Instructables
Picture of Low Power Solar Electric Kettle-Thermos
Introduction
This Instructable describes how I built a low power, electric kettle-thermos to heat up water. It is made of reused/repurposed components and is suitable for use with an off-the-grid PV panel. I have a single panel connected to a small inverter that puts out 120V AC.

Electric kettles that you typically see use 1000 or more watts, because people want their water heated ASAP. However, if you’re not in a rush, then you can get by with a lot less power. Mine uses only about 15 Watts, and, on sunny days, while I’m gone at work, it heats up 1.25 liters of water to boiling. Even on days when it has been mostly cloudy, the heater was on enough of the time that the water temperature was 160 F when I got home from work. In the evening, I can use the water to wash dishes, and since the kettle is also a thermos, the water is still hot enough for dishes the following morning. I don't use the water for drinking because I'm not sure that the heating element is completely free of materials that I would want to ingest.

Pros and Cons
I know that electricity is an inefficient way to heat water, and that a solar thermal system could easily to as well or better. However, if one has the available PV power, then efficiency isn't really an issue. Furthermore, it would be quite challenging and complex to use solar thermal to heat water in a thermos. This device is really compact, and the water will stay plenty hot for hours after the Sun goes down. By using the water to wash dishes, I save a little bit of natural gas. I dilute this water with tap water, and I get enough hot water to wash a load of dinner dishes for 2-3 people.
 
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manuka9 months ago

A great idea, especially since thermos vacuum insulation is so brilliant & that "wired sunlight" gets around all the hassles of piping & storing hot water!

However I'd not be happy for safety reasons using an inverter as you've done to
give stepped up voltages. It adds to the system costs anyway

I've trialed similar approaches with home made elements (rescued from burnt out toasters) placed inside a glass test tube & run from 24 V PVs. Automotive filament lamps can also be used to good effect. This higher 24V supply voltage - readily made using 2 series 12V PVs -is still electrically safe, but has less cable voltage drop than 12V. Thus more heating power to the element will be delivered thru' the same cabling. The copper supply connecting wires should still however be as thick as possible to reduce losses.

Perhaps consider the following-

* Your higher voltages, especially near water, raise ELECTRICAL SAFETY concerns!!

* Prevention (via different plugs etc) to stop it ever being mains connected.

* With larger panels now tending as low as US$1 a Watt, 15 W PVs are peanuts. A couple of 20W in series would do well I'd say, & they'd fold for storage and could be individually angled for best sun uptake. If you've the budget a 80 W or higher panel would heat faster OR/AND give good heating on overcast days etc.

* It's worth mentioning that hot sun will lead to reduced PV outputs too. The little darlings work best when cool!

dlginstructables (author)  manuka6 days ago
I keep hearing about $1 a watt PV, but I've never found any panels that are that inexpensive. Can you tell me where?

Yes-that "Dollar a Watt" figure certainly gets some airing! Availiability at such prices depends on the panel size (smaller ones are more costly per Watt), type ( poly/mono/amorphous) where you live,mounting hardware, greedy middle men, wiring runs/cable size, supply voltage, transport, installation ease,how handy & resourceful you are, new/used (folks are continually upgrading from smaller ) & your trade contacts etc. Check these 130 to 250 Watters for much the magic price =>

http://www.trademe.co.nz/business-farming-industry... and

http://www.trademe.co.nz/business-farming-industry...

Stan. in sunny New Zealand.