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In off grid solar power systems, the inverter draws power from the battery to run appliances. If you want to run any AC powered devices, the battery bank must provide sufficient power. In the case of a 2000W inverter, how much do you need?
A 2000W inverter requires a 200ah battery to run at full load for 20-25 minutes and 600ah to run for an hour. If you want to recharge the battery at 50%, the battery sizes have to be doubled to 400ah and 1200ah respectively.
How to Calculate Inverter Battery Requirements
The formula is hours needed to run x watts / battery voltage = battery inverter size
There are also two factors to consider, the battery recharge time and how much extra reserve power the inverter must have to handle power spikes..
Suppose you have a 2000W inverter – we recommend the Renogy 2000W Pure Sine Wave for its efficiency – and a 2000W load with a 2 hour runtime.
2000W per hour x 2 = 4000W
Divide this number by the battery voltage. Example:
4000W / 12V = 333ah (amps hours)
So a 2000W inverter running a 2000W load for two hours needs a 333ah battery. But this is where the battery recharge time comes into play.
If you use a 333ah battery for two hours, it will be completely drained. Draining solar batteries to zero is not a good idea. This will shorten the battery life cycle and accelerate wear and tear. But if you have a lithium battery like the Kcvolro 12V 100ah, you can discharge up to 80% and it has guaranteed 7000+ cycles.
AGM, gel and FLA batteries run best when recharged at 50% levels. If you are going to use a lead acid battery with your 2000W inverter, you can only use 50% of its capacity. This means you have to double the size if you want to run the load in the example.
If you have a 2000W load and want to run it for 2 hours at maximum draw, you must have a 666ah or 700ah battery. This allows the load to operate at full capacity even if the battery has to be recharged at 50%.
With lithium batteries you have 80% or better discharge levels, but it costs more than FLAs. It comes down to whether you are willing to pay the extra for lithium or don’t mind the 50% discharge rate of lead acid batteries. This is true for 2000W and 1000 watt Inverters alike.
How to Make Batteries Last on a 2000W Inverter
The easiest way to make inverter batteries last is to reduce the load. The lower the load the longer the runtime.
If you have a 2000W inverter carrying a 2000W load, that is 166.6 amps an hour (2000W / 12V = 166.6). A 200ah 12V can power this load for 90 minutes maximum, but it will be 100% depleted at the end.
But if you reduce the load to 1000W the battery life gets extended. The 2000W load running at max draw on a 700ah 12V battery can now last for 4 hours. Or you can opt for a 350ah battery and the load will run fine.
Guide to Inverter Sizing
An inverter size guide is essential for optimum battery performance, but the question is how much reserve power should you have? Some appliances have high starting watt requirements, and even those that don’t go through power spikes, so how much do you need?
A safe number is to add 25%-50% to the total number of watts needed by the inverter load. If you are installing a 2000W load, the inverter should ideally be 2500 or 3000W. In other words, a 2000W inverter should be running 1500W-1000W only.
This does not mean you cannot use an inverter to the limit. Only that most solar power users prefer to have reserve energy in case a power spike hits. The same principle is used with solar panels and batteries, it is always better to have more power than lacking.
2000W Inverter and Battery Usage Example
How many batteries would you need to run a heater connected to a 2000W inverter? The answer depends on three factors: the heater wattage, how long you need to run it and the battery voltage.
A 1500W heater requires a 150ah 12V battery to run for an hour, completely discharging the battery. Use a 300ah 12V battery if you have to recharge it at 50% level.
At 1500W is sufficient for a 2000W inverter, provided you don’t run any other high powered appliances alongside it. Technically the inverter can run a 2000W heater, but most experts do not recommend it because it is right at the inverter limit.
This example assumes the heater does not have a starting watt requirement, and most don’t. If you load a well pump on solar, refrigerator or AC, a 2000W inverter will be insufficient. Those appliances have 2500W-3000W starting watts which is beyond the inverter’s capacity. Even if the running wattage is less than 1000W, the inverter won’t run.
How to Choose the Right Battery For an Inverter
The battery size depends on the inverter load and the voltage. The higher the voltage, the lower the required amps to run the load.
Suppose you have a 2000W inverter that has to load 1500W. The formula again is runtime x watts / battery volt = battery size. If we run the load for an hour on a 12V battery you would need 125ah (1500/12V = 125). But if it was a 24V battery you only need 62.5ah (1500/24V = 62.5).
You can also use several lower voltage batteries as long as it is in a series configuration. You can connect two 6V batteries in a series and it would run the load because the total is 12V. This only works in a series configuration, because parallel setups do not add the voltage.
How Long Do Batteries Last on an Inverter?
Solar batteries are set on a 20 hour discharge rate. Roughly that translates to 1 amp for 20 hours. If you discharge 2 amps an hour, the runtime drops to 10 hours, and if you use 4 amps an hour the battery runs out of energy in 5 hours or less. Due to Peukert’s Law, batteries run out of energy the more quickly you draw amps.
This is the reason why experts recommend getting a larger battery than you need. Because of the way batteries work, you can never be certain when it is going to run out. If you have a cushion or extra energy this will not be an issue.
Many 2000Wi inverters are designed to work with 24V batteries. You can still use 12V and other volts, but 24V is preferred by some because it reduces amp requirements. You can also connect two 12V batteries in a series for 24V , that works too for stoves, and other appliances.
With this setup you can run a 1000W heater (or any load) on the inverter for two and half hours. This will not cause problems with the battery. You can also expect steady performance from the heater or whatever it is you loaded. At two and half hours the draw will be 42 amps an hour. The higher the amp draw the shorter the run time will be.
You can add more batteries for extra power. However you have to install the batteries in a parallel configuration so the voltage remains at 24V. A parallel battery setup will boost the amps but keep the volts steady. With a series the volts get a boost. In this example you want to keep the voltage at 24V, but need more battery power as backup, hence the parallel configuration.
The best way to deal with the running time is to check the runtime for the battery. Before you buy, check the runtime specs, either on the official website or the online manual. This will give you an idea of how much storage is available and how long it can last. This will all depend on how much load you will carry and for how long. Even a powerful battery won’t last long if the inverter is always drawing at the maximum.
The basic rule with solar inverters is the more powerful the battery, the longer you can run it at maximum power. Reducing the load from 2000W to 1000W or less will make the battery last longer. As long as you are prepared and know the numbers, there should not be any problems.
I am an advocate of solar power. Through portablesolarexpert.com I want to share with all of you what I have learned and cotinue to learn about renewable energy.