Hot Water


Global Warming &Hot Water &Solar10 Sep 2015 12:44 pm

Solar Hot Water Panels

The Highveld winter drought broke this past weekend with a two-day deluge. The soil needed the rain, but when you ordinarily heat your water with just the sun, it’s painful to switch the power on for the geysers. I cheered myself up with the thought that I could check how much electricity I would be using without my solar hot water system.

My home’s consumption for this sunless Saturday and Sunday averaged 30.5 kilowatt hours per day. In comparison, on the four previous weekends I was using 12 kWh/day. Assuming that hot water accounts for the difference, the sun ordinarily saves me 18.5 kWh/day, cutting my electricity bill by more than half. (I monitor my consumption using a customised spreadsheet you can download here.)

This is very close to the 19 kWh in savings I calculated in a different test here. My solar system is large — with 3 flat panels, 1 evacuated-tube panel and 600 litres of storage — and the rest of the home is very efficient, so I couldn’t promise such dramatic results on every house. But this gloomy weekend tells me that solar is saving me at least R9,000 a year, not to mention keeping 5 tons of carbon dioxide out of the atmosphere.

That’s a sunny thought no matter what the weather.

Hot Water &Solar27 Mar 2015 02:35 pm

Solar Hot Water Panels

If you are considering whether to install a solar water heater, you might want to move fast. Eskom’s rebate programme has been extended to cover solar systems installed by the end of April 2015 as long as applications are submitted by the end of May. The rebates can reduce the up-front costs of a solar water heater by up to R11,000.

This isn’t necessarily the end of solar rebates. A plan was in place to shift the responsibility for the rebates from Eskom to the Department of Energy. The extension is a stopgap measure because it appeared that the DOE was not ready to launch its rebates, and the prospect of halting incentives at a time when the grid needs all the help it can get was exactly the wrong message to be sending. The DOE has not made public all of the details of its rebate programme, but has warned that it will place a heavy emphasis on requirements for South African manufacturing content. If you can afford to install now, at least the rules are public and the rebates well-established. Better the devil you know . . .

In this era of load-shedding, there is an extra consideration to take into account when deciding on a solar system. The most efficient solar water heaters use a circulation pump between the panels and tanks, but when the electricity is off, not only does the water stop heating, but the panels can overheat. So opt for either a thermosiphon system, which needs no pump, or a pumped system that is powered by solar cells. Some hot water panels are even sold with a miniature photovoltaic panel built in to run the pump.

To help you get started, read the Guide to Solar Hot Water that I wrote for the My Green Home website.

Finally, Eskom has extended the rebate but not their solar hotline. Direct any questions to the ordinary customer service line 08600 ESKOM.

Hot Water23 Feb 2015 05:55 pm

Switched off geysers

Switched off

I’m no party animal, but I attended four social events this weekend. My takeaway from a dozen or so conversations is that South Africans are seriously looking for ways to save energy. People were telling me about their new efficient fridges and gas stoves. A property developer explained how Standard Bank is saving thousands of tons of carbon dioxide by generating its own power from gas in Rosebank.

One question came up at two different parties: Does it save energy to switch off the geyser for part of the day? This is a query I’ve heard so often that one could be forgiven for thinking that it was the Number 1 issue in energy efficiency. People take passionate stands on either side of the debate. One person told me that he’s saving hundreds of rands each month by switching the geyser on and off. Another said she had heard that it uses more electricity to heat the water back up than to keep it hot.

Here’s the disappointing answer to the most-discussed issue in home energy conservation:

It’s no big deal.

You can save a little electricity with daily switching, but you could save a lot more by lowering the temperature of your geyser thermostat, buying low-flow shower heads, or insulating the tank—not to mention the even larger savings from installing a solar water heater or heat pump.

If your geyser were perfectly insulated, switching would save nothing. Because it is not, the element will reheat the water from time to time even if no one is using hot water. If the element is off, however, the tank loses heat more slowly as the water gradually cools. All of that water has to be reheated when you turn the geyser back on, but because overall tank losses were lower than if the tank had been kept hot, it requires a little less energy than repeatedly heating the water over that same period of time.

What about the guy who said he was saving hundreds of rands? If your geyser has been off for several hours and you switch it back on, any shower you take or dish you wash before the water has been fully re-heated is saving you significant energy, because switching off and on is effectively lowering your thermostat setting. These savings can be large, but you could have saved that same energy more consistently and easily by simply lowering the thermostat on the geyser. Unconvinced? You can read more here.

Electrical engineer TC Venter has a long, technical article on the subject of options for saving electricity with hot water heaters in Watt Now and comes to this conclusion: “short switch-off periods (less than a day) do not really contribute meaningfully to energy saving.” But Venter did bring up one exception to this rule.

There is one special situation, if one thinks it through carefully, in which a timer can be used daily to eliminate practically all standby power. If the occupant of the flat is single and a creature of habit, who only needs hot water to bath or shower at 07:00 each day, a small (50L) geyser could be run like an electric kettle: an electronic timer could be set to switch the geyser on for one hour at 06:00 every morning, to ensure hot water at 07:00, but not to reheat the geyser after its hot water has been used. The geyser remains cold until the next morning at 06:00, thus no standby power is required.

Of course switching off the geyser when you leave home on a trip can add up to real savings. Switching off during Eskom’s peak hours of 5 to 9 pm is also good for the country, if not for your utility bill. And timers are essential with solar water heaters to avoid using electricity to heat up the tank after morning showers, just before the sun has a chance to do its work. Finally, if you really want to switch your old-fashioned electric geyser on and off every day during idle hours, go right ahead. Just don’t imagine that your hot-water electricity consumption is solved.

Hot Water &Water Use/Greywater03 Mar 2014 11:48 am

Shower Head

A Strong Buy

When I last wrote about low-flow shower heads, I focused on just two findings: The water savings were dramatic — I measured that my shower rose uses half the water of my neighbour’s — and the experience under the spray was as good as the old, wasteful showers.

This week I have calculated that low-flow shower heads are also an amazing investment that beats anything you can find on the JSE. Because they cost so little (R100 to R500), and you save on both water and the electricity to heat it, the returns can start accumulating within months.

Take this example: a family with a standard electric geyser that takes 3 daily showers of 4 minutes each — or one teenager in the shower for 12 minutes a day — replaces a typical 14-litres-per-minute shower head with a 9 l/m model. (All new Cobra heads use 9 l/m.) At the end of one year, the savings from water and electricity are more than R1200 at current Jo’burg tariffs. Even if they splashed out on a R400 shower rose, this family has profited R800. And the returns continue, with a “dividend cheque” of more than R1000 each year. If you know of an investment that good on the JSE, please email me.

Savings will be lower if you are using solar panels or a heat pump to heat your water, but a 12-minute-a-day family will still cover their outlay in less than a year. If you want to test whether you are currently wasting water in the shower, just put a bucket under the spray for 12 seconds. If well over 2 litres collected in the bucket, your shower head is using more than 10 l/m and could do better. Three litres in 12 seconds is 15 l/m, a real water waster.

My last discovery this week was a YouTube video on how to change a shower head that takes all of the fear and mystery out of this simplest of plumbing tasks. The video is by the same people who produce the black-and-yellow “. . . For Dummies” books. This one should be called “Investing for Dummies.”