Micro generation meets micro consumption - Energy Scavenging Wireless Networks

 In a previous post I wrote a bit about wireless mesh networks as a means to cost effectively retrofit sensors into a building to allow feedback control and continuous monitoring of environmental conditions to reduce energy usage.

One problem with wireless: batteries.
While they may last for years, they do need to be replaced eventually. If you have truly adopted a full building installation of sensors, that would be hundreds of nodes and batteries tucked into all kinds of hard to access locations where the HVAC, power distribution, and other systems are located or routed.
Replacing all those batteries in all those places: not trivial.

Energy scavenging to the rescue!
Using versions of the technology that power your kinetic watch (mechanical micro-generators) or that can be stuffed into a shoe (piezoelectric), enough power can be generated from ambient vibrations to power the sensors. It's not a lot of energy, but it's probably enough for low power network devices:

• MCU + Transceiver for ZigBee (IEEE 802.15.4) draws somewhere between ~20mA and <200mA (say 50mA) (at ~3.3V) when transmitting with <1 uA in sleep mode
• Transmissions last a few tens of milliseconds (~15ms - 48ms) and sensors may transmit ~1/min.
• Energy required is, therefore ~7.9 mJ per minute (for 48ms transmissions).
• Micro-mechanical energy generators produce on the order of a few (1-5-ish... say 2) mW of power. This could yield up to ~120 mJ of energy per minute (depending on the consistency of vibrations).

So, even with a smaller or less efficient generator than I found in a few minutes of searching, with a small battery or capacitor to store the micro-generator's energy you're in business without battery changes.

image credit: inhabitat

Product positioning if you made a cleantech widget

In the last post, I used a system diagram to look at a picture of sustainability leverage points from the perspective of the owner. That can be turned around and used to look at the picture from the perspective of a cleantech vendor. Let's say someone like Redwood Systems who makes an LED lighting + sensor system that allows feedback to a building automation system.

Key messages can be tailored to the exact circumstances and interests of the building owner but two main themes seem to stand out around energy usage and environmental quality.

Reduced energy usage:

• drives down operating costs 
• Direct savings from the lower energy consumption of the lighting fixtures.
• Indirect savings from the improved efficiency with which the fixtures, HVAC and process equipment can be operated based on feedback that the fine grained sensor network provides.
• helps the planet and, thereby, your operating risks / costs
• Reduced energy usage lowers the company's carbon footprint, reducing its impact on the environment.
• A reduced carbon footprint, in addition to helping reduce the potential business continuity costs and impacts of climate change, also helps reduce potential liability for carbon tax or cap & trade costs.

Better control of environmental quality:

• improves productivity and profits
• Fine grained feedback control over the workspace allows for a more pleasant and, therefore, productive workplace. Even small increases in productivity provide large leverage when weighed against total payroll costs, especially for highly paid, specialized workers.
• improves worker retention
•  Deployed as part of a larger program for improved retention, having a comfortable workspace with a customizable, controllable environment decreases costs of turnover both in lost productivity and in direct training.

A Big Picture of Sustainability

Where are some key leverage points in cleantech, green building and sustainable business?

This is a swag at the system, which captures, I think, some interesting connections and highlights some key leverage points.

 Before your head explodes, the theory behind it:

• A building owner's success is defined as a function of the triple bottom line (Planet, People, Profit).
• There are a lot of factors behind each part of the bottom line and some of those factors affect multiple bottom lines.
• Most factors are affected by several other factors. A few factors are "decisions." They gain their value because the owner decides to do them, not as the consequence of some other factor. These are marked in RED in the diagram.

In this post, I want to focus on the last point as I think these are key leverage points for sustainability.

Sustainable Sourcing and Sustainable Material
What materials you choose and where you get them from affects all three bottom lines:

• Planet : unsustainable harvest of materials destroys habitats, kills species (which can further degrade habitats) and depletes resources.
• Profit : resource depletion ultimately raises the cost of procuring materials. Habitat destruction increases the allocations you should make to account for and insurance costs you will likely bear due to losses associated with it (e.g. increased flooding, loss of location due to sea level rise or desertification, etc.)
• People : habitat destruction ultimately limits the locations where you can run your business and that has a big impact on how your company runs (see below).

Feedback Control
How you manage your resource usage affects all three bottom lines:

• Profit : Controlling usage to increase efficiency costs a little more to implement but can ultimately save significantly on direct operating expenses as well as on carbon costs (assuming a carbon tax or cap & trade are enacted). Good control of the indoor environmental quality also has positive impacts on worker productivity, increasing profits.
• Planet : Increased efficiency of resource usage, especially for water or energy sources (coal, oil or land set aside for biofuel growth) helps offset resource depletion which, in turn, helps preserve habitats and species.
• People : Good indoor environmental quality also increases retention, which reduces training costs and opportunity costs associated with head count gaps, thereby increasing profit.

Location
Where you locate your operations affects all three bottom lines:

• People : Location has a large impact on lifestyle. Educational, entertainment, cultural options all depend highly on where you live and that depends, most of the time, on where you work. "Better" options lead to higher retention and ultimately lower costs. If a location is too expensive, dangerous or otherwise undesirable to live near, then commute times increase, negatively affecting work life balance, hurting retention.
• Profit : More "desirable" locations tend to attract more educated, higher skilled workers. While hiring these people may cost more money, their productivity and quality of work increase profits (See this post for more thoughts on that idea). More "desirable" locations also tend to cost more money to locate in, increasing expenses which decrease profit, therefore requiring a careful consideration of worker quality available vs real estate costs (or requiring an alternative method of working).
• Planet : Locating to environmentally sensitive or pristine locations can result in habitat destruction which cascades into species loss and resource loss.

This is only scratching the surface of the connections captured in this diagram. I expect to come back and explore this some more.

LEEDing to Better Building Control and Efficiency via Wireless Mesh Networks

LEED v3 has expanded the emphasis on measurement and verification (M&V) in order to offset concerns that green buildings don't maintain designed performance over time.

The rating system where this is most evident is in the LEED 2009 Existing Buildings: Operations & Maintenance (EB:O&M) If you dig through the credits with an eye towards the ones that:

• Require or could benefit from some sort of real time or on-going monitoring
• Could use a portable monitoring system comprised of sensors and small data network.
• Address the toxicity and recycle-ability of the sensor & networking systems

You find that something on the order of half of the credits (around 46 of 92 when I last checked) could be affected by having a good sensor system available.

Sensors, of course, need a communication network to feed their data back to a building automation system, (BAS) or building management system (BMS). If you are forward thinking and lucky enough to be engaged in new construction, then you can build many of these networks into the plan. Then when you meet the USGBC requirement for ongoing performance monitoring by following the EB:O&M certification route, you will be ready. For new construction, this is probably a good way to go.

However, if you're in the position of having an already complete building and you want to obtain EB:O&M, getting such a network in place could cost a considerable sum due to the wire routing involved. In such cases, using a low power wireless network would be preferable. Given the large area to be covered by a wireless sensor network and the large number of discrete sensors needed, this kind of application lends itself to a wireless mesh network (ala IEEE 802.15). Basically a network that uses the nodes to communicate with each other rather than requiring all units to communicate with a central access point. The more nodes (sensors) in place, the better the network becomes... and it's low power enough to run on batteries for months at a time... important if you need to pay someone to replace all those batteries.

UC Berkeley has pioneered work on this topic, coining the phrase "smart dust," and spun off at least one company (Archrock) that aims to address this kind of market space.