Solar DHW with UniQ and PV Diversion

[DamonHD]

Hi,

 

Those of you who remember me from another place (no, the other other place) will know that I've have been keen on Sunamp's tech for a while but I have historically NOT been keen on diversion to DHW from FiT-subsidised PV as a scandalous waste of very expensive exergy and of someone else's potential avoided carbon emissions if that electricity had been spilled to grid.

 

Outside winter, GB grid carbon intensity is now around or below that of burning gas directly for heat (and still falling) so the last point is going away.

 

Cleverer diversion schemes where the heat storage does not waste the energy through leakage (I don't want excess heat leaking into the living space from a hot tank in summer!) and can play nicely alongside electrical battery schemes (and thus divert only after self-consumption and the battery have had their fill) seem to be making use of some of that exergy, and reduce flows on both electricity and gas grids.

 

So, here is my work in progress to take 75% of my DHW use off grid, so that I'll only use gas at all in winter in normal situations:

 

http://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html

 

I may (with permission) pick up comments from here and fold some in to my piece.  It's meant to help people trying to decide whether/how to do something similar.

 

Maddeningly the funds I was going to use to do this may have evaporated again, but I'm still aiming for February 2020 for installation!

 

Rgds

 

Damon

 

Edited December 28, 2019 by DamonHD
typo

[ProDave]

The balance on the equations of how to use solar PV electricity took a radical change earlier this year with the closure of the solar PV Feed In Tariff system.

 

New installations of solar PV will not get any payment. Though there is supposed to be an export payment scheme starting up any time now *

 

So anyone, like me, installing solar PV now has to be sure of two things.  Firstly the install cost has to be cheap. That pretty much as far as I can see means scouring the country to get the kit at rock bottom prices, and installing it yourself to avoid labour costs.  Secondly you need to use near 100% of what you generate in some productive way.

 

I got an installed cost of a 4KWp solar PV system down to £1500.  I am working on self using £250 per year worth of solar PV electricity and that will give a system payback time of 6 years, after that it will be a £250 per year saving on my energy bills.

 

Unless you have some unusually big and constant load appliances, the ONLY way you will get close to 100% self usage is to dump "spare" solar PV power to water heating or batteries.  I chose water heating.  Batteries, when I last looked were too expensive.  But knowing what I know now you don't need much battery capacity to soak up excess generation that you can't use in real time, so I am expecting at some point batteries will become viable for me.

 

* The new export payment scheme coming into force will only pay for what you export, not what you generate, but only at a rate of around 5p per KWh, not much more than 1/3 of the import rate. So you are still better off self using than letting it export, even with the payment.

 

Also in order to sign up to the new export payment scheme, you would have to have had the system installed by an MCS installer.  That rules out DIY install and for me would have made solar PV completely impractical with a ridiculous long payback time.  If I had been eligible for this scheme, my payment for the first year would have been less than £10

[Jeremy Harris]

I think that, rather luckily, any enforced delay to your plans, @DamonHD, may well have worked in your favour, at least as far as the ups and downs of the Sunamp UniQ range have been concerned.  As you know, I bought an original Sunamp PV (as have a few others here) and found that, in general, it worked very well.  There were a few very minor teething troubles, but nothing significant.  The same, sadly, wasn't true when I opted to swap my Sunamp PV for a bigger Sunamp UniQ.  I, and a few others, have had a fair few problems with the early UniQ models, ranging from some issues with the design of the case etc being inadequately stiff to deal with the loads imposed by the heat cells, through to a range of issues with the control system and even the PCM itself, for one of the low temperature models. 

 

Right now, our PCM58 unit is, at last, working reliably, but there is still an issue with there being zero information available as to the operating status of the unit (for example there's no way of knowing whether it's ready to accept charge, is fully charged, has power available either to the control side or the charge side, etc).  This is a major issue for me, as, having experienced a few "cold water events" (i.e. no hot water for a shower) I very much like to be able to see at a glance whether the Sunamp is functioning as it should, or not.  My work around (not at all recommended) is to leave the control unit cover off, as, rather bizarrely, there are a some extremely useful LED status indicators hidden behind the (opaque) steel lid of the enclosure.   Quite why these LEDs aren't external visible is a complete mystery, given how important they are.  A similar array of LED indicators was externally visible on the Sunamp PV, and were very useful, so omitting to make them visible on the UniQ range seems an odd decision to have made.

 

The good news is that pretty much all the bugs that plagued the early UniQ units have now been ironed out I think.  There are a handful of us here with them, and I think that most of them are now working as intended.

[MrMagic]

Also watching this topic with interest - have been following it on DHDs main site for a while - similar situation, 'fabric first' completed as far as possible for the moment (but will continue slower), SAP gone from F32 to B81.

 

As with a lot of people, relatively new combi, solar PV but no place to 'dump' the excess during the summer. Also looking to continue to push our carbon footprint down.

 

From the SAP - 

Est DHW - 2,323 kWh/yr 

Est CH - 11,944 kWh/yr 

 

From the bills -12,760 kWh/yr gas input to the house

Estimated split based on monthly readings, extrapolating from summer months etc - 

DHW - 2,857 kWh/yr 

CH - 9,903 kWh/yr

 

Average DHW daily requirement of 7-8kWh, this seems within the spec of using a SA to either shift the load fully or a significant part of it. Solar exports exceed this during the 'solar' season and I'd also be half tempted to charge it on a TOU tariff like Octopus GO or Agile - certainly when Agile is at or below 3.75p/kWh it will be more cost effective to charge the Sunamp rather than burning gas (estimate based on gas of 3p/kWh at 75% efficiency = 3.75p target price for change over).

 

Half tempted to ditch the lot and switch to a heat pump but best stick to more realistic aspirations for the moment!!

 

Keep up the good work @DamonHD (..incidentally our paths have crossed before kind of..."where vision gets built")

[DamonHD]

Hello Mr M!

 

My supersize LB mug has recently been home to some warming noodles you'll be pleased to hear.  But "Where vision got bilked" morelike!

 

Yes, would consider switching over during winter months to fully charge in small hours and/or or opportunistically driven by ToU tariffs and/or on demand to eliminate need for gas entirely for DHW.  Lack of status from SA would make that more tricky (access to the 5%/50%/95% outputs would help a lot).

 

Rgds

 

Damon

[DamonHD]

Another question...

 

I am told that "Sunamp recommend a quality limescale inhibitor as a must and advise using a Hydroflow h38 (see https://theintergasshop.co.uk/scale-inhibitors/1130-hydropath-hydroflow-hs38-electronic-water-conditioner-hs38a.html)."

 

According to the Thames Water tool for our postcode, we are in area "KINGSTON SOUTH" and our water is in fact hard at 257ppm of Calcium carbonate (CaCO3).

 

The HS38 seems a little 'magical' to me. It seems unlikely that anything using 1W and on the outside of a decent copper pipe can do anything meaningful to what is in that pipe, and I'm not seeing linked reports on the product page that would make me change my mind!

 

So, is the HS38 legit?  If not, do I actually need anything installed (I'm expecting the entire house to be pulled down in ~7Y), and if I do, what would actually be useful?

 

Rgds

 

Damon

 

[Dan F]

@DamonHD Sunamp suggested Hyrdopath to me, seems just a magical though....

 

 

Edited January 3, 2020 by Dan Feist

[Jeremy Harris]

13 minutes ago, DamonHD said:

Another question...

 

I am told that "Sunamp recommend a quality limescale inhibitor as a must and advise using a Hydroflow h38 (see https://theintergasshop.co.uk/scale-inhibitors/1130-hydropath-hydroflow-hs38-electronic-water-conditioner-hs38a.html)."

 

According to the Thames Water tool for our postcode, we are in area "KINGSTON SOUTH" and our water is in fact hard at 257ppm of Calcium carbonate (CaCO3).

 

The HS38 seems a little 'magical' to me. It seems unlikely that anything using 1W and on the outside of a decent copper pipe can do anything meaningful to what is in that pipe, and I'm not seeing linked reports on the product page that would make me change my mind!

 

So, is the HS38 legit?  If not, do I actually need anything installed (I'm expecting the entire house to be pulled down in ~7Y), and if I do, what would actually be useful?

 

Rgds

 

Damon

 

 

 

It's yet another, expensive, magical, electric field/magnetic field, device that supposedly does the impossible, and remove calcium ions from water passing through the pipe that runs through its centre.

 

There's zero evidence that any of these magnetic/electric widgets actually do anything to permanently change the composition of the water flowing through them, but there is a fair bit of anecdotal evidence that they tend to reduce the tendency for calcium carbonate to form scale on hot surfaces, and instead precipitate out as fine particles.  No one seems sure how this works, if the effect is real, or how long any changes made may last. 

 

Does the device provide scale protection?  I'd have to say that it might, or it might not.  There are many cheaper ways of doing this, though, as the idea has been around for decades.

[Dan F]

@DamonHD Sorry, it's same thing they told me about, just a different website https://hydropath.com/hs38/ 

 

So that thread I linked to, is about exactly the same product..

[DamonHD]

So what might be a sensible alternative, with some science behind it?

 

Rgds

 

Damon

[Dan F]

Harvey or Twintec.  Search the forum for either of these for plenty more info.  Or take a look at this thread:

 

 

 

Edited January 3, 2020 by Dan Feist

[DamonHD]

Thanks!

 

We don't seem to need to soften for any other reason, so that's £900+ and another half cupboard lost that I wasn't anticipating.

 

Do we really need one?

 

Rgds

 

Damon

Edited January 3, 2020 by DamonHD

[Jeremy Harris]

The cheapest option is probably to look at phosphate dosing, if all you wish to do is protect the heat exchanger in the Sunamp from scale build up.  This works well, and is cheaper than ion exchange softening.  @richi here seems happy with the Combimate, but there are other options, and in terms of performance all the phosphate dosing units are much of a muchness.

[DamonHD]

Thanks again!

 

Any environmental issues with dropping phosphates into the (waste) water?  I thought that that was now considered a BadThing(TM)?

 

Rgds

 

Damon

[Jeremy Harris]

9 minutes ago, DamonHD said:

Thanks again!

 

Any environmental issues with dropping phosphates into the (waste) water?  I thought that that was now considered a BadThing(TM)?

 

Rgds

 

Damon

 

Potentially yes, but the amount used is extremely low, these things take a handful of polyphosphate beads once a year, so it's not like chucking tonnes of phosphate-containing detergents down the drain.  Also, because the water is dosed with phosphate, you can probably reduce the amount of detergent used and reduce the amount of soap used, as well as reduce the amount of stuff like toilet cleaner used, so the chances are that there's little, if any, net worsening of the potential phosphate pollution problem.

 

[DamonHD]

OK, interesting.  The Combimate is within my current budget (money and probably space), and yearly maintenance seems reasonable.

 

I think I'd likely leave the kitchen cold tap come straight from the mains but route everything else through the softener/doser.

 

Rgds

 

Damon

[DamonHD]

Well, some unexpected excitement today...

 

I was installing some Radbots today for our ECO3 work and realised that I was right outside Harvey's HQ, so popped in for a few minutes to look at one of the units!

 

Size might be an issue given the space we have where it might go, but it was good to see it in the flesh.

 

(We also hit Radbot's primary fundraising target on Seedrs, so a good day in several ways!)

 

Rgds

 

Damon

[DamonHD]

Small update: Sunamp has kindly allowed me (via an installer) to put up a basic schematic of theirs that covers what I'm trying to do.

 

http://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html#Schematic

 

Nothing mind-blowing, but does the job, I think.

 

Rgds

 

Damon

[Jeremy Harris]

I can add a data point that may be useful.  It's now exactly a year since I fitted two energy meters to our hot water system, one measuring the energy supplied to the Sunamp from the PV system, one measuring the energy supplied to the Sunamp from off-peak (E7) electricity, for a night time boost if needed.

 

The total DHW energy used was 2,264 kWh.  That's for two of us, but we don't really make much effort to reduce our hot water energy usage, other than trying to do some things when the sun is shining and the PV system is generating.

 

Our daily usage works out as an average of about 3.1 kWh per person, which is close to the usual assumption that usage is around 3 kWh/person/day.

 

The PV system provided 1,339 kWh of that, and off-peak electricity provided the additional 925 kWh.

 

We currently pay 8.148p/kWh for off-peak electricity, so our total cost for all our  hot water for the year was £75.37

 

Our off-peak boost is set to turn on at 01:00, which is around the time that the grid demand is at its lowest.  Worst case boost would be about three hours, but in reality I doubt we ever boosted for longer than two hours, and the annual average boost time is about 51 minutes, so the boost will pretty much always be within the grid lowest demand period (which also tends to be the lowest emissions period).

[Ed Davies]

Thanks @Jeremy Harris, very useful figures. Any chance that in 6 weeks or so you could do similarly for Dec/Jan/Feb?

 

1 hour ago, Jeremy Harris said:

(which also tends to be the lowest emissions period)

 

Insert obligatory rant that even in the middle of the night incremental demand will usually come from CCGT (gas), particularly on days when the PV hasn't filled the Sunamp anyway.

[Jeremy Harris]

I can have a go at giving those figures.  December was pretty grim from a PV perspective this year, worst I think we've had since the system was installed, so may not be typical.  Likewise the last few days have been higher than average for the time of year, as we've had several cold, very clear and bright, days (near-perfect PV weather).

[SteamyTea]

57 minutes ago, Jeremy Harris said:

December was pretty grim from a PV perspective

Always worth plotting against the PVGIS datasets.  I think they do daily if you dig down deep enough.

When I started in the PV industry, I had a number of calls from dissatisfied customers.  These were on systems that had nothing wrong with them (was a rarity for the company I worked for).  I checked the local weather stations and it was an exceptionally dull autumn.  nothing can be done about normal variation.

Unlike the NE facing system that was installed because the customer did not want them on the SW of his house.  I should have got the salesman to add a couple of extra thousand to that for the hassle.  Can see why no one else was willing to do the job.

[Ed Davies]

1 hour ago, Jeremy Harris said:

I can have a go at giving those figures.

 

Excellent, look forward to it.

 

1 hour ago, Jeremy Harris said:

December was pretty grim from a PV perspective this year, worst I think we've had since the system was installed, so may not be typical. 

 

Interesting contrast: up this end of the island my perception is that November was particularly cloudy, probably the worst month I can remember having lived in the north of Scotland for nearly a decade, but December had quite a few decent sunny days, though chilly - e.g., heavy frost overnight which didn't clear during the day except for surfaces particularly pointing towards the sun.

 

On the other hand, November was very windy here. I calculated that a little 1kW wind turbine (Futurenergy Airforce1) would have produced all my electricity needs for the month though would have needed a big battery to get over a gap in the middle but there were a few sunny days then.

[DamonHD]

Another question: ...

 

Is there a cheap flow detector that I could insert into one or more of my water pipes (eg during my works) to monitor flow?  Either yes/no or some gradation?

 

They should not be massively expensive, nor impede flow, and ideally would be easy to monitor with (say) an RPi.  (And a free unicorn with each one!)

 

This is so that I could get an idea of DHW demand, and maybe even as clever as how much demand is satisfied by the UniQ and the residue from the combi.

 

That might also give me a better way to predict when to pre-emptively fill the UniQ in winter if grid carbon is low or we evict the combi entirely.

 

Rgds

 

Damon

[SteamyTea]

1 minute ago, DamonHD said:

Another question

I found a fairly cheap on a few years back. Was with reference to a GBF member in Italy.

Can't remember who made it, but the post should still be up there. I did talk to the supplier and I think it was s basic pulse meter.

I did try making an ultrasonic one. But had no luck.

There are instruction on how to do that on the interweb.