Commercial Photovoltaic Systems

HELCO 20kW, 480V 3-phase system at NELHA. Designed & installed by RES.

The 2006 Federal tax credit increase from 10% to 30% for commercial PV power systems combined with a 35% State of Hawai‘i tax credit, record high utility costs, geo-political uncertainty in oil producing countries and growing concern over the quality of our environment have created conditions in Hawai‘i that are very favorable for the implementation of commercial scale PV power systems.

In response to what is expected to be a large increase in the demand for these systems, Renewable Energy Services, Inc. (RES) has designed a unique, modular PV power block that can be used singly or in multiples for systems ranging in size from 7 to 100+ kWac. Based on 15 years of real world Hawai‘i experience installing hundreds of remote and more recently, grid connected residential and commercial PV systems, RES has selected the best components from the rapidly growing, international PV industry and combined them to create a PV power system designed to be powerful and reliable in our unique Hawaiian environment.

The power produced by a commercial PV power system will have a value equal to the utilities price of a kilowatt hour of energy, a cost that is always increasing. After the tax credits are taken, this income stream (money saved by not having to purchase power from the utility) is sufficient to cover the monthly cost of a lease or loan used to purchase the PV system. Under this scenario a PV system can reach payback in as little as three years or within the term of a lease,

Holuakoa Cafe's 18kW grid-connected system in Holualoa, Kona.

typically eight to ten years. After that the PV system will continue to produce power for a design life of 30 years, generating hundreds of thousands of dollars of power at no additional cost to the owner.

These favorable economics only work as proposed if the PV power system works reliably for its entire 30 year life. Successful PV power systems must be reliable, easy to maintain and their performance easy to verify in order to assure that the power and therefore the economy predicted is realized. To achieve these goals, all of the system components, PV modules, racks, wire and the inverter, must be selected carefully. RES equipment is selected for technical superiority and for the manufacturers’ ability to support their product over the life of the system. Additionally, there must be experienced, professional support personnel located in the service area and equipped with the tools and training required to quickly remedy any and all performance failures.

PV MODULES
RES commercial PV power systems use PV modules made by Sanyo Energy Corp. Due to a unique combination of single crystal and amorphous, thin film silicon technologies the Sanyo module achieves a conversion efficiency of 18.5%, one of the most powerful modules available today. This allows more power to be collected per square foot of roof area.

All modules produce less power as they heat up in sunlight. Sanyo modules, due to their multilayer design, have the least power loss due to heat. As temperatures rise, Sanyo modules produce more power than conventional crystalline modules at the same temperature. Over time,this means RES systems produce significantly more power than others in Hawai‘i’s hot, tropical environment.

30kW off-grid Ahu Pohaku Ho‘omaluhia Health Retreat, Hawi, Hawai‘i.

ROOF MOUNTED ARRAY RACK
Commercial PV arrays cover large roof areas and require multiple penetrations through the roof membrane. In order to reduce the number of roof penetrations and to increase the flexibility and strength of the roof mount design, RES commercial power systems utilize additional rack frames that can decrease penetrations by over 50%. Anodized aluminum and stainless steel rack materials are selected to reduce weight and build a mounting system that will last at least 30 years without periodic maintenance, in Hawai‘i’s severe island environment.

INVERTER
The inverter is the power conditioner for the PV array. Its job is to track and convert the direct current from the PV modules to a usable form of standard utility grade AC power. Inverters in the PV industry that tie PV modules to the utility/customer grid must contain safeguards for power quality and be able to shut down instantly in the event of a power outage. The inverter must survive utility sags and surges and lightning strikes. It is the heart of the system, the most complex component in the system and the most likely part to fail.

In recognition of the challenges that face the inverter, RES has designed our PV power systems around the use of multiple small inverters rather than one large central inverter. This approach improves system performance, minimizes the impact of an inverter failure, and allows for fast and easy repair of a failed component.

10kW off-grid at Cloud Forest Coffee Mill, Ahualoha, Hawai‘i.

Central to the design of the RES system is the use of the German made, SMA America, Sunny Boy 7000US, 7.0 kW string inverter. SMA, the largest supplier of inverters for the European solar market (the largest market in the world) is widely recognized as having the best customer support system in the industry, the most reliable equipment in today’s market and the most advanced data acquisition and data display systems in the industry.

Maximum Power Point Tracking
Inverters electronically track the conditions of sunlight and array temperature, constantly adjusting for changes in the PV arrays maximum power point. As the maximum power point changes across a large commercial PV array due, for example to a cloud passing by, multiple small inverters are able to adjust individually with the changes whereas a single large inverter can only average the entire array. Accurate, independent maximum power point tracking can increase the energy capture of the system by as much as 3-5% on an annual basis over the lifetime of the system. If the design of the system involves segments of the array at different orientations, the benefits of individual power point tracking are greatly increased.

Honoka‘a High School's 10kW 208V 3-phase grid-connected system.

Redundancy
With many inverters, if one should fail, the system experiences only a small loss of power. If a single large inverter fails, the entire power plant is down until repairs can be performed. Smaller inverters are generally “on the shelf” if a replacement is required and they can be air shipped overnight if factory repair is needed. Large single inverters can not be held in inventory and returns are costly and time consuming.

Design Wisdom
The harder an inverter works, the hotter it gets! Although the SMA SB 7000US inverter will accept a larger number of PV modules, the RES design keeps the inverter loaded below the maximum, reducing heat and extending the life of the inverter.

Holuakoa Cafe's 18kW grid-connected system in Holualoa, Kona.

Data Acquisition & Display
Performance of commercial PV power systems must be monitored continuously in order to verify that production and financial parameters are being met on a daily basis. If a problem is only discovered after the monthly utility bill arrives, thousands of dollars of revenue may have been lost. Third party data acquisition systems for large central inverters are available but they are expensive and complicated. Additionally, the data must be reviewed and analyzed by someone
familiar with large PV systems.

SMA inverters contain all necessary data acquisition components, built in from the factory. With SMA’s Web Box product, individual inverter performance is posted on the internet via SMA Sunny Portal for general and password accessibility by anyone with a computer and internet connection. Furthermore, plant performance is monitored by SMA engineers in Germany and problem alerts are emailed directly to RES personnel for immediate response.

Warranty Costs
Because the inverter is the most likely component to fail in a commercial PV system, its warranty is critical to the long term success of the power system. In addition to a 10 year warranty (the longest in the industry) SMA pays all labor costs incurred to perform repairs and replacements of their products during the warranty. Thus the continued care of the inverter is financed for the first 10 years of the PV power plant by SMA America in addition to the vendor of the components.

CONCLUSION
A combination of high energy costs and large State of Hawai‘i and Federal tax credits has enabled commercial PV power systems to be an affordable and attractive hedge against the escalating cost and sudden energy price shocks due to global oil supply disruptions. Commercial PV power systems that are visible to the public can also become unique advertisements, highlighting a business or its products to a public with a new found awareness of energy issues and global warming.

10kW off-grid at Cloud Forest Coffee Mill, Ahualoha, Hawai‘i.

With an investment payback in as little as three years, these systems will generate hundreds of thousands of dollars in revenue throughout their lifetime. In order to realize the energy production and favorable economics that are possible, PV power systems must operate reliably with little maintenance for a design life of 30 years. While the PV cells that produce the power are inherently long lived and have no moving parts, the power conditioning unit or inverter is susceptible to failure and therefore must be designed to minimize the risk of failure and maximize the ability of service personnel to repair or replace failed components quickly and easily.

With 20 years of experience designing residential and commercial PV power systems in Hawai‘i, Renewable Energy Services, Inc. has designed a unique, modular commercial scale PV power system that will operate reliably and be easy to repair if and when a problem arises. With advanced data acquisition built in to the system, a 10 year warranty and factory trained technicians located on the Hawai‘i Island, RES PV power systems represent the state of the art in solar power solutions for Hawai‘i.