By Enrique de la Cruz

The fundamentals of a well implemented solar installation project are no doubt critical for ensuring the operational efficiency of a solar plant. The owner or final user of any solar installation expects it to have a life expectancy of sometimes more than 25 years, without shortages. Many industry professionals will concur that solar design and installation is a complex but worthwhile process. Reliability, robustness and the use of highly efficient components are essential and if both the design and installation are well executed, the energy savings and the performance ratio of the installation will outweigh the out-of-pocket costs quickly.

With grid parity within reach in the next five years, it is necessary for companies in the PV industry to continue developing and sharing best practices. Over the past 60 years, AEG Power Solutions (AEG PS) has provided mission critical power control and power systems to selected end markets such as power generation, oil & gas and the solar energy industry. Building on our heritage and expertise, today we are one of the major solutions providers for megawatt utility-scale PV power plants as well as commercial and industrial properties, enabling smart grid applications with our intelligent and rugged power electronic solutions. We manufacture solar inverters and design, install and support complete solar power systems in commercial facilities.

In this article, I will share my views on important design and installation factors for end-to-end solar system installations and provide an in-depth look at the largest rooftop solar system installation completed early this year in Plano, Texas, the U.S.A.

Getting Started: Demanding High Efficiency Components

Embarking on a solar installation project involves many considerations such as selecting the correct solar panels and inverters to metering and monitoring for your project. There are some components of the system that are absolutely vital and selecting the right ones for your project will determine if your investment will generate a positive return in the long run.

Solar Inverters

Solar inverters are a key element in a solar installation even though they represent about only 10% of the total cost. With the growing utility-scale solar market, new inverter technologies have emerged alongside advancements in grid-tied inverters and PV hybrid inverters or chargers. With more options to choose from, selecting the right inverter involves plenty of research to find the correct balance between price, endurance and quality.

As with all other components, the key consideration when selecting a solar inverter is its efficiency. This is the main factor that enables you to judge if solar energy makes financial sense vis-a-vis the energy output and if the owner can recover the installation cost in savings within a reasonably short period of time. A fundamental indicator of efficiency is the performance ratio. The performance ratio of a solar installation is measured as the output power injected to the grid divided by the installed PV peak power. The ratio is a good evaluation criterion for determining the quality of the plant configuration because all components and their interaction are considered. To attain a positive ratio, system designers usually choose highly efficient components that are able to work well.

Besides efficiency, another important criterion is the lifespan of the solar inverter as this can provide an extended return on investment for the installation project. Inverters and their many electric components can be stressed to the limits over the years; cheaper converters may be able to do the same job but for a shorter period. It is important to keep in mind that solar installations need to operate well for more than 25 years, without shortages.

For utility-scale and rooftop installations, solar inverters that are ideal should have DC voltage capability up to 1000 Vdc and have a very compact and modular design that enables optimal power efficiency. In designing our new generation solar inverter Protect PV.250 for utility-sized PV MW installations, we specifically engineered it to have the ideal DC voltage capacity, meet the requirements of utility-grade applications and be customized to each specific application through a range of available options and a unique container design. In addition, we included an innovative FPGA circuit to ensure flexible, precise and rapid control needed to meet virtually all national grid standards. A recent report jointly issued by the Fraunhofer Institute for Solar Energy Systems (ISE) and Bureau Veritas showed that AEG Power Solutions’sProtect PV.250 solar inverter offers remarkable efficiency. Energy conversion efficiency testing conducted according to European Standard EN 50530 yielded a very high efficiency grade of 98.7% fulfilling all PV power plant requirements.

For utility-scale PV megawatt power plants, consistent status updates are essential. Completely integrated and single source solutions like AEG PS’s TKS-C 500 container solution has its core units fully integrated communication and monitoring components ensure smooth PV power plant operations in close cooperation with the grid operator. 

As for the trend of PV power plants becoming bigger and bigger, users need higher power inverters and containers to optimize their return on investment. Larger plants that are 20 MWp and beyond require inverters to have an increased power rating to maintain high efficiency. One way to increase the overall efficiency of the plants, especially the larger ones, is to use what AEG PS has termed ‘copain mode‘ This basically means that two inverters work in parallel to share the load by following a programmed algorithm in a way that efficiency is always optimized. AEG PS is prepared for this challenge and is about to release the Protect PV.500, a 500KVA solar inverter maximizing footprint and keeping record levels of efficiency. The Protect PV.500 allows us to design and build fully equipped 1 MW containers and integrating monitoring and MV components for proper connection to the grid.

Solar Panels

It is without a doubt that choosing the right solar panels for each application and engaging an experienced and reliable EPC contractor are critical for success. Not all solar installations are identical and, depending on the environmental conditions and the type of installation, some panels may behave much better than others.

When designing and installing the latest commercial rooftop solar system in Plano, Texas, we developed a system that features 234 solar modules and we constructed the PV panels to be tilted at a calculated 15-degree angle to maximize system effectiveness and enable the system to withstand the same wind velocity as the roof structure.

Other considerations when making a decision include the material, durability and cost. When it comes to material, wafer-based silicon solar cells are still favored by some while others prefer polycrystalline solar cells. Durability is factored in by the material of the cells which will affect the lifespan of the panels. The final criteria--cost--will depend on your budget and desired return of investment.

Monitoring and Metering

Another fundamental aspect of any installation that has to be considered from the beginning is monitoring and metering solutions. As solar installations are expected to operate for more than 25 years with minimum interruptions and at minimum cost, it is absolutely essential to have continuous information about the status of the installation. This information should be specified up to the level of each string or even panel in order to allow the maintenance team to react in time and correct any malfunctioning.

A maximum accuracy in sensing string currents is required because panels have tolerances with temperature and radiation and also different strings are paralleled on the same combiner box which means that low accurate measuring devices will not be able to detect a real failure in a given string. AEG PS solutions in monitoring and metering allow the customer to measure with 0.5% accuracy the current in each string by means of the intelligent combiner boxes, and report it remotely to the intelligent data logger normally installed in the inverter station. This information is then processed and reported to the control room where the operator is able to determine, with the help of the monitoring software, the status of the power plant in real time.

Commercial Rooftop Installation

At AEG PS, our key area of work is in the implementation and support of turnkey solar systems that enable commercial buildings and industrial parks to utilize clean, renewable energy. Our solar systems feature solar panels, solar inverters, monitoring, diagnostics and communications equipment, all of which can be supported by smart-grid-enabled standards and can be monitored and maintained by us.

We recently designed and installed a commercial rooftop solar energy system in our North American headquarters in Plano, Texas. The rooftop system took three weeks to install and utilizes a 49-kilowatt solar system for harvesting solar energy. Following the installation we have seen hefty savings of 40-50% in our monthly power bills--this result was achieved by feeding the solar energy into the building which thereby reduced the amount of electricity being purchased from our utility provider and our dependence on electrical energy.

When planning the project, we needed a robust system that allowed us to reduce our carbon footprint as well as operational costs without disturbing the building’s structural integrity or curb appeal. As we were leasing the space in the single-story, multi-tenant facility, the entire system had to meet the building owner’s guidelines, accommodate the building’s roof capacity and layout, comply with local codes and also integrate with the local utility grid. We, therefore, worked with building management and were able to design and install a low-maintenance system that did its job outside as efficiently as we did ours inside.

In the design and installation phase, the two main considerations for us were to maximize the effectiveness of the system and ensure that the system was not permanently affixed to the roof and could be moved and installed on another building if required. We, therefore, selected only high efficiency components and incorporated mobility into our system.

We chose high efficiency components that had the best performance, reliability, warranty coverage and cost. It was critical for us to utilize solar inverters that were able to transition DC to AC for immediate use throughout the building and also enable the building’s power to seamlessly revert back to the traditional utility grid for all electrical use in the evening, on cloudy days or during other instances. We used six of our Protect PV.250 solar inverters and 234 solar modules for the solar system and to further maximize the effectiveness of the system the PV panels were tilted at an angle of 15 degrees. To ensure that we are using the lowest cost energy sources at each time of the day, our installation engineers enabled wireless tracking solar energy collection data and other system information whenever the system is online. 

In addressing the second main consideration, we developed a rooftop solar system with a non-penetrating, ballasted design that anchors the system with weights rather than penetrating the roof’s surface. The design ensures that the rooftop system could be moved and adjusted for building repairs as it is not permanently affixed to the roof. 

Within three weeks, our installation engineers installed all of the photovoltaic modules, mounting hardware, inverters, communication equipment and electrical combiner box/disconnect equipment. The business remains connected to the electrical grid, ensuring a continuous supply of energy whenever it is needed. Most of the costs incurred on the system were covered using local solar incentives from the utility company and federal tax credits and through the monthly savings we expect to recoup the initial expenses through energy savings in just a few years.

Moving Forward to Decentralized Electricity Generation

The PV industry has come a long way and grid parity is now within close reach.  In the years to come, activities in the solar market will form an important entree into the development of distributed power systems and the smart grid.

From our perspective we see a clear trend towards a more decentralized generation of electricity in both developing and developed countries. This means that the PV industry will face many more opportunities related to rooftops in industrial parks or even at the residential level, not only in the U.S. but across Europe and Asia as well. Already, the Singapore government has begun second-phase trials of residential rooftop installations to save each residential precinct about 170 MWh of electricity each year.  The trials are part of a US$23 million program by the Singapore Government to reduce dependence on electrical energy and bring about more sustainable development. 

The next trend is the realization of microgrids which refer to a combination of different clean energy sources close to the consumption centers. PV installations are the first step towards the evolution of microgrids where energy is produced solutions for high-energy-use building clusters such as universities, R&D parks and manufacturing facilities. According to Pike Research’s Microgrids report, between now and 2015, more than 3.1 GW of new microgrid capacity will come online worldwide, representing a total market value of US$7.8 billion. North America is expected to capture at least US$5.8 billion, or 74%, of this market. In addition, more than 2,000 microgrid sites are expected to be operational worldwide by 2015, up from fewer than 100 in 2010.

We also believe that large solar farms will continue gaining momentum and that they will only get bigger in the next five to 10 years. For instance, construction on the world’s largest solar farm with 73 MW in Thailand, costing US$250 million, is expected to commence next year. Such large-scale solar farms will begin to demand higher powered inverters and more sophisticated monitoring and metering systems.

As a Solar Electric Power Association (SEPA) and Green Grid member, we are dedicated to providing our customers with renewable energy alternatives, such as solar which will decrease environmental impact as well as reduce energy costs. We are already witnessing the realization of a greener tomorrow, with PV power becoming an increasingly widespread and a very important part of our energy infrastructure.

Enrique de la Cruz is General Manager of Solar Solutions Strategic Business Unit at AEG Power Solutions (http://www.aegps.com/). He is an Industrial Engineer from the Universidad Politcnica de Madrid (Spain) and has completed several Master Degrees in Marketing and Business Administration.