initiatives to decrease cost and scrap through identification and implementation of new processing techniques. His electronics research has focused on development of remote power solutions for low power devices, which includes analysis of various battery types, energy harvesting integrated circuits, battery charging systems, and solar operating environments.


PowerFilm is a US based company that specializes in custom solar solutions meeting design, power-output and timeline needs of customers. Controlling each step of engineering, design, and production, PowerFilm delivers the highest quality and performing systems. PowerFilm’s amorphous silicon functions at incredibly low light levels making it perfect for IoT, indoor, and many outdoor applications.