Combined heat and power on a domestic scale
Hydrogen fuel cells are not so new in the tech world, but before long they could be commonplace in domestic boiler cupboards.
I recently followed a link posted on LinkedIn that caught my attention. Combined heat and power (CHP) using domestic fuel on a domestic scale. CHP is normally considered for large scale projects, whereby some form of fuel such as gas, oil or biomass is used to drive a turbine to generate power, and the heat produced is used for heating and hot water. Perfect for places such as hotels and student accommodation where there is a high demand for both hot water and electricity. Much like a car engine except in a car much of the heat is discarded except for a small amount to heat the vehicle’s interior in the winter.
The technology I found when I followed the link however took me by complete surprise. It was a strange hybrid that takes in natural gas (or bio gas) as its fuel source, and then delivers enough heat and electricity to supply a reasonably sized house. I researched as deep as I could to gain an understanding of the process so I could feel comfortable with formulating an opinion and be able to describe the technology to our clients as a potential energy solution for their homes.
So how does it work? Hydrogen gas is unsafe to store and transport, however natural gas comprises of 95% methane which is made up of hydrogen and carbon atoms (CH4). This makes methane a reasonably safe and portable hydrogen store.
And what does this elusive piece of kit actually do? It’s a product by a well-known European boiler manufacturer that incorporates four main processes:
1. Extraction of hydrogen gas from methane gas
This process is widely used on an industrial scale and is known as steam reforming. It is a chemical process that produces hydrogen gas (H2) and carbon monoxide (CO) from methane gas and steam (H2O). The undesirable CO by-product goes through another reaction that converts it into carbon dioxide (CO2), the greenhouse gas we don’t want, but at least non-toxic, unlike CO. The cleaned by-product is also free of Nitrous Oxide (NOx).
2. Production of electricity using hydrogen gas and ambient oxygen
This is where the fuel cells come in. The manufacturer has partnered with a large Japanese supplier of fuel cell stacks that are incorporated into the unit. From our high school chemistry we ought to remember that when electricity is passed through water (electrolysis), that hydrogen gas and oxygen are produced. A hydrogen fuel cell is generally a reversal of this process. Take the two gases (H2 and O2), combine them, and electricity and water are created. In this case, 750W of electricity, or 40005000 kWhrs per year.
3. Harvesting of heat energy from the above processes
The fuel cells’ electro-chemical process also generates heat, around 1kW. It is the harvesting of this heat that makes the unit 90% efficient. The energy is first passed into an integral heat store (buffer tank) and then used to supply hot water for central heating and general use. A separate hot water cylinder is required as would be the case with any domestic system boiler (not a combi-boiler).
4. Back-up traditional boiler to meet occasional peak demands
Within the unit is a standard gas boiler that fires up when peak hot water demands exceed the maximum heat output.
Clearly, there is a lot going on here, and the unit itself is around the size of a large American style refrigerator. In the scheme of things this is actually very small and takes up just over 1 square metre of floor area. There are some overall issues of renewable resources, mainly the use of non-renewable natural gas as the source of methane, and the production of carbon dioxide in the methane steam reforming process.
Looking further into the future however, methane is constantly being produced globally by human intervention (livestock farming), and can also be created by the decomposition of domestic food waste (anaerobic digestion). If hydrogen fuel cells are the answer to future energy needs, it’s more about where the hydrogen comes from and how it is extracted, stored and transported.
Here and now I support any technology that seeks to maximise the usage of this extremely clean and efficient fuel. Let’s just hope that in time the raw gases needed come from sustainable sources.
