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If your solar system is on the grid, you will not be able to use it in case of a power failure. It is automatically shut down for safety reasons which is why having batteries is ideal. The question is, how many 200ah batteries will you need to run your appliances? And for how long?
Four 200ah batteries is equal to 9.8 kwh or around 9600 watts. This is enough to run essential home appliances like a refrigerator, six light bulbs, a TV and a laptop charger for 3.9 hours.
How Many 200ah Batteries Do I Need For My Home?
There are two important factors to consider. First, how many appliances you want to run, and second for how long. These will determine how many 200ah batteries you will need. As to which brand to buy, our choice is the Renogy 200ah Battery as it is built specifically for off gird applications.
To calculate how many batteries you will need, use this simple formula:
Total appliances watts/kilowatts = battery size
Batteries are measured in amps, so to find its watt equivalent:
Watts / volts = amps
Amps x volts = watts
Battery Power For House Calculation Example
There are a few assumptions we need to make here. First, it is unrealistic to run an entire house on batteries for days. You can however, use batteries to run appliances in your home or cabin for several hours in case of a power outage. In our example, we will assume that you want to run only essential appliances like the following:
|2000 watts Starting / 780 running
|60W light bulbs (5)
|Mobile device charger
|45 inch TV
|Total: 2460 watts / Battery Required: 4x200ah / Runtime 3.9 hours
The total is 2460 watts or 2.5 kwh. These consumption rates are for guidelines only. Refer to the label on your products for the exact power draw.
This is only an example, but you may have other ideas on what makes up essential appliances. Just change the list above and add your own devices and compute the power consumption.
Now you have the total watts, 2460. How many 200ah batteries will you need? First we have to convert watts into amps. Assuming you will be using a 12V battery:
200ah x 12V = 2400 watts
One 200ah is not enough, so you need at least two to even start your power load. But the question is, how many batteries will you need to keep your appliances going? That is what we cover in the next section.
How Long Will My Batteries Last?
The running time for your appliances determines how many 200ah batteries are needed. Once you know the runtime you will know exactly what batteries to buy and how many.
To find out how long the battery will last:
Battery capacity / total wattage = appliance runtime
If you want to run a 2460 watt critical load for about four hours, you need four 200ah batteries. Four 200ah batteries is equal to 9600 watts.
200ah x 12 = 2400
2400 x 4 = 9600
Multiply the battery capacity (in this case 9600 watts) by the appliance wattage (2460):
9600 / 2460 = 3.9
Going back to our example earlier, your appliances power consumption is 2460 watts or 2.5 kwh. One 200ah battery is 2400 watts so it is insufficient. With four 200ah batteries, you have enough power to keep your appliances running.
If you want your appliances to run for longer periods, just add more batteries or reduce the critical load. If you add more to the load the runtime will drop.
Adding a 2000 watt window AC for instance, brings the total wattage to over 4000 watts.
9600 / 4000 = 2.4
From nearly four hours the runtime drops to two and half. Now you need to add another 200ah battery to make it last for four hours. With the formula here, you can estimate how many batteries are needed for a particular runtime.
We are using 200ah batteries in these calculations, but you can try other sizes. 200ah is ideal for homes though because of its capacity. But if you can get a large battery you can run more appliances and devices.
What Batteries Should I Use?
One thing to keep in mind with these calculations, it will completely drain the batteries. And that is important, especially if you use deep cycle lead acid.
Lead acid batteries like AGM and gel have a 50% discharge rate. This means you should not let the battery capacity drop below the halfway point. Why? Because it is not good for the internal circuits of the battery. Lithium however are designed to be fully discharged, but they cost more.
So with four 200ah lithium batteries your 2460 power load will run for approximately four hours. This will drain the batteries but with lithium it is acceptable.
Since lead batteries have a 50% depth discharge, does this mean you need eight of them? Well it depends on how often you use the system.
If power outages are rare in your area, it is all right to let lead acid batteries fully discharge when used. As long as your batteries are well maintained your power system should be fine. But if you run your appliances on these batteries often, you should double the capacity or replace it with lithium.
Can I Use Solar Panels with My Battery Bank?
Yes it is possible to use solar panels with batteries. In fact that is how most off grid homes are set up. As long as your solar array is large enough you should have no problems getting appliances to work. But how many will you need?
To run a 2.5kwh load it will require nine 300 watt solar panels. This assumes you will load all the appliances at once. If you will only load a fridge and lights, eight panels will be enough. We recommend the ACOPOWER 300W Solar Panel Kit as they provide great value and efficiency.
By running your solar panels in the morning you can conserve battery power, using them only at night. However this is only possible if you are off the grid. Grid tied systems automatically turn off solar panels in case of a power failure for your own protection.
If you are off the grid, a battery bank or another power source is necessary. To run a solar panel and battery system, add the total wattage plus reserve power (20% minimum). And do not forget the inverter and charge controller.
Just to be clear you do not need solar panels to run appliances off a battery bank. What you will need are an inverter and charge controller. Solar panels are optional. However for an off grid system you probably have an array installed already.
Tips For Using Battery Backup Power
Setting up a battery backup system can be daunting for a beginner, and it can be expensive. Here are some tips to ensure you get the best value for your money and time.
Identify what appliances you want to run in case of a power failure. Common essentials are a refrigerator, heater, window AC, lights, laptop charger and TV. Only you can decide what is essential for you and your household.
Check the maximum / peak wattage and running wattage of every device you want to run. Both of these will be on the label or manual. Refrigerators, AC units, heat pump, washing machine, well pump and stoves have starting watt requirements. Some appliances like a fridge have on/off cycles, so it will start up repeatedly, drawing more power.
Always have reserve power available. If the total load is 2460 watts, the battery capacity has to be much higher. In case of lead acid batteries you may want to double it. Remember that the battery capacity will also depend on how long you want to run the appliances. The calculations here are to run essential appliances for a few hours a day. If you need a backup power source for several days, you will need a large generator and other power sources.
Test your battery bank. The last thing you want is a malfunctioning system when the power goes out. Inspect the wires and cables because that is where problems usually start.
Make sure your batteries are filled. Run them every once in a while as batteries do not like to be static for long periods.
In the end it really comes down to what essential appliances you want to use and for how long. if you stick to basic appliances, it is very possible to use 200ah batteries to run your home in case of emergency.
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.