Category Archives: power-engineering-article

Driven by grid stability & reliability needs and by the integration of renewables, Standalone BESS (battery energy storage systems) are moving from pilot to mainstream. But anyone who has tried to develop or engineer one, especially in dense, highly...

Interconnection queues are more congested than ever, and the path to approval is increasingly opaque. Developers are spending serious money on land control, studies, and legal work, only to hit delays when grid studies surface surprises late in the...

U.S. distributed energy resources (DER) capacity is expected to increase by 217 GW by 2028, according to a Wood Mackenzie Report. A staggering number, even to the seasoned solar industry professional. One of the challenges is connecting the massive...

In the complex world of solar interconnections, cable limiters have long been a point of confusion, debate, and evolving regulation. They are key in ensuring safe and compliant system design and operation. This brief update allows developers, EPCs,...

Through our work as an Owner’s Engineer, Pure Power has extensive experience evaluating, inspecting, and commissioning PV power systems. While I-V curve tracing is an essential tool in these efforts, it is not necessarily the best tool for every...

When designing utility-scale solar energy projects, optimizing central inverters is a crucial aspect that project developers, EPCs, and stakeholders often overlook. The strategic placement and design of central inverters plays a significant role in...

This is a follow up to the article Design Recommendations for 1500V String inverters, where we only briefly mentioned "Free Voltage Drop" and wanted to dive in a little deeper here.

When we value engineer a large solar project, we can take advantage...

At Pure Power Engineering, our engineers work closely with project originators, developers and EPC firms to reduce the upfront capital costs of construction without sacrificing long-term operating costs. Given the dynamic nature of solar...

Protective Relays are an advanced area of electrical engineering and contracting that can be intimidating, but they don’t have to be! This series of 3 articles will introduce basic relaying to the non-engineers in the solar and energy storage...

Protective Relays are an advanced area of electrical engineering and contracting that can be intimidating, but they don’t have to be! This series of 3 articles will introduce basic relaying to the non-engineers in the solar and energy storage...

Protective Relays are an advanced area of electrical engineering and contracting that can be intimidating, but they don’t have to be! This series of 3 articles will introduce basic relaying to the non-engineers in the solar and energy storage...

Technical due diligence is essential to solar project success in commercial, industrial and utility applications. Large PV power systems are capital-intensive expenditures with a service life of 30 years or more. If these assets do not operate...

Unlike conventional PV modules that convert only front-side irradiance into electrical power, bifacial modules convert both front- and back-side irradiance into electricity. While the additional rear-side irradiance improves plant performance in...

The basic goal of ASTM E2848, “Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance,” is to compare the ratio of a PV power plant’s actual in-field performance to its expected performance based on a system model. The...

What is a "Neutral" conductor?

To an Engineer: A "neutral" is a current-carrying conductor that carries the unbalanced current in 3 phase systems, and is intentionally connected to the ground. In North America, the neutral is color-coded white or...

A principle goal of value engineering is to deliver long-term performance and reliability at the lowest cost practicable. One effective way to reduce the levelized cost of energy (LCOE) in large-scale or commercial and industrial (C&I) solar...

Effective grounding in photovoltaic (PV) systems is the creation of a low-impedance reference to ground at the AC side of the inverter—or group of inverters—that is designed to be compatible with the distribution network’s requirements and existing...

Pure Power performs many types of power system studies, and the Arc Flash Study may be the most important because it is all about worker safety. However, since it’s not always a code requirement and doesn’t have a direct impact on generation, it is...

NEC 2017 brings with it some advantages and disadvantages. The new rapid shutdown rules that require MLPE are the biggest change (that is an advantage for safety, but disadvantage for project costs).

This is a simplified version of my previous article on the new Rapid Shutdown codes taking effect on January 1, 2019. For those interested in the technical details of the code, refer to 2017 NEC 690.12 Rapid Shutdown – Important Changes.

The 2017 National Electric Code (NEC) dramatically changes the requirements for "Rapid Shutdown of PV Systems on Buildings." Half of the states already adopted NEC 2017 and several more will in the next few months (such as NJ and CT), so you can’t...

Its common knowledge that Aluminum (Al) conductors cost less than Copper (Cu). But how big is the difference in price? The answer may shock you.

Our first article 2014 NEC 690.12 Rapid Shutdown for String Inverters on Flat Roofs we explained the basics of implementing a rapid shutdown system using string inverters on a roof.  In that article, we gave a simple example of a single array.

The 2014 National Electric Code added a new section of code 690.12 requiring "Rapid Shutdown of PV Systems on Buildings".  Below is the first of 1 of 2 articles we put together to help you understand this code (here is the other: 2014 Rapid Shutdown...

In a previous article “The 120% Rule Explained – 2011 NEC 705.12(D)(2)” we clarified the philosophy of the 120% rule for load (supply) side interconnections of solar PV systems. The 2011 code was clean, understandable, and easy to safely apply.

480 to 208 Transformers are commonly needed to step down 480V inverters for 208V services. Unfortunately electrical rooms are often crowded with existing equipment. Sometimes there isn’t room for a transformer, so we are often forced to locate the...

Everyone knows about the 120% rule, but not everyone understands the situation it is trying to protect against. This article will explain Pure Power’s philosophy on the 120% rule.

Pure Power engineered a rooftop solar PV system with an innovative new method for mounting string inverters. The inverters are mounted on strut stands directly over cable tray, and the AC and DC wiring is all neatly and compactly run in the cable...

Thermal (IR) cameras are a great tool for preventative maintenance and inspection of your PV system. With a little thermography “know-how” and some image focusing, problems can be discovered quickly before they create a fault or safety hazard in the...

This photo is an excellent example of an inverter installation on the roof. Keeping the inverters next to the array allows the unfused string wires to be kept at a minimum length, increasing safety. Notice how the inverters are tilted to the north...

When you select the wrong transformer enclosure rating, moisture will get into the transformer enclosure and cause faults. NEMA 3R transformers are effective at keeping out rain, but sometimes no snow drifts.

While conducting O&M on a Satcon 250kW central inverter, we noticed this fan with an object lodged between the blades.

During O&M we often find combiner boxes and disconnect switches with water inside them, despite the box being NEMA 4 and fully gasketed, no top or side penetrations, and weather tight connectors properly installed.

Many roofs are designed to support thousands of pounds of HVAC units and large air handlers, so the additional weight of an inverter is feasible in many cases.

Be careful with Aluminum Conductors

The cost savings of Aluminum conductors is too good to ignore. Both the engineer and the electrician must respect the differences between copper and the less forgiving aluminum. However, if designed and installed...

When deciding what size and quantity of combiner boxes to use, always remember to use the full capacity of what you are buying.