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Solar Water Heaters

Fast Water Heater no longer installs solar-powered water heaters.

A solar hot water system turns the sun’s energy into heat. A heating fluid, usually water or a food grade anti-freeze (propylene glycol) is circulated through panels that are usually mounted on the roof. That heat is then transferred to the water of your storage tank through a heat exchanger.

There are two main types of solar hot water systems:

  1. a “closed loop” (often referred to as a glycol or anti-freeze system)
  2. a “drainback system”. The primary difference between the two system types is that water is used for heat transfer in a drainback system and a glycol solution is used for heat transfer in a closed loop system. The type of system affects overall system design and each type of system has strengths and weaknesses.

There are also two main types of solar water heating panels currently being used today:

  1. flat-plate collectors – perform better in warmer areas with lots of direct sunlight
  2. evacuated-tube collectors – perform better in an overcast environment, like the Pacific Northwest

Overall Costs & Payback of Solar Water Heater Systems

The initial cost to install a solar water heating system generally ranges between $6,000-10,000. There are multiple rebates available at both the federal and local level which lower the initial cost. Currently, there is a federal tax credit on 30% of total installation costs. States and utilities have rebates which can offset anywhere from 10%-30% of the initial cost as well.

If the replacement cost of the existing water heater is also factored in – then the incremental cost of a solar system is lowered by another 10-20%. Taking all of these factors into consideration, the net cost of installing a solar water heater ranges from approximately $1,800 to $5,000 depending on both the rebates available and whether or not the homeowner was going to replace their water heater regardless.

Assuming annual energy usage of 300 therms to heat a home’s domestic hot water, this equates to payback on a solar system on a pure energy savings basis of between 6 and 17 years (assuming no inflation in the cost of natural gas and a cost of approximately $1.2/therm.) If the existing water heater is electric, then the payback period decreases to approximately 4 to 12 years based on multiple assumptions.

Most solar equipment makers claim that solar systems should last more than 30 years before they need to be replaced. If this is correct, then over a 30 year life, a solar water heater could save you a considerable amount of money over its lifetime. Total savings would include savings on energy bills for the entire product life plus savings from reduced replacement costs. Back of the envelope calculations estimate that a solar system will save a total of $8,000-12,000 over a 30 year life without factoring in the cost of energy inflation.

Solar water heating will save a homeowner a substantial amount of money over time. However, the payback on the investment can take time given the high upfront cost. Other benefits include substantially reduced greenhouse gas emissions and possibly increased desirability of the property. The U.S. Department of Housing and Urban Development states that home values rise an average of $20 for every $1 reduction in annual electricity bills.

Closed Loop Glycol Solar Water Heater

Closed loop solar water heater systems – sometimes referred to as anti-freeze or glycol systems include the heat collectors, insulated piping, a circulating pump, an expansion tank, a hot-water storage tank, a heat exchanger, solar fluid (usually a solution of water and nontoxic propylene glycol antifreeze), a controller, valves and gauges. A closed loop glycol system tends to resist freezing better than a drainback system.

A mixture of glycol and water are stored in the heat collector, heat exchanger and pipes and a pump circulates heated fluid through the collectors and through the heat exchanger. The piping allows circulation of the glycol solution from the collectors to the heat exchanger and back again. Whenever the sun shines on the collectors, the circulating pump turns on, and the solar fluid circulates within the closed loop. Hot fluid inside the collectors is pumped back to the heat exchanger which transfers the heat from the fluid to the water inside the storage tank. A double walled heat exchanger is required to prevent glycol from coming into contact with your drinking potable water. To prevent pressure increases due to thermal expansion (as the fluid heats, it expands in a contained space which can lead to pressure spikes), an expansion tank is installed in the system. When the sun is not shining, the circulating pump turns off, and the fluid stops circulating.

The circulating pump does require power. However, if the circulating pump is DC-powered, it can be wired to a small photovoltaic (PV) panel mounted with the solar collectors. This setup also avoids the need for a controller as the pump simply shuts on and off as the sun shines. These types of systems also automatically operate at variable speeds depending on sunlight levels. They are generally preferable to AC-powered systems because they do not require a controller, which can be prone to failure.

Alternatively, if an AC-powered pump is used, the pump is connected to the home’s 120-volt electrical power system. This setup also requires temperature sensors and a controller – when the water is hotter in the collectors, the controller turns the pump on and when it’s cooler it shuts the pump off.

Closed Loop Solar Water Heater

Drainback System

A drainback system for the most part functions similarly to a closed loop glycol system except that it typically will use water as the heating liquid. Because this presents the possibility of freezing, a drainback system will drain the collectors of all fluid (if installed correctly) at night or anytime there is the potential for freezing. When installing a drainback system, design and execution are crucial. If the collector loop piping is not graded properly (1/4″ per ft minimum) the collectors won’t drain back and there will be freeze breaks.

Typically these systems will use a controller and AC-pump that requires more power than in a closed loop system (a closed loop system pump circulates fluid in a system that is always full and requires less power). While drainback systems have fewer valves and gauges and do not require an expansion tank, proper installation of the piping is critical for freeze protection.

Drainback Solar Water Heater

Types of Solar Water Heating Panels: Evacuated tube vs. flat panel

There are two types of solar heat collectors. Both types are generally mounted on the roof but can also be ground mounted in a sunny area near the home. Flat panel heat collectors can be used with either closed loop or drainback systems. They are less easily damaged than evacuated tube heat collectors but because they are heavy they typically require more than one person to install. Flat panel collectors in general are more efficient at heating when there is more direct sunlight. In contrast, evacuated tube heat collectors can sometimes be damaged in shipping but because they are lighter they are easier to install with one person. Evacuated tube collectors are only used in closed loop glycol systems. They are more efficient at collecting heat in overcast environments where sunlight is less direct. Evacuated tube collectors are generally more expensive than flat panel collectors. However, this is usually offset by a lower installation cost.

Solar Installation by Fast Water Heater Company

Fast Water Heater Company now offers installation of solar water heaters. In addition, should you be out of hot water currently, we can provide you with a temporary tank while we are performing the installation. This will ensure that you have hot water while we are scoping the project and allows you to consider a solar water heating system even if you have to have your hot water back today. If you are going to be in your home for a long period of time and are interested in saving money over time, we strongly encourage you to consider this type of solution. Over the life of the product, it will save you a considerable amount of money, will use less energy and will possibly improve the resale value of your home. In many of the areas we service – particularly in California – incentives for installing a solar water heating system are large which greatly reduces upfront cost and improves payback.