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:
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 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.
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.
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.
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.