If – like most educated consumers – you’re getting multiple quotes for your solar power installation, you’re probably having to compare between various equipment offerings by your solar vendors. Themostprominent of these offerings – both in terms of financial investment and warranty security –are the solar panels themselves.

Solar panels come in a variety of power ratings. For residential applications, the most popular panels today usually fall somewhere between 270 watts and 315 watts, with price points that usually increase with the wattage (in the standard size footprint). Less obvious, however, is the type of solar panel you may be asked to choose between.

In general, your solar quote will include a panel whose cells are made from crystalline silicon. Silicon is us

ed in solar panels not necessarily because it’s the most optimum semi-conductor available – but because of the extensive research on the processing and physics of silicon grown out of the integrated circuit industry. The processes used to access and arrange the silicon determine whether a panel is deemed to be

As the name suggests, monocrystalline panels utilize a single, continuous crystal structure in the processing of the silicon ingots from which the solar cells are made. It used to be that this high-grade silicon resulted in substantially higher efficiency rates than other solar panels. However, improvements to manufacturing in polysilicon processes have closed this gap significantly. Still, homes and businesses looking for the highest possible efficiency rating on a solar panel would likely choose a Mono panel.

The silicon ingots used for manufacturing the solar cells for Poly panels are manufactured by melting many fragments of silicon together to form the ingot. Because this results in many crystals in each cell, there is usually less freedom for the electrons to move. As a result, polycrystalline solar panels typically have lower efficiency ratings than monocrystalline panels.

Should I choose a Mono or Poly solar panel?

As with any choice it comes down to buyer preference:

Aesthetics: In general, Mono panels have more options if you are concerned with how your solar panels will look. If you want something low-profile; maybe a uniform, all-black aesthetic devoid of white lines, silver racking and diamonds – most manufacturers offer this aesthetic in a Mono panel. However, there are now a few poly panels available in all-black. For example, REC has a 280-watt poly panel on the market that is now available in all-black.

Cost:  Mono panels tend to cost more than poly panels. A small roof looking to get the highest possible solar fraction by going with a high wattage solar panel will most likely end up with a Mono panel as these include the highest wattage options (300w plus). However, if a homeowner has the roof space and is looking for the highest possible value, it may be most cost-effective expand the array by one or two more panels and go with a Poly. Many commercial applications utilize poly panels due to the focus on cost over aesthetics, particularly if the panels are not visible from the ground, due to a flat roof installation.

Performance:  Due to the amount of information out there disparaging efficacy of poly panels compared to monos, this is a subject worth broaching. It is true that under factory test conditions, poly solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels. As a result, under high temperatures, poly panels would perform slightly worse than their mono counterparts. Heat can affect the production performance of solar panels and shorten their lifespans. However, this effect is minor, and most homeowners do not need to take it into account. This is evidenced by the standard 25 year manufacturer’s warranty is the same for both mono and poly panels.

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Solar Energy Services, Inc. recently became an approved contractor with the Be SMART Home Loan Program. This State of Maryland financing vehicle offers unsecured loans of up to $30,000 at a 4.99% interest rate. Aimed towards Maryland residents looking to lower utility costs, improve energy efficiency and add value to their Maryland home. The following solar projects qualify:

Solar Electric (Photovoltaic) Systems

These grid-tied solar systems give homeowners the option of purchasing more than 25yr worth of electricity at a fraction of the cost of their “rented” utility rates. Systems are purchase outright, and are eligible for the multiple financial incentives currently available.

Solar Water Heating (Thermal)

These systems are entirely separate from solar electric (PV) systems. They are most cost-effective for a Maryland family of 4 or more who currently heats their home’s water with electric, propane or oil. They require a relatively small amount of roof space and the upfront investment is lower than solar electric.

What are the Loan Qualifications and requirements?

• Maryland resident
• Home Owner
• Verification of income
• Credit score over 640
• Debt-to-income ratio below 50%
• Completion of a home energy audit

There is up to $30,000 in financing available for eligible homeowners.

What other upgrades qualify for the Be Smart Loan program?

Other qualifying energy efficiency upgrades throughout the home could include: energy efficient roof replacement, geothermal system, air infiltration reduction measures, increased insulation, hot water system improvements, heating systems maintenance or replacement, programmable thermostats, ceiling fans, windows, doors, duct work and energy star appliance replacement.

Can any Contractor perform the work?

Contractors must be listed on the State of Maryland’s Approved Contractor List as found here: http://dhcd.maryland.gov/Residents/Documents/besmart/BeSMARTApprovedContractors.pdf

How do I Apply?

1. 1. Schedule a solar site visit with Solar Energy Services, Inc.
2. Submit the Be Smart Home Loan Application along with SES’s proposal of work to be performed
3. Be SMART will processes your Home loan application. Approval is based on your proposal specifications, satisfactory credit and affordability
4. Submit your Home Energy Audit from an Approved Contractor
5. You receive Loan Approval along with the first of two project pay-outs
6. Upon receipt of payment, your Be SMART Contractor, SES, moves forward with interconnection, permitting and subsequent solar panel installation.
7. The final payment is provided by DHCD when the work is complete and a DHCD inspector confirms that the work meets specifications

MORE INFORMATION

CONTACT: BeSMART Home Loan Program

Community Development Administration

Maryland Department of Housing and Community Development

E: BeSmartHome.dhcd@maryland.gov​

P: 301-429-7402 ​​​​

Or

info@solarsaves.net

410-923-6090

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Should we be concerned about the new Republican Administration and the future of Solar Power?

Due to its tremendous growth, popular appeal, and ever improving economics, solar power enjoys increasingly bi-partisan support on the Hill and in Governors offices around the country.  Due to this, we predict very little, if any, impact on solar growth from the current Administration and/or a Republican Congress.  To help explain this, let’s look at the three main drivers of successful solar economics for the typical solar consumer – Federal Tax Credit, SRECs, and cost of solar equipment:

Federal Tax Credit:  30% of system cost.  This has been an enormously successful tax incentive enabling wide scale deployment of solar on both a utility and distributed scale.  Economies of scale have helped to drive the cost of solar; while further increasing demand – allowing the solar industry to grow exponentially.  This has been applauded by both major political parties for the private capital investment opportunities and huge job growth in the solar sector.   In fact, the US solar industry currently employs more people than the US oil, gas, and coal industries combined.

The 30% solar investment tax credit (ITC) was extended by Congress (many of whom were Republican) in late 2015 and is designed to decline in future years to eventually fall back to a permanent 10%.  The ITC schedule from the December 2015 legislation is as follows:

2016 – 2019: The tax credit remains at 30 percent of the cost of the system. This means that in 2017, you can still get a major discounted price for your solar panel system.

2020: Owners of new residential and commercial solar can deduct 26 percent of the cost of the system from their taxes.

2021: Owners of new residential and commercial solar can deduct 22 percent of the cost of the system from their taxes.

2022 onwards: Owners of new commercial solar energy systems can deduct 10 percent of the cost of the system from their taxes. There is no federal credit for residential solar energy systems.

In a nutshell, most in the solar industry believe it would be political suicide for the majority of congressional representatives to vote for a repeal of this enormously successful Investment Tax Credit that is scheduled to decline anyway.  There are too many solar jobs and solar projects in Republican districts for the majority of Republicans to consider advocating for repeal.  The horse is out of the barn and solar is winning!

SRECs: Maryland and Washington DC offer Solar Renewable Energy Credits to solarized homes and businesses.  This is a State/District-mandated incentive that, if anything, shows signs of expanding among the 29 States that have currently adopted an RPS (Renewable Portfolio Standard).  This is largely due to the fact that State Houses wish to support the exponential renewable energy sector job growth amidst the scheduled, declining Federal Support.

Solar Technology Costs:  Advancing technology, manufacturing scale, high adoption rates, and investor confidence in solar technology continue to drive down solar project costs.  We don’t see this momentum changing anytime soon.

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PRESS RELEASE

For Immediate Release

Tuesday, January 10^th 2017

 

Father/Daughter Team Up for DC’s First Community Solar Project

WASHINGTON DC:  January 10^th, 2017.  DC Resident Rebecca Mann and her father Neal Mann are poised to be the FIRST two PEPCO customers to take advantage of Washington DC’s newly revised and adopted Community Renewable Energy Facilities of 2016 (CREF).  After a process lasting three years, the District has finally worked out all of the kinks that enable D.C. residents to benefit from solar, even if they can’t put panels on their own roof.  Community solar offers the benefit of solar to community members (subscribers) who can’t, or prefer not to, install solar panels on their homes. This also gives renters an option to purchase solar power.

For the flagship project, Rebecca Mann is unable to install a solar power system due to limited roof space and shading constraints.  Located one mile away – her father, Neal Mann, is currently having a 16.24kW grid-tied solar power system installed.  This will generate enough power to offset a good portion of both his own, as well as his subscribing daughter’s, PEPCO utility bill —  at full retail price.

The project is currently under construction and is poised to be interconnected and officially net-metered by the end of January 2017.

Solar Energy Services, Inc. is one of the region’s longest running solar installation companies.  Founder Roger Perry has been in the solar energy industry for over 35 years.  His partner, Rick Peters, is a current Board member and past President of MDV-SEIA.  Locally owned and operated, SES installs both residential and commercial solar PV (electric), as well as solar thermal (hot water) systems in Washington DC, Maryland and Virginia.

Useful Links

PEPCO’s Green Power Connection and CREF

History of Washington DC’s Community Solar

For further information, contact:

Lisa Walsh 

Solar Energy Services, Inc. 

410-923-6090 X304

443-253-6941 Direct

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Before we dive into this conversation – let’s be clear that SRECs (Solar Renewable Energy Credits) can be the most confusing part of figuring out the economics of a solar project.  Let’s also be clear that – as with anything confusing, (as well as possibly boring) – the temptation is to remove the confusion as quickly as possible.   In the world of solar installation and selling SRECs this sometimes translates to simply selling up to 15yrs of SRECs all at once to a solar installation company, who then installs the system at a bargain price.  Buyer beware – the immediate gratification of selling all of your SRECs in one fell swoop could be misleading.   When it comes to How and When you get paid for your SRECs “…the Sooner the Better”  may not be a sound financial strategy.

That said…Let’s talk Solar Renewable Energy Credits in Washington DC.

Both Maryland and Washington DC, along with eight other states have enacted the Renewable Portfolio Standards which specify that a certain amount of the renewable energy generated within that state must come from solar.   Whether residential, commercial, or institutional, each time a solar system generates 1 Megawatt hour of energy – the solar system owner generates 1 SREC.  This SREC is then sold via aggregators to an  SREC market where it is bought by Power Companies to allow them to meet their share of the compliance obligation, or else pay a legislated fine (Alternative Compliance Payment, or ACP) for every SREC they are short.  Washington DC currently generates the highest SREC values in the country largely due to the fact that the District does not have the real estate to install large solar farms which can oversupply the market and drive down SREC prices.

How Much is an SREC worth?

The value of an SREC in a particular market is dynamic due to two primary factors

1. by design, SRECs values are intended  to decline over time.  The legislated ACP which serves as a ceiling to the SREC price is usually scheduled to decline in future years. Among other factors, increased installations should lead to decreased system costs and less need for SRECs to help finance a solar system.
2. The other reason for variations is due to market mechanisms.  Brokers buy and sell SRECs in order to help make a market for them.  When the market is undersupplied, SRECs trade high, at a price close to the penalty (ACP).  This is good for those selling SRECs.  If the market is oversupplied (like Maryland is currently), then SREC prices in that market will decline well below the penalty – not so good for those selling SRECs. Varying SREC payment options are intended to allow system owners to buy down their SREC price risk. The difference between an Upfront Payment option and a Brokerage Payment option (market price) can be many thousands of dollars to a solar system owner.  In an undersupplied market like DC, where there is very little price risk for SRECs, that upfront payment option leaves a lot of money on the table.

How many SRECs will my system generate?

The number of SRECs any given system will generate depends upon the output of your system.  For example, an optimized (as in good and sunny) 5.0 kW system in Washington DC would generate close to 6.0 SRECs/year.

How and When would I receive my SREC income?

SRECs are most commonly sold through an SREC aggregator/broker such as Washington DC-based SolSystems.  However, SRECs here in the District are so valuable – as well as stable – that solar panel contractors are also offering to buy your SRECs and simply deduct the upfront payment off the cost of your solar installation.  So THIS is the heart of this article:  Solar owners have 3 choices for how to get paid for their SRECs:

1. Upfront Payment (all SRECs are forfeited for a 5yr or 15yr period)
2. 3yr, 7yr or 10yr Annuity Contract (SREC prices Locked-in for a specific term)
3. Brokerage (Current market price less broker commission).

Sticking with the aforementioned 5kW system example, the following table illustrates projected SREC values for the system, using current SREC prices (November 2016) offered by a competitive SREC aggregator).

System Size = 5kW                            SREC per Year = 6

So, reviewing the column above, this Washington DC Homeowner with a 5.0kW system has these financial options to choose from:

$$$$$:  Brokerage = $32,101.85 over 25yr life of systems (as warrantied)

$$$:  *Annuity =  $18,690 guaranteed then sign-up for another annuity or go Brokerage

$:  Upfront = $8025.60  SRECs cannot be sold again until 2032.

*Annuity is also available in 3 or 5 yr increments, as well as the 10yr

The Brokerage price is exponentially higher than the other prices, does that mean there’s a lot of risk?

Some risk – yes, because you’re not locked-in to a static price.   But remember – historically DC SREC pricing has remained stable (the geography does not accommodate  huge solar farms that can flood the DC SREC market).  You can receive an email monthly that allows you to check on current pricing AND should the price start to decline – you can, at any point in time, switch to an Annuity.  .

If I choose the 10yr Annuity Option and lock-in my SREC pricing, what happens at the end of that time period?

You simply choose another payment option being offered at the time of contract experation.  Maybe you’ll opt for brokerage – or another annuity, up to you.  Same with the Upfront Payment, after 15 years.

How do I receive my SREC income?

Via check from the SREC aggregator which most pay quarterly (except with the Upfront Payment option which would be one-time).   This generally starts around two months after your system has been interconnected by your Utility and the SREC contract set-up.   We do advise that the contractual SREC relationship be kept between a professional broker/aggregator and the solar system owner.  Third parties, such as the solar panel installation company, may find themselves in a conflict of interest.

If the solar system installer is not buying my SRECs, who sets up the contract?

Most reputable solar panel installation companies will coordinate the initial set-up of your SREC contract with an SREC aggregator, as they have immediate access to the documents required for the initial set-up (Passed Building Permit, Interconnection Approval etc.).  Many installers have one or two aggregators they’re used to dealing with – or you may choose your own.

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The Design

When planning a solar panel system for your home, the first consideration for any solar designer is the tilt and orientation of your roof areas.  We need to know which roof(s) will ensure the most optimum solar output – which translates to the best Return on Investment.   For us here in Maryland, the most optimum solar roof orientation is Due South at 180 degrees.  Of course, not everyone has this perfectly oriented roof and our customer base consists of homes that have South, West, East and everything-in-between orientations.  Occasionally we even install on North-facing roofs if the pitch of the roof is low enough that panels are close to flat, or can be tilted southerly.

For homes that face East-West, you may be wondering which roof would best suited for solar.  This is a good question given the fact that the output of your solar panels is directly related to your Return on Investment and how quickly the panels can pay for themselves.

If either East or West favors a more Southerly angle, then that would likely be a more favorable roof.  Assuming that there aren’t issues related to shadingor obstructions caused by chimneys, vents, skylights and other roof-placed items.

If the house has a perfectly split East-West orientation, with all things equal – the next consideration would be roof angle; the lower the tilt (i.e. closer to horizontal) – the more solar energy will be generated over the course of the day.  If the tilt on either side is the same then we would usually favor the West facing side.   Here in Maryland, DC and Virginia we tend to have cloudier mornings, and sunnier afternoons going into dusk.  Therefore we want to capture the late afternoon sun (west facing) more than early morning sun (East facing).  Of course, should you happen to have a tree, chimney or other obstructing factor(s) on the West roof – we’d favor the East.

The Economics

Homeowners looking at an East-West installation often have concerns as to whether or not their system will be profitable enough, compared to its south-facing counterparts.    Disqualifiers for cost-effective solar systems include shading and limited available roof space.  Rarely, however, is a home found unsuitable due to a Non-Southerly facing roof alone.

To illustrate, following is a comparison of a 10kW system’s output respective to East, West and South facing orientations.  Data compiled using the National Renewable Energy Laboratory (NREL) weather data patterns for Baltimore, MD –

10kW system installed on a 20 degree pitched roof with zero shade

	SOUTH (180 degrees)	WEST (270 degrees)	EAST (90 degrees)
ANNUAL OUTPUT	13,224kWh	11,389kWh	11,328 kWh
*Annual $avings	$1853 per year	$1594 per year	$1586

*Savings based on a conservative $3.00/watt installation, and $0.14/watt BGE rate

Data from PV WATTS

As illustrated, although perfectly South would be ideal, the East and West orientations provide a competitive amount of solar and would add only a few months to the payback period.  If you were choosing between East and West (as opposed to installing on both), the difference is nominal.  The choice of which roof may come down to aesthetic preference, distance to utility meter and regional weather patterns.

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Ways in which solar panel arrays can affix to a commercial building are as many and varied as the buildings they serve.  In this article, we’re focusing on one popular method of attachment – the Ballasted roof mounted system.

Many commercial solar prospects in and around the Maryland/Washington DC area have buildings with flat or low-sloped roofs.  These are generally defined as a roof with a 3:12 pitch or less.  For these applications, ballasted systems can offer a way of attaching solar arrays without any (or few) roof penetrations.   Many building-owners prefer this method of attachment as it negates the risk of leaking, particularly on flat roofs that may collect water.  With a ballasted system, the arrays are held down using the weight of the existing solar panel arrays, racking and – most importantly – concrete blocks.  These blocks are placed methodically throughout the system design to secure the arrays in place, resisting wind loads or other types of disturbance.

The addition of the ballast blocks to the solar system arrays adds additional weight to the roof.   As with any commercial solar project, this weight load is analyzed and approved by a licensed structural engineer as required by the permitting jurisdiction – with some differences in each locale.   Ballast racking manufacturers also specify the amount of blocks required throughout a design.  The number of blocks per panel typically varies throughout design due to array proximity to building edges, parapets, or other inconsistencies that can affect wind and snow loads.

Although ballasted systems have many advantages, as with any design, they have their disadvantages and are not compatible with every type of commercial building.   Let’s look at a generalized comparison scenario between a roof penetrated system and a Ballasted System:

	Roof Penetrated System	Ballasted System
Labor Costs and Criteria	HIGH:  Penetrations require flashing and sealing techniques – sometimes requiring coordination with a roofer.	LOW.   Labor skills required for installation are fairly straight-forward and require no roofer coordination.
Panel Count	INCREASED:  Systems attached to roof substructure require less roof space for mounting.	DECREASED:  Ballast-blocks require roof space and can limit the available space for solar panels
Roof Loading	DECREASED.  No concrete/ballast block	INCREASED:  Ballast blocks add weight to the roof
Design Criteria	FLEXIBLE:  Attached racking systems can usually negotiate hatches, HVAC equipment	LESS FLEXIBLE:  Because of the increased space required per panel – designs may be more rigid.  However most ballast racking does have reasonable flexibility.
Roof Pitch	5 – 45 degrees	Generally less than 10 degrees

 

Multi-roofed commercial applications may have a variety of racking types for both sloped and pitched roofs. There are other options for flat roofs also, including attached and hybrid solutions that use a combination of both penetrated and non-penetrated techniques.

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SOLAR OPEN HO– USE with Kirk Cummings

WHEN:  Sat, Sept 17^th 2016   |   2pm – 5pm

WHERE:  4919 Windpower Way, Ellicott City  MD  21403

Nothing says Sunshine’s a Wastin! like a freshly installed solar power system.  Join Kirk at this Howard County residence to get up-close-and-personal with an active solar system.  The homeowner will be on hand to answer questions about their decision-making process as well as working with SES.

Kirk will be on hand to tour the system with you and answer all of your questions onsite at the home of the Syed Family where Kirk designed and SES recently installed an 8.55k Solar power system including(30) Suniva 285 watt Solar panels and a Solar Edge Inverter System.

Solar Open House – $250 Discount!

All open house attendees who sign up for a proposal and sign their contract within 30 days will receive a $250 discount on their PV system installation.[/vc_column_text][/vc_column][/vc_row]

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Fannie Mae Agrees:  Solar is a MUST-DO for homeowners

Just last month, Mortgage Giant Fannie Mae announced their new mortgage option that allows solar energy projects to be rolled into the final mortgage amount.  Namely, the HomeStyle Energy Program is hot news for solar fans who use a Fannie Mae-approved lender for their mortgage; whether considering a first-time solar system purchase, or currently financing an existing solar system with an equity line of credit or unsecured loan.

Typical Solar Financing and Solar Energy

It’s no secret that solar energy system installations in Maryland and Washington DC have taken off like gangbusters.  In previous years, many Maryland homeowners were choosing to lease/rent solar panels in an effort to avoid upfront costs.  However, when compared with an outright solar purchase – a 20yr (or similar) solar lease proves to be quite expensive – as with most rental agreements.    Depending on whether the solar shopper lives in Washington DC or Maryland, the financial incentives (tax credits/SRECs) usually pay for between 40 – 80% of the system cost.  100% of this upfront solar cost needs to be sourced by the homeowner who usually use a financing vehicle such as an Equity Line of Credit or some sort of Unsecured Loan.

Fannie Mae’s Game-Changer…

As of June 2016, Fannie Mae borrowers have access to a new Energy Loan that allows them to simply add the cost of their solar system to their existing mortgage.  Here’s what makes this form of financing a game-changer:

• Super-Low APR:  HomeStyle Energy can be used for new projects or to take higher-interest unsecured loans/lines of credit and refinance them or roll them into a potentially lower-cost mortgage.   In all likelihood this will result in unprecedented low financing costs for solar energy.
• All Costs Covered:  Most financing vehicles have a non-negotiable cap on the loan amount, forcing some Homeowners to come up with a down payment.  With this program, lenders can finance up to 15% of the final property value.  For example, a typical single-family home located in Annapolis, MD may appraise for $350,000.  The available amount for the solar system on this Annapolis home would be $52,500.  In most cases, this amount would far exceed the amount of capital needed to complete the project, considering that most solar projects fall in the $24,000 – $34,000 range (before government incentives).
• Peace of Mind:  The improvements also have to come with an energy report, whether a Home Energy Score Report or a Home Energy Rating Systems report, and must specify the monthly savings to the borrower.   Homeowners can rest assured that their mortgager fully supports the home improvement investment.

Does Every Home Qualify?

At this point in time, only Fannie-Mae  homebuyers or refinancers qualify.  The program does not extend to new construction or manufactured housing.  The following are eligible to apply:

• New homebuyers
• Existing mortgage holders looking to refinance their new solar system
• Existing mortgage holders looking to refinance their existing financed solar system

All applicants have 180 days from close of mortgage note to complete the solar installation.  Bear in mind that refinancing homeowners may incur closing/additional fees in the transaction.

Contact your mortgage representative to see if the HomeEnergy Program is right for you.

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If you own or are planning to own your own solar power system, you’ve probably heard of an Inverter.    Although a vital part of any solar electric system, inverter choices can easily be overlooked in the shadow of seemingly more important decisions such as installer and solar panel options.   I mean, doesn’t an inverter just change the solar energy (DC) to house energy (AC)?  How complicated can it be?  Contrary to what your salesman or inverter manufacturers may have you believe, there is no “one size fits all” inverter.   As with many electronic devices; design, cost, warranty, time-testedness and monitoring capabilities are variables designed to offer as many choices as the different homes, businesses and climates they inhabit.  For example, you wouldn’t want to pay a premium for an inverter designed to deal with partial shading issues – if you have zero shading.  At a minimum, you’d at least appreciate knowing how the “other” inverter would affect the contract price.  So, in this spirit – let’s take a preliminary tour of the Inverter (or optional, microinverters).  Inverters have three primary functions:

1. Inversion of the incoming DC energy (direct current) into home and appliance-friendly compatible AC energy (alternating current).  This is its main function.
2. An MPPT (maximum power point tracking) function ensures that the inverter receives the maximum amount of power from the solar panel by adjusting the voltage (load) to match what the inverter wants; managing the complex relationship between sunlight and other varying conditions.
3. Various electronic monitoring sensors that will, for example, detect when there is a fault in the grid-tied solar panel or on the grid and shut down power so the solar system cannot injure power-line workers during a grid outage.

The most traditional form of Inverter is a String Inverter, so-called because it is connected to a line or “string” of solar PV panels.  One solar power system, depending on the size/number of strings in the system, may have one or several string inverters which sit in parallel and convert the arriving DC current into an AC output.

These six string inverters service a large commercial solar electric (PV) system. Each inverter services forty solar panels, on four strings of 10 for a total of 240 panels.

Micro-inverters and Power Optimizers

Another type of inverter is the Micro-Inverter.  As the name suggests, this inverter is a smaller version of a string inverter, but rated to handle the output of each individual panel.  Therefore an inverter is located on the back of every solar panel unlike a string inverter that is often located on the side of the building/ground level.  Micro-inverters have been around almost as long as string inverters.  Historically, the manufacturing costs involved with making a dozen “mini” inverters couldn’t compare to the cost of one large string inverter.  However, as the solar industry has grown  – so has the demand for the micro-inverter; driving up demand while reducing production and distribution costs.

In response to the popularity of the micro inverter, Tigo, followed by String inverter giants SMA, developed a device called the Power Optimizer that works in conjunction with a string inverter.  As with micro-inverters, power optimizers are placed on the back of each panel and provide an MPPT function to each panel – limiting individual shading and orientation effects to the panel they’re attached to as opposed to the whole string.  However, because they are designed to operate alongside a string inverter they do not require individual transformers and are therefore much smaller, lighter and most importantly, cheaper than micro-inverters.

Solar design expert, Rich Schroeher says there is a time and a place for all three of these inverters:

Q:  Aren’t micro inverters better when the solar arrays are facing different directions or have different roof pitches?

Rich:  With micro-inverters, in essence, each solar panel is it’s own solar system, independent of the other panel/ inverter combinations, so various orientations of panels are easily accomodated.

With string inverters, a different inverter must be used for an array that is facing a different direction, or at a different pitch than the other arrays.

One way around this is string inverters that contain 2 MPPT inputs. These are, essentially, 2 inverters in one. They also have the added benefit of being able to handle more of the array than their rating. For example, let’s say you have two arrays facing different directions: one South facing and one East facing.  The entire system would use a 5000 watt inverter divided into two channels of 4000 watts for a total of 8000 watts.  The inverter will still only supply 5000 watts but when the south roof starts getting sun, the east roof is losing it. If at anytime more than 5000watts is being fed to the inverter, it just limits it to 5K.

 

Q:  Some homes have partial shading on the roof. How do you know when to use a string inverter – possibly with dual MPPT, or a power optimizer – or stick with a microinverters that will ensure a shaded panel won’t negatively affect the whole array’s output?

Rich:  It depends on the situation. Microinverters and optimizers can help with small areas of shading but are not a cure-all. They work best for an application where a small % of the roof is shaded at various times during the day, such as a chimney shading a few collectors where the shadow moves during the day.

Q:  Are there any longevity differences between string and micro inverters?

Rich: Opinions vary.  A solar system with 24 micro inverters, as opposed to 1 string inverter, has 23 more points of failure.  Plus the extreme temperatures that microinverters are subjected to can be an issue; electronics generally don’t like heat.  Microinverters are also located on the roof behind each panel, as opposed to the string inverter which is usually conveniently located close to the main electrical supply on the ground level.

Q:   Enphase microinverters claim to get greater efficiency, up to 16%, than their string counterparts due to the fact that the maximum power point is matched to the solar panel as opposed to the inverter, which limits the available output.

Rich:  In a Partial shading situation this could be true. If there is no shading at all or very early or late in the day when production is very low anyway it wouldn’t be near that high.

There are only two notable benefits that microinverters offer in a zero shade situation: they eliminate the string inverter losses from module mismatch (very small differences between modules), around 2 – 3%.  They also help with DC wiring losses.  Combined those two losses may be 5% overall.  This all assumes that the module attached is not too large (powerful) as to have any appreciable amount of clipping – meaning the full power of the module is limited by the inverter.

Q:  Microinverters, are more expensive than string inverters, at $.70/watt with a twenty-five year warranty.  Although String inverters are as much as 50% less, they often come with only a ten year warranty.  Doesn’t the microinverter’s longer warranty cover the inflated cost?

Rich:  In the long run probably no. Most string inverter companies’ offer extended warranties up to 20 years. Some include the cost of labor to replace. The labor cost to replace is about equal for a string inverter and a microinverter or perhaps a bit lower for string inverters depending on where in the array a failed micro is located. Say you have a system with 20 panels and the labor cost for inverter replacement is $150.00

      String inverter cost over lifetime $150.00

      Microinverter cost over lifetime  as much as $3,000.00 Plus 19 more scheduled trips and possible inconvenience to the owner. 

Q:  SMA’s new inverters include a “Secure Power Supply” capability.  What is this?

Rich:  This is a small (15amp) receptacle that is powered up when the grid goes down. As long as the sun is shining it will provide 120 volts of AC electricity. My first thought was to power a refrigerator or freezer to help carry a system owner through the outage without food spoiling.  It can’t be used at night but it will let you use some of the system during outages.

As is often the case, there are no cut and dry answers here. Variables such as system size, shading, orientation, panel layout and budget will determine whether a String, MPPT optimizer or micro-inverter may or may not be the best choice for your roof.  Most installers/designers worth their salt will consider all of these options and come up with the best solution for your house.

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