A solar battery is a combination of photovoltaic converters (solar cells) semiconductor components that convert solar energy directly into electrical direct current, in contrast to solar collectors, which heat the heat transfer material.
Solar panels have a lot of characteristics you should consider to choose the right ones. There are some obvious aspects, such as solar panel manufacturer, price and warranty. There are also some purely technical characteristics, such as voltage at open circuit (VOC), voltage at maximum power (VMP or VPM) and nominal voltage. The latter is very important, as it shows what equipment the panel can go together.
Nominal voltage can be either 12 V, 24 V or 48 V. Basically, it means that a 24v solar panel, for example, is compatible with a 24 V charge controller, a 24 V battery bank, and a 24 V inverter. The same logic is applicable to 12 V and 48 V panels. If, for example, there aren’t batteries of the necessary voltage, they can be connected in series: two 12 V batteries connected in that way will be an equivalent of a 24 V battery. Likewise, if you have a 48 V battery bank, you can wire two 24 V nominal panels to charge it.
Nominal voltage is just a classification method. It stems from the fact that earlier off-grid systems had either 12 V or 24 V battery banks. Nominal voltage can be rather tricky: 72-cell modules are considered 24 V nominal solar panels, although they really output about 36 V. This difference is crucial though, otherwise the voltage wouldn’t be enough to charge a 24 V battery. To make things simpler, all equipment which outputs something within that voltage range (25-40 V) is considered 24 V. Another interesting thing: you will never find nominal voltage listed on a PV module’s specification sheet and sticker.
The question arises: why 24 volts? Well, today in most countries the standard residential voltage is 220-240 V AC, which is converted to 24 V DC. Essentially it means that opting for 24 V panels increases the chances that the wiring, AC appliances and lighting in the house will be compatible with your PV system and you won’t have to buy any additional equipment.
One more advantage of 24 V solar panels is that they give more power per square meter than, for example, 12 V ones. It usually helps to reduce the price of the PV solar system. It also explains why 24 V solar panels are widely used in big installations, such as homes, apartments, offices, factories, parking, etc.
This nominal voltage classification is extremely important for off-grid systems. Opposed to them there are grid-tied PV systems without batteries, where the inverter converts the DC voltage from the solar panels directly into AC to power your household appliances. So, the 24 nominal voltage doesn’t play any significant role there. Grid-tie system development allowed manufacturers to widen the range of solar panels, to make modules based on physical size and wattage characteristics, as well as to use some materials that produced module voltages completely unrelated to batteries.
To sum it up, 24 V solar panels are highly compatible modules which are likely to suit you PV system.