does mppt really make $ense @12v with the crash in solar pricing

wild01 · December 2009

so looking at the new lower prices on solar panels (and having just sent my flexmax 80 off for warranty work) I started wondering, how cost effective is mppt in today's market?

so here are some numbers
@12volts (worst case senario) a flexmax 80 is rated to take at max 1000 watts of solar. (nec rating)
best case scenario for mppt is 30% increase so best case @12 volts you get the same output from 1000 watts of panels as you would from installing 1300 watts of panels.

so at $1.74 a watt you can buy a 195 watt 17.8v sun panel warrantied by sunelec for 25 years
cheapest I've found a flexmax 80 575.00 and comes with a 5 year warranty
so 195x4x1.74=1357.20 +575.00=1932.20

or 195x5x1.74=1696.5 + (120x1.74)(sun 120 panel)=1905.3 + 218(2c-40cc)=2114.1

so IF your flexmax really increases output by 30% you save aprox. $181.90

now while this seems like a decent savings that's at the max efficiency and once you factor in the fact that the charge controller is only warantied for 5 years and the panels for 25 i'd have to say that at the moment with current pricing mppt doesn't make sense for use in a 12 volt nominal system.

considering that price per watt on the mppt cc just gets worst with smaller units (flexmax 60 xw 60 tristar60mppt rouge etc) to me it seems that there is really no longterm savings for any 12 mppt cc on the current market.

thoughts anyone?

Photowhit · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

Not sure why anyone would with a 12 volt system, then again not sure why you'd have a 12 volt system if your serious, for the most part 12 volt systems don't make sense, 24 volt 2x wattage, 48 volt 4x...

And I tend to expect things to work past their warranty, sorry you've had issues.

BB. · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

I would not disagree with your thinking...

The best use for MPPT controllers, in my humble opinion, is the ability to run solar panels in series (upwards of 100 VDC Vmp) to allow you to reduce the current to 1/9th or so--which makes it much easier/cheaper to run the solar panels a ways from the controller/battery bank building.

Another reason I like them is that in hot weather, Vmp can drop quite a bit--and even a Vmp of 17 volts may not be really high enough to charge/equalize a battery bank. An MPPT controller allows you to have a Vmp of >> 14.5-15.5 volts + voltage drop of wiring and controller and efficiently down convert and properly charge the battery bank (because there are lots of Vmp's out there--a MPPT controller allows you to buy the best $$$/Watt solar panels without having to worry about individual Vmp's being too high or two low... A Vmp of 16 volts won't work, and a Vmp of 24 volts is a waste of money with a PWM controller on a 12 volt bank). And in cooler weather, the higher Vmp of the solar panels results in more power/current into the battery bank (probably the 15% or so--not 30%+ percent).

There may be one last advantage to the PWM controller too. Some of the MorningStar PWM controllers have a low noise setting--instead of a 10-25kWHz switching frequency, they drop way down and can reduce radio/audio noise).

The PWM battery charging algorithm is standard for all Morningstar charge controllers. However, in cases where the PWM regulation causes noise interference with loads (e.g. some types of telecom equipment or radios), the TriStar can be converted to an On-Off method of solar charge regulation.

It should be noted that the On-Off solar charge regulation is much less
effective than PWM. Any noise problem should be suppressed in other ways, and only if no other solution is possible should the TriStar be changed to an On-Off charger.

-Bill

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

Photowhit wrote: »

Not sure why anyone would with a 12 volt system, then again not sure why you'd have a 12 volt system if your serious, for the most part 12 volt systems don't make sense, 24 volt 2x wattage, 48 volt 4x...

And I tend to expect things to work past their warranty, sorry you've had issues.

yeah I'm on 12 volt due to upgrading hell (started small not so small anymore but still w/ prosine 2.5/12v) which is why you can find several posts by me on here advising beginners to buy a 48v sys to start.

of course I think that with a more real world figure of 15% increase the math would still hold out for a 24v sys.

I also tend to expect things to outlast their warranty, but all things being equal no piece of sensitive electronics is going to outlast a well made panel. I make my living off one simple adage - things with moving parts wear out- even if it's just relays and cooling fans that adage still applies here. There is a reason for the difference in warranty periods.

icarus · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

12 volt makes lots of sense for small off grid systems, mostly because of the ability to do a simple hybrid system. Granted, as inverters have gotten better (and cheaper) the call for using 12vdc is less important. But to be able to use 12vdc for stereo, (much better quality for long distance reception than other radios) a number of 12 vdc appliances sch as hood fans, ceiling fans, night lights etc mostly from the RV industry. The most important use I have now is for the fridge controller on the Dometic fridges.

As for mppt. Consider this in the equation. You are going to need a controller anyway, so what will a good quality conventional controller going to cost? The real issue is what is the DIFFERENCE in cost. For my money, I love the Rogue mppt, but I have been quite happy with the Bluesky, all in the ~$300 range. Even running 12 vdc, I see ~10% boost on average until the battery goes to absorb.

Tony

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

icarus wrote: »

12 volt makes lots of sense for small off grid systems, mostly because of the ability to do a simple hybrid system. Granted, as inverters have gotten better (and cheaper) the call for using 12vdc is less important. But to be able to use 12vdc for stereo, (much better quality for long distance reception than other radios) a number of 12 vdc appliances sch as hood fans, ceiling fans, night lights etc mostly from the RV industry. The most important use I have now is for the fridge controller on the Dometic fridges.

As for mppt. Consider this in the equation. You are going to need a controller anyway, so what will a good quality conventional controller going to cost? The real issue is what is the DIFFERENCE in cost. For my money, I love the Rogue mppt, but I have been quite happy with the Bluesky, all in the ~$300 range. Even running 12 vdc, I see ~10% boost on average until the battery goes to absorb.

Tony

tony if you look at my numbers I included 80 amps worth of cc on both sys. my point is that for roughly the same money you can have highly reliable 35+year proven panel technology or relatively new mppt tech. using your numbers

418 watts of solar on a rouge cc would give me a 10% increase in power to the battery so 418 watt mppt controlled would equal 459.8 watts with a pwm controller

so 418*1.74=727.32+300(mppt cc)=1027.32
and 459.8*1.74=800.052+113.50(xan c35)=913.552
so using mppt cost 113.768 or enough money to add 65 more watts to the system

Bill did make a very valid point that they are convenient for minimizing wire loss on long runs, but it seems to me that if these low panel prices keep up mppt will either have to come down significantly in price or lose a significant market share.

niel · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

wild01,
i do have to correct you on something you seem to think. if you have a 1000w pv array, an mppt controller will not make that to produce 1300w. it does not create energy. what happens is that a great deal of that 1000w is lost to a pwm controller and an mppt controller recovers some of the power that was lost and that depends on many factors, but is typically about a 10% recovery or boost as the hype goes.

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

niel wrote: »

wild01,
i do have to correct you on something you seem to think. if you have a 1000w pv array, an mppt controller will not make that to produce 1300w. it does not create energy. what happens is that a great deal of that 1000w is lost to a pwm controller and an mppt controller recovers some of the power that was lost and that depends on many factors, but is typically about a 10% recovery or boost as the hype goes.

yes Niel I realize that, perhaps I wasn't clear

418 watts of solar on a rouge cc would give me a 10% increase in power to the battery so 418 watt mppt controlled would equal 459.8 watts with a pwm controller

I'm not saying that I would get 459.8 watts out of the panels, just that to get the same power to the battery I would need 459.8 watts of panels using a pwm cc

so 418 watts of panels using a mppt cc =459.8w of panels using a pwm cc

sorry if I wasn't clear

niel · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

still not correct.
i borrowed this explanation from my solar boost 50 with credit to bluesky for its writing.

HOW MPPT WORKS
A PV module is a constant current type device. As shown on a typical PV module voltage vs. current curve, current remains
relatively constant over a wide range of voltage. A typical single 75 watt module is specified to deliver 4.45 amps
25°C. Conventional PV controllers essentially connect the PV array directly to the battery when battery voltage is low. When a pair
of 75 watt modules are connected directly to a battery charging at 24 volts, the modules still provide approximately the same
current. But, because output voltage is now at 24 volts rather than 34 volts (2x17V), they only delivers 106 watts to the battery. This
wastes 44 watts of available power.
Solar Boost 50’s patented MPPT technology operates in a very different fashion. Under these conditions Solar Boost 50
calculates the maximum power voltage (VMP) at which the PV module delivers maximum power, in this case 17 volts. It then
operates the PV module pair at 2x17 volts which extracts maximum power from the modules. Solar Boost 50 continually
recalculates the maximum power voltage as operating conditions change. Input power from the peak power tracking controller, in
this case 150 watts, feeds a switching type power converter which reduces the 34 volt input to battery voltage at the output. The full
150 watts which is now being delivered at 24 volts would produce a current of 6.25 amps. A charge current increase of 1.8 amps or
40% is achieved by converting the 44 watts that would have been wasted into useable charge current. Note that this example
assumes 100% efficiency to illustrate the principal of operation. In actual operation, boost will be somewhat less as some available
power is lost in wiring, connections, and in Solar Boost 50.
TYPICAL CURRENT BOOST PERFORMANCE
As described above, current boost performance for a particular installation varies primarily with PV array temperature and
battery voltage. Two other factors which affect boost performance include system wiring and PV module design. The effect
wiring has on performance is power wasted heating undersized wiring is unavailable for charging. This is discussed further in
the Battery And PV Wiring section. The effect PV module design has on performance is modules with a maximum power
voltage (VMP) of 17 volts or higher will tend to produce more boost, whereas modules with VMP less than 17 volts will tend to
produce less boost. Panel types with a high VMP value in the range of 17.0−18.5V provide the best boost performance since
there is more typically untapped power to be extracted. For a 24 volt system using eight 75 watt modules with peak power
specifications of 4.45 amps @ 17 volts @ 25°C, representative boost performance under a variety of operating conditions is
shown in Table 2. Your current boost performance will vary due to a variety of factors. What you can be sure of is that Solar
Boost 50 will deliver the highest charge current possible for a given installation and operating conditions.

they rework the output of a pv and bring the voltage down to the optimal voltage needed while they up the current. think of it this way, that 17v pv to a battery at say 12.5v has lost 17v-12.5v=4.5v in the translation and when multiplied by the current would show a loss in watts over what the pv could deliver if the battery were optimally needing 17v, but that is not the case. mppt is almost like a dc transformer (note that ac only transforms in a transformer) as it takes the dc and turns it into ac and then back down to a dc voltage that is more optimized thus recovering some of the lost power.
so in the 75w pv example they are using that loss would be 4.5v x 4.45a = 20.025w and what is being used by the 75w pv is now 75w - 20w = 55w. it is not a case of 75w + 10-30% of that 75w pv, but only the lost power being re-added so that it gets closer to the original 75w and is always less than that 75w.
i hope i didn't confuse you, but it does not add to the original pv wattage, but the adjusted wattage from losses.

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

Niel you're not reading what I posted, you seem to think that I've said I'll get more watts out of the panel than it is rated. I haven't! all I have said is that if you're getting a 10% boost in efficiency using a mppt cc over a pwm cc than to get the same power to your batteries you need 10% more watts of panels.

so if you hook a 100 watt panel up to a mppt cc and get 14v @6.5amps (91watts output) in order to get the same output 91 watts from a pwm cc you would need a 110 watt panel.

My math is solid

niel · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

ok i see where you are going and sorry for any misunderstanding as you were giving what figures one would've needed after the losses.:roll:

Windsun · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

While you are right in some respects, the main advantage of MPPT is that it allows you to run a much higher voltage panel setup, which usually simplifies wiring, and reduces wiring losses (or wire costs). It also allows, in some cases, to hook up panels in a system that have different voltage or current ratings.

Also, you get bigger boost in cold weather - winter - which is when you need the extra power the most.

boB · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

You can certainly make up for no MPPT controller by adding more panels...

But then, you need more space to put them ! Space.... The final frontier, may just cost more than an MPPT controller in many cases.

boB

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

boB wrote: »

You can certainly make up for no MPPT controller by adding more panels...

But then, you need more space to put them ! Space.... The final frontier, may just cost more than an MPPT controller in many cases.

boB

hmm, I would say that most people who need a charge controller are off grid, and most people who live off grid have plenty of space.

there are rare exceptions, but for the most part imho if you are off the beaten path enough to need to make your own power, property was cheap enough for you to get a few acres.

boB · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

wild01 wrote: »

hmm, I would say that most people who need a charge controller are off grid, and most people who live off grid have plenty of space.

That's A very good point !

boB

nigtomdaw · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

Wild01 makes sense if maths and comparing smallish systems with generic parts from different manufacturers is considered.

But if planning a off grid system from scratch and future proofing is on the agenda then Manufactures like OB and Xantrex eventually make sense. These companies make complete systems which communicate with each other as well as working in one off systems. They design there components to talk with other system products in there portfolio and this has an added cost. They offer functions above and beyound basic PWM charge controllers like the best selling Xantrex C series and PWM Morning Star Controllers with added features that many will never use or required, but they are still inbuilt to there product line up to deliver what many customers want. Renewable Energy equipment is not on a DVD Blue Ray box shipping scale and with small volumes comes added cost.

The recent PV crash is good for every one but it wasnt always the case and it wont be if the future, thats why the clever people invented MPPT (IMHO) because last year when PV prices were high a quality MPPt CC made good financial sense above 800 watts of PV. ( approx)

Space ( Jim as we know it) isnt unlimited to all off gridders like me with a 2 acre patch that I own, but what about Rv's boats and city homes . I have a 2.4 kw array installed (optimum position)and have a 1.6 kw array to slot in some where. Space is not a issue, but distance and pleasing from the wifes point of view on location , with security and optimum harvest in mind without a MPPT equipped CC my options are serverly restricted

. Ive spent many hours planning the new location for my new array and without the flexibility of a MPPT unit I would be absolutely snookered. MPPT offers a great deal more than a 10-30% power harvest it offers a greater flexibility in location, costing of connections, keeping the wife happy and the grey matter thought process.

The $250 more for a quality 60a MPPT unit over a PWM 60a unit with optional display and limited functions and tune-ability is a small fish in the over all system cost factor. Just recall of my previous paragraph were location, efficency, wiring cost, keeping the wife happy aka as asthecics, and added functions that come with a FM60 or a XW60 ( I wont even mention what the new stand a lone Midnight Solar MPPT Classic promises to bring to the table ) I live off grid and when panels were costly a MPPT unit was a no brainer still is IMHO for the above reasons as the bigger issue on costs for long term off gridders sucess is battery life or death thus a battery monitor comes b4 the CC in a off grid enviorment , my advice is buy a quality battery monitor to look after your batteries then consider what funds are available for PV panels and affordable charge controllers. (simples)

wild01 · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

nigtomdaw, I would say that $300-$400 is more the price difference between a pwm 60 amp and a mppt 60 amp. looking at morningstar and xantrex for the pwm, and xantrex morningstar and outback (and hopefully midnite soon) for mppt.

I fully agree that for remote location they are handy, but at 12volt and 24 volt short run systems they are simply not cost effective. On 48 volt and or remote panel situations, by all means they are a good option.

at the current panel per watt price I would say an 60 amp mppt cc needs to be around $250 to $300 to make fiscal sense for the above systems.

as an example your 1.6kw add on array on a 12v sys would require 2 60 amp cc

nigtomdaw · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

A. Your missing the flexability that a MPPT unit affords you in site locations and added functions and wiring savings.

B. Your costings are way off even using ebay as a yard stick, you have to include the expensive LCD dispay which is a costly add on with the Xantrex C series and Morningstar amp for amp products and in the case of Xantrex the XW60 comes complete with a temp sender unit. Unlike the C series where the LCD monitor is $80+ and the temp sender is about $35+ Add to this the XW60 gives system logging and relay functions which doesnt happen on the PWM units trust me I own both !

You cant argue both ways you told boB that most off gridders arent short for space which corner do you want to fight in:p

If I was constructing an off grid 1.6 kw system it would not be at 12 volt nor 24 v it would be 48v yes Ive learn that lesson nearly 5 years ago, but I live with my system at 24 volts

On your final line on what price MPPT charge controllers should be priced at the latest is Outback recently increased the price of there MPPT units as they wernt making any money on them so a 250 / 300 $ quality 60a unit is not going to happen real soon

To have a real debate on MPPT CC for VFM you cant pick the worst senario than give them a kicking its like being the school bully, come on give them a fair hearing I gave you cudos on your maths but it was in the worst senario for MPPT units

n3qik · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

I also look at the cost difference, My setup has the display in the hallway and the CC in the basement, so here is the cost from our sponsor:

MPPT setup-
Xantrex XW MPPT 60 Amp Solar Charge Controller Price: $529.00
Xantrex XW System Control Panel (SCP)...............Price: $228.00
Total ....................................................................... $757.00

PWM setup-
Xantrex C60 60 Amp Solar Charge Controller..........Price: $189.05
Xantrex Battery temperature sensor 15 foot............Price: $27.55
Xantrex remote display for C35/40/60, 50 foot........Price: $119.70
Total......................................................................... $345.30

Difference is MPPT cost $ 411.70 more.

boB · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

Besides more space used, it does cost more for hardware just to mount the modules... Especially if they're going to be on poles.

With PWM and same nominal PV and battery voltage, there may be many times where either hot panels or partial shading will put the MPP Voltage at or below the battery voltage. Connecting the array at a higher voltage helps this problem tremendously, even for short wire runs. You can't take advantage of this scenario with a PWM controller.

And PV is still the most expensive part of a moderately sized system... so far anyway.

boB

niel · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

hmmm. my take on some of this is that some of these comments assume too much. those with mppt controllers are not always off grid as it could be an added off grid setup for somebody that uses the grid and use a off grid setup for dedicated items one may want separate from the normal grid items or is just too far from the grid wiring. there could be cost issues or utility connection issues that may have somebody elect to use one. hey that guy's cabin may not be able to use all of the land around him due to non-ownership and may not be able to cut down enough of the surrounding trees for optimal solar exposures, meaning- get as much as one can with what one can utilize. there's lots of scenarios here, even if going non gt is not the most efficient, but one could also have gt with battery backup. from these statements some of you have made it would make one think that you are either using a straight gt system or are in the middle of nowhere off grid and that's stereotyping that goes too far imho. the assumptions of those notions may be true in many cases, but not enough to warrant making it a rule of thumb.

Vic · December 2009

Re: does mppt really make $ense @12v with the crash in solar pricing

wild,

I'm with boB on this one. Think that he is not speaking of land, but rather a developed space for panels ... a roof, pole, or other area to accommodate racks or other mounts for the panels. This space needs to have good Solar exposure. AND, any racking scheme has cost. One needs more combiner space and breakers as panels are added, and so on ... more wire, conduit, labor + some upgrading of wire/pipe sizes etc.

My panels are placed on racks on a roof. This resource is limited. So, to me, it is simply not the cost of the panels, but rather, the total cost of the panel mounted and connected to the system such that it can deliver power.

Generally speaking, in Off-Grid systems, as one adds panels, one will run out of CC capacity to deal with the panels, such that more panels often means that another CC will be required. Often, this additional CC will be an MPPT unit, as they generally have the most current capability.

And in addition, the MPPT CCs are much more adjustable, have better readout of conditions, and often have months of recorded data, so they are generally much easier for the user of the system to configure, monitor and make fine adjustments.

Have no axe to grind here, will probably add some more panels soon, but am out of CC capacity, so will need to add an additional CC as well. AND it WILL be MPPT ...Am waiting for the Midnite Classic !!

Am a bit too preachy, I bet. Just MHO. HNY Vic

does mppt really make $ense @12v with the crash in solar pricing

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