Residential Solar Panels, Solar Installer
Written by Lisa Walsh

Solar on Slate Roofs in Washington DC

Residential Solar Panels, Solar InstallerWith Washington DC offering homeowners the best solar incentives in the country – its small wonder that solar panels are going up like hotcakes. In order to meet the demand, most solar installers are adept at designing and efficiently installing solar panel systems on most roof types in DC: namely flat roofs and asphalt shingle. However, homeowners with a traditional slate roof will need to shop around for a qualified, slate-savvy installer.

Slate Roof Challenge

Washington DC Solar,Solar ServiceIn this order, the most common types of residential rooftops in Washington DC are flat, asphalt shingle and slate. Asphalt shingle are generally the simplest type of roof to attach to. They are flexible, soft and flashing/sealing all of the attachments has been fine-tuned to near perfection by the solar industry. Flat roofs are generally installed using no/few penetrations either with parapet-to-parapet rails or ballast-weighted systems. Slate, however, is among the most challenging roof type to work on for the following reasons:

  1. Expertise Tools and Labor Required

    Solar Service, Home Solar PanelsTraining a work crew adept at installing solar on a slate roof takes a significant investment of time, tools and techniques. As slate is a type of stone material – specialized diamond-tipped drills and copper replacement nails are required to penetrate and reattach the slate; drill too fast – and you’re likely to break the slate. Even with the most cautious of installers, a number of slates are still likely to end up broken and spares need to be kept on hand. Ideally – artificial slate can be used for replacing broken slates. Specialized flashings designed for use with the larger slate tiles must be used to seal around the attachment.

  2. Additional Labor

    Due to the fact that slate is essentially a smooth, slippery thin stone – this can be particularly challenging for installers to navigate. Couple this with a steep pitch, and extended hours on the roof due to time-consuming drilling techniques, labor estimates can easily double or triple when compared to an asphalt shingle roof; not to mention a particularly challenging and long day(s) for the installation crew.

The above two points ultimately result in increased costs for the customer. Fortunately, for DC residents with slate roofs, the financial incentives are such that paybacks are still generally under (or around) the 5 year mark – with many years of clear income to follow. Furthermore, as slate roofs can last 100 years or more, the roof and solar combination is set for a minimum 25 year relationship – and likely a good decade beyond that.

Home Solar Panel ,Solar Service
Written by Rick Peters

Peters’ Journey to Net Zero

Solar Service,Home Solar PanelsWhat Net Zero Meant for Us? Our Severna Park based, four-person family was looking to offset some of our home’s dirty energy, but we really did not have an expectation we could offset it all, but we had to start somewhere. We took our first step shortly after I joined the solar industry in 2008.

Low Hanging Fruit. In February 2009, we installed a 120-square foot solar water heating system to offset most of our water heating, and a small portion of our space heating for the first floor of our home. We saw big savings from this 3-panel system right away. Ever since, I enjoy the act of turning off the back-up water heating in April and leaving it off until almost October. For us, offsetting a dirty and expensive oil-fired boiler was the obvious low hanging fruit. We would later convert that remaining load to natural gas when the utility extended the pipeline to our home.

Solar Electric (PV) With the rest of the heat, A/C, and appliances all running off electric, it was time to look at the next opportunity. A few years later, when budget allowed, we decided to add a 5 kW solar PV system to our second story roof which faces SSE. My best determination was that we offset just over 40% of our electric load with that PV system. We were happy, but knew we’d want to find a way to get to NetZero eventually. , . I began to evaluate the remaining rooftops and consider what it would take to get us there. Solar panel efficiencies had improved a lot over the past several years so this reduced the remaining roof space we’d need to hit our goal

Phase 2 (PV). In the spring of 2016 we finished filling the balance of the south roof with some slightly higher wattage panels. As part of the same expansion, we added 24 relatively high efficiency panels to the E/W, low slope, rooftop of our one-story garage. We now had a total of 6.6 kW Equivalent of solar thermal and 13.8 kW of PV.

Not There Yet….We almost tripled our PV with the last upgrade and according to my calculations, this would get us to NetZero electricity. We’d know for sure by April, the annual true-up time frame for netmetering with BGE. When April 2017 came around, we were disappointed to come up a bit short (unfortunately, with a couple teenagers in the house, my usage predictions were a little off). Where do we go from here? I was not ready to put panels on the north roof, there had to be something available to us on the demand side.

Oops – More Low Hanging Fruit…One thing about Energy Efficiency, there’s always more opportunity. I had changed out many bulbs to LED over the prior several years, mostly through attrition, but I had not replaced any of the more than 2 dozen canister lights we had throughout the ceiling upstairs and down. Not only were these lights very inefficient, but the heat they generated in the summer was just adding to our air-conditioning load. We found the LED replacements on sale and replaced them all, as well as the remaining few incandescent lights in the house.

Commercial Solar Energy,Solar ServiceEureka. we have arrived!… In April of 2018 we received a $46 check from BGE for the annual overage from solar. With the kids heading off to college soon and a new refrigerator around the corner, I’m confident our checks from BGE will be getting bigger for the near future. At least until we purchase an electric car…

Solar Service ,Home Solar Panels
Written by Lisa Walsh

Poly Vs Mono Panels for Residential Solar Installations

IfSolar Service, Home Solar Panels,Commercial Solar Service ,Annapolis MD – 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.

Washington DC Solar, solar renewable Energy,
Written by Lisa Walsh

Washington DC Solar Owners and Selling Solar RECs Upfront

Solar Service ,Home Solar Panels

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.

solar energy, renewable,
Written by Rick Peters

PACE Solar Financing in Maryland and Washington DC

Typical Commercial Challenges

As veterans of the small commercial solar market in this region, we are very familiar with the challenges of financing solar energy systems to this group of property owners.  Small businesses want solar as much or more than any other market segment, but they are capital-constrained like no others so they need affordable financing.

Third party solar developers have been the answer for other markets.  They can easily finance large systems because the cost of assessing the applicant’s credit is well worth the return.  In the case of residential systems, they can use universal tools like credit scores to help manage their risk.  For the small commercial and non-profit market, there hasn’t been a super-attractive  way to finance solar, until now!

Commercial Solar Systems Now Recognized as Public Benefit

Washington DC and Maryland now have laws and programs in place for commercial (and nonprofit) property owners to utilize PACE.  Property Assessed Clean Energy (PACE) is a vehicle that is used to finance energy improvements for buildings.  It operates under the recognition that energy improvements are considered to be a public benefit.  As such, PACE uses the property tax as a vehicle to structure the financing payments – much like we would finance a sewer extension, but in this case specific to one property.

PACE is very appealing to property owners because they can add significant value to their building on a cash-flow-positive basis without personal guarantees or the application of additional debt to the balance sheet.  The financing payment must be less than the savings and it’s paid in the form of a special assessment on the property tax bill over the term of the financing arrangement (5-25 years at competitive rates).  Multiple energy improvements (i.e. lighting, solar, new roof) can be bundled into one financing package.

The best thing about this approach to financing solar is that the property owner will own the system, not a third party.  The property owner gets all of the benefits, including the energy savings, the substantial incentives, the marketing value, and the satisfaction.  All it costs them is the interest on the financing which pales in comparison to the savings.

More info is available on your webpage on our PACE webpage but you may just want to pick up the phone and call us to see if your property is eligible.

Solar Service ,Home Solar Panels
Written by Lisa Walsh

DC Property Owners: Big Hot Water load = Big Solar Incentives

Commercial Solar Service, Annapolis MD

A growing number of building owners, developers and condo associations in the District of Columbia have come to realize that their building happens to be located in the most solar-friendly city in the USA .  Solar contractors, investors and financing vehicles are falling over each other to get solar panels on District roofs and start generating  the lucrative solar renewable energy credits (SRECs).   Whether via Direct Purchase, or $0 solar leases – SRECs are undoubtedly the reason for the solar season in DC (more to follow on those below).

However, before you sign on the dotted line and fill your roof with a 25-year solar PV (electric) system, as offered by 9 out of 10 solar professionals, make sure that you’re not losing the opportunity to vastly increase your return on investment with a Solar Thermal System.

Solar Water Heating Feasibility

The pre-qualification for a Solar Thermal System involves three questions:

  1. Does your building have a substantial, daily (365 day) hot water need? (i.e. apartment building/condos, restaurant, laundry, brewery, health center)
  2. Does your building have a centralized water heating system (as opposed to individual units throughout the building)?
  3. Can the building accommodate additional storage tanks?

If you answered YES to these three questions you really (really) should first consider a Solar Water Heating system either before – or at a minimum – in tandem with, a solar PV system.  (Shopper Beware – unless your solar contact has experience with solar thermal – which many do not – you’re going to have to be prepared to shop further).

What is Solar Water Heating (or Solar Thermal)?

Other than using the sun for energy generation, Solar Water Heating Systems operate entirely differently from their electron-shaking PV counterparts.  These time-tested, technologically mature systems are mechanical in nature and relatively simple.

Moreover, a solar thermal panel is 60 – 70% efficient; whereas a solar PV (electric) panel is typically 17 – 24% efficient.  Therefore, solar thermal panels generate substantially more energy per square foot than PV panels,  monetizing many more SRECs.

Solar Service , Home Solar Panels, Solar Renewable Energy

 

Let’s Review SRECs…

SRECs (Solar Renewable Energy Credits) – along with the 30% Federal Tax Credit and 100% Year 1 depreciation– are what drive the tremendous economic benefits of solar in Washington DC; one of several jurisdictions that have enacted a Renewable Portfolio Standard requiring that a specific percentage of electricity consumed 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 competitive energy suppliers 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 DC does not have the real estate to install large solar farms which can rapidly oversupply a market and drive down SREC prices.

How much are SRECs Worth?

Washington DC SRECs are currently trading at $395/SREC.  To provide a frame of reference, a 6000 sq ft rooftop in Washington DC outfitted with a 75kW solar PV (electric) system could generate around 90 SRECs/year (over $35,000/year).   Depending on variables such as system size, corporate tax rate and and project site attributes, this SREC income – combined with a 30% Federal Tax Credit and 100% Year 1 depreciation, typically result in IRR’s between 30% – 60% and a Simple payback of 3 – 5 years.    Assuming solar thermal is applicable, this same roof outfitted with a Solar Thermal System could fit a kWh equivalent of a 150kW+ system, generating 180 SRECs/year – and see an IRR of 50 – 80%, with a simple payback in the 1 – 2 year range.

Solar Service ,Home Solar Panels, Residential Solar PanelsMaintenance

Although Solar PV (electric) clients often opt for an O & M (operations and maintenance) contract through their solar installer, Solar PV Systems  have relatively minor maintenance needs; usually an annual inspection along with ongoing monitoring.    Solar thermal (water heating) requires a little more maintenance including a 3 – 5 yearly service which, at a minimum, includes a replacement of the propylene glycol/energy transfer fluid that can degrade with time.  Nonetheless, the impact of service costs on the overall IRR is relatively small and easily absorbed by the increased SREC income.

Written by Lisa Walsh

A Primer on Solar Power

Did you know that attempts to harness the sun’s power through the development of solar cells dates back to the late 1800’s? I am sure that this, and other information, may be new to our readers. This article will provide you with some basic facts about solar power and solar energy. That way, you can join the conversation, and the renewable energy movement!

  • The first successful solar cell was developed in the early 1950s. It was made of silicon, and able to power small electronic devices. This was hailed as the beginning of a new era of energy resources, even then being acknowledged as having the potential to offer a limitless supply of electricity.
  • The first true application of solar cells could be found in the space program at NASA and in Russia. They were the only ones who could afford this technology in the 1960s.
  • The cost of solar cells continued to decline incrementally, but not so significantly that solar was a common source of energy through the 1970s. But, as the 1980s dawned, and ever since, solar power has insinuated itself into all aspects of life, commercially and residentially.
  • The first solar panels for buildings were developed in the early 1970s. In truth, this initial foray into the potential for large scale residential solar power was actually a solar array built into a rooftop. Panel development followed, as the cost and manufacturing efficiency increased.
  • President Jimmy Carter had solar panels placed on the roof of the White House in 1979. Everyone was getting into the act!
  • Welcome to 2018. Today it is common to find solar-powered cars, solar-powered telecommunications, and even solar-powered aircraft. One car company, renowned for their progressiveness, has incorporated solar panels into the roofs of their vehicles!

But, there’s more! Technology continues to expand the horizons of solar energy, making it affordable and applicable in new ways and new places. For example, it is possible that eventually solar panels on rooftops will be replaced with solar shingles!

Or, consider this, a solar fabric is being finalized that can be attached to houses as a cooling device!

We here at Solar Energy Services are excited about the future applications of this renewable source of energy for personal and commercial uses. You can count on us to utilize our superior knowledge and expertise to your advantage. We look forward to serving you!

Home Solar Panels,Eastern Shore MD
Written by Rick Peters

Solar Energy Trends

Some Positive Trends:

Eastern Shore MD,Residential Solar PanelsThe Challenges:

Industry consolidation can be disruptive

Residential solar leasing is fast outpacing cash sales in many of the more developed states, like Maryland. It’s what many Americans want so it will continue to drive the market. It seems to work for more of America.   After all, we do like instant gratification and if I can save $10/month immediately, and feel good about it, where do I sign? While SES is typically strongly advocates for cash sales to our customers who are able, no one can argue the enormous impact and value that the various residential and commercial financing options have delivered. Getting solar access to the mainstream will be the most critical piece to advancing the development of distributed solar. It really has been transformational so far.

There’s other good news. System Pricing, though leveling off somewhat, has dropped dramatically in the past 5 years. While incentives decline as planned, the industry continues to drive down installation costs to maintain the impressive paybacks and internal rates of return.

Beneficiaries of solar price reductions include states like Maryland, who had the foresight to seed this industry over the last 6 years. Government and industry partnership in Maryland has built an economic environment that supports solar development and as a result, it is sustaining 2200 jobs while Maryland continues to meet its solar RPS goals. That’s right, our industry delivers over 2200 paychecks in Maryland. In fact, there is now a solar thermal equipment manufacturer in Baltimore. Much to be pleased about.

There’s also a darker side. Bankruptcies and consolidation of solar companies have carried the headlines quite a bit in the last year especially. While a natural part of the tech/business evolution cycle, consolidation and shake out are always disruptive, not only to industry members, but also to consumers of these solar energy products and services. As a result, all of the solar “investors” are asking lots more good questions – particularly about the longevity of the manufacturer and the installer. Popular questions, particularly in the solar PV panel world, are “Who will be here to support my warranty?” and “What is the design track record of these systems?”

The beneficiaries of these trends will be those with a proven commitment to the industry either through time or capital. It’s that commitment that gives customers confidence of future support if and when it is needed. Whether it’s an installer with 35 years experience or a manufacturer like SunPower that has 25 years in business, longevity is a key indicator of future availability to support the install base.

Commercial Solar Energy ,Residential Solar Panels
Written by Lisa Walsh

Inverters: One Size Does NOT Fit All

Home Solar Panels ,Washington DC Solar,Commercial Solar Energy, Residential Solar PanelsIf 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.

Commercial Solar Energy, Residential Solar PanelsThese 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.

Written by Anonymous

Offset Your Oil-Guzzling Water Heater with Solar!

Offset Those Oil-Fired Water Heaters with SOLAR

Why oil-fired water heaters?  In many parts of the country there are no local gas lines for residential distribution.   In the Chesapeake Bay region where we operate, this issue is very common in the many river communities that are close to our world famous estuary.  The reason for this is primarily because there are so many peninsulas that don’t offer the high density to justify pipeline expenses.  In these areas, customers are forced to use other fuels like electricity, propane, and oil to heat their homes and domestic hot water.  This article will focus on the oil-fired boilers that are common in this region as well as in the Northeast US.

Cost of Gas Alternatives:  Many homes have heating boilers that run on fuel oil.  These boilers have tremendous heating power and can recover loads quickly.  They also tend to be relatively inefficient, dirty, and expensive to run.  Many of these boilers also have an on-demand water heating feature that adequately satisfies the household’s water heating load without the need for a standby tank.  This all sounds great except the price of home heating oil continues to climb with recent prices around $4/gallon on in our area.  To put that in perspective, the equivalent price for natural gas on an energy density basis would be about $1.00/gallon.  When oil users are paying 4 times the rate of those who have access to natural gas, they can hardly afford to be wasteful in how they operate their boilers.

Summertime Blues:  Here’s the dirty little secret about that on-demand oil-fired water heater on your boiler.  It is typically programmed to keep that big hunk of metal hot, all summer, waiting for you to call for hot water.  So a premium for your oil (compared to gas) is not the only thing you are paying for.  During summertime your air conditioner is competing with your heat-radiating oil-fired water heater.   So, here’s the way I – a not-so-proud owner of an oil heater – circumnavigated this issue:

My Solution:  I have solar photovoltaic (PV) on my home, but when I got into the solar business in 2008 the first thing I did was deploy solar water heating in my family’s home which allowed me to shut down our boiler for about half the year.  We also did some other control modifications for efficiency.  The first simple control is used to automatically reduce the boiler target temperature as the outside air temperature increases – for example, you don’t need 180 degree water to heat the house when its only 50 degrees outside.  Secondly, we converted the boiler to “cold start”, so it no longer wastefully heats on standby when we have a big tank of solar-heated water waiting to be used.  My family’s solar thermal system is slightly oversized (there are 3 forty square foot panels instead of 2) so that it could be integrated with our hydronic space heating system to give us a little space heating help from the sun.  [See our recent blog on combi-systems (hyperlink)].

So that’s the good news.  The GREAT news is that there has been absolutely no convenience impact on how we use hot water or space heating.  The system has saved us about $800/year in oil       expenses, the majority from offsetting our inefficient water heating, and the remainder from space heating.

Furthermore, the solar heating system is optimized in the summertime, all-but-negating the use of the oil-fired water heater.  The air conditioner has to work far less without having that heat-radiating boiler inside the home – like most are.

People are learning that different homes and circumstances often can benefit substantially more than others when you consider various renewable or energy efficiency technologies.  Oil fired water heaters are some of the sweetest low hanging fruit in solar.  In fact, I joke with my residential oil supplier that we should team up so he can get out in front of this trend that is eating into his oil sales.  He said, “no thanks – I’ll ride this as long as I can”.

If you forgot to make a new year’s resolution this year and you heat your home and your water with oil, then plant your flag!  If you’ve got some solar exposure, you must commit to get a free solar thermal assessment in 2014 and stop pouring money and finite resources down the drain.

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