How to Make a Simple Solar Spa Heater on Your Roof
Alex Davies is a technology journalist and the author of Driven, an upcoming book about the self-driving car industry.
Even in the summer months, it’s nice to have hot water for the shower, doubly so if you have a spa or hot tub. To help you keep things steamy while keeping your electricity bills down, here’s a surprisingly simple DIY project. For about 60 worth of materials, you can make your own water heater, installed on your roof.
This project deals with heating a spa, but with some tweaks near the end of the process, you could use it to heat a pool, sink or bathtub. Here’s how.
This project is the work of Instructables user Greg Horejsi, aka petastream. Special thanks to him for his permission to post it here.
Why a Solar Spa Heater?
Well it’s that time of the year again here in Southern California time to fill up the spa and break out the BBQs. This has become a yearly ritual as well as a scathing reminder that electricity is not free. Anyhow, my wife has been wanting to move in a greener direction and has been rather matter a fact about it as well. We now compost our organic waste and recycle that into our garden. Her new kick was How can we heat the spa without using the electronic heater? She got up on the roof with 50 feet of black hose and ran it back and forth a few times, hooked it to a pump and came up with the proof of concept. Yay! (The original idea was sourced from my coworker Gary who has a similar setup for his pool.) Today we decided to move from conceptual proof to full on production. This Instructable will walk you through the process that we went through and try to help you avoid some of the gotchas that we found along the way. Hope you enjoy reading this as much as we enjoyed building/documenting this project.
What You’ll Need
For around 60 you can build this neat little system using the following parts purchased at your local mega hardware store:
Setting Up the Frame
This step is simple. You take the 20ft of PVC pipe and cut it down to four 5ft long sections. Glue them each in to the 4-way fitting using blue PVC cement or some similar form of adhesive. Let it dry a bit, and voila! Your framework is complete. Wish it was that easy creating frameworks at my day job! (I’m a software developer if you’re wondering.)
Your Work Area
Make sure you have room to move around the work area, as you will be doing a lot of walking (mostly in a circle). We set up a ladder with a pipe crossbeam which held the drip hose. This setup didn’t work quite as well as we had hoped, but did help keep the coil from getting horribly tangled. The frame was set up on a trash can that we filled part way with water to stabilize it from falling over. The spool unwinding was managed by my wife for the most part and my son helped guide the hose while I walked in circles like a carnival mule.
Spiral Construction, at a Snail’s Pace
The hose was spun on to the frame starting at the middle and working outwards. We took a lead of around 6ft and attached to one leg of the frame, then we guided it in to the middle to begin the spiral. There were issues with kinks and it worked out that at around 5in from the lip of the fitting, the curve was easy enough that we could form the shape without kinking the hose. I marked out this 5in using a marker and fastened the hose to the frame to begin the spiral. Working in chunks of around four to five rotations seems to work well, until the later stages of construction. After each set of rotations you loosely fasten the hose using zip ties. Working from the last tightened point, you guide the coil so that the hose sits evenly next to the previous loop. Too tight and it will overlap, too loose and it will cause grief on the next loop.
Completing the Spiral
When we made it to the outer reaches of the spiral, the weight of the hose was causing the frame to bow and was making it difficult to properly set the hose in relation to the preceding loop. To remedy this we moved to the ground for the remaining loops. To do this we removed the remaining hose from our make shift spool mount and my wife walked the hose out while I followed behind her fastening the hose to the frame.
Mounting the Spiral and Hooking It Up
Once the work was completed, we carefully migrated the beast to the roof. We set up on the south facing side of the house. We fastened a rope to the center of the frame and tied it off on the north side of the house to prevent the coil from sliding down the roof. Once it was secured, we connected the garden hose adapters to each of the leads coming from the coil and hooked up the cold water feed and hot water return hoses to the coil. (Note: Both our connectors were female, so we ran the return hose backward with the female end in the spa.) After the hoses were connected, we hooked the cold water feed hose up to a regular garden hose faucet and charged the system, so to speak, using the household water pressure. Once the water was completely through the system we connected the cold water feed to a pump in the spa and ran it for a test drive. Voila! It worked: The pump was pumping water through the coil and it was returning to the spa.
Integrating the System
This part of the process is completely custom, based on your particular spa and how everything is set up. In our case the spa is on our back porch area next to the house so plumbing some PVC and running it up the wall was incredibly easy. We started by mapping out the current way the water cycles through the internal spa heating system. After some trial and error we ended up adding a 3/4 barbed T fitting inline with the internal heater pump. The return from the roof is fed back in to the spa system and enters the water through a small vent at the bottom of the spa. The pump that is currently installed is a small magnetic pump that is installed to simply help cycle the water through the siphon system. The overall flow is around 1GPM through the solar loop. A check valve was installed to help prevent water that has been heated being recycled through the coil, and valves were installed on the outside of the spa to allow us to isolate the coil plumbing from the spa for maintenance. The rest of the plumbing was pretty straight forward, we went a little over the top by using pipe insulation but hey if your going to do it, you do it right!
Here’s how it worked out: Day #1 Time. Spa. Water from Solar coil 09:32am. 82.2. 93.9 11:11am. 85.8. 93.9 01:03pm. 91.0. 101.1 01:57pm. 93.9. 104.3 Peak reading 03:37pm. 96.8. 106.8 04:18pm. 98.6. 103.8 Total increase over the time we monitored: 16.4 degrees fahrenheit. Special thanks to Greg for his permission to re-post his instructions for this project. Be sure to follow his Instructables page for great DIY projects!
Gulf Coast Green Energy (GCGE) is the oldest distributor for ElectraTherm’s revolutionary small scale, on-site waste heat to power generator known as the Power Generator TM. GCGE serves as a distributor of this revolutionary renewable energy technology in the Gulf Coast states from Texas to Florida. GCGE holds the distinction of being the first company to install a Power Generator TM. which happens to be the first commercially viable small scale waste heat generator that we know of supplying under 1MW of power. The Power Generator TM line of waste heat to power generators can supply 75-150 kWe. And, it is American made!
Each Power Generator TM unit combines traditional components with patented, cutting-edge technology to create electricity from waste heat. The Power Generator TM uses a closed-loop Organic Rankine Cycle (ORC) to create pressure by boiling EPA and Kyoto-approved chemical working fluids into gas. The gas expands in a one way system and turns a patented Twin Screw Expander, which drives a generator that outputs electricity.
Small Scale Waste Heat to Power Generators
Historically, ORCs incorporating turbo-expanders have not been commercially viable in sizes less than 1MW. By replacing turbo-expanders with Power Generator TM ‘s patented, robust, low-cost Twin Screw Expander, users benefit from a quick return. Our systems provide unattended operation and negligible maintenance.
Power Generator TM Heat to Power Generator Details:
- Organic Rankine Cycle (ORC) waste heat-to-power generating system.
- Generates 75 kWe – 150 kWe, emissions-free electricity
- Captures waste energy from small, distributed hot water waste heat sources:
- stationary engine jacket water and exhaust gas, biomass boilers, solar thermal and co-produced (or geothermal) fluids
Power Generator TM Benefits:
- The lowest heat requirements in the industry
- Flexible and scalable options
- The lowest operation maintenance requirements in the industry
- Fuel free, emissions free solutions
- Non-combustion processes
- Modular or mobile alternatives
The Power Generator TM is proven. It has been used for more than fourteen years in working industrial environments, producing real cost savings for our clients. ElectraTherm, Inc.’s Waste Heat Generator technology became commercially available in January 2007. Gulf Coast Green Energy was the first to embrace the visionary technology offered by ElectraTherm becoming their inaugural distributor.The Power Generator TM relies on standard parts, pumps and piping along with proven proprietary hardware, controls and system design. The Power Generator TM components have demonstrated its value in high load, industrial applications for decades. This system is modular and can be coupled with multiple Power Generators TM as well as other green energy technologies like our Sopogy solar thermal products and our large scale H2P equipment made by Turbine Air Systems.
Cost Benefit of Fuel-Free, Emission-Free Electricity
As a distributor, installer and service provider for the Power Generator TM. Gulf Coast Green Energy, brings you affordable, efficient, clean and earth-friendly on-sight energy. Sounds too good to be true? Visit the Featured Projects page of our website to see how our clients are saving energy and generating zero emissions electricity. Each one of our clients is directly and dramatically lowering the cost of doing business while creating higher profits and happier shareholders.
Companies whose energy usage produces waste heat are prime candidates for ElectraTherm’s pioneering energy technology and Gulf Coast Green Energy’s expert implementation and service.
Our Technology Integrates With Many Heat Sources
- Reciprocating Engines
- Solar Thermal
- Industrial Processes (gases, liquids, discarded steam, thermal oxidizers)
- Geothermal/ Oil and Gas production
- Mid-Stream Natural Gas Processing
How It Works
Imagine a tea kettle on a stove. When heat is applied to the bottom of the kettle, the water in it boils and emits pressurized vapor through the cap and creates a whistle. By holding a child’s pinwheel in the flow of emitting water vapor, the pressure from the steam spins the pinwheel.
With enough pressure, the spinning propeller will light a small bulb if attached to a generator.
The concept of ElectraTherm’s WHG is the same. We capture a heat source, which boils the working fluid and produces a gas. The gas expands in a one-way, closed piping system and its pressure turns the expander, which drives a generator and puts out electricity.
The Working Process
ElectraTherm has employed the proven Organic Rankine Cycle in its Waste Heat Generator solution (WHG). The graphic below shows the working process for the ElectraTherm WHG which uses a non-flammable, eco-friendly refrigerant selected for high performance at low temperature.
Surplus heat captured by the evaporator is used to “boil” the working fluid into a vapor. Once under pressure, the vapor is forced through the screw expander, turning it to spin an electric generator. The vapor is cooled and condensed back into a liquid in the condenser. The working fluid liquid refrigerant is then pumped to higher pressure and returned to the evaporator to repeat the process.
Please contact us to see if the Power Generator TM is the right fit for your project. We can determine in a phone consultation if your waste heat source is compatible with the operating specifications of the Power Generator TM. The next step is to conduct and on-sight evaluation. Our engineers work with you and the ElectraTherm engineering team to ensure that your installation is maximized for the highest return for your company.
Ways to Build a DIY Solar Pool Heater
Want to heat your pool using solar power? You don’t need to buy a commercial system when you can build your own.
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Nothing beats a refreshing dip in a warm pool on a cool day. Although a pool heater won’t make your swimming pool feel like a Jacuzzi, it can make it more comfortable to swim in and a more pleasant location to spend cool summer evenings.
A solar heater is also affordable, convenient, and easy to operate. Building one yourself further lowers the cost involved and makes it much cheaper.
What Is a Pool Heater?
A pool heater drains the pool, transports the water to a storage tank, and then refills the pool with hot water. Even if it’s chilly outside, your pool will always be a pleasant temperature thanks to the alternating flow of cold and warm water. A solar pool heater is also an eco-friendly way to heat your pool, as it runs on the renewable energy of sunlight.
Most solar pool heaters work with a solar collector, a filter, a pump, and a flow control valve. Water from the pool is circulated through the filter and heated in the collector before being returned to the pool. Generally, solar-powered water heaters are less powerful than electric and gas heaters, but they are cheap and easy to build.
Solar power could be doing much more in your home than heating your swimming pool. We’ve outlined some of the best solar-powered gadgets you could be using in your home.
There are three main approaches to building a working solar pool heater, based on the type of solar collector: flat plate collector, evacuated tube collector, and batch collector.
Flat Plate Collector
This method is easily the most popular way of building a solar pool heater. The underlying idea is simple: a dark, flat surface, usually a copper or aluminum sheet, is heated using sunlight and this energy is transferred to the pool to increase its temperature. This working principle provides several advantages such as affordability, ease of installation, and low maintenance.
Flat plate collectors are usually installed facing the equator. Insulation is added to the bottom and sides of the sheet to minimize heat losses. Here is an example project that uses this approach to building a solar pool heater:
DIY Solar Pool Heater
User Bnaiver built a heater for his above-ground pool to maintain a comfortable temperature in the spring and fall. The tools and equipment required for this project are cheap and can be found at Home Depot for less than 100. It uses a 4×4 piece of plywood, a 200-foot long and half-inch diameter vinyl irrigation hose, UV-resistant zip-ties to fasten the hose to the plywood, a valve assembly made up of a series of valves and “Y” adapters, and an outdoor, mechanical timer.
The valve assembly serves the purpose of routing water into the heater and then back into the pool. It also makes it possible for the heater’s supply and outflow to be cut out when it is no longer needed.
Measuring using an infrared thermometer, Bnaiver was able to get a reading of 99℉ from the pool. By following the Instructables guide, you should be able to build your own well-working solar pool heater in less than a day’s work.
If you’re interested in building something more large-scale than a solar water heater, we have listed the components you need to build an off-grid solar power system.
Evacuated Tube Collector
An evacuated tube collector is a solar heating system with a series of glass tubes containing a copper rod or pipe. The air within these tubes is removed to create a vacuum. Also, aluminum nitrate or titanium nitride oxide is applied to the inside of the inner glass tube to maximize sunlight absorption.
Evacuated tube collectors are usually more efficient than flat-plate solar collectors. The vacuum space between the inner and outer glass tubes provides insulation and allows the tubes to retain heat energy with minimal losses. This allows them to perform consistently well.
Evacuated tube collectors, however, tend to be more expensive. An evacuated tube collector can cost as much as 20-40% more than a flat plate collector. They do require less maintenance and can serve you for years after installation. While there is usually some variation in the specifics of how evacuated tube solar water heaters are built, the core concepts remain the same.
This YouTube tutorial by Pete Stothers walks you through how to build your very own evacuated tube solar pool heater. It uses a vacuum tube array (with 12 tubes) and a 12 ~ 24VDC circulating pump. As mentioned earlier, evacuated tube collectors are quite expensive, and you can expect to spend as much as 400 on this project. Here is the second part of the tutorial.
This project can be automated with Home Assistant to monitor the temperature from time to time and regulate the pump flow rate. As Pete mentioned, this DIY project may be much better suited for pools with a smaller surface area such as a hot tub or a backyard spool.
This is the least popular type of solar collector. It is also less efficient and takes up much more space, compared to other collectors. However, the mode of operation is simple enough, and it requires much less maintenance.
Batch collectors are a kind of integral collector storage (ICS) system, which means that the tank and the solar collector are combined into a single unit. This removes the need for pumps and controls in the system.
A glass-plated, insulated box allows sunlight to heat a dark-tinted water tank, which absorbs the heat. The water is heated more efficiently thanks to a metal coil around the tank’s exterior, sucking in heat and dispersing it throughout the tank’s interior.
Most batch collectors house their water storage tank inside a glass or plastic-enclosed insulating box. For use as a batch collector, all you need is an old, regular water heater tank. Because of its insulated walls, the water storage tank loses less heat to the outside air, and its glass roof lets in solar energy to warm the water.
You can build your own batch collector by following this Instructables guide by Ganesh Ruskin. He uses as many recycled materials as possible in building his batch collector. According to Ganesh himself, this Instructable is a bit rough around the edges, but the main steps are well-detailed, and you should be able to get the gist of what is being described.
Some of the tools and equipment you will need are an old water heater tank, two sheets of plywood, a glass patio door, two lengths of copper and steel pipes, drywall screws, steel plugs, Teflon pipe tape, and primer.
Building Your Own Solar Pool Heater
Using a solar pool heater is an environmentally responsible way to keep your pool warm. DIY solar pool heaters are possible to build, even though there are numerous commercially marketed solar pool heaters to choose from online. They take a short time to construct and cost significantly less than commercial options.
Solar plus Heat Pump Water Heater – Smart Solar
(An update from our June 2013 blog) Solar is becoming more widely known as a practical way to save money on your electric bill, by making some of the power yourself rather than buying it all from the electric company. A lesser known way to bring your utility bills down even lower is to also install a heat pump water heater, also known as a high efficiency water heater, or Energy Star water heater.
Solar electric systems combined with heat pumps for water heating greatly reduce your annual costs.
Traditional Water Heaters Big Consumers of Energy Money
A traditional electric water heater is generally the second largest user of electricity in a home, and can account for as much as a quarter of a household’s electricity use. A hybrid heat pump water heater can reduce that electricity use from around 13kWh (kilowatt hours) a day to 5kWh a day. Thats an annual savings of 3,000kWh. A heat pump water heater works by taking the heat from the air, and putting it into the water in the tank. A
hybrid model also has a backup electric heating element to ensure there is always plenty of hot water available. They work the same as the heat pumps used to heat your house, but with a smaller pump that is generally built right on top of the water heater.
Solar Water Heating isn’t Solar with Heating Heat Pumps
So you may be asking yourself, what does this have to do with solar? Am I talking about solar water heating? No. This is electric water heating, by using the electricity generated by your solar electric system. In most locations, 1,000 watts of solar electric panels could provide enough electricity to power the heat pump water heater, while in comparison a traditional electric water heater would need around 4,000 watts of solar power. This is a less expensive and less complicated solution than solar water heating. What this means is if you are installing a grid tie solar electric in your house, you could get the same reduction in your electric bill by replacing your electric water heater with a heat pump water heater, with 3,000 watts less solar. Or, install the same amount of solar, and see it offset an even higher percentage of your smaller electric bill.
Swap Out that Oil Water Heater
Many people who currently heat their water with oil can see a reduced oil bill, and only need to add 1,000 watts of solar to their planned solar system to offset the slight increase in electric use seen by switching from oil water heating to electric. This is very popular in the Northeast where oil heat is common. Now you never have to hear your oil furnace kicking on every day in the summer just to heat your water. In the winter, the heat in the air surrounding the furnace can get pulled right into your water – even heat from a cool basement. Think of using solar with a heat pump for water as free “solar fuel oil” – one whose price will never change above that magical amount of 0.
Heat Pumps are also Basement Dehumidifiers
A heat pump water heater from Stiebel uses 25% the energy of a normal electric water heater.
Another advantage of the heat pump water heater is that while it is taking the heat out of the air, it is also removing the humidity from the air. This can be very beneficial in homes where the water heater is installed in the basement. Keeping the basement cool and dry in the summer can eliminate the need for a dehumidifier in the basement, even further reducing your electric bill by another 1,000kWh a year. Homes in warm climates without a basement can install the heat pump water heater in their garage, providing the same benefits there.
Financial Incentives Available in Many States
The energy savings of a heat pump water heater is so great that many states have created cash incentives to swap out your old electric water heater. For instance, in Massachusetts, National Grid customers can get a 750 rebate by having a heat pump water heater professionally installed. Go to to DSIRE and go to your state to see if there is an Energy Efficiency rebate program available in your area. Note that this is different from the solar water heating rebates, this is for high efficiency, Energy Star, or heat pump water heaters.
Partial List of Rebates Available for Heat Pumps
|California||Pacific Power||600 rebate|
|Georgia||Georgia Power||250 rebate|
|Hawaii||Hawaii Energy||300 rebate|
|Massachusetts||National Grid||750 rebate|
|Maine||efficiency Maine||500 rebate|
For more details on heat pump water heaters, see the brochure for the Stiebel Eltron Accelera 300.