In the event you can have microwave ovens, why not microwave kettles? – The economist


A small British company wants to give it a try

April 7, 2021

Declaring an economy is a big job. Coal and gas power plants have to be exchanged for wind, solar or nuclear power plants. Gasoline-powered cars need to be replaced with electric versions. Less attention is paid to heating. In cold countries like the UK, heating homes, offices and the like uses more fossil fuels than generating electricity or transportation.

The fuel is usually natural gas. This is burned in a central boiler to heat water that flows to radiators elsewhere in the building. The UK government wants to change that. From 2025 gas boilers will be banned in newly built houses. This ban will also apply to existing ones until the mid-2030s.

The question is, what should they be replaced by? In contrast to power generation, where renewable energies are proving to be popular, or cars, where battery-powered vehicles are quickly establishing themselves, the green heating market is for everyone. Common suspects (assuming the electricity being fed in is generated by appropriate non-carbon dioxide means) include electric immersion heaters, heat pumps (devices that work a bit like refrigerators, extracting heat from the surroundings of a building and then pumping it into that building) and hydrogen burn instead of natural gas. However, engineers at a small British company called Heat Wayv believe they might have another competitor: microwaves.

The principle is the same as in a microwave oven. Many molecules, including water, are electrically dipolar. This means that they have a positive charge on one end and a negative charge on the other. Therefore, they rotate to align themselves with a strong electromagnetic field. When this field oscillates, as is the case with electromagnetic radiation such as microwaves, the molecules themselves also oscillate – in the process they bump into their neighbors and bump them, thus generating heat.

But building a microwave kettle is more than just reusing the parts used for an oven, says Phil Stevens, one of the founders of Heat Wayv. Most microwave ovens use magnetrons – bulky devices built by surrounding a cathode with a carefully shaped anode designed to generate electromagnetic radiation of a specified frequency. With the help of a couple of major chipmakers, Heat Wayv developed a solid-state device that does the same job but fits on a 10-square-inch silicon chip.

Arrangements of these devices emit microwaves in a kettle in water and heat it. The pipes that carry the water are also made of microwave-sensitive materials, as is the insulation that follows them. And a heat exchanger recycles the residual heat from the waste. The result, says Mr Stevens, is a boiler that is 96% efficient. The best existing gas boilers manage about 90%.

Efficiency is important as moving away from gas means higher heating costs. Electricity is necessarily more expensive than the fossil fuels from which it is often still generated. In the UK, a given amount of energy supplied as electricity currently costs three or four times as much as the same amount supplied as natural gas. Switching to renewable energy is unlikely to change that. Although the “fuel” (wind or sunlight) is free, other costs are often higher than with traditional power plants. When customers are legally forced to switch from gas, they can be sure of the costs in view.

Heat Wayv argues that its technology offers advantages over competing methods. Immersion heaters must run continuously to provide water at a suitable temperature. This often heats water that is never used. In contrast, like existing gas kettles, microwaves heat the water fast enough to only provide it when it is needed.

Heat pumps also have disadvantages. Their efficiency drops on cold days when they are most needed. They’re bulky too. And they produce water that is warm rather than hot and often requires larger radiators or underfloor heating to be retrofitted.

Meanwhile, hydrogen must either be obtained from natural gas or generated by electricity through water. Both processes are inherently inefficient and the former is barely green. The infrastructure needed to generate and deliver large quantities of hydrogen also does not yet exist (and may never exist).

Heat Wayv hopes to have microwave boilers available for sale by 2024, in time for the first phase of the government ban. According to Stevens, the idea has caught the interest of most of the UK’s major home builders. Perhaps microwaves will soon heat people’s water and food.

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