Increasing Production with Single-Axis Tracking

Intermediate

Inside this Article

20 PV panels on 10 single-axis trackers
A single actuator arm adjusts 20 PV modules on 10 single-axis trackers.
The back side of the tracking array
The back of the tracking array, showing the mounting base, pivots, and the long actuator arm.
PV output wire routing
The routing of PV output wires and ground connections at the top of the pivot rods allows full movement without binding or pinching the wires.
Microinverter circuits and tracker disconnect
Microinverter branch circuits and tracker disconnect.
20 PV panels on 10 single-axis trackers
The back side of the tracking array
PV output wire routing
Microinverter circuits and tracker disconnect

Cloudview EcoFarms strives to farm in an ecologically sound manner, providing food to members of a community-supported agriculture (CSA) network. Installing a PV system using locally made modules and inverters matches their “buy local” philosophy, and using the clean solar energy to offset electricity usage on the farm’s new cold storage unit—which enables them to store their produce—just made good financial sense.

Washington state’s incentive program, slated to be in place until 2020, pays a system owner based on the PV system’s annual production. Currently, the base rate is $0.15 per kWh, up to a $5,000 maximum payment per year. Systems using Washington-made inverters get compensated at $0.18 per kWh. And systems using Washington-made PV modules earn an additional $0.36 per kWh, for a total of $0.54 per kWh. The system’s output is measured by a production-grade meter. Participants are paid for all of their PV systems’ production, even if the majority of it is used to power on-site loads. The utility still net-meters and credits any excess production, though it zeroes out at the beginning of a new 12-month period. After 2020, the state incentive ends and the only payback is the offset energy consumption.

Design Options

Cloudview’s system was designed to maximize the annual incentive payment. Its single-axis tracker pivots east to west to follow the sun’s path, helping the modules capture as much energy throughout the day as possible, especially during the sunny summer months. (In this region, winter production is typically low due to cloud cover.) Even with a larger up-front cost (compared to a conventional, fixed PV array), this system has only a seven-year simple payback. 

The National Renewable Energy Laboratory’s System Advisor Model (SAM), free system analysis software, was used for modeling the array output and its financial payback. The first goal was to maximize the annual incentive payment. Three options were examined:

  • 20 modules with a single-axis tracker
  • 20 modules on a fixed array (to compare production to the tracked system)
  • 26 modules on a fixed array, the number of modules calculated to maximize the annual incentive payment of $5,000.

The SAM analysis was made using the following assumptions:

  • A 30-year array life, which includes an appropriate derate for module cell degradation.
  • An inflation rate of 2.5%—the average rate of inflation in the United States over the past 10 years.
  • An 8% real discount rate, which is used to discount constant year benefits and costs and is based on the average short-term business loan rate, was used. In essence, it’s the present cost of money that is tied up in the project.
  • The 30% federal tax credit was applied in the first year.
  • Operation and maintenance costs were not included.
  • Tracker costs were based on actual installation costs; fixed array costs were estimated.
  • Avoided power costs were calculated using the current utility rate for the farm, which is $0.04 per kWh. 
  • A 0.5% degradation per year in module output was assumed.

SAM deducts the 30% tax credit in the first year and also deducts the incentive payment and the avoided cost of utility energy that the PV system offsets. After seven and a half years, the only deduction is the avoided cost of energy times the inflation rate, assumed to be 2.5%.

Comments (5)

todd j lazich's picture

To all: The individual frames for the single axis tracker are 5' apart. I was told that DH Solar has discontinued this system because of lack of volume sales. However, I just managed to place an order for 4 frames to add to my initial system of 2 frames (4-250W modules. The frames are pretty simple to replicate....galvanized pipe, a few gussets. angle steel. I tqlked with the owner and he did not have a problem with me replicating these frames. I intend to make a frame out of square tube aluminum and test it out on my system. I would think that you still could get the controller/actuator from DH for about $800.

Best regards, solar friends

hbintx's picture

I recently emailed DH for more info and was informed they have discontinued this product. No reason was offered. They still make 2-axis trackers derived from their long-time satellite dish systems.

doutmind's picture

These are very nice steps on increasing production using single axis trackers. Hopefully people who are thinking to use dual axis trackers will also give a second thought on this.

Lloyd Scales's picture

What is the horizontal spacing, panel to panel? From the article it calculates out as each panel (39.1 inches wide) then a 56.9 inch gap then the next panel. Is this correct? If so, is there a general rule for spacing on an East to West layout?
L. Scales

Michael Welch's picture

Hi Lloyd. This system's pivots were on an 8 ft. center. But in general, the trick is to figure out how low in the sun's arc you want to be able to capture the sunlight. Obviously, with the sun at the horizon only the closest end module will catch it. Then knowing the height of one module corner can let you compute the distance to the next module. Our friends at Miller Solar have developed a spreadsheet for determining row spacing, but it can be applied to this situation. Check it out at http://millersolar.com/MillerSolar/...

Show or Hide All Comments

Advertisement

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading