5 replies to this topic

[E3 wise]

From the Technology Desk of E3 Wise
By Lois Moore
One of the issues with solar that designers like myself have had to deal with is the efficiency loss from the disadvantage of voltage drop affecting entire solar array, as it does in centralized inverter systems.  This can be caused by many factors and because the panels are wired in series can affect the entire system. Meaning one bad connection in a panel or shading to any panel affects the output of the entire array.
Now however there is a new solution available they are called Micro-inverters. Because each Solar panel is equipped with its own micro-inverter, the disadvantage of voltage drop affecting entire solar array, as it does in centralized inverter systems, is eliminated. Each solar panel can work independently to produce its maximum power in all conditions. The disadvantage of possible higher initial cost is offset by increased power production from the same modules over time and the ability to monitor output at a single module level. Meaning that now these issues can be eliminated making the efficiency and therefore system payoff much more precise.
Auo’s Unison line now has two solar panel lines that produce a 220 alternating current panel thanks to these micro inverters which convert 240 watts DC (direct current) to 220 volts AC (alternating current) at each panel, so you ask what are the advantages.
First it is a plug and play application; the solar modules come pre wired with easy to use plugs that allow seamless integration. The integrated micro inverter converts module DC to grid compliant AC at each module. This increases system performance by up to 25%, reduces shading losses, and makes PV safer to install and own. Here is Auo’s listing of Features for this product
• Harvest 5 to 25% more energy than traditional systems
• Module level monitoring
• Designed for 25 Year Reliability
• Modular flexibility suits any budget or rooftop
• Simplified PV system reduces installation costs
• No high voltage DC means safe installation and ownership
• Module complies with advanced loading tests to meet 5400 Pa loading requirements
• Light Trapping Capability: Superior performance under weak light conditions such as dawn, dusk, and cloudy days.
• Enhances current transmission and module reliability
• 3 Busbar Design: Enhances current transmission and module reliability
Recently I got hands on look at these panels at a solar tradeshow and I must say I was impressed by the ease of installation and the effectiveness of the monitoring. Likewise the ability to power higher voltage appliances like electric stoves, refrigerators, and air conditioning without special inverters or electrical configurations makes this a real competitor to the home and business solar markets.
I also like the fact of the twenty five year warranty for both the panels and micro-inverters as an integrated package, meaning if there is an issue, you are not fighting between two companies as to who is responsible.  If there is a problem the panel and inverter are both replaced as a unit.
In the past I have seen that solar systems can be susceptible to voltage drop issues and this can severely affect performance and cost payoff.  This looks like a way to eliminate the chance of both.

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[eds]

Technology prices keep going down, as the price of everything else goes up.
. . . Here is another example of "Billions-of-people-using-up-the-earths-resources"

[tri-n-b-helpful]

E3 wise, on 28 April 2012 - 09:43 PM, said:

From the Technology Desk of E3 Wise
By Lois Moore
One of the issues with solar that designers like myself have had to deal with is the efficiency loss from the disadvantage of voltage drop affecting entire solar array, as it does in centralized inverter systems.  This can be caused by many factors and because the panels are wired in series can affect the entire system. Meaning one bad connection in a panel or shading to any panel affects the output of the entire array.
Now however there is a new solution available they are called Micro-inverters. Because each Solar panel is equipped with its own micro-inverter, the disadvantage of voltage drop affecting entire solar array, as it does in centralized inverter systems, is eliminated. Each solar panel can work independently to produce its maximum power in all conditions. The disadvantage of possible higher initial cost is offset by increased power production from the same modules over time and the ability to monitor output at a single module level. Meaning that now these issues can be eliminated making the efficiency and therefore system payoff much more precise.
Auo’s Unison line now has two solar panel lines that produce a 220 alternating current panel thanks to these micro inverters which convert 240 watts DC (direct current) to 220 volts AC (alternating current) at each panel, so you ask what are the advantages.
First it is a plug and play application; the solar modules come pre wired with easy to use plugs that allow seamless integration. The integrated micro inverter converts module DC to grid compliant AC at each module. This increases system performance by up to 25%, reduces shading losses, and makes PV safer to install and own. Here is Auo’s listing of Features for this product
• Harvest 5 to 25% more energy than traditional systems
• Module level monitoring
• Designed for 25 Year Reliability
• Modular flexibility suits any budget or rooftop
• Simplified PV system reduces installation costs
• No high voltage DC means safe installation and ownership
• Module complies with advanced loading tests to meet 5400 Pa loading requirements
• Light Trapping Capability: Superior performance under weak light conditions such as dawn, dusk, and cloudy days.
• Enhances current transmission and module reliability
• 3 Busbar Design: Enhances current transmission and module reliability
Recently I got hands on look at these panels at a solar tradeshow and I must say I was impressed by the ease of installation and the effectiveness of the monitoring. Likewise the ability to power higher voltage appliances like electric stoves, refrigerators, and air conditioning without special inverters or electrical configurations makes this a real competitor to the home and business solar markets.
I also like the fact of the twenty five year warranty for both the panels and micro-inverters as an integrated package, meaning if there is an issue, you are not fighting between two companies as to who is responsible.  If there is a problem the panel and inverter are both replaced as a unit.
In the past I have seen that solar systems can be susceptible to voltage drop issues and this can severely affect performance and cost payoff.  This looks like a way to eliminate the chance of both.

My first question is, "why wasn't this implemented sooner?” Converting every individual solar cell (not panel) into AC is very cheap and very simple to do with readily available local components. In fact, I've traced the designs right back to being published in England's leading electronics magazine in 1965! Where have all the good design engineers gone that actually are capable of putting some thought into how a system should best be implemented and only then building it and testing it?

Another point that could be expanded upon is that using AC means that we could now have very long transmission lines as well as much thinner and cheaper cabling with virtually no losses.

Twenty-five years warranty is far superior to what we get with the current inverters.

So, given all the different mains frequencies currently in use around the world today, would this mean that these panels won’t work or work well with different appliances?
Because there will almost always be some sort of output under all light conditions, it sounds like we could eventually do away with messy, inefficient, heavy and environmentally unfriendly battery charging systems, especially in grid-feed applications.

Well, this solution addresses just one issue of voltage drop problems. Many other problems still remain. One of these that the authorities here have verified is the issue of output being temperature-dependant, as I have shown in previous posts. Another is poor impedance matching, which I’m not sure if this solution overcomes in its entirety. Yet another issue involves installers failing to earth the systems, fire risk of the present systems and the whole grid feed system raising neighbourhood mains voltages high enough to prematurely damage or destroy appliances, in particular halogen and CFL lighting. Engineers have been calling for the present grid to be overhauled completely for a long time here now.

[E3 wise]

Nice to see you again tri-n-b-helpful.
First, I asked the same question you did when I first learned of the microprocessor for each  panel system, why had this not been sooner, same reason we are just now putting microprocessors to point individual solar panels now.  Nobody had done it.

As far as the voltage specs for each country, the microprocessors can be tailored to different grid requirements such as 50 or 60 Hertz 110 or 120, 208, 220 or 240 volts.

Yes this is a great solution to cut down or eliminate batteries for grid tied systems.

This technology was developed for electric cars. Then it was licensed to microprocessor manufactures.  For the cars I was made aware of the technology almost 5 years ago.  For the solar cells I got my first look at the technology two weeks ago at a solar conference.

Now honestly match this up with another processor to follow the suns movement and I have been seeing estimates of 35-40% increase in efficiency.

Last thing the heating issue you discussed is still being worked on several manufactures are looking at either glycol systems that fit into panel construction to maintain nighttime panel temps during the day or some kind of pump system to circulate a cooling liquid behind the cells, to keep them below that magic 145 F temp at which efficiency begins to drop as temperature rises.
I am hoping very soon there will be a new low cost solution for this issue also, today however if you have temps that are 20 degrees over the 145 F you need to put in solar concentrators instead of Photovoltaic’s – reason is that at 165F you now have a perfect solar concentrated site.

Hope this helps and hope everything is gong well with my friends down under.
Thanks for the questions
Health, Happiness and Success

[tri-n-b-helpful]

Thanks for your concern. We’re all steeling ourselves for the May budget, where the only environmental benefit in there is the Carbon Tax, plus something resembling austerity measures.

Thank you too, for the extra information. Those solar trackers have been in use here since the 1990’s. Have they gotten them right yet? On a uniformly cloudy day, they used to run the motor continuously while it constantly searched for a brighter spot than what it had. The end result was that it used far more power than what it produced, draining the batteries instead of charging them!

I used to do a lot of work with converting very low voltages up. I’m assuming they’re converting the DC output of 0.7V (maximum?) for each solar cell to AC and then correctly phasing the individual AC signals together. I don’t know if you can get details of how they do this, but normally there’s a trade-off or compromise between tuning to obtain the maximum efficiency and tuning to get maximum power out (the two were never possible at the one tuning point). The ideal, of course, would be to tune to get maximum efficiency for low light levels and auto switch the tuning to get maximum power output for higher power levels, though either way there would be significant losses.

[Phil]

This is not a new idea.  http://enphase.com/p...microinverters/  As stated, they are already on their third generation.

It is almost always cheaper to do one big inverter than it is a number of smaller ones, so it is no wonder this was slow to get started.  Solar start up costs are high enough as it is and that is the biggest impediment to increased penetration.

Also, grid tie inverters, with one exception cannot be retrofitted with battery backup, (SMA Sunnyboy inverters can).  These do nothing to eliminate batteries, you either have grid tied or grid tied with battery backup.  All grid tie inverters require no batteries.

Always, the best solution is not effiency, but mazimum power out.  Hence MPPT, (maximum power point), controllers, which are what virtually all inverters use.  My 8KW inverter will start up if it can even generate 2 watts, and won't shut down until it drops below 2 watts.  That's where the rubber meets the road!

As far as high voltage and power drops go, systems run 10AWG wire and only carry 7 amps, that loss is neglegable even for long runs.  My 600 Volt system runs at 400 volts more or less normally, (414V just now).  Meanwhile 240VAC reaches peaks of 340 volts, (240x1.414), so there isn't much difference.

These are great if you can only afford one or two panels.  For larger systems it is very difficult to justify the extra cost.  One could argue that increased volumes would bring down costs but the same would be true of larger inverters as well.