LFP and Solar Charging

I recently wrote about the need to change my shed batteries from Flooded Lead Acid (FLA) and had decided to use LiFePO4 (LFP) chemistry. I'm still waiting on the AliExpress 100Ah cells (from which to assemble a 24V 100Ah battery) but they have as yet to arrive.

Important note

I'm basing this article on my system, not your and my system is designed to be 24V from the outset. I picked 24V because:

• over 12V this choice halves the amount of amps that any power demand on the inverter takes out of the battery. This has a significant impact on cables to the battery.
• a single panel could be employed (or two in parallel on different sides of the roof) and sized very closely to the battery requirements
• ideal panels were available for very good prices used

This does not apply if you have a panel system which is significantly higher than the battery requirements, for then you'll totally need a contrller ... preferably an MPPT which does DC to DC conversion.

Playing with the unknown

During the mean time I'm playing around that battery pictured in that blog post, but as I had two of them (my mate loves to waste money on Temu shit of which he knows nothing about) I ended up dismantling and then combining them.

The bundle was basically an 8S2P arrangement so with all the tape off it just unfolded into a single linear 8 cell bundle. It was then pretty easy to combine both into an 8S4P arrangement by just removing on BMS's leads and soldering heavy guage copper wire across between the two packs. The nickle stips made for an easy point to which to solder to (to you AMerryKan readers, please note we don't sodder here in Australia we solder it, try reading the letters in the word). This also made the pack more rigid (as the soldered copper held things together better). 

They are then wired back up to one BMS (leaving me with a spare ...). I don't know what the cells are rated as as there is nothing written on them, but I estimate (based on a discharge test earlier that each cell is about 5~7Ah) and so conservatively I've got about 20Ah of pack.

This is entirely sufficient for most of my lower power needs (not the shop vacuum cleaner though) and even copes with the orbital sander. I've left it "open" like this to allow me to use the thermal camera to look for any signs of thermal issues (which could lead to thermal runaway) as well as to make cell bundle measurement easier.

Charge Controllers

This is where things got interesting, as I'm using a Victron PWM controller for a little while now (even with the FLA batteries) because I got sick of the lower end MPPT contrllers shitting themselves in the summer heat. I found that the actual amps into the battery was basically the same with either system, so why fuck around when I'm not usually in a hurry to charge up?

Its been very good and compact. I noticed however that with the LFP batteries that it was taking a long time to get fully balanced and charged. I mean like 6 days to go from 3.33V per cell (which was charged with a 24V LFP compatible externals mains powered charger) to then going to 3.35Vper cell under the control of the Victron.

So I thought I'd cave in and buy a "better charge controller" which was MPPT 

had bluetooth, and app and all manner of bells and whistles and settings.

None of which really did much worthwhile and most importantly the charging not only did not go better; instead it went worse because overnight it drained more and left me with a lower starting voltage first thing in the morning.

So this got me to thinking ... you know, about charging, voltages and that my battery already had a charge controller -> the BMS... perhaps this MPPT stuff only really makes a difference when you have higher Vmax than my panel? Perhaps I was just over complicating things with a controller that assumes there is a BMS? Maybe the BMS can be the controller? Heck the Victron even says that in the case of using LFE the battery must have its own BMS to prevent over charging.

So I thought why not?

Playing with No controler?

Before just wiring it in, I started with some evaluations; like what may panel produced (or could produce).

So I know that its well within capacity to charge the cell, and won't actually take much in the way of losses to bring that Vmpp down to nearly what the full charge capacity of the battery is ... which by the way is about 3.6V per cell (8 x 3.6 = 28.8) which is pretty close to that 3.35V I mentioned earlier.

Now I know data based models aren't perfect, but they're good indicators. So I took my values above and plugged them into this online solar panel simulator.

I used 900W/square meter (becuase its not always 1000 because for a start my panel isn't optimised to the sun angle at every moment of the day) and got this:

Open circuit voltage = 33.44
Short circuit current = 8.12
Maximum power point voltage = 27.19
Maximum power point current = 7.11
Maximum power point power = 193.39

which was interesting as that Vmpp was about what I was seeing using the MPPT unit but the battery charge amps was WAY lower. In fact I've never seen more than 1 amp flow into the battery (except when using the mains powered charger.

The production of V and A looks like  this:

Even pulling the V down to lower voltages like 25V I should stille be getting near to 7 amps passed through. *(note: that 25V and 7.48amps = 187Watts, so not the "maximum power point" but batteries charge on amps and the voltage only needs to be a little higher than the batterys. Based on the simulator even if the voltage of the panel is pulled down to 24V I should still be getting plenty of amps ... yet the battery is only accepting a tiny fraction; like 100mA or less.

Given all this it seems that maybe I could just rely on the BMS to do its job and so I wired up an XT-60, unplugged the panel from the Victron and wired it directly to the battery. 

Everything went exactly as it was going before. Voltage measured across the battery was the same, volgage at each cell was the same and the amount of amps flowing was only a fraction higher (140mA).

Someting is amiss (or I just don't understand something) or maybe I just don't need the Controller at all?. 

Uncertainty amplified

So I turned to the excellent blog post, here, to try to work out what I should be seeing. If you are interested I recommend it, as its an excellent read on LFP chemistry behaviour.

However I think that there is something missing from this, and that the Constant Voltage is not actually due to the charger but is enforced by the electro-chemistry within the cell. To me this is visible in their chart showing Voltage at different C charging rates. 

Notice that they don't show amps into the battery, only the voltage and a Capacity on the X axis. This is vexxed because they actually go to the trouble of saying (in discharging) that:

If your BMS relies primarily on voltage for SOC estimation: NMC's sloped profile is more accommodating; LFP requires dedicated coulomb counting.

we also see that on the charging (upper graph) that the Ah Capacity makes almost no change for the very steep climb in Voltage. There is no time factor on this.

Myself I've found that to get these cells above 3.3V per cell requires hours (and these don't even have a large Ah capacity).

Conclusion

So perhaps I just don't need the Controller? Perhaps this "direct wiring" is good for "some circumstances" but I really don't know.

This seems to be the limits to this system, until I can get the 100Ah cells and test the system on that I just can't know more.

In case anyone is panicked here, I've got it back on the Victron now.

Shed batteries

Well after some time I've decided that the FLA (flooded lead acid) batteries I put into the shed are past their use by date. Not bad really as they were installed new in 2022, which is about 4 years ago.

I'm presently running a pair of donated 24V LiFePO4 batteries that a mate bought (believing the Temu ad) in parallel.

you can see that the foot-print of the pair of 24V's is about half what the pair of 12V's was but they had a RC of 95 (meaning that the battery would survive for 95 minutes under a constant 25amp load before 10.5V is hit ... optimistic if you ask me) 

I've never been really satisfied with how the recharge after discarges (probably due to the internal resistance of FLA). See this post for my analysis back then. 

This is one ofthe tiddlers ... rated at 200Ah

talk about optimism ... I pulled one apart and the Cells were 7Ah and there wasn't anywhere near enough of them. Further, the BMS was clamped at 9Amps.

Well that's 400W or so, so it'll do for now ... I'll post again when the new cells arive

Winter Floor Heating effectiveness report

I just thought I'd make a post about how my "system" of the combination of

• Solar Floor heating
• Insulation in floor and Ceiling
• Use of Reverse Cycle AirCon
• Wood burning stove

is working out for me.

With overnight lows of about -1C (so frosts) but typically sunny days of about 18C, I get sufficient energy from that to heat the floor and this therefore takes a significant load off the AC because as the floor (basically) never gets heated by the warm air blowing out of that (so, upper walls and ceiling are heated) the floor heating system then brings the whole house up warmer. This is a typical winter day here:

The time zone indicated by A is where I turn on the R-C A-C and the zone indicated by B is where I lit the fire. Because the house is already warm (and insulated top and bottom) the fire requires just a fraction of what would be needed otherwise. As the sun starts to warm outside I choose that time to then turn on the AC because the exterior heat exchanger will have more advantage in raising the temperature inside if the outside is actually warmer.

Its just like the height difference between two points on a hill. The higher the difference the more energy you need. So even though I'm using technology and electricity to move and amplify that heat I'm still taking advantage of the Sun to do that. So only one component would simply not work, but all four parts work together, consequentially my house is warmed (but not 100% of the time, my power bill is much lower) and I burn less than a quarter of the wood. For example the load of wood I bought in 2023 is still serving and I anticipate that it will provide for this winter entirely too. I'm a big fan of

• understanding diminishing returns
• seeking maximum value for money

I know what it would cost to improve this situation, and so I'm quite satisfied with the additional amenity provided by my existing solar floor heating in conjunction with Reverse Cycle Air-Con and insulation to augment the little wood burning furnace that the house already had delay the need to and reduce how much I burn when I do.

The whole project is well described here: (link)

Solar 12V Lead Acid Trickle Charger

I have a couple of things which have 12V (lead acid type chemistry) batteries which get used irregularly. I know well that these batteries need to be kept 'groomed' for optimal life and to avoid disappointment when you go to use the item.

For quite a few years I've used a small 5W solar panel similar to the one above with great success. For instance my "ride on" lawn mower battery is over 6 years old and still acts like new. This is not an accident.

In the past I've gone with the "KISS" (keep it simple stupid) approach of having a 5W panel just directly (well via a diode) connected to the battery. Now I know that a "12volt panel" is not going to put out 12 volts, and I now that to charge a 12 volt (lead acid) battery you need to give it more than 12 volts and all that stuff you can read elsewhere (such as here) if you don't know. A typical 5W panel will not be able to over-charge a 12V battery unless that battery is very small. Instead (probably at worst) it will hold the battery at about 15V for the peak sunlight period and that's it. Some intelligent positioning of the panel will help you to avoid this (taking advantage of the movement of shade and the angle of the sun).

So my last panel died (no idea why, I suspect one of those fine solder joints broke or eroded) and so I went to ebay and bought the one above. Having had them before I just wanted to test the outputs (to ensure it was working) and put it into service. I'll circle back to that, because that led to some discoveries.

The first discovery was that this panel is actually (totally without fanfare) incorporating a mini PWM solar controller in it:

yes, you can see that LED blink when you initially hold it up to the light. The  "Chinglish" is a bit misleading however. When one carefully cuts the back off (held by what is similar to black Sika-Flex) one finds the controller and the LED on the board.

one can test the actual panel (hardly coinvently) of the PV+ and PV- tags (which literally solder direct to the lugs on the back of the panel).

 But one can not test the output of the panel directly by the battery clamps because this is not a simple panel: its instead a system.

This is because a solar controller typically requires an "order of things" when connecting it.

1. connect the controller to the battery (allowing it to know what voltage its dealing with, as many are 12/24V). This is also a "safety" thing for the electronics because an unloaded and cold panel  in full sunlight may exceed the safe voltage input limits of the controller.
2. connect the panel to the controller (charging now begins if there is enough light)

So, because this panel is always directly connected to the panel the above order of connection sequence can't happen. Thus the system shows nothing (yes 0V) on the battery clamps which may (incorrectly) lead you to think that the "bloody thing is broken". (guilty)

Clearly a case of "ignorance is bliss"

So, once I understood this I connected it to the battery via my Amp meter and voilla!! Current flowed and as well voltage began ticking upwards on the battery (yes, I have 2 meters).

Fantastic

Looking on the back of the panel (if one could be bothered to look and think) we see some give-aways here.

In the Specification we see a few lines we wouldn't expect to see:

• Over-charged Protection Voltage (sic) of 14.5V
• Over-charged Recovery Voltage (sic) of 13V

one would simply not expect to see these two on a plain panel, as this is the sort of stuff a controller provides.

It would have been better if the seller had made it clear that this was the case (because then they wouldn't have had to send me a second one because this one appeared faulty).

So basically I can fully recommend this little guy for simplifying my life of keeping my batteries well groomed. Something my motorcycle needs because there is a little 50mA parasitic drain which needs addressing if I don't ride it every day (I don't). 50ma sounds small but after 5 days that's 6Amp Hours and the new capacity of a AGM battery for the bike is about 8Amp Hours, so in winter, a week of not using it during the week means on Saturday you've got a dead battery.

So I can just hang it off the number plate and plug it in to the bike and my battery is kept "groomed". Naturally I had already made up a small DC jack plug to connect my previous (panel and controller) system to the bike.

This streamlines things enormously (because I don't have to connect the controller to the bike and then the panel to the controller) and instead only have one thing to plug and play.

Naturally it works well on the lawnmower too

Win Win

balancing storage

As you may know I like to get things as right as I can and if you've read my blog (and perhaps more specifically this post about my battery storage) you'll know that I keep going on solving until I get a result I'm satisfied with. Well after a little testing I'm comfortable to report that I've found a balancing solution (thanks to that guy on Reddit) for a small amount of money.

If you follow the wires you will see +ve from the A side goes to the 24V +ve, the black to the 24V -ve and the white to the place where the two 12V batteries are joined in series to make a single 24V battery.

The box is as simple as it gets, it "powers" itself from the battery its attached to and The A and B labels on the box have an LED which lights up when they are transferring the power. The manual says this about how much power it sucks from the system.

so not much goes outside the system from this and it even prevents discharging a pair of batteries not being charged regularly from being drained to death.

Its wired up like this

and as you can see will even scale up to work with more batteries easily by just adding more.

So as you may observe in the top picture there is a small voltage difference between the batteries, but this is just a calibration problem of those cheap voltage displays. I just couldn't get it to be less than 0.5V by turn and so the small differences present the way they are.

I don't mind really because at a glance I can see big problems (like more than half a volt) then I don't need to look further. Now and then I see what the voltages are with my Fluke volt meter, and they've been good.

So basically this unit helps to keep the drift of one bunch of cells (the 6 cells within one of the 12V batteries) getting too far from the other bunch of cells (within the other battery). The ideal would be cell by cell comparisons but as each 12V battery is sealed that's not going to happen without surgery. However my experience is that this system works pretty well.

As I discussed my existing system was indeed drifting, which is not surprising when you stop thinking of maths and start thinking about 1) chemistry and 2) the reality of productions. Tiny differences exist in things (except perhaps those made for NASA) and these set up the beginnings of drift. Things like

1. under load do all cells in a battery discharge the same? Does indeed each of the two batteries??
2. what about under charging?

So this system basically works electrically "inside the battery" to keep the two bundles of cells together.

The best thing is that this little box only cost $15

Fantastic

Win Win

(battery charging, and) Cells in a Battery

When I built my shed I knew I'd need power down there and so it immediately occurred to me that this was an excellent opportunity to conduct a practical (and beneficial) experiment in "Off Grid" solar. 

I knew that while I understood a lot of the theory, its often the case that some surprises occur in the actual operation. This blog post is about an expectation that was fulfilled: cell imbalance in flooded lead acid batteries.

This issue is important to anyone choosing lead acid chemistry in an off grid application because it leads to premature death of your (often expensive) investment in batteries. The reason for 24V is that I want to use the energy in the battery to power things which are made for AC, thus I need an inverter. The above mentioned blog post has a few more details.

the invisible (to most people) issue

People never think past words, like "battery".  A battery is not just an indivisible block, but basically a connected series of cells each depending on the other (check the word battery in a dictionary).

Charging a cell is straightforward, but charging batteries is more complex than people usually consider. This is because while each cell needs to be charged equally we apply a voltage across the entire battery and "magic happens"; where the battery magically stores the energy. 

If only it was this simple there wouldn't be any problems.

Above is a picture of my 24V battery system for my solar shed, the battery system was commissioned  (fancy word for the relatively simple process, sorry) in early March but as you see the battery dates are 4th of Feb (which is why dear American readers the rest of the world writes 4/2/22 and your Month Day Year format is frankly 0.o) 

As you can see I have two 12V batteries connected in series to make a 24V battery, and each 12V battery has a small volt meter on it. I did this as I wanted make voltage checking a simple matter (rather than kneel down on the floor with my volt meter). I wanted to check because I wanted this to be an experiement in exploring why batteries fail early. 

I believe batteries fail  early because of unaddressed issue in imbalances. Of course I'd like to improve on this situation, but that's pretty much impossible with the way modern batteries are made and (a big hint to off gridders to select batteries appropriately) how batteries are connected for charging.

Probably the first thing you can see there is that the voltages are different between each 12V lead acid battery. 

• B1 is 13.3V
• B2 is 13.6V

This wasn't always like this, as back in Feb they were both new and both within 0.01V of each other. Somehow that balance has changed. Leading me to my point about balance:

The Balancing Act

So we get to the thing I'd like to talk about here cell balance, and the word cell will need to be clarified here because I'd say more than 90% of readers have really never given this any thought. When the battery is made each cell is made pretty accurately to be identical, but unless this is a battery made for NASA some small variances in all the parts can mean that each cell has a slightly different reaction to charge and discharge. Over time these small variations can add up.

The nature of these differences usually is in the resistance each cell has (in the chain of cells in series) and perhaps in its actual capacity for charge and discharge. If left unchecked and unaccounted for inevitably at least one cell starts to get more stress.

The Cell

As you (should) know a 12V battery (as above) is actually a collection of 6 cells (or electro-chemical cells) each which contains some sulfuric acid and some lead plates. This cross section diagram (borrowed and altered from here)

Its tempting to just see this as a black box (well and its often in a black plastic box) but the reality is that each cell may well need individual attention.

In that above cutaway you can see that the battery is a series of  6 cells linked together inside connecting postive to negative to make a 12V battery. By joining two batteries you can make a bigger battery and double the voltage available. An off grider with much nouse would probably find themselves joining 4 12V batteries into a 48V battery, thus reducing the amount of amps that need to be carried to feed their inverter (which makes 240V AC which powers things that plug into the wall).

But returning to my more simple model (having 2 batteries or 12 cells) lets go back to that 0.3V voltage difference.

Once upon a time we had tools to measure the chemistry of each cell, this dates back to a time when (for various reasons) nobody had volt meters. The most common tool was a hydrometer and you can see how its used at this Wikipedia link. You'll notice that in that picture that each "cell" is by itself and has a hatch to allow you to suck up some of the chemistry (sulphuric acid) and measure how much is there.

You may even recall having seen batteries with 6 little caps along the top to allow you to make this measurement. Indeed more expensive and larger batteries usually still have them (see below)

But because less and less people have a clue what to do with these the makers target these to the applications where people should have a clue (and sadly this results in less and less people having a clue).

Lets get back to that 0.3V and work through this a bit more.

Because those little LED meters are cheapies ($2 each) I know they aren't perfect and I know there is about 0.1V difference on one of them (and perhaps something under 0.5V on the other meaning I can't actually see it easily). This means that when I use my Fluke digital volt meter (pretty accurate and provides 2 decimal places) I can see that the voltages are more like 13.18 and 13.38V so that's a bit better.but back on the 8th of the 3rd they were already drifting apart and were 12.91 and 12.89V (which the astute will observe is the other way around).

I noticed that differences were creeping in and so I wanted to observe these more carefully thus I bought those small LED's and fitted them.

• 14/04/22 I noted 0.1V difference when the batteries were on trickle charge
• 14/05/22 I noted 0.5V difference when the batteries were on trickle charge

I recently cycled them both down and individually (<<note that point) groomed them back up with a smart charger. Yes, this means I physically dis-connected them (so no more power coming from them if you're off grid) and charged and allowed to settle post removal from the charger. 

Both sat nicely at 13.36V when on the smart charger on "trickle". This is one measurement, but another is what's 'rested' voltage and this was 13.18 and 13.38 ... so this difference now seems to be permanent. 

While this may seem like a small small things may grow.

Is this a problem?

For me, in this situation, no not yet, because (importantly) when the batteries are under load (like when I'm running a vacuum cleaner which draws a lot of power) everything holds up ok and within expectation.

Why is this important?

well we know that the voltage of the battery is 13.18 or 13.38 depending on which we're looking at, what we don't know is what each cell is doing because on these batteries we can't measure that. If we imagine that we could only see the pair of batteries (which importantly is what the inverter or charger sees) we would see 26.56V - its only because we can measure each component we know something is amiss.

But where and by how much?

Lets say only one cell is down and that B1 has one cell that is 0.2V different. 6 of the cells are ideal at 2.23 and one cell is 2.03V ... that means that this cell will now become the weak link in the chain and will suffer more stress and eventually result in the early death of that battery because it is the weaker link.

Important note: a battery is a chain of cells ...

Worse, if I replace B1 then the new battery will be stronger than the then worn B2 (that didn't fail) so that will cause that link to fail sooner too. Meaning I'm minimising the returns on my power from what I spent on the battery.

As it happens (and partly because this is a learning exersize) I paid $90 each for these batteries (they were bought new), but they are, as you can see, small. But then so too is the load and so is the charging. Further I'd say that they are the perfect relationship between needs and cost.

However, f you were in an off-grid house and you were in this situation each battery could well be around $500 and you may have 4 or 8 of them (at least). For instance here is a freinds off grid house 48V system with each "battery" component being a 6V battery (of three 2V cells).

however you can see that each has an inspection cap so you can measure the state of charge and fix up any chemistry. Each of those boxes is nearly a $1000 now, so you can see that caring for and understanding this is crucial for your investment (unless you've got more money than sense).

So ... is there a better way to charge?

Yes, each cell needs to be monitored. However lead acid chemistry is more tolerant of over charging in terms of how it fails, Lithium ION on the other hand is not, and has a nature of catching on fire if over charged and dying (irreversibly) if discharged too deeply. Since Li-ION is expensive and fires inconvenient people have developed a management system for the battery (called a Battery Management System or BMS). This not only monitors the charge but monitors every cell being charged. This is the one out of my scooter still attached to the cells. It manages 13 cells.

As you can imagine with 13 cells in series (compared to just 6 in a regular car battery) the chances of anything getting out of balance is not just high, its practically inevitable (unless you are buying cells that are suitable for NASA). This  BMS not only governs the charge of each cell during charging it it also ensures that if any cell falls below the minimum safe voltage it shuts down the access to power from the pack.

Normally with just 6 cells there is less chance of an imbalance, which is why most small scale solar systems use 12V ... but it of course has inherent limitations in terms of the voltage and therefor the amount of Amps that are required to power much. As you should remember my system actually has 12 cells (6 in each "car" battery) because its 24V and this has no doubt created the situation where somewhere (and we know that its in B1) at least 1 cell is down. This is then going to place more stress on B2 in terms of over voltage charging because the charger only knows the entire voltage of the battery.

Is there something like this for Lead Acid batteries?

Myself I think there is, but its a bit of a fudge (and beyond the scope of this article) so the answer is basically no, and perhaps the "why we don't see things like this in Lead Acid is:

• Lead Acid is an old technology most commonly used in 12V configurations
• its perceived as less needed because there is no safety hazzard, and (probably) 
• because lead acid batteries are very recyclable and rebuildable unlike Li-ION.

Further most companies don't warrant car batteries to be used in Solar Power Systems, so if you kill your battery early then its all on you.

Right now what I see is that its on me to basically prevent this by keeping an eye on the system (and turning off the panel and disconnecting the battery from the Solar Charge Controller) when I'm not in the shed and just let it sit there essentially in storage. Fortunately that's something that Lead Acid is pretty good at.

I'll put it into another blog post for what my solution is on another day (see here for that). Mean time its been a fun ride with my system. I hope you've found this interesting and helpful so far.

Until Next time

Solar Floor heating house (again) position summary

So to complete this for a while here is a summary position of the improvements. 

Below is the data from what the house was like before I did anything, the data comes from a point in winter when I was away from the house all during the week (so no heating, just ambient).

Dear American audience, please note: as you (speaking of the General Public, not NASA or Science in the USA) are the living museum of discarded standards and practices in science (well and other things) these temperatures are in Celsius not Farrenhuffenfurter ...

Actual picture of Mr Farrenhuffenfurter the developer of the Eff temperature scale in 1724

So, today we have this measurement (photo of the screen of the temperature station cos I'm too slack to pull the data and compile as above). I chose to use the times above to match the 7:30am 24 hour slot taken here.

RED is inside, BLUE is outside (temps also in C not F)

Discussion

Firstly, what's truly amazing about this is that the area of "pipe" I have outside would suggest I can only capture (at most and assuming 100% efficiency) 500W of energy.

Outside temperature range is about similar to the graph from 2019, however its worth mentioning that the minimum outside temperature today is a little above what it should be because I'm hanging the thermometer under a tree now. The actual outside temp this morning was -0.5C (with a frost). The inside temperature goes into the night warmer (being nicely heated by the solar floor system and its attendant insulation). 

I did use a bit of reverse cycle AC in the morning (evident from the step up in the curve) and a fire was use in the evening (again evident on the graph).

Insulation fitment in both the ceiling and the floor was critical to the success of this project and it has not only enabled the (quite meagre) energy available from the outside solar to be transferred successfully into the house.  Further the insulation has meant that any heating I do inside the insulation (where I live) is far more effective.

Outcome

My house is now much more comfortable and my heating costs (electricity and wood) are significantly down (approximately 25% of what they were). If you dont' give a shit about environmental issues you may give a shit about your finances ... so its either win or win win (depending on your value sets)

If you have landed here and are unaware of the history of this project you can find it at these links:

1. Solar floor heating again
2. part 2
3. when the sun don't shine

Naturally as a perpetual tinkerer this will change and improve as I tidy up all the insulation sealing and and consider other Solar Heat Gathering methods.

PS: from Countries that use Fahrenheit in 2020

... There are very few nations in the world that use this unit of temperature. The countries and territories that use the Fahrenheit scale are the United States, the Bahamas, the Cayman Islands, Liberia, Palau, the Federated States of Micronesia, and the Marshall Islands.

I think thats hilarious. I wonder ... can the USA ever modernise? 

Floor heating when the sun don't shine

It can't only be Solar

As per my previous attempt at this 10 (or so) years ago there are times when you can't use Solar (not least because we have nigh as well as day) such as when its rainy or overcast. So in anticipation of this I wanted  to prepare a different solution to last time (which I used LP gas) that might be cheaper.

Ad mentioned in my previous post I thought I'd try this:

which is a 1000W aquarium heater (electronically themo-regulated).

So 1000W (if you think heaters) isn't likely to heat your house by itself (unless you have a small and very well insulated house) but it can bring something to the party. 

Yesterday I ran the system and recorded the following data

RED = interior GREEN = under floor BLUE = outside

So lets look at the points:

1. turned on the reverse cycle AC to heat and set that to 20C
2. the floor pumps turned on and started pumping (which meant that the heater started having to heat the water because cooler water was flowing into the junction tank from the now cooler floor)
3. I lit a fire because I wanted to spend time in the living room (and the floor pumps had just stopped as they are on a timer).
4. note the change in slope on the red (the interior) curve as it fell and eventually became the same slope as the floor. 

The final red line is when the fire went out. Now when I went to bed I set the AC back down to 16C  (and it had ceased providing heat after I lit the fire) and the house now started to cool relying only on its insulation and the AC to keep its heat.

I woke at about 5:30am (pretty usual) and noted that the AC was making some gentle stirrings as the house temp fell into the zone where it was kicking in. This means that basically the house kept its heat sufficiently just on thermal insulation alone. Not bad.

Lastly there is the slope on the red and green curves. Some things I anticipate at work here are: the higher the difference in temperature (between inside and outside) the faster the rate of loss. Then as the interior reaches about the same delta T as the floor then the thermal mass of the floor (recalling its on the inside of that layer of insulation) works to hold the whole system higher. Eventually they'll fall together at the same rate as the difference diminishes. I've seen this in other plots.

Some Further Notes 

Power consumption: The setting on the thermostat on the water tank heater is 20C but I've observed that when you use a quality thermometer to measure the water temperature in the tank its 18C when it thinks its 20C (who'd have though, its not a calibrated scientific instrument?). This is interesting because the floor temperature reading (from between the insulation and the floor boards) was almost that. So the floor reached an equilibrium temperature within 3 hours and stayed there (just as the room temperature did) for 8 hours. This despite a falling of outside temperature during that time (so yes during the day).

I have a watt meter on the tank heater and it showed that the heater only consumed 1.2kWh during the day and 1.5kWh 24 hour period (yes, including keeping the tank warm all night). 

This clearly shows the benefits of the insulation (at reducing losses) and the benefits of a more modern and efficient approach to heating (reverse cycle AC).

Other benefits: without heating the floor there are many problems with using the AC to heat the house. For instance it only heats by moving warm air and so does not directly heat the floor, far down the walls, under beds or other rooms. Sure some radiation from the ceiling eventually warms the floor, but by heating the floor directly you gain this benefit this heat coming through the actual floor boards and into the carpets and under beds ...

Basically this makes the floor boards into a thermal mass for storing some of that heat after it ends and because its on "our side" of the insulation barrier keeps our space warmer longer. Evidenced by that slow trail-off of temperature.

Where to next?

We are moving out of winter and into Spring now, but we are slated for some 0C temps next week. I'll be interested to post on the results for that then. 

I'm thinking about if a better area of Solar Collection will help, but frankly I'm not entirely sure it will. This winter has been significantly more wet and overcast than previous years, so it will remain to be seen how this impacts the generation of warmth inside the house. My current area of collector is about 0.4 square meters, this suggests that I can only capture at most 100W of energy from that. So it may be worth increasing that area. Knowing that answer will require an experiment to find out.

So, as always, further research is needed. 

Solar floor heating again (part 2)

After some interesting delays created by life involvement (and not least frustrating injuries) I've now just about completed this project and its in what I'll call the tuning phase. Back in this post (part 1, so yes 4 years ago...) I showed the laying of the pipes (and man wasn't that some hard work) and discussed the insulation and its role in making this effective.

This has a critical role in the success of the system because it confines the heat in the pipes to be all released into the floor above the insulation (and not just carried away by the breeze or radiated into the ground). Recalling from that above mentioned post this is a sample of how I run the pipes under the floor:

...and now the insulation holds that heat in as well as drastically reduces any losses from the house through the floor too. This last point is not insignificant.

So to recap the design idea, water is circulated through the (four) floor circuits (each of the above pairs of pipes flows in opposite directions, see the previous article) and out into the yard where it flows through a pipe in the sun to get warmed then back into the floor. This is done with what I call the junction box where water being circulated through the floor goes back into the junction box and meets the water being circulated through the yard in the sun. Because its a syphon arrangement (again, see the previous articles) the requirement for pump "head" is not significant and flow rate is the issue.

So lets have a look at those components. 

Junction Box showing flor circuits and outside circulation (on the left)

the pumps:

and you may have noticed in the above shot over on the left a small black thing, which is this:

A 1000W aquarium heater (themo regulated) which I'll go into later.

How it works:

Basically the design is to take heat that exists outside of the house during the day (especially when the sun is shining) and pump that through the insulation and into the house. Especially in this environment the insulation plays a critical role because if the heat losses are higher than the heat inputs then there will be no effective gain. 

Lets look at those gains, this is a picture of my 3 channel temperature recording station; the three channels are:
RED = inside the house 
GREEN = under the floor (outside the house) and 
BLUE = outside temperature (away from the house).

You can see that inside varies wildly because I heat the house in the day and then turn off the heating when I go to bed (to save money among other reasons) and begin heating in the morning.  The green line in these pictures closely tracks the outside temperature (and you'd be right in guessing my floors are cold underfoot!) which turns out to be an interesting metric (which I'll get to next)

This identifies my goal: to flatten that inside temperature curve and with less expense.

This above image is a snapshot of the 72 hours preceding my placing most of the insulation in the floor (the spike is me handling the thermometer and repositioning it so that that it wasn't trapped between the insulation and the floor forever). Note date's and times in the images.

Quite an impressive result immediately and shows clearly how much heat was radiating out of the house through the floor and out into the world (now trapped by the insulation layer under the floor)... wow.

Indeed this next image shows how now the floor tracks the inside of the house not the outside anymore (note the timebase change on the X axis to zoom in more on the 12 hour period).

again, wow.

The next phase was to then plumb up and turn on the floor heating pumps to transfer energy inside the next day and see what's happened to the floor temperature and test the system (oh, and btw, by this point the floor insulation is not 100% complete, more like 70%)

so above you can see how the house is dragged up now with the warmth of the day, and the floor heating, where I lit the fire (wood burning stove heating which explains why above I mention I don't heat at night after I go to bed), how that as the fire went out the temperature of the house fell down to the floor level and stayed on track until eventually (after this time stamp of 6:55am) the sun came up and things rose again.

Because this is an experiment in progress (still learning about how to tune this in this environment) I ran a few scenarios lets look at the outcomes from them.

Scenario 1 = increase the Junction box (water tank) temperature with the heater to put in (up to) 1000W of energy (as determined by the heater system) by setting the thermostat to 20C and continuing to run the floor pumps all night. Note: some heating with AC during the day and a fire at night. Note 2 we don't have a plot of the water temperature here.

Scenario 2 = passive heating only inside (red curve) but running the floor pumps (note: I am continuing to fit out the floor insulation during this)

Scenario 3 = fully passive with no additional energy added except solar through the heat pump, no aquarium heater (more of the insulation  fitted, nearing 100%).

Discussion

The basic tenet of my process has been to harvest energy when its there, and store it for when it goes away. This is basically energy from the Sun (and when its all said and done what isn't {ans Nuclear}). I havest this in two ways:

1. capturing heat from the sun and shoving it into my house as thermal mass and using insulation to reduce the losses (think water in a bucket instead of just held in your cupped hands)
2. using the outside heat to make reverse cycle AC more efficient (it works on the temperature differential you are facing; there is a hot side and a cold side. The warmer the cold side is the hotter it makes the hot side, the reverse is also true) and thus use less energy

The insulation (also put into the ceiling late last year) massively reduced the losses at night (convection within the room as hot air rose to heat the ceiling and shed it fast without the insulation and radiation losses too) and now this insulation on the floor reduces the losses through the floor from radiation too as well as enabling me to capture the 1000W of heat available per square meter in the sunshine.

I have now cut my wood and energy needs to heat in winter by 75% and have a warmer and more consistently warm house to boot.

Not bad if you ask me ... 

Costs?

The entire costs (ceiling insulation, floor insulation, pipes, pumps and fittings) has been under AU$1500. 

I chose polystyrene because it has both a better R-Value than the messy and horrible mineral glass wool, and unlike that product does not lose its insulation property over the years NOR does it breakdown into a filthy difficult mess in 15 years time; and bonus points for it not being enjoyed by rats or other pests (who love to nest in your ceiling insulation).

Win Win

over paneled

Well its been a lot in planning and significant preparation and then construction but my "shed project" has finally made it to "solar shed project" status with the mounting of my 250W panel... 

...but lets perhaps go back to the start and explain the title...

In the foreground there you can see a small 10W panel which I mounted some time ago which I discussed in this blog post, and has powered my simple lighting system from a humble Gel Cell 12V battery for the last few years.

The whole idea was naturally an extension of wanting a shed for tool storage and workshop (so that I'm not working on things in the house), the construction of the shed (and a bit of history) is discussed here, but in this blog post I'll focus only on the solar aspect of it, what I did and why.

Needs Assessment

My first step was an assessment of power needs which I did with one of these plug in power meters (easily obtainable from eBay or your local hardware shop).

I have been working outside on "flatish" areas when doing things such as building, and while I make pretty extensive use of 18V lithium battery tools I do still need 240V for things, a more powerful orbital sander, drop saw, circular saw, workshop vacuum cleaner and the like.

My normal process has been to run an extension lead out the window to where I'm working, which provides an ideal point to measure exactly what I use.

So doing some work on a few occasions I made some measurements and found that the number was about 200Wh for the days work (I took a few measurements over different days). Which isn't a lot really.

Basically if I got two 50W 22Voc panels that would give me entirely sufficient power to replenish my needs. Even if I used 1000Wh on a particular day that's only 10 hours charging, meaning that the battery bank would be back up to "float charge" after 2 days ... certainly no time for sulfation to occur there. However typically such a panel would cost about $60 which is about twice what I paid for this panel and I'd need two of those! Something like this was in my view ideal and was $160 per panel.

I'd need two because I will be charging 24V (2 FLA batteries) ... however I chose to go with the one higher Voltage panel because it was so darn cheap.

Storage

As I wanted to use 1200W tools in the shed (vacuum cleaner and compressor) I didn't want high amp loads coming from the battery to the inverter (not least because high amp loads distress the cables and distort the Amp hour rating of the battery) I immediately turned to 24V as the low hanging fruit (halving the Amp draw right there).

This has a knock on effect that you don't need as many Ah out of each 12V battery and so I picked a pair of batteries which were rated at RC95 (RC is Reserve Capacity), I'll spare you the cookie fest and paste below a definition (or you can seek your own)

Reserve minutes, also called reserve capacity, is the number of minutes a fully charged battery can sustain a designated constant load (usually 25 amps) before it is fully discharged. For a 12-volt battery, that means battery voltage will have fallen to 10.5 volts.

So I reckoned that I was not going to go close to needing 90 continuous minutes of 600W (by any stretch of the imagination) and so it was settled quickly there:

• 24V 2000W (4000W peak) high frequency inverter (AU$240)
• two 12V batteries

So we have energy captured by the solar, stored in the battery charge and delivered by inverter to the power points on the bench. Conveniently the solar charge controller has USB output which allows me to charge my phone and my Bluetooth speaker there. (*point, notice the multi meter on the bench? If you're even thinking about  this topic you must have something like that or frankly your're working blind.)

I recently did a draw down test on the system (panel, battery and inverter) running my fridge during an 8 hour power outage (IE most of the day) which was enough to pull the battery bank down to 24.5V. Now while this isn't ideal (and indeed is disappointing in some ways) it shows two things

1. the system is entirely adequate for my needs
2. the use of inverters off the battery does not allow the controller system to "see" what is going on and thus not divert sufficient (actually available) power to the "load" on the system (that's a long story right there) if one was to be going into the night and needing to keep sustaining the fridge (which is about 190W)

The Panel

One of the great things (for me at least) is the market distortions occurring due to government subsidies of solar. Pretty stupidly (but sadly not atypically)  what is happening is that are getting the subsidies to put new  systems on their roof and this includes people with existing (say 10 year old) systems and the older panels are removed and sold as surplus. 

This means I got my 240W 60 cell panel for just $20 ... fuck me dead, I can't even buy a (so called) 12V 100w panel for that (and BTW they aren't actually 12V), more like $120 each, and so getting a panel which is (more or less 32V (at maximum power) is a bargain.

The specs on the panel are something you should learn well, and you need to understand Voc, Isc, Vmpp and Impp.

Anyway to get that for a few bucks is just fantastic even if in excess of my needs. Basically this means that even if on a big day I run the workshop battery down to nearly "inverter power shut off" voltages, by the end of the next day it will be fully recharged and cell plate sulfation avoided (and my battery investment maximised). This is unlikely to ever happen as I simply don't need that much power in a day and I don't use the shed power even remotely hard most days.

So, next, the solar panel needs to be on the roof, and needs to be secure there.

Mounting

The shed I have (as you may have seen) is a basic 3 x 3 meter garden shed which I've used as the basic starter (for materials) and added a steel frame and other enhancements, accordingly the roof is not a trafficable roof and I'm against drilling holes (to later leak in the rain), and further because there is nothing underneath the "Trimdek" (like any battens) to screw into I decided to flush mount the brackets and to use a modern adhesive like Sikaflex 291 (rated to 1.8MPa tensile strength or about 140PSI) to secure the brackets to the "Trimdek" which the shed is made of.

The brackets (as you can probably make out in the first picture) are 25mm square section tube (so more or less an inch by an inch foot print on the Trimdek) and are 1200mm long (covering 7 high points). I added extra "feet" to extend out either side of the square section tube to prevent any rolling when I slid the panel up and across them, as well as add more grip surface for the adhesive.

To prevent any "movement" (slippage) while the adhesive was "skinning" I used two wooden "supports"

and again (with tape) on the upper side, giving me two nice mounts for the panel you saw back at the start of this blog post)

note that I've added some vertical mounts to secure the panel to the square tube too. These are screwed (and a small blob of sikaflex applied) into the aluminium frame of the panel. The whole thing then has overall 7 good joints like this...

... at each end to hold the panel down.

Now its important to note, that Sikalfex is humidity cured, and due to the thickness of the apparent bead (being squeezed in between the metals) you need to leave it for at least a few days to cure ... which I did.

A friend came over and helped me slide it up and screw the panel onto the side mounts.

So there we have it ... job done! (I might put some covers over the end ... I might not).

what's left?

basically the final sections are to

• neatly mount the Solar Charge Controller to the wall beside the door inside the shed
• add in some fuses / circuit breakers
• add in a neat isolator for the panel (I'm intending to insert a power monitor in there now and then) which I'll do with XT-60 connectors

However right now its fully functional, and so the components for this are:

• 250W panel (32v) = $20
• MPPT solar charge controller = $40
• 2x RC95 lead acid car batteries @$90 = $180
• 2000W (4000peak) inverter = $240
• sundry wiring

Now some may be asking "why didn't you just get an electrician to wire it to the house?", well the answer is that because of the distance down to the shed (about 30 meters) it would cost something over $1200, instead of $424.38 and I'd have learned nothing new.

Win Win

PS: I've now mounted the solar charge controller, run the wires neatly, and added a circuit breaker / fuse system which of course acts as an isolator.

The top one is for the panel (I sincerely doubt I need a circuit breaker, but as it has a manual operation its a handy isolator) and the bottom one to the battery is really for (hopefully) protecting the internal fuse that's built into the SCC.