A hot water tub can be run on solar energy, either using photovoltaic cells or solar thermal collectors. However, solar thermal systems are by far the most affordable option.
On average, a hot bath uses approximately 300 kWh per month, which could be supplied by 2 kW of solar panels and a 12 V 25 Ah battery.
Is Solar Energy Enough to Run a Hot Water Tub?
Let's take this one part at a time. To determine which type of solar energy system you require, you must ask yourself some questions.
1. Which Type of Solar System is Suitable for Hot Water Tubs?
Which one is better for heating water?
It's not obvious which way to go. On the one hand, solar energy is quick and easy to set up, and use. It doesn't generate electricity efficiently because only 20 percent of the Sun's solar radiation is absorbed.
If you have an electrical heat source for heating water, then using electricity from solar panels seems logical, but there's another option for powering up the hot tub - solar water heaters.
Solar thermal systems are is more complex to set up, but they can efficiently use 75 percent of the sunlight for heating purposes.
The big question is - Are solar thermal systems capable of heating water to sufficiently high temperatures?
2. What is the Amount of Power Consumed Per Hour by Hot Water Tubs?
Assuming an average consumption of 300 kWh per month (it typically ranges from 100kwh to 600kwh), we will use this figure for simplicity.
The size of solar electric panels and thermal systems can be measured using these figures. Most people use their hot water tub two times a day, so there seems to be some logic behind this.
When the water temperature reaches 100 degrees Fahrenheit, turning on the electric heating element will help keep costs down, particularly if you have an efficient covering for holding the heat in.
Solar Energy Needed for a Hot Water Tub
If you're planning on installing solar panels, you'll want to be sure they can sustain an average monthly electricity consumption of 300 kWh (kilowatt hours). You can size the panels accordingly if you decide to go that route.
As solar panels age, they lose some of their output. To compensate for these losses, an additional 50% extra capacity is added. Also, consider the impact of weather conditions, including low sun, cloudy skies, windy weather, and rain.
3. What is the Strength of Sunlight in Your Region?
The sun emits energy at different wavelengths. Its strength is measured in kilowatt-hours (kWh)/square meter/day or year. You can also call it the peak hours of the sun.
You can calculate the output of a solar panel using its wattage and multiplying it by the number of peak sun time hours.
It's also useful when calculating the energy output from solar thermal systems. Knowing the estimated efficiency of such systems, we can calculate how many panels would be needed to heat the water to the desired temperature.
Luckily, you don't need any special equipment to measure the sun's power anywhere you live, but just input your geographic coordinates into one of the sites designed to provide historical solar data based on where you live.
Is it Possible to Power a Hot Water Tub over a Year with Solar Panels?
You've calculated your city's peak sun hours for each day of the week. But these are just averages for the whole year. It will be mostly during the summer and the least during the winter.
As hot tubs become more common during the colder seasons, it becomes sensible to base your solar panel size on the lowest energy usage period, which is obviously during the cooler months.
The below-given table compares the variations in the sunlight over 12 months in Houston, Texas.
You can see from the table above that in the winter it's almost half as much in January as in July. You will probably require a larger panel …
Can you Operate a Hot Water Tub Using Solar During Extreme Winters?
It could either be a huge success or a total failure. It may be the key factor in deciding to install solar thermal or electric PV systems.
You can rely on solar power most of the time and supplement it with grid electricity during winter months. You would still be able to save a lot of money.
4. How to Determine the Number of Solar Panels Needed to Run a Hot Water Tub?
The number of solar panels needed to generate enough electricity for a hot water tub (electric PV)
For this example calculation, let's assume a few assumptions.
Location of hot water tub: Houston, Texas
Size of electric heater for hot water tub: 3 kW
No. of hours taken to reach 100 degrees F: 8 hours
Run-time energy use: 8 hours x 3 kW = 24 kWh
Note: Raising the temperature requires much energy, but maintaining the temperature requires far less.
Daily Energy consumption to keep up the temperature: 3kW x 3 hours = 9kWh or 9000 watt-hours
Now by dividing the daily energy consumption by the peak sun hours every day, we get:
9000/4.25 = 2118 watts which mean around five solar panels of 400 watts each.
Will you Require Batteries?
Yes, you will require a battery pack of 24 volts 250Ah. Batteries store the energy they generate for use at any time later on.
If you are using the instant power generated at random times, you will need double the number of panels, and even so, there might not always be enough sunlight available to meet the thermostat's requirement of heat.
Deep-cycle lithium-ion batteries are better as they can discharge up to 95 percent of their capacity without any damage. They last for a long time.
5. What are the Savings and Payback Times of Solar Systems?
To determine whether using solar power is worthwhile, you need to calculate the energy savings you get from using them. What amount will be saved by installing solar panels, and how long would it take for them to pay back their initial investment?
For example, in Houston, people pay a power bill of $12 per kilowatt hour (kW) on average, and 5 kW is consumed yearly for heating purposes alone.
Solar should save you around $250 annually.
What are the Prices of Solar Installation in Houston?
The price of a small solar panel system in the region is $3/kW solar installed, and installing a 1500 watts solar panel system would be approximately $4,500.
Let's calculate how long it will take for the investment in the solar panel system to be paid off.
4500/250 = 18 years
Electricity bills tend to go up yearly, so that number will decrease gradually over time. The payback time for each solar panel will be affected depending on its irradiation level and energy cost.
Finally – Which Solar Option to Consider for Hot Water Tubs?
To get the best results, we need to take into account all the different factors involved.
For instance, if you want to run up to temperature, you could use solar thermal collectors, possibly evacuated tube types. They reach very high water temps and would probably keep them at a steady temperature.
Once most of the liquid has been heated to 90 percent of its final boiling point, you can use solar water collectors to keep the remaining 10 percent at the right temp.
If the long solar payback time didn't concern me, you can install solar electric PV panels and use them exclusively for heating water. It's easy to maintain and doesn't need much upkeep.