Flow Micro CHP Boilers

Legacy_user

Flow Energy is offering a Micro CHP boiler for £3645 (with a basic installation cost of £1800).
A boiler which uses 35000kWhs of gas will generate 2000kWhs of electricity. Pay up front and Flow will rebate £80 per month for 5 years. The FIT goes to Flow but it is transferrable back to the owner at the 5 year point. Apart from the usual caveats of new business, new design of boiler etc, I am struggling to see how the end user would benefit given that most of us use considerably less than 35000kWhs of gas a year. I would probably use about a third of this so my monthly gas/electricity bill would be less than £80 per month. I have asked Flow to clarify what happens in such a situation.

My other concern is whether an 18kW boiler is big enough to replace a 24kW boiler in a modern 5 bed property?

Am I wasting my time even looking at the pros and cons of this type of technology? I am only doing so because I can see some benefits of free electricity in Winter when the PV solar output has fallen.

Martyn1981

Some similar thoughts on this thread:-

Anyone got a flow boiler or similar


Mart.

System

Thanks Martyn. A useful read but I confess that I still don't understand how this deal works. The boiler doesn't seem to have the capacity to heat a large home, and it needs to be on constantly to make any meaningful FIT return. Micro CHP FITs are also out for consultation which usually means ......

zeupater

Hengus wrote: »

Flow Energy is offering a Micro CHP boiler for £3645 (with a basic installation cost of £1800).
A boiler which uses 35000kWhs of gas will generate 2000kWhs of electricity. Pay up front and Flow will rebate £80 per month for 5 years. The FIT goes to Flow but it is transferrable back to the owner at the 5 year point. Apart from the usual caveats of new business, new design of boiler etc, I am struggling to see how the end user would benefit given that most of us use considerably less than 35000kWhs of gas a year. I would probably use about a third of this so my monthly gas/electricity bill would be less than £80 per month. I have asked Flow to clarify what happens in such a situation.

My other concern is whether an 18kW boiler is big enough to replace a 24kW boiler in a modern 5 bed property?

Am I wasting my time even looking at the pros and cons of this type of technology? I am only doing so because I can see some benefits of free electricity in Winter when the PV solar output has fallen.

Hi Hengus

Check out the Tech Spec ... Most technical specifications are based on standardised tests and have performance curves etc whilst here we have 'up to ...', which in a 'technical' specification is pretty rubbish by any standard. I certainly wouldn't consider making a decision on spending anything over a fiver on anything with such a sketchy offering.

Anyway, check out the thread which Mart referenced, it probably covers most of what you'd need to consider.

HTH
Z

michaels

WE are about 2100sqft EPA B and have a 20kw boiler that modulates down to 4kw and does the business. Seems to me micro chp makes most sense if you have a swimming pool....

Martyn1981

michaels wrote: »

WE are about 2100sqft EPA B and have a 20kw boiler that modulates down to 4kw and does the business. Seems to me micro chp makes most sense if you have a swimming pool....

Just pondering that, info from Z about the lower generation as the boiler modulates down, and "that thread" about warm places and going off-grid.

I wonder if one of these boilers, in conjunction with PV and batts would make sense. During the non-heating months, you'd probably be fine with the right sizing of PV and batts, and in the heating months you could run the boiler flat out (in shorter periods) to heat the house and charge the batts. No need to match leccy consumption with boiler output, as the batts would act as a buffer.

Presumably the boiler grants depend on being grid tied though, but just a thought for partial off-gridiness with an in built back up generator and heat source.

Mart (the ponderer).

Alan_Brown

Martyn1981 wrote: »

I wonder if one of these boilers, in conjunction with PV and batts would make sense. During the non-heating months, you'd probably be fine with the right sizing of PV and batts, and in the heating months you could run the boiler flat out (in shorter periods) to heat the house and charge the batts. No need to match leccy consumption with boiler output, as the batts would act as a buffer.

I was looking at this a while back with the gas boiler generating electricity in winter and solar generating electricity in summer and both working in the shoulder months. The main problem I could see was that in a reasonably insulated home, the boiler wouldn't be on very long before the house temperature was reached, so the electricity wouldn't be generated for long.

Perhaps this is why the boilers are low output? They have a longer burn before they raise the house temperature to the desired level. The obvious downside is that who wants to sit shivering when you get home from work, waiting for an undersized boiler to warm the house?

System

What piqued my interest was the thought that a microCHP boiler would fill the generation gap when my PV solar output was at its lowest. However, if 17500kWhs of gas usage is required to generate 1000kWhs of electricity, then the maths do stack up. The additional 7500kWhs of gas would cost me about £200 extra per year on my current tariff: I would get about £160 per year back in FITs, and I would save about £100 per year on electricity charges. In sum, I would be £60 per year better off, if I owned a Flow Boiler, and kept all the FIT/export payments.

BUT - I don't own a Flow Bolier. So I pay £5450 (inc installation) and get £80 per year off my Flow Energy bill which compared to my present tariffs is £65 per year more for 17500kWhs of gas and 2000kWhs of electricity (3000 - 1000 CHP generation). Moreover, even with this high level of gas consumption my annual bill will not exceed £960 per year so do I just get free energy or £4800 over 5 years?

The problem for Flow is that they are trying to sell this boiler in something of a Perfect Storm: low energy prices; an increase from 5 to 20% in VAT; high initial capital cost and possibly reducing FITs. Added to that is the unproven nature of the product, and servicing and repair costs going forward.

It seems to me that the risks of going down this route are significantly greater than putting a few panels on the roof. That said, I support innovation and I wish them every success.

Ben84

I think the trouble with CHP boilers in domestic situations is that many houses can cut down to very limited boiler use with proven, very accessible energy saving measures. We have the cavity walls insulated, the loft has lots of insulation, we've draft sealed quite thoroughly and installed secondary glazing. Some measures were cheaper than others, but the result has been very low heating use ever since. We get weeks later each year before we even consider using the radiators, use them for less hours each day, and turn the heating off weeks earlier than we used to. This winter has been mild, but we're only using the heating about 7 hours a week at the moment. Some days we're not using it at all and relying mostly on the heat from the gas cooker each evening. It's so cheap now to heat the house it doesn't even make economical sense to replace our 1970s boiler any more. It was planned, but then the heating costs plummeted and the boiler is still here.

CHP makes more sense if you're burning lots of gas, but then I would wonder why not invest in energy saving measures to stop burning lots of gas?

zeupater

Hi Ben84

I think that you've identified the issue pretty well, we also have addressed heat-loss and therefore have a relatively low heating energy demand.

The problem with micro-CHP really comes down to the generation:heat ratio, which with (up to) 1kW from a 20kW boiler works out to 1:20, that's less than 5% efficiency on fuel utilisation, moreover, when there's no or little heat demand, there's no electricity generated, there's also the issue that period generation is effectively capped by heating demand in that same period - unless wastage is both planned and accepted.

I fully understand that the concept could be sold using the argument of reducing the evening peak demand through distributed demand-side generation, but that would necessitate the boiler being run when people are returning from work, so there'd need to be a little faith in the way that consumers would heat their homes.

To be commercially successful, what is really needed is a dedicated co-gen unit having a generation:heat ratio which is closer to 1:1, utilising the heat for DHW. Enabling such a unit with centralised smart control would provide the ability to assist in smoothing grid demand, of course, temporary manual override would be necessary to allow for abnormally higher local DHW demand .... however, I still strongly believe that combining a high efficiency co-gen unit (probably fuel-cell) with heat-pump technology would provide what is ,by far, the most efficient domestic heating solution, effectively reducing the current cost of heating energy to somewhere below 1p/kWh.t, which would certainly cause general panic in the supply industry, but would address both environmental, economic, welfare and fuel-poverty issues in one hit. Obviously such a solution would naturally open up a number of central funding streams to leverage the obvious national beneficial returns.

HTH
Z

Ben84

Hi Zeupater,

Interesting thoughts. I think micro CHP does have some appeal. After all, you can turn cheap gas in to higher value electric with it. It's just that many people consider these things as ways to curb high bills, and I think mostly high household bills are down to inefficient energy use and it makes more sense economically to tackle the root of the problem. Improve insulation and use more efficient lighting, for example.

I think we could improve the bills further in our house, but right now the highest I've seen in some years is just over £20 a week in the coldest weather for both gas and electric for a household of three adults. We're fortunate to have a smart meter and can track these things quite easily. For most of the year we're far below £20 a week, sometimes as low as £10. Interestingly our gas use doesn't peak that much in winter, it's more the electric which goes up, but that's likely because I'm using a condenser dryer more often in winter, which is a pretty good size heat source in a well insulated house. Also, with the windows closed the heat from the gas cooker which I use every day, winter or summer, is kept inside, which is very efficient for heating as there's no chimney. The cooker was broken for a couple of weeks recently and I noticed we used the radiators a lot more and spent a lot more on gas. Currently, our ancient back boiler is only really used for modest amounts of top-up heat, and as a back up option. It also heats the hot water, but we wouldn't save as much as people might expect by replacing with a condensing one. Condensing boilers take a big efficiency hit when heating hot water, dropping them to somewhere not that far above even our old boiler!

We'd get very little use out of a CHP boiler - or at least as you pointed out the current generation which are designed more for heat than electric production. Current generation micro CHP might still have uses however. I can see it being useful in a laundrette for example, where there's lots of hot water and electric being used for long periods of time.