Solar Hot Water

Solar Hot Water
Solar combi system supplimenting radiant floor and domestic hot water

Thursday, February 17, 2011

Financial Benefits of Solar Thermal

Joe with Wise Improvements Blog (@WiseImprovement) asked me to discuss the financial side to solar thermal from a home or business owner's perspective. I will discuss the ROI and financial incentives associated with solar domestic hot water, solar domestic and radiant floor supplement as well as solar hot air (air collectors).


Each state varies on the incentives offered to home or business owners for installing a renewable energy system. A fantastic source for researching State and Federal renewable energy incentives is the Database of State Incentives for Renewables and Efficiency (Dsire). For example, the State of New Mexico offers a 10% tax credit up to $9,000.00 on residential renewable energy systems. This tax credit is off all expenditures of the system including installation. Dsire can also tell you about incentives offered by your local utility although I would recommend contacting your local utility before purchasing a renewable energy system to fully understand their specific programs.

Solar hot water systems qualify for a 30% tax credit from the Federal Government. The important thing to understand about this tax credit is that it is just that, a tax credit, not a rebate. If a homeowner has no tax liability the credit, unfortunately, is of no use to them. If you are a business the story is different. If a business has no tax liability but installs a solar hot water system on their building they can turn the credit into a rebate by petitioning the U.S. Treasury Dept. for a grant. This tax credit is off all expenditures of the system including installation. I always advise all my customers to consult with their accountant.


The return on investment (ROI) for renewable energy systems varies depending on the technologies. For instance a solar hot water system will pay for itself faster than a PV system in most cases and an air collector system will pay for itself faster than a solar hot water system. There are many factors that go into calculating ROI. Some of those factors would be current energy usage patterns by the building occupants, geographical location and the cost of the equipment and installation. On average a PV system will pay for itself within 12-20 years on average. A solar hot water system averages a payback around the 5-10 year mark for domestic hot water and a little more if radiant floor is incorporated and an air collector (solar space heat) will pay for itself in 3-4 heating seasons. The type of fuel used also needs to be taken into consideration. Someone using propane will see the dividends much quicker than someone using natural gas. The one thing you will notice is that the payback of a system is in direct relation to the general upfront costs associated with the technologies.

There are different ways to calculate ROI of a renewable energy system. Clean Power Finance, PV Watts and Andy Black's OnGrid programs which will calculate ROI on a PV system. To calculate ROI on a solar thermal system the best program I have found is a free program put out by the Canadian Government call RETScreen, which is a free program and can help you calculate ROI on just about any renewable energy system as well as energy efficiency upgrades.


In almost all cases, a permit from a local building department is required to install a renewable energy system and qualify for an incentive. This means that solar thermal equipment must be certified by either the SRCC or a similar state authority. For a PV system the equipment must be UL rated.

If you would like to know more about the different renewable energy systems available to you please visit our main website.



Monday, February 7, 2011

Heat Exchangers!

There are exceptions but 99.9% of solar hot water systems require the use of a heat exchanger.

Heat exchangers are made to transfer heat from a source (solar collectors) to a delivery or storage system (tank). Heat exchangers are classified as liquid to liquid, air to liquid or air to air. Heat exchangers can be designed for cooling or heating, although in the solar industry they are used primarily for heating.Liquid to liquid heat exchangers can be as simple as a coil of tubing submerged in a tank of water. This is called a single wall heat exchanger since only one wall of tubing seperates the two liquids. A double wall heat exchanger is required if the heat is being transferred from a non-potable liquid (glycol) to a potable (drinking water) system. These exchangers are designed so the fluids can never mix.

One example of a double wall heat exchanger would be AAA Solar's Quad Rod heat exchanger. The quad rod is a double wall heat exchanger made completely of copper with brazed fittings. Here are some pictures of a Quad Rod heat exchanger.

3' Quad Rod heat exchanger


A simple way you would use a heat exchanger would be to heat water in an existing water heater. A system for heating an existing water heater would include one 4'x10' collector, a heat exhanger, two pumps and a controller. In this system, a heating fluid (glycol) is circulated through the collector and the heat exchanger with a pump. This can be done with an AC pump that is wired to a controller with sensors at the collector and water heater or is can be done with a DC pump that is wired to a small PV panel. the water from the tank is then circulated through the heat exchanger with a pump as well. The two fluids should be flowing in opposite directions for maximum heat transfer. While the sun heats the glycol and the heated fluid passes through the heat exchanger the heat is transfered to the water that is passing through the heat exchanger at the same time. As the water from the tank circulated the tank is heated and will only "fire" if the solar is not able to keep up with demand.

For more information on heat exchangers and specific products please visit

Thursday, February 3, 2011

Monday, January 31, 2011

Solar Water Heating Market Watch

This is an excerpt from Solar Server's report "Solar industry on track to progressive growth: A review on Intersolar North America 2010".
This was a 7 page report on the state of the solar industry with 6 ¾ pages dedicated solely to PV. As a manufacturer and distributor of solar thermal products it is both disappointing and telling at the same time. It is apparent that solar thermal is definitely the "red headed step child" of the solar industry. This is baffling on so many levels. It also tells me that the solar thermal industry must pull their heads out of the sand and do something about it. I myself am on my way to becoming a crusty, cranky old plumber but this is the 21st Century and it's time to use the technology of the day to spread the word. We must be diligent in this.
Some suggestions:
  • PV is dominating Twitter. I am constantly scanning Twitter for quality solar thermal articles and promotions and every day I am disappointed in what I find. If you are an installer, distributor or manufacturer you must use this tool. It is the best way to get your message to a mass amount of people in a short amount of time. It's not all doom and gloom there are advocates like Tor Valenza (@SolarFred) Issac Heating and Air Conditioning out of New York (@IssacHeating) who are diligently promoting solar thermal but we need more.
  • Blogs are a great way to educate the public and other industry folks as to what is happening in your area and what you are doing to promote your business and technologies. The more we share ideas and the more we talk about it the more we will be heard.
  • Education! Education! Education! This cannot be stressed enough. We recently called 100 local HVAC and plumbing companies in New Mexico to discuss the possibilities of providing them with a series of workshops on solar hot water and solar space heating. The response we got was overwhelming. They were all eager to learn but didn't know where to start. Can you imagine what 100 more installers in one state could do for an industry? The trades are eager they just need a place to learn. Those of us who know should be teaching. We are too young of an industry to worry about market share right now. We need solidarity more than anything.
  • Politics is an area that the thermal industry could provide more focus. When you hear a politician today speak about renewable energy what do you hear them mention? It is, in almost every case, PV and wind. We need to educate our politicians as to the benefits of a solar thermal system so that the next time they give a speech they mention solar hot water or solar heating. Call your local representative and ask for a meeting. You would be surprised at how open they are to listen. In fact I would like to thank State Senator Steve Fischmann from Las Cruces, NM for sitting and having dinner with me and my father to discuss solar heating. It was an eye opening experience for both parties and we now have an advocate in the state senate. Getting to know your local representatives can also help out
Don't get me wrong I whole heatedly believe that PV has a much deserved place in the industry but I think all of us thermal guys need to get together and figure out how to market our product as well as the PV industry has done.

If you read the paragraph from the report it clearly states the major benefits of choosing solar thermal technology yet what is actually being done about it. It costs on average 30% of your utility bill to pay for heating your water. If you can save 70-90% of that 30% for as little as a ¼ of what PV system costs wouldn't you do that? Of course you would, it's a no brainer. I know there are advocates out there we just need to get to know each other and work together to build this industry to the level it belongs.

If you would like to discuss any of the topics mentioned above I would be more than happy to discuss them. You can reach me at the AAA Solar Supply's office at 1(800)243-0311 or email me at I look forward to hearing from you and let's go sell some thermal!

Tuesday, January 25, 2011

Each day is one day closer to pool season!

Each day we get one day closer to pool season! That is the good news. The bad news is you are going to have to heat that pool. How do you heat your pool; electricity, natural gas or the dreaded propane? If you use any of these a solar pool heating system will save you money on those heating costs. When I was younger, and had hair, my family had an outdoor in ground pool that was heated by coal! I didn't really think anything of it at the time other than I hated to fill the boiler from this little storage area under the pool. We've come a long way since then and that was the 90's.
Boilers have definitely become more efficient but to heat the amount of water to fill a pool still take a lot of energy. If you have an outdoor pool, solar energy just makes sense. Why not use the greatest energy source the world has known?
Pool systems offer an inexpensive way to heat your pool during the warmer months and are simple enough in design that many people install the systems themselves. You don't need to know how to sweat pipe or how to wire in a pump (in most cases). It is just a matter of connecting plastic pipe with glue fittings and some simple low voltage wiring.
In most of the country outdoor pools are used six to nine months of the year. Pool collectors are normally made of polypropylene, a high temperature plastic that can consistently operate in the 200°F range.

- The collectors are black in color and should normally keep a pool in the 80°F range throughout the pool season.

- The same pump that filters the pool is used to circulate pool water through the collectors.

A quick rule of thumb for pool design sizing is one square foot of collector surface area to every two square feet of pool surface area. This can give you a good idea of how large a pool system is required. You will need more collector surface area if your pool is left uncovered, especially in the spring and fall. The pool collectors should face within 30° of true south and are tilted at an angle of latitude minus 15° from horizontal. Virtually all of the pool systems we install today use a simple mechanical timer to control the pump.

You simply filter and heat the pool during daylight hours. Outdoor pool systems probably have one of the quickest returns on your investment of any solar energy equipment. In most cases it is simply foolish not to consider heating an outdoor swimming pool with solar energy. 

More information about pool heating can be found in the AAA Solar Supply's catalog which can be downloaded here.

Friday, January 21, 2011

Differential Controls

Differential controls are used in virtually all active systems that use liquid collectors except photovoltaic
powered designs. A differential controller uses an electronic comparator circuit which constantly measurers the output of two thermistors which are called sensors. The sensors change their resistance upon a change in temperature and the controller turns equipment ( normally pumps and blowers) on and off depending on the difference in temperature between the two sensors. This type of control maximizes the efficiency of hot water systems by always transferring energy from the collectors whenever even slight gains are available. Controllers normally turn pumps on when the collector(s) is between 5 and 20 degrees F. above the storage cold water. When the collector temperature falls to between 5 to 10 degrees above the tank cold water temperature the pump turns off. Systems with heat exchangers normally have differentials of about 15 to 20 "on" and 5 to 10 "off ". Direct pump systems have lower differentials since there is no loss through a heat exchanger.

Controllers made today also have a storage high limit of 160 to 180 degrees which is field setable. Many
controls also allow for a thermostat to be connected and also have options for digital readouts of collector and storage temperatures.

Swimming pool differentials have very low turn on and turn off differentials and high limits. Typically a
3 to 5 degree turn on and 1 to 2 degree turn off.


Resistance in K (1000) Ohms
NOTE: Resistance declines as temperature
rises - all new controls use 10 K sensors

TEMP   10K   3K            TEMP   10K   3K
27           39.8   11.9            107       5.0      1.5
32           32.6     9.8            112       4.5      1.4
37           28.3     8.5            117       4.0      1.2
42           24.7     7.4            122       3.6      1.1
47           21.5     6.5            127       3.2      1.0
52           18.9    5.7             132       2.9      0.9
57           16.5    5.0             137       2.6      0.8
62           14.5    4.4             142       2.4      0.7
67           12.8    3.8             147       2.2      0.6
72           11.3    3.4             152       2.0      0.6
77           10.0    3.0             157       1.8      0.5
82             8.8    2.7             162       1.6       —
87             7.9    2.4             167       1.5      0.4
92             7.0    2.1             172       1.4       —
97             6.3    1.9             177       1.2       —
102           5.6    1.7             182       1.1       0.3

Goldline GL-30 Differential Control has become an industry staple due to it's simplicity and reliability and can be purchased HERE.


Monday, January 17, 2011

Batch or Breadbox Solar Water Heaters

Batch water heaters are the simplest of all solar water heaters. These are also known as integral tank and collector heaters. Batch water heaters use tanks between 30-80 gallons. The tank is placed within a weatherproof, insulated enclosure with one side having a transparent or translucent glazing(s), normally two layers of glass. The side of the tank facing the glazing is painted black to absorb the solar energy which is conducted directly to the water in the tank.

Batch solar water heaters work great in the tropics. Due to nightime heat losses we do not reccomend them in climates above approximately 35 degrees latitude. The only thing on one side of the collector between the hot tank and the cold air outside is 2 layers of glass. In climates harsher than this, throughout the winter months the heater tends to lose at night most of the daytime energy gained. Batch water heaters are simple, reliable, easy to install and are tipically low cost. They can provide 50-90% of hot water needs depending on usuage and climate. The piping to and from the heater is the weak link in the chain. It should be well insullated and heat tape should be installed in harsh climates.
Sunbather batch water heater manufactured by AAA Solar Supply, Inc. in Albuquerque, NM ready to be installed. This 40 gallon batch water heater retails for $1,935 and can be purchased by calling 1(800)-245-0311.