The gap between renewable energy promises and reality | EDN

Onr analysis on solar power promises. Read also the article comments. 


  1. Tomi Engdahl says:

    Integrating alternative power and existing electrical systems

    Despite (or as a result of) an economic downturn, the use of renewable energy options has grown over the past few years. This growth has been supported by federal and state programs including federal tax credits, state renewable portfolio standards, and a federal renewable fuels standard.

    There are many renewable energy-generation technologies that can be incorporated into residential- and commercial-building energy systems. Solar photovoltaic (PV) is by far the most recognizable renewable energy source (see Figure 1). Wind turbines are a close second (see Figure 2). However, these sources are only in operation during specific environmental operating parameters.

    One advantage of PV is it can be easily installed across a wide range of projects. It can be deployed to provide a utility-scale power generation plant or scaled down to only a few modules to supplement the power needs of a single family home.

    Installation and maintenance of wind turbines are more complicated.

    Geothermal technology can be used to produce electricity at utility scale. However, applications in commercial and residential settings are mainly limited to heating and cooling.

    Fuel cells produce electricity based on a chemical reaction that strips electrons from fuel containing hydrogen and directs the electrons toward oxygen through a sandwich of close-coupled bipolar plates and electrolyte

    Biomass electricity generation uses organic waste as fuel. The fuel is burned to create steam that, similar to geothermal plants, drives large turbine engines.

    One additional renewable energy-generation technology worth mentioning is hydro. In use for more than 100 years, hydro is the most widely used renewable energy-generation technology worldwide, accounting for 70% of the world’s renewable energy generated, according to REN21 (the Renewable Energy Policy Network for the 21st Century).

    Connection to existing electrical services

    Installing a new onsite renewable energy system at existing buildings or properties can sometimes seem onerous, especially when the existing distribution was designed prior to or without the foresight of modern codes related to paralleling local generating sources of electricity with the utility.

    NEC 705.12(A) allows local power-production sources to be connected to the supply side of a utility service. However, it is restricted to the rating of the utility service.

    If the aggregate capacity of the local power-production sources exceeds the utility rating, the service equipment will be overloaded, which may cause a fire

    When integrating alternative power and existing electrical systems, take the time to understand policies, incentives, procedures, and codes to ensure a successful project.

  2. Tomi Engdahl says:

    Power Tree Generates Solar Energy and Saves Space

    Solar energy is rapidly becoming a good option to provide electricity in areas with limited grid access and plenty of sunshine, but the sheer cost and amount of land it takes to deploy large solar arrays can be deployment prohibitive in some cases.

    This issue has inspired the government in India to support a project to build what has been dubbed a Solar Power Tree to generate solar energy while also saving space and conserving land.

    In the unveiling, Vardhan said Indian officials want to adopt alternative forms of energy, but cited the problem of the scarcity of land resources in India as a roadblock. To produce 1 MW of solar power requires about 3.5 acres of land in the conventional layout of solar panels, he said. This means the country needs thousands of acres of land to really embrace solar energy.

    The Solar Tree helps alleviate this problem not only by saving space thanks to its layout, but also by allowing land on which it’s deployed to be used for other purposes, such as farming, at the same time, researchers said.

    Indeed, a 4 kW Solar Power tree needs only four square feet; comparatively in a conventional layout of the same number of panels, 400 square feet of land would be required, officials said. The tree also has the potential to be 10% to 15% more energy efficient than solar panels thanks to its height, which allows it to harvest more energy from the sun’s rays than a conventional solar-panel layout on the ground, they said.

    The Solar Tree also has a storage element to generate energy after the sun goes down, with a battery back-up system that’s good for two hours of electricity when fully loaded.

    The CSIR team isn’t the first group of researchers to come up with a tree as a form factor for solar-energy generation.

  3. Tomi Engdahl says:

    Circuit protection design for photovoltaic power systems

    DC vs AC circuit protection

    Circuit breakers are often the preferred method of protection on the AC side of a solar energy system, and it may be tempting to try using the same circuit breakers on the DC side. Although the circuit breaker method is convenient, as a general rule, it is not always the best approach. The designer must carefully determine that the circuit protection device being used on the DC side of a solar energy system has been designed, tested and certified to a PV standard by an outside agency such as UL (Underwriters Laboratories) or VDE to be confident that the device will operate properly in the event of a fault. It is much more difficult for a circuit protection device to interrupt DC voltage than the equivalent RMS AC voltage. This is driven by the fundamental principle that AC circuit voltage reaches zero volts twice during each voltage cycle, which is a key factor affecting circuit protection devices’ ability to interrupt the voltage safely and isolate the troubled circuit.

    Given that solar PV panels generate DC power, the current and voltage are constant for a given level of irradiance on the PV panels. With high voltage DC current, it is difficult for typical circuit protection devices to interrupt the circuit reliably under the range of operating conditions likely to occur in a solar energy system. In the worst case, a circuit protection device that’s not designed and certified for DC PV systems may fail violently, causing equipment damage, fire and possibly even injury to personnel. However, the most common problem will be that the devices don’t operate quickly enough under typical PV system overcurrent conditions.

    For example, in a string, the ISC (short circuit current) may not be much higher than the normal current. A typical solar string might output 4.2A in normal operation, and its forward ISC will be around 4.5A. When combined with other strings in a small 450VDC 10kW system, the short circuit current that the properly sized 10A OCPD (overcurrent protection device) will be called on to interrupt in the event of a string fault will be approximately 20A.

    Depending on the application and system design, the DC string voltage will typically be in the range of 300V to 1000V but may have the potential to go as high as 1500VDC in grid-connected systems. Fuses, disconnects, wiring devices, etc. for combiner boxes must be selected accordingly. In addition, UL and IEC standards have specific performance requirements for OCPDs used in these applications.

  4. Tomi Engdahl says:

    Selecting a solar energy conversion method

    A major problem facing solar energy system designers is determining the best, most cost effective method to extract power from a solar array and deliver it to the AC grid. Of equal importance is how to solve the problem of shading. A shaded panel can burn out and reduce functionality of an entire string of panels. Methods will be presented to solve this problem.

  5. Tomi Engdahl says:

    Very Large Lithium-ion Batteries

    Very large lithium-ion battery banks were largely unknown ten years ago. Now, it is tough to keep up with the variety of uses for them. On ships, where there were no such batteries, we are starting to see 1-5 MWh banks. Autonomous underwater vehicles, mining trucks and buses can sport ones of up to 350 kWh but it is in stationary applications that really big facilities have arrived. Here there is a multiplier effect with Li-ion gaining market share in growth markets.


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