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With solar power now more cost efficient, off grid homes are becoming commonplace. Nowadays it is also not unusual to run large appliances on a solar system, but how many batteries would it take to produce 3 kilowatts or 3000 watts?
A 250ah 24V battery can run a 3kw load for an hour with a 50% depth discharge rate. Multiply 3kw by the number of hours you want to run it. Divide the result by the battery voltage and you will know how many batteries are needed.
How to Calculate Battery Size For a 3kw Solar System
There are a lot of factors that you need to consider when setting up a solar system. In this case, it is mainly how long you need to produce the 3kw load. You can use either batteries or a combination of batteries and solar panels.
If you need 3kw for an hour, 6 x 100ah 12V batteries will be sufficient. A 100ah battery has 1200 watts (100ah x 12 volts = 1200W), but with a 50% DOD only 600W is available. With six 100ah batteries you have 3600 usable watts for an hour. If you require a 3 kilowatt load for two hours you need 12 x 100ah 12V batteries, and so on.
The higher the watt load the greater the battery voltage you should use. A good 24V battery like the Ampere Time LiFePO4 has double the watt capacity of a 12V, and a 48V battery is four times.
Though high voltage batteries are more expensive, they are practical because you don’t have to deal with several batteries. Instead of six 100ah 12V batteries, you get the same power with three 100ah 24V batteries.
Let’s try the examples above but with 24V batteries to show the difference.
100ah x 24V = 2400W
Three of these 24V batteries has 7200 watts, 3600 of which is usable per charge. With a 48V battery you just need one to generate the power your system load needs.
Batteries are heavy and take up a lot of space. If you are in an RV or live in a solar mobile home , reducing the battery footprint is essential. Lead batteries in particular are heavy and need maintenance, so the less you have to deal with, the better.
How Many Solar Panels Do I Need For a 3kw Solar System?
When we talk about solar systems this includes solar panels. Can you produce 3kw on batteries alone? Yes, but you must have solar panels to recharge the battery. But how many do you need?
If you have 6 x 100ah batteries and 3600 available watts, you need five 300W solar panels to replenish it and keep the solar system running. Five 300W solar panels can give you 1500 watts an hour. Of course this is assuming the weather is ideal, so the total may be a bit lower. If it is summer and 6 to 7 sun hours are available, 5 panels will do. Otherwise, get six panels to make up the difference for low power output.
You can also try different solar panel and battery combinations as long as the total is at least 3 kilowatts. Just remember that solar panels cannot produce power at night so your battery bank must have enough reserve power if you need the power at night.
If you need 3 kilowatts during the day, 5 to 6 x 300W solar panels and 6 x 100ah batteries will be enough. To run this load at night you have to double the battery capacity since the solar panels cannot produce energy.
You don’t have to use 300 watt panels. You can go with 200W, 250W, even 100W. But 300W is the average size used nowadays, and it is more practical than connecting several 100W panels. The fewer solar panels to connect, the less chance of a mistake or something going wrong.
What Battery Type Should I Use?
There are several options available but for a 3 kilowatt system, flooded lead acid (FLA), gel, AGM or lithium battery are acceptable. It depends really on your needs, budget and power requirements.
FLA batteries are the obvious choice because they are the most affordable. You can buy half a dozen 100ah batteries, or two 300ah batteries and you are set. AGM and gel are also more affordable than lithium batteries.
The drawbacks with FLA batteries are the weight, size and maintenance. 100ah batteries are the most popular because of the size and price. But six of these in an RV -or anywhere- takes up a lot of room. You can opt for a 300ah unit, but that costs more. If you prefer AGM, we recommend the Weize 12V 100ah deep cycle battery.
With lithium you have to pay extra dollars, but they are lighter and pack more power. For now lead acid batteries are still the preferred choice and if you don’t mind the upkeep, are fine. But if you have to power a lot of load regularly, you may appreciate the better discharge rate of lithium, around 75% to 100% even.
What Can You Run on a 3kw Solar System?
There are a lot of appliances and devices you can use with a 3kw solar system. The following are just some of the many ways you can harness this kind of power.
A typical kitchen fridge needs 1500 to 2000 surge watts, so you can run it with another thousand watts to spare. Powering an air conditioner is no problem either or a washing machine, microwave or even a solar powered shed.
You can use this guide for running appliances on solar power, but suffice to say that with 3kw you can use all the essentials. A fridge, laptop, fan, lights, TV, blender etc. are no problem. If you plan to live off grid this is the kind of power you may consider.
Even power tools will not be a problem or large motors. However you cannot run appliances on solar batteries and panels alone. You also need an inverter and a charge controller. An inverter will turn the DC power produced by the panel into AC, while the charge controller will prevent battery overloading.
While you can connect DC powered devices to the solar panels, it is best to run appliances from the battery. Solar panel output fluctuates as the position of the sun changes, which is not good for most appliances.
By letting them run on the battery, consistent power draws are assured. The charge controller ensures no overload or overcharge occurs, and the inverter has protectors built in too. Most important, you can run these devices even when there is no sun.
Factors to Consider For a 3kw Solar System
There are several things you have to keep in mind when setting up a 3kw system. The following are the most important.
Battery and Solar Panel Setup. Decide if you are going with lead acid or lithium, then choose the capacity and voltage. You also have to consider how many solar panels to install. Decide early how you want the solar panel and battery combination to be like.
in most systems both the solar panel and batteries must produce 3kw each. That would mean 10 to 12 x 300W solar panels and 6 100ah 12V batteries. You can opt for a 48V battery and a higher rated solar panel to reduce the number, but they cost more.
Inverter and Charge Controller. The inverter has to be at least 3500 watts, though 4000 watts is better in case of power fluctuations. You need a few charge controllers here, though the size depends on the battery voltage. The higher the amps, the fewer controllers required.
Installation. Unless you are familiar with solar components, let a professional installer take care of it. It is easy enough to connect a solar panel and battery. But in this case there are several PV modules and batteries that need to be configured.
Warranty. These products have different warranties, so check each one and do some research. Not just the batteries but also the solar panels, charge controller and the inverter. It takes time, but going through the details is essential just in case something goes wrong and repair is needed.
Assembling a solar system that can produce 3kw is not hard. The challenge is figuring out the best possible combination of solar panels and batteries. Hopefully this guide was able to help you get your system off the ground.