Intro to Solar Energy

as explained through my own experiences

This page is intended to explain the basics of assembling a solar power system using my experience as an example. Obviously this won't be universal, but I hope it gives some insight into the process nonetheless. Let's begin!

NOTE: this page is WIP, but I've made it live anyway so the info that is here can be referenced.

For a basic small- to mid-scale off-grid system, you need essientially three things:

• Solar panels - to collect energy
• Battery - to store that energy
• Charge controller - to interface the two

If you want to use standard AC appliances, you'll also need an inverter, but we'll get to that later.

Solar panels

Obviously, to collect the sun's energy as electricity, you need panels. These come in various shapes and sizes, but they all serve the same purpose: to turn light into electricity. You can get flexible panels, in which the cells are embedded in plastic, and rigid panels, which use glass instead. Glass panels are more durable and have a much longer lifespan, but are heavier. Flexible panels are useful in applications where the panel needs to be light or conform to a curved surface, but despite their name, I would recommend against mounting them anywhere they can flex much after they are mounted.

Panel Electrical Parameters

All-in-One Units ↑

Before we get into the rest of the details, it's worth mentioning that various all-in-one solutions exist from the likes of EcoFlow, Bluetti, and whoever else has paid oodles of YouTubers to talk about their products. The advantage of these is that they already include a charge controller, batteries, and inverter that work together, so you don't have to worry about spec'ing the individul system components. You essentially only have to ensure that the unit will accept the voltage and current of your panels, and you're off to the races. I do not as yet have any personal experience with these, but I'll update this page if that changes.

If, however, you do want the control afforded by designing the systems yourself, you'll have to consider the following sections.

Batteries ↑

Now that you're collecting energy, you need somwhere to store it. Some people have done clever things without batteries, like using their solar electricity to heat water directly, storing the energy as heat instead of electrochemically, but if you want the versitility of electricity, a battery is the way to go. On that front you have two broad options:

• Lead Acid
• Lithium

And of course there are subtypes of each, and all have their pros and cons. You can research the nitty-gritty if you want, but in the meantime, I'll give some general info based on what I've encountered.

Lead Acid

Lead acid batteries are "old tech", but are still used. Most of the lead acid batteries I have used have been the AGM variety. It is important to note that although car batteries are probably the most ubiquitous type of lead acid battery, they are not ideal for energy storage because they are designed to deliver a large current for a short time and then immediately be recharged (i.e. what happens when you start a car). Energy storage applications, on the other hand, require a battery to discharge relatively slowly and last, say, through the night before being charged again. For this reason, "deep cycle" lead acid batteries are better here, as they allow for more of their capacity to actually be used. As it is, the AGM batteries I've used work sufficiently, but are easily compromised if they ever get too discharged, which can happen during a cloudy week.

In general, lead acid batteries are cheaper than lihium, but bulkier and much heavier. They also generally can't deliver as much current, which may or may not be an issue, depending on the loads you want to power.

Lithium

Broadly, there are three types of lithium battery that I've encountered: Li-po, Li-ion, and LiFePO₄. I am currently using a lithium iron phosphate (LiFePO₄) battery I constructed from prismatic cells from batteryhookup. This seems to be the current go-to chemistry for solar energy storage because, although it is slightly less energy-dense compared to Li-ion, it is safer and a better voltage match for replacing lead acid (which a lot of equipment has been designed for).

Lithium batteries are smaller and more powerful than their lead acid counterparts, but are more expensive and require a battery management system (BMS) to keep the individial cells in the battery balanced and happy.

Regardless of which type of battery you choose, you need to choose a system voltage. Common voltages include 12v, 24v, and 48v. The higher the voltage, the more power you can transfer over the same guage wire. This also affects the charge controller you get and, if you need one, the inverter you get as well. Note as well that the nominal system voltages of 12v, 24v, and so on are in reality ranges, e.g. 10-14v, 20-28v, etc. To complicate things further, lithium tends to have a higher voltage than lead acid, so components designed to work with a "24v" lead acid battery may not have a high enough voltage tolerance to fully work with a "24v" lithium battery.

Charge controllers ↑

Ok, so you have a source of power and a place to store it. Now you need a way to connect the two. And wouldn't you know it, you've got more choices! There are two types of charge controllers:

• PWM - pulse width modulation
• MPPT - maximum power point tracking

PWM charge controllers are less expensive, but have the limitation that the panel voltage must match the battery voltage relatively closely. MPPT controllers are more expensive, but allow the panel voltage to be higher than the battery voltage. This means you can string more panels together to make better use of morning and evening sun - when the panels aren't producing peak power - without damaging the system when they are producing peak power.
[probably more to say here]

Be aware of cheap charge controllers! As Big Clive showed, the "current ratings" are basically meaningless. Make sure your charge controller of choice is actually rated for the power you plan to put through it.

Using the power ↑

So you're collecting and storing power. Great, now how do you make use of it?

If you are running a 12v system, there are a lot of devices designed for automotive and RV use that you can probably just hook straight up to the charge controller's output. If you want to run standard mains appliances, you'll need an inverter to convert your battery's direct current into alternating current. If you just need to power DC loads, there are are voltage regulators for almost every occasion.

Inverters

If you want to run standard AC appliances off your battery, you'll need an inverter. And would it surprise you if I said there were more choices?

"Proper" AC power has a purely sinusoidal waveform at the line frequency of your region. When selecting an inverter, you can choose from:

• Modified Sine inverters, which are cheaper but produce a choppier waveform, or
• Pure Sine inverters, which are pricier but produce an actual sine wave.

Believe it or not, the quality of sine wave has bearing on what devices you expect to power. Resistive loads like heaters and incandecent lights don't really care about the messy waveform of a Modified Sine, but it can have negetive effects on electronics, some motors, and anything with more complex circuitry. You can go down the rabbit hole about power harmonics of your own accord, if you like.

Also keep in mind the power of the inverter in relation the the current it will draw. For example, a 2000W inverter could draw up to 83A from a 24v battery, which is a lot! Your battery (including BMS), charge controller, and wiring have to be able to handle that.

Voltage regulators

A large number of devices we use run on DC, so if we want to supply that DC direcly, chances are we need a voltage regulator.

The vast majority of electronics charge and operate on DC. Let's take a laptop for example. It is more efficient to supply the 16-20v (depending on the model) directly than to use the AC adapter it came with plugged into an inverter. (a charger plugged into an inverter would convert DC to AC and back to DC again, which has obvious losses.) Charging phones off solar is easy, as many charge controllers come with USB ports already built in, but for everything else, you'll need a voltage regulator.

If you want more USB ports, you can get dedicated 12v to 5v converters, for example. If your battery is 24v, I would recommend getting a 24v to 12v regulator and a 12v to 5v regulator. That way, you get a 12v supply, and the 5v regulator doesn't have to work as hard.

LEDs also run on DC. Again, it is more efficient to run them directly than to use an inverter and LED bulbs, which convert the AC back to DC internally. I run some led strands off 5v as night lights, and the rest off 12v. You can get 12v LED strips, fixtures, and everything in between, so a 12v regulator is a good choice for being able to power a wide range of LED lighting. That being said, there are LED items available in other voltages, should you choose to go that route. Regardless, as far as I'm aware, DC powered LEDs are the most efficient way to illuminate a space with solar power.

Considerations ↑

As with most things engineering, there are tradeoffs involved in designing a solar power system.

• panel power / array size - more panels cost more and require more area to set up... but produce more power.
• battery size - a bigger battery is more expensive and requires potentially more intense support circuitry... but means you don't need to worry as much about cloudy days or your power usage.
• relatedly, you need to factor in the amount of sun your panels will get. e.g. to power a given load on less daylight, you need more panels and a bigger battery - to harvest more energy faster and store it longer.
• DC or AC - using an inverter instead of DC-DC converters is less efficient... but is a one-part solution because mains electricity is standardized. to run off DC directly you may need multiple voltage regulators and potentially multiple sets of wires.
• for lithium, which BMS do you need? dictated by how much current your cells can supply and how much you want to draw.
• Not all BMSs are created equal. beyond different amperage ratings, some are programmable, some aren't; some can exchange data with the charge controller, some can't.
• where are you installing the system? or is it portable? this can dictate things like panel wattage, battery capacity, whether an inverter is necessary, what DC voltages you need, etc.

You also need to make sure everything is sized to each other, which is what the next section of this page is designed to help with.

Math

Oh boy, everybody's favorite... Thankfully, because this is a webpage, we can make it do the math for us!

[TO BE ADDED]
sorry i know this would probably be very useful but i havent figured out how i want to structure it yet