There are two common types of electric current called alternating current or AC and direct current DC. AC is what you get from the electrical grid to your home to power all your appliances and equipment. DC can be found in a lot of vehicles and equipment that are used in RVs and off-grid homes. You can use direct current to power lighting, fans etc. The energy produced by a solar panel is DC energy and this is what you generally see stored in batteries. 

Solar power is used to power many appliances and they can be used to power vehicle batteries as well. But one of the drawbacks of using a solar charger is sometimes there can be insufficient sunlight depending on the weather you are having. So you will need to look for another way of charging your battery. This is where an AC DC or a DC DC charger will come in. DC to DC chargers works with two batteries. Basically, the energy of one battery will charge the other. You can use the alternator to facilitate the charging of batteries with a DC to DC charger. When the engine is not running, the vehicle is powered by a battery. This battery is charged by the alternator. It will also charge the starter battery when you are driving.

DC to DC charging is very efficient and in certain situations, you may not require a solar panel altogether. But you have to consider vehicle usage and the additional DC energy that is available to you for charging batteries.  You can see some vehicles using on-board DC to DC chargers. This can be a permanent installation. If you are using this for a boat, you can use a dockside outlet to plug in the DC to DC charger. When it comes to vehicles, you can use an outlet in parking areas. These chargers will charge the secondary batteries during your drive. This is done by using the primary battery. You can also have a solar powered system that will charge the service battery first. You will be able to sustain a full charge for a longer time and you will be able to continue staying off-grid.

You can use solar power and DC to DC chargers together but you will see them commonly used as a backup for each other. Many off-grid vans and vehicles will have solar panels installed on the roof and use a DC to DC charger when you need to increase the energy use. Generally, there is a solar charge controller that is used to charge the batteries. But you can use combination units as well. You will be able to find DC to DC chargers that have in-built solar regulators that allow them to accept solar power. This way, there is less of a strain on the alternator of the vehicle. This is a solution that is great for people who are staying in one location for a long time. You have to consider your energy use and how you plan to use the vehicle before you select DC to DC charger options.