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Sep 26 2023
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How Many Solar Batteries Are Needed to Power a House?

By How Do Solar Batteries Work?, Solar Battery No Comments

With net metering policies under attack and grid outages increasing in frequency and duration, it’s becoming more and more beneficial to pair battery storage with solar panels.

But exactly how many solar batteries does it take to power a house? The answer depends on a few things, including your energy goals, the size and type of batteries you’re using, and the size of the load you want to power.

In this article, we’ll explore the three most common reasons for investing in battery storage and how to estimate how many batteries you need to achieve your energy goals.

Compare binding battery quotes from trusted installers near you.

How many batteries do I need for solar?

Grid-connected solar systems typically need 1-3 lithium-ion batteries with 10 kWh of usable capacity or more to provide cost savings from load shifting, backup power for essential systems, or whole-home backup power.

According to a 2022 study by the Lawrence Berkeley National Laboratory, a solar system sized for 100% energy offset with a single 10 kWh battery is enough to power essential household systems for 3 days in virtually all US counties and times of the year. When heating and cooling are included in the backup load, a home needs a larger solar system with 30 kWh of storage (2-3 lithium-ion batteries) to meet 96% of the electrical load.

The exact number of batteries you need depends largely on your energy goals. So, let’s take a look at how many solar batteries it takes to achieve the three most common energy goals.

Related reading: The 8 Best Solar Batteries of 2023 (and How to Choose the Right One For You)

Goal 1: Cost savings from load shifting

In areas with unfavorable or non-existent net metering policies, battery storage is crucial to maximizing the energy cost savings of home solar. For example, under California’s NEM 3.0 Solar Billing, it’s far more cost-effective to store and use your solar electricity (a strategy known as load shifting) than to export it to the grid for little-to-no compensation.

If you are strictly interested in load shifting and have no need for backup power, a single 6-10 kWh consumption-only battery will typically suffice since you only need enough usable capacity to avoid buying grid electricity at peak time-of-use rates.

What is a consumption-only battery?

A consumption-only or “no-backup” battery is a new type of energy storage system that provides all the load-shifting capabilities of a traditional solar battery but is not capable of providing backup power when the grid goes down. Without the equipment, programming, and labor that enable backup power, consumption-only batteries typically cost around two-thirds the price of a traditional backup battery and therefore offer a greater return on investment.

Goal 2: Backup essential systems

Perhaps the most common and well-known reason to pair solar and battery storage is to provide backup power during grid outages.

Solar-only systems are typically shut off during grid outages to prevent the backflow of electricity from harming utility lineworkers and thus do not provide backup power. Adding battery storage not only allows you to store kWhs for evenings and outages; it also allows your solar system to remain active and productive when the grid goes down.

Most home battery systems are configured to power a select number of essential systems, like lights, Wi-Fi, TV, medical devices, refrigeration, and other kitchen appliances. As noted above, the Berkeley Lab found that a solar system designed to produce 100% of your annual electricity consumption and a single 10 kWh battery can power essential systems during a 3-day outage for most US households.

It’s worth noting that backup batteries can also provide energy cost savings through load-shifting, although the higher upfront cost of enabling backup capabilities makes for a longer return on investment.

Goal 3: Whole-home backup

If your goal is to power your entire home during grid outages, then you’ll likely have to combine three or more lithium-ion solar batteries to meet the large load demands and power surges of heating, air conditioning, laundry machines, electric water heating, and possibly EV charging.

For instance, three 13.6 kWh Franklin Home Power batteries can be combined to provide 40.8 kWh of usable electricity and 15 kW of continuous power, which is enough to fully back up an average home.

It’s worth noting that for whole-home backup power, you’ll need additional solar capacity to charge the additional battery storage. According to the Berkely Lab, a large solar system with 30 kWh of battery storage can meet, on average, 96% of critical loads including heating and cooling during a 3-day outage.

 

 

How to calculate the number of solar batteries you need

Once you have a goal in mind, you can start to calculate the number of batteries you need to pair with your solar system.

Frankly, the easiest and most accurate way to do this is to team up with a solar.com Energy Advisor to design a custom system based on your goals, usage, and sun exposure. However, if you want a quick-and-dirty estimate, follow the steps below.

Step 1: Estimate your storage needs

The first step to calculate how many batteries you need is identifying your storage needs (i.e., the amount of electricity you want/need to achieve your goal(s)).

If your goal is to maximize your solar savings through load shifting, then you’ll want at least enough storage to match your electricity usage during peak time-of-use periods (typically 4-9 pm). For example, the chart below shows a household that uses around 9 kWh of electricity between 4 and 9 pm (orange lines) to run the air conditioner, cook dinner, and binge-watch Outlander – this usage represents their energy storage needs.

chart showing battery needs to power household usage during peak time-of-use rates

If your goal is to provide backup essential systems or your entire home, then you’ll need to do some math to figure out your storage needs. The idea is to figure out:

  • What you want to power
  • How long you want to power it

For example, in this article, we estimated that it takes around 8 kWh of electricity to power lights, refrigeration, devices (TV, Wi-Fi, device charging), water heating, and kitchen appliances for 24 hours. So, if your goal is to comfortably power these systems for a day – even if it’s cloudy and your solar system isn’t producing much power – you would want at least 8 kWh of usable battery capacity, perhaps a little more to be on the safe side.

If you’re going for whole-home backup, simply calculate your average daily electricity consumption during the time of year you’re most likely going to need backup power, and that figure is your storage needs.

Step 2: Pick a battery size

Once you have an idea of your storage needs, it’s time to start shopping for batteries. Today’s lithium-ion batteries offer anywhere from 3 to 18 kWh of usable capacity per battery, although a majority are between 9 and 15 kWh.

In many cases, batteries can be coupled together to provide more storage. For example, Enphase IQ series batteries come in 3.36 kWh increments and can be stacked together to create various-sized battery systems.

Step 3: Configure batteries to meet your storage needs

Now it’s time to configure your system. And when it comes to batteries there is more than one way to achieve your desired system size.

For example, here are a few ways to build a 13 kWh battery system:

Battery type Number of batteries Total usable capacity
Franklin aPower 1 13.6 kWh
Tesla Powerwall 2 1 13.5 kWh
Enphase IQ 10 + Enphase IQ 3 2 13.44 kWh
Generac PWRcells 5 15 kWh

To achieve 13 kWh of storage, you could use anywhere from 1-5 batteries, depending on the brand and model. So, the exact number of batteries you need to power a house depends on your storage needs and the size/type of battery you choose.

Building a custom battery system

Battery storage is fast becoming an essential part of resilient and affordable home energy ecosystems. The exact number of batteries you need depends on your energy goals, storage needs, and the size and type of batteries you choose.

Team up with a dedicated solar.com Energy Advisor to set goals and design a solar and battery system custom to your home and electricity needs.

 

 

Aug 17 2023
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how much energy does a solar panel produce

How Much Energy Does a Solar Panel Produce?

By How Does Solar Power Work on a House? Your Questions Answered No Comments

One of the most important features of a solar panel is how much energy it can produce. After all, that’s what they’re designed to do!

Prospective solar panel owners usually have a goal for how much energy they want to produce. Maybe it is 100% of their household needs or even just 50%. In any case, there are a number of factors that will influence the energy production capabilities of a solar panel and how many panels they’ll need.

With the cost of solar dropping over 60% in the last 10 years and a 30% tax solar credit available to all homeowners, it is much more realistic for home and business owners to install solar panels on their property. In this post, we explore how solar panels function and produce energy.

First, let’s go over the basics.

How Does a Solar Panel Produce Energy?

Solar panels work by allowing particles of light, called photons, to knock electrons from their atomic orbitals. The electrons are captured on conductors in the form of an electric current and this electricity is harnessed and preserved. The area where this reaction occurs is called a photovoltaic cell or solar cell.

Solar panels (or modules) are made up of hundreds or thousands of these cells, and multiple solar panels make up a solar array. These arrays are connected into the existing electrical grid and/or battery storage so that the generated energy can be directed properly.

Key Solar Panel Terms: kW, kWh, DC, and AC

To fully understand the numbers, we need to go over some basic units.

  • Kilowatt (kW): This is a measure of electrical power, which is equal to 1,000 watts. The electrical energy that is generated by a solar panel or a solar system can be expressed as watts or kilowatts.
  • Kilowatt-hour (kWh) – A measure of electrical energy that is equal to the consumption of 1,000 watts for 1 hour. The kWh is used as a billing unit for the energy consumed by individuals. One kilowatt-hour equates to 3.6 megajoules.
  • Direct Current (DC) power: This is the form of the power that gets initially generated from the panel.
  • Alternating Current (AC) power: Most household appliances use AC power. The DC electricity generated by solar panels gets converted into AC so that it can be used efficiently by consumers throughout their house.

Related reading: How To Choose Solar Panels for Your Home

How many Watts does a solar panel produce?

In 2023, residential solar panels are typically rated to produce 250 to 450 Watts per hour of direct sunlight. Today, the most common power rating is 400 Watts as it provides a good balance of efficiency and affordability. A 400 Watt panel with 4.5 direct sun hours a day can be expected to produce 1,800 Watt-hours of DC electricity per day — or roughly 1,750 Watt-hours once it’s converted to AC electricity — which is more than enough to power a refrigerator and lighting needs for the average US household.

To measure how much electricity a solar panel produces you’ll need two figures:

  1. The solar output of the panel (measured in Watts)
  2. The number of peak sun hours per day (in hours) for your area

Solar panel output varies by model and ranges from around 250 to 450 Watts. The Wattage output rating represents how much energy the panel can produce per hour under standard testing conditions.

In 2023, 400W panels are considered standard, so we’ll use this output for our example.

Peak sun hours is a measurement of how much usable sunlight your solar panels receive. This varies from over 5.75 hours per day in the Southwest to less than 4 hours per day in the northernmost parts of the US. Check the peak sun hours for your location here.

Since a majority of the US gets 4.5 peak sun hours per day or more, we’ll use 4.5 hours for our example.

To calculate how much a solar panel produces per day, simply multiply the solar panel output by the peak sun hours:

400W (output) x 4.5 hours = 1,800 Watt-hours per day

We typically account for 3% loss in converting the solar energy output from DC to AC, which comes to roughly 1,750 Watt-hours. To convert to the standard measurement of kWh, simply divide by 1,000 to find that one 400W panel can produce 1.75 kWh per day.

 

 

How much energy does a solar panel produce per month?

A 400W solar panel receiving 4.5 peak sun hours per day can produce 1.75 kWh of AC electricity per day, as we found in the example above. Now we can multiply 1.75 kWh by 30 days to find that the average solar panel can produce 52.5 kWh of electricity per month.

In sunny states like California, Arizona, and Florida which get around 5.25 peak sun hours per day (or more), the average 400W solar panel can produce more than 61 kWh or more of electricity per month.

To put that into perspective, the average US household electricity uses 893 kWh per month and ranges from 537 kWh per month in Hawaii to 1,200 kWh per month in Louisiana.

So to offset 100% of the electricity usage for the average household getting 4.5 peak sun hours per day, you’d need a 6.7 kW solar system. (6.7 kW x 4.5 sun hours per day x 30 days per month = 893 kWh per month). That would require 17 solar panels with 400W output.

In sunnier locations getting 5.25 peak sun hours per day, you’d only need a 5.67 kW system made up of 14 400W solar panels to get 100% offset.

Get multiple solar quotes for your home. Start here.

Things That Affect Solar Panel Production

To get an accurate picture of solar energy output, you have to take into account a few factors like the type of panel and its environment.

As we mentioned above, the biggest factors are how many peak sun hours you get per day and the power output of the panel.  However, the design of the panel matters too.

Solar energy output depends on the type of panel

There are thousands of solar panel models on the market, all with unique wattages, efficiency ratings, and degradation rates. In fact, we sorted through 750 panels available through the solar.com network of installers to identify some of the best solar panels for each category.

While there is a lot to consider, a good place to start is deciding between a monocrystalline and polycrystalline panel. Here are some features of each technology.

Monocrystalline solar panels

  • Higher efficiency
  • More expensive
  • Better performance in high temperatures and shady conditions

Polycrystalline

  • Lower efficiency
  • Less expensive
  • Less efficient at higher temperatures

Check this video to find out the difference between monocrystalline and polycrystalline panels. 

As you can see, each type of panel has its pros and cons. Polycrystalline, however, is a newer technology and will become more efficient over time, but if you were looking to generate the most power in the smallest amount of space, monocrystalline would be the way to go.

Cover Your Electricity Needs with Solar

To sum it up, an average 400W solar panel getting 4.5 peak sun hours per day can produce around 1.8 kWh of electricity per day and 54 kWh of electricity per month.

Solar panel production varies based on the output of the panel and the available sunlight. And the amount of electricity you need from your panels depends on your energy usage and your goals. Some homeowners wish to offset 100% of their electricity usage while others are okay with less.

Regardless, electricity from solar panels is cheaper per kWh than grid electricity in the vast majority of the US. The sooner you switch to solar, the sooner you can benefit from the long terms savings and price stability.

Get started by setting savings goals with an Energy Advisor.