So. You’ve just upgraded your old central heating boiler to a brand new, highly efficient condensing combi boiler and you’re feeling pretty good about it. It came with an excellent warranty and service package and you’ve been advised that the central heating, the remote access control system and the sophisticated programming features are all examples of the latest technology.
Then your neighbour gleefully informs you that he is planning to install a micro CHP system. This naturally deflates your buoyant demeanour and sends you scurrying to the internet to see what advantages your neighbour might be obtaining.
Combined heat and power (CHP) boilers have been around since the 1970s. Due to their size, weight, cost and operating noise, they have generally only been suitable for industrial and large communal facilities. They have been installed to primarily generate electricity, usually by internal combustion engines and dynamos, with the secondary heat by-product being utilised for central heating purposes.
In recent years, technological advances, spurred on by rising energy costs, have enabled the concepts of the commercial CHP boilers to be adapted for domestic operation. These new compact and vastly superior devices are referred to as micro CHP boilers.
Although much of the technology is still in the developmental field, some micro CHP boilers are available on the market.
Current models are similar in size to a large domestic condensing boiler and are wall mounted. They are also plumbed into the central heating system in much the same way. They do require installation by a Gas Safe engineer and a Micro-generation Certification Scheme (MCS) approved installer. What makes domestic micro CHP boilers special is that in producing heat for domestic hot water and central heating, they also use the heat to generate electricity for the home. Any surplus electricity is then directed back into the grid. The boiler owner receives a payment for the electricity produced for domestic use and also a payment for surplus electricity fed back into the grid.
At first sight, it can all appear very attractive, and no doubt, the neighbour has seen this as an opportunity too good to miss.
There can be no doubt that electricity produced from a remote power station is a dirty, inefficient fuel. Only about 30% of the energy from the source fuel is actually available to the consumer. The rest is lost in production and supply.
Being able to produce electricity at the point of usage has great advantages and can provide energy efficiency levels in excess of 90%.
The vast majority of micro CHP models currently available employ the actions of a Stirling engine to generate electricity. Stirling engines are classed as external combustion engines. They utilise the properties of internal chambers filled with a gas, usually helium. This gas is responsive to areas of hot and cold within the chambers. Applying heat to the gas causes alternating pressures as it moves to a colder area, and vice-versa. This movement operates a displacer and piston. The piston moves up and down inside a copper coil at around fifty times a second to produce electricity, which is fed into the domestic electrical supply.
The Stirling engine generates about 1 kW of electricity as it operates.
Because these boilers use gas in a very controlled and efficient manner, the general idea is that the Stirling engine should operate continuously using small amounts of gas to efficiently generate electricity, and supplement the domestic central heating and hot water supply, with a boost heating facility to raise the hot water system to demand levels.
Every electrical kW produced and used by domestic consumption receives a payment from the energy supplier. This acts as an inducement to produce electricity and as a payment for not using the supplier’s inefficient electricity source. On top of that, any surplus electricity is directed back into the grid and receives a FIT payment (the Feed In Tariff) from the provider for each kW produced. The micro CHP boiler must be installed correctly by an MCS installer to qualify.
So where are the pitfalls?
The major drawback is the cost. Currently, purchase and installation costs are in excess of £5000. The life expectancy of models on the market is around ten years. With gas and electricity fuel prices so volatile, it becomes difficult trying to assess whether, or when, the capital expenditure and the interest payments on any financial assistance packages would justify installation.
There have been calls for a substantial increase in the FIT to make installation of micro CHP boilers more attractive, but as yet, there has been no movement on that proposal. As such, any financial advantages are likely to be very modest over the long term.
Perhaps the main obstacle for installing current micro CHP boilers is the situation in a potential buyer’s home.
Householders have responded favourably to Government incentives and environmental concerns over recent years. They have improved insulation and many have installed a variety of heat saving devices. Some have adopted technologies that supplement heat requirements with heat recovered through accumulators.
The amount of gas that is required to heat a well-adapted home is now significantly less than in previous times.
However, demand for electricity is increasing. Households now require constant electricity, not constant heat.
The 1 kW electrical output of a micro CHP boiler with the current FIT and kW subsidy does not make the installation of the boiler a realistic proposal at the moment.
The future for micro CHP boilers is, though, looking good. Manufacturers are developing superior alternatives to Stirling engines. Ceres are developing fuel cell technologies that will revolutionise domestic heat and electrical production. Within these fuel cells, heat and electricity can be generated without combustion removing all the problems associated with it.
Hydrogen cells are being developed to utilise the energy produced by micro CHP boilers and other green energy generating technologies. Hydrogen can be produced by surplus electrical activity and then used to generate electricity again at peak demand.
These green and clean modifications incorporated into, or complimenting micro CHP systems will make installation more of an attractive proposition in the future. The electrical kW output produced is much greater. Already the major energy companies are voicing disquiet about the possibility and implications of millions of micro energy producers feeding surplus energy back into the grid. And with some justification!
Perhaps lots of micro energy producers supplying a local network might be the answer to the ailing, aging and costly grid network, in addition to the public’s growing disquiet about the energy company’s extortionate energy generating profits.
In the meantime, compliment your neighbour for considering becoming a torchbearer and protagonist of nascent technologies.