Solar Power for IoT and Sensors

What makes Voltaic solar panels suitable for IoT applications?

Our small solar panels are strong, light and IPX7 waterproof. Each solar cell and the output wire are encapsulated in urethane and backed by an aluminum plastic composite substrate. The result is a tough solar panel that will last 8-10 years in the field for air and water quality applications, smart agriculture and other remote monitoring systems.

Compared to glass, Voltaic solar panels are extremely low-profile and easy to embed or mount onto a variety of designs. They are far more robust than laminate-constructed panels and the vast majority of solar panels that use epoxy or PET coatings.

Where have Voltaic panels been deployed?

solar flood monitor
solar water level monitor

How does plug and play power for IoT work?

If you have a battery and charge circuit already designed for your application, then you easily connect our panel to your battery.

If you need a battery with an efficient solar charge circuit, our V15 (4,000mAh) and V44 (12,000mAh) have been designed with IoT applications in mind. Besides charging efficiently from solar, both batteries have an Always On function that a) keeps the battery output on, even if nothing is drawing power on the other end for extended periods of time and b) features a smart restart -- if the battery is completely drained, the battery doesn’t turn on again until it builds up a reasonable buffer of power. This keeps the application from bouncing on and off quickly in extreme low light conditions.

What IoT applications tend to need solar power?

Solar can make sense when battery life of the system is between 4 and 365 days and there is no grid-based power source available. If the application lasts less than 4 days on its battery, it will likely go down when there are extended periods of rain and heavy clouds. If it lasts more than a year, it is often, though not always, economical to replace the battery annually.

The most power intensive systems tend to be systems communicating via WiMax, 2G, 3G, 4G cellular and satellite communication networks back to the network.

What factors drive power consumption in sensing applications?

There are a lot of variables based on the design of the system. In general, power is driven by:

  • 1. steady state / resting power consumption of the system - steady state / resting power consumption of the system - an Arduino will consume 5mA or less in a well-designed sleep mode, but that still adds up. Dedicated designs are often lower.

  • 2. frequency of data sampling - sensors vary in their power consumption, but we see a lot of humidity, gas, motion and light sensors in the 1-2mA range. Running 24x7 at 3.7V, that is 0.1-0.2 Watt hours a day. A GPS sensor may draw 20-25mA. Most gas sensors often require a pre-heat time of 24 hours and need to stay on to be accurate, other sensors can be turned off or put to sleep when not needed.

  • 3. frequency and duration of data transmission - GSM boards consume a fair amount of power during transmission. For example, the Particle Electron consumes between 800 and 1,800mA vs 14mA for an RF radio or 45mA for a XBee module.

Operating Current for Particle Electron GSM Board (mA)

Cellular ON - Average 180 250
Cellular ON - Peak 800 1800
Cellular ON - Powersave 50 80
Cellular OFF 2 15

We have seen well monitoring systems that send data once a week designed to last 4 years on about a 12,000mAh battery and a data logger with no communications network last about 10 days on a 3,000mAh battery. Often, the power sipping systems are custom designed boards with pretty expensive designs and the more power hungry systems are using off the shelf components like Arduinos and relatively low design costs.

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How do I estimate the power consumption of my application?

We recommend using a few simple methods.

  1. 1. Do the math based on data sheets for each of your components. Multiply current by voltage by time (in hours) to get your total Watt hours per day

  2. 2. Connect the system to a power supply and record the steady state and peak power consumption during sampling and transmission along with the length of time of each of those states

  3. 3. Connect the system to a battery with a known capacity (e.g. 3.7V, 3,000mAh) and time how long the system runs

Any reduction in power consumption translates to lower requirements for solar panels and battery capacity or a decreased likelihood that the system runs out of power.

How big of a solar panel and battery do I need?

Testing your system in real life conditions with actual solar panels and batteries is the best way to properly size solar panels and batteries. Test with the size you think you need plus one 1.5 - 2.0X that size.

We often recommend that the panel should be able to more than fully power the system on one hour of good sun a day.

Assuming you’re using a battery and in good sunlight with the panel pointed at the sun, roughly ½ of the rated power of the panel will reach the device. So if you have a 2 Watt panel, you will get 1 Watt hour of power out of the battery into your device with an hour of perfect conditions. If you’re system uses 5 Watt hours a day, you want to think about having 10 Watts or so of solar. This will vary if you are incredibly sunny or cloudy climates.

A battery provides a buffer for when the sun is not shining consistently. Again it varies based on applications and tolerance, but it isn’t uncommon to see 7 days of heavy cloud cover in many parts of the United States at some part during the year. We think the battery should be sized to get through those periods.

solar flood monitor

How can I mount your solar panels?

We have a universal solar panel bracket that attaches with a u-bolt to vertical and horizontal poles that range in diameter from 0.5 - 2.5 inches and with a pipe clamp on pipes 2.5 inches and up.

small solar panel mount
>solar panel on pipe

The back of our standard panels have a 4/40 stainless steel screw in each corner which can be attached to a range of materials. If you have other requirements, review our custom solar panel page for options.

You can use also use magnets that thread on the the back of the stainless steel screw, zip ties, or our corner mounts.

small solar panel charging battery

Does Voltaic have favorite GSM Boards? Sensors? Data Platforms for IoT?

GSM Boards: There has been a lot of innovation in this space in the last few years. In particular, we are excited that power consumption has been coming down. We really like the Particle Electron and the Adafruit Feather FONA.

GSM Boards: Sensors have come down in price and quality has increased, what’s not to like? Adafruit and Sparkfun both stock a huge range. For water sensors, we really like fellow Brooklynites Atlas Scientific.

Iot Data Platforms: We are not completely sold on any of them yet. We love the clean design of and detailed data options in Thingspeak. The most frustrating platform for us has certainly been xively. From their open roots as Pachube, we have been turned off by the walls xively puts up for demo-ing small projects.


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