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Photovoltaic (PV) Solar Electric Systems

Photovoltaic Solar Electric InstallationSolar electricity can help you cut your electricity costs and protect you from future price increases.  Solar electric systems are called Photovoltaic or PV.   A group of PV modules called an array.  These durable panels, with no moving parts, are normally installed on your roof or a ground-mounted rack.  When the sun’s radiant energy hits the solar modules  DC electrical current is created.  The DC electricity feeds into an inverter that changes it to standard AC electricity - the same kind your home uses.  The average PV module is about 40" x 60" and can face either in portrait or landscape.  In Maine to offset a $70 a month electric bill you need about 12 modules which fill less than half of the roof on an average size cape.   At the start of 2014 an average price would be about $11-12k  before the 30% federal tax credit.  


Why keep paying CMP when for LESS money you can own power plant?  

The price on PV panels has dropped sharply since 2011. In our area we are seeing prices under $3 per watt installed after the federal 30% tax credit (visit DsireUSA.org  for more information).  This puts the pay-back time for an average system near 10 years.  You can expect your system to be running long after the 25 year warranty.  That is a lot of free electricity.  Plus Maine offers Pace, Powersaver and other loans  where families can borrow up to $40,000 for energy upgrades including solar. Efficiency Maine's goal with these loan programs is to have the energy savings cover the monthly loan payment.  Financing your PV system means you can be net cash positive the very first month.  In some states there are finance companies providing leasing or Power Purchase Agreements (PPA). With these programs you do not own the system and you agree to buy the power generated for a fixed time frame and a preset (often increasing) amount that is slightly less than the utility company is charging. The problem with these "solar leasing" programs is the finance company needs to make nice profit off of you.  Avoiding that is one reason to escape from Utility power.  If you can qualify for a lease you can usually qualify for no money down financing. With a lease you may be paying for 30 years.  Leasing companies also promise to warranty your system for the term but since PV systems have no moving parts it is unlikely you will have any failures and if you choose micro inverters they have 25 year warranties just like the panels.  So there is little value in the (read the fine print) extended warranty.    

In about 10 years (a bit more if you finance) you have recouped your investment and with expected lifespan of 40 years that is 30 years of clean energy with NO POWER BILL.  With our no money down 4.99% financing your loan payments can be LESS than your electric bill. We work with both Efficiency MaineEvergreen Credit Union and Admirals bank to find the right finance program for you.  You can either pay CMP each month or you can use the same money to buy your own environmentally responsible power plant.  

The CMP standard offer supply rates took a sharp turn upward in late 2014 and commercial accounts are saw huge increases. It was expected that residential rates were increase by 25% come March 2015. Luckily the games the Saudi's are playing with oil prices drove down the electric supply prices and the utility was able to take advantage of low bid. Unfortunately it is only good until 12/31/15. To keep rates stable on residential supply the Utility takes bids on 1/3 of its needs each year.  So at the end of 2015 they will need to source 2/3 of their power requirements and predictions are that rates will soar as they are in other NE states.  The Portland Press had a great story outlining the expected increases.

Tax Credit **

The 30% federal  tax credit can be carried forward if you cannot use it all this year. This is an actual credit so provided you had the correct tax amount withheld from your paycheck you should expect a refund.  At the end of 2015 the 30% tax credit was extended for 5 more years.  The program has been quite successful in raising awareness and the solar industry is booming (outside of Maine--Gov LaPage does not think solar is cost effective or proven technology so we lag behind, again). 

**we are not tax advisers, please check with a professional 

Grid Tied Solar with Net-use meter

UPDATE:  In March 2016 Governor LePage once again vetoed the solar legislation put forth.  Shamefully some of the republicans caved to the governors repeated threats and pressure and we ended up a few votes to override the veto.  Please be advised that changes to the metering program will be evaluated by the PUC late this summer.  This situation is consistently changing.  Please call us for more details on how this could impact your purchase decision. The solar industry and so many other continue to fight on behalf of Maine homeowners and small businesses.  The NRCM web site has a nice summary.

In most installations, PV electric works just like power from the grid. No batteries are required to store electricity because you remain grid tied with a net-use meter.  The utility company acts as your battery.  With a net-use meter you are credited for any extra power you generate.  If your system is sized to meet 100% of your need you will find in summer you have excess production and in the winter or at night you pull from these credits.   In some states the electric company will buy your excess production, but not in Maine. Our electric companies use a 12 month rolling window to evaluate your credits and debits.  If there is a credit remaining in month 13 they take it, and they don't even send a thank you note.  

You can feel really good about pushing your excess watts into the grid in the summer.  Peak loads occur on hot summer days when A/C units kick in.  At these times the electric supply companies pay a premium for electricity and the grid is close to capacity. Your watts help power your neighbors homes lowering the grid demand and reducing the need for expensive grid expansion, which is paid for by all ratepayers.  They also reduce the amount of expensive electricity that your supply company must purchase and this helps keep everyone's bills lower.  You give high value watts in exchange for low value night time watts.  Solar is good for everyone not just those that own the array. 

Maine's utility companies also charge a monthly service fee to be connected to their grid.  As of 2016 with CMP this is about $11 per month.   On some level this is logical.  Despite the fact you have a PV system they still must meet government requirements regarding maintaining grid capacity to meet demand.  Should your PV system ever fail they are ready to provide power to your home. 

If your PV array is not producing enough to meet your current demand you pull your power from the grid as always. Should the grid go down, you would lose power despite the fact your PV system is producing. This is a safety feature called anti-islanding and is required by the national electric code.  It prevents power from entering a disabled line and harming line workers or causing other damage.  It is possible to install an automatic grid disconnect switch and small battery bank to switch to battery power in case of an outage although a generator is usually less expensive.  Home Power has a 1 page article that addresses the extra costs of adding batteries.   SMA, a leading inverter manufacture, released their TL line of inverters in summer 2013.  When there is a power failure these inverters disconnect  from the grid and activate a 1500 watt plug. Of course you only have power when the sun it out but it may be enough to keep your refrigerator cold and keep your phone and laptop charged.  We think all the other manufactures will quickly follow their brilliant lead. 

Off Grid Solar SystemsOutback battery enclosure

If connecting to the power grid is cost prohibitive or undesirable  a battery bank will be necessary to provide electricity.  Batteries will raise the price of the system 30% or more depending on how many days reserve you want to store.  Careful calculations must be made to determine the amount of energy you expect to use each day and the number of batteries needed to store this energy.   Properly sizing the battery bank to the loads will insure you batteries regularly gets drawn down, but not too low as to damage them. This will give them the maximum life span.   It is not a simple process to figure this out.  You will need to decide what appliances you intend to use and for how long each day.  There should be a label on each item showing the electric draw and with motors there will be a "start up" number which needs to be taken into consideration.  The number of PV panels in the array will determine how fast the batteries can be charged.  A camp used only on the weekends can have a small photovoltaic array since you have from Monday to Friday for charging.  A primary home with the same daily electric demand will need a larger photovoltaic array to quickly charge the batteries.  Off grid systems use a standard string inverter and a charge controller to direct the D/C current to the batteries or home as needed.   Some loads may be connected directly to the D/C side to avoid the small power losses from the inverter operation.  Long term battery prices are expected to go down.  In California we are already seeing more battery systems tied into the grid.  The utility company is given control over the system and when grid demand hits a peak they can pull power from battery banks, disable certain loads, and make other adjustments through smart meters.   For their participation in this program array owners receive a premium for their solar watts fed into the grid.  

There are many types of batteries available.  Historically we had deep cycle flooded batteries and you needed to careful monitor the fluid level.  These are still the best value if you maintain them properly.  Sealed batteries eliminated the filling need.  Now we have different gels, lithium, and many more options.  There is no one right choice.  Draw, storage temperature, space and more have an impact but cost is often the decision maker.  Batteries need ventilation.  A cabinet such as the Outback enclosure keeps wiring neat and safe.  Home Power magazine has a great article on making sure your battery bank is in good working order which will prolong the battery life.  

Things to consider

  • Will you actually perform routine maintenance.  If you are not sure then pick a no-maintenance battery or you will risk ending up with a big bill for replacement
  • How quickly will you usually charge the battery.  Some gel batteries can form gas pockets which reduce performance until they recombine
  • What will be the temperature range where the battery bank is located. 
  • How much space and ventilation does the area have
  • Is size and weight a limiting factor.  Some of our favorite batteries and very big and heavy so hauling them across an island by hand is challenging
  • Can you afford to pay more today for a battery that will last longer

Grid down? No Problem with SMA's new Secure Power inverter.  Provides up to 1500 watts of backup electricity.

If you are considering a battery system because you occasionally loose power now there is another option.  SMA, the leading inverter manufacture announced their new TL-US line at thSMA TL inverter SI TL-22 SMART 1 e end of 2013.  This smart inverter is a game changer and all other manufactures are likely to roll out their own versions.   When the grid goes down this inverter activates a secure power outlet and can provide up to 1500 watts directly from your PV modules.  Of course it only works when the sun is out.   The SMA website has more information and a great video.  The inverter is priced competitive and adding the outlet is generally only a few hundred dollars.  This makes it the most cost effective way to insure you can charge your laptop, cell phone, and even run a newer refrigerator while there is good solar radiation.  

Solar Site considerations

PV panels like to face south and must be in the sun, especially from 9:00-3:00. It is possible to install tracking ground stands that rotate the PV panel to follow the sun’s angle throughout the day, and the season. This can increase the panel output 30% or more, but also increases the cost and maintenance needs.  Some track horizontally to adjust with the seasons.  More expensive units also track east to west as the day progresses.  With today's module prices this only makes sense if you have limited space. 

Most installs are on the roof because they are large unused spaces, they are often a "good sun angle" and they keep the modules farther away from kids and their toys.  Arrays can be mounted on ground racks or poles.  Some of the new ground racks are ballasted with heavy cement block and do not require the digging of footings that raise the price.  Historically a ground mount rack was more expensive than roof mounting.  This is changing.   If you roof is shaded or has little space due to multiple roof lines a ground system might be the answer.   Even with a ballasted system we still need to run a wire, normally underground, from the array to the electric service panel. 

You PV modules will have a 25 year warranty so if the shingles are worn they are best replaced before the array is installed.  Removal and re-install could be costly.  In many cases homeowner choose to just redo the side where the PV is going and let the rest wear out naturally.  Since the PV goes on the south side it is the one that takes the most UV abuse and fails before the other sides anyway.   Despite the fact we use the finest caulking we still use a flashing system such as QuickMount PV or EcoFasten to provide additional protection from leaks.   We prefer not to drill holes in metal roofs so we use S-5 clamps on standing seams.

What are: Watts, Kilowatts, and Kilowatt hours

Understanding how the module output rating relates to the amount of your utility bill can be confusing until you understand the units and math.

  • A module output is rated in watts (W).  At the start of 2013 a 250 watt module was the upper end for cost effective modules.  By the end of the year it will be 270.  This is an instantaneous output reading and is based on "standard test conditions", basically an ideal full sun situation.   A CFL is about 13 watts and a hair dryer 1500.
  • If you have 4 modules and they each have a rating of 250 watts you have 1000 watts or 1 kilowatt (1 kW). 
  • if your 1kW system is in full sun** for 1 hour you create 1 kilowatt hour of energy.  10,  100 watt light bulbs running for 1 hour uses 1 kWh of electricity
  • Your utility bill is in kilowatt hours (kWh). 
  • In Maine, as of 9/14,  we pay about 15.5 cents per kWh.  About half is for the electricity and half is the delivery charge.  Starting 11/2014 commercial rates will skyrocket and 3/15 residential rates will rise about 25%.
  • Your PV system that generates 1 kWh offsets 15.5 cents of electricity
  • In Maine if you have a good site you can expect the 4 modules that make up the 1 kW system to generate about 1,300 kilowatt hours (kWh), or about 110 kWh per month. 

Your utility bill has a 12 month summary so it is easy to determine what you use per year and a monthly average.  With this information we can properly size your system.

To make the math easy multiply the system size in watts by 1.3.  So for a 3.5 kW system:  3500 x 1.3 = 4550 kWh per year.

If your electric bill shows you use 5600 kWh per year:  5600 kWh / 1.3 = 4,300 watts or a 4.3 kW system (about 17 modules)

** The module output is measured under "standard test conditions" which is 1000 W/m2, an air mass of 1.5, and 77F degrees (25C).

Reducing the cost of a PV system

None of our clients get to buy a solar system without a push to first look for ways to cut their usage.  The reason is simple.  You can either buy more PV or become efficient in the electricity you use.  We can help you figure out where your electric use is going.  Thanks to Efficiency Maine your library has kill-o-watt meters that you can borrow.  You plug in electronics or appliances to determine how much money they are costing you.  You might be surprised to know that often DVD's, printers, etc, total annual electric use is greater in standby mode than the few hours you actually use them.  They need to be on a power switch.   We have other circuit meters that can monitor larger loads such as pumps, ovens or power tools.  You will only need them for a short while so we rent them at a very reasonable rate.  Of course you should switch incandescent lighting to CFL or LED.  This can cut your lighting electric use 80%.  Quality CFL have instant on.  Buying picking the right Lumens (amount of light generated) and the right Kelvin (color temperature) you can have lighting that looks just like your favorite old fashion, energy hog light bulb.  LED pricing keeps dropping and is the wave of the future.  Home Power has a nice article comparing the lighting choices; incandescent, LED and CFL. 

Inverter choices, String, Micro Inverters or Power Optimizers.

Sunny boy 3000 4000 5000TL-USThe inverter takes the DC current coming from the module and changes it to A/C.  At this point in time there are 3 choices for inverters.  String inverters have been around for a long time and many times they are upfront the least expensive option.  They are sized to the array.  If you have 12, 250 watt modules you would have an inverter rated for about 3000 watts and physically it would be about the size of a  microwave.  Normally they are mounted near the electrical service panel but some can be placed outside.  If you want to expand your system usually you have to add an additional inverter or replace the existing one with something larger.  The inverters average $2,000-3,000+.  These types of inverters have an operating range so a 3000 watt inverter may not turn on if there is only 500 watts coming in. Sending it 10,000 watts means you would loose electricity as it can not process that volume.  String inverters are not the best choice if you might want to expand your system.

PV systems do not perform well in shade.  Generally each module has 3 bypass diode and their circuits run vertically.  If the right 1/4 is shaded then the center and left circuit can still produce power.  This reduces the modules output.  If you shade the bottom 1/4 it impacts all three circuits.  With a string inverter when one module is under performing it drags down the entire array.   This could be due to shading, snow, dirt, failure, sometimes even clouds.   One way to think of this is to consider what happens when you mix 3 new batteries with 1 old one.  The performance of the group drops.  With micro inverters the DC output is converted to A/C right at the module so and under-performing module has no impact on the others. 

Enphase on roofMicro inverters have become very popular.  Recent reports state 50%+ of residential installs are now done with micro inverters. With these you have one small inverter that plugs into each module.  The module manufactures have even started integrating micro inverters with their modules and with these each module puts out A/C power.  These are called A/C modules.  They save on installation time and thus lower cost. 

enphase m250We are a huge fan of Enphase micro inverters.  They have a long and proven track record.  Their web monitoring site, Enlighten, is by far the best.  It will even email you, and us, if your system has a problem.  You can monitor module by module or the system as a whole.  There is plenty of historical data and reports you can download.  It will even show you the positive environmental impact your system is generating.  As installers we like it because of their great technical support plus all of our clients sites are accessible in one place so it make monitoring easy.  With other micro inverters we have to first log into the panel manufacture and then into the monitoring site.  Since we sell modules made by many manufactures this means it becomes impossible for us to have 1 convenient screen that shows us everyone's system status.  We have had less than 2% failure with Enphase in the last 5 years including out of box failures.  Enphase provides a 25 year warranty.  

Solar Edge P-5 Series power optimizer


Over the last few years SolarEdge power optimizers have taken off.  They take the best features of micro inverters and string inverters and combine them.  You still have a string inverter in the basement that performs the inversion from the DC power to AC.  On each panel we install a small optimizer that constantly monitors the individual panels to gather the most power like a micro inverter does.  Shade on one panel has no impact on the remaining panels. The complicated, and more failure prone, inverter is protected inside the house.  Additionally like with a micro inverter you get very good monitoring on each panel vs. only knowing the output of the overall system with a string inverter.  The solar edge combined system is priced midpoint between Enphase micro inverters and a string inverter.  

Advantages and disadvantages to consider

With micros if one module fails, is shaded, or dirty, it will not bring down the performance of the entire array like a string inverter does

D/C current experiences more line loss so if the distance from the array to inverter is long some current is lost.

240 A/C lines are safer than 600 volt D/C

With micros if you want to expand your system you simply add another module and micro inverter.  There are no concerns of out growing the inverter size

Module output keeps increasing.  Had you bought a system 5 years ago your modules might have been 170 watt.  Today they might be 270 watts.  With traditional string inverters it is hard to mix panels with large output variances.

A micro inverter is located on each module so you can get module by module performance data.  With a string inverter you only know what the entire array is putting out.  If you have many modules it is very hard to tell if one is under-performing.   There are add on product that will provide this information with string inverters but they add to the cost.  Micro inverters have a in house monitoring panel and even more complete information over the web, even from your cell phone.  Enphase just announced integration with Facebook so you can post your system performance for all your friends to see. 

Inverters are the weak link in your system.  Most string inverters are warrantied for 10 years.  Micro inverters have a 25 year warranty.  If a string inverter fails your output is zero until it can be fixed.  If a micro inverter fails your output from all the other modules continues. 

A string inverter is in the basement and does not require a ladder to access or the removal of modules.  This keeps repair costs down.  A string inverter normally has a 10 yr warranty vs 25 on a micro.

There is no single right choice.  If you have partial shade micro inverters are the best.  If you have a hard to access roof we would suggest a string inverter.  If you want to be 100% sure your system is operating properly then you will get the most comprehensive information with a micro inverter.  If you have a mid to large sized system and your budget is tight a string inverter may be less expensive up front. If you want the most kWh from your system use a micro inverter.   If you plan to expand in the future we would recommend micro inverters.  If you are a business, a school, etc, and want to share your PV output and monitoring with the world then micro inverters are best. Enphase has a great web site to watch your system run.  You can integrate this with your web site or Facebook page

Community Solar, a great option if you have shading or live in a condo/rental

We are lucky to live in a state that allows "community solar" projects.  Many Mainer's have too much shade to install solar at their home.  Others live in Condo's that will not allow placement on the common roof and there are many renters.  Still others do not plan to stay in their current home for a long period.  Community solar is the perfect way for these people to access solar power without having the panels on their property.  The solar array can be located anywhere in CMP's area.  There can be up to 9 members that buy into the project and share the credits for the energy generated. You can buy as many panels as you choose.  The group structure must be set up when the project is installed although you can transfer your ownership should you move away.   Just like with everything else there are economies of scale when building a larger system so it can actually be less expensive than installing a system at your own home. 

Electricity standard supplier, utility companies, and how to get the best price when buying electricity

Utility deregulation leaves us with one company to deliver our power (CMP or Bangor Hydro are the 2 big ones) and another company to provide it.  Figuring out how to get the best rate is a bit tricky, but we have some hints for you.

Electric car charging

Electric cars are gaining in popularity because their operating costs are low, they have a small environmental footprint, they are very quiet, and if you drive over 25 miles to work each day they are less expensive than a gas powered car even when you factor in their higher purchase price.   Nissan (like most other manufactures)  has been offering great lease deals, as low as $199, on their full electric Leaf and this seems to make the best financial sense.  Most other electric car companies have followed their lead.  

nissan leafThe average US driver travels about 12,000 miles per year. To keep that car charged would take about 200-250 kilowatt hours. It takes about a 2 kW system, about 6-8 modules, to cover the average charging needs so you never need to buy gas again.  Just like with anything buying a small system cost more per watt than a larger system. 2 kW is pretty small so you should consider also offsetting all or part of your homes electric needs if you want to charge your car. But even if you do just the 2 kW you are in the $6,000 price range plus you get a 30% federal tax credit. If you are spending $50 a week, $2500, a year on gas you will pay for the PV in about 2 years. Yes, 2 years then no more cost for fuel. 

Plugging into an regular outlet charges slowly.  To be able to charge overnight you need a charging station that is wired to 240. Car dealers have a hefty mark up on these and we can usually install them for less than half their cost. One day we will see quick chargers at gas stations.  Since these will use 3 phase power they can quickly charge a battery. A three phase circuit is quite expensive and not practical for home use. Home Power has a great article on shopping for a green car.  

The Future of Solar Electric

The PV world keeps changing. Thin film can be applied to any smooth surface, such as a metal roof, and is flexible.  Cost wise on residential installs it is higher than standard PV modules. There are now a number of company making solar shingles that are installed as standard shingles.  The advantage with these product is you can get the 30% solar tax credit and offset some of the expense on a great looking solar roof.  The downside is on a kilowatt basis these products are more expensive than standard PV even with the tax credit and their output per sq.ft. is lower  For large high rise buildings, there is clear PV window glass.

We started 2014 with 275 watt modules and here we are in 2016 with 315 watt modules being top quality.   Most PV modules are < 20% efficient at converting the sun's energy to electricity so there is plenty of room for improvements.  Putting off your install to get a higher watt module usually does not help in the long run.  A year from now the wattage will be higher but the advantage is lost by the electric bill you pay this year. 

tesla-energy-batteryOur predictions for 2016 and beyond: Micro Inverters and SolarEdge power optimizers will continue to take over, they are already use on 60%+ of residential installs.  Prices that were driven up in 2014 by the tariffs on Chinese panels have stabilize as manufactures relocate production facilities.  More modules will be made in the US and output will increase but there will not be any game changers in the actual module.  Systems with batteries will become more common driven by programs in other states where utility companies desire to access this stored power to meet peak demand.  They will pay solar owners to store their power and allow the utility access as needed.   Since Maine has smart meters this may be possible here too.  Tesla's Powerwall battery is expected to lead the pack and are now shipping in other other countries.

sonnenbatterie-eco-boden-front 0

We recently met with Sonnen and feel their battery system is superior to Tesla.  They have better sizing and technology plus their product includes all the components needed.  Sonnen said that in 2017-18 they will have a significant price drop.   Our guess is wide spread battery adoption is  5 years off.   The price of batteries needs to be driven down.  

We also expect a lot more electric cars and powering them with solar is less expensive than buying electricity monthly from the utility. 

photovoltaic options




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PV Cost and Net Metering

Podcast explains Net Metering &  how much cheaper PV electric is vs. the utlity


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