Eosense wants to make sure our eosFD soil flux sensors are as autonomous as possible! We’ve done some research to find the best bang-for-your-buck batteries and solar panels to ensure maximum up time in the field. The recommended power supply is the Sherpa 100 Lithium Ion battery pack and the Boulder 50 solar panel, both by GoalZero.

How many eosFD’s can I use per Boulder/Sherpa Combo?

We designed this system to run one (1) eosFD unit. While single battery / panel approach for each eosFD has a higher upfront cost, it represents a substantially better long term investment for both deployment and infrastructure flexibility. With independent power, each eosFD can be located anywhere on the site, without running long (and expensive) power cabling back to a central hub. And by spending on solar equipment instead of custom wiring and cables, your infrastructure is far more general purpose and reusable for other instruments and deployments.

How long will it run my eosFD?

It depends on your desired measurement frequency and the amount of solar your site is receiving. Without any solar input, the Sherpa 100 will run an eosFD for:

• 29.2 hours at 5 minute measurement frequency
• 38.4 hours at 10 minute measurement frequency
• 48.8 hours at 30 minute measurement frequency
• 52.3 hours at 60 minute measurement frequency

At latitudes between 0-50 North/South we expect the Boulder 50 solar panel should supply enough energy to keep the batteries topped up, assuming that you don’t have a stretch of more than two very cloudy days. At latitudes above 50 North/South we recommend increasing to the Boulder 100 solar panel, or using two chained Boulder 50 solar panel units.

Sherpa 100 battery pack for scale

If your Sherpa 100 dies in the field, for example due to a long period of cloudy days, it will start back up as soon as the solar panels supply it with enough power (probably in about 4-8 hours once weather conditions improve). Once the eosFD soil flux sensor gets enough voltage from the Sherpa, it will also pick back up on its measurement cycle.

Why did we choose the Boulder and the Sherpa?

Put simply and effectively, the Boulder 50 and Sherpa 100 are simple and effective. GoalZero has done an excellent job of designing the system to make it so that users don’t have to do any wiring or similar electrical work in the field. All of the connectors are shape coded and clearly marked. Unlike Lead acid batteries, the Lithium Ion Sherpa offers similar power capacity at about one-third the weight and with the ability to be fully drained and charged back up again without damaging the battery capacity.

How should I set my system up?

The solar panel should have an unobstructed view of the southern horizon. If the view is blocked by trees, buildings, etc. it may be necessary to mount the panel on a pole. Luckily the Boulder 50 has standard mounting points for a Z bracket solar panel mount, so you can attach it to existing site infrastructure or deploy a new mounting post for the system.

Boulder 50 solar panels for scale

The Sherpa 100 is pretty robust, but its not weather proof. Depending on the conditions at your site and the deployment time, you’ll need to enclose the battery or at least shelter it from direct weather. It is critical that your battery does not get wet as moisture and water can get into the battery cells behind the protection circuitry and bypass that protection.

Cold temperatures (below freezing) can impact the lithium battery capacity. If you’ll be off-grid in sub-zero conditions, we recommend keeping your Sherpa in an insulated cooler, connected to a power source (solar panels), and charging your gear. The natural heat generated by the charger contained in an insulated cooler will keep battery capacity at its highest.