The 400-watt solar panel kit you’ve purchased to charge the boat, caravan, or power any other off-grid application may not include a power inverter that’s necessary to run AC appliances such as a fridge.
So, what size of inverter (watts) should you use and how do you go about deciding on a particular rating of inverter?
If this is you and need guidance on what inverter size to use then read on.
What Size of Inverter (watts) for 400-watt Solar Panel?
Base the inverter size (watts) you use on the combined power consumption of the AC appliances you plan to run, and not the solar panel rating (watts), in this case- 400 watts.
Think of the solar panel as a faucet slowly filling a storage tank and the inverter as the pipe that channels water from the tank to a point of use.
You can then connect a smaller or larger pipe- the inverter depending on how much water you need downstream, provided there’s water in the tank.
You can for instance connect a pure sine-wave or modified sine-wave inverters ranging from say 400 watts to 3,000 watts to your battery bank.
Note: Make sure to connect the off-grid inverter to the battery, taking care not to reverse the polarity of the inverter cable connections.
Connect the positive wire of the inverter to the battery’s positive terminal and the negative wire (red) to the battery’s negative terminal.
Do not connect the inverter directly to the solar panel! The off-grid inverter should be wired to the battery bank unless it is a grid-tie inverter.
Not sure what size of inverter to use for your appliances?
You can access the off-grid solar system calculator.
In the calculator spreadsheet, list the appliances you plan to run and their corresponding power consumption values (watts) to automatically work out an indicative inverter size (watts) to use.
If the inverter size (watts) bundled with the solar kit cannot run the appliance then the inverter overload alarm will be activated.
For example, a fridge with a continuous power draw of 200 watts may not run reliably with a 600-watt inverter.
Upgrade to a large-capacity inverter.
Best Inverter to Use with a 400-Watt Solar Panel
Again, this depends on the power consumption of the AC appliances.
I personally aim for at least a 1,000-1,500 watt inverter or larger.
It costs only slightly more than the smaller, 400-600 watt inverter yet can run more home appliances simultaneously including the ones that have a larger power draw – fridge and dishwasher.
Again, before you settle on an inverter size, ask yourself if you plan to connect larger appliances later.
Err on the side of having more capacity (watts) for the inverter than you need to avoid having to upgrade later whenever possible!
12V or 24V rated Inverter
Make sure the voltage rating of the inverter matches the battery bank voltage.
For example, using a 24-volt battery bank? Then only connect the 24V version of the inverter.
Pure sinewave or Modified Sinewave Inverter
If you’re running sensitive medical equipment like a CPAP machine or appliances that use motors such as a fridge, microwave, washing machine, power tools or a dishwasher then go for a pure sine wave inverter for the appliances to run smoothly and cooler.
If in doubt, consult the appliance user manual or manufacturer.
Otherwise, a good quality modified sine-wave inverter can run other common household appliances reliably.
Signs an Inverter May be Undersized
An appliance with a large current draw at or higher than the inverter can handle will cause it to shut down with an overload alarm!
Do You Always Need an Inverter?
If the appliances use DC power only such as some LED lights, fans, or pumps then you do not need an inverter.
So, first, check the power requirements (AC or DC) of the appliance you plan to use to determine if it uses AC or DC power. If so, then invest in an inverter.
How to Size an Inverter for a 400-watt Solar Panel
The inverter size (watts) should be able to handle both the combined continuous and surge power ratings of the AC appliances.
Match the inverter DC voltage rating (12V or 24V) to that of the battery bank.
Use this free downloadable calculator to easily work out the inverter size to use.
To use the calculator, list the appliances you plan to run and their corresponding power consumption values (watts).
The calculator will then automatically work out for you the minimum inverter size to use.
Can I Use It with a Grid Tie Inverter?
You can use it to charge a portable solar generator with an inbuilt inverter
You’ll need to check the voltage and current that the grid-tie inverter is suited for.
Make sure it can safely handle both the voltage and current of the 400-watt solar panel to avoid damage to the inverter or failure of the inverter to work!
Keep the following in mind when selecting an inverter to work with the 400-watt solar kit.
Inverter size (watts): The inverter size (watts) should be able to handle both the combined continuous and surge power rating of the AC appliances.
Inverter DC voltage rating: Match the inverter DC voltage rating (12V or 24V) to that of the battery bank.
Pure sinewave or Modified Sinewave Inverter. For sensitive medical equipment or appliances with motors, use a pure sine wave inverter.
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