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Can You Run a Hot Tub on Solar Power?

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One of the main issues people have with owning a hot tub is that they are expensive to run. Heating such a large amount of water takes a lot of energy, is expensive and also impacts the environment. But what if you could run your hot tub on solar power? A solar-powered hot tub could be much cheaper to run and better for the environment. Is a solar-powered hot tub possible? I decided to find out:

So, can you run a hot tub on solar power? You can run a hot tub on solar power in many areas depending upon the amount of sun you get. There are two main types of hot tub solar heating, firstly where the water passes through a heat exchanging panel and secondly more “traditional” solar panels connected to energy storing batteries.

How do you solar heat a hot tub?

The simplest method of using the sun to heat your hot tub is to use a heat exchanging panel. This is relatively simple technology but will be effective if you live somewhere that gets around 6 hours of strong sun, or more, per day.

In a nutshell, cold water leaves the bottom of the hot tub and passes through the heat exchanger. This is a large panel crisscrossed with small tubes for the water to pass through. The tubes are set against a black background to soak up the heat and there is often a glass or perspex layer over the front to magnify the heat.

As the cold water passes through the small tubes it is heated by the sun and then passes out of the other end of the heat exchanger and is piped into the top part of the hot tub. As the water cools it falls lower down in the hot tub and is passed through the system and warmed up again.

I came across this rather fun video which gives you a pretty good idea of how this type of heat exchanger is fitted and how it works:

So what are the pros and cons of this system and might it be right for you?

Pros:

Cheap – First of all this type of solar system is relatively inexpensive. The heat exchanger is a fairly low tech piece of kit and all you really need apart from it are the connecting tubes and probably a small pump

Makes lot’s of free hot water – If you live in a hot enough climate this will make you lots of free hot water. In fact it will just keep on pumping out hot water as long as the sun shines.

Maintenance free – Once you are up and running this system is essentially maintenance free. There’s no moving parts and no mechanicals to go wrong.

Easy to fit – It’s also relatively easy to fit, it’s certainly possibly to DIY it and won’t take a lot of time.

Easy to use alongside your electric heating system – There’s also no problem in using this heat exchanger system alongside your normal electric heater. There will be days where it isn’t sunny enough to heat your water via solar and you will still need to use the electric heater.

You will probably also find that you can’t realistically heat using solar from totally cold so, when you do a water change or switch your hot tub off for a while, you will need the electric heater to give you that first boost.

Great, so what are the cons?

Large exchanger unit – One of the main issues has to be the size of the heat exchange unit needed. Many of them are 6 feet long and maybe 2 feet wide so you will need a large space in the sun to put the heat exchanger. You could, of course put it on a roof or somewhere away from the hot tub but the further away it is the more pumping the water will need and the more heat it will lose as it travels along it’s journey.

It’s also possible that you will need more than one unit to create enough hot water for your tub. You can stack them on top of each other but we are looking at some fairly serious square footage here. No problem if you have a large garden but anyone with even slightly restricted space might struggle.

Lack of temperature control – I may be wrong about this but my understanding is that this is fairly basic technology and that there isn’t really a way to control the temperature of the water other than by putting a thermometer into the water.

This may or may not be a problem but my sense is that potentially, on a very hot day the exchanger could be pumping scalding hot water into your hot tub without any cut out or control. Your hot tub is only designed to contain water up to 40 degrees C and anything above that could cause problems.

If you are using the hot tub’s electric heater it will cut out to prevent the water from getting too hot but I’m not sure there is a similar safety device with these solar heaters.

The most obvious use for this type of solar heater would be for you to heat up the hot tub during the day whilst the sun is out. The chances are that you can’t be there all day to switch the system on and off according to the temperature so this lack of controllability strikes me as being a bit of an issue.

Can’t store energy – The other problem is that this type of system can’t store energy. Traditional solar panels can be connected to batteries which will store the energy for when it is needed. This type of solar system heats the water when it is probably least needed – in the heat of the day. Unfortunately once the sun goes down so does the water temperature.

Where can I get a hot tub solar heating system from?

So, it looks like you might have decided that this route is for you and that getting your hot tub connected up to a solar panel is a good idea. Before you start looking for panels to buy check that your hot tub is out of warranty. If it is in warranty making the modifications that you will need to make to the hot tub with almost certainly invalidate the warranty.

So, if you are still in warranty and you want to investigate the solar route you need to contact the dealer where you originally bought the hot tub. It might well be possible that they can do a conversion for you and also keep the warranty as well which could be a good solution.

It may well be more expensive than doing the conversion yourself but it doesn’t make any sense to invalidate the warranty to your hot tub if you have one.

If you are ready to get the conversion going then the main supplier of solar heating systems are here with the Sunbank Solar Hot Tub Kit

I have had a good look around for other suppliers and found them difficult to find. It might just be my local area but it seems that the Sunbank kit is the main one out there. If you look at solar water heating systems you will find a lot more choice and a number of these websites do mention how a hot tub can be plumbed in to become part of a larger domestic solar hot water system. However, there seem to be few suppliers of stand alone kits for hot tubs.

The next question has to be how much does it cost to have one of these conversions? Well, the Sunbank hot tub kit is $1799. On the Sunbank site they say that a solar kit could save you up to $900 in energy bills per year. I have written a detailed post on how much it costs to run a hot tub here. The most common area for energy expenditure is between $20 and $40 per month, so that’s around $500 dollars per year.

That is quite a long way lower than Sunbank’s claim of saving you up to $900 per year. They do state that this figure would be for someone with a high electricity usage and also in an area where electricity is expensive but many hot tub owners would not be paying $900 per year for energy – never mind saving that amount.

However, I am sure that what Sunbank are saying is true, but what we need to know is what sort of energy saving a solar system could potentially make to a more average energy consumer.

How much money could a solar hot tub save?

Unfortunately, there really isn’t a simple answer to this. It depends on so many variable factors. For example how often the hot tub is used, how thermally efficient the hot tub’s insulation is the ambient air temperature, the amount of sun, the location of the hot tub, the size of the solar panels……the list goes on and on.

However, we do know that the average hot tub costs about $500 per year to heat if it is used all year round. We also know that a Sunbank Solar Kit is $1799. You are only likely to consider retro fitting a solar system to a hot tub that is out of warranty so, your hot tub is likely to be five years old or more and will, most likely give you another five years of trouble free service.

Assuming that you do fit the solar system and it lasts for five years it would cost you $359 per year. Does this make financial sense? No, not really. Over five years the chances of a hot tub solar system paying for itself look rather slim. The solar energy would have to provide for around three-quarters of the heating for the hot tub and this does seem rather unlikely.

However, it may well be worth it if you knew you were going to keep the hot tub and system for ten years. In this case the solar system would only cost $179 per year and this seems a much more realistic amount to save out of a $500 per year energy bill. But, it’s not all about money, a solar hot tub system will give you the peace of mind of knowing that you are heating at least part of your hot tub in as environmentally friendly way as possible.

There is also another possibility if you have a quick look on Amazon here you will see the Smartpool solar heating system. This is designed for pools but is also significantly less expensive than the Sunbank solution. It will most probably not be as effective but may be an option if you are on a budget. They produce a whole range of solar heating equipment that is worth checking out.

DIY Solar Hot Tub Conversions

So, we have seen that, in order for your solar conversion to make financial sense, that you have to use it over a long period of time to make it worthwhile. Even then the financial advantage may not, depending upon your individual circumstances, be completely worth it.

But what if there was a way to install a solar system for next to nothing? Imagine if that would heat your water and save you some money? In many ways, it wouldn’t matter how little contribution the solar system made because, as it cost next to nothing to install, any saving is a big plus!

I managed to find this fantastic guide on creating a DIY solar heating system for your hot tub. It’s not particularly glamorous or stylish looking but it is cheap and easy to make and should, inevitably make a contribution to heating your hot tub’s water. It also won’t be as efficient as a ready-made system but it will cost you at least $1500 less.

Obviously, if you do want to add your own DIY solution to your hot tub you need to ensure that it is out of warranty. If that is the case and you are happy to have a homemade solution you could just be on to a winner.

Solar hot tub systems and batteries

The other way of using power to heat your hot tub is with a solar panel that converts sunlight into electricity and then stores it in solar batteries. I am not going to profess to having any in-depth knowledge in this area but there are a number of places that you can get solar kits that might just do the job.

My sense is that you would need to contact the manufacturer of the kits to see if there was one that might be suitable for running a hot tub from. However, hot tubs do need a lot of energy and I am sure that you would need to supplement a solar kit with mains electricity. How much would depend upon your usage and the amount of sun you get in your area but we would be left with the same financial dilemma.

It looks to me like these kits cost around $2000, so again you would need to use the solar kit consistently for a number of years again to get the value out of them.

However, and this is a big plus, I can’t see any reason why using a solar kit with battery storage would in any way invalidate a hot tub’s warranty. You are not making any alterations to the hot tub at all (but do check with your manufacturer to be completely sure) so you could potentially use this type of solar heating system for day one of the ownership of your new hot tub.

If can use this type of solar kit in warranty then you don’t need to wait for half of the hot tub’s lifespan to be up before installation. The solar system could be working easily for ten years or more and so begins to look like a much more promising financial proposition.

I am, of course, assuming that the system would last for ten years or more of continual charging and discharging. Would the batteries last this long? There are a few questions that you would need to ask the manufacturer before taking the plunge.

Conclusions

Whether or not a solar heating system for your hot tub is the right choice is purely dependent upon the amount of use your hot tub gets, the amount of available solar heat in your area and your personal environmental goals. I think it would be hard to recoup the cost of a water heating solar system as you probably couldn’t have it fitted until your hot tub was out of warranty which would limit the number of years you had to recoup the cost.

However, I could be wrong, if you live in a very sunny area, are a relatively light hot tub user and pay high energy costs then this type of solar system might well save you a lot of money over a period of time.

If I had an older hot tub though I would be very tempted to go down the DIY route as above. The temptation of free water heating is very strong and in many ways, as long as you are happy to do some minor alterations to your hot tub, you can’t lose.

Finally, a battery system seems well worth at least investigating. You will need specialist help to determine the right spec depending upon your own individual circumstances but this method potentially offers a much longer time to recoup your money as it most probably won’t affect your warranty.

Finally, you might want to consider solar powering your hot tub as part of a wider solar conversion for your whole house. Many governments are offering conversion grants at the moment and it seems that we are just on the cusp of this type of renewable energy being financially viable.

This post was created by Andrew. Enjoyer of hot tub soaking, fine cheese, music and photography.