Zero Carbon Swimming Pool

Go Zero – Save Money

To Stop Climate Change – Start at Home

Written by someone who has done it: David Green, author of Zero Carbon Home

Swimming pool owners can save about $1,000 a year by cutting their pool’s carbon footprint to zero. Zero Carbon Pool is the roadmap for how to make money by cutting your swimming  pool’s carbon footprint to zero.

Swimming pool’s are great. They are almost the definition of carefree summer fun. But they are expensive to run and they generate a high carbon footprint. 

Our son Jack, then 7, diving in our swimming pool.

Here is how much money we saved and how much carbon dioxide emissions we cut out:

And here is how much money we saved, how much carbon dioxide we cut out and the investment and financial returns from each action we took on our larger than average swimming pool (see below for what you could expect on an average pool):

And here is about what you could expect on a standard-sized (20′ by 40′) in-ground swimming pool:

Author David Green’s new book, Zero Carbon Pool, is the roadmap for how to make money by drastically cutting a swimming pool’s carbon footprint. By installing the “pool fab four” – a heat pump, a variable-speed circulating pump, an electric powered vacuum-cleaner, and a few solar panels for his own swimming pool in Dover, Massachusetts, he has cut the carbon dioxide gas emissions from his pool to zero or by about 9 tons a year. This is about four times the amount of carbon dioxide emissions you would save by swapping your gasoline-powered car for an electric vehicle.

The even better news is that he is saving about $3,000 a year on propane and electricity bills. His return on investment is over 40% per year. This handily beats the 9.8% annual return on the S&P500 over the last 90 years. And that’s without its stomach-churning volatility. Zero Carbon Pool can be ordered by clicking here

That return on investment also beats the return on investment he is making by going zero on his house, which is about 15% per year. If you are interested in making money by cutting the carbon footprint of their home should see his book, Zero Carbon Home which you can read about by clicking here

To stop climate change, start at home. Start with Zero Carbon Home or Zero Carbon Pool.

Please note that the Green family is saving about $3,000 a year but their swimming pool is larger than average. Savings on a typical 20’ by 40’ pool in New England would likely be about $1,000 a year. 

Who Is David Green?

I am a physicist by training so I have a solid understanding of technologies like solar panels, heat pumps, and pool-water circulating pumps. I also have an MBA from Harvard Business School and spent 20 years as President or CEO of private and public companies. So I also understand how to use discounted cash flow analysis (the standard way companies analyze investments) to make financial calculations like internal rate of return (IRR, a measure of return on investment) and payback period (how long it takes to get your investment back). I keep detailed records of my pool’s propane and electricity use in order to measure the effect of each improvement we made to our pool. My results are based on my own experience rather than generalized claims made by manufacturers or installers.

How Did We Make Money and Go Zero on our Pool?

In going zero, I only took measures that made financial sense, i.e., upgrades that paid for themselves with the savings on heating and electricity bills. This excluded doing many things typically done in deep-energy retrofits for swimming pools:

  • I replaced my old fixed-speed pool-water circulating pump with a variable-speed pool-water circulating pump and set its speed to the lowest setting needed to circulate all the pool water once each day, the rate of exchange required to keep the water clean. This reduced the pump speed from 3,450 rpm for about 12 hours a day to about 2,000 rpm for 24 hours per day. The laws of physics state that the electricity used by a pump goes up as the cube of the rpm, so slowing the pump down more than compensates for the doubling of the time that the pump is on. This effect is so powerful that it cut the electricity used to circulate the water by 87%, saving us over $2,000 a year. The new pump paid for itself in the first year with a return on investment of 100% a year. I wish I could invest my 401k in pool pumps! Our pool pump was made by Pentair™.
  • I installed an electric-powered Dolphin™ pool vacuum/cleaner to replace the old pump-driven pool vacuum cleaner. This is safe because it is connected to a GFCI (ground-fault circuit interrupter) electrical socket and because we take it out of the pool and disconnect it whenever anyone is in the water. This alone saved us about 2,000 kilowatt-hours of electricity per year or over $400 worth. It pays for itself in about 3 years with a return on investment of 55% per year. This keeps the pool cleaner too, which eliminates the dreaded summer rite of scrubbing algae off the walls of the pool.
  • We use the pool only in summer, so an air-source heat pump pool heater is ideal because in summer the air is warm, making the job of the heat pump, which is to move heat from the air to the water, easy. My pool heat pump is about four to six times as efficient as my old propane-fired heater. If you use the electricity to run a heat pump, then heating with a heat pump is also less expensive than propane for the same amount of heat. For instance, in MA, heating with propane costs about 11c per kilowatt-hour of heat. But heating with utility electricity running a heat pump cost about 6 cents for the same amount of heat. Heating with electricity from your own rooftop solar panels costs less than 2c for the same amount of heat. We installed a single heat pump, one designed especially for pools, at a total installed cost of $6,000. The savings on the propane bills, after accounting for the extra electricity the heat pump uses, will pay for the heat pump in about 16 years. That’s a return on investment of about 4% per year after tax. Our heat pump was made by AquaCal.
  • I did not add a pool bubble blanket to insulate the pool. This is because with the heat pump and solar panels, the cost of heating our pool is very low, just over $100 a year. This is using the highest measure of the cost of electricity from my solar panels (7 cents per kilowatt-hour) which was calculated as the total installed cost of the panels divided by the guaranteed electricity output of the panels. The running cost of my solar panels is zero. Including the storage rack, a pool bubble blanket for our pool would cost about $1,000 and might last ten years (the warranty is eight years) for an annual cost of about $100 a year. Spending $100 a year on a pool blanket to save a small fraction of $100 a year in heating costs makes no sense. We didn’t like the idea of having a large piece of rolled up bubble-wrap in the garden either.
  • We did not use a pool chemical blanket either. Pool chemical blankets are liquids, usually alcohols, you pour into the pool that create a thin layer on the surface that reduces evaporation (and heat loss) from the pool. Over four weeks in the summer of 2017 I did experiments with and without a pool chemical blanket. I found that they do reduce the loss in temperature of the pool overnight by about 1°F (the pool naturally loses about 2-3°F overnight) but they cost about $50 a week. I can replace that lost heat with my heat pump and solar panels at about a third of that cost and with none of that inconvenience.
  • I opted not to install solar hot-water panels because solar electric (photovoltaic or P.V.) panels powering a heat-pump water heater are more cost effective. Plus, the net-metering agreement with our utility allows us to accumulate a credit for excess electricity generated on sunny days so we can use that electricity on cloudy days. With solar hot-water panels you are out of luck getting warm water on cloudy days and you cannot store the excess from sunny days.

Instead of installing solar panels only to power your swimming pool, you are better off installing solar panels for your house and installing a few extra to power your pool. Instead of installing solar hot-water panels, I covered the roof of my house with a 15kW array of 46 Sunpower 345W panels and covered the roof of my garage with a 13kW array of 40 Sunpower 327W panels. That is a lot of solar panels, but I make money on every solar panel. Solar panels are cheaper than they have ever been and are heavily subsidized. My total investment in solar panels (for our house and pool), after the tax breaks and subsidies, was about $42,000. My savings are over $5,500 per year on electricity bills. My investment in solar PV panels produces power at about 7 cents per kilowatt-hour (after tax breaks and subsidies). That’s about one-third of what I would have paid my electric utility company here in Massachusetts, which is now 23 cents per kilowatt-hour. The solar panels will pay for themselves in about 7 years. But the most important economic measurement is the internal rate of return (IRR): 13% per year after taxes.

My overall investment (after tax breaks and subsidies on the solar panels) for the entire zero-energy retrofit of my pool was about $10,000 and I am saving about $3,000 a year on propane and electricity bills. The investments pay for themselves in just over 3 years and the IRR is about 44% after tax. That handsomely beats the growth of the Standard & Poor’s 500 stock index of 11.7% over the last 43 years. It also beats the return on investment we achieved by going zero on our house, which was about 15% per year. Additionally, the S&P return is before tax and before fees whereas my return is after tax and with no fees. My return will also increase with inflation, something that can not be said of investing in bonds. Finally, financial markets are risky especially when seeking the highest returns. The risk associated with energy efficiency improvements and solar are usually nil.

Much as I found with going zero on our house, the conventional wisdom on going zero on a pool was often wrong and did not make financial sense. I found that using the standard financial evaluation process used by companies and investors together with some simple experiments cut through the myths. So I think I’ve found a way to both go zero and make money. This represents an inflection point for the zero energy movement. Going zero is no longer like buying an expensive lifestyle statement for your house or pool. It’s cold, hard cash in your pocket, proving you can save money and save the planet!

Zero Carbon Pool can be ordered by clicking here

David Green lives and works in Dover, Massachusetts.