Tag Archives: hot water system

How to Choose a Solar Water Heater

Guest post by John Reed, originator of world-wide SolarDay. You can find more details on our site by clicking  SolarDay 2012

Here are some expert tips on saving energy for one of the biggest energy hogs in your home or office: the hot water heater. Though there is an up-front cost to installing a solar water heater system in your home or business, it will save you a bundle on your utility bills over the life of the system and they tend to be basically maintenance-free for many years. Also, many utility companies have rebate programs to help pay for solar water heater systems. Since rebates vary by city and state, check with your local utility about their current, solar water heater systems rebates.

Selecting a New Solar Water Heater

You have many options when it comes to installing a solar water heater  system.

Solar Water Heater

Here are some of the most common solar water heater that use storage tanks and solar collectors:

Solar water heater systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.

Most solar water heater systems require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

Three types of solar collectors are used for residential and commercial applications:

Integral collector-storage systems – also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.

Evacuated-tube solar collectors feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.

Glazed flat-plate collectorsare insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating —have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

Solar water heater absorber plate

Dark Absorber Plate

There are three types of active solar water heating systems.

Direct circulation systems pump and circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.

Indirect Circulation Systems pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger.  This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

Passive solar water heater systems are typically less expensive than active systems, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

Integral collector-storage passive systems work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

Thermosyphon systems: water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.

Cloudy Days and Solar Hot Water Systems

Solar water heating systems often require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a demand (tankless or instantaneous) water heater for backup.

Installing and Maintaining a Solar Water Heater

Before you purchase and install a solar water heater system, you want to do the following:

  • consider the economics of a solar water heater system,
  • check out your domestic rooftop’s solar resources (lots of direct sunlight), determine the correct system size,
  •  compare system costs and investigate local building codes, covenants and regulations.
  • When it comes to cost, check out possible incentives from your local utility company which can substantially reduce the cost of the system.

Installing and Maintaining the System

Regular maintenance on simple systems can be as infrequent as every 3–5 years

The proper installation of a solar water heater system depends on many factors. These include the solar resource, climate, local building code requirements, and safety issues. Therefore, it’s best to have a qualified, solar thermal systems contractor install your system.

After installation, properly maintaining your solar water heater system will keep it running smoothly, though these systems, especially passive systems, tend to require very little maintenance.  For active systems, discuss the maintenance requirements with your system provider and consult the system’s owner’s manual.

Plumbing and other conventional water heating components require the same maintenance as conventional systems. The glass glazing may need to be cleaned in dry climates where rainfall doesn’t provide the water to remove grime and dust.

Regular maintenance on simple solar water heater systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part or two after 10 years.

More solar and energy conservation news can be found at: www.solarday.com.

John Reed


(415) 846-4862    San Francisco, California


Quick Guidelines for a Passive Solar House

Garry Baverstock
Co-Founder & Director, solar-e.com
Email: g.baverstock@solar-e.com

The aim of this Energy Efficient House Scheme is to enable home buyers to readily identify houses and house designs which offer a recognized standard of comfort and energy efficiency. There are six important features.

  • Orientation
  • Windows
  • Mass
  • Insulation
  • Ventilation
  • Hot water service

The scheme should demonstrate than an energy efficient house is affordable.

Land subdivisions where the scheme is being promoted should have a majority of blocks which are oriented east-west and which encourage the building of energy efficient housing. To avoid conflict with other important energy conservation messages the subdivisions should be reticulated with gas, and should have public transport available.


The house should have a rectangular shape with long axis close to east-west. These blocks should form the majority of blocks in a housing estate for reasons of privacy and cost efficiency.

  • The orientation can deviate from magnetic north by 20 °W and 20 °E.
  • The ratio of long to short axis must be greater than 1.5 as a general rule.
  • Proportions become longer in cold climates and shorter, more squarish in hotter climates.


North (south in Southern Hemisphere)

The living area should be facing north and have the largest window area.

North facing windows should be shaded in summer and unshaded in winter. Shading to north windows can be fixed (pergolas or eaves), or adjustable.

  • North facing glass should be clear, not tint or reflective in temperate climates (special glass is of use in more extreme climates).
  • Fixed shading should have a projection of at least 0.25 x height sill to overhang and no more than 0.45.
  • The effective area of N facing glass should be between 20% ad 35% of effective floor area for temperate climates. This ratio increases for cold climates and decreases for hotter climates.

Adjustable shading devices such as awnings, shutters and pergolas with deciduous creepers are always to be preferred to fixed shading. Fixed shading that keeps out unwanted summer sunlight will also keep some of the winter sunlight also.

East and West

Windows on the east and west should be minimized and/or shaded or otherwise treated to keep out the sun. fixed shading provided by pergolas or an eaves overhang is not useful on the east or west walls.

  • The effective area of glass on the east and west should be not more than 5% of the total effective floor area.
  • The effective area of glass on the west should be not more than 2% of the total effective floor area.
  • The effective area of east and west facing windows should not exceed 15% of the floor area of the rooms they are in.
  • Extra glass may be used if tinted or reflective glass is used on the north, east or west elevations or if shading devices above minimum requires are used. To find the allowance glass area in tint or reflective glass etc divide the ‘effective’ glass area by the solar shading coefficient. Glass must be provided with shading with a coefficient of not more than 0.3 before calculating the area of additional glass made possible by the use of additional shading.
  • West facing clear glass windows must be provided with adjustable shading.

These ratios are for temperate climates and vary in hotter and colder climates.

Tinted glass and adjustable shading is recommended for east and west windows. Shading of east and west walls with suitable plants is recommended.


South facing glass does not require shading but should be limited to prevent heat loss in winter.

  • South + East + West facing glass should be not more than 15% of the total effective floor area. The glass area limit cannot be increased by using shading for temperate climates. This strategy is also useful for cold climates.

Tint or reflective glass is recommended for south facing windows and excessive areas facing west and maybe east, depending on computer thermal analysis results.


Sufficient thermal mass (materials like brick and concrete which absorb heat) should be provided to stablise air temperatures, particular in summer.

  • Construction should be on a concrete slab
    Internal walls in the living area should have a heat capacity of >1400kJ/m³.

A significant proportion of the floor in N-facing rooms should be covered with tiles, slate or similar heat absorbing hard surface but any surface on concrete will still work over a 24 hour period, provided doors and windows remain closed in extreme weather conditions.


Roof insulation of R1.5 or greater is required. Perimeter walls of light weight, which would otherwise heat quickly must have an R value of at least 1.0 for temperate climates. Naturally rates dramatically climb to R4 and above in extremely hot or cold climatic regions.


Doors to the exterior of the house or rooms with high-flow fixed ventilation like bathrooms and toilets should be weather stripped. Chimneys should be provided with a damper.  Adequate cross ventilation should be provided for both living and sleeping areas for summer cooling.

Water Heaters

The hot water system should be either gas or solar, gas boosted preferably where hydro-electricity is not available.

This content has been provided by RISE (Research Institute for Sustainable Energy) as part of undergraduate level revision and the expanded knowledge program associated with the
Master of Science in Environmental Architecture course.

< Back to Blogs