Solar power is now the beast of the green energy industry, and many people are looking to incorporate it into their lives.
And with the increasing demand for renewable energy sources, hot tubs powered by solar panels are becoming increasingly popular.
But how many solar panels do you need to run a hot tub?
You need around 3 solar panels to power a hot tub. However, this number can vary depending on the size of your hot tub and your local climate.
In this article, I’ll walk you step by step through the process of calculating how many solar panels you need to run a hot tub.
- Most hot tubs need between 3.5 and 6 kWh of energy to run depending on their size, model, and the climate you live in
- Over the course of a month, the total energy needed can be around 120 kWh
- At noon, the sun reaches its peak output and generates about 1,000W/m² per hour
- Peak sun hours refer to the number of hours per day that your solar panels are receiving solar irradiance of 1,000W/m²
- In California, the total peak sun hours are 5.83 per day and about 174.9 per month
- The theoretical size of a solar system to power a hot tub is about 0.686 kWh of energy
- The solar system undergoes many losses which can reduce its total output to about 14% of the total energy production
- You need about 3 solar panels of power rating 300W each to power a hot tub
- A 24V battery of 235 Ah and 80% depth of discharge can provide the necessary energy to your hot tub throughout the day and night
- The total cost of the solar system for a hot tub can be around $1,642
- Running your hot tub with solar panels can save you around $4,406 in 25 years
How to Calculate the Number of Solar Panels You Need?
1. Calculate Your Hot Tub Energy Consumption
Before we get into the specifics of powering your hot tub with solar panels, you need to know how much energy it takes to heat your spa.
Most hot tubs require between 3.5 kWh and 6 kWh of energy to heat the water and run the jets.
Of course, this number varies based on the type of hot tub, its size, and the climate you live in.
You can calculate your hot tub’s energy needs by multiplying its wattage by the number of hours it runs each day.
My hot tub uses 5 kWh of energy to heat and run the jets, and I use it for 3 hours twice a week.
To calculate how much energy I need to power my hot tub per month:
Total energy needed per month = 5 kWh x 8 days x 3 hours = 120 kWh/month
So, I need around 120 kWh of energy per month to power my hot tub.
2. Find out the Peak Sun Hours in Your Area
The amount of energy solar panels can generate depends on the amount of sunlight they receive.
And since solar panels don’t receive the same amount of sunlight during the whole day, we turn to peak sun hours.
Peak sun hours refer to the number of hours in a day when the sun reaches its highest intensity, and the solar irradiance is 1,000W/m² per hour.
To be more clear, let’s work with an example.
Say you live in a region where the peak sun hours are 5 hours.
In this case, you can assume that your solar panels will generate about 5 kWh of energy each day (1,000W/m² x 5 hours).
To know how many peak sun hours your area receives, you can use NREL’s solar calculator.
I live in California, so I’ll use 5.83 peak sun hours per day which translates to 174.9 hours each month (5.83 x 30 days).
3. Calculate the Theoretical Size of Your Solar System
Now, we know the peak sun hours in our area and how much energy we need to power our hot tub.
So, let’s calculate the theoretical size of the solar system.
To do this, we’ll use the following formula:
Theoretical Size of Solar System in kW = Hot Tub Energy Consumption (kWh) ÷ Peak Sun Hours per Month (hrs)
So, for my hot tub that needs 120 kWh per month and the peak sun hours in California is 174.9 hrs/month:
Theoretical Size of Solar System = 120 kWh ÷ 174.9 hrs = 0.686 kW
This means that I need around 0.686 kW or 686 watts of power to power my hot tub.
But, you should know that this number is only a theoretical value.
We still need to account for other factors like system losses such as shading, inverter losses, age of the panels, etc.
4. Factor in System Losses
Any solar system experiences losses due to various factors like shading, inverter losses, thermal losses, dust accumulation, etc.
These losses will affect the total output of your solar panels and can vary from system to system.
In general, the industry standard is to account for a 14% system loss.
So, the real-world size of the solar system would be:
The Real Life Solar System Size (kW) = Theoretical Solar System Size (kW) x 1.14
If we plug in the numbers for my hot tub:
Real Life Solar System Size = 0.686 kW x 1.14 = 0.782 kW
This means that I need a solar system of around 0.782 kW or 782 watts to power my hot tub and account for all other losses.
5. Find the Total Number of Solar Panels
Solar panels are rated by the number of watts they can generate.
Most residential solar panels are rated between 250 watts and 400 watts.
This wattage rating indicates how much energy they can generate for every peak sun hour (1,000W/m²) they receive.
For instance, a 300W panel will generate 300W of energy per peak sun hour.
Now, let’s calculate how many panels you need for your hot tub.
To do this, divide the real-life solar system size (kW) by the wattage rating of the panel:
Total Number of Solar Panels = Real Life Solar System Size (kW) ÷ Wattage Rating of Panel (kW)
For our example, I’ll use a 300W panel:
Total Number of Solar Panels = 0.782 kW ÷ 0.3 kW = 2.6 panels ~ 3 panels
So, for my hot tub, I need around 3 solar panels rated at 300W each.
Do I Need Batteries to Run a Hot Tub on Solar?
Solar panels collect energy from the sun and convert it into electricity that can power your hot tub.
However, the sun isn’t always available and you may experience cloudy days or periods of low sunlight.
And since solar panels don’t store any energy, you’ll need a battery system to store the excess energy generated by the solar panels when it’s sunny.
To calculate how many batteries you need, you can use this formula:
Battery Size (Ah) = Solar Panel Daily Output (Wh) / Battery’s Voltage (12/24V) / DoD (0.5/0.75/0.8)
So, we first need to calculate the solar panel’s daily output.
Since we have 3 solar panels rated at 300W each:
Solar Panel Daily Output (Wh) = Number of Panels x Rated Power Output per Panel (W) x Peak Sun Hours x (1-0.14)
So, for my hot tub:
Solar Panel Daily Output (Wh) = 3 x 300W x 5.83 hrs/day x (1-0.14) = 4,512 Wh/day
Now, let’s say I have a 24V battery system with an 80% depth of discharge:
Battery Size (Ah) = 4,512 Wh/day / 24V / 0.8 = 235 Ah
So, for my hot tub, I need around 235 Ah of battery backup to store the excess energy generated by my solar panels.
How Much Does a Running a Hot Tub with Solar Panels Cost?
The average cost of solar power in the U.S. is around $3-$5 per watt before tax incentives or rebates.
For our example, we need around 0.782 kW or 782 watts solar system, so the cost before incentives would be:
Total Cost = Solar System Size (W) x Average US Cost ($/W) = 782 watts x $3/W = $2,346
After taking into account all the tax incentives and rebates available which are about 30% on average, the final cost of your solar system would be around:
Net Cost = Total Cost x (1- Tax Credit Percentage) = $2,346 x (1 – 0.30) = $1,642
So, for my hot tub, the total cost of a solar system with battery backup would be around $1,642.
How Much Money Will Running a Hot Tub with Solar Panels Save Me?
Running a hot tub with solar panels will save you about $4,406 in electricity bills over 25 years compared to using grid power.
To calculate the total energy consumption of your hot tub over the course of 25 years, use this formula:
Total Electricity Produced (kWh) = Electricity Usage (kWh/month) x 25 years x 12 months
For our example, let’s say I use an average of 120 kWh of electricity per month to power my hot tub:
Total Electricity Produced (kWh) = 120 kWh/month x 25 years x 12 months = 36,000 kWh
Now, the average rate for electricity in the U.S. is around $0.168/kWh.
So, the total savings over 25 years would be:
Total Savings ($) = Total Electricity Produced (kWh) x Electricity Rate ($/kWh) – Solar System Cost ($)
Total Savings ($) = 36,000 kWh x $0.168/kWh – $1,642 = $4,406
Therefore, I can save around $4,406 in electricity bills over 25 years by running my hot tub with solar panels.
Can I Run My Hot Tub off Solar Panels?
You can run your hot tub off solar panels.
The size of the solar system you need to power your hot tub will depend on how much energy your hot tub consumes and how many hours of sunlight you get.
How Much Electricity Does a Hot Tub Use?
A hot tub uses between 3.5 to 6 kWh of electricity.
This will vary depending on the size of your hot tub and how often you use it.
As promised, we’ve walked through everything you need to know about running a hot tub with solar panels.
We’ve discussed the basics of solar power, how to size a solar system for your hot tub, and calculated the cost and savings associated with running your hot tub off solar energy.
And if you ask me, I’d recommend turning all your appliances to solar and start living a greener life.
Do you still have questions? If so, feel free to drop a comment below and I’ll try my best to answer.