Sizing Solar Battery Chargers for Charging Batteries

Sizing Solar Battery Chargers for Charging Batteries

Solar Chargers Produce electricity according to size. The bigger the panel the more power it produces. This however is pegged on efficiency and that’s the general rule. Portable Solar Panels range from the Smallest 5 watt to the highest which can go up to 200 watts. This also dictates the price and would range from $20 to $500, depending upon the brand and additional features.

The wattage of the panels are indicated and this can guide you in choosing for the best use such as heavy duty or light, mobile ,and either single outlet or multiple outlets. A phone needs 3watts to 5watts of power to charge while an iPad would need around 11 watts.

However if you pick the 5 watts charger for your phone it may not be dependable as this will drop drastically due to inefficiency and wont fully charge your cellphone on cloudy days.

Solar chargers are tested at STC (Standard Test Conditions) at a humidity of around 1.5 and ambient temperature 25 degrees Celsius and are flashed with 100 watt of light. These tests provide a theoretical maximum rating that will not simply work in real world conditions.

To get the wattage of a Solar Panel you simply multiply the Rated Amperage with the Voltage (This may be accurate in some instances)

Example 3A x 5V = 15 Watts 

A solar charger is easy to use and you have just to leave the charger around in the sun to charge. Dispersed light is better for solar panels than direct sunlight or sunlight at an angle and a panel can exceed 30% efficiency with dispersed light. Solar Panels can be used to charge all types of Rechargeable Batteries regardless of Voltage.

But when selecting a Solar Panel it is important that you match up Wattage and Voltage in order to get the best results.

Car Battery ChargerPhone ChargerLaptop ChargerDeepcycle Battery Charger
12V 5 Watt Solar Charger21-28W Solar Panel60W Monocrystalline Solar Charger10 - 100 Watt 12 Volt
Trickle Charges the battery. Only maintains the battery to avoid a dead battery. Phone charger for the outdoors can be attached to backpack or trees. Does not have a Battery though. 60W Solar panel charger for Laptops. Needs direct sunlight to charge a laptop but can be used for phones in low sunlightThis 100 watt Solar Panel can fully charge a 50Ah Battery in 5 hours in direct sunlight.
Solar Car Battery Charger Solar Chargers for Phones Portable Solar Panel Chargers for Laptops12v Solar Battery Chargers

Factors that Affect Output from a Solar Battery Charger

When picking the right Solar Charger to use for your battery or battery system their are various factors that come into play. Of course Size,

Size of the solar panel

Solar panels come in all kinds of shapes, sizes and weights. The general rule is that the bigger the panel the more that wattage but that’s not necessarily true. Two panels of the same size can have a very different output in the same conditions. This mostly goes down to the technology and efficiency which we’ll discuss later in this article.

Width and length

Manufactures of Solar Panels use standard sizes to build solar panels used in roof systems in homes and business. For residential solar panels you expect to find them measuring about 65 inches by 39 inches and those on the commercial side are a bit longer going up to 77 inches by 39 inches.

Though the width and length slightly vary, many organizations manufactures these systems in standard sizes. The size used for the residential connections is 65 inches by 39 inches. On the other hand, for the commercial uses is 77 inches by 39 inches.

Now on the portable solar chargers that are now more popular nowadays the width and length is up to the discretion of the manufacturer and use of the panel. You can find a 1cm panel on a calculator, or 2 by 2 inch inch panel on a solar light while most portable solar chargers will come at around 11.1 × 6 inches.


The solar panels’ depth normally ranges between 1.5 inches to 2 inches with portable ones having a depth of 0.71 inches. Again this is also influenced by the technology used.


Solar panels used in roofing systems typically weigh around 40 pounds and some can go up to 50 pounds for a 300watt panel . This is because of the additional framing used to mount the solar panes to the roof. For a portable system you can’t be carrying around 40 pounds to use for the outdoors. But typically 50 watt panel would be 3 to 5 pounds.

Solar panel on a weigh scale
7.2 Pound Solar Charger

The solar cells numbers

The cells are the electrical devices that convert sunlight into power. To produce a significant amount of power, these cells are together connected in a solar panel. The 60 cell modules are the typical standard for home applications; however, slightly large commercial solar panels have about 72 cells.

Sunpower which is a leading manufacturer in Solar Panels uses about 96 cell panels which their panels one of the most efficient in the market.

Solar Panel Cells

Rated Power wattage

Power Wattage in the Case of Solar charger is the expected is the Power output from a panel. They are normally rated by the direct current power produced in standard test conditions. The label of the Wattage on the panels are theoretic under ideal testing conditions are assumption of 100% efficiency.

Some are also labelled with the Solar Panels Capacity, Wattage and Power output. But the power output is the most important to look out for. The STC rating is given by the power wattage given under lab conditions, while PTC is from the manufacturer from the technical equipment specifications. PTC is usually 10-15% lower compared to STC.


All electrical equipment are inefficient and lose power to resistance and in the form of heat, but solar panels are notoriously inefficient. And by “efficiency” we the rate at converting sunlight to electricity or the “sunlight conversion rate”. This rate can be anywhere from 5% to 10% but the technology continues to improve with modern solar panels having a sunlight conversion rate of up to 21%.

Technology: Thin Film Vs Mono Crystalline

The most common types of Solar Panels you will find in the market are the thin film and the Mono Crystalline types. Thin film solar panels have better efficiency, occupy less space and weigh less. Thin film panels also perform better at high temperatures and can maintain efficiency when its hot.

Monocrystalline solar panels have a small advantage in colder conditions and shady conditions. They also maintain Efficiency overtime while Thin Film Panels tend to decline over time.

Solar Panels & Batteries – Planning Your System Requirements

All components in your solar energy/electrical system are related to each other. The way you’re supposed to determine that initial battery and solar panel “requirement” so you can plan around anything making sense is to add up the power requirements (watts) of the things you’re going to run during a day.

Your goal is to find out, in watts, how much electricity you need. Then figure the number of hours of sun your area gets during that day, etc., taking into consideration seasonal use. Theoretically you can put together a system that gives you that kind of power.

Interestingly enough, most people that do this with a home plan in mind often end up thinking they need way more than they really do. It’s much easier with a small simple solar system. It’s a confusing task but important; a necessity in fact. Just think about those things you’d like to have working.

It requires specifics. What thing? How long per day? How many watts per hour? How many things at the same time? A little thought in this area is better than the wild guess method. Pay particular attention to the higher watt consuming devices you might use.

Just to play around. Let’s say you know you want to run a 45 watt laptop for 3 hours a day. That’s 95 watts x 3 hours = 285 watts on computer usage. If you had a 300 watt panel pumping in 50 watts an hour (hope for bright sun) you’d still be providing only about half or less of what you’d need for that period of time.

If your battery is big enough to withstand the short fall, you could hope your sun lasts for enough hours when you’re done with your computer to make up for it before you need it again. Or, you need more panels. Solar panels can charge the battery at the same time you’re drawing energy from it.

Sometimes how big you can go is determined not by solar panel size or battery capacity but by affordability and space and you just have to deal with it by limiting or spacing your use.

Solar Charge Controllers

The solar electrical charge controller controls the incoming charge to the battery. More complex/sophisticated charge controllers do even more. Your system cannot function without one. Any battery being charged, even with a small solar panel, can be over charged and destroyed given enough time without a charge controller.

The only time you may not need a charge controller is when using a 1-5 watt panel as a trickle charger. The intention of a trickle charger is to replace normal energy loss in a battery that occurs from just sitting. The general rule is that if a trickle charge panel puts out 2 watts or less per 50 battery amp hours you don’t need a charge controller. But, when in doubt, use one. Small ones are inexpensive.

Choosing a Solar 12v Charge Controller

Charge controllers come in all sorts of sizes as determined by number of amps with a variety of features as mentioned above and more. Since they’re sold by the number of amps and solar panels are sold by watts and the charge controller needs to be able to handle the watts put out by the solar panel, it’s helpful to repeat the equation, amps x volts = watts, but not always the most accurate method here.

A 4.5 amp charge controller is considered “small”. 4.5 amps x 12 volts (battery) = 54 watts according to the math. Putting math aside however, the most accurate thing to do is just read the amp rating off the solar panel specs.  It will be listed there. It’s an alternate measurement to watts. Other influences affect the amps put out by a solar panel that may change the real amp outcome.  Comparing amps to amps is better.

The Solar Battery Charger or Panel

A solar battery charger is a charger that uses the sun’s power to produce electricity which is measured in watts There are a variety of uses for this type of charge.

Low Wattage

A low wattage charger ( generally 4 watts or under) are all small and designed to maintain batteries that do not have a load being put on them while being charged. The output of these low wattage devices is so small that they are not designed to recharge drained batteries. This type of is designed for maintenance of power sports and marine starting batteries. These devices might have stands, some are mountable, and some are panels that plug into car cigarette lighters.

A Solar Panel Connected to an Electric Fence

Mid-Range Wattage

A mid-range series is approximately double the wattage of the previous category. In these you could have panels, mounting stands or cigarette lighter adapters. This type of solar panel, which is typically 5 to 10 watt, is recommended for usage in such applications as industrial gate openers, electrical fence chargers and smaller industrial equipment

Upper-Range Wattage

A solar charger of 11 W and up begins to have real capabilities for marine and industrial use and are often used for charging RVs and boating applications. Once the solar battery charger output of 11 W it up is reached then serious work can be done for recharging. For example solar panels range from 20 watts to more than 300 W. The panels can also be wired together either in series or parallel for many different applications.

Another specialized application is for RV and marine multi-battery charging and there are multiple output panels ranging from 62 watt to  around 130 watts in this category.While a it can be simply put on the dashboard of a car and plugged into a cigarette lighter, most chargers need accessories to fully achieve their usefulness.

Solar Panels on a RV

A solar panel can also be used in off grid applications and for almost any consumer device you can imagine. For example laptop computer, for those times when you are off grid but still need to recharge your laptop’s batteries. And the RV and marine applications are perfect examples of obtaining power from the sun’s rays when electrical connections are not available.

An easy way of thinking about this battery charger is to envision them as alternatives to plugging a charger into a wall outlet. Solar Panels create their own electricity rather than taking electricity from the grid. So you can be using the grid for most electrical applications while still using the free power of the sun to recharge many devices.

So it can be either an adjunct to or a replacement for the electrical power from your wall socket depending upon what you want to achieve.

Matching Solar Battery Chargers to Batteries and Use

Car Battery charger

Solar Chargers can be used to charge batteries or to keep them maintained. Charging for any device starts after the charger is exposed to the sun. It is capable to store some energy when not exposed. Some applications can use low light technology on a cloudy day. The charger cables are easy to install and resist humidity and dust with its double insulation. With low voltage compared to electricity solar chargers wont overcharge your Car or RV Battery.

Simple Solar Chargers can supply constant voltage or current to the battery being charged without altering its output based on time or the charge on the battery. Another solar charger fit for an all-day use is a trickle charger that is simple in terms of power consumption. This charger charges a battery slowly so you can leave it for prolonged hours without spoiling it compared to other battery chargers.

Your battery will remain powered but never over charged even if it stays on the battery charger indefinitely. To prolong battery life, most manufacturers recommend using the right Solar Charger for your electronic device battery. Limiting the depth of discharge to about twenty percent and not allowing batteries to be discharged below fifty percent depth of discharge (DOD) also prolong battery life.

Timers or alarms can provide warnings when you need to disconnect your charger from the batteries. You can also preserve your batteries by using an inverter of a low voltage with a disconnect feature that will disconnect at given set points.

Phone Charger

A solar powered cell phone charger is a charging system for your phone that operates off of solar energy. This type of cell phone charger is easy to use and is portable, so it is great for people who like to travel a lot. There are two types: Direct Charger and the Power bank Charger

woman charging phone with solar charger
Charging Phone with a Solar Power Bank

With a solar charger you can be sure to have power available to your cell phone whenever you need it. It does not matter how far away from the city and electricity you get. If you own a solar charger you will be able to power your cell phone at all times. Phones usually come with inbuilt charge controllers so it is safe to use directly.

Laptop Charger

The handy solar laptop chargers come in different sizes, weights and shapes and even with their cost. This might cost you, but simply think about the help that it could provide for you such as the free energy and the long period of employment.

A 60 Watt Monocrstalline Solar Charger will be sufficient for this purpose. It is also important to make sure you match the voltage for you laptop.

Furthermore, the usage of this charger is not for laptop alone, it can also be use to charge electronic devices like the mobile, GPS systems, iPods, camcorders, PDAs and even to jump start an automobile during emergencies.

Using a Laptop on the Outdoors

Using this kind of charger is considered as handy due to it has less wiring and cabling. There are two types of solar battery available in the market. Both of these compact and user friendly but the selection will depend on your preference as well as your budget.

There is a kind of solar laptop charger that you can also fold and there are ones which is a hard case type and bring it safely. With this kind of solar panel charger, you only need to click the shut button if you are not going to use it. This will surely eliminate the chances of damaging the solar panel itself.

Solar Backpack Charger

A portable charger is a very useful addition to a backpacker’s gear set. When backpacking, weight is at a premium, and few things offer more concentrated weight than batteries. Despite that seemingly obvious fact, backpackers have come to rely on battery operated devices for everything from telling direction to providing music during the trip.

The range of use for electronic devices runs the gauntlet from life saving necessity to pleasant diversion. It’s one thing if your MP3 player goes dead while backpacking. It’s quite another thing entirely if your GPS unit goes dead, or even worse, a back country beacon. The backpack charger weighs very little, can be rolled up to take less pack space than a sleeping pad, and ensures that you don’t run the risk of having vital equipment die in the middle of your trip.

The combination to look for is a voltage higher than that of the device you need to charge and of course, the lowest weight possible. The size of the panel when spread out is typically between one and six square feet, but the packed volume is more important to consider when you are purchasing.

High Capacity Solar Battery Charger

Typically, a high capacity solar charger battery can recharge anything from 5V products such as an Ipad or cell phone, to almost any 12v Battery. With an incredible array of adapters that comes with it, you will never have to worry about which product you plug in, because you all would need to do is simply select the current for your product, attach the correct adapter, and let it charge.

This is a great device for anyone who enjoys spending time outdoors as well as at home. Major differences between a high capacity solar charger battery and a regular one is that the former features overcharge, discharge, short circuit, and heat protection.

If you are looking to solar charge an RV or cabin, this is what you want to start with. This package should include a solar panel, Charge Controller, mounting brackets, an adaptor kit and tray cables. This panel can charge a 50Ah Battery from 50% in 3 hours in direct sunlight. Used to charge deep cycle SLA, Gel or flooded batteries.

How a Solar Charger Works

The Solar charger is made up of small solar panels. The solar panel uses solar cells which are made up of monocrystalline silicon water that converts sunlight into electricity through photovoltaic effect. The monocrystalline silicon water is said to give the best result.

The ray from the sun which contains photons is absorbed the monocrystalline silicon water which heats up causing negatively charger electron to move in the material and create electricity. This electricity is then transferred to the device that is hooked up to the Solar battery charger and in turn charges the device.

Solar battery charger often comes with PV system controllers. The PV system controller regulates power to the device or battery attached to the charger and makes sure that they are not damaged by cutting or increasing the power to maintain a controlled and constant flow.

What are the benefits of Solar Battery Chargers?

There are 3 major benefits which solar battery chargers can give us: 

They do not require external electrical sources to recharge your batteries.

This gives the huge benefit of being able to recharge your batteries without being near a power source. Anywhere there is sunshine you can recharge. Let’s take an extreme case of driving through the woods and your car breaks down your mobile battery is dead and you’re stranded.

A solar battery charger will give you peace of mind knowing you can charge your phone and make the call. This point is especially relevant to hikers & and some extreme sports.

The cost 

Once you have bought your charger there is no ongoing cost to recharge. In fact I know of a family which no longer charge their mobiles from a power point. What a saving. The other cost factor is that with developments in technology the cost of solar battery chargers has reduced dramatically.

The environmental benefit.

Solar cells generate no emissions. Most energy is produced around the world by burning coal in big power stations. We all know the negative effect this is having on our environment.

Glossary of Terms

Solar terminology can be confusing at times, that’s why I’m giving you the following short list, if you’re stuck wondering what a certain term means, use it:

Activation voltage

The voltage at which a charge controller will take action to protect the batteries.

Alternating current (AC)

Electrical current the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second.

Ampere (amp)

A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere.

Ampere-hour (Ah/AH)

A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.

Angle of incidence

The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°.

Array current

The electrical current produced by a photovoltaic array when it is exposed to sunlight.

Array operating voltage

The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.

Battery cycle life

The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Blocking Diode

A solid-state component installed between the solar module and the battery. It prevents the solar panel from discharging the battery in the absence of sunlight. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

Bimodal PV (photovoltaic) system

A PV system that can call upon stored power from its own battery or, when needed, from an electric grid (utility).

Bypass diode

A diode connected across one or more solar cells in a photovoltaic module so that the diode will conduct if the cells become reverse-biased. It protects these solar cells from thermal destruction in total or partial shading of individual solar cells while other cells are exposed to full light.

Charge controller

A device that regulates battery charge by controlling the charging voltage and/or current from a direct-current (DC) power source, such as a PV array.

Cloud enhancement

The increase in solar intensity caused by reflected irradiance from nearby clouds.


A photovoltaic module that includes optical components such as lenses to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun. They can increase the power flux of sunlight hundreds of times.

Conversion efficiency

The ratio of the electric power produced by a PV device to the power of the sunlight shining on the device. Cell efficiency defines how much energy in sunlight is actually converted into electricity.

Days of storage

The number of consecutive days the stand-alone system will meet a defined load without solar energy input. This term is related to system availability.

Direct-coupled PV system

A system in which the output of a PV module or array is directly connected to a DC load (a device that uses DC power).

Direct current (DC)

Electrical current that flows in one direction through the conductor. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current.

Distributed generation

A system in which many smaller power-generating systems create electrical power near the point of consumption.


A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).


Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage.

Electric current

The flow of electrical energy (electricity) in a conductor, measured in amperes.


An electrochemical device that channels an electric current through water to break down water molecules and extract their components, hydrogen and oxygen.

Fixed tilt array

A photovoltaic array set in at a fixed angle with respect to horizontal.

Flat-plate array

A PV array that consists of non-concentrating PV modules.

Flat-plate collector

A solar energy collector that absorbs solar energy on a flat surface, without concentrating it, and can utilize solar radiation directly from the sun as well as radiation that is reflected or scattered by clouds and other surfaces.

Fuel cell

An electrochemical device that uses hydrogen and oxygen to produce DC electricity, with water and heat as byproducts.

Full sun

The amount of power density in sunlight received at the earth’s surface at noon on a clear day (about 1,000 watts/square meter).


A device that converts mechanical energy into electricity by means of electromagnetic induction. (A shaft bearing permanent magnets is turned, and the changing magnetic field creates an electrical current in a surrounding wire coil.)


The vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.

Hybrid system

A system that includes an energy source other than a solar array and (if interactive) the utility. Examples include wind and diesel power.


A business that designs, builds, and installs complete PV systems for particular applications by matching components from various manufacturers.


A device that converts DC power from battery systems or arrays to utility-grade alternating current (AC) power for AC loads or export to the utility grid.


A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Kilowatt (kW)

A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Kilowatt-hour (kWh)

1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

Maximum power point (MPP)

The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts.

Photovoltaic cell:

The smallest semiconductor element that converts sunlight into electricity. Each cell is made of silicon or another semiconductive material, like a computer chip. The silicon is treated so that it generates a flow of electricity when light shines on it.


A device that converts AC power to DC power.

Resistance (R)

The property of a conductor that opposes the flow of an electric current resulting in the generation of heat in the conducting material. The resistance is specified in ohms.

Solar module

Solar modules, or panels, are series of solar cells wired together into strings and enclosed in self-contained glass units for weather protection.

Self-regulating PV system

A type of stand-alone system that uses no active control systems to protect the battery, except through careful design and component sizing.


Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Silicon (Si)

A semi-metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It crystallizes in face-centered cubic lattice, like a diamond. It’s commonly found as the oxide in sand and quartz.

Stand-alone PV system

A type of PV system that operates autonomously and supplies power to electrical loads independently of the electric utility.

Tilt angle

The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Volt (V)

A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.


The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

Zenith angle:

The angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).