Focused Sun with Green Energy R&S

Focused Sun has partnered with Green Energy Resources and Services to develop their CorrCon concrete thermal storage for our Microgrid modules. We have created a simple viable option for power generation with capacity.

As shown in the figure below, CorrCon uses corrugated culvert pipe as the basis of its heat storage. A small diameter (2 ft, 0.6 m) concrete-filled inner pipe collects and stores heat. A larger 6 ft (1.8 m) diameter corrugated pipe is surrounded by fiberglass insulation to reduce heat loss from the concrete; it also serves as a weather barrier.

​Concrete bolsters along the length of the pipe assembly holds the pipes in place. Concentric to the outer pipe, the inner pipe is held in place by low heat conduction supports. It stores heat as it gets hot. Mounted above the concentric pipe assembly are Focused Sun Microgrid modules, held in place by mounting posts embedded in the concrete bolsters.

The key to the CorrCon storage design is its modularity. While the rendering above shows only a short string of storage and modules, module and storage strings can be extended to make long rows and large arrays from long rows.

Shown below is a rendering of a 100 kW array discussed in my previous blogs: technology, economics and a comparison to large solar farms. The array has 400 collectors, each with over 24 ft2 (2.2 m2) of collector area and a 50 ft2 (4 m2) footprint; it will require 0.6 acres (0.25 Hectares) installation area. In addition to 100 kW of electricity, the array delivers 300 kW of low-grade heat. Electricity comes from converting the concrete’s stored energy thermodynamically in an Organic Rankine Cycle (ORC) engine. Leftover heat from the conversion process can be used for space heating, process heat and desalination.

Each row has 20 collectors, making each row 130 ft (40 m) long. Between each row is a service aisle where a waterless cleaning system assures clean reflecting surfaces of the linear Fresnel reflectors. Since the reflectors are already designed for 150 mph (240 kph) winds, they can withstand desert climates.

In addition to self-cleaning and high strength, the Focused Sun-CorrCon partnership brings to market the true potential of a 24/7 microgrid. Combining storage with concentrating solar collectors allows efficient power delivery during extended periods of bad weather. With or without grid connection, backup boilers or demand generators can eliminate both demand charges and power quality issues. This complete package enables islanding when required, can serve as a distributed energy resource and responds to any site load within design.

​The microgrid is especially useful for small utilities. Often rural, these utilities have a lower customer density than cities. Typically they buy electrical energy from high voltage transmission companies and step down the voltage in substations owned by the utilities. Substations distribute the energy locally through feeders that deliver it to customers after further voltage drops from local transformers.

Since our Microgrid can be set up on near the feeders themselves, no substation improvements are needed. In rural settings, feeders often fan out radially from the substation. Switchable connections between feeders improve reliability by providing alternative paths during power outages. Locating small generators along the feeders further improve reliability with steady power day or night. When a substation has several feeders being supplied by a Microgrid array, system performance is improved.

Below is a flow diagram for the Microgrid Storage system. The sun’s energy reflects off the Microgrid module mirrors, focusing onto its absorbers. Here only 3 modules are daisy chained together, but in an actual system there would be 10 or more.

Solar energy heats the mineral oil heat transfer fluid (HTF) inside to high temperature (red color). At the end of the absorber, the hot oil is pumped down to the insulated concrete storage. As it flows through the concrete it gives up its heat to storage as cools (blue color). The cool HTF flows up from the storage and back into the string of absorbers. This forms the “Solar Loop.” Over a day, HTF heats the concrete storage. The high grade heat is available for the next 19 hours to produce energy.

The “Power Loop” is a second loop that extracts heat from storage and pumps it to the ORC turbogenerator where it generates electricity. The low-grade heat from the turbogenerator supplies heat for various applications: space heating, process heat, desalination or hot water for laundries and hotels.

​Our new partnership with CorrCon adds energy storage to a microgrid. This is a system that you can build in local factories. It supplies energy night and day with self-cleaning, backup and the lowest capital and energy costs (LCOE) available.