# Data loggers...

Re: Data loggers...

The little I understand about the device, it is designed to "match" the high voltage / low current IV Curve of a Solar Panel to the low voltage / high current of a typical DC motor.

The "programming of the device" is more or less setting the maximum output voltage to 12 or 24 volts DC maximum.

For example, lets say you choose 12 volts for the load (Vmp < 24 volts for panel).... And have a 55 watt panel that you assume will output a maximum of 65 watts when cold--The Resistor to manage that load would be:
• P= V^2 / R = I^2 * R
• R= V^2 / P = 12^2 / 65 watts = 2.2 ohms load
If the LCB behaves roughly as I expect... The device will attempt to maximize Ppanel=Vpanel*Ipanel (voltage/current conversion) by "adjusting" the voltage seen on the output (Ppanel.maximum=Vload^2/R)... Basically Maximum Power Point Tracking...

Again, this is a huge guess on my part--I have little knowledge about LCB's and would suggest that you do more research or get one and perform your own experiments.

This gets rid of the 120/240 VAC requirement that GT micro inverters would require (and may cause your instructor some heart burn).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Data loggers...

I was wondering about the MPPT.

Another question, how can this Enphase micro inverter be grid tied? So I would be selling back? Or is there possible way?

What do you mean by this?
This gets rid of the 120/240 VAC requirement that GT micro inverters would require (and may cause your instructor some heart burn).
Re: Data loggers...
Another question, how can this Enphase micro inverter be grid tied? So I would be selling back? Or is there possible way?
Without knowing anything about the Enphase (like if they have a hidden installer "key")--hook the AC side of the inverter to a 240 VAC 15 amp branch circuit and the PV input side to the Solar Panel (or small array) that meets the I*V input requirements of the Enphase.

This gets rid of the 120/240 VAC requirement that GT micro inverters would require (and may cause your instructor some heart burn).

What do you mean by this?

Enphase Grid Tied inverters require you connect to your building's AC power system. Technically, you are required to get building permits and Utility approval. And if you do this at school, your instructor's approval too. They may or may not be willing to let you do this (if done correctly, should not be much of an issue for a senior e-shop class without permits and approvals--small amount of power relative to the whole use by the school).

The LCB (Linear Current Booster)--if it will work for your needs--may be a reasonable alternative for a low(er) cost, no AC power, no Battery Bank, solution.

As a project for high school (or even college)--You don't probably have to have a 100% working/shippable project with 100% traceability certs... You just need to document your setup, and known issues (and how you would address them with more time and money) and defend your project when questioned/demo'ed.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

So the LCB is a MPPT just doesn't modify the voltage only amps? All it does is change the load correct?
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Just called Enphase for discount/ sponsership of any kind. Forgot to mention if they would donate older models... But anyway the best they can do is give me free access to the data logger thing. And also to buy 2 inverters through the school for a 50% discount. Not that bad, but I also would need to buy 3 more as a option.
Re: Data loggers...
So the LCB is a MPPT just doesn't modify the voltage only amps? All it does is change the load correct?

Again, I am guessing... This is a switching power supply from the PV input to the Load output... Basically, the unit attempts to find the peak in the Power Curve by varying the input current it will pull from the solar array. The output power is based on the P=I*V such that the (motor in this case) that the I*V output matches the power available from the solar array.

What switching power supplies do is really switch the current to vary the input/output characteristics... The inductors with current flow are what allow switching power supplies to be efficient without wasting heat.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 482 ✭✭✭
Re: Data loggers...

Enphase tare losses:

The latest units (what they've been selling for at least a year now) are specced at 30mW night-time power consumption. VA is higher than the tare indicates as the design of their inverter puts a capacitive load on the system when it's not generating power so you see about 100mA per inverter.

When the sun is shining, the inverter is completely powered from the DC side, so any power losses are accounted for as part of the efficiency rating. The older units were powered from the AC side, so tare losses were much higher.

Power/efficiency curves can be found here: http://www.gosolarcalifornia.org/equipment/inverter_tests/summaries/ They are 95% efficient through most of the curve except below 25% load (47W) where it starts dropping - by 10% they are at about 93% efficient. They will cap out at 199W AC power.

There is no way to get individual panel performance numbers from the Envoy unit without using their monitoring, so I wouldn't bother if you are on a budget.

There is an Open Source project to inexpensively build your own monitor building off the also open source Arduino box. Web site: http://openenergymonitor.org/http://openenergymonitor.org/

That should only cost about \$50-75 in parts to get a single-channel power monitor and only nominally more to monitor additional sources.
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...
drees wrote: »
Enphase tare losses:

The latest units (what they've been selling for at least a year now) are specced at 30mW night-time power consumption. VA is higher than the tare indicates as the design of their inverter puts a capacitive load on the system when it's not generating power so you see about 100mA per inverter.

When the sun is shining, the inverter is completely powered from the DC side, so any power losses are accounted for as part of the efficiency rating. The older units were powered from the AC side, so tare losses were much higher.

Power/efficiency curves can be found here: http://www.gosolarcalifornia.org/equipment/inverter_tests/summaries/ They are 95% efficient through most of the curve except below 25% load (47W) where it starts dropping - by 10% they are at about 93% efficient. They will cap out at 199W AC power.

There is no way to get individual panel performance numbers from the Envoy unit without using their monitoring, so I wouldn't bother if you are on a budget.

There is an Open Source project to inexpensively build your own monitor building off the also open source Arduino box. Web site: http://openenergymonitor.org/http://openenergymonitor.org/

That should only cost about \$50-75 in parts to get a single-channel power monitor and only nominally more to monitor additional sources.

Wasn't ever going to use there way to get the data logging.

So what your saying is I shouldn't use a 50 watt solar panel or so? since it start losing efficiency at 43 watts?
Re: Data loggers...

It just the losses from the GT inverter themselves start becoming a larger piece of the power budget... If you are measuring the DC side of the Envoy--you don't care--power consumed from the panel is all you care about (as long as the load looks like an MPPT device).

If you are measuring power on the AC output side--then you have a hidden loss of power (the inverter/conversion process)--that you will need to account for.

Lastly, if you have a small panel, it will take quite a bit of sunlight to bring the Enphase out of "sleep mode" and start converting energy (and looking like a true MPPT load). A larger panel (higher rated power) will bring the inverter out of sleep with less light energy.

In the end, you have a lot of complex devices that will take a fair amount on your side to understand how they will function in your project.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Ok, Well I am looking at the school deal, with the inverters and such. I will probably test it, and see if it works. I will see if the school will pay for it first... I think its a pretty good deal.
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Well... I am back, made a total of \$550.

Post pictures later when they post them on there website.
• Solar Expert Posts: 316 ✭✭✭
Re: Data loggers...
... made a total of \$550.

Won Bronze ...

Congratulations!

Best regards,

Bill
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Thanks.

Hope to get a sponsorship this week.
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

If any one would like to sponsor me that would be great! I would need a few solar panels, any size above 50 watt. But they would have to be the same. I would need like 4.
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Well, I couldn't log on for the last few weeks, (website error?) But I am back, and am starting next years project.
Re: Data loggers...

Back on the Weekend of April 24/25--there was DNS server setup error which knocked out the site for a couple days...

If you are/where having problems past April 25/26--then there probably was a DNS problem with your ISP or possibly even with your computer (stale DNS?).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Well, after doing endless research with some more testing this summer... I have come up of wha I want, but still need a data logger, hehe. What I am getting in the next week is 4 to 6 ~200 watt solar panels. And 2-3 enphase d380 micro inverters.

The data logger needs to be able to record watts, (volts, and amps.) It can be plugged into a computer, indoors, ect...

I do not know if I should record amps on the dc side, or amps on the ac side. What do you think would be better?
Re: Data loggers...

Well, you really need to log volts and amps to know your power (P=V*I*PF)...

AC or DC side--depends on which type of current detector you are going to use (AC coil, DC shunt, etc.).

If the Enphase inverter outputs with Power Factor = 1.0 -- Then all you have to measure is the voltage/current. If the PF is not 1.0 and/or is not consistent, then you have measure phase angle too.

If you can measure DC current--probably do it on that side (less math, less sampling issues). If you must measure AC current (using current clamp/coil)--then that is where you will have to do it. And hopefully your data logger is properly able to measure 60 Hz wave forms and (ideally) calculate Root Mean Square and possibly phase angle. If the Enphase are consistent (say PF=0.85) then you can just through in a fudge factor and don't have to measure/log it directly.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Well now your making me want to measure the dc side. Which in my case isn't bad a t all, and then I don't have to do more math figuring the efficiency lost through the inverter and such.

Can you list a data logger that measures the load on the dc side, I cannot find one. Since I am using a enphase inverter, which means there is already a load, I do not need a sensor that puts out a load. My guess is that now that I am using this inverter, I do not need a \$200-500 sensor. My guess is that I might be able to use a WEL data logger maybe? Or something similar to it.

Thanks again for all your help.
Re: Data loggers...

Sorry, I don't have any better idea for a data logger... If you can find DC loggers that will work with a current shunt (typically around 50-100 mV full scale)--it would be my choice.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Ok, and I was just talking to the WEL server support, and they don't know where to get a shunt sensor, but they know it will work. Can someone please tell me where I can get one?
Re: Data loggers...

Our hosts sells a couple like these:
Deltec 100 amp, 100 millivolt current shunt
AC or DC - common item for use with many battery monitors and amp meters

You should be able to find some surplus too (at least 40 years ago, you could :roll:).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

And how would that hook up to the wel server?
Re: Data loggers...

"Cut" the negative wire going from the solar panel to the GT Inverter and place one end on the heavy post of the shunt, and the other end on the opposite heavy post.

Connect your DC 100 mVolt data logger to the two screws in the body of the shunt.

The "blade" between the two posts is a calibrated resistor. The two large bolts/nuts are the +/- connection points.

The two small screws are where you connect your voltmeter to measure the voltage drop across the calibrated resistor.
• V=IR
• R=V/I=100 mV / 100 amp = 0.100 volt / 100 amp = 0.001 ohms
• I=V/R= for example 0.056 volts / 0.001 ohms = 56 amps
You don't want "R" resistance to be very large for a shunt resistor... The smallest NAWS sells is for 100 amps... For your needs, you probably want something closer to 10-50 amps maximum current (you don't want too small of voltage for the instrumentation to measure).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 316 ✭✭✭
Re: Data loggers...

The WEL data logger will cost you \$385 complete (before any sensors) - that includes power supply and the web site your chaarts goes to, and all data logging storage. Your sample rate will be 1 per 60 seconds.

Since the WEL is an internet appliance, there's no s/w that has to be loaded on your PC/Mac.

The WEL has two 4-20 ma analog inport ports which should well suit measurement on the DC side of a solar system.

To measure voltage you'll need to add external series resistance (precision) such that in combination with an internal 150 ohm resistor, the voltage presented at the WEL's 4-20ma port is 3 V or less (20 ma or less).

To measure current you'll need to insert a shunt into the solar's DC circuit, as Bill suggested. You'll want to size the shunt such that the voltage drop across the shunt will never exceed 3 V.

While I own a WEL I haven't used the 4-20 ma ports yet. Thus, I don't have specifics to offer as to exactly what size and precision series resistor you need to measure panel voltage, or precision shunt resistor to insert into the solar's DC circuit to measure current from. I would think, though, that pretty straight forward electrical engineering skills would guide you through the process. The key point is to never exceed greater than 3 V at the input of a WEL's 4-20 ma port.

The WEL instruction manual is here: http://www.welserver.com/support_files/WEL_User_Manual_4.0.2.pdf . Details on the 4-20ma ports are on page 31.

Good luck.

Best regards,

Bill
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...
a0128958 wrote: »
The WEL data logger will cost you \$385 complete (before any sensors) - that includes power supply and the web site your chaarts goes to, and all data logging storage. Your sample rate will be 1 per 60 seconds.

Since the WEL is an internet appliance, there's no s/w that has to be loaded on your PC/Mac.

The WEL has two 4-20 ma analog inport ports which should well suit measurement on the DC side of a solar system.

To measure voltage you'll need to add external series resistance (precision) such that in combination with an internal 150 ohm resistor, the voltage presented at the WEL's 4-20ma port is 3 V or less (20 ma or less).

To measure current you'll need to insert a shunt into the solar's DC circuit, as Bill suggested. You'll want to size the shunt such that the voltage drop across the shunt will never exceed 3 V.

While I own a WEL I haven't used the 4-20 ma ports yet. Thus, I don't have specifics to offer as to exactly what size and precision series resistor you need to measure panel voltage, or precision shunt resistor to insert into the solar's DC circuit to measure current from. I would think, though, that pretty straight forward electrical engineering skills would guide you through the process. The key point is to never exceed greater than 3 V at the input of a WEL's 4-20 ma port.

The WEL instruction manual is here: http://www.welserver.com/support_files/WEL_User_Manual_4.0.2.pdf . Details on the 4-20ma ports are on page 31.

Good luck.

Best regards,

Bill

Well, can you think of any other data loggers that would do the trick, I don't care if it is non internet, or internet use.
• Solar Expert Posts: 316 ✭✭✭
Re: Data loggers...

Actually, I can't think of a more cost effective data logger (WEL), by a long shot. Especially if you're going to do your measurements on the DC side of the solar circuit, thus avoiding the need for an AC power transducer (like the commonly used WattNode from Continental Controls, which will cost about \$300 including current transformers, and will give you 3 circuits/channels of revenue grade high precision AC power measurement).

It looks like the challenge you've got is two-fold. First, you need some assistance to do the electrical engineering (or need someone to do it for you), and secondly you need some assistance finding a couple of parts (a precision resistor to enable solar PV DC voltage measurement, and a solar circuit precision shunt that will enable solar PV DC current measurement.)

Seriously, with the WEL, and the desire to measure on the DC side of the solar circuit, you're down to needing a couple of parts to do the whole thing. The engineering and the part research is the 'elbow grease' needed to put the project together.

Best regards,

Bill
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Looking at other "cheaper" data loggers, I think I may just get 4 of these or a cheaper way like one of these.
• Solar Expert Posts: 316 ✭✭✭
Re: Data loggers...

I think these are good alternatives to consider. I'm sure there are plenty of ways to do the instrumentation for your research, that will well serve you.

This has been a good site for you. You've got 12 pages worth so far of comments relative to data loggers and/or measurement systems that might help you with your research.

I look forward to seeing you publish results of your efforts. I've always wondered if there's any benefit in water cooling my PV panels.

Best regards,

Bill
• Solar Expert Posts: 92 ✭✭✭✭
Re: Data loggers...

Well so far water cooling has increased the efficiency here in arizona by ~6% and right now I am using 50 watt solar panels, and I am getting a good 6.21 watts more, When I go full scale, I hope to see more. Right now I am trying to configure a bolt on water cooling device, it just that there are so many sizes. I think I have a good design down, and am currently making it.

Thanks again for anyone who has helped me out, I will definitely refer this site to many people.