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Batteryless electronics – Advice about how to get started with realising Energy Harvesting

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Battery consumption in the world – statistic

By Johan Pedersen

With the spread of more and more smart products, the Internet of Things (IoT) and wearable gadgets of all shapes and sizes, the need for changing and charging batteries will only become greater and greater. Growing number of batteries, which is bad for the user experience and worse for the environment. This is why a lot of people are looking at batteryless solutions, where energy is harvested from the surrounding environment through light, motion, temperature gradients or radio frequencies.

Sweet-spot in microwatt – milliwatt range

Energy harvesting is particularly relevant for products that have a low energy consumption in the range 100 µW – 5 mW, as many energy harvesting technologies lie in the energy density of 100 µW/cm, as shown in figure 1.

A standard button cell battery CR2032 can supply 1 mW for more than 45 hours, but when we go down to a consumption of a few µW, where the button cell battery can last for 2–4 years, in many cases it is not profitable to use energy harvesting because the battery can last for the lifetime of the product.

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Fig. 1 Comparison of energy density for the different energy sources in our surroundings. It is clear that outdoor light is significantly higher than the rest and that RF is only relevant for ultra low power devices. Source: CEA-LETI.

With the outdoor solar cell as their benchmark, a lot of people have high expectations for the performance of other technologies, which however, often have completely different energy conditions. The sun is our most energy rich source and therefore cannot be matched.

The primary barriers

There are several barriers that need to be overcome if wireless battery solutions are to be realised. For a company that has a battery-driven product, it can be difficult to assess the potential for energy harvesting.

The surrounding environment and practical circumstances mean everything

How much light is there actually on the wall in the office or by the machine in the production centre, with what frequencies will vibrations arise on the engine, and how large a temperature gradient is there actually between a particular hot water pipe and the surrounding air? This has to be known before it can be assessed whether there is potential for making the product energy self-sufficient. Likewise, it must be assessed how energy harvesting technologies work in practice in contrast to a data sheet, which provides peak performance during perfect conditions, something which is rarely achieved in the real world.

At the same time, the practical implementation is another factor, where the final installation has a big impact on the angle of the solar cell compared to the light source, the thermal generator’s contact with the heat source, the vibration harvester’s mechanical connection to oscillating movement, etc. This is challenging compared to just integrating a battery. Functional prototypes should therefore be tested in the intended environment as early as possible during the process.

Power management – the key to a successful battery-free product

Because of natural changes in the product’s surrounding environment, energy harvesting generator technologies rarely produce a stable 3 V, which batteries otherwise deliver. A converter can deal with a few mV from a thermo-electrical generator at low temperature differences or over 50 V in the case of a piezoelectric generator in a vibrating environment, while at the same time it must be ensured that the generator maintains its maximum output point.

Sourcing of new energy harvesting technologies

Some technologies for harvesting energy from the surrounding environment are widely available, while other technologies are only offered by a single or a just a few suppliers. When assessing which technologies should replace batteries, it is important to evaluate supplier risk.

Five good tips

  • Start by evaluating whether your product is within the 100 µW – 10 mW power consumption range.
  • Carry out thorough data logging of the energy level, so that there is a real data basis for assessing the energy potential.
  • Make functional prototypes for early testing in the concrete environment, incl. testing of mounting.
  • Power management circuits defines the efficiency of the energy harvesting generator.
  • Keep an eye on energy harvesting manufacturer’s supply stability.

Contact

For more information contact Johan Pedersen, Specialist, Energy Harvesting & IoT at DELTA, tel. +45 72 19 43 23, jep@delta.dk.

This is a translation of an article published in SPM Magasinet, August 2016.


DANISH VERSION

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Batteriløs elektronik – Råd til at komme i gang med at realisere energy harvesting

Batteriforbrug i verden – statistik
Med udbredelsen af flere og flere smarte produkter, intenet of things og wearable gadgets i mange afskygninger bliver behovet for skift og opladning af batteri kun større og større. Skidt for brugsoplevelsen og værre for miljøet. Derfor ser mange i retningen af batteriløse løsninger, hvor der høstes energi fra omgivelserne gennem lys, bevægelser, temperaturgradienter eller radiofrekvenser.  

Af Johan Pedersen

Sweet-spot i mikrowatt – milliwatt området

Energy harvesting er særligt relevant for produkter, der har lavt energiforbrug i omegnen af 100 µW – 5 mW, da mange energy harvesting teknologier ligger i en energidensitet på 100 µW/cm som set i fig. 1.

Et standard knapcellebatteri CR2032 kan levere i 1 mW i mere end 45 timer, men når man kommer ned i et forbrug på få µW, hvor knapcellebatteriet kan holde 2-4 år, så er det i mange tilfælde ikke rentabelt at benytte energy harvesting, hvis et batteri kan holde produktets levetid ud.

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Fig. 1. Sammenligning af energidensitet for de forskellige energikilder i vores omgivelser. Det er tydeligt at udendørs lys ligger væsentligt  over resten og at RF kun er relevant ved ultra low power enheder. Kilde: CEA-LETI.

Med solcellen udendørs som forbillede har mange store forventninger til andre teknologiers performance, som ofte dog opererer på helt andre energimæssige vilkår. Solen er vores mest energitætte kilde og kan derfor ikke matches.

De primære barrierer

Barriererne, der skal overkommes for at realisere batteriløse løsninger, er flere. For en virksomhed, der har et batteridrevet produkt, kan det være svært at vurdere potentialet for energy harvesting.

Omkringværende miljø og praktiske omstændigheder betyder alt

Hvor meget lys er der egentlig på væggen i kontoret eller ved maskinen i produktionshallen, ved hvilke frekvenser forekommer vibrationerne på motoren, og hvor stor en temperaturgradient er der egentlig mellem det varme vandrør og den omgivende luft. Dette er man nødt til at vide, før man kan vurdere, om der er potentiale for at lave sit produkt selvforsynende med energi. Ligeledes skal det vurderes, hvordan energy harvesting generatorteknologierne virker i praksis i modsætning til datablade, som opgiver peak ydelser under perfekte forhold, men som sjældent holder i den virkelige verden.

Den praktiske implementering er samtidig en helt anden, hvor slutmontage har stor betydning: solcellens vinkel mod lyskilden, termogeneratorens kontakt til varmekilden, vibrationshøsterens mekaniske kobling til svingningerne mv. Dette er i stor kontrast til blot at integrere et batteri. Derfor bør funktionelle prototyper testes i det tiltænkte miljø så tidligt i processen som muligt.

Power management – kernen i et succesfuldt batteriløst produkt

Grundet naturlige ændringer i produkters omgivelser giver energy harvesting generatorteknologier sjældent stabilt 3 V som man er vant til fra et batteri. En konverter kan behandle ned til få mV fra en termoelektrisk generator ved lave temperaturforskelle eller over 50 V ved en piezoelektrisk generator i et vibrerende miljø samtidig med at det sikres, at generatoren holdes på sit maksimale ydelsespunkt.

Sourcing af nye energy harvesting teknologier

Nogle teknologier til høst af energi fra omgivelserne er bredt tilgængelige, hvor andre teknologier kun tilbydes af en enkelt eller få leverandører. I vurderingen af hvilke teknologier der skal erstatte batterier, er det vigtigt at evaluere leverandørrisikoen.

5 gode råd

  • Start med at evaluere, om dit produkt er indenfor 100 µW – 10 mW i effektforbrug
  • Lav grundig datalogning af energiniveau, så der er et reelt grundlag af data til at vurdere energipotentialet.
  • Lav funktionelle prototyper til tidlige tests i det konkrete miljø inkl. test af montering
  • Power management kredsløb definerer effektiviten af energy harvesting generatoren
  • Hav øje for energy harvesting producentens leveringsstabilitet.

Kontakt

For mere information kontakt Johan Pedersen, Specialist, Energy Harvesting & IoT hos DELTA, tlf. +45 72 19 43 23, jep@delta.dk.

Denne artikel er bragt i SPM Magasinet , august 2016.

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