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CCAT solar bug out box

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Engr305 Appropriate Technology page in progress
This page is a project in progress by students in Engr305 Appropriate Technology. Please do not make edits unless you are a member of the team working on this page, but feel free to make comments on the discussion page. Check back for the finished version on May 23, 2020.



Background

The Campus Center for Appropriate Technology located on Humboldt State University in California has an extra amount of solar panels but they are unsure what to use them for. As a team we will attempt to construct some kind of solar bug out box to help students when black outs occur. This bug out box will need to be mobile and be able to charge batteries which students can then use for whatever they need.

Solar 1.jpg

Problem statement

The objective of this project is to create an easily digested bug out box made with solar panels from ccat. This box will harness photovoltaic energy so that the users can charge various devices and possibly run appliances. As a group we hope that we can make a box that is easily remade with simple instructions that creates enough usable energy to be a reasonable alternative to using a car battery during a time of no power.

Literature Review

This is a review of the available literature pertinent to the a specific project.

Solar Power basics

A simple photovoltaic(PV) system consists of one or more solar panels(a solar array), a charge controller and a battery or battery bank. While the sun hits the solar panels, those panels turn energy from the sunlight into direct current(DC) electricity which is then stored in the battery. The charge controller regulates the flow of electricity to and from the battery, preventing the electricity from flowing out of the battery back to the solar array as well as preventing overcharging of the battery. An inverter may be required to convert the electricity from DC to AC(Alternating Current) depending on what is being powered.[1] The amount of power produced by a PV system depends on the size, efficiency and amount of light received by the solar panels.

Solar Power concerns

The biggest problem with solar power is the fact that it will not generate any electricity without sunlight. A PV system will produce minimal to no power during nights, cloudy days and in shaded areas. Solar energy may not be the right answer for an individuals energy needs if they are in an area with limited exposure to sunlight. Solar panels have limited efficiency as well, with the most efficient solar panel converting roughly 22% of energy from sunlight into usable energy. Most solar panels fall within a 16-20% efficiency range. [2]

Components of Solar Power

In depth information about the different components of a photovoltaic system and what we will use for our project. [3]

Solar Panels

Solar panels are composed of many individual cells called solar cells. Solar cells are composed of semiconductor materials which generate energy when light hits the cell, the sum of which is the total energy produced by the panel. [4] The ability of a solar panel to convert sunlight into usable energy is called its efficiency, which ranges from 15% to nearly 23%. It is also important to consider that sunlight is required to strike the solar cells in order for the solar panels to generate energy so optimal placing of the panels to receive as much sunlight as possible is crucial. Shade can decrease energy output by more than 50% [5]

Batteries

The battery is where all the energy generated from the solar panels is stored. Depending on the individuals energy needs, different sizes of batteries will be required. A larger PV system will require a battery with a higher storage capacity, or will require hooking up multiple batteries to the system creating a battery bank. A batteries capacity is the total amount of energy a battery can store, typically measured in kilowatt hours(kWh). Batteries also have a depth of discharge which is the amount of energy that should be used so that some is left over, so that the battery is never fully drained. [6]

Battery Types (sourced and paraphrased from energysage.com)[7]

Lead acid

Lead acid batteries are a tested technology that has been used in off-grid energy systems for decades. Lower DoD (depth of discharge). Lower cost.

Lithium ion

The majority of new home energy storage technologies, such as the , use some form of lithium ion chemical composition. Lighter, more compact, higher DoD, longer lifespan, but more expensive than lead acid.

Saltwater

Relatively new technology. No heavy metals; no complicated disposal, relying instead on saltwater electrolytes. Saltwater batteries are relatively untested compared to the other types, one company that makes solar batteries for home use (Aquion) filed for bankruptcy in 2017. A review and the schematics of the Aquion saltwater battery are found here. [8] BlueSky Energy has created their own saltwater battery circa 2019. [9]

Load

The load for a system is the end use, the appliance or system that uses the power from the battery that was generated by the solar panels. The load determines the amount of energy required from the system and therefore dictates the size of the system needed. For example a 50 watt light bulb will require a significantly smaller PV system than an entire house.[10]

Design efficiencies

When talking about solar panels more specifically past and future uses, design efficiencies of the panels themselves is an important factor to consider. It is said that panels today are becoming harder and harder to disassemble which could be bad if you would want to recycle them after their use. But this could also be a good thing if the user wanted to reuse the panels for a different project afterwards. Reusing panels would somewhat force “design implications” in that if more panels are reused, it would generate a response to design panels to last longer and be updated to allow for easy refurbishment or parts replacement.[11]

Partial Shading

Partial Shading and mismatch losses are also something to consider when thinking about solar panels. In an analysis it was found that in an area that has slightly higher shade than average area showed a performance reduction of about 22% due to shading. This shading can be from anything such as building all the way to trees. Of that 22%, 70% was from the actual shading while the remaining 30% was power loss because of mismatch of current and voltage. There are suggestions to help alleviate some of the loss but ultimately is going to come down to the system you are working with.[12]

Tilt Angles

The tilt angles of the solar panels is also something to consider. The angle of the tilt can affect the overall annual energy yield of the whole system. And has a lot of different parts or elements that influence it. These elements can include but are not limited to the latitude, “clear-ness index”, air conditions, and climate condition. Moreover, the annual optimum tilt angle is almost shifted by 10°with respect to the latitude of the location.[13]

Designing interpretive materials

Interpretive materials for a solar powered bug out box should include a placard on how to wire a basic PV system using some sort of box/container as the body of the bug out box. This would include mounting the solar panel on top of the box, cutting or drilling a hole through the lid for the wiring to pass through and making sure that hole is sealed properly, and wiring the battery and charge controller. We want to keep the designs minimal for ease of use and convenience. [14]

Weighted Criteria and Constraints

This criterion sets our group to a standard that lines up with the expectations of our client. This also helps us personally quantify our effectiveness and execution for the solar bugout box. The scale (1-10) represents the importance level of meeting the constraint of each listed criteria.

Criteria Constraints Weight
(1-10)
Cost Within budget
8
Battery Life ≥2 years
2
Battery Capacity ≥4 hours of charge
7
Energy Output ≥110 volts
9
Weather Resistance ≥plywood
8
Daily Usage ≥2 hours/day
5
Weight <100 pounds
3
Aesthetics Must be noticeable and appealing to use
6
Educational Aspect Must include an educational piece on construction.
8
Safety & Placement Must not interfere with traffic, but be convenient to use
6
Reproducibility The structure can be reproduced by following educational aspect.
4