I had reservation it seemed dubious, however some are advertising PWM + MPPT, which is maybe a little more dubious.
Why are other MPPTs based on MCUs not 'digital'? Can you safely assert all other MPPTs only use linear IC's?
Sorry you do not understand how the Digital MPPT works.
There are two parts to the DMPPT450
First one will take energy from a large PV array and using the so called Digital MPPT method delivered as heat to a set of 6 different value resistive elements.
The Load is made variable by combination of the 6 outputs so that Load can be varied in up to 63 distinct levels (number of combination with 6 ON/OFF outputs is 2^6 = 64 including all off).
By the fact that Load can be varied with this 63 distinct steps allows to maximize the power point for the PV array.
This sort of method only works for resistive type heating and is not applicable to battery charging.
Second part of the DMPPT450 has an output for the SBMS that will do battery charging so battery is also charged from this large PV heating array.
The heating array is split in 6 separate sub-arrays of different sizes and the DMPPT450 can select any number of this 6 separate PV array and redirect them to the output used for battery charging.
Since the total output of this large PV array is much higher than what the small Lithium battery can safely take the DMPPT450 will limit the output to battery at say 50A for a 200Ah battery and will select just a few panels to redirect to battery charging when is sunny and more panels when is less sunny up to all panels if is completely overcast and all panels put out no more than 50A.
So the PV panels redirection to battery charging uses a similar method to the Digital MPPT for the resistive load output.
All energy that is not needed for Lithium battery charging will go to thermal mass storage that has a much larger storage capacity than Lithium.
To better understand all the benefits of this check the long youtube video I posted explaining all this in more details.
What you know as a MPPT used in Lead Acid battery charging is composed of two parts one is usually software in a micro controller and second is the DC-DC converter that is controlled by that software.
The DMPPT450 has the software part (a bit different) but dose not need the expensive and unreliable DC-DC converter.
That DC-DC converter is expensive since it needs large inductors and electrolytic capacitors. Usually is a step don DC-DC converter that is controlled by the micro-controller in order to maximized the charge current to battery by finding the max power point. The current can be varied in a linear way (almost linear in any case with much better resolution) with the DC-DC converter.
A DC-DC converter that will be able to support a 14kW PV array as the DMPPT450 will be extremely heavy (expensive shipping) cost at least a few thousand dollar even for a less than good quality one and have huge internal losses thus probably need active cooling in order not to be even more heavy.
Say you get an excellent efficiency of 94% for the DC-DC converter that supports a 14kW PV array then the amount of heat generated inside the DC DC converter and that needs to be removed will be 14kW x 0.06 = 840W so it will be at full load a heater by itself
The DMPPT450 will have a total TDP of just around 50 to 60W at full load thus passive cooling is simple and the weight is maybe 20 to 50x lower so shipping cost is also significantly lower. Shipping alone from Canada for a heavy DC-DC converter can be more than the price of DMPPT450
The idea is that what you think when you say MPPT is extremely different from a Digital MPPT and while they both maximize the PV array output it is done in a completely different way with different HW and SW
Good point. I'm sure all have researched trombe wall, here is one report on efficiency:
http://www.nrel.gov/docs/fy04osti/36277.pdf
That claims nominal 13% efficiency for simple non-insulated design.
What about a fully insulated trombe wall 'structure'. Three sides and bottom have insulation, and the south has double-pane glass with an insulated rolling curtain to cover at night. The structure could even be detached from the house. Use a blower to circulate heat only when needed, this is a small load to handle for the guarantee of never inducing unwanted cooling load and being able to control heat better. Plus, the fact that the V in HVAC can be seen as a separate system and is still needed, required, even with radiant heating / cooling. The trombe structure could last 'indefinitely' and has a lower upfront and amortized cost than PV too. It could also be used as a preheater and slightly reduce PV need for hot water but pumping water may in fact come at a net loss with additional complexity for hot water needs... then again with such an 'oversized' trombe structure one may get enough hot water, being only a small fraction of the heat. It should be good for adsorption chilling too, maybe 15kW or so heating capacity could give 2 ton ?? of cooling. The majority of the south facing roof could be the trombe structure instead, or 'trombe roof', reserving a smaller space for PV. And, no 'shading' issues with trombe structure for those around trees.
That sot of thermal storage and solar heating hybrid has little to do with thermal storage that I'm talking about.
That thermal mass has little isolation from outside since is also used as a collector and is not that different than having large windows for direct solar gain.
Both of those methods are obsolete when compared with PV solar.
The problem is that in clod climate a lot of the energy gained during the day will escape during the night and in cloudy days and so that net gain of that system is extremely low sometimes even negative meaning that is better not to have that installed at all.
They conducted the test in a moderate location not as cold as mine else they will have negative results and that way they get just 13% efficiency but that is not to be confused with thermal storage efficiency and that is the amount of energy delivered by the sun say 5kWh per day per square meter in average that ended up contributing to house heating and in that case it will be 5kWh x 0.13 = 0.65kWh per square meter and day in average over the entire heating season.
A better performance can be achieved with the same surface made of PV panels (17% efficient) and a much smaller thermal mass (about 8x smaller) present inside the house not behind a simple glass with little air gap that has an incredibly low thermal insulation value.
Whit PV panels there is no loss during the night as it is with large windows used for solar gain or that method presented in that paper.
Dry soil has the same specific heat as sand (19% that of water), and ~90% that of concrete. Wetting the soil (mud) will get you about 3x increase over dry.... one should be able to seal the moisture and even embed a soaker hose to easily 'recharge' if/when needed too. I wonder if dirt could be used as the sorbent media for adsorption chilling, instead of silica gel.
http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html
You can see different thermal storage options in my paper. Sand and concrete have about the same storage capacity and compared to water they have almost exactly half the storage capacity by volume.
Capacity by volume is usually important and water can have energy density similar to that of Lead Acid battery (as I mention at some point in my video).
If you want an even better energy density by volume than water then you can use the latent heat capacity of phase change materials with one of the popular ones being paraffin for low temperature storage application.
Absorption chillers can be used with almost any heat source including PV and DMPPT combination and while they are not particularly efficient COP of 0.7 to 1 they can be a solution since the energy source is extremely inexpensive with PV. I still prefer peltier
even with COP of 1.4 at 20C delta. Luckily for need I do not need space cooling at my location just heating.
Electrodacus - I can see how 'stepped shunting' the non battery reserve as heat is very attractive : ) That's exactly what you have implemented, it is very easy to understand with just those two words no? I would argue MPPT only makes sense with dc-dc conversion, the effect is very similar, though it's confusing calling it MPPT. More appropriately you could call it "MPPS" or maximum power point shunting.
See the answer above also. Not sure stepped shunting is a better definition than Digital MPPT but I'm glad you got the idea and it was simple to understand.
What I do is Maximum Power Point Tracking is just that is in discrete steps 31 or 63 max steps so I call that Digital Max Power Point Tracking.
A DC-DC converter can be used even with a single resistive element to get the same effect but efficiency will be lower and cost much higher.
MPPT with DC-DC converter used in offgrid battery charging is a completely useless technology and obsolete. I made a youtube video about that just search for MPPT obsolete and it will be the first video.