Solar Ice and Thermal Storage Reconsidered

Solar Ice + Aquaponics+ Confined Ag

Applying Aquaponics and Aquaponic Ideals to a Solar Facility

Project Proposal

This project will explore permaculture practices within a solar-powered freezer / aquaponics system on the Student Experimental Farm. Specific considerations will be given to passive cooling techniques, confined agriculture, and solar energy applications. It aims to maximize the efficiency of a facility that uses solar energy to power a freezer, making the implementation of this use of solar technology more effective and attractive in other scenarios.

Here is the proposed map of the location on the farm according to the prototype solar ice shed already built there.

shed locations.jpg

Nate Heston’s work with the Cal Poly Engineers Without Borders’ project in Thailand is developing the Solar Ice concept for fishing villages that do not often use freezing techniques to sustain their market and the fish’ shelf life. In designing and building this facility on the Cal Poly campus, perhaps our Solar Ice facility may serve a part in the iterative process as a prototype for the EWB research. The combination of an aquaponics pond and a large walk-in freezer is especially interesting for this type of use. Typical freezers as we know them require a significant amount of energy. In fishing villages such as those found in Thailand, bringing freezer preservation to those who don’t have it would do wonders for the fish market and food security. In this protoype, the growth/harvest/storage/ and sale of fish does not require nearly as many different locations as traditional fish markets.

Increasing the Efficiency of the Solar Panels

One aim of the project is to increase the efficiency of the solar panels by cooling them to optimal temperatures using natural ventilation. The efficiency of solar panels is affected negatively by increases in temperatures. For example, in one model of solar panel, for every degree above 25 Celsius, the solar panel loses about .5% efficiency. In the rolling hills of central California, we need to be wary of how the higher temperatures are affecting our power output.

The solution we would like to explore is a natural ventilation system whereby cool air would run underneath the panels. We would also like to explore how running the ventilation tube underneath a heat sink will help cool the air brought into the system. For creating our heat sink, we plan to take advantage of the knowledge on the Farm and partnering with PolyPonics to create a new acquaponic grow bed. For those of us with minimal exposure to aquaculture and hydropoic design, here is a brief explanation of this design:

Aquaponics uses fish to grow food, and food to clean the water for fish. Fast-growing plants will grow on a lattice above the pond. The plants will shade the pond to keep it cool and filter the water for the fish, and in turn the pond waters the plants. Another topic that will be addressed is the current problem with water inefficiency in typical agriculture. 90% of water used in agriculture is lost to the soil without affecting crops. So, this aquaponics system will used confined agricultural techniques when constructing the pond. This may include a vinyl or visquine water barrier lining the edge conditions.

The ventilation intake would exist at the bottom of the aquaponics pond so as to be cooled by the relatively stable cool temperature. The vent would run the length of the bottom of the pond (protected by a waterproof material), and be pulled into the facility which houses the solar panels so as to direct the cool air underneath the panels and up through a ventilation stack that heats the air as it pulled through. The air would be heated naturally by the sun and increase the movement of air through the system, because hot air would rise more quickly and pull more air through the system.

These schematic plans explain the design.

Sectional View of Facility
prelim drawing.jpg
preliminary drawing of an insulated freezer room without outdoor ventilation

Increasing the Efficiency of Freezers

By relocating the cooling coils of a typical freezer to close proximity with the aquaponics pond, we can keep the heating coils cooler than they would be on the back of a typical freezer. Reducing the temperature difference between the hot coils and the cold coils within the freezer would increase the coefficient of performance of the freezer (COP). Here is a rudimentary review of how freezers function, according to a simplification produced by Pete Schwartz.

heat pump efficiency diagram.JPG

We may explore other freezer modifications to maximize work flows.

Increasing the Efficiency of the Facility as a Freezer

The project also aims to increase the freezing capacity by enclosing the thermal storage facility in thermally massive building materials. Currently, we are looking at and comparing the benefits of ferrocement and papercrete. In the pursuit of sustainable technologies, we plan to pursue a building plan that 1) retains the freezer’s internal coolth 2) internalizes the smallest amount of embodied energy in the creation of the building materials and construction methods.

Below are examples of ferrocrete in Pabal Domes in India. And papercrete blocks currently produced by Texas manufacturer, Mason Greenstar.

pabal domes.jpg
papercrete mason green star.jpg