Elkhart, we have a problem

Modified Sine Wave HORROR! This is what I got off an inverter with a bad output filter. I believe this is proof of why you should invest in a true sine wave inverter if you’re running anything other than lighting and a refrigerator (note: a refrigerator with electromechanical controls — not an electronic control system.)

No, the scope isn’t lying here… see the last pic…

I almost missed this because I had a resistive load on the inverter. Apply a resistive load and it looks like this. Apply an inductive load and it still has those ugly spikes.

They really are that bad.

Set to trigger on the very start of one of those negative pulses. What you’re looking at is essentially a DC offset of -170vdc… with THAT on top of it. YES, THAT IS 200 VOLTS/DIV. HOLY ASS, BATMAN.

Solar Panel Specifications Explained

How to interpret solar panel specifications and use them to choose the proper panels for your application.

On a solar panel, module, cell, or laminate, there are a number of different specifications given. Here’s what you will find, and how to interpret it.

Here are some sample specs I, uh… stole for purposes of illustration. These are for a Canadian Solar CS6P-190-PE.

Power (W): 190 Watts
Open Circuit Voltage (V): 36.00 Voc
Short Circuit Current (A): 7.42 Isc
Maximum Power Voltage (V): 28.60 Vmp
Maximum Power Current (A): 6.64 Imp

Now, here’s what these mean to you!

First off, the Open Circuit Voltage (Voc). This is the voltage you will see present at the solar panel’s output when it is exposed to full sun and is not loaded. While this is not really relevant to the panel’s power output, it should be taken into consideration for two reasons: First, you should ensure that any equipment connected to the panel (meters, charge controllers, etc) is capable of handling the full Voc of the solar panel or the string of solar panels connected. Otherwise, equipment damage may occur when the sun hits the panels and they’re not loaded down. Consult the documentation on your charge controller if in doubt. Also, for your safety, be sure that any overcurrent protection devices or disconnect switches are rated for Voc or higher! Upon unpacking and installing your panels, if you’re lucky enough to get full sunlight hitting them, check the open circuit voltage – it should be close to Voc. If it’s too low, the panel may have a problem or be miswired (check the junction box).

Short Circuit Current (Isc). This measurement is useful for testing the panels and determining the sizing of your wiring and controller.  Set your multimeter to amps, and connect the leads across the solar panel’s output terminals. In full sun, you should get Isc. If you do, the panel is operating correctly. Any wiring to the solar panels, and the charge controller itself, must be capable of handling the Isc of the array. Do not expect to load the panel down to Isc in normal operation, as you will be getting almost no voltage and extremely reduced power. (See I-V curve below!)

I-V Curve. Source: pveducation.org
Maximum power voltage (Vmp) and amperage (Imp). These levels are very important to consider in selecting panels and components for your solar energy system! In short, please keep the voltage as close to Vmp as possible. The reason for this is that the solar panel has a certain internal impedance, and you will only receive maximum power when the panel output voltage *under load* is allowed to remain near Vmp. If you load the panel down to a lower voltage, it will become severely inefficient.
If you are using the solar panel with a conventional charge controller to charge lead-acid batteries, the ideal Vmp will be near the absorption charge voltage for your batteries. If you are using an MPPT charge controller, Vmp should be anywhere within the controller’s MPPT tracking range. This may be an extremely wide range of voltage, allowing you a lot of flexibility in choosing panels!
To illustrate the importance of the Vmp point, see the above I-V curve and power curve for a solar panel. Note that the power curve tapers down towards zero as the voltage falls below Vmp, and abruptly falls off as the voltage approaches Voc. If you buy solar panels and operate them too far from Vmp, you might as well be throwing money down a hole.

If you have an MPPT charge controller, it will periodically sweep the array voltage to find Vmp, which actually varies a little with different sunlight levels. For the best possible power output under all conditions, use an MPPT controller. The only exception I should point out: if you are using HF radio equipment, the switchmode boost/buck converter inside an MPPT controller may cause excessive noise on the receiver. Consider using a simpler charge controller in this case. The Morningstar ProStar series charge controllers have an internal jumper (really, a 0 ohm resistor that you can cut) to disable their PWM charge control to reduce RF noise to minimum.
Don’t toss your system efficiency and money down the toilet – choose your solar panels wisely!

Opening the Blackberry battery cover without breaking a nail

I have seen a lot of people complain in forums that opening the battery cover on a Blackberry is difficult or even causes them to break a nail. Well, here is the solution: do not go straight for the fingernail-killer notch on the bottom center. Instead, gently lift the cover at the right and left edges beside the evil notch. The latches there will let go. Now go for the center notch and it’ll effortlessly snap off. If you were going in there to pull the battery for a reboot, consider installing the free QuickPull app to allow future reboots without opening the cover.

Solar Laminates

I’ve had quite a few people ask me what the low cost solar laminates are that Sun Electronics sells. In short, a solar laminate is just the center part of the solar panel. It is a sealed, weatherproof unit, consisting of the tempered glass top, the cells and interconnections protected in a clear encapsulant, and an insulating backing. These are shipped stacked up like matzoh in a box. Unlike matzoh, however, you should not attempt to spread jam on these and eat them. The results would not be particularly good.

The laminates do not come with a frame, junction box, or leads, like a fully assembled solar panel does. They are ready to be framed and mounted, and to have a weatherproof junction box attached. The junction box is attached with a weatherproof adhesive (RTV silicone or similar), and the laminate’s protruding buss ribbons are soldered or screwed down to its terminals. The buss ribbon is tinned and will solder easily. Click to view the image in the gallery, where you can see it full size.

At left, a complete panel; at right, a laminate in a frame without a junction box. A custom J-box would probably be needed to fit this tiny panel! I’m not sure what its specs are. It’s about the size of a box and a half of spaghetti noodles placed end to end. Lots of spaghetti!

In case you’re curious, these are the same panels from the front. We hang these around the offices like some kind of strange photovoltaic portraits.

Tiny solar panels!

I would post this on the Sun Electronics website, but we’re having some technical issues with it. Such is life…

update the better part of a decade later, after removing spam links: I do not work for Sun Electronics and have not for quite some time. They screwed me over just as nicely as they did most of their customers. May they go rot in South Floridian hell. Which is to say, just, South Florida itself. BYE FELICIA