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Advanced Photovoltaic Systems

AET 230-8204 Notes-Week 6

Our guest today is:

Pete Shoemaker of the Pacific Energy Center

Many of you who have been to the Pacific Energy Center in San Francisco have seen Pete speak. Pete is planning on showing up at 10AM.

Class presentation

A few of our classmates will give us an update on the PV system in Pescadero that they are helping someone design.

Of Interest...

Can Moore's Law be applied to solar? Here is a article that says no:

Also, the CleanTech website has an interesting Summer Intern opportunity in SF. It doesn't pay, but at least it is a CleanTech job that could open doors:

Here is a very complex use of PV & storage technologies:

Solar hydrogen home Michael Strizki

The First Solar/ Hydrogen House located in Hopewell New Jersey

This week's topics are Batteries, Charge Controllers & other atypical installations.

Most PV applications that members of this class will see and where the jobs are, is in the Grid Tied arena. Battery based systems are a thing of the past, however it is important to understand batteries if you are ever going to take a NABCEP exam. Another thing, is that you never know when a rich person is going to want a battery backup system.

Charge controllers are only used in battery based systems, therefore when you read the chapters in the book on batteries and charge controllers, there is a lot of subjects that repeat themselves.

Another great source of information (as always) is SolarPro Magazine. Look in issue number one and read the article titled: Battery Backup for Utility-Interactive PV Systems.

You have to sign in first. They are using the abbreviations UIGD for Utility Interactive Grid Direct and there is UIBB for Utility Interactive Battery Backup. Both of these systems are connected to the grid, so UIBB should not be confused with a Stand Alone PV system.

One recent advance with battery based systems are MPPT charge controllers. Before the advent of MPPT charge controllers, you had to size your strings to coincide with battery voltage. Also, without MPPT, it was the battery voltage that determined where the PV power was on the IV curve. Also, this way strings can be longer, voltage greater and current less, which means less voltage drop and smaller wires. Another thing that lower amperage means besides smaller wires is smaller charge controllers, which are sized like wire. This however requires a transformer to step down the voltage to match the batteries.

Battery bank sizes are usually 48 volts, but can be 24 or 12 volts.

With batteries, it is best to have one string of batteries, but 2 will do. 3 or more strings are not recommended, because the batteries will get out of balance. Another thing it that when you have 2 strings wired parallel, that you should have the positive and negative cables some out of opposite sides of the strings. This is because you do not want more current running through one series string than the other.

There are 2.1 volts in a lead acid battery cell (.5 or .6 in a PV cell). A 12 volt battery has 6 cells. It is common to find large 1 cell batteries on the market, which are called 2 volt batteries. This way, you can have 24 large batteries in 1 string for a 48 volt system.

Here are some popular battery manufacturer websites:

Batteries when charged have more than the normal amount of volts and when undercharged, have less than the normal volts. One trick thing to understand is that when a battery is low on volts, that when powering the inverter, it is putting out more Amps. This is because Volts x Amps = Watts and to get the same amount of Watts with less volts, you need more Amps. For this reason, when you size the wires for this side of the system, you need to take the low voltage (dead battery) condition into consideration.

Another big difference to be aware of with systems that have the ability to work off the grid is that with a UIGD system, you size your inverter with respect to how much your PV produces at one time. On the other hand, when you are sizing an inverter to power your loads and surges, you will probably want a larger inverter. You will not just be feeding as much as you produce into the grid, you will be powering everything that you turn on at once. You need to be aware that when you turn on an electric motor, it temporarily draws extra power to get it going, which is called a surge.

FLA (Flooded Lead Acid) Batteries are the typical battery that PV systems use and they use the Deep Cycle kind, which are also called traction batteries as opposed to SLI batteries (Starting, Lighting & Ignition). SLI (automotive) batteries are also almost always lead acid batteries.

Deep cycle batteries have thick lead active places in them. This way they last for a long time and can supply continuous power for a longer period of time. An SLI battery on the other hand is made to supply "cold cranking amps" for long enough to get your car started, which is hopefully about a second. These thin plates have a lot of surface area for a lot of quick power. When SLI batteries are used for PV, they do not last very long.

You should have all of your batteries the same make, model and age. Batteries, like PV, need to be similar. One exception to this rule can be when you have 2 separate charge controllers and each would charge a different battery bank and operate different loads.

As always, it is good to look at what is on the market. In Northern California, OutBack is a popular manufacturer for battery based power conditioning products & you can see their product specifications at:

They are also very accessible on the phone for product support, which you will probably need for a battery based system a lot more often than for a basic UIGD.

After some playing around with signing in to the site, I was able to view some free online lessons at the OutBack website.

Another popular battery based power conditioning equipment manufacturer is OutBack's arch rival Xantrex, which used to be called Trace (the inverters on the wall in Tom's classroom). You can see their products at:

SMA has the Sunny Island, which can be used as a battery based inverter, however it is geared to be a "Micro-Grid" which means that it can hook up with other sources of power, such as Sunny Boy inverters, wind turbines, the grid, a generator, etc. and coordinate everything with batteries. This would be a good system for someone who has a retreat center or a commune in the woods, or if you have a desert island.

Batteries are very recyclable. The lead, the acid & even the plastic is recycled. The acid is used to make things like laundry detergent and the plastic is turned into plastic pellets, which are then again turned into batteries. The lead is also melted down, cleaned up and turned back into batteries.

Atypical installation:

Solar Islands (TM)

Video of Solar Islands -- a concept by CSEM, Switzerland (

Does anyone want to play "cite the code violations"???

DIY The Cheapest Solar Panel System EVER Cheap Solar Power

See this solar panel system with lights. Inexpensive, easy to install, reduce your power bill. Cheap Solar Power. Cheap Home System. See my part 2 video.

Like how he vents the batteries and how he uses guitar parts?

Here is an example of how to cause leaks in your roof, which causes rot, which causes your solar system to fly and your house to fall & smell.

How to Install Solar Panels : Mounting Rails on Roof for Solar Panels

Reusing materials from other projects is one way to recycle. Learn how to mount rails on a roof for solar panels from a professional in this free energy conservation video.Expert: Roger BaconBio...

Here is a very interesting UIGD setup. Once again, name the NEC violations.

GRID TIE INVERTER SOLAR POWER EASY SOLAR SOLUTION POWER INVERTERS is a grid tie inverter that is 200 watts. It actually reads a bit higher for various reasons. This was to see how well it worked. POWER INVERTERS.

There is a lot of information and youtube videos at

which should keep you entertained for a while.

Here is the quiz with the answers:

quiz week 6 answers.pdf (PDF — 55 KB)

This webpage is an archive and has not been updated in over 10 years. Much of the information is still relevant. To see our more recent website, go to

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