AIDG Blog [Appropriate Technology, Development, Environment]

UCB Batch Solar Water Heater install at Papa Carlos & Mama Coney’s in Guatemala

Ducking down in the shower trying to avoid the occasional errant shock, I have many times wished that solar water heaters would replace calentadores in Guatemala. The calentadores, or on-demand water heaters, most often used in urban homes there are electric shower heads. In these systems, a large amount of electricity (3400-5000W) heats a small amount of water before it trickles onto you. During my visits, I’ve noticed that the quality of installations varies widely from home to home. Sometimes and rather worryingly, wires are sloppily covered in electrical tape and hang exposed with no conduit caps or obvious grounding wires.

Electric shower heads such as these use a large amount of electricity to heat water and can deliver a nasty shock even when properly installed.

In terms of heating water for cooking rather than bathing, propane gas or electric stoves are the norm for urbanites. Rural families, 70% of whom are without access to electricity or modern fuels, tend to use firewood for heating water. Overall, obtaining hot water is a very energy and resource intensive process for rural and urban dwellers alike.

Despite the abundance of sunlight even in the cooler highlands where we’re based, the use of solar thermal power as a source of energy is rare in Guatemala. There are a few providers like Casa Solar who are trying to have a go at it, but they tend to cater to a wealthier clientele. Typical systems range from $400-$1000+.

Annual solar potential in Guatemala, Belize, Nicaragua and Honduras

XelaTeco’s Candido Morales checking out Casa Solar’s evacuated tube solar water heater

Few local manufacturers or retailers are trying to create these green products for the lower end market. At AIDG Guatemala, we have 2 very promising solar water heater designs that we’re hoping our incubated businesses can produce for about $100: a serpentine flat plate collector and a batch collector. The latter is being designed by a research team from UC Berkeley headed by Ashok Gadgil, that we’ve been partnering with since spring 2007. Of the 2 systems, the UCB solar water heater is the closest to being ready for manufacture by XelaTeco.

While solar water heaters can be very complex with integrated pumps and rotary elements as seen in active systems, the simplest ones have no moving parts and don’t use an external energy source to move water through them. Instead they take advantage of gravity and good old thermodynamics. These passive systems require less maintenance and repair and tend to be less expensive.

Solar water heaters can also vary in how heated water is stored. You can have an integrated storage-collector (a.k.a. batch) systems in which the solar collector and water storage are one unit. The other option is a separated storage-collector system where water is maintained in a separate insulated storage tank.

UC Berkeley Passive Solar Batch Water Heater
In essence, the batch solar water heater consists of a sheet of glass for glazing, a heat-collecting surface (absorber), a water bladder made of thick black high-density polyethylene, insulating material to cut heat loss and inner and outer casings.

Since their first tests at the Lawrence Berkeley National Laboratory last year, the team’s designers (Sara Al-Beaini, Kenneth Armijo, Merwan Benhabib, Alissa Johnson, Margaret Harper, and Howdy Goudey) have made many improvements to their initial design and have optimized components based on what is readily available in Guatemala. The end goal is to create a well-performing design that can be mass-produced efficiently in Guatemala and elsewhere in the developing world.

2 earlier prototypes of the UCB solar water heater

This past summer, prototypes were installed at the homes of 10 low to middle income families in Xela. A major design challenge the team still must address is how to retain heat overnight and cope with the variability in temperatures and sunlight between Guatemala’s dry and rainy seasons.

In the coming months, the Berkeley team’s business/implemention members (Samantha Engelage, Adam Langton, Ernesto Rodriguez, and Jing Yuan) will be working with AIDG and XelaTeco on plants for production and distribution.

Related Articles:
Building affordable solar water heaters [CNN]
Students invent affordable water heater [ABC News]
Domestic Solar Water Heater for Developing Countries [pdf]

For more information on solar hot water systems see Appropedia and the US DOE’s Energy Efficiency and Renewable Energy site

Related Posts:
10 Everyday Technologies That Can Change the World
Casa Solar at XelaTeco
Earthships in Taos, New Mexico [Photos, Video]
Cart before the horse: generating demand vs. early capacity building

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