Magnum ME-RC50 – Settings Menu

Learn about the Magnum Energy ME-RC50 setup features, and how the can benefit you! Features like Search Watts, Low Battery Cutout and Charge Rate can improve battery performance. Learn more and watch our video.

Monitor Your PV System With Web Monitoring Software

web monitoring software

PV system inverters and charge controllers are typically equipped with some sort of control panel and indicators, but it’s often rather rudimentary. The equipment manufacturers may offer an optional interface panel to allow for a wider range of local configuration, control, and performance reporting.

A step up in configuration, control, data logging, and reporting is web monitoring software. By connecting your PV system to the web – either directly via a router or via a PC, hard-wired or via Wi-Fi – you can monitor and even control your system remotely.

Some systems can be configured to send a message when certain conditions exist, such as low battery state of charge or some other fault. This feature allows you to take corrective action before serious damage could occur.

Unfortunately, there’s not yet a standard data set for the PV industry. Accordingly, owners typically must buy proprietary hardware and software from the inverter and controller manufacturers. However, by monitoring, logging, and analyzing system performance, either locally or remotely, you may be able to optimize your specific system’s performance and load scheduling.

Monitoring is a popular option for residential, business, and utility installations. Additionally, detailed local monitoring and control may be useful in your RV or on your boat. Give Inverter Service Center a call at 800-621-1271, and we’ll be happy to discuss the web monitoring software options available for your system.

Grid Offset vs. Sell Back

off-grid tiny house

Grid-tie inverters – those without batteries – are key components of a broad range of PV systems for residential, commercial, and utility-scale applications. These systems are popular, in part, due to high reliability and low maintenance needs. At the residential and commercial levels, these systems connect at the building power panel(s), and they enable customers to locally generate electrical energy during the day. The local electric utility, building inspector, and fire department may require design drawings and calculations, applications, reviews, permits, inspections, and/or special meters before such a system can be installed and switched on.

PV array and inverter size, solar radiation, location, orientation, and various environmental and seasonal factors affect how much energy a system produces. A “small” system may generate enough energy to reduce (“offset”) consumption from the grid. A “large” PV system may generate enough energy to not only meet a customer’s electrical demand during parts of the day – effectively reducing part-time consumption to zero – but even have excess energy available to “sell back” to the utility grid.

Either way, customers realize reduced monthly energy bills as returns on their investments, utility generation station pollution is reduced due to lower energy demand, and the need to build additional utility generation stations is similarly reduced. System costs may be reduced by federal, state, local, and/or utility incentives, and Time-of-Use (TOU) rates and tariffs may affect the cost of energy bought and sold.

Going a step further, a “net zero” PV system configuration is a goal for some, where the total amount of energy generated by the grid-tied PV system over a year essentially equals the total amount of energy consumed by the home or business during the same period. In short, energy generated less energy consumed equals zero.

Note, however, that the “net zero” customer still relies on the utility grid to one degree or another for all or some power during some parts of the day (i.e., at night or during cloudy daytime periods) or times of the year (i.e., in the winter when the days are short and the sun is low), and then sells excess energy back to the grid when the sun is shining brightly. Put another way, “net zero” systems still require electric power stations.

An awkward limitation (possibly) of this architecture is that due to “anti-islanding” safety features, virtually all of these PV systems stop generating power and disconnect from the grid during brownouts or blackouts, be they local or regional. It’s frustrating for many to sit through a blackout with a costly alternative energy system on the roof literally doing nothing until at least five minutes after stable utility power is restored.

Battery-based inverters offer useful and even intriguing alternatives to the grid-offset vs. sell back discussion.

Like battery-less grid-tie inverters, battery-based off-grid inverters can be installed on a home or business to reduce utility energy consumption. Ideally, the inverter loads are powered from the PV array and the batteries are recharged during the day. These loads are powered from the battery bank at night. If the battery state-of-charge drops too low, then the inverter automatically connects to the grid to power its loads and help recharge the batteries.

A unique benefit of this configuration is that (assuming sufficient battery SOC) the batteries represent a backup energy source and will continue to power the inverter loads while the grid is down. For example, these loads might include some CFL or LED lights, an energy-efficient refrigerator, a microwave, and a cell phone charger. And, this type of architecture does not require special utility connection approval since it doesn’t sell back to the grid.

For those who want to sell excess energy to the grid and have a battery backup, battery-based grid-tie inverters are available.

Grid offset, sell back, and battery backup systems require different design strategies, component configurations, and permitting. Give Inverter Service Center a call at 800-621-1271, and we’ll be happy to discuss your goals and the possible solutions.

Battery-Based Charge Controller Technology Explained

Morningstar Solar Charge Controllers

The charge controller in a battery-based PV system has but one main function: to keep the batteries from being over-charged. Most charge controllers can now be configured for battery voltage (12, 24, 48 V nominal), battery type (flooded-cell, AGM, gel), and they offer multi-stage charging algorithms (bulk, absorption, float, equalization), resulting in dependable performance and enhanced battery life.

Some controllers offer temperature compensation (increase target voltages when the batteries are cold and reduce voltages when they’re warm), can be fine-tuned to a particular application, offer voltage-controlled switches, and provide status indicators or displays. At least one controller can now talk to the operator!

PWM vs. MPPT Charge Controllers

One key remaining difference in battery-based charge controller technology and pricing is pulse width modulation (PWM) vs. maximum power point tracking (MPPT) architecture. PWM charge controllers are among the first “smart” controllers, and they may include many of the features mentioned above. These controllers use PWM technology to accurately maintain target voltages for the absorption, float, and equalization stages by varying and limiting charge current.

However, a characteristic of the PWM controller is that the PV module operating voltage is essentially set by the battery charging voltage when the controller is operating in its bulk stage. For example, although a module’s maximum power point voltage might be 17V,  it will operate at 13V if the battery’s instantaneous bulk charging voltage is 13V. The 4V loss means a 24% power reduction under these conditions, which translates into a longer bulk charge period.

An application complication when using a PWM charge controller is that the module- and array specs must be carefully matched to the operational environment and the particular battery target voltages. Module voltages that are too high will not deliver full power, resulting in less than expected system performance.

This can be especially disheartening in the winter when module voltages are typically higher than in summer. And, large low-voltage arrays require (expensive) large gauge wiring to minimize power losses in the wiring home run between the array and the controller.

Charge Controller Breakthrough Technology

MPPT charge controllers are a true technology breakthrough. They effectively operate as smart DC-DC converters and provide many benefits to PV system design and operation. At the most basic level, an MPPT controller can track a module’s optimal voltage and current points independently of the battery voltage to deliver maximum power (maximum voltage x maximum current = maximum power).

Borrowing from the example above, a module operating at 17 V and 4 A in bulk mode via an MPPT controller can deliver 13 V and almost 5A.

By converting “excess” module voltage into additional charge current, the bulk charging state is shortened compared to a PWM unit. This feature is especially valuable during short winter days when a cold module’s even greater “excess” voltage is converted into even more charge current.

High battery-current MPPT charge controllers can be even more sophisticated. For example, these can take arrays in the 18 V to 60 V (nominal) range and convert the “high” array voltage down to a lower voltage battery bank, all while proportionally increasing the available charge current.

This feature allows for much broader and more competitive selection of PV module specifications, all while providing for an optimized PV system which can more easily meet operation expectations. And, by using a “high” voltage array to charge a “low” voltage battery bank, you can reduce your home run cabling costs.

MPPT controllers invariably cost more than PWM models. However, everything else being equal, MPPT controller-based systems require smaller – as less costly – PV arrays. Including reduced balance of system costs, an MPPT controller-based PV system can be quite competitive from a financial perspective.

Give Inverter Service Center a call at 800-621-1271, and we’ll be happy to discuss your system configuration options.

About the Author – Jim Goodnight – also known as “crewzer” — is a retired solar industry application engineer, product manager, and forum moderator and has previously written for Home Power and Solar Professional magazines.