Solar water heating, an example of solar thermal technology, has become increasingly popular with Hawaii's homeowners. Using the sun to heat water is efficient, saves money, and reduces pollution. There are over 65,000 solar water heaters in use in Hawaii today, including thousands on the Big Island. In fact, Hawaii ranks number one in the nation when it comes to using energy from the sun to heat water. It's a great way to use the sun's energy!

Diversifying the State of Hawaii's mix of energy resources by using more renewable energy, such as solar, helps to make Hawaii less dependent on non-renewable energy sources.

	What's hot, What's not about solar water heating?
	How solar water heating works
	Saving with solar
	Environmental Benefits
	Utility Rebates
	Maintenance
	Is your solar heater functioning properly?
	What if the system leaks or the collector glass gets broken?
	Vacations and Extended Absences
	Solar Water Heating – Pools

What's hot, What's not about solar water heating?

+ Positive       

	+ Saves on your electric bill
	+ $1,000 utility rebate available for qualifying systems
	+ 35% Hawaii State tax credit available through June, 2003 (subject to individual qualification)
	+ Estimated minimum system life is 15 years with proper operation and maintenance
	+ Highest potential savings over life of system, compared to other efficient water heating technologies
	+ Hawaii is a prime location for solar water heating - over 65,000 solar water heating systems in use in Hawaii
	+ Proven technology, reliable with low maintenance requirements
	+ Good for the environment - approx. 227 gallons of oil saved annually per system

- Negative       

	- High initial investment cost
	- Minor annual maintenance
	- Collectors must be placed in an un-shaded location, often on rooftops
	- Reduced efficiency during inclement weather
	- Roof-top installations usually require roof penetrations
	- Collectors may need to be temporarily removed for roof maintenance such as painting or re-roofing

How solar water heating works

Sunlight is absorbed by one or more solar collectors, which transfer the absorbed solar heat to water circulated through the collector(s). For homes in the Northern Hemisphere, the collectors are usually located on a south-facing roof.. The heated water is then stored for use throughout the day and night in a hot water storage tank.

There are two basic kinds of solar water heaters:

1. Active (forced circulation) systems that use pumps to circulate the water, and
2. Passive (thermosiphon) systems that rely on natural convection for water circulation.

Solar water heating collectors for an “active” system located on a residential rooftop in Hilo, Hawaii.

An active system (forced circulation) uses an electrical pump to circulate water between the solar collectors and the storage tank. The pump may be either a 120V AC pump or a DC pump. An AC pump is plugged into regular house current and relies on temperature sensors and a differential controller to turn the pump on and off. The sensors indicate whether the water in the collector is sufficiently hotter than the water at the bottom of the storage tank. If it is, the differential controller turns the pump on. Water will then circulate through the system with the hot water in the collectors flowing to the storage tank and being replaced by colder water; then the pump will automatically turn off while the water in the collector heats again. The pump will cycle on and off repeatedly during the day, depending on the amount of heat generated by the sun.

A DC pump gets its power from a small photovoltaic (PV) panel usually mounted on the roof next to the solar collectors. At the same time electricity is being generated to power the pump, sunlight is shining on the solar collectors heating water. When the sunlight is bright enough to generate electricity and power the pump, it is usually also hot enough to heat water. This synchronous use of the sunlight ensures that when the water in the collector is hot, electricity is generated to pump the hot water to the storage tank. The more sunlight received, the faster the water heats and the faster the pump works.

A “passive” solar water heating system with the storage tank mounted above the collectors providing hot water for a Hilo residence.

A passive (thermosiphon) system relies on natural convection to circulate the hot water. Hot water naturally rises so no mechanical pump (AC or DC) or access to electricity for a pump is needed. It is essential, however, that in a passive system the storage tank be higher than the collectors. As long as the sun shines, water in the collector will heat and move slowly upward into the tank with the colder water descending to replace it. As the storage tank is usually mounted horizontally above the collectors on the roof, the added weight is a consideration. In the County of Hawaii, the system (structural) design must be approved by a State of Hawaii licensed structural engineer.

Saving with solar

On average, a large part of the electric bill in an all-electric household goes towards heating water. This means that every drop of water that you heat with the sun's energy will save you money by reducing your electric bill.

Solar water heating may save about $6 to $12 or more per person per month when replacing a standard electric resistance water heater. Savings will vary by household based in part on each person's hot water usage.

Using solar water heating can help keep electric rates down by reducing electricity demand during the peak evening times from 5 p.m. to 9 p.m. (when people often use hot water for washing dishes, taking showers, and so forth). To meet this evening peak demand, less efficient electricity generation units must be brought on-line. These less efficient units cost more to run. If we work together to reduce the demand for electricity during this most expensive time of day, it can help keep costs down and save customers money.

The length of time required to recoup your original investment (payback) will vary widely and depends on whether the purchase is paid for outright or financed and how much energy (electricity, gas, etc.) is saved. Simple payback is the length of time required to recover your investment through reduced or avoided costs. You can expect a shorter payback in areas that have higher energy costs, where the family uses a moderate to large amount of hot water per person, and for homes with more occupants. Finance charges will lengthen the payback period.

In determining the payback of a solar water heater, think in "net" terms. "Net cost" refers to the gross system cost less any tax credit(s) and utility rebate deductions. Divide the net cost by the annual savings on your electric bill to calculate the payback in years.

Example*:	Gross Cost	$4500
	Utility Rebate	-$1000
	Subtotal	$3500
	Tax Credit (35%)	-$1225
	Net Cost	$2275

**Annual savings based on a family of 4 saving $12 per person per month.	(4 x $12 x 12 mo. = $576)
***Annual savings based on a family of 4 saving $6 per person per month.	(4 x $6 x 12 mo. = $288)

Following the payback period, savings continue for the life of the system which may be 10 to 15 years or more depending on how well the system is maintained. Solar water heating can provide a great return on your investment!

*Values are estimates only. Your actual savings and payback may vary. State tax credits and utility rebate program are subject to individual qualification and availability.

Benefits of Purchasing Solar with Your New Home

There are additional benefits when the cost of a solar water heating system is included in the mortgage for a home purchase. The interest rates are usually lower than on a short-term loan. In addition, the small additional increase in the monthly mortgage payment may be more than made up for in reduced energy costs (electricity or gas).

Environmental Benefits

Not only can solar water heating save you money each month on your electric bill, it is also good for our environment. At the rate of 227 gallons (5.4 barrels) of oil saved per installed solar water heating system per year, approximately 113,400 gallons of oil were saved on the Big Island in year 2001 alone! Over a 15-year minimum system life span, these Big Island solar water heating systems will save over 1.7 million gallons of oil and prevent the release of over 26,000 tons of carbon dioxide. The environmental savings will grow as more systems are installed.

Utility Rebates

Hawaiian Electric Company (HECO), Maui Electric Company (MECO), and Hawaii Electric Light Company (HELCO) offer varying rebates (co-payments) to residential and commercial customers who install program approved solar water heating systems to help their customers use energy efficient technologies. As of May 2002, HELCO and MECO’s rebate for approved solar water heating systems is $1000 for both new and existing construction, while HECO’s is $750. For more information visit www.heco.com. These rebates are subject to change without notice.

Maintenance

Suggested Maintenance Schedule

Ask your solar contractor for a maintenance schedule and advice when your system is first installed; the following suggestions are general guidelines. For more complex maintenance issues, most solar professionals offer routine maintenance services at reasonable fees.

Annually

1. Check your solar system visually, especially the equipment, such as the collectors, which are always exposed to the elements. Confirm that the sensor is still weather-tight (if you have an active system with an AC pump).
2. Look for evidence of leaks.
3. Examine the pressure-relief valve and air vent (if installed) on the pipes exiting the collector to ensure that they’re not corroded or leaking.
4. Remove dirt on the collector glass. It can be rinsed off or cleaned off with a mild soap-and-water solution. It’s best to do this when the glass is cool, on a cloudy day or early in the morning.
5. Examine the pipe insulation. It will break down when exposed to ultraviolet radiation (direct sunlight). It can be painted or otherwise covered with an ultraviolet-resistant seal. Repaint or reseal as necessary.
6. Be aware of the pump’s operation in a forced-circulation system. If it cycles off and on during a normal day and you have plenty of hot water, it’s unlikely that you have a problem. The pump should not normally operate at night.
7. Check the mounting structure supporting the collectors. Metal should be solid and not corroded. There should be clearance between the collectors and the roof; make sure no leaves or other debris are trapped (which can contribute to rot or corrosion).
8. The roofing penetrations - where the mounting structure is fastened to your roof system - should be watertight. A roofing compound (or “tar”) can be added at the point of penetration to renew the seal, and is easy to apply with a caulking gun.
9. It’s a good idea to flush your storage tank semi-annually. See your owners’ manual for details.

Every 5 years

Replace the anode rod.
Most water heater tanks are fitted with an anode rod. This magnesium rod dissolves to protect the tank from corrosion. The anode rod needs to be periodically replaced to continue effective protection.

The standard industry recommendation is to replace your anode rod every 4-6 years. If the tank temperature runs between 130°F and 160°F, you may want to replace it every 3-5 years. See your plumber or solar installer for these repairs. Because the hexagonal head of the rod is sometimes beneath the exterior shell of the tank, and because an impact wrench may be required to move it, this job is not easy for the average do-it-yourselfer. Anode rods may be purchased from solar supply or plumbing stores.

Used Anode Rod – showing effects of protective action

New Anode Rod – segmented type for ease of replacement

Is your solar heater working?

A properly functioning solar water heating system will heat water during the day and store the heated water in the tank for use both during the day and night. During periods of sunny weather, a properly sized and functioning system should provide hot water to meet normal hot water demands. During periods of excessively cloudy weather or above normal demands, hot water may be provided by an electric or gas (propane) backup. Of course, always be aware of your hot water use and stop any leaks promptly. Incorporating water conservation measures such as modern (2.5 gallons per minute or less) showerheads will ensure that your solar-heated water isn't wasted.

How do you know if your system isn't working? Here are some signs: a significant loss of hot water during the night (some minor standby heat loss is expected); the running of an active system circulation pump during the night or the constant running of the pump; no hot water produced either on sunny days by the solar system or on cloudy days by the backup heater; and water that is either too hot or too cold.

If your system is malfunctioning, it is recommended that you contact the system's installer, a local solar water heating contractor, or a plumber familiar with solar water heating systems. Most water heater tanks are warranted for a period of 5 years and most solar water heating collectors (panels) for 10 years.

Installing a temperature gauge to the storage tank is a good way to get daily information about how your system is operating. The systems installed through HELCO's solar water heating program include a temperature gauge as a standard feature.

If thermometers are also installed on the pipes leading to and from the collectors, you'll be able to see how hot the water is as it comes to the tank from the collector, plus the temperature at the bottom of the tank as the water circulates to the collector panel. If your system is the forced-circulation type with an AC pump, these temperatures can help identify possible problems with the sensors. These additional thermometers enhance the ability to monitor the system, but are not required for normal operation and may increase the system installation and materials costs.

WARNING! Read the water heater tank manufacturer’s manual or solar water heating system manual, including all warning labels before attempting any diagnosis or repairs. The possibility of scalding from hot water or electrical shock may exist.

What if the system leaks or the collector glass breaks?

Leaks

Leaks in the tank are not repairable; the tank must be replaced. Leaks in the pipes may be hard to locate since all exposed pipes are (or should be) insulated; usually drips show up at low points or elbows in the plumbing and must be traced back to their source.

Leaks in the collector plate or pipes are not common. But evidence may include corrosion or discoloration surrounding leaks from the collector plates. There might also be a rainwater leak into the collector caused by poor sealing.

Excessive water within the collector box will show up as condensation on the inside of the collector's glass. Since the collector is not airtight, there will always be a little moisture to condense on the glass. Only excessive moisture may cause a lack of performance. The fogged glass won't let all of the sunshine into the collector, so it won't operate at its peak potential. Most collectors have small "weep holes" to let out excessive moisture.

Broken Glass

On rare occasions, the glass in a solar collector may shatter due to an impact. The metal collector plate and pipes will still pick up heat when the sun shines, but they will lose heat rapidly if the glass is not intact. Your solar system cannot operate optimally without intact glass. Most solar installers can replace the glass on a collector.

Vacations and Extended Absences

Refer to your solar water heating system installer or local vendor for recommendations on what to do when taking a vacation or when the system will not be used for extended periods.

Here are some general guidelines:

Active Systems

• When you take vacations longer than 3 days, change the controller switch setting from "automatic" to "on." This lets the pump run constantly, day and night. While this uses some electricity, it does keep the tank from overheating. Be sure to change the controller setting back to the "automatic" setting when you return.
  
  
• Turn off the back-up heating element. If the weather has been normal during your absence, the water should be fairly warm when you return and will heat rapidly once the backup is turned on.
  

All Systems

• Another option is to cover the collectors. Some solar companies have frames with shading screens that fit over the collectors, preventing sunshine from heating the water.

Solar Water Heating – Pools

Not only is Hawaii an ideal location for solar water heating for household use, it is also an ideal location for solar pool heating. Solar pool heaters generally do not have to heat the water to the temperature used in most households and the type of solar collector which is used for pool heating is usually different than the glass covered collectors used for domestic water heating. If you want to heat your pool energy efficiently, a great place to start is by reviewing the U.S. Department of Energy web site at http://www.eren.doe.gov/erec/factsheets/swimpool.html.