Could a microwave be used to heat a home?

15 November 2016

Question

Why can we not install and use microwave technology for domestic central heating systems, to heat the water and radiators in the home, cost effectively?

Answer

We put this question to tech investor Peter Cowley...

Chris - Here's one for you Peter: this might be a potential new money-spinner for your business arsenal who knows? This is a question from Jules who wrote to us to say:

Could we install and use microwave technology for domestic central heating systems, to heat the water and radiators in the home, cost effectively?

Peter - Yes, thank you, yes. This amused me quite a bit because I actually misread it to start with and I thought could a microwave be used to heat a home? And I thought Um, you could put the microwave around the home.

Chris - It wouldn't look so good in the fireplace though would it?

Peter - Well actually the other way round. So yes, interesting idea actually because we use microwaves for heating small items very, very effectively compared with putting them on the stove, but it isn't going to work for a number of reasons.

First of all based on a consumer microwave it's actually very inefficient. Its at the order of 70 percent efficient and that means that for every kilowatt, 300 watts are disappearing in heat.

Secondly, the cost. My own gas boiler at home is 91 percent efficient compared with 60 or 70 percent and it works out about £35 a kilowatt. Whereas a microwave would probably cost about £100 to £150, so it's about four times more expensive.

Thirdly, and a very big one here, at the moment with the consumer microwaves the MTBF, which is the mean time between failures, is only about 2,000 hours. So 2,000 hours is about 12 weeks of heating so you'd have to change your "boiler" every 12 weeks. A boilers about the order of about 10 years, we hope, but probably a bit less nowadays, but that's 88,000 hours compared with 2,000 hours. And so, it works out because of that reliability the capital cost is about 100 times more.

And then on top of that, mains gas, which my boiler is, is about 3 or 4 times cheaper per kilowatt hour than electricity. So, all in all, something very major would have to happen or destructively change in order to use a microwave to heat the water in a house.

Chris - Georgia.

Georgia - I have a question about the waste. You said there was about 30 percent wasted energy but it was wasted as heat. Surely that's not a problem if you're trying to heat things.

Peter - No, that's right. But it's heating in the environment where the microwave is, so you'd actually also have to cool and take water through that air as well. But you're right, that is converting electricity.

Comments

Can you put enough microwaves through a house to kill roaches or would this not be feasible?

It's notoriously difficult to kill cockroaches and other infestations with microwaves owing to the wavelength of the wave:

https://www.thenakedscientists.com/articles/questions/can-ants-survive-m...

https://www.thenakedscientists.com/podcasts/ask-naked-scientists/can-you...

It's more likely you'd end up setting fire to your house in the process. Then again, that would kill off the cockroaches, so I suppose it would work in that respect...

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