All the basic knowledge in one place that you need to choose the unit that is right for you and your campervan.
When I built Violet the Campervan in 2018 I knew that I needed an external source for power. At that time the choices were between building your own system or buying an expensive all-in-one solar generator. I chose the latter option, but I have been upgrading and modifying my system ever since. I have used a variety of brands and capacities, and so I thought I would share my knowledge with those who may be considering their first home-on-wheels.
Why do you need a power source that is separate from your car’s battery system?
If you plan on spending any time living in a vehicle you won’t want to tax your car’s system for your charging and powering needs as this could result in a dead starter battery.
A cell phone is now a necessity, and there are a multitude of other van items that consume power ranging from vent fans to 12-volt refrigerators. How much power you require will depend on your personal needs. If all that you are doing is charging your cell phone and headlamp, you don’t need much charging capacity. However, van dwelling additions like a 12-volt fridge and a roof vent fan will require a more robust system. Lastly, if you make your living while on the road you may need to charge laptops, drones, and camera batteries. Your house battery system should take into account what you need to run, what you need to charge, and how you plan to replenish your house battery when it is depleted..
If your goal is to keep a cell phone charged for a week or less you can likely get by with a simple battery bank. These small bricks come in a variety of capacities and are reasonable in price. However, if you have greater needs you are probably going to need a power station, also known as a solar generator. These units combine the ability to recharge from the car’s 12-volt system, AC power, or solar panels. In addition, they provide a variety of 12-volt and 5-volt (USB) outlets as well as at least one AC outlet. The rest of this post will be about these devices.
Solar generators come in a variety of battery capacities. The greater the capacity the larger, heavier, and more costly the unit. Early solar generators used lead acid AGM storage batteries that had limited capacity and were very heavy. Their one advantage was that they could charge under very cold conditions.
Newer solar generators use lithium batteries which are more efficient and lighter. Lithium batteries are constructed using a variety of chemistries. Usually, if the manufacturer says that a battery is a Li-ion variety, then it is the type of battery that is used in products ranging from cell phones to electric cars. In rare cases, these batteries can catch on fire (especially if they are poorly designed). However, in most cases, this is not an issue. Another lithium battery chemistry is called LiPO4. These batteries are theoretically safer and can be recharged more times than traditional Li-ion batteries. However, they are bigger and heavier than Li-ion batteries, which can make a high-capacity unit big, heavy, and bulky.
A quality solar generator will have a good BMS (battery management system) that monitors and controls the health of the battery. For instance, a good BMS will prevent charging during freezing temperatures as doing so can permanently damage a lithium-type battery.
All batteries degrade a bit every time they are discharged and then recharged. Most manufacturers list how many discharge and charge cycles a battery can have before its overall capacity is reduced to 80%. Some units will be in the low 300-500 cycle range, while others can be recharged several thousand times before their capacity is reduced to 80%. If you are on a limited or fixed budget it makes sense to go with the battery system that allows for the most recharges. However, batteries are getting cheaper while growing in both capacity and technology. A battery with 1000 or more cycles will probably last the average user 4-5 or more years at which time they will likely want to upgrade to newer technology. In addition, if you are a weekend warrior a battery with a more limited 300-500 cycles will still last you many years.
If you partially discharge your batteries before recharging them they will last longer. Remember, a battery will still have 80% capacity even after it reaches its cycle limit. Think of your cell phone which uses a lithium battery. As time goes on it holds its charge is less and less but, it is likely that you still use it. Eventually, its capacity becomes so low that you are forced to replace either the phone or its battery. It is the same with a solar generator.
Regulated 12-volt power
This feature means that the unit has special circuitry that keeps the 12-volt output constant, which can be important for some devices that won’t operate if the voltage drops too low. Old AGM batteries showed significant voltage drops over the normal course of their discharge cycle. Newer lithium batteries also drop, but that drop can be less precipitous.
It is great to have a constant voltage from your 12-volt outlet, but that consistency comes at a price. The electronic circuitry that maintains the voltage does so at the expense of some additional power use. In other words, the solar generator consumes some power to regulate power. Many larger units use circuitry to regulate their 12-volt outlets.
As an aside, when your car is running its 12-volt outlet is putting out over 13 volts so most regulated 12-volt outlets on solar generators regulate their 12-volt outlets between 13.2 and 13.6 volts, not 12-volts.
12-volt outlet types
Almost all solar generators will have a cigarette lighter style 12-volt outlet. Many will have additional 12-volt outlets in a variety of types that range from barrel plugs to aviator-type connectors. I like units that have these outlet options as I find that a traditional 12-volt cigarette-type plug can jiggle loose when traveling on bumpy roads. This can be a problem if you are powering devices like a 12-volt fridge. The more secure the outlet the better.
The batteries in a power bank may be 12-volts, 24-volts, or possibly some other voltage. Most units have 12-volt DC as well as USB outlets on them. A USB outlet’s output is 5 volts. Solar generators use converter circuitry to change from one DC voltage to another. Converters use a small amount of power to make this adjustment.
All solar generators have circuitry (an inverter) to convert DC power into the AC (Alternating Current) power that many household appliances use. In most cases, the inverters are of the pure sine wave variety. These inverters closely replicate the type of power that comes from a home AC outlet, and this pure power may be necessary for sensitive electronic devices like a CPAP machine. I have only seen one off-brand solar generator that used a modified sine wave inverter. Modified sine wave inverters produce an approximation of regular AC power and should be avoided if possible. Most inverters provide the standard 120 volts of power, but some may cheat the system a bit by only generating 110 volts. This lower voltage often works well enough for most things. Inverters use 10-20% (depending on their efficiency) more power than what is being used during the conversion from DC to AC. If the power used by an appliance is 100 watts the total draw on the battery will be between 110 and 120 watts depending on the inverter’s design.
Inverters are rated by their operating and surge outputs. Some units can be as low as 125 watts AC output, while others may have outputs that exceed 2000 watts. When some devices (especially those with motors) start-up they momentarily require a surge of power. Because of this inverters will also list the amount of surge that they can momentarily handle. For instance, an inverter may say that it has a 500-watt continuous output with a 1000-watt surge capacity. Capacity is not the same thing as use. For instance, a 100-watt appliance will only draw a bit over 100 watts (considering operating overhead) whether the inverter’s capacity is 200 watts or 2000 watts. However, large inverters may be a bit less efficient due to their larger components and complexity.
All appliances list the maximum input of power that they use. This will be on a label that is typically on the bottom or back of the appliance. It is a good idea to exceed the requirements of an appliance. For instance, if an appliance uses 800 watts try to get an inverter that can sustain 1000 watts.
In the recent past, all you needed was a standard USB type A outlet, as all USB devices using them. Now there are power ports that deliver enough power to charge a laptop and quick charge ports that allow faster charging of small items like cell phones. Some solar generators will just have USB type A sockets while others will have both A and C styles. Lastly, some units will provide a wireless charging station on the top of their case.
There are ways to compensate for a lack of a specific port on a given unit. For instance, you can always use your laptop’s power brick and the AC outlet on the solar generator if you don’t have a 60 or 100-watt USB outlet on your unit. However, you will lose some battery efficiency in the process. In addition, you can buy little adapters that will convert a type A USB outlet to a type C USB outlet and vice versa. However, it is always best to power or recharge something in the simplest way possible.
All units have displays to give you information about the status of your solar generator. All will indicate (in some way) how much charge you have left on the battery, and most will give you information on how much power is coming into the unit and how much is going out. Additional information like hours to discharge may also be listed.
Some units will offer an Eco-mode that will power down the unit if it is left on but its not being used. Turn this feature off if you are using your unit to run a fridge as its power use is intermittent which could result in the solar generator turning off power to it.
Some units have a feature called power boost that allows you to run higher wattage devices than the AC inverter’s limit by lowering the AC voltage. Using this feature can be tricky as this brown-out power may damage electronic circuits and motors due to overheating. However, it could be useful when powering simple appliances like an old fashion hotplate.
Some units will work in tangent with an App allowing you to monitor and control your device from your phone. This can be a nice, but non-critical addition.
Lastly, some costly units are modular allowing you to add additional battery capacity. At this time if you have very great power needs for your camper it is cheaper to build a traditional electrical system rather than buy a modular unit. This will likely change in the future.
Pass through charging
When most units are plugged into an AC outlet they will preferentially take their power from AC and not the unit’s battery. At the same time, they will charge the battery.
Ways to charge
Most, if not all, units will allow you to charge your batteries three ways (car’s 12-volt cigarette outlet, solar panels, AC/Mains power). Many units will allow you to simultaneously charge your unit using several sources at once, for instance, solar and your car’s 12-volt outlet.
More on charging
It is critical to be able to quickly recharge your unit. If you are depending on your solar generator to keep your 12-volt refrigerator running you don’t want to wait 12 hours to recharge the unit. Older and cheaper solar generators can take a very long time to recharge from any source. This is OK if you charge at home and then use a unit on a trip without a need to recharge the unit. It is also OK if your power needs are fairly low. Otherwise, it is worth it to get a fast charging unit. Let’s look at some common ways to recharge.
12-volt cigarette outlet charging
The 12-volt outlet on your car’s maximum output is about 120 watts of power, but most solar generators will accept less than that to make sure that they don’t overtax the car’s electrical system. Depending solely on the cigarette outlet is feasible only in situations when you need to replace a small amount of power. Naturally, using your car’s system to recharge your solar generator should be done with the engine running.
In many cases, it makes more sense to recharge specific devices rather than a solar generator using the car’s 12-volt system. I tend to charge small gadgets like my cell phone, earbuds, or headlamp via the car’s system when driving. Remember, you can buy a 12-volt cigarette to a 5-volt USB converter if your car doesn’t have a built-in USB outlet.
Many small units quickly charge with a 12-volt, 80-100 watt solar panel. Larger units can accept higher wattage solar panels which will allow for quicker charging. Some large units need solar panels that produce a higher voltage (beyond 12 volts) to charge.
It is important to check the maximum wattage that a solar generator will accept from solar, as well as the voltage required. Some units will accept more watts than specified, but will still limit the charging rate. Older Jackery units could be over-paneled (you could connect several hundred watts of solar power) but they would limit the actual charging rate to around 65 watts via solar.
There is a welcomed trend in better units to accept more watts from solar. However, some of these larger units require higher voltages to recharge properly. You can accomplish this by running several 12-volt panels in series. For example, two 12-volt panels in parallel will output at 12-volts, but when connected in series they will output 24 volts.
If you are a van dweller or traveler you will have limitations on how many solar panels you can carry. I use 4, 12 -volt 100-watt solar panels connected in series giving me an output of 400 watts at 48 volts. Note that this is a theoretical output as no solar panel is 100 percent efficient. I have my panels flat on my van’s roof. My panels would be more efficient if I could aim them at the sun at all times. However, I like the convenience of having my system passive and always charging, even if it is suboptimal.
I’m limited by my roof’s area, as I can only mount so many panels on it. However, portable panels also are limited. Your solar generator may accept 1000 watts of solar, but you are not going to want to carry and set up 1000 watts of solar panels.
The bottom line is that getting a solar generator that generously allows for solar charging is best. However, you may not be able to fully utilize this feature based on your particular solar panel array.
All units will come with either a charging brick or an internal charger. Some newer units have much more powerful chargers than older units (always check specifications) and this can dramatically decrease charging time, which is useful if you need to recharge on the go. As a gross approximation, a 200-watt (output) adapter will recharge a 1000-watt battery from zero in about 5 hours (1000/200 = 5 hours), whereas a 400-watt unit will do the same job in 2.5 hours (1000/400 = 2.5 hours). This is an oversimplification as units charge slower as they reach full capacity. However, the more powerful the AC charger the better. Some units will allow you to buy a second charger that you can connect to the unit to double your charging speed when connected to AC. If you are charging at home for a weekend trip it doesn’t make much difference how quickly you can charge. However, it can be a big deal on the road. A small unit that can quickly charge is a plus if you are recharging at coffee shops or libraries. Additionally, a big unit that you can quickly charge is plus if you have high power needs.
Also, I use a separate free-standing AC inverter directly connected to my car battery. When I’m driving I recharge my solar generator via the solar panels on my roof as well as by the unit’s AC adapter connected to that inverter. The inverter set-up also assists when there is a string of cloudy days. I can drive or run my engine for a bit to top off my solar generator’s battery.
MPPT vs. PWM controllers
When you connect a solar panel to a battery you need a solar controller. This device properly controls the charge from your panels so that you don’t damage your system. There are two types of controllers that are built into solar generators, MPPT and PWM. PWM controllers are simpler (and cheaper) and are used in less expensive units. MPPT controllers are more complicated (and more expensive) than PWM controllers. However, they are more efficient in adverse conditions. An MPPT controller will do a more efficient charging job on cloudy days or if your panels are partially shaded.
Many units will have some sort of light built into the unit. This sounds like a silly feature, but it can be surprisingly useful, especially on smaller units that you may move around.
How much power do you need?
Generally, more is better, but more is also more expensive. Determine your use needs. You can add up the watts or amps needed. Watts and amps are related and interdependent based on the following formula:
amps x volts = watts.
A milliamp is 1/1000 of an amp.
Let’s say that all you need to charge is your cell phone which has a 5000 milliamp battery. If you had a simple 10,000 milliamp power bank you should be able to recharge it (approximately) 2 times.
Many devices will list watts used instead of amps or milliamps. If your LED cabin lights use 10 watts and your solar generator is rated at 500 watts you can expect that you can run the lights for around 50 hours.
Please note that the above are approximations. No system is 100% efficient and all battery systems reserve some of their power to preserve the longevity of the battery.
Let’s look at some battery options and what they are suitable for.
These small and inexpensive units typically have USB outlets and come in a variety of capacities. They are recharged via a power brick that the owner provides. They may be all that you need if you are only recharging small devices like your phone. You can also buy small, inexpensive small solar panels in the 10-25 watt range specifically designed to charge USB devices like battery banks. Additionally, you can extend the battery time of your phone by turning off options like WiFi and Bluetooth if they are not needed.
100-400 watt solar generators
These are very versatile units that are also relatively inexpensive. Cheaper units likely will not feature an MPPT solar controller or a regulated 12-volt power supply. Depending on their size they can provide many recharges of electronic devices, and also operate other things, like cabin lights, and USB fans. They are generally small and lightweight and are easy to carry from home to van, or van to a picnic table. I often use one of these to recharge my small electronics and to power gadgets, like a 12-volt TV that I sometimes carry. Because they are small they can easily be charged by a portable solar panel. Portable solar panels are great because you can angle and position them towards the sun. However, you have to remember to set them up, and you probably should not leave them unattended as they carry enough value to make them targets for theft.
500-1000 watt solar generators
These units can do all of the above, but they can do much more. In some cases, they may be enough to run a 12-volt fridge, and they have enough power to maintain bigger items like a laptop. If you are using many items on the road you may want a unit in this range. Many of these units feature the more efficient MPPT solar controller, have a regulated 12-volt power supply, and can accept a greater charge for faster recharging. Their AC inverters are usually in the 500-1000 watt range. However, always check a unit’s specifications.
Solar generators greater than 1000 watts
There are now some units that have 1500 watt-2000 watt (and beyond) capacities. These units can be heavy and expensive, but also very useful. Many of these units have very fast AC chargers and can accept high wattage from solar. Their AC inverters range from 1000-2000 watts (sometimes more), which opens up the ability to use many household appliances.
I use a large power station (solar generator) to run a Webasto heater and a Dometic 12-volt fridge. I routinely use small electrics like an induction burner, coffee pot, microwave, and even a 3-quart electric pressure cooker. Be aware that I purchased these small electrics with an eye to how much wattage they use. For instance, my microwave’s output is only 650 watts and uses 950 watts of input power. My system can handle that load, but I only use the microwave for short amounts of time, in the 5-10 minute/day range (80-160 watts used). My coffee pot uses 600 watts of power and it takes less than 5 minutes to brew one K-cup of coffee (only 30 watts of power used). Using a small electric with a house battery is only feasible in short bursts and when I am in a situation where I can replenish my battery easily (access to shore power or on driving days or sunny days).
When using my 1700 watt/hr solar generator and 400 watts of solar on my roof I have never run out of power. However, I’m very careful to monitor my battery. If I’m facing cloudy days I go into conservation mode when I reach around 60% battery capacity. At that time I’ll switch to my butane stove for my cooking and coffee needs, and do other things to conserve power so my battery is available for my fridge.
What brand to buy?
Well-known brands include Goal Zero, Jackery, Ecoflow, and Bluetti. I guess that many off-brands are made in the same Chinese factories. Generally, check the unit’s specification for all basic parameters including the amount of solar accepted, power of the AC inverter and charger, and life cycle for the batteries..
I hope that this has answered some of your solar generator questions. Happy camping and happy van life!