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Post by cye on May 22, 2011 5:03:13 GMT -5
So you're saying a sensible rule of thumb would be to size your battery bank for say 5 days worth of expected electric usage. Your electric usage must be very light at ~1 kwh per day - I think the average domestic household uses 3000-4000kwH per year, so guessing there's typically 3 people per household, you're only using 25-30% of Joe Public's consumption. Well done. Have you found a very efficient fridge, washing machine, etc and any brands etc you recommend? Re the engine/solar hookup, it didn't occur to me about the extra complexity of thinking about pressures, you're right to rule it out. EV sizing with solar is a not as straightforward as F&E tank sizing. With an F&E tank & solar you simply go with 4-5% system volume, as the steam is vented, and the F&E tank normally tops up with water automatically. However, with using an EV with solar, steam has to be considered as the panels can boil/stagnate and the EV should be designed to accommodate all the water likely to be displaced by the steam, without the relief valve blowing. Appropriate consideration of EV sizing will in turn enable automatic recovery of the system (i.e., without you refilling!), say once your pump power is restored or once whatever problem caused the stagnation in the first place has gone. If you want to study the subject, a good guide is www.iea-shc.org/outputs/task26/A_Hausner_Stagnation.pdfIf not deliberately oversizing the EV and wanting to use the smallest possible EV, I would recommend an approach such as: [1] measure the volume of the fluid in your panel(s) plus the contents of the pipework a few metres either size of the panel(s). This is in most cases is an acceptable estimate of the volume of water that will be displaced in the event of stagnation. Oil/gas central heating EV sizing doesn't have to consider this element because the CH system will never get to boiling temps, ever. [2] Add to this 4% of your total system volume. This is the element that solar EV sizing has in common with F&E tank sizing. [3] Add to this the cold volume of fluid you will have in your EV. This is the min volume of solar fluid that will permanently sit in your EV, and this in turn is determined by your chosen system (liquid) and EV (air) pressure settings, etc. I'll put up some notes in the guidance section of the forum on how to work this third figure out. If you expecting 9-10L in your solar loop, I'd say there's a good chance a 2L EV will be too small. Particularly so if you are oversizing your panels, and you decide to go for say 2 sq metre ( and I hope you do oversize your panels now that you have a solid heat dump mechanism). Checking the sums early in the design is probably worth the trouble if you want to avoid the prospect of the solar fluid blowing out of the PRV on a regular basis.
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Post by johnboy on May 22, 2011 14:32:56 GMT -5
Didn´t really explain the sizing issue very well..
The totally figure for your daily usage is the absolute minimum you need to think about generating from your pv´s. A 5 day storage cushion is nice though. I try not to use more than 20 percent of my storage capacity daily. Taking deep cycle batts down to empty is ok now and again but not everyday. Think my cells are rated at 500 complete cycles so only using 20 percent give them a good long life.
My usage is frugal, forget household figures. Straight 12volt is good, inverter is bad. Shoreline Fridge freezer 30amph, LED lighting next to nothing, Akura TV/DVD 12amph (4 hours), Alpine car stereo 5amph (10 hours), Jabsco waste and fresh water pumps not on long enough to make much impact. Oven, hob and grill are gas. These are just sample figures, don´t watch much tv as i´m usually messing with something else.
In an ideal world i would over size my collector but space on boats roof is a real issue so i´d like to get it about right and defo not too big. Probably just under 1 sq metre. My tank is so small i THINK that will do. If not i will have fun making the mk2 collector eh.. I probably was a bit hasty buying the EV before quizzing you guys. What kind of pressure relief valve would you fit and where?
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Post by cye on May 22, 2011 17:31:04 GMT -5
Thanks for the info. Had a look at the shoreline specs, that stuff looks very efficient, wonder why 12v stuff is efficient. Is it just because the manufacturers of 12v stuff know the users need to limit consumption, whereas domestic whitegoods makers know most of their customers are blissfully ignorant?
How do you monitor battery charge levels?
what about reliable brands such a tristar and morningstar etc, are these the best or just good valve and what are the considerations?
Back to solar thermal: PRV should be 3bar standard central heating type, normally teed onto the EV port.
location/sequence of EV, NRV, pump etc is a matter of some debate, with strong views held by followers of different schools of thought. My preference is for the following order on the cold side of the solar loop, starting from the calorifier/tank coil and working out towards the solar panel:
tank coil (cold side) pump tee off to branch feeding EV (with PRV and guage teed onto the EV port, and a filling pipe with a double check valve teed into the same spot, i.e., right beside the PRV) Non return valve NRV panel (cold side)
That way when panel boils the steam (or very hot water) can't get straight at either the EV or the pump to damage them, and is quenched by the tank coil first.
EV should be mounted upside down with schrader valve on bottom and PRV on top, that way sediment/muck in the fluid doesn't collect around the PRV and when the PRV blows it has a good chance of resealing. also, being mounted upside down tends to help the EV membrane stay cooler in normal working conditions which makes it last longer.
PRV blow off should be to a collection container. i use a plastic petrol can, others use recycled fire extinguishers and just about anything else is ok too provided it won't leak if it gets a blast of boiling water. Branch off the solar loop pipework to the EV should ideally dip down 6" and do a foot or so of horizontal before rising towards the EV - This helps prevent hot water from the loop rising up to the EV in normal use and prolongs the life of the EV. If you position your EV somewhere else less protected you need to use a solar-rated EV (where the diaphragm/balloon is rated for 130c), but if you protect the EV as described above a normal CH EV is fine (rated ~99c).
To facilitate periodic maintenance of the EV, put a gate or ball valve on the branch to the EV a foot or two away from the EV with a drain cock next to the gate/ball valve on the EV side. This allows you to drain the EV periodically to check the air pressure without having to drain the whole solar loop, and recommissioning only requires refilling of the fluid on the EV side of the gate/ball valve.
after having written the above i see it would have been easier all round to draw a sketch! hope it makes some semblance of sense.
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Post by johnboy on May 23, 2011 4:58:17 GMT -5
Picture paints a thousand words and all that. Quite a small space under my bed where the calorifier lives so might have to put the EV and PRV in the cupboard under the where the pipes go through the roof.
As for the 12v stuff being energy efficient it is but i am acutely aware of my power usage. When i go to peoples houses they give me funny looks when i with out thinking switch stuff off that's not being used. Once your 'in the zone' for living off grid it's second nature to be frugal or as i see it sensible. If i'm in the kitchen then i have the kitchen lights on and not else where etc.. I don't live like a nun but but i am not wasteful in any way. That extends to water usage too. The fresh tank holds 150 gallon and when i'm on my own i can make it last 3 sometimes 4 weeks. I don't waste a drop if i run the hot tap i run off the cold water that comes before the hot arrives into the kettle and use it for brews, same in the shower, i use that for rinsing the shower out after use. I'm not an environmentalist but i am aware how much power and water folk waste. I could go on about this subject but it might not be what you want to hear..
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Post by cye on May 23, 2011 15:06:08 GMT -5
john, please do continue.
to my mind it doesn't matter whether someone's an environmentalist or not, if they're doing what they need to be doing it's got to be a good thing and there's plenty others can learn from it.
I once found myself listening to two people arguing about global warming and the cause of it, one a believer & one not, yet both were in agreement about the need to reduce energy usage (one on economic grounds and the other on environmental grounds). It occurred to me that their point of disagreement about the environmental issue was pretty much unimportant, because, whether one believed it or not, the key thing was that they both knew what they needed to do energy-wise, and on this point they agreed . So they should have been focussing their attention on that common goal, and, e.g., spent their time learning energy-saving tips from one another, comparing notes etc, rather than firing up an argument which was going nowhere. Now that's my meandering over for the evening!
your narrowboat working example i think is a fantastic case study for people to think about and learn from. firstly it's small scale and focussed, highlighting just how little energy an individual needs to use yet still meeting all the basic requirements. no matter the motivation for what you've done and are doing, it's a very good thing and we should all take note.
Re plumbing layout for EV, PRV, pump etc, i'll sketch up a pic of the pipework this evening hopefully and post it up here.
all the best
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Post by cye on May 23, 2011 17:04:55 GMT -5
here's a rough sketch of the plumbing layout. There is another school of thought whereby, in the event of panel boiling (stagnation), the rush of hot water caused by steam in the panel should have a free path down both sides of the solar loop, and should not be forced down just one leg of the loop. This thinking is all very well if you have the money for a solar rated expansion vessel and a brass-bodied super high temperature pump, but otherwise you're best using the NRV to force the rush of hot water through the coil to quench it before it gets to any easily damaged components such as pump and standard EV. I've drawn the 3bar PRV, the guage, and filling loop stuff all very close to the neck of the EV because you can buy 'easy plumbing' kits for EVs which contain all these components on one fitting, e.g., the Robokit. If there's any risk of the gate valve ever being closed when the sun's heating the panel, you may want to de-risk this by placing a 6bar PRV just to the left of the gate, or indeed anywhere else on the cold side of the main solar loop. Otherwise take the handle off the gate when your system is commissioned to prevent kids etc from playing with the gate. Attachments:
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Post by cye on May 26, 2011 13:22:00 GMT -5
john, i had meant to explain earlier that the only reason the PRV and guage is right at the EV in my diag is because most people, to simplify the plumbing of the EV, use a multi-port adaptor which you plumb into the EV. It provides the extra ports needed for guage, PRV, solar/heating loop, and filling loop. & saves a lot of extra plumbing.
the one i use is called a robokit fitting kit, made by altecnic, and plumbers merchants stock them to sell with the EVs
are you familiar with these? do you want me to post up a pic of one?
if i wasn't using one of these i would probably have fitted the PRV & guage to the left of the gate to de-risk someone inadvertently turning off the gate and blowing the solar loop.
tell us some more about your PV please!
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Post by johnboy on May 27, 2011 11:17:52 GMT -5
Hi Cye I'm back in UK now and gathering the bits i need to cobble the system together. Got big reel of 10mm copper tube, air vent, 3Bar PRV, check valve, pressure guage, your pump and my 2 litre EV. Also got a sheet of 1.2mm aluminium for the back plate of the absorber. I was wondering if it was possible to get a multiport block to fit into the EV so thats cool. One thing i'm not sure about is the location of the gate valve on your sketch. Shouldn't it be next to the check valve on the filling loop? If not what purpose does it serve? My EV is an Italian Varem 2 litre jobbie precharged at 3.5Bar. Max temp 99 c so should be ok on the return leg of the loop. I know your concerned about me only using a 2 litre EV but space is a massive issue for me and if i can get away with it then i'll run with it. If it turns out that i'm blowing fluid out of the PRV then i'll up size it. www.bigginhill.co.uk/solar.htm This is the basic design i'm going for on the absorber front. Nice simple design!
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Post by cye on May 27, 2011 13:44:13 GMT -5
hi john,
when setting or checking air pressure in EV you can't do this reliably with fluid in the EV, therefore must drain fluid from EV. gate and draincock allows one to drain the EV without having to drain the whole solar loop. much easier altogether.
air pressure should be checked periodically at EV either as part of annual maintenance or when diagnosing problems. procedure as follows:
-close gate -open draincock -use car tyre guage to check or set target air pressure (see below) -use car pump to repressurise if necessary -close draincock and open gate -attach modified garden sprayer to filling loop and refill/top-up solar loop to desired system pressure(see below) - run pump and bleed air, and increasing system (fluid) pressure again if required
3.5bar far too high. use 1.2bar system pressure and 1 bar air, or 1.5 system and 1.3 air. always system slightly more than air to allow some fluid to permanently reside in EV (by way of buffer), and to facilitate expansion in the event of high system temps or and/or panel stagnation
see pics of dermot leonard's system for modified garden sprayer (galway installation)
manual air vents should be placed at all high points in solar loop, preferably atop a few inches of vertical pipe to retain trapped air. if you don't use air vents youmay have airlocks in loop which could be very troublesome to shift.
hope this helps
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Post by johnboy on May 27, 2011 14:49:07 GMT -5
Sure does. Top tips cye keep em coming.
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Post by johnboy on Jun 4, 2011 4:23:22 GMT -5
Hi Cye Just about got all the bit i need now and have started making the collector. The one thing i haven't got is a NRV. Can you recommend one that doesn't give too much resistance to the pump please. Link would be good. Cheers mate.
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Post by cye on Jun 4, 2011 4:46:33 GMT -5
john, flap type seems best. i use a std spring and ball type but it chatters like mad, offers significant resistance to flow (pressure drop), and is 'on the list', i.e., it's coming out and soon to be replaced by a flap type. Colin lloyd also used one of these spring and ball types and the thing seized up on him in the closed position and possibly damaged his pumps. here's a link which explains the flat type design www.aquatext.com/images/systemph/nrv.htmit will need fitted vertically. strangely the plumbers merchants in NI here don't stock the flap type NRVs, but they are very popular in RoI. you can buy mail order from pulsardirect.co.uk , e.g., product code NRVH01
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Post by johnboy on Jun 18, 2011 3:57:02 GMT -5
Cye, can you recommend a 12v pump controller as my idea of using a 20 watt stand alone PV doesn't work to well. It turns the pump even when it's cloudy and thats only going to suck any stored heat out of my tank. Also having problems attaching pics of what i have made...Tried using the `Choose File` but to no avail.... Help please......
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Post by cye on Jun 18, 2011 5:43:04 GMT -5
Hi john, if you are making a controller see norm's post on modifying the £5 vellemann thermostat kit from maplins. this seems to be the cheapest option. i think dave miller (dpmiller) knows how to do the mod as well perhaps. the most basic prebuilt kit is the reuk 12v controller (available on their site for about £30). you still need to extend the 2 temp sensors, say, using alarm wire, and you will need to 'pot' the sensors in epoxy such as araldite or bison. we have one of these to show at workshops, if you want i can post up a pic. next up is the ready-to-use 12v controller supplier by solarproject (links to their site on our www.solarco-op.net website ). this is about £50 or thereabouts, and the guy that makes them, Peter Crayfourde, is a very decent bloke and offers good support for his controller. both colin lloyd and i use his controllers, though i have modified his control program logic somewhat. next up is the professional 'central heating' lookalike 12v controller, with temp displays. again solarproject sells this for £90-£100. We can also get these for co-opers for about £80 if there's a few people interested, but there is a lead time on ordering, whereas solarproject has these in stock. George Row (see Derry installation) uses one of these sourced i believe from solarproject. we have one of these to show at workshops, so i can post up a pic if you like. the photos will not upload if they are more than 1k. saving the photos for email or webpage compresses the files and should then upload. Failing that email me the photos and i will upload for you. just because it's cloudy doesn't mean there isn't energy there to bring in. working without a controller requires experimentation, and you may be able to make it work with with your individual setup if you measure the flow of the pump in different light conditions and slow the flow as required (say with a gate or PWM speed controller). Or,e.g. use the £5 vellemann stat kit as a stat (it has a pot to adj the switching temp), and only allow power to the pump when the panel is above X degrees? thanks for letting us know how you're getting along. cye
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Post by cye on Jun 18, 2011 7:23:06 GMT -5
john, thanks for the pics, looks like a cracking good job... Attachments:
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