Why would I want MPPT?

triumph406triumph406 Posts: 4Registered Users
Hi,
I'm newly registered here, but have read a lot of threads here, so this what I'm looking at.

I have a pop-up camper that I want to add solar too (flat no tilting), it has a heater with a fan, led lights, and I want to be able to use a laptop for work purposes. My intention is to be able to go out the desert, get away from it all and work, for maybe 3-5 days at a time. The laptop would ideally be a 17", but that requires a 130W powersupply, alternatively I would likely use a 15" laptop with a 70W power supply. I would run the laptop from either a dc-dc converter, or the Laptop cigarette lighter adapter. I haven't measured the power draw of the 15" laptop yet. I want to be able to work 12-14 hours a day on the laptop.

I'm looking at 2 Trojan T-105s for the battery banks.

For CC and panels I'm looking at:

1) a rogue 3048, and a 24v 270w panel. $394+$202.5 = $596.5 ($394 includes shipping)
2) a rogue 2048, and a 24v 270w panel $269+$202.5 = $471.5 ($269 includes shipping)
3) Tristar TS-45, temp comp thermocouple, and 2 x 120w panels $147 +$27 + $214 = $388

I like the idea of using the Rogue 3048, as I can add another 270w panel, plus as an engineer I like the bells and whistles, and now the data converter is included in the price, I can hook up the laptop and monitor the operation overtime.
The 2048 Rogue may be limited as to how many panels I can add in the future

This is the dilemma.

If I want to be cost effective, the Tristar TS-45 is the clear winner. I can add more panels in series and have more W's at a lower cost. It would seem that I can add another 120W panel, and offset any percieved advantage in using an MPPT CC.

There are times I may be up in the mountains (Big Bear, Sierras) where there may be significant shading.

And yes I have been overthinking this??

Thanks for taking the time to read this.

Comments

  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Why would I want MPPT?
    triumph406 wrote: »
    I haven't measured the power draw of the 15" laptop yet. I want to be able to work 12-14 hours a day on the laptop.

    I'm looking at 2 Trojan T-105s for the battery banks.

    Welcome to the forum,
    You are premature looking at batteries. You need to nail down your loads first. Do you know what the heater fan draws?
    triumph406 wrote: »
    There are times I may be up in the mountains (Big Bear, Sierras) where there may be significant shading.

    Will you have another source of electric power (vehicle alternator or small generator)?
    triumph406 wrote: »
    It would seem that I can add another 120W panel, and offset any perceived advantage in using an MPPT CC.

    You might be right... in a small system the expense of an MPPT is not always cost effective. One reason to use MPPT is that the least expensive panels require it because their voltages are too high to be efficient with a PWM controller. The money you save by using a PWM controller may be spent on the more expensive lower voltage panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Posts: 27,694Super Moderators admin
    Re: Why would I want MPPT?
    triumph406 wrote: »
    I have a pop-up camper that I want to add solar too (flat no tilting), it has a heater with a fan, led lights, and I want to be able to use a laptop for work purposes. My intention is to be able to go out the desert, get away from it all and work, for maybe 3-5 days at a time. The laptop would ideally be a 17", but that requires a 130W powersupply, alternatively I would likely use a 15" laptop with a 70W power supply. I would run the laptop from either a dc-dc converter, or the Laptop cigarette lighter adapter. I haven't measured the power draw of the 15" laptop yet. I want to be able to work 12-14 hours a day on the laptop.

    Get yourself a Kill-a-Watt type meter and plug in your laptops and run them for at least 24 hours (each) as you would be using them in the field.

    Computers are probably (on average) the 2nd worst off grid loads after a refrigerator... If you have a low power/efficient net book type--You may get 200-400 WH per day... If you go with a 17", full power, etc. and you may be looking at ~1,000 WH per day (just about the same amount of power as a full size Energy Star Refrigerator).

    If you want to use a 12 VDC power supply for the computers, you can get a Doc Watson type DC AH/WH meter to measure your DC usage.

    Accurate power measurements are going to be a big help for you. Computer usage is highly variable. Nailing down your needs will be a big help.

    Personally, I really like a small 120 VAC inverter--DC adapters are a pain--And some do not like the higher DC voltages you find when charging deep cycle batteries. Many are designed for cars with ~12.5 to 14.4 volt range. A true deep cycle system will run from 10.5 to 15.0 or even 16.0 volts (very cold batteries, some industrial batteries need higher charging voltages).
    I'm looking at 2 Trojan T-105s for the battery banks.

    Typically, for off grid cabin use, we would suggest 2 days of storage and 50% maximum discharge, which will be ~25% discharge per day:

    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 1/2 days of storage * 0.50 maximum discharge = 574 Watt*Hours average per night

    But, for an RV/Small trailer--You might choose 1 day of storage and 50% discharge, or even to pull down the batteries to 20% SOC over night (battery replacement more often--But for RV's, the usually are used only a few weeks or months a year--Not daily for 9+ months a year).

    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 1 days of storage * 0.50 maximum discharge = 1,148 Watt*Hours average one night
    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 0.80 maximum discharge = 1,836 Watt*Hours draining all useful energy from battery

    For CC and panels I'm looking at:
    1) a rogue 3048, and a 24v 270w panel. $394+$202.5 = $596.5 ($394 includes shipping)
    2) a rogue 2048, and a 24v 270w panel $269+$202.5 = $471.5 ($269 includes shipping)
    3) Tristar TS-45, temp comp thermocouple, and 2 x 120w panels $147 +$27 + $214 = $388

    I like the idea of using the Rogue 3048, as I can add another 270w panel, plus as an engineer I like the bells and whistles, and now the data converter is included in the price, I can hook up the laptop and monitor the operation overtime.
    The 2048 Rogue may be limited as to how many panels I can add in the future

    Any of those would be good choices... Midnite solar is coming out with a new mid-sized MPPT controller.

    http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=43&productCatName=Charge%20Controllers%20-%20KID
    If I want to be cost effective, the Tristar TS-45 is the clear winner. I can add more panels in series and have more W's at a lower cost. It would seem that I can add another 120W panel, and offset any perceived advantage in using an MPPT CC.

    MPPT controllers are very helpful if you have 1) a long distance from array to battery shed -- Or 2) if you can buy large panels for less $$$/Watt (usually larger arrays >~800 watts or so).

    For RVs, many times the smaller (150 Watt or smaller) panels fit better and are available in Vmp~17.5 volts -- Which is fine for PWM controllers.
    There are times I may be up in the mountains (Big Bear, Sierras) where there may be significant shading.

    Shading kills solar array/panel output... Just assume that any shading will knock out a panel or a string of panels (depending on array configuration). There is nothing you can do that will "fix" shading issues other than parking where there is no shade--Or some folks will park the RV in shade (keep cool) and put some panels in the sun (stake to ground to reduce chance of blowing over/theft).
    And yes I have been overthinking this??

    Yes--But that is how you will learn. Focus on the loads first. That will define the battery bank size. Loads+Battery bank size then define the size of the array (or alternate charging such as small genset, etc.).

    In the end, it is a balancing act. The battery is what you want to treat "well". They are easy to "kill". The rest of the hardware is less of a problem (add more solar panels when needed, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • triumph406triumph406 Posts: 4Registered Users
    Re: Why would I want MPPT?
    vtmaps wrote: »
    Welcome to the forum,--vtMaps
    Thanks!!
    vtmaps wrote: »
    You are premature looking at batteries. You need to nail down your loads first. Do you know what the heater fan draws?
    --vtMaps
    Not yet, as far as I know it draws a lot of current, I'll get out a meter on it to see what 'a lot' is. I don't use the heater, but my wife does. The camper is small, 5 minutes of running the heater gets the interior like a sauna!
    vtmaps wrote: »
    Will you have another source of electric power (vehicle alternator or small generator)?
    --vtMaps

    In all the camping we have done we've only ever had 2 occasions where we had access to a hookup. We don't carry a generator, but hooking up to the vehicle alternator is possible.
    vtmaps wrote: »
    You might be right... in a small system the expense of an MPPT is not always cost effective. One reason to use MPPT is that the least expensive panels require it because their voltages are too high to be efficient with a PWM controller. The money you save by using a PWM controller may be spent on the more expensive lower voltage panels.
    --vtMaps
    I guess that's what my conclusion has been. The Tristar TS-45 is reasonably priced, plus you can adjust it's set points.
  • triumph406triumph406 Posts: 4Registered Users
    Re: Why would I want MPPT?
    BB. wrote: »
    Get yourself a Kill-a-Watt type meter and plug in your laptops and run them for at least 24 hours (each) as you would be using them in the field.

    Computers are probably (on average) the 2nd worst off grid loads after a refrigerator... If you have a low power/efficient net book type--You may get 200-400 WH per day... If you go with a 17", full power, etc. and you may be looking at ~1,000 WH per day (just about the same amount of power as a full size Energy Star Refrigerator).

    If you want to use a 12 VDC power supply for the computers, you can get a Doc Watson type DC AH/WH meter to measure your DC usage.

    Accurate power measurements are going to be a big help for you. Computer usage is highly variable. Nailing down your needs will be a big help.

    Personally, I really like a small 120 VAC inverter--DC adapters are a pain--And some do not like the higher DC voltages you find when charging deep cycle batteries. Many are designed for cars with ~12.5 to 14.4 volt range. A true deep cycle system will run from 10.5 to 15.0 or even 16.0 volts (very cold batteries, some industrial batteries need higher charging voltages).

    I have a Kill-a-watt meter, I didn’t think of using that, I was relying on the maximum of the powersupply as a guide.
    None of my laptops are of the low power type. I do have a lot of spare batteries, so that might help, I can use up the spare batteries before I use camper battery power.

    BB. wrote: »
    Typically, for off grid cabin use, we would suggest 2 days of storage and 50% maximum discharge, which will be ~25% discharge per day:

    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 1/2 days of storage * 0.50 maximum discharge = 574 Watt*Hours average per night

    But, for an RV/Small trailer--You might choose 1 day of storage and 50% discharge, or even to pull down the batteries to 20% SOC over night (battery replacement more often--But for RV's, the usually are used only a few weeks or months a year--Not daily for 9+ months a year).

    So the CC/panel combination would be sized to bring the batteries back to 100% SOC every day, even if I go down to 20% SOC overnight? My plan is to be independent for many days at a time, i.e. get away from civilisation.
    BB. wrote: »

    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 1 days of storage * 0.50 maximum discharge = 1,148 Watt*Hours average one night
    2x 225 AH * 6 volt per battery * 0.85 AC inverter eff * 0.80 maximum discharge = 1,836 Watt*Hours draining all useful energy from battery

    Let’s say the Kill-a-watt confirms that a laptop needs 60W to run, I assume then that if run it for 12 hours, then I need 60W*12hrs = 720W going into the batteries. So if I get 10 hours of sun, then I need at least 720W/10hrs/14.8v = 4.9A into the battery minimum. Is that correct?


    BB. wrote: »
    MPPT controllers are very helpful if you have 1) a long distance from array to battery shed -- Or 2) if you can buy large panels for less $$$/Watt (usually larger arrays >~800 watts or so).

    For RVs, many times the smaller (150 Watt or smaller) panels fit better and are available in Vmp~17.5 volts -- Which is fine for PWM controllers.

    From the panel to the CC will be less than 10’, and less than 3’ from the CC to the batteries.
    BB. wrote: »
    Shading kills solar array/panel output... Just assume that any shading will knock out a panel or a string of panels (depending on array configuration). There is nothing you can do that will "fix" shading issues other than parking where there is no shade--Or some folks will park the RV in shade (keep cool) and put some panels in the sun (stake to ground to reduce chance of blowing over/theft).

    Understood, these panels will be mounted flat to the top of the camper. I had thought of mounting them to a tripod externally that I can move around to get the best sun advantage. However I’m lazy, so hard mounting them to the camper is better (for me)
    BB. wrote: »

    Yes--But that is how you will learn. Focus on the loads first. That will define the battery bank size. Loads+Battery bank size then define the size of the array (or alternate charging such as small genset, etc.).

    In the end, it is a balancing act. The battery is what you want to treat "well". They are easy to "kill". The rest of the hardware is less of a problem (add more solar panels when needed, etc.).

    -Bill


    I just killed the battery on my Coralla, another +$60 down the drain. Could I use a voltmeter on the wall to tell me when to stop draining from the batteries, or should I use a Trimetric or similar to tell me the state of charge?
  • BB.BB. Posts: 27,694Super Moderators admin
    Re: Why would I want MPPT?
    triumph406 wrote: »
    I have a Kill-a-watt meter, I didn’t think of using that, I was relying on the maximum of the powersupply as a guide.
    None of my laptops are of the low power type. I do have a lot of spare batteries, so that might help, I can use up the spare batteries before I use camper battery power.

    In the end--Energy use is a highly personal set of choices.... What works best for you. Lead Acid batteries have a limited operating range (state of charge, charge/discharge rates/floating/setting unused, etc.) where they are happy. If you can supplement with battery backs for your computers--Why not. In summer, will probably have more than enough power--In winter, you will have to make trade-offs.

    If the Lead Acid battery is kept "small"--Then replacing every 1-3 years may not be a bad trade-off.
    So the CC/panel combination would be sized to bring the batteries back to 100% SOC every day, even if I go down to 20% SOC overnight? My plan is to be independent for many days at a time, i.e. get away from civilization.

    The rules of thumbs we (I) use around here are usually designed around an off grid power system that supplies power daily for 9+ months a year.

    RV systems are (usually) used on weekends or short trips, with one or two longer trips a year (which may involve driving--setup to do some charging from the vehicle power system) or not (pick RV parks, backup genset like a Honda eu1000i or eu2000i and a few gallons of gasoline).

    If you want to use X,000 Watt*Hours per day--Ideally you should have enough (under average sun) to recharge the batteries every day.

    Batteries, you can have a battery bank 4x your daily load and go on a trip, and a combination of panels+battery storage to give you 3-4 days of off site power, then recharge on your way back home.

    Or, you can have a battery that is 1/0.8 = 1.25x your daily load and recharge it every day (panels+genest+etc.). Battery will be deeply cycled, but probably will still last 1-3 years (if never taken dead). 3 batteries that last 3-5 years vs 1 battery that lasts 1-2 years--Same overall costs, physically smaller battery bank in RV, less weight, etc... But no carry over if the second day if there is no sun and no generator... Your choice?
    Let’s say the Kill-a-watt confirms that a laptop needs 60W to run, I assume then that if run it for 12 hours, then I need 60W*12hrs = 720W going into the batteries. So if I get 10 hours of sun, then I need at least 720W/10hrs/14.8v = 4.9A into the battery minimum. Is that correct?

    You need to pay attention to battery charging too... Laptop may run 30 watts (set to power conserve mode) and charging another 30 watts if battery is not full--So you can be double counting your power usage vs just leaving computer plugged into AC inverter power. That is why it is nice to put the laptop/loads on Kill-a-Watt type meter for a few days and get your "real life" average usage.

    Or you can end up with an off grid capacity that is 1/2 or 2x your "real needs"--Neither is a great fall back position.
    From the panel to the CC will be less than 10’, and less than 3’ from the CC to the batteries.

    Yep--A PWM controller (less cost) plus ~140 watt 17.5 volt or so Vmp panels (more expensive) may pencil out the the best costs.

    Note in very hot water, Vmp-array can fall below optimum charging conditions for cool battery banks and MPPT controller (with "high" voltage Vmp-array configuration) will provide better hot day charging--But this is usually not an issue for RV systems (don't need to equalize batteries at high charging voltages when on a trip).
    Understood, these panels will be mounted flat to the top of the camper. I had thought of mounting them to a tripod externally that I can move around to get the best sun advantage. However I’m lazy, so hard mounting them to the camper is better (for me)

    What works best for you. Tripod mounts are usually not a good idea unless they can be staked down and withstand 20-40 MPH winds--Panels are easy to blow over and break.
    I just killed the battery on my Coralla, another +$60 down the drain. Could I use a voltmeter on the wall to tell me when to stop draining from the batteries, or should I use a Trimetric or similar to tell me the state of charge?

    It helps... The "gold standard" is using a hydrometer. You can match hydrometer readings to your typical system usage and get an estimate of when to cut back on power usage (i.e., around ~11.5 to 12.0 volts, start thinking about reducing energy usage). Battery voltage is very dependent on State of Charge, charging/discharge current levels, temperature, age, etc.). As you watch your bank/installation, you will pick numbers that make sense for you.

    There are "smart volt meters" that can make better "guesses":

    http://www.solar-electric.com/mnbcm.html
    http://www.smartgauge.co.uk/smartgauge.html

    Battery Monitors usually work a bit better--You put a current shunt (precision resistor) to measure current flow into/out of the battery bank. However, they require programming and do drift from actual SoC over time. Typically the use something like >14.5 volts for 2+ hours to reset back to 100%, etc... Very handy for day to day use (and probably about mandatory for Sealed/AGM batteries). Not cheap, but if you save from killing or to two battery banks, can be worth the extra money:

    http://www.solar-electric.com/metersmonitors.html (Trimetric popular meter)
    http://www.victronenergy.com/battery-monitors/bmv-600s%20and%20bmv-602s/

    Just watching with a volt meter can tell you a lot... If you do not see >14.4 volts for 1-4 hours per day when the sun is up--There is a good chance the battery bank is not getting fully recharged.

    If you see <11.5 volts--You are looking at serious battery state of charge questions.

    Regarding the Corolla battery... A standard automotive battery will discharge by 15% and quickly recharge very nicely. If you take the battery down by 25% or more often (i.e., parking waiting to pick up family members at after school activities while using a computer--Did lots of that), the battery will not last that long (my three year old battery is starting to crank my Honda Accord slowly again--About time to get a new battery).

    You can use a Deep Cycle battery as a car battery... In theory, it will have about 20% less starting current--Usually not an issue. And, ideally, it should be recharged with a higher voltage (normal care is ~13.8-14.2 volts charging--Deep cycle typically is ~14.5 to 14.75 volts). Deep AGMs use lower charging voltage (14.2-14.4 volts typical) and can be very nice as a car battery (except for the 2x increase in cost).

    But you have to find Deep Cycle AGMs, there are many types and the label is not always clear. For example Optima batteries where both the top and case colors matter:
    REDTOP®: Use this for normal engine starting where an alternator immediately monitors the state of charge and provides energy to the battery whenever it is needed. This would describe most stock vehicles.
    • Automotive and RV underhood starting
    • Heavy equipment where starting is the primary function
    • Diesel-powered vehicles with no aftermarket electronics
    • Dark Gray Case not-deep cycle [-BB]

    YELLOWTOP®: Use this when electrical loads are higher than average, or when the discharge cycle is more than typical engine starting, such as vehicles without alternators. This also includes vehicles with significant electrical loads that may exceed the average alternator output (for example, aftermarket audio systems, GPS, chargers, winches, snowplows, inverters, drag cars). This can also include vehicles that have a lot of electronics from the factory, such as a minivan with power sliding doors and a DVD player, especially if the DVD player is used when the engine isn’t running.

    • Racing vehicles without a charging system (alternator or generator)
    • Dedicated drag-racing vehicles
    • Diesel-powered vehicles with aftermarket electronics
    • Car audio/video applications exceeding 250 watts over the OE system
    • Vehicles or heavy equipment with inverters, hydraulics, winches or other accessories
    • Electric vehicles
    • Light Gray Case deep cycle [-BB]

    BLUETOP®: The BLUETOP® starting battery (dark gray case) is to be used when a dedicated starting battery is required; it should never be used for cycling duty. The dual-purpose BLUETOP® (light gray case) can be used for both starting and deep cycling; it is a true deep-cycle battery with extremely high cranking power.

    • Trolling motors, marine applications with heavy electrical accessories and RVs should use a dual-purpose BLUETOP® (which is both a starting and deep-cycle battery)
    • Use a BLUETOP® starting battery for marine applications and RVs when the battery’s only function is engine starting

    Note: The difference between BLUETOP® and YELLOWTOP® deep-cycle batteries is that BLUETOP® batteries have both automotive (SAE) posts and threaded studs, while YELLOWTOP®S (other than D31T) only have SAE terminals.

    If you ever get confused on the colored tops, just remember: if it has a dark gray case, then it’s a starting battery; if it has a light gray case, then it’s a deep-cycle (dual-purpose) battery.

    I may see if I can slide a Light Gray Optima in my Honda (fit, terminal location, cost). Let you know in three years how it works out.

    I have found that Costco sells (on average) heavier batteries (more lead) than the typical O'Reilly autoparts battery. And I have found I can sometimes fit a larger battery in the vehicle--with the +/- terminals reversed--And I can "reroute" the cables to fit the larger battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,801Solar Expert ✭✭✭✭
    Re: Why would I want MPPT?
    triumph406 wrote: »
    ....There are times I may be up in the mountains (Big Bear, Sierras) where there may be significant shading.....

    At those times, with even a small amount of shade on your panels, do not expect any charging to happen. neither style of controller can invent power.


    As to "cost effective" with PWM, you loose at least 20% of potential harvest, because of voltage mismatch. MPPT ameliorates this with 95% efficiency.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Posts: 27,694Super Moderators admin
    Re: Why would I want MPPT?
    mike95490 wrote: »
    As to "cost effective" with PWM, you loose at least 20% of potential harvest, because of voltage mismatch. MPPT ameliorates this with 95% efficiency.

    I am not sure that in warm/hot weather that a properly configured array for PWM vs MPPT will see much difference (get Vmp-array depression with hot solar cells, that cuts MPPT output vs cold panels).

    In cold weather, especially sub-freezing weather when Vmp-array increases by 10-20%--Yes, certainly.

    If you have a miss-configured array (i.e., Vmp~30 volts on a PWM + 12 volt battery bank), yep, you will lose ~40% of available array output power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zonebluezoneblue Posts: 1,218Solar Expert ✭✭✭✭
    Re: Why would I want MPPT?

    Something about your numbers dont look completely happy to me. A laptop that draws 60W, running for 12+ hours is quite a bit of power for a roof that is of necessity, rather small. Lets hope its flattish and uncluttered, and that you are willing to cover every sq inch of it, and that your desert has nice high sun hours.

    For a motorvehicle in this situation id be possibly designing backwards. With the available area of PV, what can i run...

    The first question for research is how many sun hours per day, for the target season. That will dictate how much PV power you can produce. Then, say we can generate X Wh/day, what size laptop will run on that? etc.

    The other route would be inverter genset, but if you want to concentrate, which i presume you do, that could be problematic.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • triumph406triumph406 Posts: 4Registered Users
    Re: Why would I want MPPT?
    zoneblue wrote: »
    Something about your numbers dont look completely happy to me. A laptop that draws 60W, running for 12+ hours is quite a bit of power for a roof that is of necessity, rather small. Lets hope its flattish and uncluttered, and that you are willing to cover every sq inch of it, and that your desert has nice high sun hours.

    For a motorvehicle in this situation id be possibly designing backwards. With the available area of PV, what can i run...

    The first question for research is how many sun hours per day, for the target season. That will dictate how much PV power you can produce. Then, say we can generate X Wh/day, what size laptop will run on that? etc.

    The other route would be inverter genset, but if you want to concentrate, which i presume you do, that could be problematic.

    I can get 2x270W panels on the roof, it's a tight fit, but it will work, or 3x120w(12V) panels side by side, and one across the front. I'm adding gas struts to the roof, so lifting the roof with the panels shouldn't be too hard (famous last words)
  • BB.BB. Posts: 27,694Super Moderators admin
    Re: Why would I want MPPT?

    To quote Tim Taylor from Tool Time: "More Power!"

    Home Improvement (TV series) - Wikipedia


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.