The fact that most people don’t think twice about their safety when plugging an electrical device into a wall outlet is no accident. Homes and businesses today are powered by standardized, safe alternating current (AC) electricity, but that was not always the case.

Over a hundred years ago, Thomas Edison and Nikola Tesla were the generals in what was then called ‘The War of the Currents’. Tesla championed AC electricity, and Edison did the same for direct current (DC) electricity. When the dust settled on a battlefield that saw everything from intellectual property to political maneuvering, Tesla was left standing and safe, low-voltage AC power became the gold standard for homes and businesses. Yet, when homeowners are considering rooftop solar or home energy storage once again face the decision between AC and DC systems.

AC power’s historical advantage

AC power and DC power both move energy through a circuit. Not unlike water in a garden hose, when you disconnect the hose from the spigot, water stops flowing. In AC power systems, current cycles between positive and negative values; they alternate. In DC systems, current is fixed at a constant positive value, hence ‘direct’ current. So why are most modern homes served by AC power?

Thomas Edison, the DC power proponent, believed that neighborhoods would use energy from small generators located close to those neighborhoods. Nikola Tesla, the AC power proponent envisioned a system in which large, centralized generators would send out energy through long transmission lines. George Westinghouse, the father of the modern electric grid, opted for Tesla’s AC system, and the rest was history.

Why AC systems are safer

Homeowners use a different set of criteria than electric companies do when comparing the merits of AC and DC power systems. But if safety is the key consideration, AC power wins again. Here’s why.

DC power systems are higher voltage and have to be closely monitored for arc faults, which pose significant risk of fire and bodily injury. Even the smallest equipment failure, such as a damaged cable or a loose electrical connection, can generate an arc fault. Once an arc fault is triggered, it can be difficult to stop because voltage in DC systems is constant, and you have to be able to interrupt the circuit or the arcing will continue.

In an AC power system, voltage continually passes zero as current cycles between positive and negative values, making it possible to virtually eliminate the risk of an arc fault.
Rooftop solar systems using DC power also tend to rely on hazardous high voltage to move energy from a full array of solar panels to a centralized string inverter, while AC power systems like the Enphase Microinverter System always operate at low voltage. That is a safety feature from which solar installers, homeowners, first responders, and utility workers all benefit.

It’s important to be able to trust that friends and family will be safe around the products you bring into your home, including rooftop solar and energy storage systems. By choosing an AC system, you’re as safe as with any quality home appliance introduced in the last hundred years or so. In the War of the Currents, AC electricity won the day for households because of safety and reliability. There is no reason for homeowners to fight this war again on their rooftops, and introduce unnecessary risk. Our advice: Stay safe and keep it AC.

California Installers: Are Your Inverters Ready for the Rule 21 Mandate Coming in September?

The State of California has been working on Rule 21 for over four years. This regulation mandates new safety features, as well as requirements for advanced grid functionalities (AGF) for inverters, and therefore affects solar installers and homeowners. It is important to note that Rule 21 governs interconnections made to California's Investor-owned utilities (IOUs), those regulated by the California Public Utilities Commission (PUC), like Pacific Gas & Electric Co. (PG&E), Southern California Edison (SCE), and San Diego Gas & Electric Co. (SDG&E). Other municipal utilities in the state, like SMUD or LADWP, are likely to voluntarily comply with or adopt similar standards.

Haven’t been following along? Have no fear. We’ve got you covered. In this post, we’ll discuss all the most timely and relevant details.

OK, so what is Rule 21?

California Rule 21 governs the interconnection agreement that homeowners and utilities sign before new solar energy systems can send electricity to the grid. Starting Sept. 8, 2017, California utilities including PG&E, SDE&G, and SCE will require additional functionality from the inverters that are allowed to interconnect to the grid. Smart inverters may proceed. Others may not.

Many states often follow the lead of California, so installers around the country might want to pay attention as well.

Why crack down on dumb inverters?

According to Governor Brown’s “Goals for Adding Renewable Capacity in California,” the state is on the path to installing 12,000 megawatts of rooftop solar systems and other distributed energy resources (DERs) by 2020. These resources have great potential to reduce energy costs and improve grid reliability, but first they require some upgrades to the grid. Namely, the grid must be able to handle two-way power flows and it must be able to better handle intermittent resources like solar energy.

Before the solar industry started adding huge amounts of generating capacity to the grid, solar inverters were instructed to switch off at the first sign of a grid disturbance. This approach backfires when there’s a lot of solar on the grid, because the sudden loss of generating capacity can set off a cascading effect that inadvertently increases grid volatility.

This is why Enphase has often said that a solar inverter needs to be smart to in order to be a good citizen of the grid.

Rule 21 will take effect in three phases.

Phase 1 covers an initial set of AGF requirements, including voltage and frequency ride-through, extending the times that solar energy systems can continue to operate while grid conditions are in flux, as well as methods of reactive power control to help regulate grid voltage. For more information about how solar inverters handle reactive power, check out this article from IEEE Spectrum.

Phase 1 also addresses anti-islanding, which is the ability to sense when a power outage has occurred and automatically shut solar systems down so they don’t keep feeding energy into the grid when utility workers are (or might be) repairing power lines.

Phase 2 will set a common language for how inverters, solar energy systems, and utility systems talk to one another. Systems must also be able to communicate over the internet, although they can’t yet be required to have an internet connection because California has yet to decide who should pay for internet connection, the utility or the homeowner.

Phase 3 will cover additional inverter functions, like data monitoring, remote connection and disconnection, and maximum power controls.

The timelines for adopting Phases 2 and 3 have not been settled yet.

What does this mean for Enphase installers?

All Enphase S-Series and IQ-Series inverters already perform all the advanced grid functions (AGF) required by Rule 21. In addition, Enphase’s cloud-based infrastructure ensures that our inverters will be able to keep up with changing requirements in the future.

For an example of how Enphase can remotely upgrade large numbers of microinverters to promote grid stability, please have a look at our groundbreaking collaboration with Hawaiian Electric Company.

The trendlines are clear. State policymakers are nudging utilities and homeowners to adopt smart technologies like energy storage and home energy management systems to pave the way toward a more stable grid that can support more solar and other DERs. Enphase has built the technology platform to help realize California’s vision—one that increasingly resembles our own vision of what’s possible with smart energy.

SolarPower Europe has today published our “Regulatory asks on solar and digitalisation” to ensure that policy-makers support the transition to a fully digitalisation solar offering. Thanks to the whole team for this pioneering document.

These are the 10 policy asks

1. Remove barriers to the peer-to-peer trading of electricity, such as (but not exclusively) supply license requirements, concluding contracts between peers, network charging and existing and future systems for the delivery and billing of electricity.
2. Ensure that the implementation of regulation does not preclude new technologies and business models for the trading of and accounting for electricity, such as Blockchain and cryptocurrencies that create incentives for PV and enable prosumers to participate in energy markets.
3. Encourage regulation that allows aggregators to compete with conventional generators in all electricity markets and offer services in these markets via new or different digital technologies, such as Virtual Power Plants. Allow aggregators to combine resources from all voltage levels and use appropriate measuring equipment for the size of the installation.
4. Use digitalisation to develop flexibility markets with more automated tools and standardised products, as well as standardised requirements for the provision of system services both behind the meter and at distribution and transmission level. Reform intraday and spot-markets to enable large-scale solar and solar-plus-storage plants to take on balancing responsibilities.
5. Accelerate the deployment of smart grid technology, so that more solar can be integrated into the system and both utility-scale and small-scale solar can provide services to the grid. In conjunction, reform incentives for network operators, to encourage them to implement smart grid technology as an alternative to strengthening cables and transformers. Also provide more funding to smart grid and smart market integration projects such as within the Connecting Europe Facility funding instrument.
6. Reward the speed and accuracy that distributed energy resources such as solar and storage can provide in terms of grid support services.
7. Accelerate the deployment of smart metering functionality, real-time measurement of consumption and grid feed-in, as smart metering is a catalyst for new solar business models. Ensure that consumers have access to their smart meter data and guarantee that the roll-out of smart meters will not discriminate against new and existing innovative solutions and solar prosumers. Avoid imposing extra costs on smart meter customers, or mandating a single gateway for all energy data in and out of a building. Ensure that self-consumed electricity is not subject to taxes, fees or charges
8. Ensure that proposals within the market design package for metering and consumption data to be made available between DSOs, TSOs, customers, suppliers, aggregators and energy service companies are maintained. Guarantee that state of the art and up-to-date data protection and cybersecurity standards are put in place.
9. Maintain provisions in the proposed revision of the Energy Performance of Buildings Directive on a ‘smartness indicator’ for homes and ensure that on-site electricity generation is given a bonus within the methodology for setting cost-optimal minimum energy performance requirements for new and renovated buildings. Ensure that this methodology takes a holistic view of sector coupling, so that excess PV electricity can be used and stored e.g. as heat via heat pumps, or hot water storage.
10. Ensure that EU-level work on standards and interoperability, within the Digital Single Market includes solar PV systems, smart buildings and smart grids. Encourage the Commission to come forward with its ‘baseline’ standardised data format as soon as possible, which individual device or service manufacturers will then add additional features to.

Find more information on the SolarPower Europe website.

solarpowereuropelogoSolarPower Europe’s “Regulatory asks on solar and digitalisation” were drawn up by the Digitalisation and Solar Task Force, a group of members within the association working together to ensure that the solar PV sector in Europe makes the most of the opportunities arising from the digitalisation of the energy system.

It follows the Solar industry’s seven commitments on digitalisation. An in-depth report on the market opportunities for digitalised solar will follow later this year.


Click here to download the document as PDF.

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Each improvement to the Enphase System brings time savings and materials savings to the installer. Within the IQ System, the latest generation of Enphase technology, we replaced a four-wire cabling system with plug-and-play two-wire cabling. A double-insulated polymer enclosure for the IQ Microinverter enabled us to eliminate the grounding conductor. Adding line-to-line communications between the Microinverters and the Envoy eliminated the neutral wire. These changes have helped make Enphase smarter, lighter, and faster than ever.

While standardizing around a system that reduces electrical parts count and provides greater installation flexibility, we recognize that installers have been busy standardizing workflow at the job site. That’s why we created the IQ System with two radically simple design options for installers to link branch circuits from the rooftop to the electrical service panel, the IQ Combiner and the Q Aggregator.

In this post, we’ll describe each of these products and provide reasons why some installers will opt for IQ Combiner while others may prefer Q Aggregator.

Designing with IQ Combiner

If you’re already installing Enphase with the AC Combiner Box, a durable, prewired enclosure that consolidates interconnection equipment for systems with the Envoy-S, you’ll immediately recognize the benefits of the IQ Combiner. The two products are strikingly similar, but with one big difference. IQ Combiner houses an IQ Envoy that’s compatible with the IQ Microinverter, enabling the production and consumption monitoring and energy storage control that you’d expect from an Enphase combiner.

If you haven’t experienced an installation with an Enphase combiner box, here are three reasons to learn more.

Standardized, reliable installations

Instead of bringing one box for combining branch circuits, a second box for the revenue-grade meter, and a third box to hold the Envoy, IQ Combiner puts all networking and metering equipment into a single, UL-certified enclosure. The product also provides peace of mind with a five-year warranty.

Fast, reliable system communications

The preconfigured IQ Combiner improves system availability by completing electrical and networking connections in a controlled factory setting and minimizing installation variables at the job site. Installers can connect any combination of up to three branch circuits of IQ Micros or IQ Batteries within the enclosure.

Perfect for systems with energy storage

The IQ Combiner makes an Enphase customer storage ready, simplifying the connection of IQ Battery circuits alongside solar installs or for future system upgrades. When you do connect storage to the IQ Combiner, pay attention to best practices on configuring current transformers (CTs). We always recommend installing the optional Consumption CTs, as this data gives the system owner more insight about their energy usage and will significantly help size the correct storage system later.

Designing with Q Aggregator

Some installers prefer to use their own outdoor enclosures to house interconnection equipment and may wish to concentrate on reducing the assortment of electrical components on the roof. The Q Aggregator was created to maximize value for these installers. Q Aggregator is a roof-mounted box that replaces the standard junction box and includes internal 20 Amp overcurrent protection for up to three branch circuits. This allows running a single set of output conductors, Line 1 and Line 2, in the homerun along with the equipment grounding conductor (EGC) required for the array’s non-current-carrying metal parts in the racking and modules. The Q Aggregator includes a grounding lug for connecting your EGC to the racking or modules.

Here are three reasons to connect with your distributor or participate in an upcoming Enphase training event to learn more about Q Aggregator.

Realizes the promise of a plug-and-play solar install

A single Q Aggregator can support up to 11.5 kWac of rooftop solar, including branch circuits spread out across multiple sections of a customer’s roof. Q Aggregator not only eliminates the need for installers to stock a variety of parts on the electrical bill of materials—including junction boxes, cable glands, breakers, conductors, and conduit—it neatly splits out roof labor from electrical work.

Improves design flexibility

In the IQ System, a single branch Q cable can be fed to the Q Aggregator at any position along a branch circuit where an open connector is available. This process of dividing a circuit into smaller branch circuits, known as center feeding, improves design flexibility by mitigating excessive voltage rise and improving AC line losses.

Enhances system reliability

In Microinverter systems, the transition from rooftop AC wiring is always done in a J-box. Installers and electricians can choose from many hardware options to terminate and transition to homerun field wiring, such as wire nuts and terminal blocks. This can introduce inconsistencies across a fleet of systems and, in time, may lead to unreliable connection points. Q Aggregator eliminates this risk by accepting Q Cable connectors or Field Wireable Connectors on branch inputs and using an easy-to-connect clamp-style connector that doesn’t require tools or torquing for homerun conductors up to 4 AWG in size.

Additional Resources

The Enphase website is fully stocked with support for installers who are transitioning over to the IQ System. Resources include data sheets, installation guides, component lists, and more. Our technical brief, Planning for an IQ Microinverter System, has lots of helpful tips, including sample photos and descriptions of third-party enclosures for housing the IQ Envoy in systems with Q Aggregator.

For a full list of resources, visit the solar professionals support page and type: IQ.



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