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Post by johnboy on May 18, 2011 15:34:04 GMT -5
Hi folks, here's my problem.. I live aboard a narrowboat with a very efficient kubola diesel stove which heats the boat and my hot water via a back boiler and calorifier. In summer it's hard to keep the boat cool at the best of times so lighting the stove is not good.
The plan is to replace the second loop from the engines cooling system to one from a pressurised solar loop with small 12v pump powered by it's own 20watt pv panel. The calorifier is small, only 50 litres so i plan to build a relatively small well insulated collector. Any thoughts on collector size are most welcome, Cye has already said around the 1 sq metre mark would be about right. As for the design of the collector i am torn between a radiator and a serpentine of 10mm copper. Again any thoughts welcome. The collector also has to able to be lowered for cruising so connections at the base need to be flexible
Items already purchased are 12v pump from Cye and a 2 litre expansion vessel (the total liquid volume of the system will be small especially if i go for a 10mm copper collector).
All ideas and advice gratefully received.....
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Post by solajoe on May 19, 2011 14:50:05 GMT -5
sound like a good project and well worth considering solar hot water. calorifier, thats just a mini hot water tank or how does it differ? vented or unvented and if unvented how is excess temp or pressure released? aye, rule of thumb is about 1 sq metre per person, or 1 sq metre per 50Litre. you could go for more area too but then youll definitely need a means of dumping excess heat, but then, you should always build in some way of dumping excess heat no mattr what size of panel, say, by switching on the pump to your diesel stove but not lighting the stove (stat on your tank)? bigger area panel should mean getting useful heat in mar + oct and maybe even some on brighter winter days? 20w pv could be about right for a 6-7w pump but you may expect some trial and error without a pump controller as different makes of 20w panel will be rated differently, and different pv technologies (mono, poly, thin film, amorphous, etc) all have different characteristics in low and poor light, though they'll all produce around 20w on a scorching summer's day. pump also possibly needs a minimum voltage to fire up and this may be another problem with low light or cloudy conditions. get your voltmeter out , rig up the pump in a bucket and wire up the the pv and experiment. now what happens when the 20w panel is at full tily with the pump only drawing a smaller power, does the pv voltage rise much above 12v? test it, and if it rises much above the spec voltage for the pump you'll need some form of device to lose the extra voltage, say by building a voltage triggered switch to charge a battery www.electronicspoint.com/voltage-activated-switch-t220175.htmlor possibly by losing the surplus voltage using zener diodes. theres at least 2 guys on this forum who know electronics well , i don't know very much... if it all gets too complicated just run a pump and a pump controller off a car battery and charge the battery somehow?
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Post by johnboy on May 19, 2011 15:36:23 GMT -5
Yep you got it, my calorifier is a 50 litre twin coil hot water storage tank, one coil for the stove and one for the engine at present. It´s got a 3 bar pressure relief valve to relieve excess pressure that builds as the water gets hotter. This is vented to the outside of the boat. No stat on the tank, just a thermocouple type thermometer so i know when the stored water is hot enough. I´ll defo need coaching through the heat dump side of things, switching on the stoves pump is a great idea which i hadn´t thought of although electronics isn´t my strong point. I had been wondering how to get rid of the excess voltage if it occurs. I´m pretty up on pv stuff as i live off my pv´s and batts(400amph of agm cells) which are charged via 200 watts of polycrystalline panels through a morningstar solar controller. Only in the depths of winter do i have to resort to alternator charging through a sterling digital unit. Maybe to keep things simple i could use a 10 or 15 watt panel to minimise the possibility of hitting the pump with too much voltage. i.e. 14volts? Never heard of zener diodes... Had a look at your link and to be honest it´s a bit over my head. Also like the idea of running the pump fro it´s own batt which i could charge from it´s own pv. Food for thought. Thanks for all your advice.
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Post by solajoe on May 19, 2011 17:35:35 GMT -5
hi there.
Heat Dump: all you need to control the diesel stove pump is a tank or pipe stat (bimetallic jobbie) strapped onto your calorifier and set at say 85 or 90 degrees. Siemens make one less than a tenner on fleabay. when the temp is reached the stat closes a switch to feed power to the stove loop pump to disperse heat (assume stove not lit!). not sure whether it's mains or dc pump you have for your stove loop, but either way perhaps consider asking someone more knowlegable than I whether you need to use something like a diode or a changeover relay ( SPDT or DPDT) to protect whatever controller normally controls the stove loop pump.
Zener Diodes: zeners can be fitted across the pv output to limit maximum voltage output. say you use 15v worth of zeners across the pv, then if the voltage of the pv tries to exceed 15v the zener(s) allow current current to flow partially thus reducing the pv output to 15v. again, ask one of the electronics fellas here for advice on how to wire and rating of zeners.
Re the voltage triggered switch to allow excess PV watts to charge a battery, well maybe one of the other folks here knows of an off-the-shelf kit or something that can be used?
rgds
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Post by johnboy on May 20, 2011 3:35:20 GMT -5
Diesel stove pump is controlled by a simple on off switch. If the stove is lit then i have to have the pump running as the system gets far too hot. The pumps is a bolin very low draw 12v model. From memory think it uses less than half an amp which is cool as living off grid like i do do every amp counts. Could you send me a link to the siemens bimetalic switch on ebay please? Presume you would hook it up in parallel with the switch? Who´s the persn to ask about zener´s on here? Cheers.
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Post by solajoe on May 20, 2011 13:04:51 GMT -5
from reading the other posts, the two members who seem to know a fair bit about circuitry are:
norm
dpmiller
suggest you pm them both
will try n find you a link to ebay item for stat. yes you simply wire in parallel to your switch then and no need for thinking about relay or diode. sounds like a very simple job indeed. or, if you end up going with a solar pump controller for your solar pump, these normally come with a heat dump trigger facility, thereby avoiding the need for a stat at all, just the wiring to the stove pump.
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Post by solajoe on May 20, 2011 13:44:17 GMT -5
link to fleabay theremostat
160580962049
less than 8 quid incl P&P
pls tell us more bout ur electricity generating panels and setup
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Post by cye on May 20, 2011 14:55:32 GMT -5
hi john, good to see you here.
only thing i would add to the other advice is perhaps to locate the thermostat close to the base of the tank, maybe just above the very bottom of your solar heat exchanger. that way the dump is triggered only when you've got a full tank of solar heated water.
if norm and/or dpmiller are unable to advise you on your electronics queries i'll ask conor to see if he can help.
i think the calorifier thing is really interesting. it's essentially scaled down domestic solar you're putting together, albeit focussing on low voltage gear with low power consumption and off grid. i've heard that calorifiers generally have a very high efficiency heat exchangers, possibly better than those in domestic solar tanks?
please let us know how you get along!
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Post by johnboy on May 20, 2011 15:24:25 GMT -5
Thanks for the info.
Re my pv set up... It was a hybrid wind pv system until about a year ago. The wind side was a 12v Rutland 913 which just didn´t cut the mustard. Marlec´s output claims are in a perfect world. I had it up on a 6 meter pole on top of the boat and yes it went like the clappers but just didn´t have the balls to do anymore than give my pv a small boost. On a dull windy day it couldn´t raise my 2 200amp/h agm cells anywhere near charging voltage of 14.5 volts. So to cut a long story short it got the heave ho. It was a royal pain in the backside raising and lowering to cruise anyway. The original setup was a Kycera 130watt pv and the turbine, when it went i bought another 2 40watt BP panels to bring the system up to 210watts. The pv´s are routed through a 45 amp tristar which uses 4 stage charging ending with pulse width modulation charging then back to float at 13.6 volts. In winter i mount the Kyocera panel on a mount that holds the panel at 45 degrees and also turns (manually) through 360 degrees to follow the sun through the day. If i´m at work i just leave it pointing south. In summer all 3 panels are mounted flush to the boats roof and provide adequate charging. As for appliances on board i´m nearly all 12 volt, fridge/freezer, tv´s, stereo, 4 watt cree LED lighting throughout, waste pumps, heating pump etc. I also have a 1600watt phoenix inverter to power the washing machine and a few kitchen appliances. I try to keep the inverter usage to a minimum as it canes the batteries, in fact i run the engine whilst using the washing machine so the batts get some help from the alternator.
I now steer people away from wind turbines as the small ones just don´t provide enough power to charge larger batt banks.
Is this the kind of stuff you wanted to know?
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Post by cye on May 21, 2011 2:53:37 GMT -5
Hi John
I have been eyeing the rutland/marlec 913 up for a few years now, watching the secondhand prices and dreaming up ways of fixing to a pole that could be taken down regularly to keep the planning authorities at bay! you've just put me right off that so grateful for the tip.
Your pv sounds really interesting! I have to admit i know very little about what one needs to cobble a working system together, other than that there is a hell of a lot i need to know!i've got my hands on 65W worth of raw pv sells and tabwire, and will be making up a trial panel soon. If that works out, I'm keen on getting a load of the pre-tabbed 'seconds' cells perhaps from the US to make up a larger array. That's probably the easy bit though for me, because i have almost no idea what is needed to get from the PV bit to running a battery bank and managing loads like fridges etc.
Can you explain what a tristar is & what a 4-stage charger does? E.g., Does your charger do the desulfation trick on the batteries while they charge? Are your batteries lead acid or something else? PWM modulation - is that the morningstar does that and how does it work? i had heard morningstar do a mppt controller but i'm not sure how that differs from PWM - can you provide some introductory type info on the technology you use and why you've gone with X rather than Y?
I think it would be really great if someone like yourself would consider, at their leisure of course(!), setting out a short 'dummies guide' for keen but inexperienced folks like me on what you feel are the basics one needs to know when first starting out small with pv, and then perhaps what one needs to think about when gradually building up the panel wattage and the battery bank AH/capacity in size.
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Post by johnboy on May 21, 2011 11:48:27 GMT -5
A calorifier is any hot water storage tank that is heated indirectly via heat exchange loop or electric element. Just a fancy name. Yes it´s on the small side, big enough for a couple of showers and washing up.
First thing you need to do before you go down the off grid route is do a power audit of your appliances that you intend to use and from that work out your combined daily usage in amp hours. Watts divided by volts equals amps drawn by the appliance. ie and LED bulb that is rated at 4 watts will draw just over .3 amp. This is never going to be perfect unless you are very consistent in your daily routine. The biggest power grabber for me apart from the inverter is the fridge freezer but it´s easy to work out how much it uses. Once you have crunched a figure out for daily amp hour usage it´s just a case of sizing your charging and storage capacity appropriately. For me that works out at around 400 aph/h of storage and around 200 watts of charging or more to the point on a sunny day at midday in summer 17 amps. This said on the flip side even with pv´s pointed at the low in the sky sun in mid winter i get less than half of that amperage. In other words you need to either go for shed loads of storage capacity and store the amps when the sun is shining or as i do have a secondary means of producing a charging current (alternator). The first option would be a non starter for me for cost, weight and room taken up by the batt bank. Think that´s it for system sizing. Ok, any pv over 20 watts thats used for battery charging needs to go though a solar charge controller to prevent over charging/gassing of the batt / batts. These controllers use a couple of different methods for final stages of charging. The cheaper ones actually switch the charging current on and off to regulate charging. The Tristar uses Pulse width modulation technology which put simply is constant current current charging tapered off gradually as the batteries reach a fully charged state. Apparently it´s better for the batteries and charges them to a slightly fuller state than the on off types. Mine uses 4 stage charging, Bulk, Absorbtion(PWM), Float, Night. During the bulk phase the charger allows all the available amperage to the batts to bring them up to charging voltage. PWM already explained. Float phase the charger reduces charging voltage down to 13.6 volts until the output from the pv´s diminishes due to lack of light at which point the system goes into night mode(no charging). Got to go out for a meal. More to follow if your´re still interested.
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Post by cye on May 21, 2011 13:32:17 GMT -5
Very interested, more please!
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Post by johnboy on May 21, 2011 15:16:55 GMT -5
Ok so your´re system is sized appropriately, you need to decide what kind of battery technology you are going to use. Several options here. For storage/cyclic usage purposes deep cycle batts are the ONLY option. Forget ordinary car batts and steer clear of batts sold as leisure batts. The heavier the cell the thicker the lead plates are and the longer the cell will last. Proper deep cycle cells have solid lead plates not the spongy plates that other starting type batts have. The good old vented Lead Acid wet cell is in my eyes still the best as they can be aggressively charged at high amperages without suffering damage and with a good maintenance regime they are the best.. Having said that i don´t/can´t have them on my boat as the current regs don´t allow vented wet cell lead acids in a non vented batt compartment and thats what i have.. So i have AGM sealed cells which can´t be charged as aggressively as vented cells and are sensitive to prolonged charging voltages above 14.5 volts hence the fancy Tristar charging setup. In AGM cells the electrolite is held between the plates in glass fibre matting. This type of cell can vent in the event of over charging/thermal runaway but it can´t be topped up with water after the event so it´s an expensive hobby cooking them. Mine were 300 quid each!! The next option is a gell cell, similar to and agm but the electrolite is in gell form, even more sensitive to charging voltages and once again a throw away job if you cook em. The advantage of the sealed cells is that they can be housed in areas that conventional wet lead vented cells can´t, ie in the bottom of my wardrobe in my bedroom... There are also a couple of other batt option such as Lithium Ion which are VERY expensive but claim to be very quick on their recharge times and can can handle LOTS of amps during charging. I´m sure this is the future for deep cycle batts and i suppose in 10 years time it might well be affordable. Anymore??
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Post by cye on May 21, 2011 16:15:15 GMT -5
Excellent stuff, please continue.. A few aside questions too: Sizing of your battery bank. 400ah on a 12v system, that's 4.8kwh (or nearly ~5 units on the household lecky meter) - Is that your daily usage or two day' worth or how did you figure your required battery capacity? What about golf trolley batteries - these any good (gel I think)? I've heard of people using PV with used forklift batteries - any good? Venting - There was a guy on the Navitron forum kept wet batteries in his house but vented them to outside using the clear pipe used for fish tank airlines - is this acceptable/safe? (and before i forget, re making your own solar thermal system ....few new thoughts... for making your own solar thermal panel, did you check out the american guide on our website? quite a good read solarco-op.net/Downloads/American_pamphlet.zip I mentioned your proposed thermal setup to Conor and he suggested you could retain your engine heating and link in with the solar thermal panel. You may also be able to use the engine circuit as a heat dump, but i think your stove circuit already covers this. To have the engine and the solar thermal share the same calorifier coil, both the engine and solar panel would of course share the same coolant {with antifreeze} and you could use a three port valve, either manual or powered, to switch between heating from engine and heating from solar thermal on the shared coil. I can post up a sketch/schematic if you like? Regarding your 2L expansion vessel, I'll dig out some notes on sizing an EV and post them up here - Your 2L expansion vessel may be borderline. Rule of thumb for the average house is 12-18L for the EV and, as your proposed solar thermal setup is perhaps a 3rd the size of a normal house (?), you should ideally do the sums in advance. Failing that, to be on the safe side, over-engineer and use a bigger EV or use another 2L EV alongside the one you've already bought.)
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Post by johnboy on May 22, 2011 2:59:08 GMT -5
400amph is well over sized for my usage. I rarely use more than 20 percent on my storage daily, this is not only good for the batteries it gives me a good cushion and gives the batts a long service life. Just remembered you asked about sulphation, the tristar is programmable to do an equalization phase but sealed batts don´t like the 15 or so volts that it employs to do it so i don´t. The best thing to keep it at bay is regular usage/cycling the batts which they always get. Lead Acid vented cells are ok to equalise as any water used can be topped up, all part of the maint regime with that type of cell. Golf trolley batts are ok, lots of folk don´t like gel cells due to their sensitive charging nature. Fork truck batts are true deep cycle cells and if you ever try and pick one up or buy one you will realise what i mean earlier. Thick solid lead plates equals long life and the ability to absorb plenty of amps during charging. Wet vented cells though so no good for me. As for keeping this type of cell onboard it´s a no no and fails the boat safety testing scheme thats used for inland craft in the UK. My batt box is in the base of my wardrobe which is under the water line and unvented.
I´d already read through the american download. Good stuff.
As for keeping the engine loop and using as a heat dump i think it´s a non starter combining two pressurised loops with varying pressure in each loop. Using the stove vented loop controlled by pipe stat and the stoves 12v pump is a no brainer and a great idea. Simple too, i like simple. Less to go wrong.
Think my 2 litre expansion pot is big enough as the solar loop will be very small as i am going to use 10mm micro bore for the collector and all the pipe work. The calorifier is directly under where the collector will sit on the roof so i´m guessing a system volume of under 10 litres. What do you reckon?
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