Running your Picarro GasScouter and eosAC Off-Grid – Part 1
Introduction to the Picarro Gas Scouter and eosAC Automated Soil Flux Chambers
Gas analyzers have become increasingly more precise over the past 10 years with the adoption of laser-based sources and ultra-long path length optical cells. However, usually this has been at the cost of power consumption, making them difficult to easily deploy in the field, especially off-grid.
More recently, products like the new Picarro GasScouter have been designed to reduce the power consumption of these precision instruments and enhance their portability. For comparison, a standard Picarro analyzer usually draws about 200 W on average (for the analyzer and vacuum pump), whereas the GasScouter has an average draw of only 25 W. This low power consumption, plus excellent precision for CO2 and CH4 concentrations, make it an ideal instrument to measure greenhouse gas fluxes at off-grid field sites including agricultural fields and wetland sites.
Eosense’s eosAC and eosMX-P automated soil flux chamber and multiplexer systems are being integrated with the Picarro GasScouter as we speak, and offer a low power (9W average) solution for Picarro users to continuously monitoring of greenhouse gas fluxes. While the GasScouter does have an internal battery that allows it to run continuously for 8 hours, researchers may want to use the analyzer for longer-term, unattended deployments. In this three part blog we’ll talk about how to power the GasScouter and eosAC system for off-grid unattended deployments, and how to build a solar power solution and enclosure using off the shelf parts you can usually find at your local hardware stores.
Power Requirements, Solar Panels and Batteries
As I mentioned in the introduction, the Picarro GasScouter and Eosense eosAC/eosMX-P system draws about 34 W of power on average. This means to run the two systems for a full day of operation we’ll need about 816 Wh of energy (34 W * 25 h). We’re going to have to size our solar panels based on this number, and the peak sun for the location of our study. I’ve made these handy maps so you can see what the rough peak sun kWh/m2/d values are for your location during the winter and summer solstices (and man, does the UK ever get any sun?).
Since we’re going to be doing our testing in Nova Scotia, I am going to do a few quick calculations based on the summer (4-6 kWh/m2/d) and winter (2-4 kWh/m2/d) solstices (see maps above).
Summer = 816 Wh/4-6 kWh/m2/d = 136-204 W
Winter = 816 Wh/2-4 kWh/m2/d = 204-408 W
So if we only really want to deploy our system in the summer we can likely get away with 200 W of solar power, and if we want to extend our deployment into the winter then we should probably double our solar panels power output to 400 W. If you want to do some more precise calculations for your field site, please follow either the Application Note (less detailed, and for the eosFD) or Blog Post (more detailed) written by Eosense’s Electrical Engineering Manager, Darren Wall.
Obviously we’ll need to store this solar energy (unless we’re hanging out in the Arctic during the summer solstice). The Picarro GasScouter has a 223 Wh Li-Ion battery that will give us about six and a half hours (6.5 h) of backup, but not enough to make it through the night. So we’re going to supplement that with a few marine deep cycle batteries, but how many? To be safe we’re going to say we want the system to run for 3 days of absolutely miserable weather (no solar charge), which will be about 2450 Wh of energy at 12 V. Remembering back to your first year physics, P=IV, so we need about 200 Amp Hours of battery. But safety first, if we drain a lead acid battery its not going to charge back up, so we’re going to add 50% to that and assume we need 300 Ah to keep the system safe and sound (again Darren’s blog goes through this in more detail). Checking out our local suppliers, it looks like we can get three 115 Ah deep-cycle batteries for about $450 CAD, not bad for just over 3 days of total autonomy.
We obviously can’t dump all of this expensive (and electrically charged) equipment in the field without hiding it away from the elements – in the next post we’ll show you how to build an enclosure for your equipment and in part three we’ll show some test data from the system in the field.