Solar / renewable hot water and heating

tigertedd_2

Hi,
I'm contemplating a rather large investment into a new heating system, and wondered if there were any experts on here who can advise before I give the final go ahead.
We already have solar panels, with a battery storage, which charges off the grid on an economy 7 tariff when there's no sun.
Our boiler is about 17 hearts old now, and has been on it's way out for a couple of years, requiring 3 or 4 bodge job repairs. So seeing as we'll need to invest in a new boiler anyway, my thoughts are to put that budget towards a whole new, electric heating system.
I have two options, and both include a relatively new thermal hot water system, called the Bunsen system, I can't find anything else about it on here. Threads I've read in the past say that the problem with solar hot water is that it doesn't work at night, when you most need it. But I'm reliably informed that this draws energy from the environment in a number of ways, which allows it to generate energy 24/7.
Option A) There's a version of this system that can also handle your central heating. It plugs into the existing system. It just involves a new hot water tank being installed. However, they say this will cope with about 90% of your heating needs, and you still need your gas boiler for the occasional boost. Cost is about £9,500 for the system and the new hot water tank and installation. But I'm concerned that I'd still need to invest in a new boiler at some point, even if it's work is reduced to just 10%.
Option I use this system just for my hot water, and then install infra red panels throughout the house. This involves removing the current boiler and all the radiators.
Ideally, I would like to get rid of the boiler and radiators, and go completely gas-less, so option B is preferable to me. Cost is about £4,500 for the hot water system, and £3,000 for the infra red heaters, and then another £2,000 for the installation and removal of the old gas system and radiators - so £9,500, about the same.
I have a couple of questions though:
1) does this seem like a good investment for starters? I could just get a new boiler for a couple of grand. Nearly £10k seems like a big chunk of money.
2) Why do I even need hot water? I've realised that the majority of water is heated at the point of use, so the dish washer, the washing machine, the electric shower (with which we could fill up the bath if we wanted), we haven't got one, but we could even get one of those boiling taps for the kitchen. I know that trying to sell the house later saying we have no hot water would be quite a difficult conversation, but when you think about it, do we really need it? Of course I'll probably need up getting some sort of hot water solution, but it does make me wonder, maybe I'm missing something.
3) Has anyone heard of an Octopus tariff? I've heard that it's a great way to charge batteries from the grid in your solar PV system, as they'll only charge at specifically the time of day when it's cheapest. I've heard of people get their electricity at -1.4p, using that to charge up an attic full of batteries, and then never having to pay for a penny of electricity, using that to charge their electric cars and everything. Sounds genius to me, but it's the first time I've heard of it, so any insight from any one else with experiences of it would be good.
As far as I can tell, with this Octopus system, everyone should just be getting an attic full of batteries, whether you'v e got solar panels or not, and just charge off the grid at 2:00 am, when you'll actually be paid for all the electricity you take. Seems too god to be true really. 
Anyway, any insights would be gratefully received.

matelodave

Electricity is an expensive way to heat your place and please remember that solar power whether it generates leccy or hot water doesn't do much in the winter when the days are short, the sun doesn't shine and it tends to be when most people need to heat their houses.

Perhaps you need to try and work out how much hot water costs to heat compared with heating your house and TBH it's a pretty small proportion of your energy bill. I've got an air source heat pump and we get all our hot water needs for around 2-3kwh a day (less in the summer) which equates to around 35/p a day on my tariff. Even my heating only uses around 3500kwh (£420) a year, equivalent to around 10,000kwh with a conventional boiler.  But, as we use all of that in the winte,r then solar panels wouldn't really help all that much so I don't have any. even the installer recommended that we didn't bother with solar hot water as the £1500 outlay at the time would take around 12 years to pay back probably a bit less with the RHI but in his opinion not worth it although I was fairly keen at the time.

Dunno what you are actually contemplating because I've never heard of it but any form of heating using renewables needs careful sums to be done otherwise you can spend a lot up front and get very little or no return on your investment. Be very wary of claims especially for super duper whizzo things that you can't get a lot of info about, frequently they dont achieve and even more frequently the company that makes them goes bust leaving you with a very expensive mistake - just my opinion you understand.

My heat pump cost me just under 6k ten years ago and so far I've had nearly £5k back in RHI payments (and still more to come) It's hard to compare running costs because we cant have mains gas so my alternatives would be oil, LPG, pellet or even storage heaters. IMO opinion, mains gas would still have been cheaper but the ASHP is probably a lot cheaper than the others.

Also be wary about just bunging a heat pump or similar onto an existing heating system - it rarely works properly the system and especially radiators have to be correctly specified to work at the much lower flow temperatures otherwise it will just flog it heart out, it will cost you a lot to run and you'll still be cold.

MWT

The Bunsen Air Heat Exchange System is essentially a reverse refrigerator circuit...

I would be sceptical about the ability of this system to respond to significant demands on the hot water supply and I'd be very surprised if it could come close to handling a wet central heating system.

I would ask them for contact details for a few existing users and even then I'd be highly suspicious of the claims they are making.

matelodave

OK then it's just a heatpump with a different method of collecting the heat using a solar collector.

Most are Air Source where it extract low grade heat from the air. Ground source where the heat is collected from the ground, either via deep boreholes or gridded or coiled collectors buried a metre of so under the ground. Water source where the collector extracts the heat from a river, stream or lake.
The big flaw that I can see with the solar arrangement is that there's no heat when it's not sunny or even daylight, whereas the other systems have a continuous supply (even from cold air overnight) so you need some way of storing any heat that you collect to make it available overnight or when the sun doesn't shine. Sounds a bit iffy to me. Lots of sun and heat in the summer and no easy way of using it and very little in the winter when you need lots so you'd need to supplement it with full price leccy.

I think you need to look at the return on investment and the concept of diminishing returns where once you've made your major savings with the first investment every investment after that gives you a lot less back in benefit especially when any grants or feed-in.RHI payments are getting lower and lower.

I use nearly 70% of my energy when its cold and the sun doesn't shine all that much, so generating lots of it in the summer when I cant actually use it just seems like a waste of money and, as I said, the cost of hot water generation for me is only around 10% of my annual energy bill  £864/10 = about £86.40 a year so your system could pay for it'self in 5 - 6 years but if you then decide to heat your house with it and need to use supplementary heating rather than the gas you've got rid of you might well find that your energy costs for heating far outweigh any saving on your hot water generation.

Lots of sums and head scratching methinks

tigertedd_2

Thanks matelodave, that's really interesting insight. given me some things to think about, but I'm still not put off.
I've heard that air source is good in terms of being renewable, but the costs to actually run the pump with electricity make it no cheaper than gas (but if gas isn't an option, then it's a good option). And we were advised if we wanted to go down this route, it would require all new radiators. So although the RHI payments were tempting, I don't think it's the right option for us for a number of reasons.
MWT is correct, the Bunsen panels work with a refrigerant. I'm not an expert on the physics of it, but it has a boiling point of -26C, so pretty much any environmental energy can be transferred to it to then create energy to heat the water. It doesn't need the sun and can work 24/7/365. There is a small electricity cost in making the water pump work. Sounds great, but it's quite new tech, so hard to get much insight. Apparently this can just hook into the existing system though without the need for new radiators (if I got the system that does heating too, which is a tank-in-tank system), but that's why you need to keep the boiler for the extra boost where it's needed. You're right not to think to rely on this to keep a liquid heating system topped up by itself.
We've got a battery with our solar panels, so this means we can store any excess we make during the daylight hours, and use this at night. But it also means, when there is no sun at all, we can charge the batteries off the grid, but at the cheapest rate possible in the middle of the night. 
So although I realise it's more expensive to heat a house with electricity, IR heaters are super efficient, and we're able to run them off about 4p a unit. 
And I'm pretty convinced that will be a thing of the past in the not too distant future, and all electric is the way to go, which is why I'm trying to get off gas 100%. But then there's always the problem of being an early adopter, that something twice as good comes out next year. Imagine being one fo the first people with an iPhone thinking you were the bees knees, but being locked into a 10 year contract on that same phone. That's what always scares me about jumping into this new tech with both feet.

theoretica

Just to add to your considerations, have you read about the Sunamp heat batteries?  Not sure if your use would be right for them, but they do look interesting.

ElephantBoy57

Have a read of this, The key metric for this kind of technology is the so-called coefficient of performance (COP), which measures the amount of heat generated for each unit of electricity put into the system. An immersion heater, for example, has a COP of 1, while air-source heat pumps typically have a COP of between 2 and 4. Suppliers of thermodynamic panels say they have a COP of between 2 and 7.

Results from the only independent tests of thermodynamic panels in the UK “aren’t that great”, according to Tom Bradley, senior project engineer at Narec Distributed Energy, which conducted the research.

The organisation tested the system using a cycle that mimics the hot water usage of a typical family home, from January to July last year. The maximum monthly average COP of its thermodynamic panels was 1.6, or 2.2 when taking account of heat losses from the tank.

https://www.theguardian.com/environment/2015/sep/07/should-you-install-thermodynamic-panels-on-your-home

Talldave

I'd just replace the boiler.  When your batteries are fully charged,  do you use excess solar power to heat water?
If you're wanting to spend big, go underfloor heating, with ASHP or GSHP. Better than the large radiators alternative. 

MWT

matelodave said:

OK then it's just a heatpump with a different method of collecting the heat using a solar collector.

I think it would be better to regard it as a passive ASHP, it doesn't appear to use a fan on the external panels so it should be less disruptive to the neighbours, but less efficient, especially at night.

The 'noisy' bits (pump/compressor) are inside the house from the looks of things.

I can imagine that this might handle hot water needs as long as you don't expect it to recover from large volume use quickly.

I don't see how this is going to be efficient enough to use for general heating requirements, but I am not experienced in the use of heat-pumps.

Fly100

Ive just completed our New Build house, without boring you all to death. I have a 6kw Solor PV system ( limited to 5kw inverter) on 35 degree roof pointing slightly East of South. Its produced 7.5 Mw of electricity in 12 months. I have a 300L hot water tank and I send all spare generated Electricity to the immersion.My boiler will prob not fire between April and October ( other than the once a month maintance run). With the power we use during the non production times our usage is very small on average 8 units per day over 12 months. ( Yesterday we used 5.5 units.  Hot water tank at 65C, 3 loads of washing done and tea cooked in the oven for an hour).

I have looked at the Battery side of things, but if you work it out over 5 years and the loss of capacity the Batts cost about 18p per unit, where as you can buy it fo 13p ish.Until those to figures merge its not an option.

Happy to answer question as I researched everything to death., but didnt wont to cluter the thread.

tigertedd_2

Thanks for the link ElephantBoy57.
Still not put me off yet, it takes a lot to put me off once I've got my mind set though. Although it would be nice to know the government had adopted it for the RHI. And they still haven't 4 years on from this article.
I can't find any more recent independent research though. I found this Irish article, still 4 years old: https://www.irishexaminer.com/lifestyle/homeandinteriors/hot-water-the-technology-behind-thermodynamic-panels-427090.html that says despite those reduced COP based on this study, it would still save you money compared to traditional hot water solutions. But low estimates are at €200 a year, and high are at €1500 a year. So if I take the low estimate, it would take about 25 years to pay for itself!
When I had the solar panels fitted though, I said I don't mind if it's cost neutral over a period of time, or even costs a bit more, some of the motivation would be saving money, but a big part of the decision is environmental. Turns out, after I did all the maths, we should save money over the lifetime of the solar panels though, so it's a no brainer (although there are of course more lucrative ways to invest £20k over 20 years, so I'm very reluctant to use the term 'a good investment'), but it's certainly not a bad or money loosing investment.
In the case of this thermodynamic hot water system, it may well be a bad investment, but I'm keen to get off grid as much as possible, definitely in terms of gas, and think that will ultimately be the best investment. But that's more of a Trump like gut feeling than based on any actual science.