Stand-alone meters can be mounted some distance from the shunt in a convenient and easily visible place for viewing the display. Integrated and internal meters may have a simple display at the unit, with the rest of the details available through the remote monitor display.
Even the simplest and least expensive of modern amp-hour meters have serial data output, and the more advanced models make it easy for you to connect the system to your PC. You’ll need a PC interface and software from the meter manufacturer. Note that to collect detailed historical data, a computer that’s running all the time is required. Some enthusiasts use an old laptop that’s been retired from daily use just for these logging operations. You can watch your system performance live with a “dashboard” application, analyze your data with a spreadsheet, or even send data to your website or smartphone.
Some system monitors are designed to communicate directly with your home computer network, either through a LAN cable or by wireless. For this data communication, your Internet service and/or routers must be powered on, but your PC doesn’t have to be running. Unless you are a computer programmer, you’ll also need to subscribe to an Internet system monitoring service (which in some cases is free) to establish a secure site to log into your meter, and a way to build monitoring “widgets” to insert into your website or blog.
Your Internet service must include a static IP address to use any of these web-monitoring features, and that may cost extra. With some satellite Internet services, putting a system monitor online may not be allowed—be sure to check with your Internet provider first.
Amp-hour meters are easy to install, but be sure to follow the manufacturer's instructions. Before you start, shut down your entire power system using the main DC disconnect. Turn off the PV array breaker and disconnect the battery output cabling in the battery box. You'll need to find a good location for the shunt, keeping in mind that all energy moving into or out of the battery bank must pass through it on the main negative wire. A good location is inside the inverter power panel; many panels have spaces reserved near the main negative buss just for this purpose. You'll need a short cable with lugs on both ends that's the same wire gauge as your battery output cable (since this is part of the negative-side circuit pathway to/from the battery bank).
Next, mount the display panel in a convenient and visible location, and run the cable from the shunt to it. Most displays mount in standard electrical boxes. The cable used is a special multiwire, shielded, twisted-pair bundle that should be purchased directly from the meter manufacturer to make sure it is the right type. If you are installing a system-integrated meter, things are even easier—the special cable from shunt to monitor box will be short, and then you simply plug the monitor into the system network hub with a LAN cable or wireless-to-LAN interface.
After meter installation and powering up your system, your new meter will need to be programmed with your battery bank’s amp-hour capacity, the system voltage, and the voltage level at which your charge controller considers the batteries to be full. Then, you must charge the battery bank to full capacity, usually with a generator, until that “full” voltage level is reached. At that point, your meter takes over, and you are in the monitoring business!
A simple amp-hour meter and shunt costs about $200—a small price to pay considering the total cost of an entire renewable energy system and the relatively fragile nature of its battery bank. If you monitor your battery bank regularly and react accordingly, you can extend its life by many years before replacement is needed.
Author and educator Dan Fink has lived 11 miles off the grid in the northern Colorado mountains since 1991. He teaches classes about off-grid systems and small wind power, and is the executive director of Buckville Energy Consulting, a NABCEP/IREC/ISPQ-accredited continuing education provider. Dan is the coauthor of Homebrew Wind Power.
Bogart Engineering • www.bogartengineering.com • Amp-hour meters
Samlex • www.samlex.com • Unitek Batteryguard
Xantrex • www.xantrex.com • Amp-hour meters
System-Integrated Amp-Hour Meters:
APRS World • www.aprsworld.com
Magnum Energy • www.magnumenergy.com
OutBack Power Systems • www.outbackpower.com
Schneider Electric • www.schneider-electric.com
SMA America • www.sma-america.com
Data Acquisition, Networking & Internet monitoring:
APRS World • www.aprsworld.com
Atkinson Electronics • www.atkinsonelectronics.com
greenHouse Computers • www.greenhousepc.com
WattMetrics • www.wattmetrics.com