MPPT PV voltage

drraptor

it's 9:30 in the morning, battery is being drained, but the Voltage I see on my PV array is 13.7V and voltage on battery is 12.1V.
PV array total VOC is around 58V. CC is a EPSolar MPPT 3215RN. Isn't it strange ?

BB.

Re: MPPT PV voltage

How much current is the controller pulling from the array (and/or outputting to the array). What is the array Wattage? Is the array in good sun at that time?

It sounds like 1) the array is not in full sun (off angle to sun, shading, etc.)--Low array power/current prevents the MPPT controller from stable operations. Or 2) the MPPT controller is not functioning correctly/as expected--It is operating like a PWM controller--Not as a MPPT controller.

-Bill

drraptor

Re: MPPT PV voltage

I recorded the following right now
@10:25
Array current 3.64A
CC current 4.58
Array voltage 14.81
CC output voltage 13.63
Battery voltge (measured on terminals) 13.49.

Weather according to google
35C/95F
Haze

mike95490

Re: MPPT PV voltage

drraptor wrote: »

I recorded the following right now
@10:25
Array current 3.64A
CC current 4.58
Array voltage 14.81
CC output voltage 13.63
Battery voltge (measured on terminals) 13.49.

So your MPPT gain/effectiveness is low. your PV should be up around 18V. In fact, it seems to me, that you may be nearly (80%) of full charge, and the controller has dropped back to PWM mode, where input V = batt V.

niel

Re: MPPT PV voltage

the fact that you have a draw down on the pv voltage is normal. this can be a sign things are doing well in its utilization for your 12v battery. even without a cc on it the pv voltage will be drawn down toward the battery voltage, but never quite reaching it. i see this from my setup all of the time. as the draw is lessened by the battery through your mppt cc, the voltage read at the pvs will rise.

drraptor

Re: MPPT PV voltage

Today @ 9:55
PV current 3.36A
PV Voltage 49.2V
CC current 11.64A
CC output Voltage 12.83V
Battery Voltage 12.51V
Load current between 8-12A

Weather according to google
36C/97F
haze

So now that extra voltage is being converted to actual current, which wasn't the case yesterday, and this seems odd.

niel

Re: MPPT PV voltage

that looks fine to me.

now before when you sited this, "CC output voltage 13.63 Battery voltge (measured on terminals) 13.49." that could be a sign there is a bad wire or connector between the cc and battery as these should be the same. worth checking.

drraptor

Re: MPPT PV voltage

I logged this graph today. Are these fluctuations normal ?

http://solarshogun.tumblr.com/post/92237441059/mppt-charge-controller-voltage-fluctuation

drraptor

Re: MPPT PV voltage

Attachment not found.

With increase in Current, voltage is pulled down.

drraptor

Re: MPPT PV voltage

BB. wrote: »

How much current is the controller pulling from the array (and/or outputting to the array). What is the array Wattage? Is the array in good sun at that time?

It sounds like 1) the array is not in full sun (off angle to sun, shading, etc.)--Low array power/current prevents the MPPT controller from stable operations. Or 2) the MPPT controller is not functioning correctly/as expected--It is operating like a PWM controller--Not as a MPPT controller.

-Bill

A little bit of cloud cover when the above graph was plotted using a data logger.

niel wrote: »

the fact that you have a draw down on the pv voltage is normal. this can be a sign things are doing well in its utilization for your 12v battery. even without a cc on it the pv voltage will be drawn down toward the battery voltage, but never quite reaching it. i see this from my setup all of the time. as the draw is lessened by the battery through your mppt cc, the voltage read at the pvs will rise.

Shouldn't a MPPT maintains the Voltage and current at it's MPP knee ?

Cariboocoot

Re: MPPT PV voltage

drraptor wrote: »

Shouldn't a MPPT maintains the Voltage and current at it's MPP knee ?

Not sure what that means.

MPPT charge controller maintains steady output Voltage during Absorb and Float stages. Input Voltage and current will fluctuate according to what the controller thinks is the best power point at the moment (or whenever it does an evaluation, depending on the model of controller). This will not be steady nor will it necessarily be Imp * Vmp even in Bulk stage.

drraptor

Re: MPPT PV voltage

Cariboocoot wrote: »

Not sure what that means.

By Knee I mean the MPP, whatever it is at a particular point in time. As you explained in your post
Attachment not found.

Cariboocoot wrote: »

MPPT charge controller maintains steady output Voltage during Absorb and Float stages. Input Voltage and current will fluctuate according to what the controller thinks is the best power point at the moment (or whenever it does an evaluation, depending on the model of controller). This will not be steady nor will it necessarily be Imp * Vmp even in Bulk stage.

When I recorded that Voltage vs Current comparison graph the batteries were in absorb just before the last steep dip in the current ? loads were turned on just before that dip.

Why does those dips signify ? there are 4 of those in Current's graph and 3 in Voltage graph. In Voltage those dips are followed by sharp spikes.

In morningStar's case(it records data every 30sec, correct me I'm wrong) there are just 2 in in over a hour

Attachment not found.

While I was searching I found this useful graph
Attachment not found.
Which essentially says, Shading and increased temperature moves the PV's IV (current vs Voltage) graphs to the left.

also found this nice explanation of what you call using loads in direct sunlight. I think, this might help you in explaining that point to new users.

Attachment not found.
http://netdensity.net/2014/01/06/3223/
incidentally that blogger, used the reference http://www.solar-electric.com/mppt-solar-charge-controllers.html

drraptor

Re: MPPT PV voltage

Attachment not found.
The Current Vs Voltage graph for the same data. Most of the values are near the MPP, but some are way off the mark e.g those 2 values around the 28V mark and a group of values between 56 and 60V.

More interactive version of the same graph
http://solarshogun.tumblr.com/post/92644368509/mppt-current-vs-voltage-graph

Cariboocoot

Re: MPPT PV voltage

If you had a MidNite Classic you could probably expect a more linear I*V response to changing conditions. With controllers that 'sweep' periodically there can be 'incorrect' I*V points occurring in between sweeps as either insolation or load demand changes. The controller will not adapt instantly to these changes so you see 'power points' outside the expected. They are nothing to worry about.

Shading is a vague term. It can be anything from a small shadow momentarily blocking a single cell of one PV to a large shadow covering a significant portion of the array. This is the difference between "not noticeable" and "huge power drop". When significant shading hits and array between controller sweeps you will see odd I*V. There is a loss of available power, current drops (because PV's are current-based), Voltage may go up or down depending on variables (including the controller's response to changes).

Increase in panel temperature has a small downward effect on current, larger on Voltage.

If you are expecting linear, precise, fixed responses to varying conditions you are expecting the impossible.

drraptor

Re: MPPT PV voltage

Thanks. :-)

I would like to see the similar scatter I*V graph for the midnite classic controller , Outback FM60, Outback FM80 and Schneider xw 60-150 in real world scenarios. I just want to compare different controllers and how they respond in under everyday conditions


With midnite classic it is so easy to draw a graph, just download the data and open it in excel and insert a I*V graph.

@Carboocoot can you post data for Outback MX60 ?

stephendv

Re: MPPT PV voltage

drraptor wrote: »

When I recorded that Voltage vs Current comparison graph the batteries were in absorb just before the last steep dip in the current ?

If you're interested in looking at the MPPT values from the array then you should _only_ measure them during bulk charging, as this is the only time the controller is guaranteed to be in MPPT mode. It looks like the midnite classic uses the part of the MPPT curve beyond the Vmp of the panel to reduce the output. E.g. my array has a Vmp of 90V and it will be close to this value during bulk.
When the classic goes to absorb mode then the V input steadily increases to more than 90V because the controller wants to draw less current. During float, the V input is more than 100V.

vtmaps

Re: MPPT PV voltage

Cariboocoot wrote: »

Increase in panel temperature has a small downward effect on current, larger on Voltage.

I think current increases (slightly) with temperature, but the voltage sag is greater and reduces the overall power production despite the slight increase in current.

--vtMaps

Cariboocoot

Re: MPPT PV voltage

I'd love to post a short video of the numbers dancing on the MX60.
Couple of problems with that: can't afford the bandwidth for video upload, and right now the output is zero because it's pouring rain again today and dark as night outside.

Generator time. Again.
This has been one weird Summer.

zoneblue

Re: MPPT PV voltage

The vmp varys primarily according to insolation and temp. The former is actually quite small, the latter more so. Current on the other hand varys pretty much linearly with insolation.

drraptor

Re: MPPT PV voltage

Cariboocoot wrote: »

I'd love to post a short video of the numbers dancing on the MX60.
Couple of problems with that: can't afford the bandwidth for video upload, and right now the output is zero because it's pouring rain again today and dark as night outside.

Generator time. Again.
This has been one weird Summer.

Doesn't Outback allow you to download the data on your PC ?

zoneblue wrote: »

The vmp varys primarily according to insolation and temp. The former is actually quite small, the latter more so. Current on the other hand varys pretty much linearly with insolation.

What are the possible ways to keep the solar panels cool other then these news technique http://forum.solar-electric.com/showthread.php?24187-Self-cooling-Solar-Cells-Boost-Power-Last-Longer&p=196375#post196375

Cariboocoot

Re: MPPT PV voltage

drraptor wrote: »

Doesn't Outback allow you to download the data on your PC ?

Yes, that can be done even with the old MX60. I don't because it's useless. The system works or the system doesn't work. Obsessing over data is something for engineers analyzing the operation and planning improved function to do.

What are the possible ways to keep the solar panels cool other then these news technique http://forum.solar-electric.com/showthread.php?24187-Self-cooling-Solar-Cells-Boost-Power-Last-Longer&p=196375#post196375

There are no practical ways to cool solar panels. Every scheme devised (so far) uses more power than it creates. This is not surprising given the laws of physics.

drraptor

Re: MPPT PV voltage

Cariboocoot wrote: »

Yes, that can be done even with the old MX60. I don't because it's useless. The system works or the system doesn't work. Obsessing over data is something for engineers analyzing the operation and planning improved function to do.



There are no practical ways to cool solar panels. Every scheme devised (so far) uses more power than it creates. This is not surprising given the laws of physics.

but it could be interesting to see how system works. I can't understand, why some solar power users don't want to see data and all those beautiful graphs.

Passive cooling system like the article I posted, which is no where to be see, can be used.
Law of physics state that, heat follow from hot end to cool end. you just need to maintain a steep enough gradient. :cool:

Cariboocoot

Re: MPPT PV voltage

drraptor wrote: »

but it could be interesting to see how system works. I can't understand, why some solar power users don't want to see data and all those beautiful graphs.

Never the same two days in a row.
Most of the people I encounter just want the system to work. Sometimes they are in tears over it not working.

Passive cooling system like the article I posted, which is no where to be see, can be used.
Law of physics state that, heat follow from hot end to cool end. you just need to maintain a steep enough gradient. :cool:

Yeah; just stick the bottom end of the panel in snow ....

drraptor

Re: MPPT PV voltage

Cariboocoot wrote: »

Never the same two days in a row.
Most of the people I encounter just want the system to work. Sometimes they are in tears over it not working.

Not everyone is same. some people are too curious to know how things work.

Just want to know, how it performs on a particular day.

Yeah; just stick the bottom end of the panel in snow ....

Did anyone tried a Absorption refrigerator, with Solar panels ?

Cariboocoot

Re: MPPT PV voltage

In theory this is possible.
A couple of things to keep in mind, though:

1). Operation temperature difference between 'desired' panel temp (about 70F/21C) and normal operating temperature (about 140F/60C) and its effect on panel output Voltage (converted to power via MPPT function). This is usually <0.5% Vmp per degree C or <20% of Vmp - about 5 Volts on a GT panel. Multiply out by Imp and see how much power you gain. It's not a lot for a 70F temperature change.

2). Cost of bringing this increase about (even if energy efficient) vs. same money invested in additional PV.

In other words about as practical as a chocolate hammer with PV at $1 per Watt (or even less).

BB.

Re: MPPT PV voltage

drraptor wrote: »

Did anyone tried a Absorption refrigerator, with Solar panels ?

Are you asking about solar thermal panels to bring heat to the Absorption cooler, or using solar electric to run the resistance heater in the cooler?

Using an electric heater is hardly ever worth the effort--Absorption cycle is only 20% as efficient as using a compressor:

http://en.wikipedia.org/wiki/Absorption_refrigerator

Solar Thermal refrigeration--There should be product out there already--Wonder if I can find some... Hmmm. They are probably out there--But many seem to be custom built for demonstration projects.

One comply that got a Scientific American write up on Absorption--Is now selling the "solar electric" heat pump unit we have discussed here a bit over the last month or so.

And this may be why:

http://shellcenter.rice.edu/Content.aspx?id=271

Indeed, this was demonstrated at full-scale (Fig. 1A) by Prof. Jose Manrique-Valadez and co-workers at Tecnologico de Monterrey in Monterrey, Mexico over a decade ago. They were among the first to realize that simple thermally-driven refrigeration cycles, e.g. ammonia dilution, could be used in place of the nearly ubiquitous Freon-compression cycle. Since the ammonia-dilution cycle only needs a heat source of about 150C, evacuated tube solar collectors (ETSC, Fig. 1B) are used as the primary energy source. The evacuated tubes used in the demo system can reach a peak temperature of 300C, even without concentrating mirrors or active pointing devices. Cooling is performed using a commercially available Servall ammonia refrigeration unit after retrofitting with a custom generator (ammonia separator; white component in Fig 1C). Comfortable temperatures are achieved with roughly 80% reduction in electricity consumption (electricity is still used for fans and pumps).

While technically successful and environmentally appealing, this approach has not yet entered wide-spread use, however, due primarily to the cost of the evacuated tube solar collectors. These cost today about $1K - $2K per m2, and 10-20 m2 are needed for a typical American residence.

10 to 20 m² is around 107-214 sq feet--Does not sound like it is too large of thermal array--But it sounds like you could run a full mini-split array on a solar electric array--Less plumbing issues and the energy can also drive the circulation fans and other household appliances (as well as using net metering or battery bank for power when the sun is down).

And it sounds like you would still want a traditional mechanical compressor system for no-sun heating/cooling (sun down/bad weather) anyway... So, seems a bit difficult to justify the extra installation costs.

-Bill

Cariboocoot

Re: MPPT PV voltage

Bill;

I thought he was talking about using absorption refrigeration to cool panels. Maybe not. It would be very complex and expensive for a small gain.

BB.

Re: MPPT PV voltage

If the amonia cycle needs a 150C temperature source--That is way over the operational temperature of a silicon solar panel.

The last link said that is why they needed vacuum tube thermal collectors to obtain higher temperatures for their system.

-Bill

Cariboocoot

Re: MPPT PV voltage

BB. wrote: »

If the amonia cycle needs a 150C temperature source--That is way over the operational temperature of a silicon solar panel.

The last link said that is why they needed vacuum tube thermal collectors to obtain higher temperatures for their system.

-Bill

Right but you don't use the PV to collect heat for the ammonia cycle. Instead you use the vacuum tube for that and put the cooler under the PV to lower its temperature. Crazy, complex, and expensive.

One of the biggest problems with cooling PV is the materials they're made of aren't very efficient at conducting heat. It's not like someone is going to back them with finned aluminium panels.