Lithium batteries are safer, charge faster, and won’t occupy as much space as Lead-acid batteries. The biggest advantage is that you can almost use 100% capacity of a lithium-ion battery compared to 50% of a lead-acid battery. This means that a lithium battery of the same capacity as a lead-acid battery will have almost twice the capacity.
Whole-home batteries are now common in the market due to this technology. But can a battery power the whole house and how many will you need? This article takes you through the numbers and starts at the Inverter in determining the number of batteries to run a house.
How Inverter Size Affects the Battery Size
The size and number of batteries needed for an off-grid solar power system also depend on the amount of power that needs to be stored to meet the demands of the loads. The inverter’s power rating will determine how much power can be delivered to the loads. The load turn will determine how much power needs to be stored by the batteries.
Voltage
The efficiency of an inverter is determined by its ability to convert the DC power from the battery bank into usable AC power for your home. When the voltage of the inverter matches the voltage of the battery bank, the inverter operates at its highest efficiency. This means that more of the DC power from the battery bank is converted into usable AC power, reducing energy waste and increasing the overall efficiency of the system.
Different types of Inverters have different voltage requirements, and using an inverter with an incompatible voltage to the battery bank can damage or even destroy your batteries.
Amperage
Voltage and amperage are two critical factors that determine the amount of power being used in an electrical system. In a solar power system, the voltage of the inverter can influence the amount of amperage pulled from the system.
In general, the higher the voltage, the lower the amperage, and vice versa. This is due to the relationship between voltage, amperage, and power, which is expressed by the formula:
Power (in watts) = Voltage (in volts) x Amperage (in amps)
When the voltage is high, the inverter can produce the same amount of power with fewer amps, which means less stress on the electrical components and wiring in the system. Conversely, an inverter operating at a lower will pull more amps to produce the same amount of power, which can result in increased stress on the system.
For example, let’s say you have a 1500-Watt inverter and you want to power a 1000-watt load. If the inverter has a voltage of 12 volts, it will need to pull approximately 83 amps (1000 watts / 12 volts = 83.3 amps) to power the load. However, if the inverter has a voltage of 24 volts, it will only need to pull approximately 42 amps (1000 watts / 24 volts = 41.7 amps) to power the same load.
Amp-hour and Watt-hour Rating
From our previous example, we’ve seen if you are powering a 1000-watt appliance on a 24-V system you’ll need 42 amps. If you are powering this device for 5 hours then you’ll use up around 210 Amp-hours.
If you remove efficiency losses a 24v 200Ah Battery will power a 1000-watt Appliance for up to 4 hours through Inverter rated 1500 watts or more. You can also replace this load requirement with the Inverter. For example, a 1000-Watt Inverter will be drawing 42 amps from the Battery. So you can choose a 24V 200Ah Battery for a 1000-Watt Inverter.
How Much Power to Run a Home?
In order to size your battery requirements, you’ll need to add up your power requirements. The wattage of every appliance is indicated on the nameplate. Take every appliance in your home take the Wattage and multiply by how long you use the device. This will give you the Wh requirements for your Battery Bank. Be sure to also take into consideration the surge watt rating of the devices vs the running watts.
| Appliance | Wattage (Watts) | Running Time | Watt-Hours |
| Refrigerator & Lights | 300 Watts | 8 hrs | 2400 |
| Air Conditioning | 1000 Watts | 10 hrs | 10000 |
| Kitchen Appliances | 3000 Watts | 1 hr | 3000 |
| Entertainment Units | 600 Watts | 6 hrs | 1800 |
| Bathroom & Laundry | 2000 Watts | 5 hrs | 10000 |
| Total | 27,200 |
The numbers above are estimates but the average power consumption in a home is almost 30,000 Watt-Hours per day or 30kWh. This is an astronomical figure compared to most battery bank setups.
How many Batteries to Run a House
So we have figured we need around 27.2 kWh to run the home. We need to convert this to Amp-Hours so that we can get the number of batteries you need. Some batteries will have an indication of the Watt-hours. The Tesla Powerwall is around 13kWh so you will need around two of these to run a home in a day.
But if you intend to build a DIY system to convert the Watt-Hours to Amp-Hours you simply divide the Watt-Hours by the voltage.
Let’s say you running off a 24-volt system:
27,200 Watt-Hours / 24 Volts = 1133 Ah
You will need 6 200 Ah lithium batteries wired to power your home. The batteries will be wired in series and parallel to make a 24v battery bank.
What are the Costs of a Whole-Home Battery Bank
A whole-home system is practical but it can be quite expensive. An affordable 200 ah LiFePO4 Battery like the ExpertPower will cost around $1000. For six batteries you will need around $6,000. These costs do not include all the other components that will be required to make the system usable in your home. A full 13kWh Tesla Powerwall battery system costs up to $10,000.
You will need a powerful inverter preferably over 3000-watts, Battery Management and Monitoring System, and protective units. If you also choose to add solar panels to the system it will also add on a few thousand bucks. For a system like this one, you will need a professional installer who will guide you through the permits and ensure your safety.
To run a smaller system that just runs your essential appliances like your lights or a refrigerator and acts as a backup will only need 3000 Watt-hours a day. For 3000 Watt-hours you will need 125Ah if you double the capacity for reserve then you’ll get 250Ah. You can use two 100Ah batteries or even one 200 Ah battery.
This can be a more affordable system to run. Adding solar panels will be another added advantage, with a 400-watt solar panel you can recharge the battery (up to 80%) in 5 hours. This can add to the days of storage.
You can also opt for a solar generator that will save you the hassle of having to do all the wiring and risks that come with a DIY system. A whole-house solar generator can supply power to your entire house during a power outage. This can be a lifesaver during a storm or other emergency when the power is out for an extended period of time. .
How many lead-acid batteries will this be?
Compared to lithium batteries lead-acid are heavier, bulkier, and less efficient. However, there might be instances where you might favor lead acid especially AGM batteries over lithium-ion batteries. This can includes using your batteries in low temperatures or you just favor them because of their lower pricing.
Because the usable capacity of an AGM battery is 50% this means you’ll have to double up on the batteries. For our small system, we put the requirements at two 100 Ah batteries and one 200 Ah battery. You will need four 100 Ah batteries and two 200 Ah batteries.
What type of lithium battery is for battery backup?
There are 4 types of lithium-ion batteries that are used for batteries backup. The first is the lithium iron phosphate (LFP) cell, usually abbreviated as LiFePO4 or LFP. This type of battery uses a solid electrolyte made from lithium iron phosphate ceramic which makes it more stable than liquid electrolyte cells.
This type is very stable and offers a long cycle life of more than 5,000 full charge/discharge cycles before losing around 5% of its capacity. In addition, the cell has low internal resistance that’s why it’s good for solar applications. We actually recommend this type of battery for solar and deep-cycle applications like battery banks.
Another type is the lithium titanate (LTO) cell, usually abbreviated as Li4Ti5O12 or LTO. This type of lithium battery has better specific energy (energy density) than the LiFePO4 cell which means it is capable of holding more power. This makes it ideal for high-drain devices like electric tools and bicycles. The only downside of the cell is that it has a lower cycle life which means it can only withstand around 1,000 cycles or less.
The other two types are lithium nickel manganese cobalt (NMC) and lithium nickel cobalt aluminum oxide (NCA). These cells are very similar to the LFP and LTO cells but they use different materials for the negative electrode (cathode). The downside of these types is that they can swell after many cycles which can crack their housing. They are mainly used in Electric Vehicles.
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