Ultra low power home DC electrical system - 2nd iteration

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The problem

Nowadays, installing solar photovoltaic panels on big city buildings is limited to the roof area of the building. This means little power generation capabilities for energy savings when considering each individual apartment.

The idea

The idea of this "Smart Home Solar Power Management" Project is to develop simple components and accessories that enable easy, "for dummies" kind of installation of solar photovoltaic cells. For that to happen is required installation of additional wiring in the apartment electrical network. Staring with a 5V DC wire, suitable for most small home appliances such as vacuum cleaners, smartphones, tablets, and any other smart device or technology. And another with 12V DC suited for computers, gaming consoles, and OLED TV displays. This can be achieved by installing "power delivery" technologies, common in USB-C power solutions.

Energy storage methodology follows a decentralized architecture of installation, where each individual room or compartment has its own "independent" battery storage upwards 40.000mAh. All connected to a Smart Home device I made available on my Github.

The solar panels can be assembled in a Lego-style kind of way. Due to the reduced size of the photovoltaic solar cells, can be assembled into any shape or area. For instance glass door windows and doors. For instance in a terrasse or a terrasse exterior wall regardless of floor area shape..

Prototyping a support for a Polycrystalline 78x39mm Solar Cell

Polycrystalline solar cells are known to break too easily when handing and assembling all together when building a solar panel.

To protect this kind of solar cells I've designed and order fabrication a support hardware electronics where any solar cell can be soldered , in particular the ones below i used for this testing.

This is a simple PCB for a direct fit on commercially available blue solar cell tiles with dimensions 78x39mm. This support hardware PCB is intended to be connected to the distributed Indoors power storage and installed at the ttop side or at the bottom side of transparent glass windows at a home or office. This PCB, when assembled with a blue solar cell tile, can be used to power a low voltage 4.2V indoor illumination network using ultra-low power micro LED strips. For instance, this one sold on AliExpress.

When connected in series and installed on several windows and networked, can power off the grid 4.2V DC LED lights on all rooms and compartments at a home or office. During evenings and at night until bedtime. If one intends to use it to power indoors LED illumination during the day is required a High Capacity Power Bank connected to all first tiles of all the series. For instance this power bank here. One important takeaway about this prototype project is the ability to be installed on any traditional apartment or home in a big city.

On the photo below is possible to see one solar cell placed in one of my apartment's windows for evaluation of aesthetics and total area required for an installation directly placed on the window. This one in particular requires 124mm of window glass estate, at the top or at the bottom and has an height of 80mm. This setup and installation is able to connect to existing home automation networks or systems (see my next iteration of this project to learn more).

Below is possible to see solar cell array assembled in series to output 4.5V DC and 1.3A and installed (taped) at the bottom of window. The solar cell support PCB works really well on protecting the fragile solar cell from breaking when handing and installing. Defiantly a must have when thinking on fabricating and assembly these kind of fragile solar cells.

Current Status of Development

1st iteration

The current status of development of this project has now the following preliminary conclusions:

A dressing room with an area of 20-25 m2 and with a glass window where the sun shines only in early morning can be powered

• by a single photovoltaic 6V DC solar cell for micro LED illumination usages of up to 5 to 10min a day and at night.
• A dressing room with an area of 20-25 m2 and with a glass window where the sun shines only in early morning can be powered
  by a single photovoltaic 6V DC solar cell for micro LED illumination usages of up to 5 to 10min a day and at night.
• A bathroom with an area of 20-25 m2 , indoors no glass windows , with glossy tile walls , micro LED illumination produces the best light

Initially i was aiming at an additional 10 euro a month savings on the utilities bill , however, recent prototypes show that is possible to repurpose any apartment on any big city to become independent of the main power grid for the following home appliances :

• indoor illumination
• small home appliances such as a battery powered vacuum cleaner , manual operated or a robot
• Smart devices such as smartphones, tablets or any other smart appliance
• OLED TV screens, and laptop computers

Additional energy savings can be achieved, if installed with a "home occupancy management system" to monitor occupants habits:

• to provide an optimized electricity usage schedule to each of the occupants
• to detect empty an room/ compartment
• to regulate light intensity during evenings and at night before going to bed. Synchronizing with the human biological clock cycles.

Conclusions

Soldering the solar cell tile into the support PCB is makes much easier the assembly process of a solar panel , however there are some considerations to take:

• The solder paste needs to be a "low temperature "kind of solder paste. Any other, when heating will cause the solar cell to break due to differences in temperature.
• when placing the solar cell is required to add just enough flux to the contacts on the solar cell. This will also helps fixate it to the support PCB during initial soldering.
• is mandatory to have a clean flat surface to do this properly. Glass or aluminum base will do .
• The soldering iron requires 2 different tips for this job. One with a conic shape, able to soldering into the connection hole and another with a flat surface for soldering the "tabbing wire" directly on the solar cell.

This revision of the support PCB was fabricated with copper connections on both sides. The connections height alone on the PCB are enough to break the solar cell. The next revision (already available on my GitHub) corrected this and includes many other improvements. The improved and final revision is selling on my Tindie store.

Next:

The third prototype iteration of this same project, advances into the next milestone. Replace the 18650 LiPo batteries with a 20, 000mA "power bank". Here's the link to the article.

#openInnovation #DIY

one final note about the author

The PCB Design Files I provide on GitHub for anyone to use are free. If you like this Smart Device or use it, please consider buying me a cup of coffee, a slice of pizza or a book to help me study, eat and think to work on new PCB design files.

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