Technology

THE EQUIPMENT AND ENGINEERING BEHIND OUR CUSTOM SYSTEMS

Aside from our portable products and accessories, Grape Solar has three main categories of custom designed systems.  These categories include:

Grid-Tied systems feed their output directly to the utility grid through an inverter.  The power produced by these systems does not power someone’s home or business, but rather feeds the grid, which reduces net consumption, resulting in a lower utility bill.  Grid-tied systems do not utilize any form of power storage or energy buffer (i.e. batteries) and only consist of panels, an inverter system, mounting and possibly combiner boxes for cable management.  Grid-tied systems usually produce the best return on investment and are therefore the most common multiple panel systems.  The main weakness of Grid-Tied systems is that they cannot function without a utility grid being present and will not provide power during a grid outage.

Off-Grid systems can be anything from a panel on an RV to a small solar generator for a gate opener, to a standalone residential back-up system.  Off-grid systems do not feed power to the utility grid and therefore must be designed very carefully so that their output matches the electrical consumption.  In order to design a cost effective and functional off-grid system, Grape Solar engineers would need to know the wattage of each device that is to be used on the system and the average runtime of each device over a given period of time.  One of the biggest challenges in designing off-grid systems is sizing the inverter to handle the startup current of the various loads.  Off-grid systems typically cost 150% to 200% per Watt more than grid-tied systems because they require batteries, charge controllers and more complex inverters.
 
Grid-Interactive systems take the power storage feature of the off-grid systems and combine it with the grid-feeding ability of grid-tied systems.  These are most commonly used as back-up systems for critical appliances in areas where utility outages are frequent.  A grid-interactive system functions the same way that an off-grid system does, except that the inverter draws power from the grid to charge the batteries when they are low and feeds power to the grid when the batteries are full.  When the batteries are full and the grid is active, the system feeds its output to the utility grid.  When the grid is down, the system draws from the batteries, which are being charged by the panels, to supply power to a critical load on a home or business.  Grid-interactive systems have a cost comparable to off-grid systems, about 150% to 200% that of strictly grid-tied systems.

Each type of system above uses a variety of components.  By talking with each customer we are able to assess power consumption goals, budget expectations, space requirements and the likelihood for future expansion.  With this information, we select components like putting together a puzzle, choosing the pieces that combine to form a system that best meets the customer’s goals.  These components include:

 

Panels

Because of Grape Solar’s unique, horizontally integrated business model, we are able to offer a wider variety of panels than any of our competitors. Panels come in a variety of types, voltages and sizes. 
 
Monocrystalline (mono) cells are made from an ingot with a uniform crystalline structure.  These cells are dark blue, almost black and have beveled corners, giving them an octagonal shape.  Polycrystalline (poly) cells are made from an ingot with an irregular crystalline structure which gives them a more bluish tint.  Poly cells do not have the beveled corners and are rectangular in shape.  In the early days of solar there was a large difference in performance and price between mono and poly, with mono being more efficient (generating more watts per square foot) and more expensive.  But, recent advancements in manufacturing have reduced mono manufacturing costs and increased poly efficiencies, making them nearly identical in price and performance.  A more efficient panel is not necessarily a better or longer lasting panel, it just means that it has a smaller surface area than a less efficient panel of the same wattage.
 
The voltages of panels vary depending on the number of cells (or number of pieces of cells) in a panel.  Panels with an open circuit voltage of between 16Voc and 25Voc are ideal for small off-grid applications where a low cost PWM style charge controller is preferred.  Higher voltage panels can only be used in grid-tied applications, or in conjunction with MPPT charge controllers that have transformer circuitry to bring their voltage down to what can safely be fed onto a battery bank.
 
Sometimes we get requests for “the biggest panel” we have, because they want to produce a large amount of power.  Typically, multiple panels would be a better way of producing large amounts of power because they can be produced, shipped and installed easier.  Panel size is typically limited by inverter or charge controller specifications and space limitations. 




 

Grid-Tied Inverters

Grid-tied inverters come in two varieties, micro inverters and string inverters.  Both types can only be used in grid-tied systems.  Micro inverters are when each panel is connected to its own inverter and multiple inverters are strung together in parallel with a trunk cable.  Only 60 cell grid tied panels (typically 250W or less) are used with micro inverters.  Micro inverters individually optimize each panel’s output which makes them better for situations that involve shade or panels pointing in a variety of directions.  Micro inverters are more expensive than string inverters, but make future expansion and installation easier.  The most common micro inverter we use is the Enphase M215. 
 
String inverters take one or more parallel strings of panels connected in series.  The voltage range of inputs that string inverters typically take is between 350V and 600V which is achieved by adding the voltages of many panels connected in series.  On larger systems, multiple string inverters can be used.  String inverter based systems have to be designed carefully to ensure that the voltage and wattage of the array fit within a certain tolerance window of the particular inverter being used.  String inverters cost less than micro inverters but do not work with all panel counts and they do not function as well when part of the array is shaded.  The string inverters we most commonly use are KACO, SMA and Solectria.


                     

 

Mounting

Solar panels can be mounted in a variety ways and Grape Solar can provide several options depending on the particular installation.  For customers in the Northern hemisphere with fixed tilt racking, we recommend pointing the array to the South at a tilt angle about 5 degrees less than the latitude of the installation.
 
Roof mounted solar is the most common.  In designing a roof mounted system we would need to know the type of roofing material, such as:  Asphalt Shingle, Flat Tile, Curved Tile, Corrugated Metal, Standing Seam Metal, Shake, etc.  For flat roofs we offer ballasted and penetrating racking options.  In situations where extra tilt is required, we can supply tilt legs.  Racking systems are designed to last 10 years and not harm a roof or cause leaks.   Typically Quickmount provides our roof attachments, and rails and panel clips are provided by Haticon.  For flat roofs we use either UniRac Rapid-Rac or PanelClaw.
 
Ground mount arrays are designed with four and sometimes five rows of panels in landscape orientation.  Ground mount arrays are slightly more expensive than roof mount arrays because of the support structure required.  Our most common types of ground mount racking include UniRac and IronRidge. 
 
Pole mounting is the simplest way to mount solar panels and ideal for small projects like gate openers, lighting and electric fences.  Pole mounted systems are best for just a couple of panels and get very expensive when large numbers of panels are added to the array.  We typically recommend DPW or IronRidge for pole mounted systems.
 
Vehicle, like RV or Boat mounting, is very popular with our small off-grid kits.  Depending on the budget, vehicle mounting can be accomplished with do it yourself kits utilizing 3M double sided tape, “Z” feet, or the deluxe adjustable tilt systems designed by AM Solar.
 
Do It Yourself racking is a very viable option for small off-grid systems.  Our panels have “C” channel aluminum frames with mounting holes.  Pressure treated wood, angle iron or “C” channel can be used to construct a panel mounting system.  For design inspiration do an internet search for “solar panel mounts”.
 
Tracking and Adjustable Tilt Racking were much more popular when solar panels were at about twice the price that they currently are.  For example, when a tracking system may add $1.50/W to the cost of an installation and increase performance by 20% and that same $1.50/W could just be used to buy more panels and increase performance by 100%, tracking becomes less attractive.  The cost of these systems and the maintenance required to keep them functional makes them practical only in very rare situations where space is limited.  Similar to tracking, Adjustable Tilt Racking does not produce enough extra power to justify the added costs.  Grape Solar does not currently offer any tracking or adjustable tilt racking solutions.

            

            



 

Charge Controllers

The main duty of a charge controller is to safely transfer power from the solar array to the battery bank.  Charge controllers regulate this power flow in a way that prevents the batteries from overcharging, maintains a proper voltage to the battery bank, and preserves the lifespan of the battery bank.
 
There are two main categories of charger controllers, PWM and MPPT.  PWM type charge controllers are typically only used on 12V battery banks with arrays that have an open circuit voltage of less than 25Voc.  The PWM stands for Pulse Width Modulation which means that the battery is charged with a pulsed direct connection to the solar array.  The pulses vary in length depending on the charge level of the battery with empty batteries getting long pulses and full batteries getting short pulses.  We commonly recommend Sunforce, EcoEnergy and Xantrex PWM charge controllers.
 
MPPT charge controllers have a feature called Maximum Power Point Tracking which means that they draw power from the panel at a voltage where it most efficiently produces power.  That voltage is then transformed down (while the current is increased) to a voltage that can safely be fed onto a battery.  This feature is critical when the Voc of the panel is much higher than the voltage of the battery bank.  MPPT charge controllers cost at least twice as much as comparably sized PWM style charge controllers and increase system performance by at least 15%.  We commonly recommend BlueSky, Morningstar and Outback MPPT charge controllers.


When selecting a charge controller or determining what panels to put on a charge controller there are four rules that should be followed.
1) Array voltage must be higher than battery bank voltage Make sure the voltage of the solar panel array going into the charge controller is at least a couple volts higher than the battery bank voltage over a wide range of temperatures and charge levels. For example, a 12.0V panel (if there was such a thing) would not charge a 12V battery because there would no “pressure” differential that would cause current to flow. The voltage of the panel would have to be at least 14.0V to charge a 12V battery bank.
 
2) Array voltage must be under charge controller limit Make sure the open circuit voltage of the solar array is not above the voltage limit of the charge controller. For example some Sunforce charge controllers have a voltage limit of 25V. Because of this, you would not be able to use our 250W panel because it has an open circuit voltage of 37.7V. Also, Outback charge controllers have a voltage limit of 150V. Because of this you would not want to put more than three 250W panels in each series string because on a cold day (panel voltage increases as temperature decreases) their combined voltage would exceed 150V.
 
3) Current must not exceed charge controller limit Make sure the current going from the charge controller to the battery bank does not exceed the charge controller current rating. The calculations for current have nothing to do with the current coming off the array since current coming into a charge controller and going out of a charge controller are not necessarily equal. To calculate current, take the total wattage of the solar array, multiply it 90% to take into account losses and real world solar irradiance, then divide it by the voltage of the battery bank. For example, two 250W panels on a 12V battery bank would produce about 37.5A (2 x 250W x 0.90 / 12V = 37.5A). This would not work on a charge controller rated for 15A.
 
4) Use MPPT when needed Use MPPT when there is a large differential between the panel voltage and the battery bank voltage. There are two types of charge controllers, PWM and MPPT. PWM charge controllers feed the batteries with a direct connection to the solar panels. MPPT charge controllers utilize a transformer to step down the voltage and increase the current before being fed onto a battery bank. For example, even though the Xantrex C35 charge controller can handle the voltage of a 250W panel and is compatible with 12V systems, it uses PWM and would force the panel to operate at 12V instead of its more efficient 30.7V. An MPPT charge controller would be a better choice and result in much better production.
 
For additional power, multiples of all of the charge controllers above can be connected to the same battery bank in parallel. When designing systems with multiple charge controllers, make sure that all the charge controllers in the system are the same brand. For example, an Outback FlexMax 80 can be used with an Outback FlexMax 60, but it would not be a good choice to combine it with a Sunforce 60032 30A. One larger project I designed used a dozen Outback charge controllers.

Common charge controller recommendations
105W or smaller, single panel, entry level PWM, 12V – Sunforce 7A, Sunforce 10A
105W or smaller, one to four panels, entry level PWM, 12V – Sunforce 30A Digital
105W or smaller, one to five panels, midrange PWM, 12V – Xantrex C35
105W or smaller, one to four panels, deluxe MPPT, 12V – BlueSky 2512ix HV
160W or smaller, one to three panels, midrange PWM, 12V – Xantrex C35
160W or smaller, one or two panels, deluxe MPPT, 12V – BlueSky 2512ix HV
300W or smaller, single panel, deluxe MPPT, 12V – Grape Solar GS-MPPT-320W
250W or smaller, one or two panels, deluxe MPPT, 12V – Morningstar TS-MPPT-45
250W, three to nine panels, deluxe MPPT, 48V – Outback FM60
250W, three to fifteen panels, deluxe MPPT, 48V – Outback FM80
280W, two to twelve panels, deluxe MPPT, 48V – Outback FM80



                  
            


 

Off-grid and Grid-Interactive Inverters

Inverters come in two main varieties modified sine and pure sine.  Grid power, what comes out of a typical electrical outlet, is pure sine, meaning that its oscillations from negative to positive happen in smooth arcs.  Modified sine, on the other hand is a square wave pattern.  Modified sine inverters are cheaper and work well with lights, laptops, cell phone chargers and anything that converts the output to DC.  However, loads with moving parts, like refrigerator compressors or electric motors, will not function with the square waveform.  Inverters also have to be sized to match the load of the system.  Sometimes pumps or other electrical motors have a startup current that is about five times that of their steady state current and systems have to be designed carefully to take this into account.  Some of our small off-grid kits use Xantrex modified sine inverters.  For pure sine inverters we use Xantrex or Outback.  Outback also makes the pure sine inverters for our grid-interactive kits.
    


 

Batteries

Off-grid and grid-interactive systems require batteries.  We typically recommend using 12V deep cycle sealed AGM type batteries for best performance.  Golf cart, lead acid and 6V batteries will also work as long as they are connected in way that results in a voltage that is compatible with the charge controller and inverter.  Car batteries will not work because they are not deep cycle and will not handle the charge and discharge that would be expected with a solar power system.  After about a week of use, the car battery would eventually stop working.
 
We recommend that the total Ah capacity of a battery bank be at least half of the wattage of the solar array.  For example, a 200W kit should have at least a 100Ah battery bank which will allow the panels to fully charge the battery bank in one day.  If a smaller battery bank is used it will likely reach a full charge while there are still some hours of sunshine left in the day.  When the battery reaches a full charge, the charge controller will disconnect it from the panels and the panels will sit there useless, until the batteries are discharged.  Larger battery banks on the other hand just allow for more back-up time and make it so all the batteries in the battery bank don’t have to discharge as deeply, thus prolonging the lifespan of all the batteries in the system.  Batteries that are regularly discharged to only 20% will last longer than batteries that are discharged to 50%.
 
To convert battery Amp Hours (Ah) to usable Watt Hours (Wh), multiply the Ah number by the voltage of the battery (typically 12V) and multiply that by the depth of discharge (typically 50%). 
 
On small systems we usually do not include batteries because of the high cost of shipping.  To find a battery dealer near you go to the Trojan Batteries website and enter your zip code in the top right corner.  On our larger systems we get better rates on shipping and can supply batteries by MK Deka or Outback.

        

 

Combiners, Cables and Connectors

Combiner boxes, cables and connectors are included in some of our kits.  Each Grape Solar panel comes with two leads, approximately 3’ foot long each, one for positive and one for negative.  To connect panels in series (positive to negative) the leads built into each panel will be long enough if the panels are next to each other.  Each lead has a durable, weather resistant MC4 connector on it.  We advise that customers do not remove these connectors because that will void their warranty and potentially shorten the life the panel.  To connect to our panels we recommend using MC4 cables that can be purchased through our Accessories Page (linked).  A single MC4 cable can be used for both the positive and negative leads by cutting the cable in half.  The ends with connectors go to the panel and the bare ends can be stripped and sent directly to the combiner box or charge controller, or can have longer cables spliced onto them.
 
When making a parallel connection it is best to use an MC4 T-branch or a combiner box.  A parallel connection is when all the positive leads are grouped together, separate from all the negative leads which are also grouped together.  For higher current systems, or systems with more than five parallel connections, a combiner is recommended.

        


 

Fuses, Breakers and Grounding

  Some of our kits come with fuses, breakers and grounding hardware.  Fuses are typically used within the combiner boxes of grid-tied systems between the panels and the inverters because breakers aren’t designed to handle the higher voltages that would be present in these types of systems.  In off-grid systems breakers can be used in the same manner.  Fuses are also used occasionally between charge controllers and battery banks to prevent the possibility of a current overload that could damage the charge controller.  On our smaller off-grid kits, fuses and breakers are not required due to the relatively low power and low likelihood of a surge, but customers may add them if they wish.  Most string inverters and large off-grid or grid-interactive inverters come with built in breakers.

 
The mounting kits for Grid-tied systems come with grounding hardware as per code requirements.  The smaller kits do not include grounding hardware because it isn’t necessary.  Panels, mounting rails, charge controllers and batteries can all be grounded with 10AWG cable connected to a metal stake 2’ into the ground, but it is not necessary and will not affect performance.  None of our panels require positive grounding.  We do recommend that inverters be grounded for safety reasons.


 

For questions and design recommendations contact Grape Solar Technical Support by phone or email. 

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