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Home Power Article: MPPT Charge Controllers (Aug / Sep '14 Issue)


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Paul

MPPT (Maximum Power-Point Tracking) offer the most current technology on the market, as far as charge controllers go. However, they are also the most costly controllers on the market today, as well. Typically, you could buy two or three PWM (pulse width modulated) controllers for the same cost that a single MPPT controller will run you. 

 

I am a long term subscriber to Home Power Magazine. Until today, I did not have an opportunity to view the August / September '14 Issue #162. Fortunately, though, Home Power Magazine chose to put this article on their site, as well as in the issue. At the bottom of this post is a link to the entire article. Please read on:

 

In a battery-based PV system, a charge controller is used between the PV array and the battery bank to monitor battery voltage, optimize charging, and keep the array from overcharging the batteries.

 

There are a few common types of charge controllers: single or two-stage (shunt or relay type); pulse-width modulated (PWM); and maximum power-point tracking (MPPT). While non-MPPT charge controllers are less expensive and still have their place in the battery-based PV market—especially for lighting and small developing-world systems—just about all modern home- and cabin-scale PV systems include an MPPT charge controller, as they offer several advantages.

 
MPPT Advantages
 
More watts. Recall the power equation—volts × amps = watts. The more voltage captured from an array, the more power (watts) can be sent to the battery bank. An MPPT charge controller keeps the array operating at the peak of the current-voltage curve, and converts array voltage above battery voltage into extra amperage, thus absorbing more watts from the array. A non-MPPT charge controller chains the array’s voltage to the battery’s voltage, effectively limiting the array’s power output.
 
Array voltage varies with cell temperature. For example, when the cells are cold during winter, yet receiving full sun, the array voltage is higher. Higher array voltage translates into greater wattage. Here’s an example: Considering average winter and summer temperatures in Boulder, Colorado, there would be about a 12% difference between average winter versus summer array power output, and up to a 25% difference on a cold winter day versus a hot summer day. For off-grid systems that have higher loads in the winter, the extra energy input offered by MPPT-based systems can be a big benefit. At higher temperatures, which usually occur in the summertime or year-round in mild climates, array voltage drops, and an MPPT controller may be less advantageous.
 
Step-down. Voltage conversion is another benefit that is built into MPPT charge controllers. An MPPT charge controller is a DC-DC converter—with computerized controls. It can take a higher voltage and lower amperage, and convert those to a lower output voltage at higher amperage. For example, instead of an array producing a nominal 24 V and charging a 24 V battery, an MPPT controller can step-down an array producing 60 V to charge that battery. This frees the array from having to be matched to the battery voltage, and mitigates some wire-sizing (and cost) issues.
 
In that example, pushing 30 A at 24 V a distance of 40 feet would require large-gauge (expensive) cable—2 AWG—to keep voltage drop under 2%. For the same amount of power, pushing 12 A at 60 V that same 40 feet with 10 AWG will keep voltage drop under 2%, with the MPPT charge controller stepping the output voltage down to 24 V for the batteries. THHN #2 wire retails for about $1.24 per foot, and #10 sells for about $0.19 per foot, saving $84.00 on that two-way wire run, even without considering conduit size and the physical difficulties of pulling large wire.

 

MPPT Charge Controllers Full Article on Home Power's Website

 

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easydrifter

That's all very interesting. I'm thinking of shipping a controller to Davao in a balikbayan box before we return. Wonder if that is allowed? Or if electronics need to be shipped another way. Maybe in checked luggage? By the way, how is the KIDD working out for you? I'm looking at that one or a Rogue from Oregon. Easydrifter

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Paul

That's all very interesting. I'm thinking of shipping a controller to Davao in a balikbayan box before we return. Wonder if that is allowed? Or if electronics need to be shipped another way. Maybe in checked luggage? By the way, how is the KIDD working out for you? I'm looking at that one or a Rogue from Oregon. Easydrifter

 

I am quite sure you can ship them in balikbayan boxes. Another member here had a controller shipped to him not long ago. You could probably bring them in checked in luggage as well.  

 

My Beta Kid is working quite well. I am happy with its performance. I don't think I could ask for a better small-mid range charge controller. I had some issues at first, but Midnite's people are great and will go out of their way to help you. 

 

After reading the article on the HP website, Rogue actually came to mind. I meant to post a question at the bottom of the article asking why they didn't add Rogue to the list of MPPT controllers in that article. Not really sure why they (Rogue) are not more popular.

 

I think either would work well for you, depending on your application and size of your array.

 

I have to admit, I like the features on the Kid. The menu is pretty easy to navigate after you get comfortable with it. It also works with wind and hydro.

 

Links to fliers on my DropBox account, below: 

Midnite Kid Full A (PDF)

Spec Sheet Kid Front Back (PDF)

 

ADVICE:

1. If you buy a Kid, make sure you have a good quality multimeter on hand. You WILL have to calibrate the battery and PV voltages after you connect it.

2. I would also suggest, if buying a Kid, to get a WhizBang Jr. battery monitor as well. The WBJr will work hand in hand with the Kid.

Edited by South'rn Boy
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Agreed that MPPT is the way to go. I used to have this setup on my boat.

But I would prefer to buy this kind of kit directly from China, where typically it is all made anyway. Even with import taxes, I would think this would be a better deal.

You will find tons of items on eBay, along with reviews etc.

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easydrifter

Thanks for the advice. I just want to set up a small battery backup system with an inverter for use durring brownouts in Panabo. Thought I should gather some quality components while still here in Washington. As for the panels, i'll have to find them in Davao.

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Paul

Agreed that MPPT is the way to go. I used to have this setup on my boat.

But I would prefer to buy this kind of kit directly from China, where typically it is all made anyway. Even with import taxes, I would think this would be a better deal.

You will find tons of items on eBay, along with reviews etc.

 

Midnite's controllers are made in the US. Rogue, that easydrifter is also considering, is made in the US. Outback, when the current owners of Midnite owned it, were made in the USA. Now, I believe they are outsourced to India? Not 100% sure, but that is where I believe they are made. Steca, I believe are made in Germany.

 

I want to let you know something that I have learned about "Chinese Made" MPPT controllers.

 

First, Chinese companies will sometimes ship you a PWM controller, having sold it to you as a true MPPT controller.

 

Second, I have purchased chinese made controllers just to compare them to American made controllers. So far, they are pure shit in comparison. I would not trust a Chinese made controller with my batteries. 

 

Remember, you get what you pay for. And, when buying the controller, you are buying the brains of your system. If you buy a shitty controller, you will end up with shitty charging and shitty batteries.

 

 

Thanks for the advice. I just want to set up a small battery backup system with an inverter for use durring brownouts in Panabo. Thought I should gather some quality components while still here in Washington. As for the panels, i'll have to find them in Davao.

 

Definitely the right move. When back in Davao, if you can locate some Yingli Panels, check them out before buying others. I have seen a lot of positive reviews on their panels. Currently, Yingli are number one on the market, in size, manufacturing and distribution around the globe.

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Mikala

I've been using Outback products on my ranch in Hawaii and they've given pretty good service. I had to replace 3 inverter circuit boards in 6 years, but I have a 12kW inverter bank (4 inverters). I bought them originally because they're sealed against humidity, insects, etc...

 

I plan to buy a new 6 kW inverter bank in September and add an Outback MPPT that's also sealed against the environment. I'll pay extra for the 10 year warranty as I wasn't too thrilled about having to replace circuit boards.

 

Since I'm an electrical / electronics engineer, it didn't take much effort for me to implement repairs, but the average guy might not have enjoyed it.

 

Oh, with a bank of inverters, if 1 fails, I can rely on the others to pick up the slack and continue along until I have time to repair whatever's gone wrong.

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Paul

Keep in mind, the same people no longer own it. Also keep in mind, they (Outback) now outsource their product builds. It's all about the money for some companies. With Midnite, their products are quality AND they have great customer service. MorningStar - the first controllers I purchased, are good products. But, I will not buy them any longer because MorningStart staff act like you are imposing on them to even ring them up and ask them a question. I have considered Rogue for future business, and of course, Midnite Solar will remain on my list for future business I may need. 

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Mikala

I've got a buddy that does solar power engineering designs on the Big Island of Hawaii and he only recommends the sealed Outback Power MPPT and inverter banks. He's been doing it for about 8 years now and says he's had no complaints from customers about failures. It seems I have the biggest number of failures, but I'm the only one with a 12kW bank running. Others might have a 6 kW bank at most. I wanted 3 phase power in the event I wanted to run larger motors or equipment for processing crops.

 

That being said, I do plan to buy a few extra circuit boards to have on-hand.

 

I guess the concept of having a sealed unit really hit me hard after all the garbage I found in the electrical outlets in my old home on the island of Oahu. I feel lucky the place didn't have an electrical fire from all the dead bugs, gecko eggs and such. Now I'm on a crusade to keep critters out of my electrical equipment.

 

On top of that, the humidity on my ranch is insane. It's nice all day with a good breeze and fabulous view, but the clouds build up their moisture all day long, then every evening it rains HEAVILY from about 6 pm to 2 am. Even in a drought, it rains like that!

 

But the view across the ocean and the city of Hilo, plus over towards the active volcano is FANTASTIC! I've got about 170 degree view with 1/2 of it being the ocean.

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Paul

Maybe you are just driving yours too hard? For example, just because an 80 controller, say, will send 80 amperes to a battery bank, doesn't mean you should drive it at full output all day every day. Maybe that is the issue you are having? 

 

Typically, I run my controllers at 85% capacity, no higher. Inverters, I run even lower, primarily due to the heat and humidity here. 

Edited by South'rn Boy
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Mikala

 

 

Maybe you are just driving yours too hard?

 

My problem is that I don't drive them hard at all. I'm rarely home and even my renter was not around much. I over-sized with the hopes that the equipment would last longer, but it seems the opposite happened. I really need to look at the warranty on the new equipment I buy. They show a 10 year warranty is available. I might go with that.

 

My battery bank is way oversized too, but they've lasted a good long time. This time, for the outbuilding, I'm going with a VRLA (valve regulated - lead acid battery) instead of the regular lead acid batteries. I'm interested in putting them into a seismic rack.

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Paul

Working your equipment too little can be as bad as working it too much. How OVER sized is your battery bank? 

 

Honestly, you should probably check into going with NiFe (Thomas Edison's Invention) batteries. Environmentally safer, will last many years longer, but are much more costly.

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Mikala
you should probably check into going with NiFe (Thomas Edison's Invention) batteries.

 

My reasoning to going with maintenance free batteries for the new installation is two-fold. First, I'm rarely home and it seems nobody else will check on the battery electrolyte levels. Secondly, the new installation is going into my outbuildings (two 40' refrigerated containers set on concrete pedestals) that this young guy is now renting to use as his home. I'm sure the VRLA batteries will be almost useless after several years, but at least they won't be damaged by neglect and I can set the system up to start the generator at 80% discharge to give them an even greater life.

 

I'd consider the Ni-Fe batteries for an installation in Cebu though. The cost isn't a factor for me. But first need to get closer to retirement as I'm sure nobody in the Philippines would be interested in maintaining a battery bank either.

 

Edit: almost forgot, I sized my battery bank for 3 days of supplying normal household loads without the generator kicking in and complete darkness. Kind of ridiculous as most installs on my island only have a 1/2 day reserve as they expect the sun will rise in the morning to recharge the batteries.

Edited by Mikala
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Paul

 

 

Secondly, the new installation is going into my outbuildings (two 40' refrigerated containers set on concrete pedestals) that this young guy is now renting to use as his home.

 

Powered by solar as well? How do you charge him for power usage?

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Mikala

Powered by solar as well? How do you charge him for power usage?

 

The outbuilding isn't fully setup yet, so there are no solar panels. Actually there's no roof (I posted a photo in some other thread). My plan is to setup the inverter and battery bank in mid-September, the a concrete floor installed between the containers (24' x 40'), plus on the uphill (mauka) side of 1 container for utilities (15'x40'). Then install a roof with solar for electric and hot water. Walls shortly thereafter with garage doors (3 each).

 

How to charge the kid? I don't know yet. I wasn't planning on charging him anything, but now thinking I could charge him the same rate as the local utility. The setup will provide me details of power usage over the internet to my cellphone or computer. Hmm... that's a good idea. He shouldn't get free power.

 

With that daily deluge of rain, I was also thinking of catching it and diverting it off to the stream below and setup a micro-hydro in the piping. With a 50' drop and that much roofing, that would also charge the batteries easily.

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