Solar Southwest Florida

Last Thursday FPL took applications for the remaining 2012 solar rebate funds. As expected, funding ran out quickly… as in under two minutes!

My employer had quite a few rebate applicants lined up for solar electric systems. I decided before the rebate website went live that I wouldn’t post the results or my reaction in a knee-jerk manner. While I was angry and disappointed, I wasn’t surprised. Now that the dust has settled, I can respond effectively.

We did secure rebates for some of our customers, but any process that rewards rebate applicants for being able to type fast is just silly. I have criticized the process and the program before, but now I am more convinced than ever that it needs revamping. Its not good for consumers or contractors, and it fails to effectively reach the stated goal of increasing adoption of distributed solar energy in Florida.

I’ve recommended a lottery approach in the past, but that is hardly fair either. I truly believe that the only way to fix the program is to significantly reduce the rebate amount (per watt), or the maximum rebate per customer.

Florida has a sad history of overly-generous solar rebates with unintended consequences. The press from these botched programs feeds two beliefs that are severely damaging to the industry:

1. Solar electricity is only viable with a state or utility rebate. While free money certainly helps, the unintended consequence is that few people are willing to go solar, or even contemplate an investment in solar if the handout is not available. With prices so much lower than just a year or two ago, this is no longer the case!

2. Rebates are not guaranteed. This is the sad result of the Florida Legislature’s failure to fully fund an incentive program that was passed into law and was clearly intended to be funded. The FPL rebate is “guaranteed” to the extent that you follow through with some basic obligations, and to its credit the company has been lenient and helpful toward rebate applicants and contractors.

I applaud FPL’s willingness to implement a solar incentive program. I wish they would make it so much better by reducing the rebate amount, allowing more consumers to participate, helping contractors develop a sustainable industry, and maximizing the amount of installed distributed solar energy with the limited availability of rebate funding.

FPL has announced that the remaining 2012 solar rebate funding will be released on May 3, 2012 for solar photovoltaic (electric) and solar water heating systems.

If you want any chance of getting in on the best solar rebate in Florida history, you need to act NOW. Call your favorite solar contractor (hopefully Fafco Solar) and they will walk you through the application process. Because the rebates are highly competitive and the amount available will be very limited, it is likely that the funding will run out in the first 10 minutes. The online application process requires advance planning and detailed information about the system you intend to install.

FPL Solar Rebates can cover over 30% of the cost of a solar electric installation up to $20,000 for residential and $50,000 for commercial systems. Paired with a 30% Federal Tax Credit and the lowest component costs in history, the total installed cost of a solar energy system has never been lower.

Pentair SolarTouch Solar Controller

Pentair has released a new solar pool heating controller called the SolarTouch. This great controller fills a gap between a simple analog solar controller and the Pentair SunTouch pool automation system.

A simple analog solar controller uses a dial and an on-off-auto switch to control the operation of a solar pool heating system. The SunTouch is a digital controller that has advance pool heating control for a pool/spa combination and with multiple heating sources (solar and auxiliary heater). It can also control additional relays for features and lighting and has an optional remote control.

The SolarTouch does everything that the analog controller does except it has precise control with a digital readout. It can also control Pentair’s Variable Speed and Variable Flow IntelliPro pumps. That means you can increase the pump speed when solar pool heating is required and drop the speed back down to normal filtration speed when no solar heating is required or available.

Our first SolarTouch controllers will be installed soon and I will report back with the verdict. I am quite certain that this will become our “go-to” controller, particularly because of the attractive price, digital control, and ability to control a variable speed pump.

Here is the marketing information from Pentair and a SolarTouch Brochure:

Announcing the new SolarTouch™ swimming pool solar controller, which offers full digital control for the most precise, efficient swimming pool heating possible!

Now pool owners can control their pool temperature with the touch of a button. Just set the digital thermostat and SolarTouch will monitor the temperature of the pool water and solar collectors. SolarTouch also integrates with IntelliFlo® and IntelliPro® Variable Speed Pumps, so customers can enjoy unparalleled efficiency, unbeatable digital precision and ease of use. SolarTouch is the smart, easy, efficient way to go solar.

SolarTouch features include:

• Digital calibration of water and solar temperature sensors allow more precise measuring. Temperature control can be set in one degree increments.
• Digital touch controls eliminate the imprecise settings and moving parts of mechanical dials.
• Customers can set their pool temperature and solar temperature differentials with the touch of a button.
• Solar valve automatically drains the solar collectors when the pump shuts off. Durable PTFE seal is maintenance-free for years of dependable service.
• Savings up to $1,500 on your energy bills when you combine SolarTouch with an IntelliFlo® or IntelliPro® Variable Speed Pump.
• LCD display gives sharp, clear readings of air and solar collector temperatures.
• LED indicator lights confirm that SolarTouch automation is working. Service indicator LED indicates when attention is needed.
• Motorized valve actuator is built to last with sturdy steel gears, a highly efficient low-voltage motor, service switch for flow direction and a weatherproof composite enclosure.
• Includes nocturnal cooling and recirculation freeze protection, with filter-pump timer override. 3-year warranty.

There are lots of Spanish tile roofs in Southwest Florida. There are lots of hip roofs and broken up roof surfaces, too. These present some challenges, but as this picture shows, pretty much anything is possible.

With three different panel lengths in two banks of panels, there is complex plumbing, but it gets the job done – the pool is warm!

As inefficient electric pool heat pumps and gas pool heaters are, they have their place in heating Southwest Florida pools. It’s no problem to have both solar pool heat and a heat pump or auxiliary gas heater. In fact, the whole system can be automated with fairly simple controls and automatic valves.

A system of valves and actuators control solar pool heat and a heat pump for a pool/spa combination.

Many thousands of heat pumps are installed in Florida, the result of aggressive advertising campaigns and irresponsible claims by manufacturers about how efficient heat pumps are. The fact of the matter is that heat pumps cost an arm-and-a-leg to operate. Heat pumps are important when the desired temperature is critical to attain and maintain at all times. For example, hotels, condos, and individuals with medical hydrotherapy needs often require a constant and elevated pool temperature. In these cases, the holy grail is a solar pool heater in conjunction with a heat pump.

Because gas prices are relatively high in Florida, the only reasonable application for a gas heater is in situations where raising the pool temperature quickly is required or where swimming is anticipated during cold ambient temperatures. Long-term constant heating with gas heaters is outrageously expensive.

If you choose to have a heat pump or gas heater, or you already have one installed, integrating solar pool heat is easy. An automatic controller can set the solar pool heater as the primary heat source and revert to auxiliary heating. In most cases, a solar pool heater is installed, and the auxiliary heater is only operated on-demand by the homeowner manually switching on the heater. This can be as easy as pushing a button on a controller or even using a remote control to switch on the auxiliary heater.

SunTouch Controller

The AquaLink RS, Aqua Logic, and other high-end pool controllers are very capable at controlling multiple heat sources. If you already have a pool automation system, it is likely that solar pool heat and a heat pump can already be controlled from it. If not, I have been recommending the affordable Pentair SunTouch with the optional Quicktouch II Remote. Once programmed, operating the pool equipment is as simple as pressing buttons on a remote. It can work with any combination of heat sources and can even control your spa and a variable speed pump. In some cases, pool lighting and landscape lighting control can also be integrated.

Fafco Solar installed a solar pool heat system this week at a home that already had a heat pump. Adding a SunTouch controller allowed the homeowner to optimize the operation of their solar pool heater, while providing the option of supplemental heat at the press of a button if desired. This time of year, solar pool heating alone typically gets a covered pool to around 85 degrees. The grandkids were coming in town this week, and he wanted the pool to be 88 degrees. The controller allows the pool to be heated by solar if possible, then switches on the heat pump to get the last couple of degrees needed at a reasonable operating cost.

NOTE: See UPDATE at the bottom of this post.

Southwest Florida is starting to see all Lamar Advertising’s Billboards getting solar panel upgrades. My frustration level with this project is quite high already, first because I believe it was ill-conceived greenwashing, but also because it was poorly implemented. Here is a picture of a billboard in Fort Myers (which thankfully does not host Fafco Solar’s advertisement). Can you spot anything wrong?

Lamar Advertising Solar Billboard in Fort Myers on US41

Lamar used cookie-cutter prefabricated steel racks on their billboards. It would have been far more efficient to install all of these 12 solar panels on a single rack system, purpose-built for the billboard. But that is not the main problem here.

This system was installed by an electrician, whose name I will not mention. Electricians are authorized by Florida Statute to install solar electric systems. That does not make them experts, and here is a prime example. Still looking for the reason that this was done wrong?

A rack mounted solar array at optimal tilt and orientation has all solar panels facing the same direction.

There is only one ideal tilt angle and compass orientation for grid-connected solar photovoltaic systems in Southwest Florida. This tilt angle and orientation will harness the maximum amount of solar energy over the course of a year. Unless there are other cost, aesthetic, or technical reasons for an alternate orientation, solar panels should always be installed in manner that maximizes solar output. All six of the solar arrays are installed with different tilt angles and different compass directions. Although they are generally pointing south, and at a reasonable tilt angle, there is no physical constraint that would cause someone to design the system this way. Plus, it looks terrible.

The optimum tilt and orientation for solar modules can be found using publicly available resources that use a long history of local weather and solar radiation. It’s no secret where to find this information. The National Renewable Energy Labs is the preeminent source used in the U.S. to help solar installers maximize performance under given circumstances.

I would love to give Lamar and the installer the benefit of the doubt, thinking that this would be a test system to see what orientation works out best. After all, each of the six arrays features it’s own microinverter (the now obsolete Enphase D380). It would be easy to monitor each array to determine which produces the most energy over time. However, I can’t imagine this was the intention. I believe it is just a sloppy installation, bordering on complete incompetence.

The lesson: hire a solar professional, preferably someone local.

UPDATE February 29, 2012:

I have been having a lively discussion with Lamar’s Director of Sustainability and Product Research both in the comments below and by email. I am happy to report that the solar panels were askew in the picture above at the time of an upgrade to a digital billboard. It certainly makes sense that more solar capacity is present on this billboard than others, as the electrical draw will by significantly greater. I’m not sure how “sustainable” it is to use an electronic billboard, but it does look great and at least it is powered in part by solar energy.

It’s clear to me now that Lamar does take this project very seriously. After all, just having a Director of Sustainability shows significant commitment. We have a legitimate and passionate disagreement about how the money was spent on this project, and that’s fine with me. My position is borne out of financial reason. His position is that I am being short-sighted.

To be clear, I acknowledge that Lamar is vigorously and sincerely trying to encourage people to use solar energy, and that they are dedicated to a prominent sustainability program. I also appreciate the Director of Sustainability’s passion in defending the program.

There’s no perfect way to spend money to encourage people to “go solar.” Case in point is FPL’s $15.5M per year funding of its solar rebate program. Of this money, $5.6M was allocated to residential solar electric projects in the first round of financing for 2011, resulting in 2.8 megawatts of solar electric capacity (estimated based on the $2/w rebate amount). That’s a much better bang-for-the-buck than Lamar got with it’s spending to encourage solar energy. By the way – the funds for the rebate were exhausted in about 15 minutes after the rebate windows was opened. But, there have been negative consequences of the program. Primarily, the funding strategy limits the number of  ”lucky winners” in a very short window and discourages adoption of solar energy by those that cannot access a rebate because of the perception that solar energy needs rebates to be viable.

I have to ask – how much solar capacity has been installed in Florida as a result of the $2.5M of Federal grant money and $10.0M investment made by Lamar? Unfortunately, unlike the FPL rebate program, Lamar’s advertising campaign does not have people banging down the doors of solar dealers in Florida. I should probably be saying “thank you” for the free advertising, but I still contend that it’s solar done wrong.

Should you do-it-yourself (DIY) for a solar panel installation in Florida? While is is completely permissible and possible to install solar on your home or business, it is not recommended.

I’m a self-taught guy in many disciplines, and I love to do home maintenance myself. Learning new skills is part of who I am. Learning the solar energy trade was not easy. Here are some reasons why you may not want to do-it-yourself:

Solar Electric (PV or Photovoltaic Systems)

1. PV Systems involve dangerous DC voltage and AC voltage electricity. You may be able to wire a ceiling fan or a light. That does not qualify you to perform complex wiring for a solar electric system. Grounding is a special concern for PV systems and can be quite complex.
2. Requirements vary from jurisdiction to jurisdiction. The City of Fort Myers’ and Lee County’s building departments have very different interpretations for some key code sections. Navigating this maze will cause you serious frustration and cost.
3. The larger solar panels popular today are heavy. Working with solar panels on your roof is not an easy task.
4. There is no such thing as a cookie-cutter or plug-and-play solar electric system. Even newly introduced microinverters require careful electrical design considerations. You will need both a structural engineer and an electrical engineer to draw up plans for you.
5. Solar energy systems can be monitored by your dealer, ensuring that you have a second set of eyes on the system to maximize performance and identify problems.

1. Roof mounted solar energy systems usually require roof penetrations. Do you know how to maintain your roof warranty? Who are you going to call if you get a roof leak? Amateur roof attachments are the #1 reason that DIY solar installations fail.
2. The labor to install solar energy systems is a relatively small fraction of the price of a system. This can easily be recouped by a trouble-free installation. The competition in the Southwest Florida market is robust, so dealer prices (and profits) are held to a minimum.
3. Design wind speeds required in Southwest Florida range from 120 mph – 150 mph. Do you know how to ensure proper roof attachments?
4. Solar dealers have relationships with building departments that enable smoother inspections. Knowing the requirements (idiosyncrasies) of particular jurisdictions is very valuable.

If you choose to proceed with a do-it-yourself installation, plan to be mostly on your own. Your local solar dealer can’t compete with online retail pricing, so you are better off getting solar products online for DIY projects (except solar pool heating). That means you are probably going to be on your own. Make sure you understand the job ahead of you fully, because dealers are hesitant to work with equipment purchased from another source. These products are often incompatible with the dealer’s typical brands, and specialized knowledge in the product may not be readily available locally. And assisting with DIY projects may open a solar dealer up to liability risk they are not willing to take on.

It’s not that your local solar dealer doesn’t want to help you with a DIY project. It’s just not cost feasible. If I could stock solar panels and sell them to you for a DIY project at a price you would find acceptable, I certainly would!

I obviously have a dog in the hunt here. I want you to use Fafco Solar for all of your solar needs. With the labor being a relatively small fraction of the cost to install solar, you are honestly best off leaving it to the professionals. It’s not rocket science, but you will save yourself a lot of headaches, and probably money in the long run.

A couple of years ago we had a thriving Florida state incentive program that paid $4 per watt to buyers of solar electric systems in the form of a rebate. At the time, that covered between 40% and 50% of the cost to install solar electric for your home or business. Two things happened with the rebate program: the incentive was shut down due to lack of funding/desire by legislators to spend taxpayer money, and the existing rebate applicants were hung out to dry, many collecting only 52 cents on the dollar. That was the end of state rebates for Florida property owners.

So why should you buy solar electric now in Florida without a state rebate?

Fast forward two years to the beginning of 2012. The bottom dropped out of the Photovoltaic panel market, with wholesale prices dropping by over 75%. This resulted in almost a $4 per watt decrease in wholesale price for a big part of the cost to install solar electric. Other fixed and variable costs remained the same or decreased slightly. Today, solar electric systems are sold for almost $4 less at the retail level.

In short, if you were lucky enough to get the state rebate, you would have paid about the same two years ago with a state rebate as you will pay today without a state rebate. If you had purchased two years ago and not received all of your rebate money like thousands of Floridians, you would be better off buying today to the tune of $2 per watt. That’s about $10,000 on a typical household system!

The point is that now there is no risk of failed rebate programs and legislative nonsense. Prices today are lower at regular retail rates, and you are no worse off than someone who purchased a couple of years ago with a promise of a fat rebate from the State of Florida that never came through.

So the next time someone asks me, “what incentives are available,” I can respond that they are no longer necessary to make solar energy economically viable!

The best way to control a solar pool heat system is with an automatic controller. If you do not have one, you are missing out on great convenience, and not maximizing your solar pool heating investment. Most people who do not have a controller just leave their solar pool heating system all the time. That means any time the pump is running, water is flowing through the solar panels.

Unfortunately, solar panels can also act like a radiator, giving pool heat back to the atmosphere. On very cloudy days or during rain, you may actually be cooling your pool if you solar pool heater is running. Usually this is not a huge problem, but it is definitely less than optimal.

One thing you can do is set your pump timer with ideal times to run the pump when you are most likely to get good performance from your solar panels. If your panels are mounted on the south roof, 10:00 am – 2:00 pm are the prime hours, and you pump should be run during this time. If your panels are mounted on the east roof, you will want to start you pump a bit earlier, and definitely don’t run it too late. The biggest mistake I see is when panels are mounted on a southwest or west roof, and the homeowner has the pump set to start at 8:00 am. On a cool morning with no sun hitting the panels, some cooling is highly likely. I recommend no earlier than 10:00 am for a pump start time, but the stop time depends on the time of year.

The best thing to do is observe your panels and make sure you pump is running when the sun is hitting them. Shading and time of day are important to evaluate.

Again, an automatic controller is your best option for controlling your solar pool heat, but if you aren’t willing to make that investment, take some simple steps to maximize your system’s performance!

My New FPL Smart Meter

FPL is in full swing installing Smart Meters around Southwest Florida.I had mine installed last week, but the communications network is a work in progress, so there’s no benefit to me yet. Despite all of the complaints and fears about Smart Meters, I believe the benefits will be great, allowing a granular look at your energy consumption down to your hourly usage, all available from FPL’s website. It’s not as good as some of the energy monitors on the market that can give you a per-second look at your consumption, or even monitor individual appliances or circuits, but it will provide significant insight into your electricity usage.

Some claim that the meters are bad for our health, are inaccurate, or disorient bees. Seriously!

I’m not going to make a call whether some of the claims out there are accurate, but I can tell you one thing for certain – understanding your energy consumption by learning when you use energy is key to reducing your utility bills. As my father-in-law says, “just like a business, you can’t manage energy without an accounting system.”

Unfortunately, those with solar electric systems that are under a netmetering agreement will not get the new smart meters. It is unclear whether the meters are bi-directional, or whether FPL or the manufacturer just hasn’t tested the accuracy measuring energy fed back to the grid. I’m trying to get clarification on that matter from FPL and will let you know if I hear back from their netmetering department.

Here’s a video from FPL about the new Smart Meters:

FAFCO Collector Layout Strategies

It has long been the basis of solar pool heat design to have an opposite end feed and return. In fact, it’s published in several books and manuals about solar pool heating. This is not the case with FAFCO solar pool heating panels, which can be installed with same side feed and return!

Opposite end feed and return simply means that the plumbing that brings up to the solar panels and connects to the lower header is connected at the opposite end of the bank of solar panels from where the plumbing connects to the return line to the pool. Conceptually, this is done to ensure that all solar panels get filled with water and the flow rate is even throughout the bank of panels.

The FAFCO system is a bit different, mainly because FAFCO’s panels have a 2 inch header, 78% more volume than the competition’s 1-1/2″ header, and a subheader that helps to balance the flow among all panels in a solar array/bank. This ensures that all panels have the same flow rate.

It is important to note that you cannot exceed 12 panels in a row with same side feed and return (see Figure 4). Also, split feed and multi-bank systems with varying heights must use opposite end feed and return lines (see Figure 5). The FAFCO manual is very clear about the layouts that are permitted.

Same Side Feed Return Example for Solar Pool Heat Plumbing

SunTouch Controller Installation

I finally got around to installing my Pentair SunTouch Solar Controller at my Fort Myers home. I don’t have solar pool heat (yet), so I have been procrastinating. Why install a SunTouch without a solar pool heating system? Because it does so much more than just control a solar valve!

The SunTouch is made to work with an actuator to automatically turn solar pool heating on and off based on the desired temperature and the available heat on the roof.

Here are several great reasons to install a SunTouch Controller:

• It’s a great compliment to my Pentair Variable Speed Pump (VS-3050). The SunTouch takes over the control of the pump functions and speeds, allowing you to program various speeds for things like water features, automatic cleaners, solar, and auxiliary heaters.
• It will control a heat pump or gas heater with or without solar pool heat. I happen to have a heat pump (I know, not good, but it came with the house).
• I can control my landscape lighting (LED, of course) with one of the auxiliary relays and put the transformer on a timer.
• I can control the pool lights and program run times.
• With the QuickTouch remote, I can activate features from the handy remote control. While I have the landscape lighting and pool lights on programmed schedules, I can manually turn them on from the remote. I can also manually force the pump on at various speeds.

QuickTouch Remote and Receiver

Because my pool and landscape lighting were on the same circuit, and because I still have old energy-hog incandescent pool lights (2 x 300W), I am excited to be able to run the landscape lighting independently now. For added security, and because they use virtually no energy, I set my landscape lights to run all night – something I wasn’t able to afford with the pool lights. One day I’ll spring for the LED pool light upgrade.

I set out to do this project yesterday and it took a little longer than expected with all of the auxiliary features I wanted to control. I also had to rewire the lighting transformers because the pool and landscape lighting were on the same circuit. I went ahead and installed the water and solar sensors so I’ll be ready to go when I add solar pool heat this spring. Finally, I took the opportunity to wire a GFCI outlet next to the SunTouch for extra convenience when running my electric trimmer.

The initial programming of the SunTouch is a bit complex, but fortunately my experience at Fafco Solar had me prepared for this challenge. The menu operation is not very intuitive, but once you understand it the button functions, it all makes sense. The SunTouch documentation on the variable speed pump programming is a bit confusing, but once you read the pump manual itself, it all comes together. I was able to easily configure my remote control to control my pump and lights. The QuickTouch remote connection is also

I didn’t connect the heat pump relay, partly because I ran out of time, but after thinking about it I would rather not have it on a controller. I want to feel the pain every time I manually turn it on, and remember how much that thing costs to run! I can see the benefit of connecting it for people who have pool/spa combinations to fully automate spa heating.

Overall, I am very impressed with the system, and I look forward to installing my solar pool heating system soon!

My Pool Equipment with SunTouch Solar Controller Installed

When you’ve got it all, things can get pretty complicated. Solar pool heat plumbing with a heat pump and a spa can result in a spaghetti factory of plumbing at your pool equipment. Pictured below is an Estero, FL system containing:

• Solar Pool Heat
• Auxiliary Electric Heat Pump
• Pool and Spa with Blower Combination
• Cartridge Filter
• Pool Drain Valve
• Aqualink automatic controller
• Landscape lighting

Complex Solar Pool Heat Plumbing

The good news is that the automatic controller does just about everything you can expect to control the pool and spa heating automatically. The only user intervention required is to set desired temperatures and priorities for heating sources. The owner may also want to manually adjust the spill-over waterfall from the spa to the pool.

Note: Fafco Solar added the solar pool heat to the existing system installed by others and connected the solar pool heat to the Aqualink controller.

What does the Acronym PV stand for?

PV = Photovoltaic

a.k.a Solar Electric Panel, Solar Photovoltaic Panel

PV is the term used in the solar industry to shorten the tongue-twisting word Photovoltaic, which describes a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect (Photovoltaics, 2012). The photovoltaic effect is how electricity (voltage and current) is generated from light. The term is often used in the context of PV Panels, PV Modules, or PV Systems.

PV Panels

References

“Photovoltaics.” Wikipedia, The Free Encyclopedia. Wikimedia Foundation, Inc. 12 Jan 2012. Web. 22 Jan 2012.

Solar water heating systems obviously heat water only during the day when solar radiation is hitting the solar collector. You might realize why it is important for Solar Water Heating Systems to store water, but to what extent should this be considered?

Source: Fairey, P., & Parker, D. (2004). A review of hot water draw profiles used in performance analysis of residential domestic hot water systems. Florida Solar Energy Center. Retrieved from http://www.fsec.ucf.edu/en/publications/pdf/FSEC-RR-56-04.pdf

In North America, most hot water is consumed in the morning, presumably for personal hygiene. The second most water is consumed in the evening, as people clean the kitchen and prepare for bed. This creates a scenario where hot water is required at times when the most energy is not available. Much of the water stored in a tank may be exhausted in the evening with no solar resource available to heat water for the morning requirements!

The solution to this is to provide adequate storage of hot water so that there is enough solar heated water available when needed. On the other hand, providing too much storage becomes economically unreasonable, and in many homes, is impractical because of the space available. Here in Southwest Florida, water tanks are typically in a small closet or garage where storage space is at a premium.

The rule of thumb given to us by the National Renewable Energy Labs for solar water heating systems in residences is to provide at least 1.5 gallons of storage for each square foot of solar collector area (Urban, 2011). (Note: this applies to typical glass-copper flat plate collectors, not polymer collectors like the Fafco Revolution system). A typical 40 square foot solar collector would require a minimum 60 gallon tank. An 80 gallon tank is generally recommended.

However, this analysis is based on averages, and your water usage may not be average! For example, we have a lot of retirees in Florida who like to play golf in the morning and shower when returning from the course in the mid-day. Meals are often eaten earlier than in working families. Some families only shower in the mornings or evenings and some families do not cook often. The point is, if yours does not fit the typical or average U.S. household, your hot water demand might be vastly different and should be discussed with your solar dealer prior to installing a solar water heating system.

Possibly even more complex is hot water storage for commercial applications. Restaurants, offices, and hotels all have vastly different water heating needs. For example, in a recent study, “Monitoring And Modeling Hot Water Consumption In Hotels For Solar Thermal Water Heating System Optimization,” (Urban, 2011) it was determined that the optimum storage capacity for hotels was between 1/2 and 8 gallons of storage per square foot of collector area. Four gallons would be a good rule of thumb, but the author cautions that an analysis should be done on a case by case basis. Unfortunately, a full demand analysis is typically economically impractical, and estimating by solar professionals is the norm.

Typical Solar Water Heating Collector, 40 sq ft.

In addition to these factors, decisions need to be made whether to provide a dedicated solar storage tank that preheats water, or simply heat the lower half of an existing or new electric water tank. This is particularly the case in residential applications. Usually an adequately sized tank can be retrofit with a solar panel, and the bottom electric element is disconnected. The top electric element remains connected to provide a backup to the solar heated water. In the case of a dual tank configuration, both elements remain connected on the electric water tank, but the incoming preheated water from the solar tank results in greatly reduced electric heating costs.

Ideally a demand analysis would be performed on a case-by-case basis, but the cost of such an analysis would unreasonably reduce the savings and increase the payback period for solar water heating systems, especially in residential situations. As solar professionals, we are required to make judgment calls after making assumptions about and listening to our customers. Using generally accepted rules-of-thumb, we can supply economical systems that are sure to save homeowners significantly on water heating costs.

References

Urban, Eric J. “MONITORING AND MODELING HOT WATER CONSUMPTION IN HOTELS FOR SOLAR THERMAL WATER HEATING SYSTEM OPTIMIZATION.” (2011): 28+. Web.