SF Environment recommends obtaining at least three bids from different solar installers prior to proceeding on your solar project. It's important to ensure that your solar contractor holds all appropriate licenses, certifications, and insurance policies for your project. For a list of solar water heating installers that serve San Francisco, click here. Installing a solar water heating system on your property allows you to decrease your natural gas bills and reliance on fossil fuels.
In addition to the economic and environmental benefits provided by solar energy, it can also increase your property value, decrease your carbon footprint, and help hedge against future utility rate increases. All rights reserved. Skip to main content. San Francisco Department of the Environment. Residents Business Contact.
Solar Water Heating Consumer Guide. Today, San Franciscans are searching for more information about renewable energy options, and while solar electric has received a good deal of attention, solar water heating has been largely overlooked. With the federal tax credits and California solar water heating incentives available, solar water heating is becoming an increasingly attractive option.
The first map shows the basic solar radiation available in the United States.
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As noted previously, many sites with an average solar radiation rate above 4. But, even a site with a less attractive solar resource can have good potential for solar water heating if the energy rate it offsets is high enough or incentives are available. To depict this, the National Renewable Energy Laboratory NREL has put together a series of maps that combine solar resource with an assumed system cost and depict factors needed to make a system cost effective. These maps are available for systems that will offset electricity use and for those that will offset natural gas.
As an example, the two maps below depict the electricity rate needed to make a solar water heating system cost effective.
Available incentives would improve this even more. This map does not account for any available financial incentives. The second map also includes incentives available to Federal agencies. Of course, break-even rates change significantly if the system cost varies from the maps' assumptions or if incentives change from the ones depicted. This map accounts for financial incentives.
To determine if a project is a possible candidate for solar water heating, agencies can use Federal Renewable Energy Screening Assistant software. It also evaluates many renewable technologies including solar water heating, photovoltaics and wind. Once preliminary viability has been established, it will eventually be necessary to evaluate system performance to generate more precise engineering data and economic analysis. This can be accomplished by using hourly simulation software or by manual correlation methods based on the results of hourly simulations.
For this task, consider using:. Solar water heating systems should be designed to minimize life-cycle cost. Other design considerations include maintenance, freeze protection, overheating protection, aesthetics of the collector mount, and orientation. Also, utility rebate programs may impose additional design requirements. When designing a solar water heating system, there are specific steps that are recommended. First, it is important to ensure the proper location of the solar collectors. The best annual energy delivery is achieved by facing toward the equator with a tilt up from the horizontal equal to the local latitude.
Recent studies show that adequate performance may be obtained with tilt angles and orientations that vary from this considerably. Also, it is important to optimize the tilt of the collecting array. A tilt angle equal to the local latitude provides close to the maximum year-round solar gains and is usually appropriate for solar water heating.
Solar water heating
It is usually acceptable to mount the collectors flush on a pitched roof—and as close to the optimal orientation as possible—in order to reduce installed costs and improve aesthetics. Second, damage can be caused if water freezes in the collector flow passages or connecting piping. There are several strategies for protection against freeze damage.
The most common is to circulate a solution of propylene glycol never use toxic ethylene glycol and water in the collector loop of an indirect system. Another strategy is to drain the water from the collector back into a drain-back tank sized to contain all of the collector loop fluid. This drain-back configuration has the added advantage of protecting the system from excessive temperatures if hot water consumption is reduced due to seasonal use patterns, remodeling, or vacations.
Where freezing is uncommon, a controller function that circulates water in the collector loop when temperatures approach freezing in conjunction with freeze protection values may be adequate, but can significantly reduce net energy gain. Another step is to provide a tempering valve and bypass capability. The tempering valve is very important to ensure that water with a consistent temperature is delivered at the taps, even when solar storage is well above the water heater setpoint.
Bypass piping and valves allow the conventional system to provide hot water if the solar heating system is down for any reason.
Finally, conducting periodic maintenance for all systems is necessary. Check for obvious damage such as broken collector glazing or wet pipe insulation. Check pH and freeze point of heat transfer fluids. Compare control temperature sensors against thermometers to be sure sensors are functioning. Also, be sure to check proper pump operation and other system functions. For a simple comprehensive test, check the preheat tank temperature—it should be hot after a sunny day. Specifically, when integrating a solar water heating system into a larger construction project, be sure to:.
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For large systems, a lower cost is usually achieved by mounting the solar collectors on un-shaded ground area adjacent to the building and near the heating equipment to prevent losses. An excellent guide to design and installation of commercial-scale solar water heaters was produced in the s by ASHRAE, based upon experiences with active solar in the Solar in Federal Buildings Program. Oamp;M is similar to that required of any hydronic heating loop and may be provided by site staff, with experts called in if something should fail. Regularly scheduled maintenance includes:.
Additional maintenance can include replacing temperature sensors that have been disconnected, replacing pump capacitors and motors, repairing leaks or damage from freezing, and replacing glass broken by hail or vandalism. At some point in time—typically in excess of 10 years—the storage tank may need to be replaced.
The special considerations to consider when designing and installing solar hot water systems include solar access, solar rights, and relevant codes and standards. Solar access laws protect a consumer's right to install and operate solar energy systems on a home or business, including the property's access to sunlight. Access to sunlight refers to the ability of one property to continue to receive sunlight across property lines without obstruction from a nearby home or building, landscaping, or other impediment.
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The most common type of solar access laws are solar easement and solar rights. Solar easement grants the owners of solar energy systems the right to continued access to sunlight without obstruction from a neighbor's property and prevents future property developments that could restrict solar access. Solar easement agreements must be in writing and are subject to the same recording and indexing requirements as other property interests.
The majority of solar easement agreements stipulate the following elements:.
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Solar rights provide protection for homes and businesses by limiting or prohibiting private restrictions e. The laws vary in their provisions for protection of solar equipment, types of buildings covered, applicability to new versus existing construction, and enforcement of rights. Vague or absent provisions in solar rights laws have led to lawsuits and delays in a number of states. Solar Heating Installer Certification is a voluntary certification that provides a set of national standards by which solar heating installers with skills and experience can distinguish themselves from their competition.
Certification provides a measure of protection to the public by giving them a credential for judging the competency of practitioners. The Solar Rating and Certification Corporation SRCC is an independent, nonprofit trade organization that creates and implements solar equipment certification programs and rating standards. SRCC certifies collectors and publishes performance ratings and collector efficiency equations needed for projecting system performance generally under its OG standard. SRCC developed a solar water heating system rating and certification program, short-titled OG, to improve performance and reliability of solar products.
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