Solar Water Heater


Our mission is to research and design a simple, sustainable, and affordable solar water heater
that is safe for home use in San Pablo. We want to make sure that our design takes into account
the weather conditions and seismic activity in SP, and is socially acceptable within the community.
In doing so, we also strive to potentially create a new market in San Pablo for solar water heaters.

We are focusing our efforts on creating a simple yet efficient system that is built from materials
local to San Pablo and/or readily available from nearby areas.

Logramos investigar y disenar un simple, sostenible, y economico calentador de agua solar que
se puede usar en los hogares en San Pablo. Hay que asegurar que nuestro diseno tiene en cuenta
las condiciones climacticas y la actividad sismica en San Pablo, y que es acceptable en la sociedad.
Idealmente, este proyecto funcionara para crear una economia en San Pablo para calentadores de agua solar.

Somos enfocando nuestros enfuerzos en crear un sistema construido de materiales locales
que se pueden adquirir en los alrededores de San Pablo.

• Expand our knowledge of existing solar technology in developing countries.
Help the residents of San Pablo become more self-sufficient and sustainable in their everyday lives, specifically by providing
them with an easy-to-implement solution for harnessing solar power to heat water
• Gather information on local conditions, environmental and social, within San Pablo community;
build upon the progress made by students Fall Quarter 2010, and utilize the data acquired during the Winter Research Trip.
To view the work done by SOL POWER, Fall Quarter’s solar water heating group, click here.
• Reestablish communication with San Pablo students Henry and Miguel, who collaborated with SOL POWER



• What materials are available in San Pablo and nearby areas that would be integral to this project (piping, insulation, etc.)?
• About how much water is used daily in San Pablo?/ how many gallons of hot water per day is a reasonable goal?
• How much do the residents know about solar energy and solar water heating?
• Can the houses handle a rooftop system, or must the system be angled from the ground?
• On average, how often do temperatures reach below freezing in San Pablo?
• Is it worth considering a (partially) below-ground system to aid with insulation?


active_heater.png active system
water circulation powered by pump
(requires electricity)


passive_heater.png passive system— water circulation
powered by a thermosiphon (hot water
rises via convection— heated H2O
moecules expand and are more buoyant
than cold H2O molecules) and relying on
gravity for distribution = no electricity

A thermosiphon can be either an open-loop circuit or a closed-loop circuit. The former means the heated water
moves in one direction, and is transferred to a storage tank and distribution point higher than the heating system.
This is the simplest system, and implemented in tropical areas where freezing never occurs. An open-loop circuit
could potentially still be an option if the system was completely drained whenever the temperatures were expected
to be ≤ 0°C. A closed loop circuit is a system in which the water circulates up through the system and back down
to the original vessel to be reheated. This requires an antifreeze solution or freeze-tolerant piping.


flat-plate z-pattern
flat-plate 1/2″diameter
PVC(?) grid
flat-plate 1″diameter
PVC(?) grid
flat-plate ABS/PEX grid flat-plate
copper grid
batch collector
cost 9 8 8 7 1 8
weight 8 7 7 7 4 8
aesthetics 5 5 5 5 5 5
performance 6 7 7 9 10 8
constructability 8 7 7 7 4 9
ease of use 8 7 7 7 5 8
durability 4 4 4 9 10 8
capacity 9 9 9 9 9 6
repair 8 7 7 7 2 8
social acceptance 5 5 5 5 5 5
overall value 70 66 66 72 55 73

Our initial decision matrix was mainly a product of educated guesses and speculation; we could not precisely evaluate
many of the criteria, but our assessments were guided by the information provided by SOL POWER. The highest-scoring
systems, as determined by SOL POWER’s research, were the “Integrated Collector Storage System” (batch collector)
and the “Convection Heat Storage System” (thermosiphon), and are the two systems we are going to experiment with.

We learned that PVC pipe was not a good choice because of its inability to withstand high temperatures, so we
eliminated it from our matrix. Acrylonitrile Butadiene Styrene (ABS) pipe, Medium Density Polyethylene (MDPE) pipe, High Density Polyethylene (HDPE),
or cross-linked polyethylene (PEX) pipe are viablie alternatives when considering the tradeoff between price and
durability. For a more detailed comparison see PVC vs. PEX.

SOL POWER also mentionted pumice-crete, a good insulator that is lighter-weight than regular concrete,
so we are considering investigating this material further.


W_storage.jpg C_roof.jpg C+W_roof.jpg

From this model we learned that the tubing, as it crosses back and forth along the flat heating panel, must never dip back down otherwise the water will not flow properly (because the heated water has to follow an upwards path that pushes it below the cooler water lower in the system) and the thermosiphon’s performance is compromised. We need to correct storage tank leaking issues, and take steps to prevent air from entering the system. We also took note of the myriad of variables we have yet to experiment with— flat-panel material, diameter & length, as well as conducting batch collector trials. Finally, in subsequent models we plan on recording the temperature at various parts in the system and how well it retains heat over an extended period of time.

We made use of resources provided by SOL POWER, as well as some links we found in the course of our own research:


solar hot water basics

Build It Solar

Calsolagua – a Berkeley team that developed a solar water heating system for use in Guatemalan households

R-Value table for various insulation materials

We have corresponded with community leaders in San Pablo, and directed questions to Henry and Miguel, who worked with SOL POWER. We also sought information and advice from Chris and Bryan of last quarter’s group, as well as outside resources individuals in our group have contacted. Their collective feedback has been a valuable tool in guiding our choices in systems, testing methods, materials, etc. The questions we asked included:
• Do you have hot water in your home?
• What do you think a family would be willing to pay for access to hot water?
• Where does the water in your home come from? Is it from a tank or pond that is somewhere at a higher elevation? Or is it pumped to your home, or just fed through gravity?
• Do you know how much power the instant water-heater shower heads draw, in watts? If not, does it have an amperage rating on it?
• What type of materials can you easily (and economically) buy locally? For example, PVC or ABS piping, sheet metal, corrugated tin, etc.


After devising and constructing an inititial model, as shown above, our group split into two teams to ensure we explored the efficacy of as many systems as possible. One team tested the potential of a batch collector system, combining three 5-gallon water jugs into a single storage vessel, housed within an insulating box to retain the absorbed heat. Though it proves to be a viable solution because of its affordability and because it can function on the ground rather than the roof, it only heats 15 gallons at a time and it remains unclear how exactly hot water would be dispensed from our system…


ground.jpg work.jpg


P2130499.JPG P2130497.JPG DSCN0035.JPG

(Questionable) Data Logger Results:

Q = mCp∆T

= (60kg H2O)(4.184 kJ/kg*K)(40 deg C – 10 deg C)

= 7500 kJ = (7500kJ)*(1 hr/ 3600 s)

= 2 kWh

This batch collector produced about 2 kWh in a day

from the sun’s energy —> cost = FREE!

compare.png co$t$.png


• pretty cheap ($95 US) and available

• more durable than plastic bag system

• sexier



• difficult to create watertight connections

• not pressure-tolerant

The other team experimented with various materials and configurations for a flat-plate system that, ultimately, will passively transfer heated water to a storage vessel as it rises and is replaced in the layout of pipes/tubes with more cold water entering the system. Using thermocouples to record data, five different kinds of tubing were tested: PVC, spa tubing, irrigation tubing, heater hose, and crosshatch-reinforced tubing…


haley.jpg h+w.jpg corbin__.jpg box.jpg

IMG_0054.jpg IMG_0056.jpg Picture_1.png

w_diagram.png jbdkv.png graph_1.png

willie's.png embodied CO2 from flat plate collector

Plumbing is difficult!
• a solar water heating project is essentially a plumbing expedition
• recommended for those with previous plumbing experience

Explosions under pressure…
• Batch heater exploded from city water pressure
• Corrugated metal collector “fizzled” from heat


GUATER Batch heater:

• Viable for use in San Pablo/ developing communities
• Cost effective? ($95)
• Can be scaled up for more capacity

Corrugated metal collector:

• Connections are difficult with irrigation hosing came undone with heat application
• Material not recommended for use in San Pablo
• Further research needed before implementation

• Active system
Small pump required, about 1/10 hp —> Available? (cost, obtainable, electricity)
• Interchanged components of batch heater: jugs/piping/connections
• Copper

“Build your own solar water heater”. Campbell, Stu. Garden Way Publishing. Charlotte, VT. 1978.

“Passive Solar Water Heaters: How to design and Build a Batch System”. Reif, Daniel K. Brick House Publishing Co. Andover, MA. 1983

“Solar Water Heating”. Bob Ramlow & Benjamin Nusz. New Society Publishers. Gabriola Island, BC, Canada. 2010.