Module efficiency characterizes a PV module’s ability to convert available sunlight into useable power within a given area.
The formula to calculate efficiency is:
The module area is the total area of the product that includes both the active and inactive area.
Aperture efficiency is when only the active area of a PV module is considered. This does not include the inactive area.
Maximum rated power of a PV module is the nominal power rating that is based on STC.
STC stands for Standard Test Conditions. STC has three conditions:
1) Cell Temperature 25 deg C
2) Irradiance 1000 W/m2
3) Air Mass 1.5
The tolerance is specified on the datasheet by a“+/‐“label by a nominal rating.
This is the nominal deviation from a specification.
On the datasheet, you’ll notice 3 different temperature coefficients:
1) Temperature Coefficient of Pmpp
2) Temperature Coefficient of Voc
3) Temperature Coefficient of Isc
The performance of a PV cell behaves differently depending upon applied sunlight and temperature. The sunlight (aka irradiance) significantly impacts the current of the PV cell. The temperature has a significant impact on the voltage of PV cell.
At higher irradiance levels, the current goes higher, which means the temperature coefficient is positive.
At higher temperatures, the voltage goes lower, which is why the temperature coefficient is negative.
The Pmpp temperature coefficient is the factor that impacts the maximum rated power per deg C.
For example, if the temperature coefficient is ‐0.35 %/deg C, this means that for every degree above 25 deg C cell temperature (based on STC), you’ll see a ‐0.35% impact on the nominal voltage rating.
“System performance”is a term we use to describe how closely the energy output of the PV system matches up with expectations. When determining whether a PV system is outperforming, meeting expectations or underperforming, it is very important to establish expectations based on technically sound assumptions.
There are a number of factors that can contribute overall to the absolute system performance of a PV system which may include:
1). Type of PV modules: product, technology, electrical specifications etc.
2). Installation location (determines environmental factors)
3). Ambient Temperature
4). Irradiance at the PV module
5). Shading
6). The azimuth (Direction of PV plane in relation to due north) and tilt angle of the PV modules
7). The cell temperature during operation: is there air flow on the back of the modules?
8). The type of inverters being used
9). System Application: Directly Adhered vs. Ballasted system
10). Length of DC wiring: i.e. Homerun Wiring (cables between PV Array and Inverter)
11). Module level power electronics, for example DC optimizers
12). Soiling: dirt on the PV modules, debris, leaves
1) Flexible – conforms to curved surfaces
2) Lightweight – structures don't have to be reinforced to support the weight of racks and panels
3) Powerful – the efficiencies are superior to other thin‐film modules, rivaling rigid silicon modules
4) Wind resistant – low profile modules offer little resistance to wind
5) Theft resistant – once attached, FLEX modules are difficult for a thief to remove (but can be removed by the owner if necessary)
6) Easy to install – peel‐and‐stick application requires very little training. In addition, the modules offer superior resistance to damage in seismic events and are difficult to steal once installed
7) Shatterproof – FLEX modules will not shatter when struck by debris
8) Improved shade performance – FLEX modules use bypass diodes for every two cells that ensure that every cell receiving lights contributes to the module output
9) Improved aesthetics – the thin modules are unobtrusive and blend into surfaces
10) Doesn't require ballasting – many municipalities are restricting the use of ballast to secure solar modules. FLEX modules adhere directly to surfaces using peel‐and‐stick adhesive
11) No roof penetrations – no increased risk of leaks or damage to surfaces
Since FLEX modules are flexible, lightweight and frameless, the modules can be directly adhered to the surface.
This avoids the necessity of a mechanical racking system and ballasting. This also provides the benefit of having no roof penetrations.
For the electrical installation, all other BOS components like combiner boxes, wire management, and inverters would still be required.
On non‐metal surfaces, any type of inverter is compatible with modules. For metal surfaces, Please consult with a technical engineer.
Central inverters start at around 100kW to as large as 10MW inverters. These inverters can be very large and heavy. The central inverter design is optimized for utilizing the least number of inverters at the site and is usually ideal for large ground mount projects.
This is typically the most cost‐effective solution from an installed cost standpoint. However, if a 1MW project utilizes a 1MW central inverter, the production at the site has a single failure point at the inverter. This adds O&M cost for any loss of energy production and the need for more skilled labor for any maintenance and repair in the case of an event. This is the reason why more EPCs are starting to use the string inverter configuration for large projects. There is a higher potential for cost savings from an O&M perspective.
String inverters are usually 10kW‐80kW sized inverters that are ideal for commercial rooftop applications. Although you may need more string inverters for a project when comparing to a central inverter configuration, you can take advantage of multiple failure points, more max power tracking throughout the system, string level monitoring and lower skilled labor that is required for maintenance and repair.
Micro‐inverters are designed to attach to a single or a couple of PV modules at a time. Although this configuration is more expensive than the other inverter configurations, it offers more maximum power tracking throughout the system, module‐level monitoring and better energy output in shaded conditions. Micro‐inverters are ideal for the residential market where the projects are smaller and more likely subject to shading conditions that are difficult to avoid. Also, since they are attached at the module‐level, they can provide more control over the system with the ability to shut off the power and energize the DC homerun cables between the PV system and the inverter.