I’ve lost a lot of the links I used to have when I was looking into this stuff, but I’ll throw a few things out there in the hopes that are able to use something from the pile to search up on google etc.

Disclaimer, I’m typing a lot of this stuff from memory so some of it may be wrong

I prefer DIYing things that I can, but for anything related to power, I will purchase off the shelf components that are know to work - just to keep my risks as low as possible.

The basic circuit would look like this: SOLAR PANEL --> SOLAR CHARGE CONTROLLER --> BATTERY --> OUTPUT LOAD

Solar Panels

You will find a lot of different “types” of Solar Panels, but that is mostly in their rating. The bigger a solar panel, the more electricity it can generate. The ratings will usually be given in a combination of Power (Watts, W), and Voltage (Volts, V). These two are related with the following equation:

Power (W) = Voltage (V) * Current (I)

The quicker you want to charge your batteries, the more Watts you will need.

(You can combine Solar Panels (in either Parallel or Series) to give you more Power. Combining multiple panels may be a little bit more advanced (but not really as long as you know what your doing). I would recommend to start off with one panel, and then design and add as required https://battlebornbatteries.com/solar-panels-in-series-or-parallel/#:~:text=When you wire multiple panels,output voltages stay the same.

Solar Charge Controllers

Whatever Solar Panel you end up getting will have a rating. This is most likely going to be in Watts (W), which is a combination of the Voltage (V) and Current (I) (where Power (W) = V * I). When you measure the output of a solar panel, you will see that the Voltage fluctuates (due to clouds, orientation etc.), and hence, your overall Wattage will fluctuate.

For various reasons, having this type of fluctuation is not the best when your are tying to charge a battery. Hence, we use “Charge Controllers”. A Charge Controller is specific to the type of Battery you end up using (There’s a brief breakdown of some common battery types below). A Charge Controller will take the output from your Solar Panel, and will regulate what it needs to regulate, and output energy into the battery. As an example, Jaycar has a lot of different Solar Charge Controllers (They are in no way the best, but have linked them because people are familiar with them. Look for other offerings as well) https://www.jaycar.co.nz/power-batteries/solar-power/solar-charge-controllers/c/0HC?sort=popularity-desc&q

You will notice that there are “PWM” type and “MPPT” Solar Charge Controllers. MPPT are more expensive compared to their PWM counterparts, and with the way they work, they are basically more efficient in getting the Energy that you gather from your Solar Panel, into your Battery. PWM is still a valid option. When choosing your Solar Charge Controller, make sure they are compatible with the Voltage rating of your Solar Panels & Batteries, and that they are able to handle the amount of current your system will be pumping into the battery at max.

The Solar Charge controller should have Output Terminals as well, where you can connect the Load that you want to power (or you can connect them directly to the battery if your Voltage requirements are the same as your battery voltage). Here’s a User manual of a MPPT Charge Controller that also includes some diagrams as to how everything would be wired up (page 14) https://www.jaycar.co.nz/medias/sys_master/images/images/9959654293534/MP3741-manualMain.pdf

For the microcontroller work that I do (very lower power usage), I use these Solar Charge Controllers https://www.adafruit.com/product/4755

Battery Type

You have a few choices for different types of Batteries

1. Sealed Lead Acid (SLA) Batteries - These are your common car battery types. They are usually good for giving you a short burst of power, but they aren’t very energy dense (i.e., for the same physical size, other types of batteries will give you more energy/capacity). Adding to this, they cannot utilize their full rated capacity (usually good for about 50% of their rated capacity), and their rated life (counted in number of times you deplete the battery (discharge cycles)) is comparatively quite low. Per unit, they are the cheapest (but be sure to take into account, actual capacity available, and the lifespan of the battery).

2. Lithium Ion Batteries - These are the batteries found in our phones and most portable electronics. They are very energy dense, and you can utilize all of their capacity. They have a longer life, but they are known to catch on fire / explode when not taken care of properly. You MUST take care when using Lithium Ion batteries, and really know what you are doing. This includes ensuring you use a Battery Management System (BMS) specifically for Li-Ion Batteries. However, with proper care, the risk becomes very low.

3. LiFePo4 Batteries - Very similar to the above mentioned Lithium Ion (In fact these are Lithium batteries too), but they are said to be safer than Li-Ion batteries. They also have a much greater life when compared to Li-ion, but they are more expensive.

4. NiCad Batteries - For the same amount of energy, they are bigger than lithium based batteries. They also suffer from a “memory effect”, where if you keep charging them before they are fully depleted, your batteries capacity will decrease (as the battery “thinks” the point at which you charge is empty).

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