Solar23 Mar 2011 01:32 pm

GeyserWise GeyserWise Power Save Mode

GeyserWise . . . . . . not saving in Power Save Mode

As far as I’m concerned, my GeyserWise thermostat timer paid for itself within a few weeks. Then it started costing me money.

The GeyserWise is an electronic device that replaces both a timer and the thermostat on an electric geyser element. As I have stated before on this website, a timer is an essential part of a hot-water solar system. The GeyserWise would appear to be the ultimate geyser timer, allowing the user to set multiple programs to turn the geyser element on and off, to see the temperature inside the tank, and to adjust the thermostat setting from a comfortable position several meters away from the geyser itself. No more crawling into the roof space with a headlamp and screwdriver.

I paid R1300 for my GeyserWise, including installation by an electrician recommended by the manufacturer. Here’s how it paid for itself so quickly. Monitoring the temperature inside my tanks, I started noticing that the water would cool off by a few degrees in the late afternoon every (more…)

Appliances &Solar11 Feb 2011 01:15 pm

Dishwasher Plus Solar PanelsEqual SignGreen Smiley

When I first wrote on GreenerHouse about dishwashers, I lamented that I could not find one with a hot-water inlet. For most of the year, I have an excess of solar-heated hot water sitting in tanks, so it is a waste for my dishwasher to be electrically heating cold water. At the time, I had been misinformed by a Bosch technical expert that the inlet to my dishwasher could handle a maximum of 40 degrees. Like an idiot, I hadn’t read the manual, which says that the inlet can take up to 60-degree water.

Water heated by flat-panel solar collectors does not tend to rise much above 60 degrees, and my kitchen is far—too far—from my water tanks to ever get to 60 degrees at the tap, according to my thermometer. (Vacuum-tube panels do often produce much hotter water, and may require a thermostatic mixer to keep temperatures at safe levels.)

So I recently asked my plumber to connect the hot water to my dishwasher. My hypothesis was that the thermostat inside the dishwasher would switch off the heating element more quickly with warm water entering the machine. Using a cold-water feed, this Bosch, A-rated model uses approximately 1 kWh per load at the 35 degree “Quick Wash” setting. After connecting the hot water, I recalculated the energy consumption, using the technique outlined here. It has fallen to 0.7 kWh per wash. Over the course of a year, this simple change should save about 100 kWh preventing some 100 kilograms of carbon dioxide from being released into the atmosphere.

If my dishwasher were located closer to the hot water, the savings would be far greater. In designing a new house, ideally the north-facing roof, solar panels, hot-water tanks, bathrooms and kitchen should all be as close as possible. If this is not possible, small-diameter Pex pipes can help overcome heat loss over long distances. (Combining Pex pipes and vacuum-tube solar collectors is asking for a meltdown, however.)

I compensate by running the hot water in the sink, usually while washing pots and pans, immediately before switching on the dishwasher. That way the water enters the machine hot for the wash cycle, though only slightly warm after the copper pipes have cooled the water for the two rinse cycles. One day I will try insulating the pipes and see if I get even better results. In the winter, when the sun does not always provide enough hot water, I will try to run the dishwasher in the late morning, so as not to deplete the evening supply of hot water.

Coincidentally, just days after my plumber had made the connection and before I had a chance to measure my results or write about it, a GreenerHouse reader published a comment here, reporting how pleased he was with his hot-water connection to his dishwasher. All green minds think alike.

Appliances &Solar18 Nov 2010 02:35 pm

The early summer cold-front that has been chilling Johannesburg for the last few days has me scratching my head. I measure my electricity consumption regularly and record it on a spreadsheet, and suddenly found that the household’s daily usage had jumped from about 15 kilowatt hours to about 25. Then we ran out of tea just a few days after we opened a box of 80 bags. Could there be a connection? Four children are at home studying for exams in the cold, and teacups have been piling up on their desks. With a thermometer, a stopwatch and a calculator, I set out to solve this mystery.

To raise a litre of water by one degree Celsius theoretically requires 0.0011 kilowatt hours, so heating my 1.7 litre kettle from tap temperature to boiling, 17 to 97 on my thermometer, should use 0.15 kWh. But since it took 3:48 to boil while using approximately 2750 watts, the actual consumption was more like 0.175.  (My Watts Up meter cannot handle appliances over 2000 watts, so I could not measure directly.) The inefficiency probably comes from the heat lost warming up the stainless-steel kettle itself—a plastic kettle might reduce those losses—and the delay between when the water reaches boiling and the kettle shuts off.

Of course, they don’t all share a pot of tea at once, so I used a spreadsheet to simulate two scenarios. In one, my children have suddenly become green angels, and measure out exactly one mug full of water into an empty kettle to boil. Under these ideal conditions, their additional 24 cups of tea a day would use just 0.59 kWh. The worst-case—and very common—scenario is to fill a kettle and boil it over and over again  until nearly empty before repeating the process. Under these circumstances, those same 24 cups of tea use nearly three time as much electricity, or 1.61 kWh. (Even after taking into account the warm water that is being re-boiled.)

My mystery is not entirely solved. The kettle could account for a sixth of the increase, but the rest must come from addition lights burning at desks, the refrigerator door opening and closing for study snacks, and those electronic devices that seem to take over study breaks.

Still, I’ve learned something useful. Changing kettle habits can make a significant impact on consumption. The Eco-Kettle is designed to make this simple, saving you from running back and forth to the sink to measure another cup of water. The water reservoir at the top of the kettle can release measured cups of water to the element at the bottom. It is available from a few sources in South Africa for R450 and up. Six people drinking 4 cups of tea a day with a full-kettle habit to break could probably save enough to pay for the expense in a couple of years.  I’ve seen a few complaints on the internet about durability, however, and I wonder if a simpler solution wouldn’t suffice. I plan to put a water jug next to the kettle and ask my family to measure out the water in their teacup before pouring it into the kettle. (Our kettle has a flat bottom. If yours has a raised element, it may need extra water to cover the element.) It should save them time, too. My stopwatch tells me that a cup of water boils in 51 seconds. A full kettle takes nearly 4 minutes.

While on the subject of kettles, I sometimes use ours as a back-up geyser. I try to keep the electric elements in my two, 300 litre solar-heated geysers switched off, and most days I don’t need them. But occasionally I have been seen pouring a few kettles full of boiling water into a bath on a winter night to keep my wife from grumbling about my solar fanaticism. This causes her to ask, “wouldn’t it use less electricity just to turn on the element in the tanks for an hour?” My spreadsheet provides the definitive answer. Boiling even five kettles of lukewarm water from the hot tap uses 2/3 of a kilowatt hour. The 4000 watt element on the geyser would use 4 kWh in an hour. There are times when a full kettle is green.

Heating and Cooling &Lighting &Solar &Water Use/Greywater29 Jul 2009 01:43 pm

Real Simple 1 Real Simple 2

The July issue of Real Simple magazine is now off the newsstand. So in case you missed it, I am reprinting my article about green renovations. The editors asked that the information be presented  as a series of questions for the various contractors that might work on a home renovation. I couldn’t really do justice to any of the subjects covered in that format and the space allowed, so I will try to expand upon some of them in future posts.

Crumbling house prices and economic jitters have convinced many homeowners that it’s safer to adapt what they have to what they need, rather than jump into a shaky housing market. But can a renovation help your house adapt to the planet as well?

Throwing a few photovoltaic solar panels on the roof won’t make your home green. And environmentally sensitive architects have moved beyond the singular obsession with energy efficiency. The catchphrase of green building in the 21st century is “embodied energy.” How much fossil fuel went into the bricks, cement, steel and glass that make up your house? What quantity of greenhouse gases is your home responsible for even before you switch on the first light? For some houses, the embodied energy of day one will exceed the sum of a few decades worth of electricity and gas bills.

Building in harmony with nature means working with the local climate, local suppliers, and even local soil. There is no one-size-fits-all solution. Instead of waiting for easy answers, start with the right questions. And if a contractor stares blankly at the ceiling in response to your queries, you may want to look for someone with greener credentials.


How earthy can our house be? Green architects agree that adobe, cob and rammed earth are wall materials of first choice for low embodied energy. An architect who has worked with them will know whether they suit your project. The biggest concern: banks will not approve a bond for new structures supported by such raw materials. A home renovation, however, may be able to get financing.

Can we aggressively pursue passive solar? The right combination of windows, walls and floors can supply most of your heating needs in sunny South Africa. But a large roof overhang is vital to keep the high summer sun out. If your architect cannot calculate the ideal overhang based on your latitude, orientation, roof pitch and height, find another architect.

Can we build around a wood stove? If you have a local source of sustainable wood, such as suburban tree fellers, a closed-combustion wood stove is the greenest way to heat. But with all of your warmth concentrated in one spot, careful designing is needed to help the heat reach colder parts of the house. Keeping the stove central to an open plan but away from any double-volume ceilings is a good start.

How can our home use nature’s air conditioning? Your architect should know how to take advantage of prevailing winds. Low windows on the cooler, south side of the house can draw breezes to force out summer heat from high windows on the north side. Drain the pool of heat on your ceiling with small, high windows that you can leave open all night without worrying about cats or cat-burglars. Transom windows aid the flow between rooms. Trees or shutters can shield western surfaces from the afternoon sun. Don’t let some sweet-talking salesman convince you into electric air-conditioning until you’ve given nature a chance.


Global Warming &Solar09 Jun 2008 03:28 pm


Since the issue of Maverick containing my Solar Photovoltaics vs. Diesel Generators article is off the newsstands, I can now publish the article in full on Greenerhouse. Enjoy:

Bringing Back the Light:

Diesel vs. Photovoltaic

It began with an email. My brother-in-law asked me, the family’s resident green guru, to weigh up the relative merits of diesel generators vs. solar power.

Load shedding is clearly driving him to distraction. Computers are crashing in his home office, and he has scrambled to reschedule meetings of 30 and 40 people to stay out of the dark. He wants to know that the power will be there where he needs it, when he needs it. “I’m looking for a complete solution, and I don’t want hassles,” he told me, admitting that he was close to choosing the diesel route.

But he also knows that his green credentials need some buffing since he traded in his Honda Jazz for a Land Rover Discovery last year. Is solar electricity an affordable alternative?

Until the beginning of this year, the answer to his question would have been simple: In South Africa, solar cells may be virtuous, but they don’t pay for themselves. (Solar hot-water panels do pay for themselves, but you can’t run your PC on hot water.) Even the national sales manager for Sanyo photovoltaic panels in South Africa, Win Kurzyca, says, “it doesn’t pay me to put 10 of these on my roof—even at staff price—instead of paying 32 cents a kilowatt hour for electricity.”

But suddenly everything has changed. In fact, the question has changed. My swaer is not asking whether photovoltaic panels pay for themselves; he wants to know whether solar electricity is competitive with diesel-generated electricity.


Solar20 May 2008 03:26 pm

I cannot yet reprint my article on solar photovoltaics vs. diesel generators from Maverick magazine as long as the issue remains on the newsstand. But I can share a  few thoughts from what I have learned while reporting the article:

Prepare Ye the Way of the Panel. For years we’ve been promised that photovoltaic panels will come down in price as volumes increase. Well, volumes increased, but prices went up. Demand rocketed in Germany, Spain and elsewhere as governments made solar attractive financially. Solar-cell factories couldn’t be built fast enough to accommodate the new buyers, so the law of supply and demand took over. This is a temporary situation. As new factories are commissioned, prices will fall to not-yet-seen lows. If you’re feeling flush with cash and impatient, go ahead. Early adopters play a great role in advancing the acceptance of any new technology. But for most of us, it makes sense to wait, especially if the S.A. government implements a feed in tariff—like the one in Germany or Spain—which pays households for surplus solar electricity they feed into the grid.

In the meantime, there is plenty of work to do while getting your home ready for cheaper solar. Photovoltaics produce less electricity than you would expect. They belong in houses that already have low electricity consumption. Replace that old fridge. Install compact fluorescent light bulbs. Invest in a gas stove. Install a solar hot water panels, perhaps with gas back-up instead of electrical back-up for cloudy days. Consider space heating with gas or wood. And if you are doing any remodeling, plan a space in advance for batteries and an inverter. They need protection from the elements and ventilation, preferably in a location close to your circuit board.

It’s Your Health, Too. Burning more diesel is not just bad for the planet, it’s bad for you. Diesel fumes are known cancer-causing agents. Would you want your neighbour to idle his 1979 diesel Land Rover Defender in your driveway for several hours a day, spewing carcinogenic fumes toward your family? Running a diesel generator is no different.

You Get What You Pay For. People are always telling me that generators are cheap. And to look at the advertising inserts from D.I.Y. stores, you would think so. But some of these generators do not even have voltage regulators, leading to blown TVs. Even better generators with voltage regulators can create brief surges that are harmful to sensitive equipment. Seamus Finnegan of Northern Technologies SA recommends two layers of surge protection to protect against electrical current spikes as well as an uninterruptible power supply to keep computers operating during the lag between the beginning of load shedding and the start-up of the generator. “We see a lot of damage done by generators,” say Finnegan.

Heads Solar Wins, Tails Diesel Loses. Okay, maybe I’m biased, but diesel has problems under both scenarios facing South Africans. If load shedding becomes a serious regular occurrence, then the fuel expense begins to eclipse the upfront capital expense, and solar becomes more attractive financially. If Eskom gets its act together and load shedding ends, anyone who opted for solar still has a source of free, green energy. Those who bought a diesel generator are stuck with a rusting eye-sore.

Solar &Uncategorized14 May 2008 05:20 pm

The latest issue of Maverick magazine, which is arriving on newsstands this week, includes an article I wrote comparing diesel generators with solar photovoltaic panels. The point is that solar cells are normally considered pricey, with little hope of paying for themselves in the near term and maybe not even in the long run. Load shedding changed all that, however, because many South Africans are now shelling out tens and even hundreds of thousands of dollars for diesel generators to make themselves Eskom-proof. In my article I compare what happens if that money is instead put into generating solar electricity on the roof. I use actual quotes for systems for one house and then run the numbers to see how the two options compare over time.

When this issue of Maverick comes off the newsstand, I will post the article in-full on GreenerHouse. In the meantime, I will share a few insights from my reporting here in the next few days.

Solar &Uncategorized21 Nov 2006 04:36 pm

Solar Hot Water Panels

Spring, summer and fall, I take pride in keeping the electricity to my geysers off. The water is heated purely by the sun. With a little bit of luck I can even make it through one overcast, rainy day with the hot water stored in my tanks.

But when we were hit this weekend by three successive gloomy, soggy days, I threw in the towel. With the electricity flowing, I sensed an opportunity, however. I had always wondered how much I was saving with my solar hot-water panels. When I installed them, I was making a hundred other changes to my house. Simply comparing my electricity consumption before and after the solar panels won’t answer that question.

So yesterday morning, I decided to experiment. Assured of no sun, I switched off the pump to the panels and recorded my municipal electricity meter reading. [Switching off the pump was essential because even in cloudy weather, solar panels will warm up enough to heat water to a small degree. Waiting for a cloudy day was essential to avoid overheating the fluid in the panels that was not circulating.]

This morning, I ended my experiment and checked the meter again. My household had used 45 kilowatt hours of electricity in 24 hours, compared to 26 kilowatt hours on a normal weekday in recent months. (I monitor the meter rather obsessively.) This means the solar panels are cutting my electricity consumption by approximately 42 percent.

If we have 300 days a year of decent sun, the panels are saving about 5,700 kWh a year. That translates into sparing the atmosphere 5.7 tons of carbon dioxide annually. My financial savings are not quite as dramatic—and not as important in my mind—but still worth noting. At the current Johannesburg charge of 31.18 cents per kilowatt hour, I am saving R1 777 per year. At this rate it will take me at least 20 years to pay back my large and complicated solar hot water system. Simpler systems cost less than half as much and will pay for themselves much more quickly.

Is my 42% saving typical? Dylan Tudor Jones of Solar Heat Exchangers, the company that installed my system, tells customers that they may save up to 50 percent on their electricity bill. Given that my house used to have two electric geysers, I may have cut back that much. I doubt, however, that most people can slice their electricity consumption in half with solar panels. I have a larger-than-average system—3 panels and 600 litres of storage—and my vigilance against wasting power throughout the house means that geysers were using a disproportionate share of the total. But whether a solar hot-water system saves 20, 30 or 40 percent, it is the smartest step a South African can take toward creating a greener house.