Lifetime Power(TM) is a concept dreamed up by Powercast Corporation.  It is really best explained in looking at situations that we believe creates a compelling vision for how portable electronics should be powered.

Wireless Sensor Networks

An IT Manager working in conjuction with the Building Engineer have decided to create an eco-friendly building.  They have proposed to their corporation that by upgrading the HVAC system, the power distribution system, adding eco building materials, and adding alternative energy solutions … that they can save the company substantial money.  They believe that the operational saving for this building can realize a $750,000 savings year over year, and can pay back the additional investment in 4 years.  The presentation was impressive, and managment approved their program.

As someone who has had experience with this very scenario, I can bear witness in the “best intentions” of this kind of arguement and can bear witness in the “breakdown” in the execution of this scenario.  So lets fast forward to 1 year from implementation.

Several suprizes have now occured during the year.  First, the savings projections of the solution were overstated by a factor of x2.  We believe that this is a result of three important real world observations:

• Overstatement of our vendors as to the impact that their product solutions would have, and because we served as the integrator, it is hard to pin down which element is underperforming as advertised.
• The human condition … by this we modeled the solution and saving based upon perfect or expected behavior of people in the building.  However, we discover that they are unpredictable and uncontrollable.  Inhabitants disable the systems (tempurature sensors, automated window blinds, security doors, etc), they open windows, they leave the door open to the outdoor smoking area and so on.
• Understatement of the granularity required to control costs.  The sensor company told us that we needed temperature sensors set up to take a recorded measurement every 1 hour.  The lighting controls were set up on a 90 minute turn off period.  However in both cases, we recognized that by gaining sensor measurements every 10 minutes and shutting lighting down after 30 minutes, we could aggressively recover savings.

Batteries become the achillies heal

With this familiar scenario, the operators soon realize that their increased challenges, both financial and operational, drove them to over-use the systems they put in place.  At that point, they will recognize a significant limitation … primary batteries used.  One Wireless Sensor Manufacture CEO recently was speaking at a Sensor Trade Show, and stated that they expected their sensor batteries to list 1 year.  The audience reacton was almost as if the CEO had told a good joke.

Batteries are the most limiting factor in deployment of wireless sensor networks.

But as the scenario above illustrates, the greater the need or use of the eco-friendly systems, the greater the limitation of primary batteries.  Meaning the more the system is used, the greater the problem.  And in a case of 1,000 nodes using primary batteries, the cost of changing these batteries out every month starts to mount up (batteries, labor, overhead, downtime and disposal).

Lifetime Power in Wireless Sensor Networks

Lifetime Power is a concept where a Powercast Powerharvester Module(tm) is integrated into each node.  That node now has essentially a renewable power source on board.  This Powerharvester can provide power to a rechargeable battery, to a capacitor board, or to an ULP device directly.  Coupling energy harvesting with the power system of the node creates an important realization.

• The operator never has to change batteries out again.
• The node itself remains at peak operation, rather then become inaccurate as battery power dissipates over time.
• System operation is optimized because downtime resulting from battery discharge is eliminated.

This is what Lifetime Power is.  It doesn’t necessarily guarantee that the sensor will always remain powered, because there are always defects, component failure or a use case that is problematic to energy harvesting.  However, Lifetime Power is the promotion of an idea that batteries, capacitors and ULP devices should be engineered to always be optimized by a wireless power system.