Solar Water Heating technologies for potable hot water or for heating (radiant and hot water forced air) are simple, reliable, and cost-effective; harnessing the sun's energy to provide for the solar thermal energy needs of homes and businesses. And now the new Energy Policy Act of 2008 allows you to receive a federal tax credit worth 30% of the system cost! This is the best time to reap the numerous benefits of solar power!

Potable hot water represents the second largest energy expense for an American household. A typical 80 gallon electric hot water tank serving a family of four will consume approximately 150 million BTUs in its seven year lifetime. This will cost approximately $7,000 (at $0.15 per KWH), not accounting for fuel cost increases. Then it will be replaced by another one just like it. Hmm. Maybe we should rethink this...

An investment in a solar water heating system either for hot potable water or home heating, will beat the stock market any day, any decade, risk free. Initial return on investment is on the order of 25 percent, tax-free, and goes up as gas and electricity prices climb. Many states have tax credits and other incentives to sweeten those numbers even more. What are we waiting for? Forget the stock market. If you have invested in a house, your next investment should be in solar hot water.

Fully installed Residential systems starting from $7,000.00.
Residential solar thermal installations limited to Southern NJ and DE
unless accompanied by another RE system

                Solar                                    Conventional Water Heater

Below: A Typical Solar Flat Plate Water Heater.

A Checkered Past, A Bright Future
Solar thermal's past is a good example of why everyone should be skeptical of government involvement in energy. Lucrative federal and state tax credits for solar energy were initiated under President Jimmy Carter in the '70s, and abruptly eliminated under President Ronald Reagan in 1985. This dealt the solar industry a devastating "one-two punch" from which it still has not recovered.

The intention was to stimulate sales for solar thermal systems. But the tax credits resulted in an aggressive promotion of tax credits rather than solar energy. The infant industry was overwhelmed to meet the demand. The demand vanished when tax credits were eliminated, and a majority of solar thermal companies went out of business. Thousands of orphaned solar thermal systems were left behind looking for a service technician.

Today's solar thermal industry includes reliable, efficient products and well-seasoned professionals who have seen it all. Solar hot water is one of the best investments you can make for your house and for the environment.

First Things First
The best savings in hot water come from no cost or low cost options. Before you tackle solar hot water, take these steps:

• Turn the thermostat down. Many water heaters are set to between 140 and 180°F (60 and 82°C). See how low you can go. Try 125°F (52°C) for starters. A hot tub is 106°F (41°C). How much hotter do you need?
• Wrap the water heater with insulation. Insulated water heater "blankets" are usually available where water heaters are sold. (Be careful with natural gas or propane fired water tanks. They use an open flame to heat the water. You need to provide a space for air at the bottom of the tank, and at the top where the flue exits the tank. Safety comes before efficiency!)
• Fix those drips. They may not look like much, but they are a constant and persistent drain on your water heating load, and they waste water too.
• Use flow restrictors and faucet aerators to reduce your hot water consumption.
• Find other ways to use less hot water. Wash only full loads of clothes and dishes.
• Insulate your hot water pipes.

How Large a Solar Hot Water System Do You Need?
Hot water usage in the U.S. is typically 15 to 30 gallons per person per day for home use. This includes primarily bathing, clothes washing, and dish washing. But your commitment to efficiency has a lot to do with your actual usage.

Below: A 40 gallon batch heater.

The hot water tank is usually sized to handle one day's worth of consumption. So for a household of four, it would be reasonable to use an 80 gallon tank based on daily hot water requirements of 20 gallons per person per day.

We have put forth generally accepted rules of thumb for solar thermal collector sizing based on your climatic region:

• In the Sunbelt, use 1 square foot (0.09 m2) of collector per 2 gallons (7.6 l) of tank capacity (daily household usage).
• In the Southeast and mountain states, use 1 square foot of collector per 1.5 gallons (5.7 l) of tank capacity.
• In the Midwest and Atlantic states, use 1 square foot of collector per 1.0 gallon (3.8 l) of tank capacity.
• In New England and the Northwest, use 1 square foot of collector per 0.75 gallon (2.8 l) of tank capacity.

Based on these rules of thumb, a household of four with an 80 gallon (300 l) tank will need approximately 40 square feet (3.7 m2) of collector in Arizona, 55 square feet (5.1 m2) of collector in South Carolina, 80 square feet (7.4 m2) of collector in Iowa, and 106 square feet (9.8 m2) of collector in Vermont.

Of course, these are big ballpark calculations that will be affected by your incoming water temperature, hot water temperature set point, actual usage, and the intensity of the solar resource at your site. You should generally expect that this will give you 100 percent of your hot water in the summer and about 40 percent of your hot water year-round.

Your Choices? An Overview
The type of system you choose will depend mostly on your climate. Freeze-free environments allow for simple, low cost designs. A batch heater uses a storage tank as a collector. A direct pump system circulates water from a collector to a storage tank. A thermo siphon system requires no pump for circulation, just the natural flow of gravity.

Most systems will require some measure of freeze protection. Drain back and closed loop systems with antifreeze and heat exchangers are the best choice for freezing locations. The extra parts increase cost and reduce efficiency, but since one frozen moment can turn into a disaster, it's worth the cost.

Direct pump recirculation systems, which circulate hot water through the collector, are often used where freezing is an infrequent occurrence. That's a risky strategy. Drain down systems, designed to drain water from the collectors to avoid freezing, are the most problematic of system designs. 

The KISS (keep it simple, stupid) rule applies to solar heating. 

Multiple collectors can be installed in series for larger capacities. The outlet of the first collector becomes the inlet of the second in order to deliver higher temperatures. Before you put too many on your roof, consider the panel type, for example  a 40 gallon (150 l) batch heater will weigh approximately 500 pounds (225 kg).

Most solar hot water system designs separate the collector from the storage tank. This can optimize both functions. Why not bring the tank in from the cold, insulate it well, and leave the collectors out in the sun where they belong?

What are the other advantages of separating the collector from the storage tank? Increase the surface area of a collector, compared to the amount of water being heated, and its temperature will rise more quickly. Configure the storage tank to keep the hottest water apart from the coldest water in the tank and you'll have hotter water available sooner. (See sidebar Maintain Temperature Stratification In Your Tank.)

There are also advantages in freezing climates. By separating the collector from the tank, you can put your tank and piping indoors out of a freezing environment, and insulate them better for greater efficiency.

Below: Two roof-mounted flat plate collectors.

Flat Plate Collectors from JBS Solar
Flat plate collectors are the most common solar thermal collectors. They are most appropriate for low temperature applications (under 140°F; 60°C), such as domestic hot water and space heating.

A flat plate solar thermal collector usually consists of copper tubes fitted to a flat absorber plate. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with low-iron, tempered glass. (See the diagram on page 45.)

The most efficient collector design maximizes solar heat gain, minimizes heat losses, and provides for the most efficient heat transfer from absorber plate to tube. Operating temperatures up to 250°F (121°C) are obtainable, although neither common nor desirable. Remember, you want hot water, not steam.

Selective Surface
A selective surface, often referred to as "black chrome" is far more efficient than a black painted absorber surface. Although a black surface is most efficient at absorbing solar radiation and converting it to heat, it is also highly efficient at re-radiating long wave infrared heat back out. These losses reduce collector efficiency.

A selective surface combines the best of both worlds; high absorptance with low emittance. Sound high-tech? It's been around since the 1950s, and is used on all of our flat plate collectors. Its performance is worth the marginal additional cost, particularly in cold climates where radiant heat loss is greatest.

Below: An evacuated tube collector.

Evacuated Tube Collectors from JBS Solar
If you want the highest efficiency solar thermal collector, you'll be interested in an evacuated tube collector, such as the one manufactured by Apricus. Although evacuated tube collectors are more efficient than conventional flat plate collectors, they are more costly per square foot.

Each tube and fin of the collector is contained within a glass tube from which all the air has been evacuated. Why? Air carries heat from the hot surface of the tube to the cooler surface of the glass to accelerate heat loss by convection. Eliminate the air and you have eliminated convective heat loss.

To minimize radiant heat loss, the tube is covered with a selective surface. Evacuated tube collectors are most appropriate for high temperature applications (over 140°F; 60°C). They are useful for more common low temperature applications too, such as domestic water and space heating.

Below: Direct Pump Recirculation System.

Collector to Tank Interface
With the collector and the storage tank separated, the system design must provide a flow of water (or antifreeze) from tank to collector and return. Small circulating pumps provide the necessary flow with very modest energy requirements. Small hot water systems may use a direct current (DC) circulating pump powered by a single PV module (10 to 30 watts depending upon power requirements). 

If you require freeze protection, it's not hard to do. The collectors can be filled with an antifreeze solution (propylene glycol is the most common). The heat can be transferred to the domestic water via a heat exchanger.

Direct Pump Recirculation
The direct pump system uses an electric circulating pump to move heat from the collector to the storage tank. The pump can move heat from the collectors on the roof to a storage tank in the basement. Good sense still calls for minimal length of pipe run for efficiency.

A differential controller turns the circulating pump on or off as required. There are two sensors, one at the outlet of the collectors, and the other at the bottom of the tank. They signal the controller to turn the pump on when the collector outlet is 20°F (11°C) warmer than the bottom of the tank. It shuts off when the temperature differential is reduced to 5°F (2.8°C). Some systems let you adjust this hysteresis.

Below: Closed Loop Antifreeze Heat Exchanger System.

In climates where freezing occurs infrequently, a recirculation-type differential control will turn the circulating pump on when the collector inlet temperature falls to 40°F (4.4°C). The philosophy behind this design is that the cost of heating your collectors with hot water from your tank is low cost freeze protection if only required occasionally.

These systems were commonly used in the sunbelt, and only where freezing is a rare occasion. Recirculation systems are no longer very commonly used due to vulnerability to freezing as a result of power outages, malfunction of sensor or controller, or damaged sensor wires.

Drain down System (Not Recommended)
A drain down system is an open loop system in which the collectors are filled with domestic water under house pressure when there is no danger of freezing. Once the system is filled, a differential controller operates a pump to move water from the tank through the collectors.

A drain down valve, invented in the 1970s exclusively for these systems, provides the freeze protection function. When the collector inlet temperature falls to 40°F (4.4°C), the drain down valve, activated by the controller, isolates the collector inlet and outlet from the tank. It simultaneously opens a valve that allows water in the collector to drain away. A vacuum breaker is always installed at the top of the collectors to allow air to enter the collectors at the top so water can drain out the bottom. Right next to the vacuum breaker, you'll find an automatic air vent to allow air to escape when the system fills again.

Drain down systems have proven to be the most problematic of all freeze protection systems. They are vulnerable to frozen vacuum breakers and air vents, damaged sensors or wiring, lack of proper pipe drainage, and malfunctions with the drain down valve. This type of system is rarely installed new any more, and is not recommended. Many were converted to drain back or closed-loop antifreeze systems.

Closed Loop Antifreeze Heat Exchanger from JBS Solar and Wind
Closed loop antifreeze systems provide the most reliable protection from freezing. These systems circulate an antifreeze solution through the collectors and a heat exchanger. Non toxic earth friendly  glycol is the most common antifreeze solution we use. Unlike ethylene glycol (used in automobile radiators), propylene glycol is not toxic.

The closed loop antifreeze systems generally have the most parts. You'll find an expansion tank to allow the antifreeze to expand and contract with temperature change. You'll find a pressure relief valve to protect against excessive pressures in the closed loop; a spring-loaded check valve to prevent reverse flow of the closed loop at night so the collectors won't dissipate the heat from the water heater; an air vent and/or air eliminator to help get the air out of the closed loop (air is your enemy?it can block fluid flow through the system); and a pressure gauge so you can tell if your system is still charged. A couple of temperature gauges are a good idea in any system so you can tell how well your system is operating.

There's also one more assembly of fittings. Two boiler drains with a shutoff valve in between will allow you to charge the system with your charging pump. Once ready to charge the closed loop with your antifreeze solution, a charging pump is used to circulate the fluid throughout the loop, expelling all the air in the process.

Closed loop systems like this are quite common, whether they be for solar domestic hot water, radiant floor heating, or hydronic baseboard heating. Despite the many additional parts and fittings, they have a high degree of reliability.

Below: Closed Loop Drain back System

Drain back: A Simpler Closed Loop
Although similar in name to the draindown type system, the drainback system is far different and much more reliable. It also provides some advantages over the closed loop antifreeze system. Drain back systems may use water as the heat transfer fluid, since the collectors drain when not in operation. Antifreeze provides an extra measure of freeze protection from poor drainage and controller or sensor malfunctions.

A circulating pump operated by a differential control is turned on when the collector outlet is at least 20°F (11°C) warmer than the tank outlet. Water or an antifreeze solution is lifted from a small reservoir tank and circulated through the collectors and back to the tank. Heat is transferred to the domestic water via a heat exchanger in the reservoir tank. The circulation loop through the collectors is a closed loop. The water or antifreeze solution is installed at the time of installation, and does not present a recurring supply of oxygen.

A drain back system requires a larger pump than any of the other systems described here. It must have sufficient capacity to lift the fluid to the highest point in the system. When there is no more heat to be collected, the controller turns the pump off, and all the fluid drains back to the reservoir tank. The collectors are empty. They can't freeze, and they can't overheat the antifreeze. When it comes time to change the antifreeze, you can just drain and refill the reservoir tank.

Solar Hot Water System Types: Advantages & Disadvantages

The Choice is Yours
The system you choose will be determined first by whether you need freeze protection. If you live in a freeze-free climate,  a batch heater or small thermosiphon unit for small systems serving one to three people. Larger needs can be met with an open loop direct pump system circulating water from storage tank to flat plat collector.

If you need freeze protection or have hard water, one of the JBS closed loop systems with antifreeze and a heat exchanger. Either one will heat your water without fear of freezing.

Solar hot water is a good investment. To find out more about our products and services we have to offer, and which is the best fit for your needs and climate, give us a call. 

Sidebar 1
Maintain Temperature Stratification in Your Tank

Hot water returning from the collector should enter the storage tank about a third of the way down from the top. This water may not be the hottest water you have collected all day, because solar insolation and outside ambient temperatures vary during the day. You don?t want this water to disturb the water at the very top of the storage tank. Draw water for use from the very top of the tank. That is where its the hottest.

When hot water is drawn from the tank, it is replaced by new cold water, which should enter at the very bottom. Water circulating to the solar collector should be drawn from the bottom of the tank. Why? Efficiency! Always supply your collector with the coolest water you have available. The cooler a solar collector runs, the less heat it loses to the surrounding environment.

Sidebar 2
Rust Never Sleeps: Open Loop vs. Closed Loop

A hydronic system is one that uses a liquid as its heat transfer medium. The most common alternatives to hydronic systems are air systems. Hydronic systems are nearly always categorized as open loop or closed loop often referred to as direct or indirect respectively. If you are not aware of the difference between these, you run the risk of discovering one day that your system has been eaten alive by a slow yet persistent killer oxygen.

Open Loop
Open loop systems are subject to a periodic fresh supply of oxygen, ready to trash every bit of cast iron, steel, or other corrodible part in your system. Whenever you draw water at the tap or bath, new water simultaneously moves in to replace it. Along with that new water comes a fresh supply of oxygen.

You have two lines of defense against damage by corrosive oxygen. You can prevent oxygen from entering the system, or you can use materials that are resistant to corrosion. Copper, bronze, brass, stainless steel, plastic, and the glass lining of a hot water tank have no problem with oxygen. Use these materials when dealing with fresh water supplies associated with open or direct  systems.

Closed Loop
If your system is a closed system, you wont have to worry about oxygen. You will be able to use cast iron components (pumps), which can save you money. Closed systems are charged with fluid at the time of installation. As a permanent part of the installed system, new oxygen is not introduced, and corrosion is not a problem. Read on and you will see several examples of open and closed systems.

Another important consideration with open or direct systems is whether or not you have hard water. Over time, calcium deposits from hard water will clog the collectors, ruining them. These deposits can be removed with periodic use of a descaling solution. But if you have hard water, youll be better off with a closed loop system.