Choosing a solar panel for maximum efficiency
Hello Jeff,
Putting together an off-grid system, I am inquiring as to how best choose/purchase the solar panels for optimal efficiency in relation to their voltage output. There are panels that put out similar wattage, however the vp/imp can vary greatly.
Let’s imagine for example the system objective is approximately 2kw using a 24v to 110v inverter with battery back-up.
Which would be the best solar panels to use for maximum efficiency?
* 12 – 160w panels @ 24vp/6.80imp
* 10 – 190w panels @ 26.7vp/7.12imp
* 10 – 190w panels @ 17.8vp/10.96imp
* 10 – 200w panels @ 53.8vp/3.16imp
Thanks!
Jon
Jon,
As we say on the web site, we cannot answer specific design questions because there are too many variables we would not know about your specific application, and we are trying to keep this a free service. However, I can provide some general answers that should help you narrow down your choices.
First, there are many things that go into the design process and the first is inverter input limits if grid tie, and solar charge controller input limits if battery based. In other words, if your solar charge controller has a limit of 75 volts DC input, this will require the number of solar modules wired in series to be well below this high limit. The NEC Article 690 provides more specific design guidelines related to safety multipliers that you must use.
The maximum input amp rating of the solar charge controller (or inverter if grid tie) will determine the maximum number of parallel strings and total amps from the array after the required NEC design multipliers are added.
Once you know the maximum voltage and maximum current your system can safely handle, this will define the solar array that your system can handle. Once you know this maximum total array wattage, you want to select the highest quality module you can buy that has the lowest cost per watt.
Take the total delivered price of a specific module and divide by nameplate wattage to get the $cost/watt.
If this process does not give you the solar array you want, then you will need to make changes to the inverter if grid tied, or the solar charge controller if a battery based system. Normally I first select the exact solar array wattage and physical size I want for a specific budget, then I select the inverter if grid tie, or the solar charge controller if battery based, but it sounds like you are working backwards and trying to base you design on comparing output voltages and amp ratings of the modules to fit a specific requirement.
In other words, its like taking a car and trying to replace the engine with a bigger engine to get more power. However, if you do not also upgrade the transmission, tires, drive shaft, fuel system, exhaust system, and brake system, then the vehicle cannot take advantage of the higher horsepower.
Hope this helps,
Jeff Yago
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