Appliance Review: Solar vs. Traditional Water Heater Comparison

Introduction

When it comes to choosing between solar and traditional water heater, like with any appliance decision, it will ultimately come down to a balance of capability and cost. That said, it is arguable whether or not the estimate of 1/5 reduction in monthly energy cost will balance with the initial cost of a solar water heater. Though the solar water heater has greater energy efficiency, the benefits are short-term due to the initial cost.

Heating Element

Traditional heaters typically use natural gas, often paired with electric heating elements. Though a reliable resource, natural gas cost varies. Solar water heaters use the sun’s energy, a no-cost natural resource… provided it’s a sunny day. When it isn’t, the solar water heater will likely require assistance to provide a back-up heater to compensate for the lack of sunlight.

Technology & Design

A traditional water heater is an insulated storage tank (usually glass) that takes in fresh, cold water and, with a gas or electric flame at the bottom of the tank, heats the water to the programmed temperature. Because the temperature is maintained whether the water is used or not, keeping it hot all the time can be costly. If not used, the water will cause corrosion and bacterial growth, both of which negatively impact the overall water quality.

Solar heaters can be as simple as a passive system that uses a solar panel and water tank, keeping it cost-effective and reliable in the long term or more advanced, incorporating circulation pumps for an active system. All solar water heaters use a heat exchanger to deliver solar energy to the residential tank, and vary; its greatest affect being to the overall efficiency of the water heater.

Both the passive and active systems require a solar collector, of which there are two basic types: flat-plate collectors (tanks) and evacuated-tube solar collectors (tubes). Residential heaters typically use glazed flat-plate collectors, which are dark absorber plates stored beneath at least one layer of polymer or glass and sheathed by a weatherproofed, insulated box.

The second type of solar active system is known as the evacuated-tube solar collector, which includes two or more transparent, parallel glass tubes, each containing a glass outer tube and an internal metal absorption tube mounted to an energy-capturing fin. These models achieve efficiency by preventing heat from radiating away from the system. Each tube, in a sense, is its own solar collector. A third type, known as the integral collector-storage system (CSS) or “batch” system, can be either flat-plate or evacuated-tube systems into which cold water flows for preheating before continuing to the traditional backup heater. CSS systems are not suitable for freezing climates because the outdoor pipes could burst in severe cold temperatures.

Durability, Longevity, Corrosion Resistance

Some ways to obtain and maintain optimal conditions for your traditional water heater would include recycling all of the water in the tank regularly, setting it to an optimal temperature, and using appropriate materials to maintain the appliance. Traditionally, anything below 120 degrees Fahrenheit saves energy and prevents calcium buildup (scaling) associated with higher temperatures while temperatures above 140 degrees Fahrenheit will guard against bacterial growth. The most important of these components is the drain valve, (brass provides a more minimal the risk than plastic to avoid failure) and provides optimal water quality in the actual tank, which could be used as an emergency water source.

In traditional models, anodes connect the drain valves to the traditional water heater. While inexpensive, aluminum anodes tend to dissolve into sludge that can clog the drain valve at the bottom of the tank, blocking it and lowering the overall water quality. Conversely, magnesium and electrified titanium anodes, although initially more expensive, can significantly extend the life of the water heater.

Depending on the model, solar heaters may or may not require anodes. They can generally last longer than traditional water heaters, but are more dramatically decayed by corrosion and scaling. These problems can be minimized; however, by using water softeners and acidic solutions, which can keep an in-tank heat exchanger somewhat free of scaling. To avoid the issue altogether, one could also opt to use an external exchanger that wraps around the tank instead.

Stainless steel solar tanks require little maintenance and are less susceptible to corrosion, but do not fare well when the water quality is poor. Copper tanks, usually found in homes with a rooftop solar heater, last even longer and resist corrosion in most water quality conditions.

Display Screen & User Controls

Some active solar models come with digital control units to regulate the amount of heat the electrified system gathers. However, since they are dependent on uncontrollable solar energy, solar water heaters don’t allow for direct controls as precise as those in traditional models that are either digitally controlled or set using a knob, (which some argue provides more nuanced control).

Size & Space Requirements

A traditional water heater is only as big as its tank and utility connections, as well as any small moorings keeping it firmly attached to the wall. A solar water heater system includes the outside collectors, tank, and backup tank, and contractors tend to allocate twenty square feet of (flat-panel) collector area for the first two household members and between 8’2 (sunny) and 14’2 (colder, more cloudy climates) for each additional person.

Storage tanks can also vary in size, depending on the size of the household, from about 50 to 100 or more gallons.

Safety

Since 2003, traditional water heaters have been required to follow in accordance with “flammable-vapor ignition resistance” (FVIR) codes.  Safety features that tend to run standard on hot water tanks include the following: a temperature/pressure relief valve releases tank pressure when it exceeds a certain limit, internal temperature adjustment, anchoring the tank to a wall to prevent the device from tipping over and breaking gas and water pipes, proper ventilation, and the water heater’s shell (what you actually see).  It is just as important; however, to appropriately maintain the appliance.  Safety features found with a traditional water heater also ring true for the solar water heating systems, since solar water heaters often include a traditional backup heater.

Conclusion

While startup cost, climate, and space all contribute to the overall picture, the relevancy of whether a solar water heater or traditional water heaters is the better fit for your home largely depends on value and cost. The traditional water heater, though it runs on fuel that varies in cost per month, has a lower start-up cost and tend to be better understood in the short term.  If the choice is for a solar water heater, it is still advised to correspond with a professional contractor to find the right model for the home in consideration.