What are the signs of solar panel death?

[R&B]

I have been trying to find out how to know if your solar panals are working as they should.....From what I have been told solar panels break down with time, slowly loosing their charging ability...but I cant seem to find any hard facts on the subject....My panels at best guess have been onboard about 12-14 yrs in the caribean...Not know much about solar energy could anyone enlighten me....Thanks

[Alan Wheeler]

Everything ages and eventually breaks down with sunlight or UV. But as far as I know, theis is rather a slow process with Silicon and so I doubt you will have problems witht eh internals breakign down in your life time. However, what can break down is corroison of connections on the outside world of the panel. This can cause current loss under a load. So the only way to truely test the panel is to place a load on the panel when in sunlight. In bright sun, a pnale is capable of producing a voltage significantly above 12V. So a light bulb is not the best idea. A bildge pump will work wonders. Just use a pump near the current output of the panel and see how well she spins up. If you want to get sophisticated, use a multi-meter set to current and place it inline and read the current. If you want to get really onto it, use a current meter and a voltage meter and a known test load and measure the current and voltage and convert that to wattage. But all in all, if it works, most likely it is working.
However, I stand for correction on this one.

[GordMay]

As Wheels suggests, a load test is the most reliable way to determine output performance.

The projected life expectancy of most PhotoVoltaic panels is around 15 - 25 years. Most panels come with a 10-year warranty, although some only have a 5-year warranty (and I think I may have seen a 25-year warranty).

Test results* suggest that a drop in performance of 1-5% per year may be common for both amorphous and crystalline silicon PV technologies.

[size=1]* Sorry, I cannot locate the report, for verification.[/i]

[hellosailor]

Wheels is spot on. An automobile headlight (preferably 24v but 12v would do) could be used for the load test. A single inexpensive multimeter can usually be found that will handle up to 10A in current, but to measure larger DC currents you'll need a "current shunt" adapter for it, which can be made up inexpensively as well, or bought from surplus houses like All Electronics Corp - Parts, Supplies and Components to be used with a specific ammeter.

A 12v headlight running off a "raw" solar panel, which might be 17+, will be overvolted and is best used for very short periods, i.e. hook it up, read the ammeter, and disconnect because they won't last very long. A 24V headlight, or two 12V headlights in series, would last "forever" in the same application. For single panels up to 100W or so, where the wattage rating of the headlamps is similar to the panel, that's good enough.

There are battery test loads available, used for (duh!<G>) load testing car batteries, sometimes as little as $30-40. Won't work any better than the headlight but would be better if you had a very large array and wanted to test, say, 500-1000 watts at once. And, you can also test starting batteries with it.<G>

[Kapena]

Your solar panel should have a current meter in the system. It also requires a regulator. If you suspect it's not charging at the proper rate it could be the regulator is the diversion type or PWM instead of the new mppt regulators. In bright sunlight, clean panel (this makes a difference) and panel pointed towards the sun...a 100 watt panel will not be giving you 10 amps of power...probably more like 5 to 6 amps in my experience.

The thing that really helps is the regulator. The mppt regulator will boost the voltage and provide charge current even when the panel is putting out less then 12 volts (early or late day, cloudy, etc.). It's provides 30 to 50% more energy then the old regulators.

[hellosailor]

Kapena, what's an mppt regulator? Clever idea to use a buck-boost converter to increase the voltage from a panel but that's gotta cost dearly, too.

[Jentine]

Originally Posted by Kapena

The mppt regulator will boost the voltage and provide charge current even when the panel is putting out less then 12 volts (early or late day, cloudy, etc.). It's provides 30 to 50% more energy then the old regulators.

My panels put out 17v and the regulator reduces it to a preset level to charge the battery. The only device on my boat that increases voltage is the inverter. What kind of regulator increases voltage?

[Paul Elliott]

MPPT stands for "Maximum Power-Point Transfer", and it is equivalent to two switching regulators back-to-back. It operates the solar panel at the load where the panel delivers it's maximum output power, then converts whatever Voltage this may be to a Voltage appropriate for the battery (depending on the battery's charge-state).

This is in contrast to the series-pass, Pulse-Width-Modulation (PWM), or shunt regulators. In these, the panel output is essentially connected directly to the battery during the charge-acceptance portion of the charge cycle, and the panel output is reduced once the battery approaches full-charge.

An example from my boat: I have three BP 110W panels, wired in parallel. Each panel has an open-circuit (no-load) output Voltage of 21.7V (ratings at full noonday sun conditions, with a cell temperature of 25deg C). Each panel has a short-circuit current of 6.9A. The panel has a maximum output power of 110W, at 17.5V and 6.3A. At any other output Voltage the panel will deliver less than max power. When I am charging a low battery at (say) 12V, using a non-MPPT controller (or directly hooking the panel to the battery), the panel is not operating at maximum power. Looking at the output curve for the panel, at 12V the panel will be delivering about 6.8A, which is 81.6 W. (I am reading these Volt/Amp numbers from a chart in the panel specifications.)

With a MPPT controller, the panel would be operated at 17.5V, and be putting out 110W. Switching the 17.5V down to 12V (assuming 95% efficiency, a number I pulled out of the air) would give me 8.7 A into my 12V battery. This is a 28% increase in charging current.

Of course, the battery won't stay at 12V for long. As the battery Voltage rises, the current-boost will be less. At 13.5V, a directly-connected panel would deliver 6.75A (91W). With an MPPT controller the charge current (at 95% efficiency) would be 7.74A -- still one amp better.

Once the battery reaches full charge and the controller goes into trickle-mode, an MPPT controller will have no advantage.

These numbers will be different in practice, as the panels won't see constant full sun, and the panel temperature will usually be hotter. Still, the MPPT controller ought to give some charging improvement. MPPT controllers don't use fixed settings, but are constantly dithering the panel load, monitoring the panel Voltage, and looking for the point of maximum power.

These days, many panels are wired for 24V (instead of 12V) output, and the MPPT controller can efficiently convert the output of these panels for use in charging a 12V battery.

I still have the old-style controller for my panels, but I will probably be installing MPPT before too long. I may end up putting a seperate controller on each panel (instead of one controller driven by the three panels in parallel), because my panels are often partially shaded, and I think I will get more output if each panel can be independently optimized. I need to do some testing or modelling to be sure of this. I can't easily add more panels, so I need to make maximum use of the ones I have.

Hope this helps.

[Kapena]

Nicely said Paul. Cost for non-display is about $100 to $150 depending on the capacity of the solar panels. Most cruisers will have a battery monitor so you don't need a solar charge display. Alternative Energy has excellent articles and prices.
Charge Controllers - The Alternative Energy Store