DC optimizers have emerged on the market as an alternative for module level power management and monitoring over microinverters, combining the benefits of module level MPPT of microinverters with the higher operating efficiencies of string inverters. Manufacturer’s claims of 25% increased production with use of DC optimizers hasn’t been sufficiently corroborated with third party field testing which begs the million dollar question: will DC optimizers live up to the hype and become the next evolution in PV system design?

Benefits of DC Optimizers
DC optimizers allow each module to independently operate a maximum power point tracking algorithm, ensuring that each module is producing the greatest amount of energy possible while getting the benefit of the higher DC voltages of string inverters and subsequent higher efficiencies. This arrangement has numerous benefits including mitigating the impacts of module shading, module mismatching, and over or under performing modules. This allows unprecedented versatility in the system design including multiple module types, azimuths and tilts connected to a common string inverter. Some DC optimizers also offer a safety shutdown which interrupts DC current at the optimizer mounted behind the panel resulting no hot DC conduits in the event of an emergency. DC optimizers give you better resolution of monitoring than is possible with string level monitoring and provides the added benefit of increased production.

Applications for DC Optimizers
Perhaps the most exciting aspect of DC Optimizers is their compatibility; they can be used cost effectively in grid-tied and off-grid applications from residential to commercial scale, they’re compatible with 60-cell, 72-cell, 96-cell and thin-film modules – a hurdle that most microinverters have yet to overcome. Additionally, the cost of DC Optimizers is reduced with increased scale making it particularly appealing for larger and commercial arrays, unlike microinverters whose cost is linear in terms of installed cost in $/Wp. Microinverters often require expensive AC trunk cable from the manufacturer and have fixed costs for the components which don’t experience the same economies of scale as large string inverters.

Module level monitoring and levelized cost of energy (LCOE)
When evaluating PV system cost, it has become standard industry nomenclature to evaluate various products and components in terms of $/Wp but this metric does not consider the single most important aspect of the PV system; total lifetime production. In response to this many owners, integrators and financiers are beginning to consider both $/W and Levelized Cost of Energy (LCOE) which is defined as Total Life Cycle Cost over Total Lifetime Energy Production) when making design considerations.

LCOE is a more useful but often nebulous number to determine and requires modeling and analysis that are outside of many installers’ skill sets and available time. If you don’t want to spend time analyzing the time value of money and estimating operation and maintenance expenses over the 25 years, your next best option is to design your PV system to be as versatile, resilient and with the highest resolution of monitoring possible. I often think of the mantra “You can’t manage what you don’t monitor” when designing a system and the greater resolution of data you have, the faster and easier it will be to trouble shoot and repair the system over its lifetime. Similarly, it is incredibly difficult to detect a single point source of failure in a system if you only have array level monitoring; what’s the value of a system that was the lowest $/watt installed but you can’t determine underperformance during 25 year life? With the resolution of monitoring and versatility module MPPT offered by DC optimizers, it is estimated that LCOE can be reduced by 20% or more.

Available DC Optimizers
Californian based Tigo Energy has emerged as the frontrunner in the budding DC Optimizer industry and has had their MM-ES Maximizer( (link to Alt-E Page) lab tested by Photon Magazine and found that Tigo Energy “significantly outperformed all competition”:

Perhaps most visible are the recent breakthroughs in BOS electronics which bring DC power maximization, safety features and advanced system management to the PV project. In the recently completed lab tests by Photon, the journal examined the benefits of five commercially available solutions. The results found Tigo Energy demonstrating clear advantages in energy production and highlighted the unmatched over-all value of the complete Maximizer solution. Tigo Energy departed from the conventional approach of DC/DC voltage conversion to develop a patented Impedance Matching technology. This superior energy harvest can be attributed to the 99.6% statistical efficiency and unmatched distributed MPP control accuracy of the Impedance Matching approach. Tigo Energy generated 3.5 times more power production from unshaded arrays than other tested solutions. These test results solidify Tigo Energy’s position as the clear market leader in DC maximizers and help to explain the rapid worldwide market adoption of the platform.

You can check out the Entire Photon Article Here:

http://www.tigoenergy.com/sites/default/files/photon_test_results.pdf

Solaredge also has a DC optimizer product, but it is only able to integrate to Solaredge’s inverters (http://www.solaredge.us/files/pdfs/se_system_overview_na.pdf). Silicon Valley start up eIQ is also offering a DC optimizer as is Oregon based Azuray Technologies. SMA and PowerOne have recently entered the microinverter market and PowerOne now offers a DC optimizers as well.

For more information on DC optimizers check out these resources:

• Cost-Benefit of Microinverters vs. Maximizers, by Andrew Wilkins, Renewable Energy World
• PV Micro Inverters and Optimizers: Not Just for Lazy Designers, by Joseph McCabe, PE, Alt Energy Stocks

They make it clear right away that there are a few things that are very important to East Penn. First and foremost, they are insane when it comes to environmental responsibility (in a good way). In order to limit any traces of lead seeping into the land, their facilities or their employees, the manufacturing areas are kept super clean. Continuously throughout the day, even the fine lead dust that could accumulate on the floor is vacuumed up, any crud that may wash into the floor grids is cleaned out and everything is fed back into the on-site smelter to melt down and be used again. They don’t stop there though, they also have facilities for employees to shower and change clothes before heading home so that East Penn can launder anything that was worn in the plant, and then clean and process the laundry and waste water themselves. The end result is that the water they give back is cleaner than what they get and they are easily exceeding any environmental laws or expectations for managing lead waste.

East Penn also takes serious pride in the fact that they make everything they need for their batteries. It was amazing to be able to see every piece of the battery being created individually from scratch. You can start at the beginning with the grid being stamped out, pasted, cut, dried and then easily walk upstairs to see where the paste came from, how it was made and how it makes it’s way down to the grid. They were especially proud of the tiny seals that are used in their VRLA model sealing valves, which they also make and test themselves. In each department the staff was happy to show off their sweet, state-of-the-art gear and explain their role in the production process.  You can tell that the main goal is to make each piece high quality and exactly the same every time.

As the batteries are going through the manufacturing process they all go through over 250 quality control checks along the way. Some are done by robots and machinery and others are done by the staff at East Penn (as a side note, the robots were incredible). I was really impressed by how many added steps there were just to make sure that each part had gone together perfectly, and then to test it over and over.

The resounding theme was that whatever they were doing at East Penn, they were doing it the very best that they could. After seeing the different types of batteries being made and chatting with the people that monitor everything from their lead content to the cleaning of the smelter, I was blown away by how each step went above and beyond what was expected. It’s clear their company culture has allowed them to make a great product responsibly. Hopefully they can be a role model to show other companies how to be successful and green at the same time too.

A few years ago, when there were shortages on MC4’s – module manufacturers had to make provisions on their connectors, so that they could continue production. Customers were left with the only option of mating with “compatible” connectors. Manufacturers were hearing from their customers that these “compatible” connections were starting to fail. The issue, they found, was that the metallurgical chemistry of the contacts were going to be different unless they were from the same manufacturer. Over time, the difference in chemical composition could cause oxidation that could lead to temperature rise and other problems. Another issue is that, the manufacturers don’t release tolerances for their products, which could result in possible gaps in the contacts when cross mating. **This could lead to arcing, or possibly eventual connector failure – who needs that??

So, what should you do to ensure a UL approved connection?

1. Ideally, you want to choose modules with the same connector types in a single array.
2. If, for whatever reason, you need to add or replace a module, and you find you must mix the connector types, the best solution is to use a small Connector Adapter Cable – for example: MC4 to H4, SMK to MC4
3. In addition, National Electric Code (NEC) now stipulates that when PV modules are installed in readily accessible locations, connectors that click and lock must be utilized. You’ll need a special tool (key) to unlock the connectors.

We just had our 2nd Annual Dealer Conference, and this was a hot topic. Ultimately in talking to the module manufacturers, there is agreement that there needs to be an Industry Standard for the connectors, so customers don’t run into these issues. Even if two brands of connectors were found “compatible” today, either one of the manufacturers could change their specifications without notifying all necessary parties, since there is no standard currently.

But, for now, let’s put an end to the mystery. When connectors of different makes are mated, the safety aspect that they were designed to perform, is not guaranteed. So, no – cross-mating any connector, regardless of the brands involved, is not a UL approved connection. It does not matter that both connectors may have independent UL approvals, as they were tested to their own, specific individual tolerances and specifications. So please, do your part to install a safe and trouble-free system, and be mindful of your connectors!

Buyer’s Remorse.  “Why, oh, why didn’t I buy a battery backup PV system?” Or, “I hate looking at my new PV system shut off when the grid’s down.”

You may already have a fabulous grid-tied solar system installed on your house, making power when the sun is shining, and turning back your meter. That is absolutely fabulous!  Grid-tied systems are the most cost effective and easiest systems to install.  Until the day the grid goes down, and your house is without power while your neighbor with the loud, smelly generator is sitting in their house drinking frozen margaritas and watching TV.  What to do now? No, you can’t run an extension cord to your neighbor’s house and hope they don’t notice. Electrical code requires that our grid-tied system shut down if the grid goes out to prevent accidentally electrocuting the linemen while they are working on a power lines to restore power.

You may think you are locked into the option you bought, or have to get rid of a lot of your equipment and start over.  Not so.  There is an increasingly popular configuration called AC Coupling.  AC Coupling uses your existing system to feed into a grid-tied, battery backup (GTBB) inverter/charger to charge the battery bank.  Here’s how it works.  You keep your existing system exactly as is, except you add a GTBB backup inverter/charger and battery bank.  The battery bank doesn’t need to be huge, just large enough to run your critical loads needed during a power outage; the fridge, well pump, furnace or boiler system’s electrical components, a few lights, and maybe recharge your cell phone or iPad to let friends and family know you are OK.

A GTBB inverter/charger connects to a new subpanel called the “critical loads panel”.  It’s the breaker box that the most important circuits are connected to.  The GTBB inveter is also connected to the grid.  When inverter detects that the grid is out, it turns off any connection to the grid, and only powers the items wired into the critical loads panel.  Therefore it complies with the requirement to not send power down the lines, but allows you to have some power in your house.  In an AC Coupled system, your existing grid-tied inverter is also connected to the critical loads panel.  When the grid is up, it sends power through the GTBB inverter, out to the rest of the house, and any excess power gets sent to the grid to spin the meter backwards.  But when the grid goes out, the GTBB transfer switch flips, and it turns off any connection to the grid, and only to the critical loads panel.  Since the grid-tied inverter is also connected there, it instantly sees the output from the GTBB inverter, and thinks it’s the grid.  The inverter doesn’t turn off.  It keeps sending solar power to the GTBB AC charger component, to charge the battery bank that the GTBB inverter is getting its power from.  So you are powering your critical loads off the battery bank, while the solar panels are recharging the batteries during the day.  Once the grid comes back up, the transfer switch flips back, and the grid-tied inverter goes back to powering the whole house and spinning your meter backwards.

Certain restrictions apply depending on which inverters you have, give us a call to see if AC Coupling is a good option for you.

So how does one measure the maximum possible voltage for a given panel in a given area?

1. Find the open circuit voltage (Voc) of the solar panel in question. That is the highest voltage it can operate at under standard test conditions. The Voc is usually located on a sticker on the back of a solar panel.

2. Find the temperature at standard test conditions. This would be found in the spec sheet of a given solar panel. Usually it is 25°C or about 77°F.

3. Find the temperature coefficient for the panel in question. Also found in the spec sheet of the panel. Usually it’s expressed in the form of a percent change per degree of temperature, like -0.34%/C, for example.

4. Determine the coldest it is ever likely to get at the installation site. This is not the average cold temp, it’s the record cold temp, because it can only take once for the strings of panels to operate at a voltage above the capacity of the controller and ruin it.

5. Make your calculation using this formula:

Voltage open circuit (Voc) at ambient temp of installation at ambient temp of interest   =
Voc (at STC)   +   (Module Temp Coefficient   x   Ambient Temp of Interest   -   25°C)

Here is an example:

Let’s say I live in Warsaw Missouri and I want to install 16 Solar World 240 watt solar panels on my house. What is the highest voltage each panel will ever see?

The coldest temp recorded in that area is -40°C.

The open circuit voltage of the Solar World 240 panel is 37.3 and the temperature coefficient is -0.37%/K. Kelvin? That is what’s on the spec sheet, and fortunately the conversion from Kelvin to Celsius is easy – it’s a one to one ratio. 1 degree Kelvin = 1 degree Celsius.

Now we need to find the difference in temperature between the standard test condition and the record low temp at the installation site. STC is 25°C. Subtract -40 from that and we get -65°C.

Next, multiply that by the temperature coefficient. -65°C   X   -0.37% = 24.05%.

Finally, calculate the max increase in voltage due to the drop in temp. The Voc is 37.3 volts, but the voltage could increase by 24.05% if the record low was ever reached. So 37.3 x 24.05% = 8.97 V. Add 8.97 to the 37.3 Voc, and we get 46.27V.

That is the voltage for each panel that one would use when determining the voltage of a string. In this case, I hope to have strings of 4 panels, so 4 x 46.27 = 185.08 Volts. So if I want a charge controller that can handle strings of 4 solar panels, then it will have to have a voltage capacity of at least 185.08 volts.

In conclusion, including a voltage coefficient calculation is a necessary part of the process of sizing solar panels to a charge controller. The change in voltage is greater with colder weather, but whatever the climate, it’s better to make the calculation in the design stage of a project than to experience a surprise once you’ve got the system up and running.

Our purchasing has power. It’s often a vote for what we believe in with every dollar we spend. All of us in the renewable energy and solar industry know the current market is flooded with low cost solar panel manufacturers looking to gain market share. There is nothing wrong with that. In fact, it may have even helped get more renewable energy systems installed, and ultimately, this is what’s truly important.

Although, when you have USA made equipment options that offer just as good a technology (and usually better) at a cost comparable to other non-USA made options, I personally believe you should choose USA made/local options. By doing so, you may be helping a neighbor or friend and decreasing the amount of fossil fuel it takes to ship the product across our great oceans. Additionally, when you take into account the cost of an entire system, choosing USA made doesn’t usually increase the cost of your installation very much, if at all.. In fact, it’s a great marketing idea for companies to offer USA made choices, since most of us believe in keeping our dollars local. Of course, one can argue from many different vantage points about the cost/benefits of USA vs. foreign made equipment. Many make it their life’s mission to be contradictory forces, but we can only rely upon ourselves to do the right thing. In the end, if we can support USA made products and still accomplish our renewable energy goals, then even better.

For those that don’t know each part of a system and which equipment to choose, I can offer many suggestions since I’ve been in the Solar distribution field now for over nine years.  For panels, there are a lot to choose from that are made in the USA.  Below are a couple of choices I have experience with working at altE. I can say that with all the choices out there, altE has picked a few to partner with that we feel provide the best level of technology and long term viability needed in this competitive and tumultuous market we’re currently in.

Quality USA made products with great technology and competitive pricing:

PV Manufacturers: SolarWorld and Kyocera (select models),
Combiners and BOS: Midnight, Outback Power and Wiley Electronics/Burndy Products
Racking:  IronRidge,  DPW
Off-Grid Inverters: Apollo Solar, Outback Power, Magnum Energy
Grid-tie Inverters: Solectria
Charge Controllers: Apollo Solar, Outback Power, and Blue Sky Energy
Batteries: Trojan and MK/Deka

Regardless of which manufacturer you buy from, if they have a solid brand name, build USA made equipment and are competitive in today’s marketplace, then you’ll have used your purchasing power to not only support your local Manufacturers, you’ll also have made your choice to do what’s right by sourcing what you need locally.

It is certainly nice to be able to series a bunch of modules together, but keep in mind that the balance of system components that are required will change from the norm. Once the temperature corrected open circuit voltage of the module string exceeds 150VDC we need to make sure that the components between the PV and controller are also rated for that voltage. Most of the DC rated breakers are rated for 150VDC which is fine for most of the controllers that have a 150VDC max input, but with higher voltage units now available these breakers are not always viable. There are some manufacturers out there that are now making 300VDC breakers to accommodate their high voltage charge controller units. These breakers are actually a combination of two 150VDC breakers, so this means that the size is equal to two breakers. So when choosing a combiner box or enclosure, it is important to keep in mind that the 300VDC breaker will be taking up two breaker spaces. One manufacturer is also manufacturing enclosures specifically for their high voltage breakers. When using a controller that has a 600VDC input, the enclosure options also get a little more expensive. One option is to use a combiner box with touch safe fuse holders and 600VDC fuses, but since the code requires both overcurrent protection and a means of disconnect, a 600VDC rated disconnect would also be required. If you are not combining any strings you could use a fused 600VDC disconnect.

So before you jump into a high voltage unit remember not to use the good ‘ol standard breakers that you are accustomed to. High voltage breakers and enclosures are a must in a system with a high voltage charge controller.

In theory, the answer is yes if the panels match closely enough in voltage and current. In practice, we don’t recommend doing this.

There are several reasons why it is difficult to mix panel types:

• The output power of panels changes over time. Existing panels that have been installed have power outputs that have degraded over time, and most likely will not meet the specifications on their nameplate. By trying to match new panels to the ratings on the nameplate specification, even a panel that seems to be an exact match, most likely would not have a matching output to the degraded output of the existing panels.

• Panel voltage is additive when panels are wired in series. The only way to wire in additional panels and guarantee that the voltage of all strings would remain equal is to add the exact same number of new panels to each string. The drawback to doing this however is that within each string all panels will produce the same current as the current of the lowest panel. So if you buy a panel that has a higher current it won’t produce the amount of current that is listed on its nameplate (it would perform at the lowest performing panel’s current), and you’d essentially be paying for a panel that will produce less power than its rating.

• Panel current is additive when panels, or strings of panels are wired in parallel. Say you were to try to just add the new panels all in one or more strings composed of only the new panel types. While each of these strings would be able to produce the maximum amount of current they are rated for, the voltage difference between the old strings and new strings becomes a problem. If the panels in the new strings had a higher voltage rating than the panels in the old strings, the new string, and each panel within it, will only be limited to operating at the same voltage as the old strings. So again, you’re essentially paying for a panel that will produce less power than its rating.

• If you are using an MPPT charge controller, mixing panels of different voltages and/or currents within an array will have an adverse effect on the entire system.  Different module outputs make it impossible for the controller to determine the optimal operating voltage and current because they will be different between the different types of panels.

So how do you handle a situation where you have an existing system and want to add additional capacity?

The answer to this is very simple actually. The one known constant within any off grid or grid tie with battery backup system is the operating voltage of the battery bank. So the best approach is to combine the output of the new panels with that of the old panels at the battery bank. The only way to accomplish this  is to use one or more additional charge controllers (and combiner boxes where appropriate) with the new panels.

With an additional charge controller for the new panels, the entire array of new panels is a 2nd “sub-array” of your overall system, and  the original set of panels now called the 1st sub-array. Each sub-array is connected to it’s own charge controller, and each charge controller has a charging output set to charge the battery bank at the proper voltage. With the matching outputs of the charge controllers, you can now combine 2 or more power sources of equal voltage together in parallel and the current from them adds together. This allows you to add additional panels to an existing battery based system and still maximize the output of both sub-arrays.

The above is fine if you have a battery bank, but what if you have only a grid tied inverter and no battery bank? Unfortunately in this situation your best approach is to simply purchase an additional grid tied inverter and connect it up to a breaker in your main AC power panel. By doing this you again take advantage of the fact that for 2 or more power sources of equal voltage joined together in parallel the current from them will add together. The only difference is that instead of this addition being done at the battery bank with charge controllers it is being done right inside your main AC power panel.

Ben Farmer's Ground Mounted Solar Array

Most of the PV installs people see in their community happen to be placed on top of a home’s roof. While this is aesthetically pleasing, space saving on the property and out of the way from people’s hands there are a few drawbacks to this method, which I have outlined below.

1. If the angle and orientation of the roof is not ideal then you will lose some percentage of your overall production. Ground mounting allows you to be more flexible in both regards.

2. Maintenance on your PV array may be required in the future and having to trouble shoot an array on the roof is much more time intensive and dangerous than a ground mount array which allows you you to walk right up to the array and easily navigate around it for maintenance and trouble shooting.

3. Performance with a ground mount system will always be better than roof top arrays since the system on the ground has more airflow to cool down the panels vs. having the array on the roof and within inches of a hot surface.

4. Your PV system is designed to run for many decades to come and the odds are your roof will need to be replaced before the end of the PV systems lifetime. Ground mounting will make sure you will not have to take down and reassemble your array when a new roof is needed.

5. For roof top installs the racking system has to penetrate the roof with lag bolts and as any roofer knows the more hole penetrations you have the more chances for failure in the future. Installing your PV array with a ground mount will guarantee not to interfere with your existing structure and will also allow you the space to mount the panels anyway you like vs. having to conform around roof vents, antennas, and other misc obstructions.

6. Room for expansion is usually not as much of an issue with a ground mounted array.

I do see the reasoning to put PV on roofs in locations that do not have adequate space or a good solar window on the ground within the property boundaries. Also, some properties have other problems such as tall trees or a heavily wooded property in general.  I guess one could also say wiring runs are shorter for roof top than ground mounted arrays, but with high voltage grid tie inverters the wire size can be smaller even for longer distances. And for battery based systems there are now high voltage charge controller options such as the Midnight Classic’s or the new Xantrex XW MPPT 80A Solar Charge Controller (up to 600V DC input!) to keep wire size down. I’m sure others could come up with a host of “custom” situations where roof would be better. But that’s just it, most all installs are custom, but I’d say in general, a ground mounted array is the best choice if you have the option to do so.

2. Noise. Have you ever had a critter in your attic? Were you relieved when you finally got rid of it or when it finally went away? A turbine can be like that – random noises at times that may not be so convenient. The level of sound generated by a wind turbine will vary from model to model, but generally speaking the homeowner will notice a difference. So if you’re sensitive to noise, this is something to take into consideration. Read the turbine product literature and ask questions about different models to see which one has the lowest sound impact. Consider installing on a barn or a detached garage – a place with a roof you aren’t sleeping under.

In the long run, you are better off installing a turbine where the quality wind is; as high in the sky as is possible. Your turbine will produce more energy and last longer. Sometimes it can make sense to install a small turbine on a roof. Just beware of the sounds turbines generate, and don’t be surprised if the turbine doesn’t produce as much as the performance charts say they will.