U.S. Department of Energy - Energy Efficiency and Renewable Energy
Federal Energy Management Program
Solar Hot Water Resources and Technologies
This solar hot water system tracks sunlight using a standalone, single-axis mount to optimize hot water production for residential applications.
This page provides a brief overview of solar hot water (SHW) technologies supplemented by specific information to apply SHW within the Federal sector.
Although a large variety of solar hot water systems exist, the basic technology is simple. A collector absorbs and transfers heat from the sun to water, which is stored in a tank until needed. Active solar heating systems use circulating pumps and controls. These are more expensive but are also typically more efficient. Passive systems work without added equipment.
Visit the Department of Energy's (DOE) Solar Technologies Program for in-depth information about solar energy basics and technologies.
Solar hot water systems can be cost-competitive when reducing electricity consumption tied to hot water generation. A typical SHW system reduces the need for conventional water heating by two-thirds. Before conducting an assessment or deploying SHW systems, Federal agencies must evaluate a series of questions and considerations.
What are my energy goals?
Energy goals range from meeting regulatory requirements to powering remote applications to increasing energy security.
Regulatory Requirements: While SHW does not fall under the Energy Policy Act (EPAct) of 2005 definition of renewable energy, the Energy Independence and Security Act (EISA) of 2007 requires 30% of hot water demand in new Federal buildings and major renovations be met with SHW equipment provided it is life-cycle cost-effective.
Remote Power: SHW systems are typically cost-effective in residential and commercial buildings wherever solar resources are available.
Energy Security: Solar energy is natural and renewable. The energy source is found in abundance across the U.S. and can be leveraged to increase energy continuity.
What kind of energy do I use?
Federal agencies must understand what type of energy is used before determining if SHW is applicable. Solar hot water systems generate thermal energy.
When do I need the energy?
Although solar resources can be quite predictable, SHW cannot be guaranteed to generate heat where and when it is demanded like a fossil fuel generator.
Where am I located?
For a broad overview of your facility's solar resources, the National Renewable Energy Laboratory (NREL) provides solar energy resource maps of the U.S. Before initiating a project, solar resources in your area must be measured and verified. Resource maps are a good start, but resources vary at a micro level. It is important to consult an expert for a professional evaluation before implementing energy projects.
Temperature is another location-based consideration. In colder climates, features must be integrated into SHW systems to safeguard against freezing. Frozen water lines can often rupture or damage the system. A resource map showing the probability of frozen pipes is available.
Is this an existing facility or new construction?
Retrofitting solar hot water systems into existing buildings is possible, but can be complicated by the need to provide access for installing pipes and space in mechanical rooms for larger water storage tanks. Therefore, SHW systems are easier to install in new construction or major renovations.
In addition, new construction and major renovations are required by EISA 2007 to generate at least 30% of hot water from SHW systems.
Is solar hot water cost-effective for my facility?
SHW systems are typically the most cost-effective in small, residential-sized facilities that would otherwise depend on high-cost energy sources; large facilities that require large volumes of hot water (more than 1,000 gallons per day); large facilities that use high-temperature hot water; and swimming pools.
SHW economics depend on several variables, including:
- Cost of the fuel SHW replaces
- Hot water demand
- Hot water usage patterns
- Incoming water temperature
- Availability of solar energy
What resources are available for operations and maintenance?
In general, solar hot water systems are reliable and do not require much maintenance because they have few, if any, moving parts. The primary components of SHW systems (collectors, heat transfer systems, heat storage, and controls) require routine, periodic maintenance. From time-to-time, individual components may need repair or replacement.
Climate can also impact operations and maintenance costs. In colder climates, steps must be taken to safeguard against freezing. Frozen water lines can often rupture or damage the system. A resource map showing the probability of frozen pipes is available.
Visit the project planning section for detailed information on planning and deploying renewable energy projects. Federal case studies are available to provide specific examples of viable solar energy projects.
Detailed information on solar energy resources and technologies is available through:
FEMP Solar Hot Water Calculator: Online tool to help Federal agencies meet Energy Independence and Security Act (EISA) of 2007 Section 523 requirements for new Federal buildings and major renovations to meet 30% of hot water demand using solar hot water equipment if life-cycle cost effective.
DOE Solar Energy Technologies Program: Program providing information and resources on solar energy resources and technologies.
American Solar Energy Society: Leading association of solar professional and grassroots advocates.
Solar Energy Industries Association: Organization working to expand the use of solar technologies, strengthen research and development, remove market barriers, and improve education and outreach for solar.
Procuring Solar Energy: A Guide for Federal Facility Decision Makers: Guide to help Federal agencies turn their interest in solar energy projects into success installations through a concise, easy-to-understand, step-by-step process.
Solar Water Heating with Low-Cost Plastic Systems: Newly developed solar water heating technology can help Federal agencies cost-effectively meet EISA requirements for solar water heating in new construction and major renovations. This document provides design considerations, application, economics, and maintenance information and resources.
Solar Water Heating: Federal Technology Alert detailing solar water heating as a well-proven technology that pays off in multiple situations.
Solar Water Heating: Describes how to use the sun to heat domestic water and why it makes sense in almost any climate.
Parabolic-Trough Solar Water Heating: Federal Technology Alert on using parabolic-trough solar water heating as a renewable source for reducing water-heating costs.
Solar Ready Buildings Planning Guide: Checklist for building design and construction to enable solar photovoltaic and heating systems after the building is constructed.