I found Tim Nolan's information at his website ( www.timnolan.com ) a few days ago, but note that the account is now suspended.
I plan to design and build a similar controller for two 80W panels on my 12 volt caravan, with a few changes:
I'm using a UNO style Arduino, with parallel interface to 16x2 LCD display.
I will base the MPPT feedback algorithm on only the battery current, as that is the output I want to optimise, using a maximum of 250 for the PWM value to allow good operation of the charge pump associated with the IR2104 driver.
I will modify the algorithm to control float voltage to a lower value than that used to trigger change from bulk charge to float.
I consider that 1 optimisation per second is fine for realistic conditions - a major light change can be handled in at most 10-20 seconds.
I will use a Hall-effect current sensor (DFROBOT SEN0098) based on the ACS758 device rather than the MAX4173H and 5 milliohm resistor. I'll use this to measure current to the battery. Without any additional amplification, that will give me around 0.1A resolution which should be quite accurate enough.
When I see the results of this setup, I'll look at whether I need to consider separate optimisation for each of my two 80W solar panels for situations where one panel may be partially shaded and the other in full sunlight.
If that's necessary, I believe the UNO can readily optimise two DC-DC converters.
When I get it all running I plan to post details & results here. Comments invited.
Hi there. Thanks pemic & Roger for contributing.
I am travelling now &have deferred work on this till I get back to Melbourne. I expect to start again mid august.
Yes I have seen articles like those mentioned and several that look like student theses that look for minor improvements in hill-climbing algorithms.
Some efforts try hard for very small improvements, but miss critical items.
At the time I bought my solar panels a few years ago MPPT controllers were very expensive and I couldn't convince myself they would justify the cost. I am using the solar panels to reduce the amount of time I need to run my diesel engine to recharge my batteries.
I thought (back then) that I could make my own MPPT controller but I gave up after frying a few Mosfet drivers and not having a clue why. This was before I had any Arduinos.
Now I'm wondering whether I might try to build something like the Tim Nolan project.
But I'm still very unsure of the practical economics because batteries can't necessarily take the extra power energy that may be available and I can't afford to allow the battery charge to fall to a low level today just in the hope that tomorrow will be sunny. I have never seen any test data from MPPT retailers showing how much extra watt-hours are produced in an real-world test. And because such a test would be very easy to do I am suspicious that it has been left undone deliberately to hide embarrassing data.
I wonder if anyone here has given any thought to this economic question?
You get roughly around 25 - 30% improvement in power input to the battery, at least that what I get from my
home made MPPT charger.
The cost / effort needed depends a lot on how much power is available from the Solar Panels and how big the batteries are.
Mosfets are very easy to blow up if you get something wrong , you have to be very careful.
Tim Nolans design is a good one to start with, but be very careful if you start changing the design.
Mppt charge controllers need a fair bit of design work to make sure you arnt stressing the Mosfets,as if you do
they will either blow up the instant you turn it on , or after an hour or so.
mauried:
You get roughly around 25 - 30% improvement in power input to the battery, at least that what I get from my
home made MPPT charger.
Interesting. I am very interested to learn from other people's practical experience and I would very much appreciaate it if you would describe your setup and how you have calculated the 25% - 30% improvement.
I suspect sunshine is more predictable in Australia than in the UK and I wonder if that makes it easier to make full use of solar power.
The referenced article from Tim Nolan included readings taken intermittently with the dcdc convertr set to a 100%mark-space ratio so that the circuit then operated as a direct connection from solar panel to battery. This gave good comparison MPPT vs direct connection, showing 20% - 30% improvement.
Yes, sunshine is more predictable in most parts of Australia than in UK as we don, t have gulf stream affecting climate as in uk, but ther is great variation across a huge continent! Panels are also greatly affected by temperature - mine are sometimes running in 35c to 40c ambient temperatures.
Fyi I did purchase supposed mppt controller from local electronics shop (jaycar) that was less effective than my sraight through controller!
JimB:
This gave good comparison MPPT vs direct connection, showing 20% - 30% improvement.
I understand the theory of why an MPPT controller should be better and I can't help suspecting that these figures represent instantaneous differences rather than the accumulated watt-hour difference over a whole year in a practical application that must also use another conventional power source to ensure constant energy availability.
Hi Robin, Nolan,s results showed consistent improvement as quoted, all samples showed similar result so I would be confident that integrated result over continuous usage would be v v similar.
Mppt optimises output from solar. Whether/when you need alternative is a v different question. I,d also comment that solar output I expect would never exceed absorption capacity of my batteries. If necessary output current limit could easily be added to charge control algorithm too. I would love to have $$$ & space for enough panels to have that problem!
Ciao jb
Mppt controllers.
They seem expensive , why not size the solar panels for your local conditions and use traditional simple control methods.
Lead acid batteries can accept a wide range of current.
If you have low light, add extra panels to boost voltage.
In high light make sure you have enough batteries to soak up the current.
MPPT controllers are expensive , but theres no reason why they need to be .
Theres not much in them in the way of electronics.
I would guess its the small market.
As to why MPPT controllers make a differance, you need to understand how Solar panels work.
For example , a 12V solar panel isnt really a 12V panel at all.
Its really a somewhere in between 12V and 21V panel depending on what load is connected to it and how bright the sunlight is.
Solar panels will only deliver their rated power at one specific voltage and load, and this voltage and load moves around as the
sunlight intensity changes.
The ones Im using are rated at 100 watts STC , 18V at 5.5 amps.
What does this mean?
The STC means that panels power rating is measured at 25D cell temperature with a irradiating intensity of 1000w/sq meter.
The 18 V @ 5.5 amps means that the Solar panel wants to see a load of 3.2 ohms.
With any other load the panel will deliver less than 100 watts.
If the load is a 12V battery, the panel will only deliver 66 watts as the battery clamps the solar panels voltage to 12 V , but the current stays the same at 5.5 amps.
This happens because Solar Panels behave like current sources, so the current is determined by the available sunlight.
The Solar panel is now behaving like a 66 watt panel.
All a MPPT controller does, is fools the Solar panel into thinking its still connected to a 3.2 ohm load, so the battery gets the full 100 watts.
At differing levels of sunlight, you get less improvement, so if you live somewhere, where you never get 1000w/sq meter, there wont be as much differance.
All grid Tie Inverters, which are the type that are used by roof top solar systems to feed power back into the grid have MPPT trackers in them , as the improvement gets better economically the bigger the installed panel capacity.
In its simplest format , all a MPPT controller needs is a small micro, 1 Power FET, one inductor,a couple of transistors,one or 2 diodes ,one opamp,a current shunt, and a small number of resistors and capacitors.
JimB:
Hi Robin, Nolan,s results showed consistent improvement as quoted, all samples showed similar result so I would be confident that integrated result over continuous usage would be v v similar.
I guess I haven't explained myself very well.
I understand that the MPPT will deliver benefits at most sunlight levels.
What I'm trying to figure (hopefully with input from someone with practical experience) is how much of that extra can actually be used in a situation where the panels are being used to reduce the need for charging with a diesel engine.
To simplify a little, lets assume the battery needs to be near full charge every evening so it can supply power through the night. If there has not been enough sunshine the charge must come from diesel power. AND the battery needs to be near full charge in the morning in case there is inadequate solar power during the day - for example a day of heavy rain. That means that the battery may need a top-up diesel charge in the morning if the night time load was high.
Then if there is a lot of sunshine it is likely that the battery will not have sufficient spare capacity to take all the available current. In that situation adding an MPPT would have no benefit. And I think there is the opposite problem in winter - there is often so little solar output that for practical purposes I can't rely on it at all.
An obvious technical answer to this conundrum would be to increase battery capacity so there is a sink for the extra MPPT output but 30% extra output couldn't possibly pay for an MPPT controller and the extra battery capacity..
And, of course, the problem is that I don't have the facilities, space or capital to carry out back-to-back tests of two systems, one with an MPPT and one without - so I'm hoping someone else here may have some information that would be useful to me,
The idea of adding another solar panel rather than an MPPT controller seems to have a lot going for it, except that I don't have space for another panel.
He did it because in winter he could not get enough charge into the battery to keep it alive using 1.
The why, i was referring to the explanation, its the best iv seen.
Similar to you iv been considering a solar installation for a while but the cost means i need to get it right first go.
Edit
Im currently thinking of a switchable series parallel arrangement, it will not be used much in winter anyway but i would like to keep the batteries charged.
This may not suit your application though.
In winter i have both uk weather and tree shading to contend with.
I have two sets of domestic batteries (each 12v 200Ah) which I use in turn for 3 days at a time. The idea is to use the 3 days to allow the "spare" set to reach a full charge. The main source of charge is a diesel engine at an approximate fuel cost of £1 per hour. The solar panels are used just to save on diesel fuel. I have 3 x 80w solar panels. In the summer 2 of them feed the in-service battery through a regular (non MPPT) controller and the third feeds the spare battery without any controller. In winter I use two panels to feed the spare and the single panel (through the controller) to feed the in-service battery. I have the solar panels 3 years now and I reckon they have paid for themselves comfortably.
At present they just lie flat for convenience. Recently I saw a simple wooden arrangement that would allow them to be tilted and rotated so I might do that for the coming winter when it would be most valuable because of the low angle of the sun. I suspect that would be a more profitable investment than an MPPT controller.
The mppt controller simply helps get max amp hours from whatever is available from panel(s) & sunlight hours.
Given what you already have, I would use two battery sets inparallel, and thus exploit total capacity. I am unable to comment in lots of detail now, but may have better web access next week. Ciao
Would i be better off saving the cost of an mppt controller and buying an extra panel do you think ?
Total power is likely to be under 200 w and not sure which would give best results.
I have 2x 80 with enough space for an extra 20 w panel.
If someone comes up with a cheap shield i could add later i suppose.
Your total solar array power is under 200W, at most from an MPPT controller a "maximum" gain of 30% can be seen.
Not to dissuade you from trying to build your own MPPT controller, buying an additional 50W panel would give you a "constant" 25+% gain over your current setup.
MPPT is fine for large arrays greater than 1000W, then the price of the controller and it's real world gains can be more reasonable compared to the price of an additional 25% more panels.
Same with a tracking system, it's only economically efficient if the solar array is at a size where the cost for the % of gain from tracking is less then the cost of additional panels to achieve that same % of gain.
Have to keep in mind that "quality" panels need almost zero maintenance over their 20+ years of operation, MPPT controllers and tracking systems will need repair/replacement before 20 years, that expense needs to be considered when designing a solar setup.
For your setup manually keeping the panels facing the sun at the correct angle will allow you to harvest more energy then keeping them stationary and using an MPPT controller.