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June 3, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

SepiSolar project engineers use one powerful solar design tool to perform many system design functions. Some are completed in minutes. Others take hours. This points to a perennial challenge we face as a customer service organization committed to continual improvement.

When all support requests go into a single queue, quick and easy tasks don’t always get resolved quickly enough.

The fact is, our solar design tool is necessarily complex for highly trained engineers working through a streamlined process. But if you separate the pieces, you’ll find several user-friendly tools that contractors can use themselves. A wire size calculator and a string configuration calculator, for example.

Later this year, SepiSolar will provide six web tools for contractors to perform quick and easy design tasks. Our engineers will continue to handle any project design changes, or all of them if you’d like. We are always available with a wide variety of customer support resources. This is just one opportunity, when the cost of waiting for support on a simple design change exceeds the benefit, for SepiSolar to empower our customers to use some of our solar design tools yourself.

When to use our design tools

Each time a change request comes in to SepiSolar, an assistant project manager or operations manager tags it according to priority, complexity, time needed, and root cause. Tickets go into queue for the engineering team sorted by priority.

If a contractor submits a support ticket to resize a run of wire estimated to be 100 feet but later measured at closer to 200 feet, the complexity and time required would be set to “low.” The same might be true for a contractor wanting to move an inverter from inside a building to a location outdoors, who needs to know if the wire size must change.

Using SepiSolar’s wire size calculator, you enter inputs such as current through the conductor, number of wires in the conduit, and the project site’s maximum ambient temperature. The calculator auto-populates electrical resistance and generates the wire size that you need.

When there’s no urgency, let SepiSolar run the calculation. On the other hand, if you’re in the field and a quick calculation can prevent a return trip to the project site, direct access to our wire size tool can save time and money, eliminating a costly truck roll.

Complex and time-consuming design changes will continue to go directly to the engineering team. For example, an EPC might want to replace 60-cell modules with 72-cell modules in the plan set for an 850 kW agricultural project. Our engineers would use the new module specifications to recheck wire sizes and overcurrent protection and redraw the module array as needed.

If an EPC wants to replace central inverters with string inverters, in order to optimize the project for cost, then instead of using these calculator tools, our engineers would begin a consultation to help with inverter selection, AC wiring design, and DC wiring design, which is what creative, solutions-focused designers do best.

DIY solar design tools

The solar design tools that SepiSolar will make accessible to our customers on the web are simple and user friendly. These tools are not revolutionary. They just make a contractor’s job a little easier, one day at a time. Here’s how they work.

Wire sizing calculator

Oversizing electrical wire means overspending on materials, given the current that will flow through the system. To undersize means the system is carrying so much current that you risk melting conductor wire or insulation. Correct wire sizing avoids both extremes based on conductor material (copper or aluminum), current through the conductor, environment (in conduit, direct buried, or open air), how many conductors in conduit, insulation type (THHN, THWN-2, USE-2, XHHW), and ambient temperature plus adders for the environment.

String sizing calculator

Module string configuration introduces another set of tradeoffs. If you connect too many modules in series, the system can exceed an inverter’s maximum input voltage, causing equipment damage. Connect too few modules and you might fall short of the minimum input voltage required to start up the inverter. To determine string configuration, look at your solar module datasheet and input the following data points into the SepiSolar calculator: solar module manufacturer, model name or number, and quantity; inverter manufacturer and model name or number; racking type (e.g., flush or tilted roof mount, ground mount); maximum, minimum, and average high and average low temperature at the project location.

Conduit sizing calculator

The National Electrical Code limits how much wiring can go inside a conduit. It does so to control heat gain, manage risk of wire damage, and preserve space to eventually add more wires. In the NEC, you can find fill tables for frequently used wire and conduit types and equations for any application. Or input wire and conduit specifications into our conduit sizing calculator to get a fast and dependable conduit size.

120% rule

The 120 percent rule refers to a simple calculation used to confirm that the size of an electrical distribution panel in a home or business facility is large enough to handle the capacity of the circuit breakers feeding it. Most of these residential electrical panels have a 100 amp or 200 amp main breaker. For solar projects interconnected on the customer side of the meter, the National Electrical Code allows total ampacity from all sources up to 120 percent of the busbar or conductor rating. Why? In brief, it’s because when you connect a supply source to the service panel, it has the opposite effect of connecting a load source to the service panel. Instead of reducing capacity on the busbar, the solar generator actually increases capacity.

Voltage drop calculator

Voltage drop is a measure of efficiency in an electrical circuit. A 1 percent drop in voltage equals a 1 percent power reduction at the end of the line. Electrical calculator programs are generally available, but they don’t always consider all solar project inputs, as noted in Solar Pro. (See Issue 3.2, ‘Voltage drop in PV systems’) To calculate voltage drop, input circuit type: AC (1-phase or 3-phase) or DC, nominal voltage, current, wire gauge and material (aluminum vs copper), and the length of your conductor run.

Load calculator (structural and electrical)

Before issuing project permits, local authorities will compare system specifications to the electrical load and structural load requirements on site. Using SepiSolar’s load calculator, customers can size a building’s electrical service capacity based on service voltage (1-phase or 3-phase) and the sum of all motor loads, continuous loads, and non-continuous loads. To generate structural load limits, customers can also enter module weight and quantity, the number of modules racked in portrait and landscape, racking rail weight, rack type (tilt up or flush mount), weight adders (microinverters, optimizers, ballast blocks), and a measurement of wind exposure, such as wind speed, exposure zone, or the mean height of the roof.

Unlike other design tools

Contractors looking for solar design tools will find a variety of options on the market. Some products generate project proposals for use in the sales process along with plan sets for permitting and interconnection. Others require experience with sophisticated CAD software.

SepiSolar’s user-friendly tools are relatively simple in comparison. These are calculators used by licensed engineers, governed by codes and standards that protect public health and safety. They do not take the place of a licensed engineer. They complement the engineer’s work, empowering contractors to make code-compliant calculations yourself and increasing the value of the SepiSolar service.

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March 7, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

On January 31, 2019, the CPUC (California Public Utilities Commission) signed into law the most recent changes to the long-standing NEM (Net Energy Metering) tariff. While our white paper describes many of the financial benefits to the decision, we have received a variety of inquiries from industry stakeholders from across the value chain with interesting use cases of this policy change that are worth sharing. Like a fine, red wine, these ground-breaking policies often only get better with age, setting new precedents for future policies to come.

Electric Vehicle Chargers

For example, we reviewed a solar + storage + EV charging commercial project in California that was applying for EV charging credits from the State (contact us at blogs@sepisolar.com to learn more about these lucrative credits that start at ~$0.19/kWh!). In addition to DC-coupling the solar + storage, the developer also wanted to DC-couple the EV chargers.

Upon deeper analysis by SepiSolar, it became clear that the CPUC’s final decision sets a precedent for any DC-coupled device (not just storage) that charges exclusively from renewables (including EV chargers), since these EV charging credits get more valuable (anywhere up to ~$0.25/kWh) the more they charge from renewables. Based on our financial calculations, the difference in monetary ($) values between grid-charged-EV’s and PV-charged-EV’s is over 35%, so charging EV’s from PV in a DC-coupled framework adds a significant bonus to the ROI (Return on Investment) of the project.

SREC’s & AC Limitations on the Utility Grid

Another example comes to us from the east coast, where Pepco is evaluating SREC’s (Solar Renewable Energy Certificates) for energy storage as well as restricting the amount of PV power on their grid, due to infrastructure capacity constraints. Among the questions were: can SREC’s could be granted to exports from batteries that are exclusively charged from PV?

We are still going through the process of getting these approvals on specific projects, and so far, the answer appears to be a resounding “yes”! Not only do similar rules apply for the issuance of NEM and SREC credits, but de-rating the AC nameplate of the inverter (or, alternatively, “super-sizing” the DC nameplate rating of the PV system) appear to allow these projects to interconnect with the utility grid in a far more cost-effective manner. This is inherently because batteries are less expensive to install than infrastructure upgrades by utility companies.

In this particular use case, we are working on getting a 250 kW PV system approved with only a 50 kW AC interconnection limit. The only way to do this (cost-effectively) is by using a DC-coupled, solar-only-charging 400 kWh rated battery. At a $300k price tag for the battery with a 3-month lead-time, this resolves several problems for the customer, including:

  • Deferring a $500k “surprise” infrastructure cost from the utility (with a 10-month lead-time)
  • Allowing the customer to retain 100% of the original PV system size needed to offset electricity usage
  • Enabling demand charge reduction, which increases NPV and IRR
  • Adding back-up and resiliency capability, so the battery can supply energy to on-site loads when the grid goes down

REAP Grants

Recently, we have come across a number of agricultural businesses (rural businesses and agriculture producers) throughout the US who are now asking SepiSolar to evaluate the implications of this DC-coupled NEM framework in the context of the lucrative REAP (Rural Energy for America Program) grant. For those of you who do not know, REAP is a USDA-administered grant that can offset up to 25% ($500,000) of the total installation costs of a renewable energy system.

The question is this: Does the REAP grant apply to energy storage components? We, at SepiSolar, believe it absolutely does, and we’ve just recently submitted a grant application claiming the storage as part of the renewable facility property. The jury is currently out, but we’ll report back with hard answers to this question as soon as we hear back from the USDA.

When we set out to get solar-only-charging, DC-coupled batteries approved by the CPUC for NEM purposes, one of the first risks we wanted to investigate was whether or not such a policy change would result in a lengthy legal battle, or legislative nightmare, in the event that new (or existing) laws needed to be created (or changed).

We quickly discovered that there was precedent for our request in the RPS Standards (see Renewable Portfolio Standards Eligibility Guidebook), since it described energy storage as an addition, or an “enhancement,” to the renewable facility property, if and only if that storage device only charges from a renewable resource. This was unbelievably fantastic news because it meant that the legal structure, definitions, and policies were already in place, and no laws or bills would be required. Nobody had simply exercised the laws that were evidently already in place…that is, until now.

This discovery implied not only that a solar-only-charging energy storage system could (and should) accrue NEM credits, but also that the very definition of storage as an “enhancement” to the renewable facility, makes it just as exciting as adding a tracker motor, ballast racking system, auxiliary or lightning electrode, fuse, breaker, wire, conduit, combiner box, or perhaps any piece of equipment to the solar energy system. Basically, the more boring the legal repercussions appeared, the more exciting the policy work became.

So, if solar-only-charging batteries are just another type of “combiner box,” and are effectively part of the solar energy system (as an addition or enhancement), why shouldn’t ITC, MACRS, and, of course, the REAP grant apply?

All of these policies and legal precedents serve to reinforce the direction that DC-coupled, solar-only-charging batteries are headed – into the mainstream, and as an integral part of the renewable generating facility itself. Storage, by itself, can of course be treated as a stand-alone system with all the benefits thereof, but by reinterpreting storage as an enhancement to a renewable generating system, we get to leverage all the rules, laws, and policies already in place for renewables. This is a great benefit to storage, since renewables effectively give storage a legal and policy runway for accelerated adoption, without having to go through all the time, pain, and politics that solar and renewables had to go through (and are still going through). It’s 2 technologies for the legal / policy price of 1. That’s a good deal, and we should stop leaving money on the table for our customers.

As always, if you have more questions, please submit them in the comments section or send them to blogs@sepisolar.com. We’ll continue to keep you up to date on our progress in all these efforts and projects, and we look forward to bringing ever more value to our valued clients.


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February 20, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

When it comes to choosing the equipment used to interconnect the combined output of a PV system to the utility grid, it is important to ensure that the equipment is sized in order to withstand the full amount of power capable of being delivered by the PV system.

SepiSolar’s recently published a white paper that describes what our engineers consider before recommending PV system output equipment.

Download this resource and learn how SepiSolar engineers conduct a comprehensive evaluation.


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February 14, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

If you’re ever in the market to buy or sell an existing solar project, you’ll want to have an independent solar engineer to technically review and evaluate those assets.

SepiSolar’s recently published a white paper that describes our solar PV evaluation procedure. This PDF download also includes a case study of our evaluation of a 409 kW rooftop solar project.

Download this resource and learn how SepiSolar engineers conduct a comprehensive electrical and structural evaluation.


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February 8, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

Do you install EV chargers in California? SepiSolar just learned about an existing State of California incentive program that added EV charger installations to its list of eligible technologies. Here’s the scoop:

Who is eligible?

  • Any commercial, industrial, agricultural, utility-scale, or other non-residential property.
  • You can also go back to previous EV charger installations you’ve installed in the past to claim this credit moving forward.
  • The incentive can be assigned to the asset owner, the developer, the EPC, the property owner, or any 3rd party vis-a-vis any discretionary bilateral agreement.

How much is it worth? (A lot!)

  • California will pay $0.20 – $0.25/kWh (roughly $4,400/year, assuming one full EV charge per day) for each EV charger installed.
  • The incentive amount has grown about 800% over the last 6 years. (See the above chart.)

How long will the incentive last?

  • You’ll keep receiving the incentive for as long as the program lasts (currently budgeted through 2030).

Why is SepiSolar telling everyone about this?

As a solar design and engineering company, we care about the success of our industry. If you develop or install solar and energy storage projects in California, EV chargers are easy to include, add tremendous value to a project, and now have an additional substantial revenue stream to capture.

How can I learn more? 

The program is complex and difficult to explain in a blog post. Contact Tony Smith to learn more about how SepiSolar can help you process this incentive for your projects today!


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February 1, 2019

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

When I saw this article about LG lithium-ion energy storage fires in Korea, I couldn’t help but think of the fires that PG&E is being held responsible for in California. Those fires have ultimately lead PG&E into bankruptcy and will inevitably increase energy costs to ratepayers.

It’s amazing how something as seemingly simple as a campfire, power line, or a 18650 lithium cell—about the size of a lipstick container–can cause so much damage to California, one of the wealthiest states in the world and PG&E, the largest utility in the state, and, of course to the loss of lives and homes.

Some of these hazards defy logic or at least expectations. When SepiSolar was providing technical due diligence and engineering review services to NRG Home Solar from 2014 – 2016, we came across residential projects on the East coast that had unexpected dangers. For example, there was a solar PV system installed on top of the garage where snow had piled up on the PV system. Some rain had turned that snow into a giant slab of hardened ice. When the ice slipped off the solar array, it crushed the car parked in the driveway–not dented, dinged, or scratched. It completely totaled the car. The homeowner told us “that’s exactly where my children play in the summertime.”

Having just become a father at the end of December 2018, I think it’s fair to say that safety cannot, should not, and will not ever be taken for granted on my watch.

Risks vs Benefits

I don’t mean to suggest that we ought to over-design, over-engineer, over-regulate, over-install, or somehow bullet-proof every single component or assembly in a traditional solar or storage system.  That’s like saying “Since car accidents kill people, let’s require everyone to drive army-grade tanks down the street.” That line of thinking effectively kills an industry and becomes a zero-sum game. Instead, I would pose that taking risks is a part of life and is healthy for us, since taking risks and stepping outside our comfort zones is exactly how we grow, learn, and evolve.

The goal is to take calculated risks, or, alternatively, educated risks. What’s a calculated risk? It’s a risk that you’re aware you’re taking. The difference between educated risks and blind or reckless risks is awareness.

We then need to weigh those risks against the benefits in order to make effective decisions. After those decisions are made, we need to be ready to revisit them again soon because the learning process never stops. Assumptions will need to be revised, data recalculated, risks revisited, benefits re-weighed, and decisions re-evaluated. This is how we evolve and approach an ever-safer future, together.

So, let’s build some awareness, shall we? Let’s have a data-driven discussion about the fire risks associated with energy storage systems, and let’s turn our blind risks into calculated ones. Having helped build Green Charge Networks into a nationwide energy storage integrator (acquired by Engie in 2015), engineered solar and battery systems for over 10+ years, and having worked with utilities, UL, code officials, etc. on safety standards, I think I might have a thing or two to say about this subject.

Evaluate the Energy Storage Technology

To minimize risks in energy storage, perhaps the most obvious approach is to work with a technology that inherently works with chemicals and materials that have no fire risk associated with them. This is particularly difficult with batteries because when almost any battery is short-circuited, they instantly become a fire hazard. But that’s the nature of batteries – they can produce insanely high amounts of current, since the resistance in the battery circuit is governed by however fast (or slow) the chemicals involved can react with each other, allowing the free flow of electrons to accumulate. Of course, these chemicals are designed to react with each other in order to release electric charge. So, fire hazard is almost inherent in any battery (with at least 1 exception).

I love this side-by-side technology comparison authored by Fire Captain Matthew Paiss, a 22-year veteran of the San Jose Fire Department. Captain Paiss is the Fire Department’s subject matter expert on energy storage and is the IAFF primary representative to NFPA 70 (National Electrical Code) and NFPA 855 (Energy Storage System Standards), which has been incorporated into UL standards such as UL 9540. It was surprising and gratifying to know that there’s at least 1 technology that rises above the rest when it comes to safety.

Codes & Standards

There are a ton of uber-smart tradesmen, engineers, officials, and subject matter experts who love to wordsmith and craft codes and technical language (God love them!) in order to impose a minimal, universal set of health and safety standards designed to protect personal property and life. Some of these codes go all the way back to 1897, as is the case with the National Electrical Code, when electricity was thought of as a liquid! (Check out Leyden jars.)

Bottom line, let’s be sure to read and understand the modern codes thoroughly, including NFPA, NEC, UL, among others. Every word, comma, and comment were crafted with the care one would expect of a nationally applicable set of requirements, even if you disagree with many of them. It’s important to follow voltage, current, and sizing requirements, naturally. NEC 706, for instance, was just added to the NEC in the 2017 edition. That’s the first time batteries have been overhauled in the NEC since Article 480 was written back in the early 20th century! Let’s expect this new code section to evolve with the times as more data becomes available and continue to think of these codes as a “minimal” set of safety standards that we can go above-and-beyond as necessary to ensure the safety of the systems we design and build.

Real-time Data

While codes and standards are important, one of their drawbacks is that they are slow to change. Technology and data often evolve faster than codes and policies. Because of this, it’s important to look at the data, stay up-to-date on the latest-and-greatest information available, and dynamically build this data into your systems as it becomes available. Basically, I’m advising you to read. Read articles, publications, journals, media newsletters, and absorb as much as possible to keep up-to-date.

For instance, now that the above Korean article has surfaced about LG battery fires, it’s imperative to find out the root cause failures that led to these hazards. There is much to learn from failure, thereby converting failure into learning opportunities (which perhaps negates the use of the term “failure” in the first place – nothing is a failure, so long as you learn something from it!). We don’t have to wait for new technologies or new codes to come out. Instead, let’s use the data right away in any or all systems that we may be using with LG batteries, or any battery, for that matter.

The first time I thought about the risks associated with batteries was when I heard that Boeing grounded the Dreamliner. Our Co-Founder and CEO of Green Charge Networks at the time was a retired Boeing executive, so this naturally caught our attention. Wikipedia does a decent job summing up that experience, and you can get the full investigative report here.

The general takeaway is that regulatory bodies, manufacturers, and engineers were not “up to snuff” on the risks associated with battery technology. To a great degree, as the above Korean article shows, we are still learning these risks. At our time at Green Charge Networks, we understood that this meant that the safe deployment of battery systems would largely rest on us, since codes, standards, products, and regulations were still too much in their infancy to support us.

Direct Experience and Training

Nothing prepares you for danger, uncertainty, or risk more than education, experience, and training. The more hands-on experience you have with a particular product or technology, the more you will understand its limitations, weaknesses, and risks. Understanding not only what and when a battery undergoes thermal runaway, but also the “how” can really help put battery risks into perspective. What I learn from this is that it’s not just the battery one should be cautious of, but also the environment the battery is in. For example, does the battery have a fire suppression system? Is the battery located near any buildings or structures that have no fire suppression?.

One time I dropped a wrench on an old golf cart battery, and it just so happened that the wrench landed perfectly on both positive and negative terminals simultaneously. It was the first time I saw metal turn bright red, orange, and then white, and eventually melting all over the battery. This was just a regular ol’ lead acid battery, so it was surprising to me that such an old battery could have such a great impact on something as solid and stiff as a wrench. Needless to say, I am very cautious around terminals of batteries, since most batteries cannot be inherently turned “off” (again, with some exceptions).

In a nutshell, if you’re working with lithium batteries, make sure to identify the risks and retire them as much as possible. For instance:

  • HVAC systems for lithium are not just there to support battery performance, but they are safety devices as well. Make sure they’re appropriately sized and adequate for the operating environment the batteries will be in.
  • Lithium batteries that get too hot can result in thermal runaway, and other types of hazards, aside from accelerated degradation of the cell capacities and efficiencies. Fire suppression systems are required with the appropriate cleaning agents.
  • Closely monitoring and isolating cells that are approaching their end-of-life is critical. Battery degradation not only leads to capacity loss, but also battery failure.

There are many other aspects to keep in mind, and nearly all are avoidable if you’re aware of them in the first place.

I strongly believe that lithium-ion battery systems will continue to grow and thrive in our new renewable energy world, but as the Korean article shows, there are risks. As engineers, it’s our responsibility to be aware of these risks, evaluate them, and to find the solutions that will decrease those risk and perhaps even eliminate them with new safety innovations.

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January 24, 2019

This post contains a follow up on the NEM white paper written by solar industry leader Josh Weiner, Solar Expert Witness . Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

UPDATED: The CPUC has unanimously passed this California NEM Storage decision on January 31, 2019. The information in our white paper reflects the final decision.  

In December, SepiSolar published a white paper that reviews a proposed CPUC decision to include net energy metering (NEM) with DC-coupled energy storage for commercial solar systems. As of the writing of this blog post, the CPUC is set to vote to finalize the decision on January 31, 2019, and is expected to pass. However, it’s possible the vote will be postponed due to other priorities, such as PG&E’s bankruptcy filing. (Check the latest CPUC agenda here.)

While our white paper describes many of the financial benefits to the decision, several energy storage and inverter manufacturers had questions about the firmware solution that we designed for NEXTracker’s NX Flow system, a DC-coupled energy storage system.

Below is a list of some of these questions and the answers. As always, if you have more questions, please submit them in the comments section or send them to blogs@sepisolar.com.

Is DC-coupled storage with net metering approved in California only with NEXTracker’s NX Flow product?

As soon as the CPUC approves the policy change (hopefully by the end of January 2019), the NX Flow would be immediately eligible, since its firmware has already been verified by UL. However, other DC-coupled storage manufacturers may design similar firmware for their products. Eventually, UL will update their 1741 standard to include these protocols. In the meantime, utilities are allowing discretionary approvals of this policy, even though the CPUC hasn’t fully adopted it yet.

The white paper says that SepiSolar co-developed the firmware. Does that mean that energy storage or inverter OEMs need to license the code from SepiSolar or NEXTracker?

No. SepiSolar wrote the specifications, designed the testing protocol, and demonstrated the underwriting and verification process with our client, NEXTracker.

As with NEXTracker, OEMs will need to develop their own code and implement into their California NEM/Rule 21 compliant product after UL verification. Based on our experience, a manufacturer can typically develop the code within a day or so.

While SepiSolar does not write the firmware code, as an independent engineering firm, we’re able to help inverter and energy storage manufacturers with the functional and technical requirements to comply with this updated NEM energy storage policy for DC-coupled systems. Having gone through the UL process ourselves, we can advise on firmware design, testing pain points, pitfalls, and how to get through the UL approval process as expeditiously as possible.

Eventually, UL will update its 1741 standard to include the protocols that SepiSolar developed.

What do you mean by “firmware”? Don’t you mean “software”?

In order to adjust to this NEM storage proposal, utilities asked that the associated OEM software not be changed after interconnection, and that it be “hard-coded” into the hardware device’s “firmware” itself. They wanted to be certain that nobody could come back to the system later, after PTO (Permission to Operate) was issued, and re-program the battery to charge off the grid, thereby breaching the system’s interconnection agreement with the utility company.

While “firmware” involves software coding, it’s typically installed once at the manufacturer’s facility and implies that the software can’t be modified after installation or interconnection. On the other hand, “software” is inherently adjustable and can often be updated remotely by the system owner, OEM, or even third parties.

As a result, the “NEM software” (firmware) cited in the proposed CPUC decision must be hard-coded into the DC-coupled inverter device. It must then be recorded, tested, and verified by a Nationally Recognized Testing Laboratory (NRTL), such as UL or TUV. The inverter product must also have a specific version number and checksum that cannot be confused with other non-NEM-compliant hardware.

In the future, it’s possible that we’ll find ways to allow “un-editable” software to be located outside of the DC-coupled inverter device, perhaps in an EMS (Energy Management System) controller. However, the EMS would need to prove to the utilities that it, indeed, cannot be updated post-PTO. These alternatives are currently being discussed.

What happens if you update the firmware after interconnection?

As mentioned, the firmware protocol that SepiSolar developed ensures that the software is hard-coded by the OEM and verified that it was installed correctly by an NRTL. In our UL-verified protocol, if the firmware is changed after installation or interconnection, it will necessarily void the UL verification and put the entire installation in breach of its interconnection agreement (and Rule 21) with the utility. The utility will then be able to shut down the system and potentially fine the customer for any damages the utility may have sustained for the breach.

What are the firmware requirements?

The firmware requirements that any DC-coupled system would need to satisfy to receive NEM credits are fairly straight forward. It must be designed so that the battery can never charge from the grid. In addition, the firmware solution must be tested and verified by an NRTL, such as UL.

If you’d like to learn more about the specific tests themselves (there are 5 total), feel free to reach out to us at blogs@sepisolar.com, and we can share, specifically, what these tests entail. In summary, the tests involve:

1) The inverter’s ability to sense a potential “battery-charge-from-the-grid” event (which would violate this NEM policy) and mitigate it by controlling a DC bus voltage in order to turn the battery “off,”
2) The battery’s ability to be turned “on” or “off” by the inverter vis-à-vis this DC bus voltage control method described in (1) above,
3) The verification of software version number,
4) That no other software-controlled device (like an EMS) can override the inverter’s firmware, and
5) Sensitivity testing on all the above in the event that the PV supply varies widely (say, with variable cloud cover events).

Instead of inverters, can DC-DC converters adopt the firmware?

Yes. We see a clear use-case for getting a DC-DC converter approved under California NEM, but it would require a slightly different testing regime than the one we’ve developed for NEXTracker’s NX Flow product.

Is NEM with DC-coupled storage only available in California?

Yes, for now, due to this pending CPUC policy change, DC-coupled NEM with energy storage will only be available in California. However, other states typically follow California’s lead with policies like this. As of mid-January, 2019, we haven’t seen a system get approved outside of California.

***

We hope these responses answer your questions about the UL-verified firmware that is required for DC-coupled energy storage. If you have further questions, please add a comment or contact us at blogs@sepisolar.com.

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January 15, 2019 0

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

Welcome to the new SepiSolar website. Here’s how we listened to you. 



If you’ve ever been to SepiSolar.com for design and engineering services, you’ve probably just noticed that our website has changed–a lot.

Why did we redesign our website? Because we listened to you, our customers and potential customers, who wanted a better user experience. With that in mind, here’s a brief tour of the new SepiSolar website with some highlights of what’s changed.

Better Navigation

We’ve heard from you that extra clicks mean extra time finding the exact design and engineering services that you want. To improve navigation and user experience, we made all of our core services visible on the home page. With one click, you can now learn more about, say, our commercial design services,  or energy storage. The home page also has direct links to information about or our various technical consulting services, administrative services, and SepiAcademy, our new online training platform.



Still can’t find what you’re looking for? Use our search windows at the very top and in the blue footer of the website.

More Resources

SepiSolar website visitors often never knew they could download sample designs, site survey checklists, and more. To make these assets more visible, we now have “Resources” on our main navigation bar. There you’ll discover that we’ve added utility and microgrid design examples, as well as find pages for SepiSolar case studies, white papers and finished project photographs.



More Personal

As you’ll see in our About page, SepiSolar’s mission is “to build a community of designers who care about solving tomorrow’s energy problems today.” We take that mission seriously, so the new website reflects that in several ways. First, we put a face to the designers and engineers and staff that you often speak to.  You can also read some of our engineer’s thoughts on the home page, as well as get to know them a little better via our team page, another new section of the site.



You’ll also see quotes from our customers and why they use SepiSolar for their design and engineering services. Blogs will also be more personal and written by specific team members, not a nameless admin.

Finally, you might also notice a new FAQ button on our website. These are all general questions that we often here, but you’re always welcome to contact us directly for your personal question. If you’re new to SepiSolar and need a quote for design or technical consulting, well, there’s a big orange button in the top right of every page. There you can register for our SepiPortal and get a fast estimate for one or several designs. Already registered? Log in, as usual, using the red SepiPortal button at the top right of every page.



That’s the new SepiSolar.com new website tour. If you find a broken link or have other improvement suggestions, please let us know at blogs@sepisolar.com (also new!)

It’s always a team effort here at SepiSolar, but I have to give a special shout-out to Lean Digital Systems, our web designers. If you love this website, we’re confident they’ll create a beautiful, personal, and user-friendly solar website for your solar or energy storage company too!


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December 8, 2018 0

This post was written by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

As we approach this holiday season, I’d like to take a moment to look back at 2018 and share some of what’s in store at SepiSolar for 2019.

First, on behalf of our entire team, we want to thank you for selecting SepiSolar as your 2018 solar design and engineering partner. This year has seen many changes in the solar industry–as well as at SepiSolar.

In addition to our usual design work, we redesigned our logo and then redesigned a new HQ, expanding to larger offices in Fremont. The move was largely due to adding new team members to our engineering and operations teams, enabling us to design more efficiently and deliver plans on time.

Along with new team members, SepiSolar instituted new quality control measures and new design tools that are helping SepiSolar engineers design solar-plus-storage systems with increased speed and accuracy. In fact, we’re proud to report that nearly 90% of our customers’ residential designs receive permits without any revisions. For commercial, industrial, agricultural, and multi-family projects, 80% of projects receive a permit without revisions, even in America’s most demanding jurisdictions.

2018 also saw the launch of several new services, including Salesforce consulting for solar companies and Sepi Academy, our new NABCEP solar and energy storage training program.

What’s in Store for 2019

For 2019, SepiSolar will be keeping up with all the new permitting changes here in California and across the U.S. With a 100% renewable energy goals set for Hawaii and California, plus California’s new Title 24 solar roof mandate, we’ll be informing our clients on all the latest requirements and best design practices.

You’ll also see a new SepiSolar website that will be easier to use and filled with more resources, such as our site survey checklists and more new downloads and White Papers. Of course, we’ll also be generating new useful blog content and continuing our Ask SepiSolar Anything webinar series.

Thank you for being a part of SepiSolar in 2018. We’re excited for 2019 and look forward to working together on bringing more GW of solar and energy storage to the U.S. and the world.

From all of us at SepiSolar, we wish you and your family a wonderful holiday and a prosperous and happy new year!

Sincerely,

Josh Weiner, CEO of SepiSolar

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November 12, 2018 0

This post expands on a LinkedIn conversation initiated by Josh Weiner, Solar Expert Witness & Solar Engineering Expert. Mr. Weiner has been at the forefront of the solar energy industry for over 20 years and is an industry leader on solar-plus-storage engineering & design. Josh’s expertise spans both in-front of and behind-the-meter initiatives including residential, commercial, utility, grid-scale, and ev charging solar and storage applications. 

In a recent LinkedIn conversation, I was asked by Carlos Montiel, Lead Electrical Engineer of VEPICA, about the difference between designing solar for “reliability” vs “availability.”

CA Small Business Enterprise

Certification ID:
2015743

Bidder/Supplier ID:
BID0068933

NAICS Codes:
541330 – Engineering services
541340 – Drafting services
541490 – Other specialized design services
541618 – Other management consulting services
541690 – Other scientific and technical consulting services
541990 – All other professional, scientific, and technical services

D-U-N-S number:
065817064
CAGE:
8F5K7

UNSPSC Code:
811024, 81101701, 81101516, 81101604, 43232614, 81101505




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