Attention: TDR Forum Junkies Here comes another really long and wordy Dieselman reply..... But I am a solar fanatic because of the remote radio sites I build.
No, there isn't any real concern regarding leaving your solar system connected even when hooked to your rig... . unless you wear a pocket protector
There are actually 3 types of charger/regulators.
The simple charge controller which is a relay that either places the panel across the battery or shorts out the solar panel.
PWM, which essentially does the same thing except it charges the battery by 'pulsing' power across the load/battery when the voltage is below the set-point, and decreases the width of the pulses as the voltage increases, up to the shut off point.
MPPT Solar Tracking, this is the pocket protector types favorite. Solar tracking is not the mechanical tilting of the panels, but is instead the tracking of voltage and current, essentially impedance, between the solar panel and the battery/load.
I stole most of the rest of this reply from my friend Pat Luzon's website, because I'm too lazy to type it And he is the proud though non-TDR member/owner of a new 3500 DRW. A brief shameless commercial plug in exchange for my plagerism... . http://www.windsun.com
OK, to continue.....
A MPPT, or maximum power point tracker is an electronic DC to DC converter that optimizes the match between the solar array (PV panels), and the battery bank. (These are usually called power trackers for short - not to be confused with PANEL trackers, which are a top-of-pole panel mount that follows, or tracks, the sun).
So what do you mean by "optimize"?
Solar cells are neat things. Unfortunately, they are not very smart. Neither are batteries - in fact batteries are downright stupid. Most PV panels are built to put out a nominal 12 volts. The catch is nominal. In actual fact, almost all are designed to put out from 15 to 20 volts, with most being in the 16. 0 to 18. 0 volt range. The catch is, is that a nominal 12 volt battery is pretty close to an actual 12 volts - 10. 5 to 13. 2 volts, depending on state of charge. Under charge, most batteries want from around 13. 4 to 14. 4 volts - quite a bit different than what most panels are designed to put out.
OK, so now we have this neat 75 watt panel. Catch #1 is that it is rated at 75 watts at a particular voltage and current. The Siemens SP-75 is rated at 4. 4 amps at 17 volts - 4. 4 times 17 = 75 watts. Other brands and types have very similar ratings.
Where did my Watts go?
So what happens when you hook up this 75 watt panel to your battery? Unfortunately, what happens is not 75 watts.
Your panel puts out 4. 4 amps. Your battery is setting at 14 volts under charge: 4. 4 amps times 14 volts = 61. 6 watts. You lost 14 watts, or almost 20% of your power. That 18 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery. With a very low battery, say 11 volts, it's even worse - you could be losing as much as 35% (11 volts x 4. 4 amps = 48 watts.
One solution that pops to mind is - why not just make panels so that they put out 14 volts or so to match the battery?
Catch #22a is that the panel is rated at 75 watts at full sunlight at a particular temperature (25C). If you have a cloudy day, or the temperature is high, you don't get 17 volts. (actually, temperature is the most important factor, as lowered light reduces the AMPS quite a bit, but the voltage only a little, up to a point). At the temperatures seen in many hot climate areas, you might get 15 volts. If you started with 15 volts (as in some of the so-called "self regulating" panels), you are in trouble, as you won't have enough voltage to put a charge into the battery. The panel will just sit there looking dumb, and your batteries will get even stupider than usual. Nobody likes a stupid battery.
Maximum power point tracking - this is electronic tracking, and has nothing to do with moving the panels. Instead, the controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the absolute best power that the panel can put out. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Most modern MPPT's are around 92-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-20% in summer.
How Maximum Power Point Tracking works
Here is where the optimization, or maximum power point tracking comes in. A MPPT takes that 17 volts at 4. 4 amps and converts it, so that what it puts out to the battery is no longer 4. 4 amps at 17 volts, but 5. 77 amps at 13 volts. Now you still have 75 watts, and everyone is happy. (Actually, you get about 72 watts, as PPT's are not quite 100% efficient). In an extreme case, such as a fully discharged battery at 10. 5 volts, you would get nearly 7 amps at 10. 5 volts out of the MPPT into the battery.
A MPPT tracks the maximum power point, which is going to be different from the STC (Standard Test Conditions) rating under almost all situations. Under very cold conditions a 75 watt panel is actually capable of putting over 80 watts because the output goes up as temperature goes down - but if you don't have some way of tracking that power point, you are going to lose it. On the other hand under very hot conditions, the power drops - you lose power as the temperature goes up.
MPPT's are most effective under these conditions:
Winter, and/or cloudy or hazy days - when the extra power is needed the most.
Cold weather - solar panels work better at cold temperatures, but without a max power tracker you are losing most of that. Cold weather is most likely in winter - the time when sun hours are low and you need the power the most.
Low battery charge - the lower the state of charge in your battery, the more current a MPPT puts into them - another time when the extra power is needed the most. You can have both of these conditions at the same time.
Catch 22b: Some MPPT's on the market don't give you as much you would hope for. The reason is efficiency. So you gain 25% by adding a MPPT - that does not help you much if your MPPT is 85% efficient. You've only gained about 5 watts - not much to get excited about. It's an unfortunate fact of life that so far the only PPT we have seen that really approaches 98% under all conditions is the AERL Maximizer (made in Australia). The RV Power Products "Solar Boost" can approach 97%, but typical is more like 92% to 96% - still a good gain, but not ideal. It is also much better than older designs, which averaged around 75% to 85% - almost a waste of time except for water pumping systems. Although nobody has been able to match the AERL performance in the 15 years that they we have been selling them, their market has always been pretty small because they are very expensive (3 to 8 times other brands). The new MX60 MPPT 60 amp charge controller made by Outback products is rated at 97 to 99% efficiency - we have not had a chance to do long term measurements on it yet, but so far it appears to be a very good unit, although a tad pricey at around $500, it is still much cheaper than the AERL unit or buying extra panels.
What a Maximum Power Point Tracker is:
The Power Tracker™ is a high frequency DC to DC converter. They take the DC input from the solar panels, change it to AC, and convert it to a different DC voltage and current to exactly match the panels to the batteries. MPPT's operate at very high audio frequencies, in the 20-50 kHz range. The advantage of high frequency circuits is that they can be designed with very high efficiency transformers and small components. The design of high frequencies circuits can be very tricky because the problems with portions of the circuit "broadcasting" just like a radio transmitter. Noise isolation and suppression becomes very important. The advantage of using high frequency is that high efficiency is easier to achieve, and component parts, especially transformers, can be made much smaller.
The power point tracker (and all DC to DC converters) operates by taking the DC input current, changing it to AC, running through a transformer (usually a toroid, a doughnut looking transformer), and then rectifying it back to DC, followed by the output regulator. In most converters, this is strictly an electronic process - no real smarts are involved except for some regulation of the output voltage or current. This is the type of conversion used in the RV Power Products brand MPPT's. You don't get quite the full efficiency as you do in the "smart" ones, but the price is considerably less - and you still gain 15 to 30% under most conditions. The AERL MPPT's are microprocessor controlled, but do not have a computer interface. They do, however, have some models that will match almost anything to anything, up to 185 volts, and have the best conversion efficiency of any MPPT.
I have a couple of Concorde AGM batteries, an RV Products 50 Amp MPPT, and two 100 watt panels powering a 2Kw True Sine inverter. I need to finish the three way transfer switch installation, Shore/Gen/Inverter in my Desert Fox similar to Erics.
Whew... DM.
No, there isn't any real concern regarding leaving your solar system connected even when hooked to your rig... . unless you wear a pocket protector
There are actually 3 types of charger/regulators.
The simple charge controller which is a relay that either places the panel across the battery or shorts out the solar panel.
PWM, which essentially does the same thing except it charges the battery by 'pulsing' power across the load/battery when the voltage is below the set-point, and decreases the width of the pulses as the voltage increases, up to the shut off point.
MPPT Solar Tracking, this is the pocket protector types favorite. Solar tracking is not the mechanical tilting of the panels, but is instead the tracking of voltage and current, essentially impedance, between the solar panel and the battery/load.
I stole most of the rest of this reply from my friend Pat Luzon's website, because I'm too lazy to type it
And he is the proud though non-TDR member/owner of a new 3500 DRW. A brief shameless commercial plug in exchange for my plagerism... . http://www.windsun.comOK, to continue.....
A MPPT, or maximum power point tracker is an electronic DC to DC converter that optimizes the match between the solar array (PV panels), and the battery bank. (These are usually called power trackers for short - not to be confused with PANEL trackers, which are a top-of-pole panel mount that follows, or tracks, the sun).
So what do you mean by "optimize"?
Solar cells are neat things. Unfortunately, they are not very smart. Neither are batteries - in fact batteries are downright stupid. Most PV panels are built to put out a nominal 12 volts. The catch is nominal. In actual fact, almost all are designed to put out from 15 to 20 volts, with most being in the 16. 0 to 18. 0 volt range. The catch is, is that a nominal 12 volt battery is pretty close to an actual 12 volts - 10. 5 to 13. 2 volts, depending on state of charge. Under charge, most batteries want from around 13. 4 to 14. 4 volts - quite a bit different than what most panels are designed to put out.
OK, so now we have this neat 75 watt panel. Catch #1 is that it is rated at 75 watts at a particular voltage and current. The Siemens SP-75 is rated at 4. 4 amps at 17 volts - 4. 4 times 17 = 75 watts. Other brands and types have very similar ratings.
Where did my Watts go?
So what happens when you hook up this 75 watt panel to your battery? Unfortunately, what happens is not 75 watts.
Your panel puts out 4. 4 amps. Your battery is setting at 14 volts under charge: 4. 4 amps times 14 volts = 61. 6 watts. You lost 14 watts, or almost 20% of your power. That 18 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery. With a very low battery, say 11 volts, it's even worse - you could be losing as much as 35% (11 volts x 4. 4 amps = 48 watts.
One solution that pops to mind is - why not just make panels so that they put out 14 volts or so to match the battery?
Catch #22a is that the panel is rated at 75 watts at full sunlight at a particular temperature (25C). If you have a cloudy day, or the temperature is high, you don't get 17 volts. (actually, temperature is the most important factor, as lowered light reduces the AMPS quite a bit, but the voltage only a little, up to a point). At the temperatures seen in many hot climate areas, you might get 15 volts. If you started with 15 volts (as in some of the so-called "self regulating" panels), you are in trouble, as you won't have enough voltage to put a charge into the battery. The panel will just sit there looking dumb, and your batteries will get even stupider than usual. Nobody likes a stupid battery.
Maximum power point tracking - this is electronic tracking, and has nothing to do with moving the panels. Instead, the controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the absolute best power that the panel can put out. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Most modern MPPT's are around 92-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-20% in summer.
How Maximum Power Point Tracking works
Here is where the optimization, or maximum power point tracking comes in. A MPPT takes that 17 volts at 4. 4 amps and converts it, so that what it puts out to the battery is no longer 4. 4 amps at 17 volts, but 5. 77 amps at 13 volts. Now you still have 75 watts, and everyone is happy. (Actually, you get about 72 watts, as PPT's are not quite 100% efficient). In an extreme case, such as a fully discharged battery at 10. 5 volts, you would get nearly 7 amps at 10. 5 volts out of the MPPT into the battery.
A MPPT tracks the maximum power point, which is going to be different from the STC (Standard Test Conditions) rating under almost all situations. Under very cold conditions a 75 watt panel is actually capable of putting over 80 watts because the output goes up as temperature goes down - but if you don't have some way of tracking that power point, you are going to lose it. On the other hand under very hot conditions, the power drops - you lose power as the temperature goes up.
MPPT's are most effective under these conditions:
Winter, and/or cloudy or hazy days - when the extra power is needed the most.
Cold weather - solar panels work better at cold temperatures, but without a max power tracker you are losing most of that. Cold weather is most likely in winter - the time when sun hours are low and you need the power the most.
Low battery charge - the lower the state of charge in your battery, the more current a MPPT puts into them - another time when the extra power is needed the most. You can have both of these conditions at the same time.
Catch 22b: Some MPPT's on the market don't give you as much you would hope for. The reason is efficiency. So you gain 25% by adding a MPPT - that does not help you much if your MPPT is 85% efficient. You've only gained about 5 watts - not much to get excited about. It's an unfortunate fact of life that so far the only PPT we have seen that really approaches 98% under all conditions is the AERL Maximizer (made in Australia). The RV Power Products "Solar Boost" can approach 97%, but typical is more like 92% to 96% - still a good gain, but not ideal. It is also much better than older designs, which averaged around 75% to 85% - almost a waste of time except for water pumping systems. Although nobody has been able to match the AERL performance in the 15 years that they we have been selling them, their market has always been pretty small because they are very expensive (3 to 8 times other brands). The new MX60 MPPT 60 amp charge controller made by Outback products is rated at 97 to 99% efficiency - we have not had a chance to do long term measurements on it yet, but so far it appears to be a very good unit, although a tad pricey at around $500, it is still much cheaper than the AERL unit or buying extra panels.
What a Maximum Power Point Tracker is:
The Power Tracker™ is a high frequency DC to DC converter. They take the DC input from the solar panels, change it to AC, and convert it to a different DC voltage and current to exactly match the panels to the batteries. MPPT's operate at very high audio frequencies, in the 20-50 kHz range. The advantage of high frequency circuits is that they can be designed with very high efficiency transformers and small components. The design of high frequencies circuits can be very tricky because the problems with portions of the circuit "broadcasting" just like a radio transmitter. Noise isolation and suppression becomes very important. The advantage of using high frequency is that high efficiency is easier to achieve, and component parts, especially transformers, can be made much smaller.
The power point tracker (and all DC to DC converters) operates by taking the DC input current, changing it to AC, running through a transformer (usually a toroid, a doughnut looking transformer), and then rectifying it back to DC, followed by the output regulator. In most converters, this is strictly an electronic process - no real smarts are involved except for some regulation of the output voltage or current. This is the type of conversion used in the RV Power Products brand MPPT's. You don't get quite the full efficiency as you do in the "smart" ones, but the price is considerably less - and you still gain 15 to 30% under most conditions. The AERL MPPT's are microprocessor controlled, but do not have a computer interface. They do, however, have some models that will match almost anything to anything, up to 185 volts, and have the best conversion efficiency of any MPPT.
I have a couple of Concorde AGM batteries, an RV Products 50 Amp MPPT, and two 100 watt panels powering a 2Kw True Sine inverter. I need to finish the three way transfer switch installation, Shore/Gen/Inverter in my Desert Fox similar to Erics.
Whew... DM.
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