Article written by Gregory Grochola (physicist)
So you're looking at pool heating options and considering a solar pool heater - this comprehensive write up will help you get the low down on different types of options and all the things you'll want to consider. There's no doubt, solar pool heaters are by far the longest-lasting and cheapest way to heat a pool, but are they right for you, read on ...
Basics of Solar Thermal Pool Heating
Solar thermal collectors (or panels, or array - these terms mean the same thing here) work on the very basic principle of passing cold water through warm solar collectors typically mounted up on the roof. The warmed water simply comes back down directly into your pool. Solar thermal collectors are different to solar electric PV (PhotoVoltaic) collectors which collect energy via photons (light) hitting and exciting electrons creating a voltage across cells.
Solar thermal collectors are made as black as can be to turn all light hitting the surface into heat which are then conducted and taken away by the flowing water. Water is a perfect heat transfer fluid as it has the highest heat capacity of any known liquid, which basically means it takes a great deal of thermal energy to warm water even 1°C.
Different Ways to Heat a Swimming Pool
These can be classed into two distinct groups, solar-based and utility-based. Solar-based means the energy is taken from the sun, while utility-based means the energy is taken from either gas or electric utilities.
Solar-Based Pool Heating Systems
PVC strip collectors are made by extruding a strip of tube water channels. They are typically mounted with strips going across the roof with their main header pipe (also called the manifold or feed pipe) going up/down the roof. The PVC material typically has a softening agent (a plasticizer) which makes the strips flexible. Individual tubes are joined to barbs on the manifold and are either glued in or held in place using mechanical clamping means. They are very popular here in Australia due to the fact that they can be laid and wrapped around a couple of different roof aspects.
Solar pool heater panels are one-piece construction blow-molded plastic panels with internal water channels. These are typically made from HDPE as are our solar pool heater panels. These panels have large internal water channels with a low pressure drop across them and turbulent water flow characteristics.
These hybrid "panels" are typically made from extruded PP or PP blends with channels that are either made joined together or loose tube arrangements installed going up the roof, which are welded into the main header pipe going across the roof. They are very popular in America due to the larger roof space of American roofs, and are becoming more popular here in Australian.
Enclosed solar panels are basically polymer collectors that are covered with a glazing material (glass or transparent plastic). The glazing material increases the efficiency of the panels during adverse heating conditions like spring and autumn, which can have cold and windy but yet sunny days. These types of collectors are best reserved for heating premium indoor pools where the water temperature is substantially higher than the air temperature during winter.
Evacuated tube collectors are typically used for solar hot water service systems, but have been adapted by some companies to heat swimming pools. They are made from air evacuated glass tubes with internal strips of black painted copper absorders. Heat is either conducted or transferred via copper tube water channels from the sheet absorbers to the main manifold heat sink. Again the glazing material and vaccum increase efficiency of these tubes during adverse heating conditions like spring and autumn, which can have cold and windy but sunny days. Again such collectors are best reserved for heating premium indoor pools where the water temperature is substantially higher than the air temperature during winter.
The combination of solar electric panels (PV panels) and heat pumps can also be classed as solar-based heating systems. These systems work by firstly, harnessing electric energy via the solar electric panels, which is then used to run a heat pump to warm the pool. Modern PV panels are typically only 15% - 20% efficient, as compared to a modern solar thermal pool panel which are about 80-90% efficiency, however an efficient heat pump with COP factor 5 can make these system about 87% efficient, which is comparable to pool heating panels.
The main issue with these systems is the large upfront cost, of course the PV panels will produce electricity during non-pool heating times, unlike solar thermal collectors, which can off-set the price difference in installation, however the payback times will be substantial.
We can class a solar pool cover as a solar-based heating method as normally the surface of the pool itself forms the largest natural solar collector. A solar pool cover is typically transparent and works by letting light through into the pool while forming an insulating layer to keep the heat in by preventing evaporation.
Utility-Based Pool Heating Systems
This is basically a bar heater or heating element, emerged in flowing water, electricity is used to heat the element and in turn the water. Typically, used to heat highly insulated spa pools, they are the least efficient means to heat a pool or spa. Their COP factor (energy in to energy out ratio) is 1.0 - meaning for every 1 kWh worth of electrical energy you put in you get 1 kWh worth of thermal heating.
Heat pumps work by using electricity to "pump" or transfer heat from the air into the pool water. They work on the same principle as air conditioners but in reverse. If you ever stood next to one you'd feel they exhaust cold air, much colder than the surrounding air. This means they are pulling heat from the surrounding air into the pool water. Unlike an electric element, since they are pulling thermal heat from the air they can have average COP factors as high as 5, meaning for energy every 1 kWh worth of electrical energy you put in you get 5 kWh worth of thermal heating. Just to compare however, a solar pool heater can easily have COP factors of 100.
Gas heater basically burns domestic gas to heat a heat exchanger with flowing water, in turn heating the water. They have typical efficiencies of 87%; meaning of the total energy obtained from burning gas, 87% will get transferred into the pool water, the rest will get blow out with the hot exhaust air.
The Advantages & Disadvantages of Solar-Based Systems
The main advantage of a solar-based systems is going to be cost of ownership over say a 10 year period, as this includes running costs. We'll talk more on running costs below, however since solar-based systems draw the bulk of the heating power from the sun, they are much less extensive to run. Although, utility-based heating systems have greatly reduced running cost if a pool cover is used.
The main disadvantage of solar-based systems over utility-based systems is that they are not an "on-demand" type heating system, namely if the suns not shining over a few days the pool will get cooler.
This disadvantage is partly be offset in a couple of ways, firstly, a pool cover can stop the pool from getting too cool over cloudy, windy and or rainy days when combined with a solar pool heating system.
Secondly, most people don't realize but when the air temperature falls below a certain threshold people simply don't want to get into an outdoor pool no matter how warm the water due to the wind chill factor. It's partly why the Aus Stand doesn't recommend over-sizing a heating system past a certain collector size. A lot of people choose a heat pump or gas heater based on this "on demand" aspect - namely I can warm up the pool and swim whenever I like - technically yes, but keep in mind that fact; not many people want to get in a pool when it's cold and windy out. And when it's warm out, solar pool heating systems work great, even in party cloudy weather there is still significant solar radiation around as long as the roof air temperature is warm.
How well do Solar Pool Heaters Work?
How Much Warmer Will the Pool Be?
So how much warmer can they make your pool? Well this depends on a lot of factors and heat loading computations are quite complex. We've done these calculations as we show in our blog article - How Warm Can a Pool Get With a Solar Heater and Cover.
The table below summarizes various heat loading scenarios for a pool heated using our OKU solar pool heating panels with a total collector area 67% that of the pool's water surface area (termed the coverage) or equivalently equal to approx. 100% coverage of an older style well spaced PVC tube system - used in conjunction with a transparent bubble type pool cover on 100% of the time.
Averaging the temperature boosts over shoulder pool heating months only (not including peak hot summer months) for all Australian capitals we get the following temperature boosts.
Temperature boost from a 67% coverage OKU panel pool heating system using in conjunction with a transparent bubble pool cover on 100% of the time.
In the table: "Shade" means shading on a pool. "Windy/Exposed" or "Clam/Sheltered" specifies the pool is either fully exposed to a windy area or fully sheltered and situated in a wind clam area respectively (two extremes). "Light/DarkWalls" refers to the colour of the pool floor and walls.
So the first column shows the temperature boost if one was to install a solar pool heating system with a pool cover on an unsheltered, wind exposed pool, in a windy area (like a hill or beach front) with 50% shading on the pool. The last column shows the temperature boost for a wind-proofed pool, in a wind sheltered area (like a valley), with dark pool walls and floor, and no shading.
As can be seen you can get temperature boosts anywhere from 5°C to 18°C depending on the heat loading specifics and location. For an average pool you're looking at an average 11-14°C temperature boost depending on location. Remember though these are averages - averaged over night and day, cold and warm spells; most people tend to swim in the afternoons during a warm spell, so during those time, you're going to see larger boosts.
By How Much Will It Extend My Swimming Season?
This depends on the state and the amount of solar collector coverage installed, the largest factor effecting your total season is weather or not you are going to use a solar pool cover, however to give you some idea of typical season swimming month in various states we've produced this table:
* Potentially non-heating months
As a general rule a solar pool heater and pool cover will easily double your season, if you have a specific set of heat loadings on your pool, try our online pool heating running cost calculator to see exactly how much a solar pool heating system can extend your season.
Main Physical Factors Effecting Solar Pool Heaters
Main Physical Factors Influencing How Warm a Pool Is
Things to Consider When Choosing a Solar Heating System
Comparing Solar Pool Heater Collector Efficiencies
Let's have a look at all§ the design factors that actually impact collector efficiency. This will help you see through all the marketing fluff (written by Dr Gregory Grochola - thermodynamics physicist).
§ excluding glazing, back insulation and/or surface emissivity/absorptivity treatments - none of which is practical or economical for a pool heating panel.
And that's it! Forget all the marketing fluff, what you want in terms of efficiency is a collector with good polymer thermal conductance, moderate face thickness (considering durability), no hot spots, fast turbulent water flow and a flat collector face. You can now easily compare other collector designs and see which aspects they have. We estimate that the best collectors are about ~50% more efficient (in the shoulder months) than the worst collector designs, which corresponds to 33.3% less roof space requirements. But keep in mind, efficiency is only one aspect to consider; a low-efficiency collector can easily be as effective as a high-efficiency collector, you just need a larger area.
Comparing Other Pool Heater Collector Design Aspects
Apart from efficiency below is a comprehensive list of things you might like to consider when choosing a solar pool collector type.
Comparing Solar Pool Heating System Design Aspects
So we've compared collector efficiencies and collector design aspects, what about actual system design aspects.
Getting a Cost Estimate
So you've decided on a specific solar pool heating system and now you want a cost estimate, here are the specifics you'll need to consider.
1) Should I DIY or Use a Solar Pool Heating Company/Installer?
Possibly the largest cost consideration is going to be whether or not you DIY or get a pool heating company or installer to quote on an installed system. Due to the seasonal nature of the work this can get very expensive. Depending on system size and the amount of plumbing required you can budget about $1,000- to $3,000 just for labour and installer mark-ups on supplied components (and installers will push their components due to the marks ups they get). So is it worthwhile taking some time for a DIY project? We've seen and heard about a number of overpriced, shoddy, low quality component installs to say absolutely, if you are able to do it safely you should seriously consider DIY. You can source the best quality components from reputable suppliers (here we only sell the best) and you'll have full control over how the system is installed. Make sure a supplier has extensive manuals to guide you and many years of experience to answer any technical questions you may have during installations. You'll end up owning a higher quality more reliable pool heating system for less money sometimes than inferior competing kits AND you'll have better quality install that you'll know how to service.
It's understandable why shoddy installs happen sometime; pool heating installations are seasonal, full-time installers wait around all year then all of a sudden they get bombarded with more jobs requests than they can handle so they feel they can charge an arm and a leg and be picky with their jobs. Companies and installers then need to take on part-time workers that may not be well trained, and they are rushed and under pressure to finish the job fast. If there are complications, installers have no motivation to take their time and do it properly to make sure the system will last as they are not paid by the hour. Most of the shortcuts they may use appear many years down the track typically with no recourse for the consumer.
We've seen competitors use self-tappers or rivets as fixings on metal corrugated roofs as that's the easiest and fastest thing to do. In 5-10 years these superficial metal to metal fixings are likely to corrode drill holes and are likely to pull out in a strong wind storm. The only proper metal roof fixing method that we recommend (as stated in Solar PV Australian Wind Loading Standard) are long roofing screws, sunk deep into battens or rafters. We've seen other companies drill tile perforations for fixings that in time are likely to leak water down the screw onto the batten. We only use non-peforating solar roof hooks as standard tried and tested tile fixings in the PV industry. In terms of other hold down fixings we see some competing products use glass filed plastic fixings which are subject to UV degradation - after 10 years of baking in the hot Australian sun what level of strength will these plastic fixings retain? The only plastic that has a proven long term pedigree in the sun is polyethylene. Our philosophy is that fixings must last the entire life of the system.
An Important Note on Safety
Having said all of that; you should only consider DIY if you're confident of performing the work safely. If you need to get up on a pitched two story roof and you are not 100% confident, best leave it to the professionals, as you should never underestimate the chance of a fall. If you can't DIY try to source a trusted installer - at the very least go with a company with good component and installation quality control standards.
2) Sizing Your Solar Pool Heater - What Kind of Season Extension Should I Aim For
It's important to understand the limitations of solar pool heating, as mentioned above solar pool heating is not an "on demand" system, however if sized higher it can come pretty close to an "on demand" system, by virtue of the fact that it works well when the air temperatures are still warm enough to get in a pool, while almost no level of heat pump or gas heating is sufficient to entice people to get into a pool in windy cool conditions. In the industry we talk about "season extension" months. The Australian Pool Heating Standard recommends about a 3 month extension. What this means is that you'll get the same pool water temperature 1.5 months earlier in the season and 1.5 months later in the season with solar heating. We recommend sizing can range from a minimum of 2 month extension; as some people really just want to swim in the summer months - to a 4 month extension for people that use the pool more frequently or want to swim at night, and hence want that almost "on demand" pool heating experience.
When sizing a new system there are a number of factors to consider. We provide an interactive sizing calculator that takes into consideration almost every imaginable factor, see below. This calculator is based on minimum Australian Standard pool heating sizing and will include weather, solar sunlight hours per postcode, combined with installation specific factors to come up with the best possible sizing for your budget. It gives sizing advice for PVC strips and panels.
Professional Solar Pool Heating Sizing
It's important to factor every aspect affecting a pool's temperature, as some pools can suffer from a number of cumulative cooling factors, for example our calculator instantly assess:
Surface Area of More Complex Pool Shapes
To work out the surface water area of odd shaped pools use the following trick:
3) System Plumbing Options
Next thing to Consider what kind of plumbing system you want to set up. We always recommend Independent Systems, see definitions below. These systems run a small independent pump, typically for 8 hours per day and are actually more energy efficient than systems running through the main filter pump which have to run the large filter pump for 8 hours per day just to pump the solar side. Of course independent systems require separate solar suction and return lines, whereas for older pool these might not have been installed. If that's the case you'll need to go with a plumbing configuration that taps into your existing filter return line to divert water to your roof. There are a few configurations that can be chosen, see below or one of our pool heating manuals. Most people that do not have independent solar suction and return ports will choose a Manual/Timer System and place the main filter pump on a timer to run during the warmest part of the day. These manual systems can be automated down the track. We have three class of listings:
If you need to set up a specialized system like for a Booster/Retro Fit System (requires AquaSmart 5 FS or CD controller) or the Motorized Ball Valve System (requires AquaSmart 5 AV controller), please contact us at EcoOnline.
4) Solar Pool Heater Pump Sizing
If you're considering installing an independent or retro/booster type system you'll need to consider solar pump sizing. If you're purchasing a new pump make sure it's specifically suited for solar pool heating systems, as pool filter pumps are geared differently. In terms of sizing, a grossly oversized pump could not only limit collector lifetimes, but will cost you more in electricity usage (literally thousands of dollars over a systems lifetime!). An undersized pump conversely will limit collector efficiencies and not turn the water over sufficiently, resulting in poor system performance. To help you size a pump, we've written quick table guides in our manuals, but if you really want to optimize your pump power saving you can use our panel system pump sizing calculator or our - PVC strip system pump calculator - these simulate various pump sizing choices and their respective effects on collector efficiencies and energy savings.
5) Get a Cost Estimate of Our DIY EcoOnline Pool Heating Systems
As you can see EcoOnline.com.au has intimately considered all aspect of pool heaters and has chosen to sell particular systems not by accident, but by extensive research into them. We only sell, develop and support the best systems that are excellent value for money. In fact we won't be beaten on the cost of an equivalent system so just ask. We sell two types of pool heating systems: PVC tubes and OKU panels with an extensive history of longevity in the field. Check out more details on these systems by clicking on the linked images below.
Frequently Asked Questions (FAQs) On Solar Pool Heaters
Q. Will a solar pool heating system work in part cloudy conditions?
A. Partly, yes but only if the air temperature is sufficient and there is enough solar isolation. Keep in mind that pool heaters also heat the ground around the pool. Hence a pool will not completely lose heat in one day of cold weather, although it might be substantially cooler, it'll get back to temperature quickly the next day if there is sun. Eventually, it's the overnight cold air loses that make it impractical to keep heating the pool and the season over.
Q. Can I split the collectors and install on two different roof aspects?
A. Collector arrays that face different compass directions are not recommended unless the roof pitch is less than ~15º. What will happen is - depending on the location of the roof sensor the controller will turn the system ON with one bank of collectors in full shade, this can cool the water and be counter-productive.
Q. What size PVC piping do you recommend?
A. For panels, generally we recommend 32mm on the roof, except for larger multiple row arrays with a secondary header pipe feeding multiple rows of panels, for which you should use 40mm. Coming down the roof the pipe size can then be adapted to the pipe size you have for your solar line ground run i.e. 40mm or 50mm. For strips we just recommend 40mm as the manifold connections are 40mm.
Q. Should I paint the PVC pipe black for extra heat absorption.
A. We don't recommend this (unless perhaps on the ground where it will be filled with water constantly) the issue is PVC will soften substantially at 70ºC, hence in summer on really hot days during stagnation on a hot roof we've observed black PVC pipe soften to such an extent that it loses structural integrity and collapses in on itself. The second issue is PVC will expand more when it's black due to larger thermal temperature variations hence care must be taken to ensure long lengths of PVC pipe runs have enough room to expand and contract without putting pressure on right angle connections.
Q. I have a long run from the pool to the roof, do I need a larger pump?
A. Generally no, your pump size will only be determined by the pump height, having said this keep in mind that it's very difficult to determining a pump height level across a long distance. If you have a long pipe run we simply recommend using 50mm PVC to reduce the frictional losses.
Q. I have a long run from the pool to the roof, should I insulate the PVC piping?
A. Generally no for outdoor pools, as the temperature difference between the air and the pool water is small, hence the loss in this pipe will be small. For spa pools and indoor where the water temperature can be substantially different to the air temperature this can be of some benefit, however if the PVC piping is exposed to a north facing aspect and gets sun, then it's sufficient to simply paint the PVC pipe black saving on insulation (note the caveat mentioned above).
Q. What collector plumbing arrangement do you recommend?
A. There are a multiple of different plumbing arrangements available for both the panels and PVC strips systems, too many to mention here, we refer the interested reader to our download section where you can download the manuals and see each configuration.
Q. Do I still need a pool cover if I have solar heating?
A. Yes, we highly recommend solar pool heating systems be combined with a pool cover due to the synergistic effect between the two, see this article for a description.
Q. What if I already have a gas or a heat pump pool heater?
A. Solar systems can naturally be combined with auxiliary heating systems, in fact not only will they lower the cost of heating your pool but they'll extend the life of the auxiliary heater by reducing the load on it.
Q. What kind of maintenance is required?
A. Solar pool heating systems require maintenance from time to time, depending on the system installed, we refer the interested reader to our download section where you can download the manuals and see each configuration.
Q. We live on a hill - can I install a pool heating system below the water level?
A. So this is generally not recommend if the collector system is more than 1m below the water level. This is because panels and tubes will experience constant pressure from the force of the water, this is especially an issue in summer when the system is stagnating in the extreme heat. Such events will act to limit collector lifetimes as polymer longevity is sensitive to pressure and heat. Any breakage in the collector system can also drain the pool potentially flooding lower areas, so this must be considered.
Q. How much do solar pool heating collectors weigh?
A. OKU pool heating panels weigh 6kg empty and and 12kg full. PVC strips weigh 4kg empty per sqm and about 7kg per sqm when full.
Q. How many panels do I need?
A. Please use our interactive sizing calculator to accurately size your panel or strip needs, if you have any difficulty please contact us. Note: we frown upon the practice of selling you more panels than what you actually need for your heating goals - to back our smaller sizing recommendation we provide a panel sizing guarantee.
Q. I was sized a much larger rubber mat system - why is your panel area recommendation smaller?
A. Besides the increased efficiency in cooler weather during critical season extension months - we absolutely frown upon the industry practice of selling you a larger system. The Australian Standard 3634-1989 for sheltered pools only recommends 60% (rubber strip) coverage in southern regions, 50% for mid regions, and 40% for northern regions. Over-sizing a system will result in polymer collectors stagnating at detrimental temperatures of up to 80°C for longer periods during hot days when the controller shuts the system down. As such over-sizing reduces collector lifetimes, requires a larger pump and higher upfront costs – all for diminishing gains in water temperature. If you require higher temperatures beyond our maximum collector recommendation we recommend a solar blanket.
Q. Can I undersize my system and upgrade as needed later?
A. For panels yes, but only to an extent and we don't recommend it. You should not go below our minimum 2 month extension recommendation, see our interactive sizing calculator. No - we are not trying to sell you a larger system. There are very good reasons why a system should not be dramatically undersized. Effective heating requires a minimum daily turnover typically 50% of your pool water volume. However, there are flow limitations on panels; hence an undersized system may not handle the flow required which could over-pressurize panels or if the flow is insufficient, will result in an unmixed stratified layer of warm water which will cool excessively overnight.
For PVC strip, we have to say no, it's difficult to slice in an extra manifold section into the main manifold pipe once it's all glued up; it's best to size your system right the first time.
Q. Can I use my existing controller and mains power pump?
A. You can use your existing controller if it’s in good working order - however pressure pumps that power rubber mat systems are typically too strong for these panels. Over-sizing the pump not only uses more electricity but has the potential to limit panel life times due to large pressure fluctuations in the panels. EcoOnline (and OKU) only recommends typically 0.25HP to 0.5HP pumps for small 8 to 30 panel systems.
Q. Can I use my filter pump and save electricity by not installing a second pump?
A. It is a false economy to use a large filter pump for solar applications – the pump still has to expend energy to pump water to the roof, putting back pressure on the pump reducing filter flow, hence there is no free energy gained. Besides this we don’t recommend running a high power filter pump for 8 hours per day for the solar side (potentially over pressurizing panels) if you don’t need to filter for that long. An independent system with a well matched small pump will save you money in running costs and look after your panels in the long run.
Q. Can I use a low energy usage variable speed pump?
A. No, after witnessing customers try such pumps and struggle with them our advice now is not to use them, unless they can be set to run at a constant speed without a start up surge. We find variable pumps start at full power then taper back, this puts a lot of pressure fluctuations through the panels on start up which could limit panel lifetimes. We only recommend pumps that can pump at a constant set pressure.
Q. I don't have independent solar lines installed on my pool can I tee into my main filter pump suction line?
A. Generally we don't recommend this as you may have priming issues with your main filter pump during start up due to air been drawn in from the solar line tee you installed. Whether your filter pump will deprime in this case will depend on how far below the waterline you installed the solar tee. Note, a non-return on the solar line will not help here as non-returns are not generally air tight over time. If you do not have independent solar lines and can't install the tee far below the water line (minimum say 1m below) then your options are a manual system, a booster system or a motorized ball valve option, see manual for plumbing diagrams.
Q. Do we have installers?
A. At present unfortunately no we do not have installers as we ship around Australia. However, our manuals are very comprehensive and cover most situations and issues. There is also unlimited tech support available. Most handymen/tradespeople can install our systems. From what we hear, solar pool heating installs are very seasonal, hence most specialist pool heating installers are run off their feet during the install season, this means they charge an arm and a leg for poor rushed installs. Our advice is if you can DIY safely or source a trusted installer that will take his/her time, you will save a great deal of money and headaches.
Q. Can I download your comprehensive manual before I purchase?
A. Yes, in fact we highly recommend you check over the manual to get a good idea of installation requirements before you purchase. The manual can freely be downloaded from our EcoOnline download page.
Q. Is this system easy to install for tiles?
A. OKU panel installation on tiles are more difficult and we recommend should only be attempted by experienced DIY or tradespersons. PVC strips are easier to install on tiles. (Please note safety notice when climbing up on a roof.)
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