24V Solar Panel Systems
Given that many people nowadays are using 24V (24 volt) solar panel systems espcailly on boats and yachts, you would expect that it would be very easy to set up a 24V solar system. However, a quick trawl of the internet quickly highlights that nearly everything written talks about 12V systems and that it is very difficult to find good information about using 24 volts.
The primary problem is that all charge controllers, whether PWM or MPPT technology, are simply not capable of significantly increasing the system voltage without losing power. Whilst thet claims of some manufacturers that their MPPT controllers can charge a 24V battery using 12V panels are true, the power loss remains untenable. The only reliable way of using solar panels with a 24V battery bank is to ensure that the solar array is at 24V or higher. In this case, the charge controllers can drop the voltage without losing significant amounts of power.
The range of 24V+ solar panels designed for off-grid use is, unfortunately, not particularly wide at the more cost-effective end of the market. Sunware do manufacture 24V panels at 48W and 70W, but there is a price attached. Other manufacturers, such as Yingli and Kyocera, manufacture a wide range of 'grid-tie' panels that operate at 24V plus, but again these are more expensive products. In short, there is no easy answer and a 24V solar panel installation is always going to be more expensive. There are of course benefits, such as reduced voltage losses and cable sizes, but these may well be overshadowed by the cost penalty.
To install a 24V system using standard off grid panels, it is necessary to wire the panels in 'series pairs'. For example, wiring two 100W 17V (5.9A) panels in series will result in a solar array of 200W and 34V (still 5.9A):
Another important factor to bear in mind when looking at 24V systems is that their are different types of electrical devices, some which operate at a constant current and others with a fixed power consumption in watts. Generally, while many people do talk in amps or amp-hours, it is much more meaningful if we use watts and watt-hours in our calculations - this is a much more realistic figure for power consumption as opposed to current draw (amps).
Whilst at first glance it may seem as though a 24V system is producing less power than a 12V system with the same number of panels, the truth is that this is only really true if we are talking about current production in amps. In most instances, the combined wattage of the panels is the same regardless of system voltage. Only where a device operates at a fixed current, independent of the voltage do we start seeing changing wattages:
Constant consumption:
120W @ 12V = 10A / 120W @ 24V = 5A
Constant current:
10A @ 12V = 120W / 10A @ 24V = 240W
Contact us at Cleversolar for help and advice or a look at our Solar Panels Advice & FAQs to find out more about 24 volt solar panel systems.
