More Generating 240 volt AC

I wonder what flowrate you actually need to move the heat available ? I bet its not as much as a CH pump can deliver is it ? I certainly wouldn't dream of inverting a 12V panel to drive a CH pump - like you said "Keep it simple"

Steve

If you're playing with the big boys it still does, it's just that you have a huge capacitive inverter and some seriously clever switch gear between the generator, the grid and the site...

I wasn't thinking of a 240V inverter, as much as the problem of finding and maintaining a lower voltage pump (and potentially altering the control system). The big advantage of the present system is that the components are standard, and it has a single moving part (no valves etc. required).

It's not a circulating application either - it's a lift pump, and it's not quite as simple as "when there's sun, pump", as there needs to be an over-temp cut-out (it's a drainback system, for efficiency and safety). Mine currently cuts out at about 102C, and it's very necessary in summer. I've recorded temperatures as high as 107C at the panels (that's the roof's outlet manifold, not the actual panel(!) and I don't know the accuracy of the thermometer at that extreme). If steam were ever produced in quantity the system would be thoroughly dangerous (yes it's got a safety valve, but even so...).

So on balance, although it probably could be done by solar generation, it's probably best left as it is.

I suppose I ought to be able to work out how hard the pump is working, as there are flow meters and I know the head it has to produce (about

Worth pondering though - I'll give it some thought whilst huddled round the candles later this w/e :^)

Regards,

Simonm.

On or around Thu, 31 Jan 2008 06:59:44 +0000, Steve Taylor enlightened us thusly:

ours runs a small CH pump at minimum speed. Probably takes about 100W, but it only runs when there's a temperature difference of (IIRC) 5 degrees between the tank and the collector, and if it drops to 3 degrees it cuts out again. Those levels are customisable, if you can be bothered.

In summer, the water mostly gets heated by the sun. In winter, it'll get the water to about 40 on a really good day, or about 20-odd on a crap day, which is still above the normal CW temp of about 10 degrees or less.

I think the record was to have the whole tank at about 85C, in the summer. Of course, you have to be careful of the hot water then, especially if you have young children.

You might need to install an automixer to maintain a safe water temperature. Common on boats where the water is heated via a calorifier from the engine water to 85C+. Cleghorn Waring do them.

In article , Austin Shackles writes

Sounds like the same controller as ours. I've got mine set to +6 on +2 off, which is probably too optimistic at the off- end.

Ours gets to that too, but I'm thinking of dropping the over-temp cutout down a bit, for the same reason. It's rather hot if you aren't expecting it, and the thick insulation on the pipes only adds to the element of surprise :-(

Regards,

Simonm.

Plenty of options here

I've got the panels and pump but the controller looked a bit expensive, where's yours from?

I'm actually in no great rush to fit anything because the cost of the plumbing looks a bit high as I'd need to fit a second dhw tank downstairs because of space limitations.

On the too hot water issue: how about looking at a thermal store with plate heat exchanger rather than mixer taps? It gives the ability to store more heat.

AJH

In article , AJH writes

Resol, "Deltasol B." It's obsolete now, but the manual is here:

They do a range of controllers, the closest current one probably being the Deltasol BS. It was part of the package, so I don't know what it costs separately, but there's practically nothing to it (three thermocouple inputs and one 240V switched output), so it shouldn't be pricey.

It's all in and functioning now - 2-coiled 75 gallon pressurised tank (Telford Tempest). I wanted a thermal store but was talked out of it because of the difficulty of plumbing it in (condensing gas boiler to consider too). Broadly speaking, if the primary loop doesn't have sufficient delta (7C from memory), the boiler can't operate in condensing mode and is therefore inefficient. The hotter you get the tank the harder it is to achieve the necessary delta.

Solar complicates matters with a thermal store too, because it has to couple to the primary circuit somehow. With a 2-coil 'conventional' system there's no complex interaction between the two (or three) different heat sources. Solar takes 1st priority heating the water. If it gets it hot enough without help the boiler (or immersion heater) never fires up, otherwise they provide topping-up heating as required. The only drawback is that when there's little solar energy available (like now), the effective tank capacity is greatly reduced.

I am looking at adding a second "pre-heat" tank (say 30-40 gallons), so as to make better use of the solar energy when it is available.

On balance I'm very pleased with the setup, as it certainly works very well on sunny days, and it's not complex and near-zero maintenance. If you're interested it was done by Southern Solar, and I'd recommend them for tidiness and efficiency (can't compare prices easily so I don't know, but they weren't extortionate by any means).

HTH.

Regards,

Simonm.

Yes but the reason you have the 75 gallons is to store solar heat for a few days not the heat from the gas boiler. So the idea is that the gas boiler thermostats are set to only warm the top of the tank, sufficient only for any requirements that the gas cannot keep up with. It's better to store the energy outside of this as chemical energy in the gas. Thus if the thermal store is capable of 90C (and I service a solar system with one than can store 3000 litres at 90C) and there is a call for gas heating for dhw at 50C then there will always be a return temperature of

Don't get me started ;-). I snagged the system in a block of flats that red ken opened and they still don't believe me when I tell them what's wrong with the design!

That's good then, I've just been involved on a thread in uk-diy about how my father was sold a set up which wasn't installed or run properly. The general consensus there is that commercial installations aren't likley to be a good return on investment, at current fuel prices, in UK but it's difficult to quantify satisfaction.

AJH

What IS the way to use solar and a combi-boiler ? Any pointers ?

Steve

UK diy is a good place to ask for general plumbing advice, there is a faq on central heating and boilers.

As to the specific question the easiest way is to heat a tank with the solar and then take the output from that to the combi, via a heat exchanger, except many combis do not like a hot feed, this way the combi tops up the water from the solar tank. You'll need a plate heat exchanger to manage the power transfer.

AJH

For a low flow rate like a combi ?

Steve

In article , AJH writes

The existing arrangement is elegantly simple. In particular I like the way the solar system doesn't need to alter or interact with the conventional gas system and its controls. I'm contemplating a variation (with an additional tank) because we have excess collecting capacity on the roof for most of the year, and I want to take better advantage of it, but I've no firm plans just yet.

Regarding payback period, I think it depends on how you consider ROI. If you take the 'blunt instrument' approach that fuel savings are directly balanced against capital cost, then payback is probably more than a decade (not good). That however assumes no residual value for the system, which is unrealistic.

The system we have is virtually maintenance free, with a design life in excess of 20 years (external corrosion is likely to be the biggest factor). Thus a certain capital value will inevitably be factored into the price of the property should we sell it meanwhile. The exact value one couldn't say at this stage, but it's not a poor capital investment in that sense. And there's a nice feeling about running a hot bath of entirely solar-heated water in the summer!

Regards,

Simonm.

In article , AJH writes

I defer to m'learned colleague, however in a typical domestic installation the Irish answer applies - don't start from there! We have a condensing system boiler (heats a tank of HW), not a combi. The tank is tall+thin and has two heating coils. The lower coil is heated by the solar array, and the higher coil by the gas boiler. If the solar array produces enough heat, there is no need for the gas boiler to fire up, and it doesn't.

There is no connection between the two control systems, as it's not necessary. The boiler is timed to switch off in time for the tank to empty of hot water at the end of the morning rush, so that the solar starts the day with a full tank of cold water to heat. This optimizes the thermal transfer, especially at this time of year when you can't collect as much energy. The boiler kicks back in late afternoon/early evening, and tops up the temp. as needed.

Works for us...

Regards,

Simonm.

Really, don't go there :(

Regards,

Simonm.

Yes but the thermal store has its own pump, the hot water is at mains pressure. Like you I haven't done it because my current gas central heating has life in it and in my case my dhw demand is low. I use a couple of wood burners for space heating (but the gas fires up radiators in the kitchen and living room for first thing.

AJH

It's the heat transfer from the thermal store to the mains pressure water that counts, the combi is just topping this up if necessary, when the solar heated store is cold it simply makes no difference from a normal combi installation.

It can get more complicated as I said because many combis don't like a hot inlet, so the solar tank heats the mains cold inlet which is blended in parallel by the combi to the desired temperature (about

AJH

Don't get me wrong I'm no expert but I've been dumped in the deep end because one of our pellet boilers backs up a big solar system, in fact it doesn't even keep it afloat if the temperature sits in the single digits for a few cloudy days, one thing about solar enthusiasts is their optimism!

This is how my father's was set, trouble was the gas coil was only just above the solar when it would have been better nearer the top.

In fact there is, the temperature gradient in the tank, this is sufficient feedback path for the rest to work with no electrical connections.

Yes that's how it should be but there is a case for changing the way the solar contribution is made between winter and summer.

Now that delta T problem, preventing condensing mode, you earlier referred to would be solved by better heat transfer in gas coil, which is limited because it is a coil.

AJH