How many watts do you need to power a house with solar panels?

Quick Answers

The number of watts needed to power a house with solar panels depends on several factors, including:

– Location and sun exposure
– House size and energy usage
– Type of solar panels and system efficiency

As a general estimate, a typical 2,000 square foot house uses about 30 kWh per day. With a solar panel system that’s 20% efficient, you would need around 7,500 watts (7.5 kW) of solar panels to provide enough power. This would require 20-25 panels rated at 250-350 watts each.

Location is key – areas with more sun exposure will need fewer watts of panels. Energy efficient appliances and lighting can also reduce the watts required. Most solar installers will do a site evaluation and energy usage analysis to determine the optimal system size.

How Much Power Does a House Use?

The amount of power a house uses depends primarily on its size and the number and types of appliances and devices inside. Here are some typical energy usage estimates:

– 1,500 square foot house – Uses around 20-25 kWh per day
– 2,000 square foot house – Uses around 30 kWh per day
– 3,000 square foot house – Uses around 40-45 kWh per day
– 4,000+ square foot house – Can use over 50 kWh per day

Larger homes with pools, hot tubs and central air conditioning use even more power. High-efficiency LED lighting, EnergyStar appliances and good insulation help reduce energy usage.

Some typical appliance power draw figures include:

– Refrigerator – 500-800 watts
– Clothes washer – 300-500 watts
– Clothes dryer – 1,800-5,000 watts
– Dishwasher – 1,200-2,400 watts
– Oven – 2,000-5,000 watts
– Air conditioner – 3,000-6,000 watts (central)
– Pool pump – 500-1,500 watts

Adding up the average load for appliances, lighting, HVAC and other devices gives a reasonable estimate for overall home power needs.

Average Home Electricity Usage

The average home in the U.S. uses about 893 kWh per month. This equals about 30 kWh per day. Homes are different sizes and have varying numbers of occupants, but this gives a reasonable ballpark figure to work with when estimating solar power needs.

The U.S. Energy Information Administration provides this average electricity usage breakdown for U.S. homes:

– Heating – 42%
– Air Conditioning – 17%
– Appliances (refrigerator, washer, dryer, etc) – 22%
– Lighting – 12%
– Other (TVs, computers, etc) – 7%

This shows that over half of home energy use goes to heating and air conditioning. Upgrading to an efficient HVAC system can significantly reduce power needs.

Factors That Determine Solar Power Needs

The main factors that determine how many solar panel watts are needed to power a house include:

Location and Sun Exposure

Areas with high levels of sun exposure need fewer watts of solar panels to produce the same amount of electricity. Phoenix, Arizona averages 5-6 peak sun hours per day while Seattle, Washington averages 3-4. A location with more sun can use smaller solar panels systems.

Orientation matters too. Solar panels tilted to directly face the southern sky will produce more power than misaligned panels or ones with partial shade coverage. Optimizing panel placement is key.

House Size and Energy Usage

Larger homes with more devices, appliances and systems require larger solar panel systems. A good energy audit will account for all electrical loads. Energy efficient upgrades can help reduce power needs.

Solar Panel System Efficiency

Solar panels have gotten much more efficient over time. Typical panels are now 17-22% efficient compared to 13-15% a decade ago. More efficient panels produce more watts per square foot, requiring less overall area to meet power needs.

Type of Solar Panels

Monocrystalline silicon panels are the most efficient, followed by polycrystalline and then thin-film panels. Output can vary by panel material. Monocrystalline panels range from 17-22% efficient.

Inverter Efficiency

The inverter converts the DC output from solar panels to usable AC electricity. High-efficiency inverters waste less energy in this conversion, making the system more productive overall. Most inverters are 85-95% efficient.

Battery Storage

Adding battery storage allows excess solar power to be stored for use at night. This allows downsizing the panel system since it doesn’t have to meet peak power demands solely during daylight hours when the sun is shining.

Sizing a Solar Panel System for a House

Taking the average household electricity usage of 30 kWh per day, here is how to calculate the solar panel watts and system size needed:

1. Allow for Inefficiencies

No solar power system converts 100% of the sun’s energy into usable electricity. We assume a conversion efficiency of 15% to account for panel and inverter losses.

30 kWh / 0.15 = 200 kWh of solar energy required per day

2. Determine Peak Sun Hours

Peak sun hours are the equivalent number of hours per day where the sun provides its peak 1,000 W/m^2 irradiance. Phoenix might average 6 peak sun hours while Seattle only sees 3-4.

We’ll assume 5 average peak sun hours for this location.

200 kWh / 5 hours = 40 kW of solar panels needed

3. Convert to Watts

To determine the number of Watts needed, we multiply the kW by 1,000:

40 kW x 1,000 = 40,000 Watts

Therefore, for a typical 2,000 square foot house using 30 kWh per day in a location with 5 peak sun hours, a 40,000 Watt solar panel system is recommended.

4. Factor in Battery Storage (Optional)

Adding battery storage allows downsizing the panels by 30-50% since excess daytime power can be stored for nighttime use.

With batteries, the system could be reduced to 20,000-30,000 Watts.

Number of Solar Panels Needed

Most residential solar panels have power ratings ranging from 250-400 watts, with an average of around 300-350 watts per standard 60-cell panel.

For a 40,000 watt system, you would need approximately:

– 114 x 250 watt panels
– 100 x 350 watt panels
– 80 x 400 watt panels

So around 100-120 standard solar panels are needed to power a typical 2,000 square foot home with average energy use.

With battery storage, you may only need 50-75 panels. Installers will determine the optimal number of panels based on your actual site conditions and energy consumption.

Solar Panel Sizing Guidelines

As a general guideline for sizing a solar system, use the following estimates:

– 1,500-2,000 square foot house – 6-8 kW system – 18-24 panels
– 2,000-3,000 square foot house – 8-12 kW system – 24-36 panels
– 3,000-4,000 square foot house – 12-16 kW system – 36-48 panels
– 4,000+ square foot house – 16-20 kW system – 48-60 panels

These assume an average house with energy efficient appliances and 5 hours of good sun exposure per day.

Houses with electric heating, air conditioning and other high loads may need more panels. Solar installers will provide detailed load calculations and recommendations after assessing your specific home.

Cost to Power a House with Solar

The total cost to power a house with solar panels will depend on:

– System size – More watts and panels add cost
– Type of panels – Premium panels cost more per watt
– Location – Labor rates vary regionally
– Roof type – Rooftop vs ground mount affects labor time
– Other equipment – Racking, wiring, inverters etc

For a typical 5 kW system, the avg cost is $2.50 to $3.50 per Watt including installation:

– 5 kW x $2.50/Watt = $12,500
– 5 kW x $3.50/Watt = $17,500

So most homes require a $10,000 to $30,000 total investment to install solar panels. Federal and state incentives can reduce costs by 26% on average.

Operation and maintenance costs are minimal. And solar panels can slash electric bills by 50-90% while providing clean energy for 25+ years. Return on investment averages around 6-8 years for residential solar.

DIY Solar Panel Installation

For DIYers, solar panel kits can provide an affordable alternative to hiring an installer. But technical expertise is needed for proper sizing, wiring, safety shutoffs and grid connection.

Building permits are usually required and the system needs to pass inspections before operation. DIY solar for a whole house can be challenging, but it’s feasible for smaller systems if you have electrical experience.

Most homeowners choose to have an experienced local solar company size, procure equipment, install and activate the system. This ensures proper operation, safety and optimization.


Determining the number of watts needed to power a house with solar comes down to home energy usage, location, panel efficiency and sun exposure. For a typical 2,000 square foot home, around 7,500 watts (7.5 kW) or 20-25 panels rated at 300 watts each is usually sufficient, given average conditions.

Energy efficiency, battery storage and oversizing for future loads are good ways to optimize a solar panel system. While sizing calculations can seem complex, a professional site evaluation is key to designing the optimal system. Most solar installers provide free assessments and will collect all necessary data to recommend the ideal system size for your home.

Leave a Comment