When looking to install an inverter to power your home, determining the right size inverter is crucial. Selecting an inverter that is too small will result in the inverter overloading and shutting off when high loads are applied. On the other hand, an oversized inverter will come with an unnecessarily high price tag. So how do you determine what size inverter you need to run your house?
Calculate Your Home’s Power Consumption
The first step is calculating your home’s total power consumption. This will give you an estimate of the minimum capacity the inverter will need to handle. Here’s how to calculate your home’s power usage:
- Make a list of all electrical appliances and devices in your home. For each one, note their wattage (power consumption). This should be printed somewhere on the device, or you can look up specifications online.
- Estimate how many hours per day or week each appliance or device is used. Multiply the wattage by the estimated hours of use to get the kilowatt-hours (kWh) consumed.
- Add up the kWh for all appliances and devices to get your total estimated household power consumption.
As an example, here is a sample calculation for a household with common appliances:
| Appliance | Wattage | Estimated Hours of Use Per Day | Daily kWh Usage |
|---|---|---|---|
| Refrigerator | 200W | 24 hours | 4.8 kWh |
| Microwave | 1000W | 0.5 hours | 0.5 kWh |
| TV | 150W | 5 hours | 0.75 kWh |
| Lights | 400W total | 5 hours | 2 kWh |
| Total | 8.05 kWh |
Based on this sample calculation, this household uses approximately 8 kWh of power per day. This provides an estimate, but it’s a good starting point for determining inverter size.
Factor in Peak Power Surges
After estimating total daily energy consumption, the next step is to factor in peak power surges. Many appliances like air conditioners, refrigerators and pumps briefly draw much more than their rated wattage when starting up or cycling on. This causes spikes in power draw that your inverter must be sized to handle.
As a rule of thumb, size your inverter to be 25-30% larger than your estimated total daily power consumption to account for these peaks. So in the example above, for a household using around 8 kWh per day, a 10-12 kWh inverter would be an appropriate minimum size.
Determine Your Backup Power Needs
In addition to daily loads, consider any backup or emergency power needs when sizing your inverter. Essential items like lights, a refrigerator, phone/internet modem and other critical loads should be accounted for. Make a list of what you want to power during an outage and use the wattage and estimated runtimes to determine backup power needs.
For example, backing up the following essential loads for a household during a 6 hour power outage:
| Appliance | Wattage | Estimated Runtime Needed | Total kWh |
|---|---|---|---|
| Refrigerator | 200W | 6 hours | 1.2 kWh |
| Lights | 100W | 5 hours | 0.5 kWh |
| Internet modem & router | 10W | 6 hours | 0.06 kWh |
| Phone charger | 10W | 2 hours | 0.02 kWh |
| Total | 1.78 kWh |
In this example, the backup loads require about 1.8 kWh during the outage. Adding this to the daily usage gives a better estimate of the minimum inverter size needed.
Choose the Right Voltage
Inverters come in two main voltage outputs – 120V and 240V. In the US, 120V is typically used for smaller portable loads while 240V serves larger household appliances. Make sure to get an inverter that provides the appropriate voltage for the loads you need to power.
240V inverters are generally recommended for whole house power as they can more efficiently power high-draw appliances like air conditioners, water heaters and clothes dryers. However, for smaller or more portable setups, a 120V inverter may be sufficient.
Get an Inverter with Enough Output Capacity
In addition to total energy capacity measured in kWh, inverters also have a maximum power output rating measured in Watts. This determines the ceiling for the largest single load it can support at one time.
Checking the power rating is crucial to ensure your inverter doesn’t overload. As an example scenario:
- Your household requires 5 kWh of backup power per day.
- You have a 5500W air conditioning unit in your home.
Even though a 5 kWh inverter could provide enough total energy, it would overload and shut off if the A/C tries to start up and draw 5500W. In this case you would want an inverter with at least a 6000-7000W output capacity to safely handle spikes from the A/C.
In general, choose an inverter with an output rating at least 20% higher than your largest single load.
Get an Efficient, Durable Inverter
When comparing inverter options, make sure to consider:
- Efficiency Rating – Inverters waste some power converting DC to AC. Look for high efficiency models (90% and up).
- Surge Capacity – Can briefly provide up to 2-3x rated capacity.
- Protections – Overload, short circuit, high/low voltage, temperature protections.
- Durability – Robust casing and components resistant to weather, shocks, dust, etc.
- Warranty – At least 2-5 years on parts and labour.
Investing in a high-quality inverter from a reputable brand will provide reliable service for years to come.
Get Professional Help Designing Your System
Properly sizing an inverter system can get complex quickly when factoring in all household loads, backup needs, surge capacities, battery storage, etc. Consulting with a qualified solar installer or electrical contractor is highly recommended.
The experts can:
- Conduct a full residential energy audit and analysis.
- Recommend the ideal inverter size and components for your unique needs.
- Ensure your electrical system can handle the inverter output.
- Install and integrate the inverter safely with batteries and panels (for solar setups).
While it may add to your upfront costs, having a professionally designed system will provide you with the best reliability, performance and return on your investment in the long run.
Common Inverter Sizes for Whole House Power
As a general guideline, here are some typical inverter size ranges for powering an entire house:
| Home Size | Typical Inverter Size |
|---|---|
| Small cottage or cabin (500-1000 sq.ft.) | 3-6 kW |
| Average 2-3 bedroom home (1500-2500 sq.ft.) | 8-12 kW |
| Large 4+ bedroom home (3000+ sq.ft.) | 12-20 kW |
These provide a good reference point, but an accurate calculation based on your home’s specific loads and backup needs is always best.
Inverter Sizing for Off-Grid Solar Systems
For a solar-powered off-grid house, the inverter size should match the solar array’s peak output capacity for the most efficient system design and energy harvest. Common solar array sizes for off-grid homes include:
- 4-8 kW array with 4-8 kW inverter for a small cottage or cabin.
- 8-15 kW array with 8-15 kW inverter for an average sized home.
- 15-25 kW array for larger luxury off-grid homes.
The solar panels, batteries and inverter should all be compatible and properly integrated for an optimally functioning renewable energy system.
Frequently Asked Questions
How do I know if my existing electrical panel can handle an inverter?
Your main electrical panel must have sufficient amperage capacity to safely deliver the added load from the inverter to your household circuits. Have an electrician inspect your panel to determine if upgrades are needed for the inverter size you plan to install.
Should I get a stackable inverter system?
For large solar-powered houses, stackable inverters allow you to start small and add additional inverter units as your power needs grow. This provides flexibility and avoids oversizing initially. However, stackable systems are more complex to install and tune properly.
Can I use an inverter and generator together?
Yes, an inverter system designed for generator backup will synchronize with your generator when it turns on and disconnect when not needed. This prevents damage to the inverter and provides uninterrupted power during changeover.
What maintenance does an inverter need?
Inverters require very little routine maintenance. Just occasional dusting and checking wiring connections. Heat sinks and fans may need periodic cleaning. Check your owner’s manual for any maintenance recommendations from the manufacturer.
Conclusion
Determining the optimal inverter size for a home’s energy needs takes careful calculation of daily loads, peak surge demands, and future expansion plans. While the process can be complex, an accurately sized inverter system pays off in the long run with abundant clean energy, reliable backup power, and optimal solar array utilization. Consult with experts and use the guidelines provided here when embarking on your inverter system project for a house.
