Solar hot water panels

[ilikecobwebs]

Our current hot water tank has been in the house for around thirty-five years. It should really have been replaced a long time back, but it involves making a lot of mess in the kitchen, which is where it lives, in a large airing-cupboard-style alcove. However, we are seriously contemplating a kitchen refit (since after fifteen years most things are getting threadbare) so this might be a good time to consider the possibility of installing a solar hot- water panel.
I understand that such systems involve new water tanks anyway, so all the mess could "happen" at the same time as the other stuff.
I know that some of you have had them fitted, so was wondering what sort of companies you approached; and what key issues there might be to look out for.
Our normal heating is via oil (no gas available in the village); we normally run from end April to mid-October with no central heating on, so during those times our oil-boiler is really only used for heating water (baths, washing-up, etc). The idea of using solar hot-water seems feasible, so wonder how efficient others have found it.

 

[FamilyWiggs]

Great thread topic cobwebs - I'm really interested in this issue too.

And solar PV panels for electrickery too.

Please pour forth, oh wise counsel of PPUK.

 

[Flyfisher]

My knowledge is all theoretical at present but I'm also very interested. From what I've read, solar tubes for water heating is about the most efficient renewable energy source at present, although I may be out of date now that feed-in tariffs (FITs) are available for photovoltaic solar cells, which rather changes the economic position.

I was in Germany last month and was amazed at how many houses and businesses had PV panels on their roofs. I know they introduced FITs some years ago but didn't realise how successful they had been in encouraging such installation. Even flat roofs could be seen with multiple slanted rows of PV panels together with the occasional installation in a field.

I also heard a recent R4 programme talking about how PV 'farming' can now be more profitable than growing food and that chappie that runs Glastonbury has installed a large PV system that, apparently, generates £60k per annum. :shock:
http://www.guardian.co.uk/environment/2010/nov/10/solar-power-glastonbury-michael-eavis

As for practical experience, I trust skier-hughes will be along shortly to describe his solar water heating system.

 

[Penners]

ILC - you might find this website interesting and useful. I have no personal experience of the success of its recommendations.

http://www.solarfriend.co.uk/

 

[fluffytail10]

Hi there,
We had 2 solar pannels fitted a year ago now. We have an old combi boiler which couldn't get the water hot enough for baths so decided to try solar. We had an old airing cupboard, into which the new tank was fitted, and the fitting process took a couple of days in total.

It does work but is nowhere near as wonderful as all the adds say. We get hot water (enough for baths etc) from March to Nov - depending on the amount of sun there's been. Any cloud and its useless. All this talk about about ambient sunlight being good is rubbish, it needs direct sunlight. We have to make do with an electric shower for could winter days.

We too only have oil, so it is great for not using the boiler during the summer.

So overall my opinion is great for summer but you'd still need a back up for the winter. BTW it cost about £4000 ti install.

 

[citizensmith]

We have a pair of Worcester "Greenskies" Solar Hot water panels inset and flashed into the slates on our south facing "extension" roof. They feed a twin coil 300ltr tank that is in the loft just behind them. The tank is at mains pressure at all times and comfortably pushes water through the showers as if they were powershowers. Daytime water temp at present is 60 deg C and they don't take too long to recharge during the day if the water is used up in the morning.
However, my teenagers seem to like showering at night at present and dont understand that moonlight is not an effective source of radiant heat for the panels! :twisted:

 

[d49xc]

Google for 'navitron forums'
...and then specifically look in the the 'solar thermal' sub forum

It is a bit tailored towards the navitron product - and the forum is run by navitron...nevertheless a good source of info.
Look out for the arguments of whether you need a emergency heat soak radiator in the circuit (some say only in med countries where the sun is hotter). It's to take care of what happens if you go away for 2 weeks so the system is not being used to take away heat and it's boiling hot sun at home and the solar panel/circuit gets hotter and hotter and hotter and hotter until it melts the solder on the copper tube and self destructs (or something)

I've looked at soalr thermal but its not justifiable for me even if I DIY it which I could - partly as I'm shaded from the sun until 11am at midsummer, and partly being an engineer I just view it all as something else to go wrong, need cleaning, parts need replacing whatever (Bit like we glider pilots say our aircraft are safer than powered aircraft as there is no engine to pack up........)

 

[Penners]

We had 2 solar pannels fitted a year ago...

It does work but is nowhere near as wonderful as all the adds say.

Well, that's amazing! You mean... the ads exaggerated?? :shock:

I've never encountered that before.

I have no experience whatsoever of solar panels, but I'd always understood that they work best as a kind of pre-heat system to your domestic hot water, using a secondary coil in your indirect cylinder. That way you get benefit from them even if the water they heat is only a degree or two above the cold water in your system. However, I also understand that this technique implies a requirement for circulation in that secondary pre-heat system to be shut off when the water in the cylinder exceeds that in the secondary coil.

But - as you can tell - my understanding of the details is... er... hazy. :?

 

[skier-hughes]

We spent nearly £15k on having a new heating system, 50 solar tubes, new wood burner with back boiler, 900 litre buffer tank with 200l DHW inside, our rayburn is also connected.
Best thing we ever spent money on to be honest.
Yes bright sunlight provides more power, but ours works well on cloudy days.
Last year we only lit the fire twice during the summer (May-Sept) to boost the water temp. Too much hassle to light the rayburn (oil) for a bit of heat.
Our electricity bill - DHW from emersion and rayburn previously - went down by £50 per month.
During the winter our buffer tank is heated by rayburn, wood burner and solar. Nowhere near as much as the summer for the solar, but the tank provides us with cetral heating for the morning, as the radiators take out the heat from the water, if it's a bright day the solar will put some back in before we light the fire as the sun goes down.

We were just about to cover the rest of the roof with PV, but with Jo not working and no income for 3 months, that's had to go on the back burner :roll: :lol: :lol:

 

[AMc]

Your consumption of hot water is unlikely to be a significant factor in your overall heating bills compared with space heating unless you use a great deal of hot water - in which case you may struggle to size an appropriate solar thermal hot water system.

The payback period for solar thermal water heating is quite slow and the systems require moving parts and servicing and don't attract subsidies - I was advised I wouldn't see a payback at all when I was specifying the heating systems for our house (using Air Source Heat Pumps).
Evacuated tube sysems are more expensive but more efficient - there is some debate about the life span of the thermal tubes.
Flat panel collectors are cheaper and simpler but less efficient.
If you DIY then the installation saving is significant and shortens the payback period considerably.
Navitron is a very good place to research.

Solar PV has been made dramatically more economic by the Feed In Tarrif which artificially subsidises the production of renewable energy to offset the lack of major commercial production. It's being skewed towards small domestic installations not larger commercial microgeneration - the political implications of that are fairly obvious. FIT payments are generous, index linked and backed by government commitments so can be fairly reliably counted on.
If you have the capital to buy a system or can borrow the money at a low rate then you will almost certainly see a return on investment within the lifetime of the system. My parents are about to fit 4kwh peak of panels as the projected ROI is better than the income on the money in a savings account.

To gain FIT payments you need a MCS certified system installed by MCS certified installers.
http://www.microgenerationcertification.org/

Which? did a recent report on the Solar PV industry including a honey pot project that caught a number of companies providing a less than accurate estimation of the costs and benefits. There are a lot of short term sharks out there at the moment and a badly fitted system will not make you as much money as a more expensive but more durable one fitted by a skilled team.

The Centre for Alternative Technology have a long term research installation and impartial information on solar PV and thermal
http://info.cat.org.uk/

The Green Building Forum and their associated Green Building Magazine and Green Building Bible are a wealth of well researched independent experience in all manner of building techology issues - esp. solar energy at the moment. The Green Building publications also cover lime and breathable buildings which has some resonance with Period Properties.
http://www.greenbuildingforum.co.uk/newforum/

 

[biffvernon]

I built my own solar thermal water heating panel made from aluminium sheeting from an old caravan. It forms the roof of an outbuilding. We also have 4kWp of solar pv, which has performed very well this spring. The Navitron forum, mentioned earlier, is the best place for advice. http://www.navitron.org.uk/forum/

 

[ilikecobwebs]

Well, that was all useful! Will follow up the links and peruse details.
We would not be borrowing money to fit a hot-water system and, if we were going for a PV system I wouldn't be sucked in by the FITs offers. They might be government-backed but I wouldn't rely on or trust anything backed by government these days. I look on the fitting of either or both as more of an energy "security" rather than making money...... when the Grid fails, the lights go out and your neighbours' houses are in darkness and they have cold water, then hopefully we wouldn't be joining them.
Anyway, plenty to read, so must get cracking!

 

[d49xc]

All the "grid tied" PV panel systems have to be arranged such that if the mains power goes off then so do they.
So there is no possibility for you to run the system isolated without incoming main power.

The reason for this is what happens when there is a fault/break in the lines supplying properties?
While the electricity company can ensure that their end is safe and 'locked off' to enable work to repair the fault proceeding, they cannot control PV panels from peoples houses backfeeding into the fault from the other end.
Hence the requirement for safety reasons that the inverter controlling the PV panel link to the grid cuts their output if they sense mains failure.

Of course none of the above applies if you have a totally standalone 'off grid' PV panel system which is not connected into the mains in anyway.

 

[Flyfisher]

Surely it would be possible to arrange for the grid to be isolated from the household circuits in case of failure, allowing the PV to still feed the house?

Wouldn't such a system be required for standby generators as well?

 

[ilikecobwebs]

I acknowledge the power feedback problem in such a situation. Thus it would seem wise to forego FITS and be independent of the National Grid completely. Otherwise, if "they" can shut off your PV panels' power output to your own house, what's the point of having them in the first place?
Very interesting forum, that Navitron....have recommended it to a few other people as well, last night.

 

[biffvernon]

The thing is that the FiT scheme is paying 43p for every unit generated. The money doesn't come from government but from the electricity industry (i.e. everybody else). They have a legal obligation to pay it for 25 years and the price goes up index linked. It's tax free. It is highly unlikely that government would introduce primary legislation to reverse this obligation and so it is about as copper bottomed as anything in this world.

Of course, when the great collapse of the global financial system comes it will be a relatively trivial job to rewire the hardware and become independent of the broken grid, but until then it seems a no-brainer to game the system and pocket the FiT payments.

 

[d49xc]

Surely it would be possible to arrange for the grid to be isolated from the household circuits in case of failure, allowing the PV to still feed the house?

Wouldn't such a system be required for standby generators as well?

I believe the German system is indeed different
They do indeed have some sort of changeover switch such that in the event of mains failure your house can operate independently in "island mode" as its called totally seperate from the grid.

It is however more complicated that just having a switch.
Once seperate in island mode and now totally disconnected from the grid it is quite possible (virtually certain) that the frequency of the AC (50Hz) power generated by the generator will start to differ from the grid. The island section will move away from being in synchronism from the grid as the generator's frequency moves up and down. So come the time to re-connect you must ensure that as well as the frequencies being at 50Hz they are both at the same cycle in the waveform.
This is usually done automatically by a synchroniser unit (so thats another piece of kit) - though it can be done manually by adjusting the speed of the prime mover to move the waveform into synchronism with the aid of a set of lights which shows the mismatch between the units and when they all go out you press the connect button fast: I've done it on much much larger generators and you need to anticipate the lights as you press the button to connect the circuit breakers as the breakers take a finite time to operate.
The same would apply to all forms of generation being re-connected to the grid - they must be sychronised first. In these calc's the grid is assumed to be infinitely huge so is not affected by having an additional generator connected.

For a rotating generator if you get it wrong the effect is that the grid effectively 'pulls' the generator into sync. The stationary part of the generator experiences a large pull in one direction and the rotating part has its speed 'instantly' adjusted. The forces and the power flows are quite considerable and on much bigger generators where the rotor can weigh 50 tons it can be felt through the foundations(!) if a manual sync is tried and you get it a bit wrong - assuming the trips don't all come out from the huge current flows. Get it more than a bit wrong and you end up with a wrecked generator - but then all the safety trips are there to ensure it can't happen

Sorry for the thread drift into power system operation and generator design......

 

[Flyfisher]

I understand the synchronisation issue (though, to be honest, have never really understood how it was handled with domestic standby generators) but have always assumed that a PV system, being entirely electronic, wouldn't have the mechanical challenges of a generator. Wouldn't the inverter just 'free-run' at 50Hz with no grid connection (i.e. during power failure) and then become phase-locked when the grid is reconnected. Some sort of sync mechanism must surely be present with a grid connected PV system, if only to handle the first time it is all connected up.

 

[AMc]

I acknowledge the power feedback problem in such a situation. Thus it would seem wise to forego FITS and be independent of the National Grid completely. Otherwise, if "they" can shut off your PV panels' power output to your own house, what's the point of having them in the first place?
Very interesting forum, that Navitron....have recommended it to a few other people as well, last night.

The "point" is to generate electricity and supply it to the grid which everyone uses and get paid above the market value for it. You make money and cut a tiny amount of fossil fuel consumption in the process. Your grid connection allows you to use power when your panels aren't providing any.

"They" don't shut off your system, your system shuts itself off when the incoming voltage disappears - how could "They" shut everything off in the event of a grid connection problem - they connection has just broken?
This is a requirement of a grid connected system for the safety of those working on it. Also if you trip your own breaker in your house - say by drilling into a cable - you probably don't want your PV panels giving you a 240V shock through the drill either.

The FiT is money in the bank for up to 25 years. As Biff told you you get paid 43p per unit if you use it on site or not. The cost of a peak unit (the sun shines in peak periods BTW) is about 15p per unit. So if you generate a unit and use it locally the value is 43p FiT + 15p saving on purchasing the unit from the grid = 58p value!
By contrast if you go totally off grid you get the equivalent value of 15p a unit when the sun shines but have to pay the whole cost of the PV system and get no subsidy. Before FIT and Clear Skies grants the payback periods on PV systems were borderline on the life expectancy of the installation at 15 years or so.

Wise to forego FITS (sic)?
You would have to be mad to go off grid if there is a connection available - what are you going to do when the sun goes down?
If you were to choose to go totally off grid then a low voltage system and battery storage is the way to go but this isn't cheap or simple.

-----

Some solar thermal systems have small DC PV panels integrated to run the pumps and provide hot water even without a grid connection available. That would strike me a sensible solution and you'll still get hot water when the fuel apocalypse comes. :roll:

 

[Lime]

Re. island mode.

Why not use a radio broadcast similarly used for radio clocks to synchronise the home generator?
My comment assumes the home generation is producing enough or any power at all !

(I'm aware that the mains frequency is used to control country-wide power variations and is not stable albeit operates an overall 50hz mean.)