Installing or building the perfect site requires planning beyond the system itself. In ground-mount applications, for example, field drainage is an underrated attribute.
Typically, the energy dissipation methods on a solar site are aggregate, fabric cloth and perforated pipe. This requires excavation and removal of excess soil as well as the logistics and expense of supplying the aggregate to a remote and often difficult-to-access location. The maintenance requirements are time intensive and expensive.
These traditional drainage systems have a lifespan of one to seven years with most failures occurring in year three. These systems fail because of the migration of fines and silt — small particles that are suspended in the water. Often, you have a pipe that is surrounded by aggregate and a geotextile. As the aggregate or gravel settles and compresses over time, movement of the surrounding soil and fines increases. When the soil and fines migrate, the geotextile and pipe fill with these fines and become impacted.
A Better Way
Instead of going that traditional route, HydroBlox, a drainage and filter product made from 100 percent recycled plastic, is the first geotextile that conveys fluid.
HydroBlox has a compressive strength of 40,000 lbs per ft and an irregular patterned composition with an internal void space of 50 percent, referred to as a permavoid. The pressure in this void space is naturally lower and will remain that way due to the non-compressive nature of the HydroBlox. During natural settling, the plank of HydroBlox will not compress and therefore does not become impacted and clogged.
Also, HydroBlox transports water from high head pressure to low head pressure, creating a path of least resistance. The water then moves through the irregular void path of the HydroBlox plank, with the surrounding soil acting like a filter. This way, water will continuously pass through. In fact, this method moves water over ten times faster than sand.
“This is called the Tergazhi effect. The water movement is based on Darcy’s principle,” says Ed Grieser, owner of HydroBlox. “The working example that seems to resonate with everyone is when standing at the ocean’s edge at the beach, recall how quickly the water travels back into the sand when the wave recedes.”
Lee Supply is the exclusive distributor of HydroBlox with stock at all of their locations.
The installation method is very straightforward. Simply trench 2 in. wide and 7 in. deep. The trench should be 18-ft to 24-ft down the slope from the drip line. This will allow for 2 in. of HydroBlox to remain above grade. The downhill side is backfilled by the trenched material.
Alongside the potential O&M savings, Fancher says HydroBlox installation costs approximately one-quarter of existing methods.
“The costs associated with traditional systems are approximately $26.50 per foot,” he said. “The perforated pipe which is often compared to the price of HydroBlox is the least expensive component of the standard system. In reality, the true cost is much greater than HydroBlox because of the labor and equipment required. The installation costs for HydroBlox is approximately $1 per foot.”
Each foot of installed HydroBlox could net a savings of $19.50. On a 25-acre solar field site, the costs of installation are reduced by $780,000.
Also, heavy equipment and large vehicles are not necessary for maintenance. This allows for the solar panels to be placed closer together than would otherwise be possible. The maintenance for HydroBlox is simply keeping the rocks and debris clear on the uphill side of HydroBlox and the drainage swale that carries the water to the retention pond clear.
Product to Watch: NRG Systems’ Soiling Measurement Kit
Photovoltaic modules often collect more than sunlight after they are installed. Depending on the siting location, particles ranging from dust to snow can accumulate on a PV module’s surface, reducing its performance and ultimately leading to significant power losses. This buildup — commonly referred to as soiling — can be compounded by such weather parameters as wind speed, relative humidity and ambient temperature, as well as localized activities near or around the PV plant.
To address and ideally avoid power losses caused by soiling, the new IEC 61724-1:2017 standard for PV system performance monitoring suggests that operators of utility-scale and large PV projects measure soiling ratio, which is defined as the ratio of the actual power/current output of a PV array under given soiling conditions to the power/current that would be expected if the PV array were clean and free of soiling. By measuring soiling ratio, operators are armed with the vital information needed to make practical decisions, like scheduling solar panel cleanings, that can better optimize the performance of their PV plant.
NRG Systems recently introduced a Soiling Measurement Kit specially designed to help PV developers and operators obtain the information needed to quantify the site-specific impacts of soiling on prospective and current PV projects. The turnkey solution is offered as an accessory to the company’s Solar Resource Assessment System and comes with three PV modules (one for data logger power, one clean panel and one dirty panel), pre-installed back-of-module temperature sensors, flexible mounting hardware and an integrated soiling interface module.
The Soiling Measurement Kit connects with NRG Systems’ SymphoniePRO Data Logger and provides a wealth of raw soiling measurement data that can be used to determine soiling ratio.
Specifically, the kit measures short circuit current and back-of-module temperature with the user’s choice of statistical interval as well as optional 1 Hz sample data collection, providing flexible analysis options to meet data demands. Generally, solar module performance decreases with increasing temperature, so back-of-module temperature measurements provide the critical information needed to accurately predict a PV plant’s power output.
— Solar Builder magazine