Everactive Solar Harvesting and Ambient Light Specifications

Solar Harvesting and Ambient Light Specifications

Everactive sensor technology can be powered up using energy harvesting from ambient indoor and outdoor light.  Capturing ambient light is done through the solar harvester, also known as the photovoltaic (PV) harvester. The image below shows an Everactive sensor with the indoor solar harvesting capability attached to the sensor by way of the Thermal Electric Generator (TEG) -- a harvester that uses temperature differential.

Differences in appearance of harvesters

In the above photo, the indoor PV harvester is on the left.  The outdoor solar PV harvester is on the right.  The outdoor harvester has a notably smaller bank of PV cells.

Indoor solar (PV) harvester

In order for the sensor to power up using the indoor solar harvester, ambient light level must be greater than 200 lux.

What is lux? Lux is a standardized unit of measurement of light level intensity, which is commonly referred to as "illuminance" or "illumination". For a more technical reference definition of lux, 1 lux is equal to the illumination of a one meter square surface that is one meter away from a single candle. Lux can be measured with many tools and can be roughly estimated using a lux meter. Lux meters are even available as downloadable applications on your mobile phone. 

If reliant on indoor ambient light for harvesting, we recommend using a lux meter, like a mobile application, to determine the optimal placement of the solar harvester to capture the greatest amount of lux. 

The indoor solar (PV) harvester is visually distinguishable from the outdoor harvesting as the indoor solar harvester has a larger solar cell. Indoor light has a lower power density than outdoor sunlight, and as such the indoor solar cell is larger than the outdoor solar cell. 

The graph below provides this comparison.

Outdoor solar (PV) harvester

The outdoor solar (PV) harvester is pictured below and is optimized to take advantage of outdoor ambient light from the sun. Furthermore, the enclosure is more robust and rugged to withstand prolonged outdoor exposure to the elements. We do not recommend attempting to use an indoor solar (PV) harvester in an outdoor environment.

As mentioned in the previous section, this outdoor solar harvester has a smaller cell than the indoor PV cell. 

For optimal placement of the outdoor solar (harvester), we recommend using an irradiance meter as outdoor light is measured differently than indoor light given the different light spectrum. To power the sensor from ambient outdoor light, the cell should have at > 2 W/m2. 

Harvesting Best Practices

In general, we recommend using multiple harvesting sources as harvesting types can vary throughout the day. For example, solar harvesting might not be optimal during times of dawn and dusk if outdoors while temperature differential may be more ideal.

You can connect TEGs with PV harvesters -- as shown in the first picture -- to optimize for both temperature differential and ambient light (either indoor or outdoor). This ensures that you receive the most continuous data reporting as possible.

If you have additional questions about harvesting and best practices, please contact success@everactive.com.