Dacian Todea

+ Follow
since Mar 22, 2015
Apples and Likes
Total received
In last 30 days
Total given
Total received
Received in last 30 days
Total given
Given in last 30 days
Forums and Threads
Scavenger Hunt
expand First Scavenger Hunt

Recent posts by Dacian Todea

frank li wrote:
There was a drill motor with a pv module attached to it in your house build video. I am all over it.

I think I know what you say now That was a cordless drill that has 4s3p LifePO4 battery 12V 3Ah I made (I use that during the house build) while my wife used the same exact drill model with original NiCd batteries 12V 1.5Ah and he needed about 3 to 4 of those batteries exchanged while my needed recharging.
The solar panel was a small 10W and was directly connected to the battery (battery fully discharged) it as just an improvisation that day to get a bit more energy to use the drill in that day. Normally one full charge will last all day and I was charging at home (rented apartment in the city at that time).
4 years ago

frank li wrote:The figure you gave is instantaneous power (2.88kw) a solar day has hours. 28,000 btu/hr is accumulated over the solar day. Solar thermal systems often have 50% and higher total system efficiency on the thermal side. Please dont think i do not see your point.

Again you have a path based on your environment, resources and capability and your tech is good. My comment is for others.

I have given problems to solve to whole classes of industrial engineer grad students and watched them miss by a long shot for the lack of listening.

I'm not to used with imperial units but I think BTU/hr is unit for power not energy even if the unit looks confusing by having hour in there.
In average here in winter I get about 4h equivalent of sun so 2.88kW (power) for that 4'x8' area x 4h = 11.52kWh (energy) This is for a 100% efficient collector.
If you have that same area covered with solar PV cells you get about 16% or 1.84kWh / day of energy.
PV panels will have the same 16 to 17% efficiency no matter how cold it is. A simple air thermal collector will have realy bad efficiency in a cold sunny day since a lot of the energy will be lost by thermal conduction radiation. Here will be completely useless in January even with just -20C outside during the day.
Also the air collector is not free to build and may cost the same or more than same area of PV. A large 250W 60 cell PV panel can be purchased for $200 has about 1.6 x 1m so two of this will have the same area as that 4ftx8ft air based collector.
Is end of March and today at this time 13:51 I have -4C (that is below freezing) cloudy with some sun breaks and last nigh I got a bit of snow 10 to 15cm (4 to 6").
But now I need almost no heating if I do a bit of cooking that is enough to keep my house warm.

4 years ago

frank li wrote:
What is the duration of extreme delta-t at your location? The reason i ask is not to convince you of the merits of solar thermal, rather to clear the pad for others adopting RE to know that extreme cold temps are generally not the major portion of heating degree-days. There is much benifit to collecting heat in the fall, much of the winter and in the spring, temp and solar availability-wise in my area of operations (northern michigan).

Also, i have made a living designing and installing these systems, part of that work was bringing orphan systems back online. Most of the ones that stopped operating needed a sensor or controller. Pumps rarely were the cause and air blower-motors, occasionally, a rotten copper waterway...once, heat transfer fluid turned to goo or acidic from stagnating 5 years...yup.

Funny thing, the thing that brought most systems down is new roofing and no service proffesional or handy person. They would re-mount and never charge with fluid.
most of these systems were 30 plus years old when i serviced them starting 12 years ago, they are ready for another 30-60 years of service or as long as the polyiso insulation survives... then 1.5 sheets of iso and a screwdriver to get another 60 years.

If distilled water is used in a drainback system that is pv direct circulated, an evacuated tube system could easily be a 100 year machine that requires a rare frequency of parts replacement. I excluded thermosiphon with antifreze and heat exchange and plain thermosiphon systems because of our extreme climates and the need for expensive chemical antifreeze, because distilled water is so easy and impervious.

Solar air heaters may leak 'fluid/air' but it is not as problematic if it were to occur. They require no freze protection and sometimes no blower or automated damping for regulation. They produce 28,000-32,000 btu/hr per day per 4'x8' collector at my lattitude and weather conditions. Thats like many peoples furnace at full blast for an hour per day per collector or 9kwh per!

Saskatchewan is tough territory. I am checking climate data now, for my own curiosity.
I am keenly awaiting data-logging details of your heater. Because we get smarter every day!

Yes I live in Saskatchewan and while I get decent solar energy (same amount of sun as Sydney Australia) is quite cold here I think -17C is the average temperature for January with many days with extreme -30C and -40C
When I mentioned 12C delta I was referring to concrete slab. To increase the temperature of the 14 cubic meters concrete floor you need about 8kWh and of course it will give all that back with temperature drops with one degree Celsius.
Usable range will be from 18C minimum and 30C maximum so 12C difference where the concrete can store 100kWh. I like to use kWh for energy it has more meaning to me.
My house is just 65 square meters (around 700sqft) and has good thermal insulation about R40 for walls and R70 for roof there is no thermal bridge anywhere including foundation as you probably seen in my video.
An 4'x8' collector is 1.2m x 2.4m = 2.88square meters and with 1000W/sqm that is 2.8kW power from the sun at noon. The efficiency of such a collector will depend on temperature and how it is build but even with spring like temperature I will expect well below 40% efficiency. In the winter here those will be completely useless and just vacuum tubes will make sense.
btu/hr is a unit for power and 28000BTU/hr = 8.2kW that is not possible since on that surface area what you get max is 2.8kW from the sun.
A good quality vacuum tube collector can can get to 60 - 70% efficiency and the temperature difference between ambient air outside and the hot fluid has less of an impact on efficiency do to excellent insulation proprieties of vacuum.
Where one of those air heaters will be way less efficient especially in extreme low temperature and can easy get below 16% efficiency of a typical PV panel.
Efficiency of the solar collector is only important when space is a problem else amortization cost is a more important parameter. Solar PV panels will slowly degrade over time and most manufacturers guarantee more than 80% of original power output after 25 to 30 years for PV panels. So all you need to do in 25 years is just increase the PV array size by another 20% to get to the same original power output and use that for another 25 years.
PV panels are so inexpensive right now that it makes for a great amortization cost as I mentioned for my location below 3 cent/kWh (getting close to 2 cent/kWh) but this assume you will be using all the available energy. The Vacuum tubes have comparable cost per Watt so an array that can output the same power made of PV panels or Vacuum tubes will cost the same the difference is that the vacuum tubes array will use about 2.5x less space.
But after the collectors on PV you just have copper wires to transport the energy and same copper wires can be used as heat elements inexpensive and with almost infinite life no moving parts just electrons. With thermal solar you need a few high temperature fluid pumps isolated pipes to move the energy from collectors to the house most probably a heat exchanger and some electricity to run the pumps (not much but still something).
Vacuum tubes also degrade over time but if good quality should last as much as the PV panels not a problem there but water pumps may need a replacement in 10 to 20 years (if they are good quality ones).
Still the part after collectors is more complex less reliable and more expensive that for the solar PV and the only advantage (may be important in some cases) is the smaller area needed to install them. If I have just the roof space that lower area will be important but I will install the array on the ground and space is no issue in my case.
PV panels will continue to drop in price where vacum tubes not so much.
Also the additional advantages of electricity vs hot fluid makes the solar PV heating much more appealing to me and uses can be found for electricity even in sumer nut so much for a hot fluid and even if you do not use the energy there is no need to cover the panels or use a dump load as with vacuum tube collectors.
4 years ago

frank li wrote:Our consumption here is 450-650whr/day avg. or 15-20 kwh/month. The boiler system has its own 223w module and 85ah gel cell, so the main pv system only powers lights, communications and well pumping. We garden and pump alot of water in the summer. I have been installing solar thermal and pv since 2004 and i would like to talk with you about your drill motor. I use a morningstar sysem (cc and inverter) in a dewalt drill case for charging an sla with a 10w module...but i live in an off the shelf world of lead acid!!!
Pv direct charging i love it.
Next thing here is to supply power over ethernet from a dc to dc sps(s) to every powered load i can, the coffe table, light fixtures, display screens, computers, routers and other comms, control for boiler and solar hydronics, and monitoring. I install sps devices to dc systems in cabins with existing dc power for lights and well pumps already for conditioning and low voltage protection and p.o.e systems are interesting. Thanks for the chat Dacian, and i hope to hear about your drill!

That sound really good. My lowest day(24h) power consumption is around 800Wh. In those days I do not use any large appliances just LED lights two computers a laptop 10W idle and a larger all in one (ASUS P1801 about 30 to 35W idle) then there is the small peltier fridge normally a 12V but runs from 5V with a DC to DC converter that alone takes 10W in winter 12W in summer so 240Wh to 280Wh. I have some DC pumps for now since I heat with propane small 20lb (8kg) barbecue type propane tanks each contain about 100kWh of energy and I use at most 10 to 12 of those in the cold months.
Internet is over 4G/LTE so is just an android phone and I have a raspberry PI A+ logging the energy data from the older SBMS4080. The new SBMS100 has internal data log on a 128Mbit (16Mbyte) flash that can store all data for 12 months then can be downloaded over WiFi so no need for Raspberry PI (not that it use any significant energy).
The 3x 240W panels in an overcast day in winter produce at least around 300Wh so I need to cover the difference from battery to 800Wh and I can get around 4 days with bad whether (usually not the case for more consecutive overcast days here) If there are more there is at least a half day with some sun that will recharge the battery back to 100%
Not sure what is the question about the drill. What drill ?
4 years ago

frank li wrote:
I love your home and i could picture a few thermosiphon driven air heaters or hydronic solar collectors on there for reducing the array size. However...copper cables do not leak water or air! I noticed that you do not live in woodland. We rely on a woodfired boiler system attached to our stove inside for dhw and space heat distribution. It dries clothes, heats the house and water and cooks our food all at the same time. I use pv direct-drive pumps and pv direct delta-t controllers for solar thermal and battery powered control and pump of the same type for the boiler side. I am shifting toward a destruction free source and so i applaud your clean style. We did find research that showed that wood heat, even at low efficiency can be much more efficient than industrial fuels. We harvest only dead wood and use mainly manual labor to harvest and haul (used to use a bow saw) and use an electric chainsaw with organic soybean oil as bar and chain lube. An outdoor combustion air inlet to the stove completes the picture. Sorry about the book but your house build and location got me all excited. Like yourself, we do it on 740wp of pv. These systems are micro to my clients but i live this way with great effect.

Yes thermal collectors (vacuum tubes the only ones that work in this climate) are a good choice if space is a constraint. The PV panels that can give the same output will use 2.5x as much area but space is not a problem for me (I live on a 20 acres lot). The 9 to 10kW PV array is not that large if I will have considered this a few years when I designed the house I could have incorporated all that in to the house structure.
Wood is more expensive here than pellets but none can compete with 3 cent/kWh for PV. Thermal solar if you consider that will last at least 25 to 30 years as PV will have similar cost amortization for the panels and use less space but the problems is pipes with hot liquid and pumps instead of copper wires only.
I prefer the the solid state nature of electric heating there are no moving parts or hot liquids.
Another advantage is that is electricity so in summer when there is no use for hot water from thermal solar I can still find some use for all the excess electricity. I do not need cooling since the building with all the thermal mass will keep the house comfortable in summer here.
What is your energy consumption with the 740W array ?
I had 720W (3x240W) array but recently got much more now I have a total of 3kW installed before the winter but did not use the extra as of now just connected manually some extra panels to charge the battery when I had more than a few overcast days.
The solar heat controller on top of heating will also be able to select how much of the heating array is diverted to battery heating up to all 15kW possible since in overcast days here I get about 12x less than in a sunny day.
It will not be so important to conserve energy (electricity) in winter since it will end up as heat anyway if used inside the house but will still need to keep the electricity consumption low in summer since that will contribute to heating.
I was able to use between 50 and 80kWh/month from that 720W PV array together with the 2.5kWh battery worst months here for solar are November and December when the 720W panels will produce just around 60kWh/month so I use almost all but in spring summer I have up to 50% excess (unused energy from that array).
4 years ago

frank li wrote:Im a pv system designer and also live off grid. We are always looking for equipment that solves problems and shaving off equipment and problems when possible. Your solar electric system outline makes me think that you like to shave! I do not run lithium, but am adjusting to the tecnological landscape.

These chats help evolve the techniques that are our toolbox and capability. I will take a look at your devices.

Vehicle propulsion is one of the most extreme purposes an electric battery can be put to use for. The guys at evtv show that they bottom balance a battery of cells and use 80% of its rated capacity, for years of commuter use without getting any significant unbalance. They do monitor cells and use auto contactors to avoid low voltage induced failure. The battery has enough ampacity to soak up the difference between cells as long as the application does not require every nameplate amp-hour to be used. Sometimes this is referred to as not getting your best dollars per amp hour capacity, and sometimes doing so solves problems and shaves equipment.

The only reason I selected Lithium (LiFePO4 to be more specific) is because of the cost amortization that is better than Lead Acid traditionally used.
The manual bottom balancing is useless in my opinion. All EV car manufacturers use a similar top balancing that I use with my SBMS.
The thing is that battery in both EV and solar energy storage ins fully charged way more often than fully discharged (in most conditions battery will never get to be fully discharged in a proper EV or off grid solar installation).
My battery is fully charged almost every day around noon and except for 3 or 4 occasions over the last 3 years never fully discharged.
As long as you monitor each cell the is no danger of overcharging or over-discharging any cell. A LiFePO4 is to expensive to run without a BMS and will get damaged without one.
The SBMS is an open source hardware and software device but is designed specifically for 12V and 24V offgrid installations.
I will next design an Solar PV heat controller with what I call Digital MPPT. I will give soon more details about that (open source of course). I need that to fully heat my small offgrid house with solar PV electricity since is by far the least expensive heating method at this point.
Solar PV panels amortization cost is below 3 cent/kWh (based on 1$/Watt initial cost 25 years amortization and the amount of sun at my location).
The Heat controller will use restive loops embedded in my concrete floor. The Heat part will not use a battery but will store energy in thermal mass. In my case a 14 cubic meter concrete floor with no thermal bridging to outside that can store 100kWh at 10 to 12 degree Celsius delta.
The large heating array (up to 15kW with two heat controllers) will also be used to charge the small 100A lithium battery so even in overcast days I can get a full charge so battery will only need to be able to provide energy over night all there rest of the energy will be stored in the much larger capacity thermal mass.
Even if large water tanks are used for energy storage the cost amortization will be below 1 cent/kWh stored where for best LiFePO4 the amortization cost is 20 to 30 cent/kWh so for heating it make a huge sense to store energy in thermal mass.
You can see detail about the SBMS on my google+ page there are the most up to date info https://plus.google.com/+electrodacus/posts
4 years ago

frank li wrote:These are great sources of off the shelf solutions to the lithium issue.

The problem with the bulk of lifepo4 batteries designed for sla replacement is, that they are made of multitudes of paralelled cells of tiny capacity and too many connections inside...plus bms circuitry. Stay away from this or...fire and economic failure and or overall disappointment in/of an otherwise well designed system may occur.

Pv system design just broke the 4s20p battery habit and ev hobbyists are doing it right without bms and doing it in single series strings with big cells (100ah-500ah not a quadruple gross of 5000mah cells), big cables and great results.

Maybe you noticed that I'm the designer of that SBMS (Solar BMS) that I just started shipping today to bakers.
I know I sound biased but that is the only solution for LiFePO4 in offgrid solar on the market.
The SBMS100 uses the ISL94203 can check the spec as BMS IC and will do maintenance cell balancing based on all cell voltages not just based on fixed voltage threshold on a single cell.
You can of course disable the cell balancing if you want but then you will need to do manual balancing each few months.
Based on my experience (I have 3 years of full offgrid with 100A 24V LiFePO4) with daily use and no cell balancing at all my GBS cells will get a max 2% unbalance over 3 to 4 months of use.
The SBMS4080 my older SBMS model that I used for the last year has just a 50 to 100mA cell balancing current that is activated when difference between any cells is higher than 10mV and that is more than enough to keep the cells in balance for unlimited period of time and can do that even with much higher cell capacity.
The SLA replacement batteries are just a scam in my opinion. You can not do that (not easy and sure none on the market will work).
First as you mentioned is the charge in low temperature if you want to use this in cars.
For solar they can not work. They have just two terminals and charging and discharging path needs to be separated else yu can not protect the cells inside from over-voltage.
When any of the LiFePO4 cells inside gets to 3.55 or 3.6V you should terminate the charging and if you do that with a two terminal battery (positive and negative terminal) the you also cut the load (not acceptable).
So what they do is to accept overcharge of the highest cell in the hope that it will last enough to not get complains to soon from the users.

SBMS of course has the charging and discharging path separated so you can stop charging and continue discharging.
My 100Ah 8S GBS has 4 years since I purchased and 3 years since it powers my off-grid home every day.
The battery is 2.5kWh capacity and I use in average 1.3kWh/day with a minimum of 0.8kWh/day from battery and max >3kWh/day (3kWh is possible from a 2.5kWh battery since the battery gets charged and discharged many times per day).
I will do a capacity test this spring but I do not expect more than a few % capacity loss since I can not see any degradation in capacity.
I have a youtube video with the original capacity test 4 years ago and I will repeat the same exact test with the same equipment so results should be comparable.
4 years ago

frank li wrote:
One limitation of lifepo4 is that they generally are not able to be charged at low temps (0 deg f) and need an automated climate control system (insulation, heat source, controller etc.) in order to operate reliably unattended, and need a heated location either way for 4 season use in areas with cold winters.

Yes you are right. Since I use this for an off-grid house and the battery is inside the house they are at ideal charging temperature all the time no insulation heat source with temp control needed.
If it needs to operate unattended in non heated location then yes it will need to be heated to above freezing before charging. Energy directly from solar panels can be used to heat the battery to appropriate temperature before charging can be done.

4 years ago

No I do not know websites that track the price of solar panels. There are sure a few. Most concentrate on the price of solar cells and those are so low that I do not see possibilities of much more reduction and even if that is the case there is not much savings on there. The glass and aluminium frame are probably the expensive part already and they are also heavy contributing to shipping cost. But those prices seems about right. One of my solar BMS bakers in US mentioned that he got a full pallet 24 PV panels 250W each at 82 cent delivered so shipping is included in this price.
Here in Canada with shipping included is around 1 CAD but CAD is quite low now compared to USD


I do not think battery will be a solution for individual house that soon. And large grid batteries will probably be more and more common in the next few years to deal with the increase of solar PV connected to the grid.
Still grid price can not go up in the future even if they will sell way less electricity. They will need to restructure close quite a few coal power plants and make the grid much more automated and smart.
Off grid price starts to get down with LiFePO4 and will continue to do so so grid price can not go up since they risk completely losing the grid.
So I think grid will be the main provider of energy in the future but it will need to be much smarter with a lot of smart appliances (IoT) that will use energy based on availability.

5 years ago
Thanks Bill.

Terry Ruth wrote:
Here is a thread and post from an installer that discuss micrometers vs DC optimizer. Is this accurate? What is your take on them are they worth the COP and how they differ from the efficiency of your efforts? I've read the studies out of CA showing higher efficiency from west-south facing hybrids....are you facing any west? https://permies.com/t/45940/solar/micro-central-inverter

Here is my video explaining why mppt is obsolete and may other technologies aimed at optimising the energy output of solar PV panels all this because of the huge drop in price of solar PV panels.
A typical 60 cells (250W) PV panel cost now around $200 having anything on it to optimise the power will not be cost effective.
I'm mostly interested in Offrgid and not grid tie so I do not care about inverters or micro inverters. As for DC optimisers in order for them to be cost effective they will need to be high quality to last 25 years and cost less than $30 (15%) for a 250W PV panel to make up for the 15% annual average they can get additional at best but since is about offgrid that will be useless since the unused energy will be way more than that. You can not use all available energy do to finite battery capacity.
So there is nothing to optimise if you need more energy just by an additional PV panel that will produce way more for less than any optimisation method.

5 years ago