This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
This analysis is so sketchy and so flawed that it cannot be taken seriously.
I don't for one moment believe the £3,000 for a packaged and installed 20KW CHP system. Even doubling to £6,000 seems to be pushing it. You give no figures for the heat/power split but I'd guess something like 13 to 15 KW generator capability is about as low as you can go to make a reasonably widely applicable unit. Say 20 HP engine then. Without battery/inverter back up its going to be running 24/7, much of the time at light throttle, low efficiency. Leaving aside what the neighbours think you still have to budget for service visits. At least one, probably two, a year. With battery/inverter back up the running time can be cut and overall power generation efficiency improved as light power load periods can be supplied from the batteries. Even with inter conversion losses, which are by no means negligible overall gains are possible. However you still may need to run the motor for heat even when you don't much power so gains are limited. Also the battery & inverter units push the cost up. Perhaps you need heat storage al-la eco-house too. More costs and not trivial ones either.
Even if your £3,000 is correct you haven't factored in the loss of investment income on that capital. 5% is £150 per year which eats up most of your theoretical saving. Servicing will more than swallow the rest. If you have to borrow the money for the plant then interest will more than eat the savings anyway.
Realistically a standard diesel engine is unsuitable for this job anyway. Much better to develop a variable expansion ratio engine e.g. modified Atkinson cycle or variable stroke opposed piston (Prof Timoney) as these give far better low load efficiencies and can run very, very slowly off load. More costs to develop the prime mover.
Bottom line is micro CHP always fails because its impossible to do effective input-output load balancing which destroys the overall system efficiency. Large CHP systems can work because either the heat or the power can be got as an unwanted by product from a process that is already being run. Hence only capital, installation and servicing costs have to be funded and, in general, these will be fairly comparable with those for a conventional system. If they are widely out of line then the CHP won't be installed. In this situation the CHP becomes pretty much all gain as the worst, zero load, case only brings you back to the original single use plant situation. Grid supply systems can load balance pretty well by switching capacity on or off line as required. It doesn't hurt that industrial and domestic loads peak at different times.
It's not clear to me how such generation would ever be attractive to a CO2 hating policy department. Nor how fuel delivery efficiency (and cost) could be anticipated, at least not with free choice in the matter. And I don't mean by that some sort of system where all the fuel (assuming liquid) arrives in a tanker at a common location and the property holder then pays one of a number of suppliers for it based on some 'efficiency' fallacy as we have for electricity and gas at the moment.
In the same way I wonder that food production seems to have delivered more and better food with greater consistency in recent decades than thousands of small farms and allotments did in the last century.
In both examples the efficacy of a localised solution, if such a thing is possible, would seem problematic in the cities and the majority of people live in cities with, I read, the proportion ever increasing. Thus to change to local power production (and even more so food production) would require a considerable social structure change. And in a short time if it was to have any sort of impact as normally demanded.
So which would be worse? Enforced social re-engineering rapidly deployed in the short term or run the risk, if there is one, of having to adapt once more as so many times before, to a changing environment in the medium and long terms?
My advice to younger people today would be - Gordon Brown may have been a man ahead of his time. He recognised that most people will not need a pension in the future and so started to re-appropriate those that existed. Follow his lead - don't have a pension plan. By the time you are old enough to make use of it the world will be in such turmoil that pensions will be worthless and meaningless.
That should make things interesting in the City ... it may even mean that 'Micro-Generation' research struggles to find funding.
Your challenging ripost was illuminating, but rather inappropriate because you refer to a non-existent analysis. I was not giving Dave an 'analysis' of CHP machinery; I was giving an analysis of a Political statement by David Cameron, as reported in The Guardian article by John Videl. I was making the point that, regardless of the economic argument for or against micro-generation schemes, the reality is that in the real world, to make it work on the scale of “1million householders and businesses”, you are talking about an industrial product. All industrial products to be marketed on this scale will be decided on by the prevailing vested interests in the private commercial sector. It cannot and never has been and never will be implemented by Political edict.
The example figures which I gave, and qualified as exercise in the design and commercial viability study for a domestic scale CHP machine actually happened. It started during the miners strike of 1984/5. Margaret Thatcher was exploring every avenue to achieve energy conservation and efficiency, and CHP was just one of many set up and managed by the DTI (unfortunately). As I was working on closely allied developments, I was asked to join a team of engineers to carry out viability studies which were then submitted to the DTI. This was a competitive industrial undertaking, and in my opinion, we had some of the best proven talent available.
What our team had in common, was a solid belief in the fact that CHP in its current form was outmoded by about 50 years, now 70 years. We had input available to us from Hydrovane, Dowty, BP Engineering, Worcester Heat Systems (now Bosch), and other parties. All had only one interest, expansion into new markets for commercial gain. So, Clive, your mistaken assumptions about my Post serve perfectly to illustrate the fact that conventional CHP thinking is technically, and economically, a dead end.
But just so no one gets the idea that the above is all waffle, here are some brief technical specs:-
Based on a minimum production output of 1,000 units per Month with a 3 year lead time for production infrastructure and Tooling:--- The heart of the system was a brand new liquid fueled power unit, purpose designed and built to do this one job. The generator was integrated with the main power shaft and shared the same bearings. A 'Quill Shaft' arrangement allowed the generator to be coupled and un-coupled by electronic control. It was 3 phase A.C. with solid state frequency stabilization. Hence, the generator could spin over a wide speed range to match the power module.
A little bit about the 'engine' module:--- Basically a rotary piston engine hybrid from the gas turbine, air cooled, thermally regenerative continuous combustion, 10 to 1 turndown ratio, with a 12v battery dyna-start system. Running on a modified Atkinson Cycle (yes, I remember Prof. Timoney, first rate man) and was multi-fuel, diesel could be used without comp. ignition or loss of efficiency. This power unit could run up from cold start in 5 seconds, and the generator could be soft coupled to run up in 10 seconds. As a consequence, battery back-up and inverter was redundant.
If I had the opportunity to do it all again, with the advantage of the last 25 years improvements in technology, I would expect to see a user price of around £2,500 if made here and around £1, 250 if made in the East! And do bear in mind that a comparable conventional central-heating condensing boiler costs around £1000 today.
Thanks for taking the time to post more details about the modern micro-generator CHP plant. That study sounds interesting. Is there any way of obtaining a copy, if its a government document covered by the official secrets act I probably still have the necessary security clearances to see it!
I'd be particularly interested to see how it was proposed to get round the efficiency problems inherent to the wide output load range which a single dwelling CHP needs to cover. Everything from one light on at mid summer midnight (possibly LED these days) to full heat and full power on a freezing mid-winter evening. Far too great a range to be covered at anything like optimal efficiency by a live running plant. Even at optimal efficiency the savings relative to grid supply aren't that great so it becomes important to ensure that efficiency is high under as much of the load range as possible. Not an easy task especially as most of the time demand will be in the lower output regions so optimisation for low output reduces efficiency at higher output where more fuel (and costs) are consumed.
The engine generator combo described is interesting. Are there any published performance figures for it? I presume a prototype was built. I'm sure its only the space constraints of a forum reply which makes the description sound contradictory.
In particular your reference to continuous combustion and Atkinson cycle is strange. Generally the Atkinson cycle refers to intermittent combustion engines where asymmetry between compression and expansion phases is introduced to increase system efficiency. Ideally the modified cycle is used whereby the degree of asymmetry can be varied conferring most of the benefits variable cut off gives the reciprocating steam engine. Not the least being the ability to size an engine to run with high efficiency where only a moderate output is needed whilst having over-driving capability when maximum output is needed. This of course was the thrust of Prof Timoneys work on the TS3 engine. There is a good deal of interesting, but unlikely to be practical, stuff on rotary Atkinson engines on the Internet. Sliding members in the combustion chamber, they have gotta be joking!
If it wasn't for the mention of 12 V battery and Dyna-start I'd have said that, given the costings and proposed design to production lead, time your description sounds like a mono-tube boiler (flash) steam engine system. Which is the way I'd do it. Not least because that concept does at least get round the heat/power mismatch problem as direct connection between boiler and a conventional heating system can be arranged when power generation needs don't produce enough heat. I guess the Atkinson bit could refer to a variable number of stages on the expansion side. Easily done with a double acting triple expansion reciprocator, optimising valve gear cut-off variation switching and number of stages employed against load sounds a nice post grad problem! Not quite so easy with a multi stage turbine but still possible.
Common bearing and clutched quill shaft is an odd way to drive the generator. End on drive via coupling is easy and cheap besides being far more convenient at service time. Given you want AC output a constant speed drive makes a lot more sense. High efficiency over wide speed range is not a normal generator characteristic. Presumably this was a de-costed 400 Hz design as satisfactory single phase can then be got with fairly simple circuitry. High generator speed also allows flywheel energy storage for spin up / coast down cycle so the prime mover doesn't have to run continuously at low output.
However you do it this beast is going to be much, much more complex than a condensing boiler so I still find it hard to accept your costs. In particular my professional experience as a scientist/R&D engineer make me leery of accepting the outcome of any pure paper studies. I've been bitten on the backside too often by the real world not behaving the way the most eminent authorities claim it should do. I've also seen these high powered committee studies miss the blindingly obvious, usually out of enthusiasm for novelty or neatness, on several occasions. Explaining practicalities to an assemblage of PhD's buttressed by pages of mathematics can be difficult.
Thank you for your interesting insights into prime mover and generator design. Before I comment on your Post, I would reiterate my original purpose: to draw attention to the dreamworld pronouncements of politicians, bureaucrats and unfortunately academics, who really should know better. Dave kicked off the discussion without mincing words, as the “daft idea of micro-generation”, I followed with a supporting Post which drew on my industrial experience to make two points in one example. First , Dave seemed to support his comments, by drawing our attention to the pre-war establishment of our national grid with the inevitable consequences of a state run electrical power industry. Yes, they halved coal consumption, but the built in bureaucratic management inefficiencies actually increased the cost to the consumer. (I know this because my Father lived through the changeover).
So, my first point highlighted the fact that private industry, if left alone, will always out-perform state industry, and my second point was that the state never willingly relinquishes regulatory powers over major utilities. My reference to the DTI programme was, (unfortunately). I did say that it was an 'exercise', but the real exercise was to prove to industrial interests that they would be ill advised to 'take the Queen's shilling', even if it was offered. It wasn't, because we refused to accept the DTI's onerous contingency clauses, do it by numbers routine, jump through these hoops, quarterly technical and financial audits, ad (sickening) infinitum!! As it was, the DTI were the losers, (of taxpayer's money); all of the schemes that they backed were abortive. CHP is still very bad news for bureaucrats today, they have very long memories: politicians don't, which is why they never learn.
My comment on your Post Clive:-
Frankly, the technical questions that you raised and some of which you rhetorically answered, are totally inappropriate on a public forum. Professionally I could see your questions as a 'fishing expedition', but as you describe yourself as a “professional scientist/R&D engineer”, I assume that you adress the technology of CHP from an academic viewpoint. This is a mistaken pursuit, for there is no common ground between applied technology and academia. Especially in the R&D of private industry,
the language, the motivation, the skills, and the rewards are radically different. For example, the official secrets act: government agencies can never get their heads around the fact that when they seek to engage industry in collaborative funding of R&D, uppermost in industry's mind is to protect their knowledge base from industrial espionage. In the market place, Patents are Crucial. Making what are, in effect, Prior Disclosures to civil servants is a very risky business, despite their assurances of confidentiality, it is a leaky sieve!
So Clive, if you wish to satisfy your curiosity about my industrial activities, please e-mail me privately with your 'commercial' need to know particulars as most of the answers to your technical requests are not in the public domain, and some of the research is still extant, but moved into different fields. In the meantime, would you care to apply your obvious scientific mind to the other rubric of the Conservative Party's Policy Review Committee in the Guardian article on micro-generation:-
Chairman Oliver Letwin spouts thus: based on David Cameron's promise of 1 million units in place within 10 years, “Our costings suggest that by 2020 ---- they could be producing 2GW of electricity. (Big deal, 2 billion/1 million = 2,000 watt hours, say worth 25p!). Then he says that two-thirds of energy used in power stations, “is lost in the wires that transmit it”. (Go to the 'horses mouth', the National Grid transmission losses are between 12 and 14%). Finally, they expect to see mass-market finance packages available on the high street! Do I exaggerate when I say 'Dreamworld'?