Photovoltaic Tutorial:

Optional Equipment

Here are some extras to consider when planning your PV system:

The Deck Monitoring Residential Solar Pack allows users to track system performance, including power output, irradiance, volts, amps, cell temperature, weather data, and wind direction/speed. For more info, check out the PDF brochure. At $1,750.00, it's a little pricey, but more monitoring products have hit the market in recent years, and prices continue to drop.

System Monitoring

A solar array that sits on the roof is not easily accessible, which means if problems develop, you might not notice them immediately. Although the modules themselves are mostly maintenance-free, they don't come with windshield wipers. If leaves or snowflakes collect on the glass, or a rodent chews into a module cable, a loss of power output may result. And before you know it, the solar kilowatt hours not generated will push the payback time on your PV investment several months or a year. That's why it makes sense to purchase some form of system monitoring.

Technically, a device that monitors and reports on power generation is known as a data acquisition system (DAS). A set of measuring instruments is combined with data recording hardware, and the info is typically transmitted to a computer or the internet. Then a software app translates the data into layman's english, giving you a rundown of what's going on.

Measuring devices may include:

• Multi-meter (voltage and amperage)
• Kilowatt Hour Meter
• Pyranometer - measures direct and diffuse sunlight
• Temperature/Heat Sensors
• Barometer
• Relative Humidity Probe
• Wind Vane

With these instruments, it's possible to deduce that --

• the output of a module has tanked.
• there's signifant shading across the array.
• the ambient temperature around the array is extremely high
• high winds or an approaching hurricane may threaten the array if extra measures to secure it aren't taken.
• your array tilt and orientation may be off target.

There are three ways to go when choosing data monitoring for your solar electric system:

1. Buy a DAS from the company that makes the inverter you're using.

Most of the top inverter manufacturers now market a range of data monitoring products that work in tandem with the inverter. Fronius, for example, sells a data logger which can be used in conjunction with Fronius Solar.access software available for free from its website. SMA likewise sells a data monitoring package called the Sunny Beam, which works in conjunction with Sunny Data Control software. These and other products are discussed in an article posted at CivicSolar.com.

Fronius Datalogger Web

The downside to inverter-based monitoring is that it's conducted at the inverter, rather than at the array. You won't be able to track the output of each module, just the performance of the array in general.

2. Use microinverters or DC optimizers that attach to each of the array's modules.

This option is the most popular and will be described below.

3. Select a third-party DAS solution.

Heliotronics
These instruments and hardware are part of a data aquisition system for a home solar array. You can read the product description at the Heliotronics website.

Some companies offer data monitoring specifically designed for a PV system, while others service multiple needs and client interests. In the case of the latter group, it's possible to customize a system based on whatever types of data you want to track. To get a better idea of what's available, click on the website links below:

Deck Monitoring

Solar-Log

Heliotronics

Locus Energy

MicroDaq.com

Microinverters with Data Tracking

When shading across an array is inevitable, the most common mitigation strategy incorporates micro-inverters. The company Enphase pioneered this technology, which converts PV electricity to alternating current as soon as it leaves the module. This has the distinct advantage of isolating the output of each module, and that prevents shading in one area of the array from reducting the production elsewhere.

Enphase also provides a data monitoring component, allowing a homeowner to effortlessly track the production of each module in his or her array 24/7/365. The "Envoy Communications Gateway" delivers the information to your computer or mobile device. Click here to learn more about Enphase products.

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An Enphase microinverter is attached to the rail of a solar array under construction. The module will sit on top. At right, part of a screenshot showing the Envoy gateway in action, providing realtime monitoring of module output.

One downside to micro-inverters is their exposure to the elements outdoors, especially atop roofs. Although they're positioned beneath the modules, they are still far more exposed to extreme heat, cold and moisture than a central inverter. Enphase provides a 25-year warranty to calm the nerves of anyone concerned about the device's long haul performance.

DC to DC Optimization

Like a micro-inverter, a DC to DC optimizer attaches to each module to monitor its performance and regulate the power output. This component provides the equivalent of an MPPT circuit to insure that maximum production is achieved. However, since the current's polarity is not altered, you will still need a central inverter downstream of the array. DC optimizers cost about a third or a fourth the price of micro-inverters, and include a data monitoring scheme.

Tigo Energy
For shading problems and to monitor performance without adding micro-inverters, you can use a new impedance-matching technology developed by Tigo Energy that includes a DAS. Since panel efficiency is increased as a result, you may see up to 20 percent more production from your array.

Tigo Energy is leading the way with this technology. It's DC to DC optimizer costs about $50 a pop. The "Management Unit" that provides the data tracking will set you back another $500. For example, a ten-module array equipped with DC to DC optimizers would cost a total of $1,500, although the investment should qualify for the 30 percent federal tax credit on home solar installations. If you're working with a solar contractor, you may be able to negotiate a better price. (One of the bigger installers, REC, currently uses Tigo products in its residential solar power division.)

For more info, here's the Tigo brochure. For more info on microinverters and DC optimizers, here's an article from altenergystocks.com.

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Optional Equipment Continued on Page 2... (Battery Backup, Wind Turbine, Solar Water Heater & AC Generator)

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