Grid Tie Wiring Diagrams Enphase M250 Micro Inverters Feeding Smart Meter
Emerging inverter topologies
L. Ashok Kumar , ... Madhuvanthani Rajendran , in Power Electronic Converters for Solar Photovoltaic Systems, 2021
4.2.2 Microinverters
In microinverter architectures, each solar panel has its own inverter that performs power conversion for each module. Microinverter architectures are more expensive than the other two but offer the highest power optimization and design flexibility and also avoid a single point of failure. Microinverters have several advantages over conventional inverters. The main advantage is that small amounts of shading, debris, or snow lines on any one solar module, or even a complete module failure, do not disproportionately reduce the output of the entire array. Each microinverter harvests optimum power by performing MPPT for its connected module. Simplicity in system design, lower amperage wires, simplified stock management, and added safety are other factors introduced with the microinverter solution. The primary disadvantages of a microinverter include a higher initial equipment cost per peak watt than the equivalent power of a central inverter since each inverter needs to be installed adjacent to a panel (usually on a roof). This also makes them harder to maintain and more costly to remove and replace. Some manufacturers have addressed these issues with panels with built-in microinverters.
The main focus is on microinverters, particularly microinverters that are based on the interleaved flyback converter topology. Solar energy systems based on microinverter architectures are gaining in popularity as they are less prone to shading and PV cell malfunction since each solar panel in a system has its own low power inverter. A number of microinverters are single-stage flyback inverters that are based on the DC–DC flyback topologies.
Like their name suggests, microinverters are much smaller in size and capacity than standard string inverters. While the latter ranges from 1.5 to 5 kW in size for residential applications, microinverters are usually around 200–250 W in size. Instead of one central inverter that converts all the DC electricity your panels collectively produce, microinverters are usually installed on the back of every individual panel and are only responsible for the conversion of the panel on which they are installed. The advantages and disadvantages are as follows.
| ✓ Pros | ✘ Cons |
|---|---|
| Microinverter solar PV systems usually perform better than standard string inverter systems. As every panel's output is collected individually, underperforming panels (whether due to shading or degradation) do not negatively impact the output of other panels. | Microinverters are significantly more expensive than standard string inverters. |
Fig. 4.13 shows the microinverter configuration.
Figure 4.13. Microinverter.
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The Economics of Solar Photovoltaic Systems
Russell H. Plante , in Solar Energy, Photovoltaics, and Domestic Hot Water.., 2014
8.6 Payback Analysis with Tax Credit Incentives
With the generous federal tax credits and some state rebates, grid-tied PV systems can be an excellent investment. Now let's include the federal tax credit into the previous graph of Figure 8.3 to reflect the actual cost of the solar PV system after subtracting the available tax credits from the cost of the system. We also will include a possible state tax credit of $2000, which depends on the location of the proposed system.
Example 1: Configuration with Microinverters
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Example 2: Configuration with One String Inverter
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Example 3: Configuration with Two String Inverters
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Our new graph, Figure 8.4, illustrates the payback period with the added federal and state tax credit incentives.
FIGURE 8.4. Conventional electric utility and solar energy costs after tax credits.
The payback period realized from savings after federal and state tax credits can be seen in Figure 8.4 to have been reduced to the following number of years for each example:
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Example 1: From 16 years, 6 months to 10 years, 5 months (reduction of 6 years, 1 month)
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Example 2: From 14 years, 11 months to 9 years, 2 months (reduction of 5 years, 9 months)
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Example 3: From 16 years, 3 months to 10 years, 2 months (reduction of 6 years, 1 month)
If future worth of savings (as discussed in Chapter 6, Section 6.1) is considered throughout a 20-year period for each of the yearly savings in Table 8.3, column 5 at a 5% compounded energy inflation rate, the resultant future worth savings can be determined using Chapter 6, Eqn (6.2) and the single payment compound amount factors (SPCAF) in Table 6.1 for each year as follows:
Where:
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S = future worth of money,
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P = savings for a particular year (Table 8.3, column 5), and
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(5%—SPCAF) = single payment compound amount factor (Table 6.1 factor)
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Developing the future worth of savings from the information previously included in Table 8.3, we have the yearly future worth of savings as shown in Table 8.4.
Table 8.4. Example of Utility-Provided Electricity Costs and Future Worth of Savings Realized
| Years | Cost of Utility-Provided Electricity at 5% per year Energy Inflation | Savings Realized from Solar PV versus Electric Utility at 5% per year Energy Inflation | Future Worth of Savings through 20 years at 5% Compounded Inflation | |||
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| (1) Yearly | (2) Cumulative | (3) Yearly | (4) Cumulative | (5) Yearly | (6) Cumulative | |
| 1 | $853.76 | $853.76 | $845.22 | $845.22 | $2242.62 | $2242.62 |
| 2 | $896.45 | $1750.21 | $878.52 | $1723.74 | $2219.93 | $4462.55 |
| 3 | $941.27 | $2691.48 | $913.03 | $2636.77 | $2197.30 | $6659.85 |
| 4 | $988.33 | $3679.81 | $948.80 | $3585.57 | $2174.65 | $8834.50 |
| 5 | $1037.75 | $4717.56 | $985.86 | $4571.43 | $2152.03 | $10,986.53 |
| 6 | $1089.64 | $5807.20 | $1024.26 | $5595.69 | $2129.33 | $13,115.86 |
| 7 | $1144.12 | $6951.32 | $1064.03 | $6659.72 | $2106.67 | $15,222.53 |
| 8 | $1201.33 | $8152.65 | $1105.22 | $7764.94 | $2084.00 | $17,306.53 |
| 9 | $1261.39 | $9414.04 | $1147.86 | $8912.80 | $2061.44 | $19,367.97 |
| 10 | $1324.46 | $10,738.50 | $1192.01 | $10,104.81 | $2038.69 | $21,406.66 |
| 11 | $1390.69 | $12,129.19 | $1237.71 | $11,342.52 | $2016.11 | $23,422.77 |
| 12 | $1460.22 | $13,589.41 | $1284.99 | $12,627.51 | $1993.40 | $25,416.17 |
| 13 | $1533.23 | $15,122.64 | $1333.91 | $13,961.42 | $1970.85 | $27,387.02 |
| 14 | $1609.89 | $16,732.53 | $1384.51 | $15,345.93 | $1948.14 | $29,335.16 |
| 15 | $1690.39 | $18,422.91 | $1436.83 | $16,782.75 | $1925.50 | $31,260.66 |
| 16 | $1774.91 | $20,197.82 | $1490.92 | $18,273.67 | $1902.86 | $33,163.52 |
| 17 | $1863.65 | $22,061.47 | $1546.83 | $19,820.50 | $1880.17 | $35,043.69 |
| 18 | $1956.83 | $24,018.30 | $1604.60 | $21,425.10 | $1857.48 | $36,901.17 |
| 19 | $2054.68 | $26,072.98 | $1664.29 | $23,089.39 | $1834.88 | $38,736.05 |
| 20 | $2157.41 | $28,230.39 | $1725.93 | $24,815.32 | $1812.23 | $40,548.28 |
| Total | $28,230.39 | Total | $24,815.32 | Total | $40,548.28 | |
At this point, we should determine whether it would be wiser to invest in a solar PV energy system or in a bank savings account. So what is our money worth if we simply put the initial cost of the solar PV system into a savings account? Currently, we are only going to get a taxable 1% interest rate at best and more likely only 0.5% interest for our money in a bank (for rates available in 2012–2013). But, let's calculate which would be the better investment for each of our inverter combination examples even at a 1% rate of return from a savings account.
Example 1: Configuration with Microinverters
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Example 2: Configuration with One String Inverter
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Example 3: Configuration with Two String Inverters
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The savings bank investment in comparison with the three examples of solar PV investment clearly illustrates that the solar investment in supplementing electrical energy demands provides a positive cash savings. The solar investment also provides a better use of cash flow throughout the 20-year period. Considering the future worth of money over 20 years, Example 1 illustrates that purchasing a solar PV system produces a future worth difference of $43,674.02 between the actual money lost from a bank savings investment ($14,434.14) and the actual money saved ($29,239.88) from energy generated. Example 2 produces a $47,409.75 difference and Example 3 produces a $44,323.59 difference. The solar PV system cost, just like the solar DHW cost, is "self-liquidating," in that once the system cost has been repaid, there are few or no additional costs associated with the remaining years of normal system operation.
Although every solar PV system represents an individual case, an economical evaluation will indicate that solar energy is an excellent application in using the sun's energy to supply electricity rather than paying escalating electricity costs. The example costs and calculations used throughout this chapter have been conservative. It is assumed that the system is exempt from sales tax and exempt from property tax, which is true in some, but not all states. In many situations (i.e., using $0.16/kWh electrical rates), the return on investment averages less than 10 years.
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Rooftop and BIPV solar PV systems
Rabindra Satpathy , Venkateswarlu Pamuru , in Solar PV Power, 2021
8.3.1.2 Microinverters
A microinverter is an alternative solution for the string inverter. There are two types of microinverters for solar PV system applications. One type directly converts DC power to AC power in the module level itself. The other type boosts the DC voltage in the module level using a DC optimizer and connects to the inverter. Microinverter-based options are called module level power electronics. Each module is connected in these systems to an inverter that is usually connected just below the panel. Each panel with one inverter prevents the dependence of the generation of one module on other modules. Each panel is going to be independent. This type of system is best suited to a place where shadow problems occur on one or more number of modules, roofs with different directions, etc. In these types of systems, module level monitoring is possible. It helps in the easy maintenance of the system. One module or one inverter failure wouldn't affect the generation of the rest of the system.
The electrical parameters of each module can be monitored and the data can be sent to a database center where the performance details can be monitored and analyzed. It is of great benefit for the operation and maintenance of solar plants. These microinverters are more efficient and produce more power compared to standard string inverters. Though they are expensive, they have better durability and a longer life.
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Solar Photovoltaic Systems
Russell H. Plante , in Solar Energy, Photovoltaics, and Domestic Hot Water.., 2014
5.2 Basic PV System Components
A basic solar PV system consists of the following:
- 1.
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solar photovoltaic modules,
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proper electrical disconnects and overcurrent protection systems, and
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a string inverter or microinverters that change the DC generated electricity to alternating current (AC) used in most residences.
A system composed of these basic components with two arrays of modules, as illustrated in Figure 5.2, can generate electricity for your household and deliver any excess electricity back to the electrical grid for retail credit. Such an arrangement is called a grid-tied PV system. You should check with your utility company to ensure that you can connect a solar PV system to their electrical grid. Some rural electric cooperatives are exempt from the national law requiring interconnection. Ideally the utility company should buy back any excess electricity that your system produces at the same retail rate that you purchase from them. This arrangement is called " net metering ," which provides a simple way to set up a grid-tied PV system. In this type of system, you normally have only one utility meter that is allowed to spin in either direction dependent on whether or not you are buying or selling energy. In a non non-net-metered system, the utility company normally will install a second utility meter to record any excess energy that you sell back to them in which case you may be reimbursed energy costs only at a wholesale versus retail rate. Check with your particular state for the most current incentive programs and any limitations on the net-metered systems that can be connected to the grid in a specific utility service region. Such information normally is available from Internet database sites, such as the Database of State Incentives for Renewables and Efficiency (DSIRE) (www.dsireusa.org). A grid-tied type of system is designed to provide decades of economical and trouble-free electricity generated by the sun. Battery backup also can be incorporated in the system design; however, this will add to the complexity and cost of the system. Unless you are in a remote area without grid access, a battery backup system is not recommended for most residential applications. You should realize, however, that if the electrical power grid has an outage so will your PV system. The grid-tied solar electric inverter will shut down upon sensing a grid outage to prevent power from backfeeding to the power grid and injuring line workers. Because power outages are normally of short duration, it would be more cost-effective to install a backup generator than to include a more expensive battery backup system. Let's briefly discuss each of the basic component parts of a photovoltaic system.
FIGURE 5.2. Grid-tied photovoltaic system with single inverter.
Courtesy of www.DreamHomeConsultants.com. (For color version of this figure, the reader is referred to the online version of this book.)5.2.1 Solar PV Modules
The majority of residential solar modules consist of PV cells made from either crystalline silicon cells or thin-film semiconductor material. Crystalline silicon cells are further categorized as either monocrystalline silicon cells that offer high efficiencies (13–19%) but are more difficult to manufacture or polycrystalline (also called multicrystalline) silicon cells that have lower efficiencies (9–14%) but are less expensive and easier to manufacture. An example of a monocrystalline PV module is shown in Figure 5.3.
FIGURE 5.3. Suniva OPTimus 270 W monocyrstalline PV module (Model OPT 270-60-4-100).
Photo courtesy of Suniva, Inc. (For color version of this figure, the reader is referred to the online version of this book.)Thin-film solar cells, on the other hand, are manufactured by vaporizing and depositing thin layers of semiconductor material onto substrates, such as glass, ceramic, or metal. Although they absorb light more easily than crystalline silicon cells, they are much less energy production efficient (5–7%). They are, however, less costly to manufacture. The most efficient thin-film solar cells usually have several layers of semiconductor materials, such as gallium arsenide, that convert different wavelengths (i.e., colors) of light into electricity.
String ribbon manufactured modules also are available; however, current efficiencies are similar to thin-film modules requiring more surface area to produce the same output as the polycrystalline modules. Research advances in cell efficiency, materials, and methods of manufacturing continue to reduce costs and improve PV modules. The inherent inefficiency of PV modules is due to the fact that many of the electrons that have absorbed some energy from low-energy photons do not hold onto that energy long enough to absorb energy from another photon to free an electron. As a result, energy is lost as heat. To assist in cooling, these module arrays should be supported by framework that raises the entire system 3–6 in off the roof, allowing air to circulate keeping the system cool. An example of a 36 module array representing an 8.64 kW system is shown in Figure 5.4.
FIGURE 5.4. 8.64 kW array composed of 36 Canadian Solar CSP6M monocrystalline silicon modules at 240 W each.
Photo courtesy of ReVision Energy Corp. (For color version of this figure, the reader is referred to the online version of this book.)5.2.2 Electrical Safety Disconnects
Electrical disconnects consist of additional switching that shuts off the AC power between the inverter and the grid, as well as a DC disconnect to safely interrupt the flow of electricity from the PV array to the inverter for system maintenance and troubleshooting possible system problems. An example of a PV disconnect system is shown in Figure 5.5. Utility companies that require these separate and overlapping circuit breakers want to ensure that the inverter drops offline during a power outage to prevent sending power to the grid, endangering repair personnel. These disconnects add costs and complexity to the photovoltaic system but ensure a redundancy to safety and overcurrent protection. Wiring should be of sufficient gauge (size) for the length of run to keep transmission losses to less than 3%. Normally, 12-gauge wire is sufficient for wiring between the solar array and a string inverter if less than 100 ft, and 10 gauge if more than 100 ft.
FIGURE 5.5. DC/AC Disconnect Arrangement.
Courtesy of www.DreamHomeConsultants.com. (For color version of this figure, the reader is referred to the online version of this book.)5.2.3 DC to AC inverters
A solar electric inverter is a component that converts DC electricity from the output of the PV array into grid-compliant AC electricity that is used in most homes. An inverter takes the DC power from the PV module array and causes it to oscillate until it matches the frequency of the power grid at 60 Hz (cycles per second). An inverter with ground fault protection also constantly checks for DC wiring shorts and bad connections, shutting the system down if problems are detected. If there is a power outage, the inverter will discontinue supplying electricity to the grid preventing electrical feedback to the power lines and personal injury to repair personnel. Most inverters have an efficiency of 85–96% depending on make and model. The power losses in the conversion of DC to AC as well as wire and switch-gear losses should be accounted for when determining the number of PV modules required. The inclusion of this loss factor when sizing a PV system is illustrated as step four of Table 5.3 (Section 5.4).
Table 5.3. Sizing Method for the Determination of the Number of Photovoltaic Modules
| Sequence | Method | Example Calculation (i.e., Billings, Montana 1 ) | Example Result |
|---|---|---|---|
| Step 1 | Annual kilowatt-hours from 12 months of utility bills | Annual kWh = 10,800 kWh | 10,800 kWh/year (Annual demand) |
| Step 2 | Average daily kWh | 29.6 kWh/day (daily demand) | |
| Step 3 | Divide daily demand by peak Sun hours (Table 5.2) 1 | 5.92 kW (System size solar output required to yield 100% of daily demand) | |
| Step 4 | Multiply step 3 by 1.15 2 to account for DC to AC inverter power and wire run losses (efficiencies) | 5.92 kW × 1.15 = 6.81 kW | 6.81 kW (System size output including system energy losses) |
| Step 5 | Divide daily supplied solar energy system output (step 4) by the CEC wattage rating output per solar module | (Assume selection of a solar module with a PTC/CEC wattage output of 220 W where 6.81 kW = 6810 W) | Total number of photovoltaic modules = 31 (number of modules required to produce 100% of electrical demand) |
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- Sun hours per day; National Average for Billings, MT (see Table 5.2).
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- Multiply the solar output by 1.15 to adjust for efficiency losses to determine the number of modules required to produce 100% of the energy demand. The inverse is true if the number of modules is known due to limited roof area, in which case the known output for the array would be multiplied by .85 to determine the actual output of the array assuming efficiency losses of 15%.
A traditional, centrally located inverter, as shown in Figure 5.6, is called a "string inverter" (because it is connected to a string of PV modules). It converts all of the DC current from the entire PV array into grid-compliant AC power. In a string inverter arrangement, the PV modules are connected in a series delivering accumulated DC voltage to the inverter for conversion into AC power that is fed into the power grid. The main shortcoming of a string inverter system is that every module in a typical string inversion system is limited by the weakest performing module. In other words, the maximum output performance of the string is defined by the poorest performing panel. For instance, if a single PV module is partially shaded and loses 40% of its output, every module in that string can become limited to the same 40% output. Inverters use a technique known as maximum power point tracking (MPPT) to optimize PV output by adjusting applied loads. The PV array then can best use the available power at particular levels of available insolation. Because the effects of shading, snow covering, and module defects can cause variations in the output of an individual module, the inverter will change MPPT settings causing a divergence from an inverter's optimal performance. If a string inverter has multiple MMPT capabilities, as does the string inverter shown in Figure 5.6, the operating point with the highest performance can be found using more of the energy supply from the PV modules under shading-obstruction conditions.
FIGURE 5.6. Sunny Boy 3000 TL-US/4000 TL-US/5000 TL-US string inverter.
Photo courtesy of SMA Technology, AG. (For color version of this figure, the reader is referred to the online version of this book.)Varying angles and nontraditional layouts and rooflines can present a problem for some string inverter systems because for those systems to function at their peak, all the PV modules need to have the same intensity of sunlight. All the modules, therefore, must be mounted at the same angle of incidence and facing the same direction. In addition, string inverters can have a limited selection of power ratings, which means that the power rating of the solar modules have to be matched with the power rating of the string inverter. This can place limitations on the option of expansion of the collector array.
An alternate type of inverter is a "microinverter" that converts the DC output of a single PV module into grid-compliant AC power. These are actually small inverters rated to handle the power output of a single panel. Each solar PV module has its own microinverter. Arrays of modules are connected in parallel with each other, and the AC power travels upstream through an ordinary branch circuit and then to the service panel. This type of microinverter system is a combination of multiple microinverters all along the branch circuits converting DC to AC power, all injecting their individual current supply. This individual parallel AC output structure as opposed to the DC series structure of a string inverter system has the advantage of isolating each panel. Reducing or losing the output from a single panel does not disproportionately affect the output from the entire array. Each microinverter is able to maintain optimum power by performing MPPT for its own individual module. The failure of a single panel or inverter in this type of system therefore will have minimal impact on overall system performance. PV module types and manufacturers can be mixed as long as they are compatible with the particular microinverter. The use of microinverters allows PV modules to be controlled independently, eliminating susceptibility to a reduction in system power output due to soiling, shading, and PV module defects. Unlike a single inverter functioning for an entire string of modules, there is no high-voltage wiring, and inverter outages only affect a small fraction of the PV system. A typical microinverter layout with rack mounts for the PV modules is shown in Figure 5.7. Using microinverters allows more flexibility in module arrays. Harsh weather conditions, however, are more likely to affect multiple electronic microinverters versus one string inverter. Costs also can be more prohibitive depending on the number of PV modules used, and selection of inverter configurations is primarily dependent on site conditions. Microinverter systems are scalable. If a project planner or builder wants to increase the capacity of a solar PV system at a later point, additional modules can be added incrementally by simply extending the AC wiring to the next set of modules. Microinverter systems also can be monitored independently, making maintenance and upkeep simpler. A microinverter can be a good solution for installations with three or more roof orientations, difficult or rooftop shading issues and orientations, or very small systems under 3 kW.
FIGURE 5.7. Microinverters and mounting system for PV modules.
Photo courtesy of ReVision Energy Corp. (For color version of this figure, the reader is referred to the online version of this book.)The technology and design of inverters is continuously improving, and the use and cost of string inverters versus microinverters should be discussed with the solar energy installer or dealer for each particular application.
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Solar thermal energy and photovoltaic systems
Muhammad Asif Hanif , ... Umer Rashid , in Renewable and Alternative Energy Resources, 2022
4.2.14.2 Grid-tie inverter or microinverters, power meter
4.2.14.2.1 Grid-tie inverter
The actual job, and a major function of a regular solar invertor, is to regulate the flow of current and voltage, received by the solar panels. DC of the solar panel is converted into AC, and most of the electrical appliances use AC, as a major source of energy. The specially designed "grid-tie-invertors" also named as "synchronous inverters" or "grid-interactive invertors," help to synchronize the frequency and phase of the electrical current, to fit as per the requirements of the utility grids (working at 60 Hz mostly). The output voltage is adjusted quite higher than the regular grid voltage, in order to ensure the flow of additional electrical energy toward the main grid.
4.2.14.2.2 Microinverters
The microinverters are usually attached on the back of all individual solar panels, instead of a single inverter on entire solar array. Till date, lots of scientific investigations are underway to check the relative effectiveness of microinvertors, in comparison with the central invertors. Microinverters are highly cost-inefficient, but offer the high energy efficiencies. The ultimate statement about relative effectiveness of microinverters, depend on the situation and area of the working solar power plant.
4.2.14.2.3 Power meter
With the advancements of the solar system, the conventional power meters need to be replaced by the advanced power meters, compatible with the net metering. A special type of a device, capable of measuring the bidirectional power, starting from the grid station to the houses and buildings, is called "two way meter" or "net meter."
4.2.14.2.4 Grid-interactive invertor
Irrespective of the design of solar based power generation systems, all the renewable energy systems, constitutes "invertor" as a major component, for the conversion of DC (produced by the solar energy, wind power, or hydro energy) into AC, for the efficient functioning of electronic devices, and home appliances. In an advanced grid-interactive-system, inverters are more agile, much smarter and capable of three simultaneous actions, as opposed by the one-trick-grid-tied-inverter, like (1) grid-interactive inverters are capable of conversion of DC of solar energy into the AC for the power supply, (2) it can also store the electrical energy in the batteries and large storage systems, for the number of residential and commercial scale applications, and (3) conversion of battery produced DC into the AC, during the hours of need. By using the backup systems for the batteries, the running time of the generator and fuel consumption, can significantly be reduced. The major advantage of the grid-interactive-system is the use of smart invertors and backup batteries, for the storage of electrical energy, resulting in the reliable and a cleaner backup power, during the outages. These processes are accomplished by the grid-interactive invertors through advanced circuitry like (1) capability of communication networking and (2) switching for the bidirectional operations.
4.2.14.2.5 Grid-interactive component design and cost
The advanced "grid-interactive-components" are usually based on the off-grid design of the counterparts that are used in the solar power, wind energy and hydropower, other than the regular generator. These types of systems include the wide-ranging applications starting from field hospitals to the military outposts, and Arctic research stations. The quality and reliability of the grid-interactive inverters and their associated components, is based on off-grid technology. This technology is ideal and superior for residential uses, and premium commercial applications. The efficiency of the delivery of electric current by the "grid-interactive design" is almost doubled than the other relatable technologies however; the cost of this system is not twice accordingly. According to an estimate, the cost difference of about 15% is found in between "grid-interactive inverters" and "grid-tied inverters," depending upon the attachment of essential back-up systems, usually in case of (1) lighting equipments, (2) heating furnaces, (3) internet and personal computers, (4) televisions, and (5) refrigerators. Some extra lavish homes or apartments and larger buildings, may demand the additional backup systems, and it is the major advantage of "grid-interactive inverters."
These inverters are highly amendable for a building-block-approach, as they are capable of adding the enlarged storage devices and additional invertors, for the emergency situation. According to some recent reports, the residential setup specified for some special buildings is mainly powered by the solar based energy resources, constituting the 18 solar panels. By excluding the purchasing incentives and national tax, the approximate cost of the solar system equipped with the grid-tied technology, costs around 27,000 USD. On the other hand, the more efficient solar system using the advanced grid-interactive technology, with approximate capacity of 48 V, can be obtained in just 31,000 USD. By including the 8 year's payback period, factoring in all utility incentives, state incentives and federal incentives, this difference came out to be 500 USD/year. With the passage of time, these grid-interactive systems; would become more prevalent and more attractive for the future generations.
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Who Will Fuel Your Electric Vehicle in the Future? You or Your Utility?
Jeremy Webb , ... Clevo Wilson , in Consumer, Prosumer, Prosumager, 2019
7 EV Household/Grid Charging Regime Case Study
In order to provide an example of residential EV charging using distributed energy resources, the following case study of a Brisbane house has been included in this chapter. This Brisbane house has a 6-kW solar system (6-kW REA Solar microinverter system 8 /12 degree tilt/30 degree azimuth), a Tesla Powerwall 2 battery (13 kWh), a Mitsubishi Outlander PHEV (50 km driving range/10 kWh battery), heated swimming pool, air-conditioning, electric hot water, and electric kitchen appliances. Table 18.2 provides an overview of the electrical generation and load figures for the case study house.
Table 18.2. Household energy consumption and generation
| Household energy consumption: | 25 kWh per day (9,125 kWh p.a.) |
|---|---|
| - Pool (averaged over year) | - 5 kWh per day (20%) |
| - Pool heating (averaged over year) | - 4 kWh per day (16%) |
| - Hot water (averaged over year) | - 4 kWh per day (16%) |
| - Electric vehicle (35 km per day) | - 6 kWh per day (24%) |
| - Other loads | - 6 kWh per day (24%) |
| Day/night consumption split: | 70% day/30% night |
| - Per day | 17.5 kWh (day)/7.5 kWh (night) |
| - Per annum | 6,389 kWh (day)/2,737 kWh (night) |
| Tesla Powerwall 2 capacity: | 13.4 kWh (90% roundtrip efficiency) |
| - Night energy requirement | 8.3 kWh per day (3,042 kWh p.a.) |
| Total solar energy required: | 6,389 kWh + 3,042 kWh = 9,429 kWh p.a. |
| 6-kW solar PV system energy generation | 26 kWh per day (9,490 kWh p.a.) |
Examples of the house's electricity generation and consumption during a summer and winter day are also shown in Figs. 18.6 and 18.7. On a clear summer day, the house's rooftop solar system produces a maximum of 40 kWh. This is more than sufficient to power the house's electricity loads, including charging the EV. As such, the excess electricity generated by the solar system is exported to the grid after the battery is charged (as denoted by "grid export (solar)" in Fig. 18.6). While there is little to no pool heating load during the summer, this is partly offset by increased air-conditioning use, particularly during the evenings.
Figure 18.6. Brisbane household consumption and generation – summer.
Figure 18.7. Brisbane household consumption and generation – winter (as mentioned, the illustration of a winter day's energy generation and consumption for this household shows an ideal, clear sunny day's RRS generation, which leads to provision of enough energy to meet the household's daily requirements, including EV charging. This compares to the previous cloudy day, which did not generate significant solar energy, and led to grid reliance during the early morning for hot water heating and EV charging).
In contrast to summer, on a clear winter day, the house's rooftop solar system will produce a maximum of 26 kWh. While this is generally sufficient to power the house's average daily electricity loads, it depends on the prior day's weather. As shown in Fig. 18.7, while this winter day had near ideal solar generation, the prior day was cloudy. As a result, the battery did not store sufficient electricity to charge the EV and power the hot water system overnight, and therefore, grid electricity had to be relied upon for these electrical loads during the early morning. Even after accounting for the higher pool heating loads during a winter's day, the system still charged the battery close to full, providing enough electricity to charge the EV for the next day's travel.
On the basis of green electricity 9 consumption rates averaging $AUD 0.35 per kWh over the next 5 years, the household's annual electricity cost would normally be $AUD 3,194 ($AUD 798 per quarter) – excluding connection fees.
The combined cost of the solar PV system and battery, including installation and off-grid capabilities, was approximately $AUD 21,000. Ignoring the minor amount of surplus solar energy generated (after accounting for the 90% roundtrip efficiency of the battery, and the low solar feed-in tariff rate of 0.14 per kWh), this system results in a payback period of approximately 6.6 years. While this system already makes economic sense based on current battery/solar pricing, on the basis of continuing reductions in prices, the payback period for new systems will continue to fall further, increasing the attractiveness of installing distributed energy resources at residential premises.
The house's battery is warranted for 10 years and the solar PV system for 25 years. Even after assuming the battery will need to be replaced/supplemented after 15 years (at an additional cost of $AUD 5,000), and accounting for degradation of the solar system's performance, this house's solar and battery system still equates to locking in electricity rates at approximately $AUD 0.12 per kWh for 25 years – a 65% saving over estimated grid electricity costs.
Focusing on the cost of charging the house's EV, on the basis of electricity costing $AUD 0.12 per kWh, this equates to a transport energy cost of $AUD 2.06 per 100 km. The equivalent gasoline Mitsubishi Outlander uses approximately 7 liters per 100 km. Given the volatility of oil prices, it is difficult to forecast future pricing, but even based on current Australian gasoline pricing of $AUD 1.50 per liter, this equates to $AUD 10.50 per 100 km. In other words, the switch to an EV will result in an 80% saving in transport energy costs.
It's important to note, however, with a price premium of approximately $AUD 15,000 for the Outlander PHEV over the equivalent gasoline model, even with the lower operating costs, the payback period is approximately 13 years. However, as this price premium continues to fall over the coming 5–10 years, EVs will become increasingly cost competitive from a total cost of ownership perspective.
While this house's distributed energy resources come close to eliminating the need for grid electricity, this is dependent on reliably clear weather, which is not guaranteed, despite Brisbane's relatively sunny climate. As such, while the house's grid dependency has been significantly reduced, at the current level of electricity consumption, the grid connection is still required to provide additional energy security.
It could be argued that if the house installed additional battery capacity, it may be able to disconnect from the grid. However, the constraining factor in the achievement of nonsumer status is roof space and panel efficiency. Given most suburban homes in both Australia and California have gabled roofs, only 25–50% of this roof space is facing in the correct direction for solar. Thus, for the average 3–4 bedroom Australian house, the utilizable space available is in the region of 30–40 m2, which would at most accommodate a 6–8 kW system RRS. Accepting that solar panels have only around 20% efficiency, 10 such a system would generate around 40–50 kWh in summer – more than sufficient to power the average suburban home including 150–200 km worth of electric driving per week. However, in winter on a clear day, power output is likely to fall to around 20–25 kWh; roughly equal to daily consumption. Thus, even with a standalone battery, grid backup will likely be required in order to maintain an adequate level of household energy security. 11
Furthermore, in Queensland, solar PV systems cannot export more than 5 kW per day to the grid (at single-phase households), meaning that any electricity generated in addition to this which is not consumed by the house or stored in the battery, is lost. This can have significant cost implications for solar PV systems with inverters greater than 5 kW.
The assessment of this case study highlights the fact that while single-vehicle households may be able to significantly reduce their grid dependency, the addition of even one more vehicle – assuming a similar utilization rate of 35 km per day on average (Australian average distance; requiring approximately 6 kWh per day) – would increase the total house's energy consumption by almost 25%, with two EVs accounting for almost 40% of the house's daily electricity consumption. As such, despite RRS and batteries leading to decreased dependency on the grid, on average, EVs are likely to necessitate some level of grid dependency. Moreover, grid utilization provides support not only for the uptake of EVs but also facilitates (through V1G and V2G bidirectional charging technologies) the possibility of greater battery storage as the uptake of grid renewables rises. These trends should be viewed as a positive – given the significant investment of governments in grid distribution assets (poles and wires).
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Advanced multilevel inverter topologies
L. Ashok Kumar , ... Madhuvanthani Rajendran , in Power Electronic Converters for Solar Photovoltaic Systems, 2021
3.4.1 Breaking down string inverters
String inverters have the benefit of being a short-term cheaper solution due to the lower equipment need compared with micro inverters. One string inverter can handle the energy produced from a row of 5–10 panels. Therefore, you can save on the upfront equipment cost by buying one string inverter instead of 5–10 microinverters. However, the long-term costs associated with string inverters far outweigh the benefits.
A string inverter system can only perform as well as its lowest performing panel. So if a panel is experiencing obstruction from debris or shade, every other panel connected to that inverter will produce at the diminished capacity.
On top of all that, there is high-voltage electricity constantly on your roof. With the energy being converted at the end of the row of panels and not directly at the panel, up to 1000 V of DC electricity transferring across the roof. This can be a major hazard that can lead to arc-faulting and fire.
Over the past few decades, the demand for RE has increased significantly due to the disadvantages of fossil fuels and greenhouse effect. Among various types of RE sources (RES), solar energy and wind energy have become the most promising and attractive because of advancement in power electronic technique. PV sources are used nowadays in many applications as they own the advantage of easy maintenance and pollution free. In the past few years, solar energy source demand has grown consistently due to the following factors: (1) increasing efficiency of solar cells; (2) manufacturing technology improvement; and (3) economies of scale. Meanwhile, more and more PV modules have been and will be connected to utility grid in many countries.
Now the largest PV power plant produces more than 100 MW all over the world. Furthermore, the output of PV arrays is influenced by solar irradiation and weather conditions. More importantly, high initial cost and limited life span of PV panels make it more critical to extract as much power from them as possible. Therefore, MPPT technique should be implemented in DC/DC converter to achieve maximum efficiency of PV arrays. Several algorithms have been developed to achieve MPPT technique. As the capacity of PV system is growing significantly, the impact of PV modules on power grid cannot be ignored. They can cause problems on the grid such as flickers, increase of harmonics, and aggravated stability of the power system.
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CPV Systems
Eduardo F. Fernández , ... Pedro J. Pérez-Higueras , in McEvoy's Handbook of Photovoltaics (Third Edition), 2018
4 Concentrator Photovoltaic Systems
A CPV system consists of several subsystems: CPV generator, sun tracker, inverter and auxiliary elements. The CPV generator is a set of electrically interconnected CPV modules, which allows the required voltage, current, and power levels to be reached. The CPV generator is mounted on one or several mobile structures, known as sun trackers, which increase the solar irradiance incident on the CPV modules over time. The inverter converts the DC power received from the CPV generator into AC power with the same characteristics as the electrical grid. In addition, auxiliary elements such as wires or electrical protections are required.
This section is focused on two of the main components of a CPV system, the inverter and the sun tracker, since the CPV modules which compose the CPV generator have been described in previous sections.
4.1 Inverters for concentrator photovoltaic system
The inverter is a sophisticated power-electronic device with two main functions: (1) to convert the DC power into AC power with the same characteristics as the electrical grid and (2) to keep the CPV generator operating at its maximum power point (MPP).
CPV systems use the same types of inverters as conventional PV systems. However, the specific operating conditions of these systems are somewhat different than those of conventional systems, mainly because the input of the system is the direct irradiance instead of the global irradiance. This component of the irradiance has faster variations in the field, so that the MPP of a CPV generator shows a more changing behavior than the MPP of a conventional PV generator. This implies that tracking the MPP of concentrator systems is more complex and difficult. However, to date, no specific MPP tracker for CPV has been developed or commercialized, so that the inverters for conventional PV are also used. There is a type of inverter called "tracking inverter" [103], which incorporates the control of the engines of the sun tracker, but they use the same MPP trackers as conventional inverters. Nonetheless, the state-of-the-art algorithms to track the MPP are quite complex and able to follow the maximum power quickly, even in situations with rapid changes of irradiance, e.g., due to partial shading on the modules or cloudy days.
There are several types of photovoltaic inverters. These devices can be classified according to different criteria: (1) power (from a few Watts to Megawatts), (2) number of phases (single-phase or three-phase), (3) type of transformer (low-frequency transformer, high-frequency transformer or transformerless), and (4) inverter configuration in the CPV system. Regarding the inverter configuration, the following classification is widely used in CPV [104]:
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Central inverters: Several trackers of the CPV system are connected to one inverter.
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Tracker inverters: One inverter per tracker is used.
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String inverters: Several inverters per tracker are used, one per string of CPV modules.
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Module inverters or microinverters: Each CPV module is connected to its own inverter.
4.2 Trackers for concentrator photovoltaic system
The sun trackers are the mobile mechanical structures on which the CPV modules are mounted. The aim of these structures is to orientate the CPV modules in different positions throughout the day in order to increase the energy yield and/or to keep the CPV modules perpendicular to the sun's rays if required. It is possible to classify the sun trackers from a mechanical point of view according to their number of mobile axes:
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Single-axis: These trackers are not able to keep the CPV modules perpendicular to the sun's rays in every moment, but they allow the incident irradiation to be increased with respect to a fixed structure. They are built with the axis that determines the motion placed in different orientations:
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Horizontal axis: The axis is parallel to the ground and is always oriented along the North-South direction or the East-West direction.
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Inclined axis: The axis is inclined with respect to the ground and is oriented along the North-South direction.
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Vertical axis: The axis is collinear with the Zenith. This type of tracker is also known as azimuthal solar tracker.
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Two-axes: These trackers act on two degrees of freedom in order to keep the CPV modules perpendicular to the sun's rays, so that they can get the maximum incident irradiation.
Low and medium concentrator systems use any of these trackers depending on the optical concentrators employed. However, high CPV systems must always be pointing to the sun due to their narrow acceptance angle. Therefore the sun tracker of high CPV systems is a high-accuracy two-axis tracker. These types of trackers can be classified according to the following categories, see Fig. 28:
Figure 28. Types of two-axis sun trackers for high-concentrator photovoltaic (CPV), i.e., point-focus dish, pedestal-mounted, Carousel (rotate-and-roll), and tilt-and-roll.
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Two-axis Tracker for Point-Focus CPV Dish
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Two-axis Tracker for Point-Focus CPV Module:
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Pedestal-mounted two-axis tracker
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Carousel (rotate-and-roll) two-axis tracker
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"Tilt-and-roll" two-axis tracker
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Techno-economic performance evaluation among different solar photovoltaic system configurations
Prabodh Bajpai , Dinesh Varma Tekumalla , in Design, Analysis, and Applications of Renewable Energy Systems, 2021
12.3.2 Modeling of SI and MI
The preceding work published in Pal et al. (2016) gives a comprehensive simulation model of the SI and MI and a concise overview of these models.
A grid-connected SI has two stages of a two-level PWM inverter and is illustrated by the schematic diagram in Fig. 12.7. For DC–DC conversion stage, boost converter with k-factor III control is utilized. Series inductance, L, of the boost converter is determined by taking into account 1% current ripple. Likewise, 10% and 1% voltage ripple is used to determine its input capacitance, , and DC link capacitance, , respectively. More specifics are available in Pal et al. (2016) for the boost converter parameters.
Figure 12.7. Schematic representation of a grid connected PV array with SI.
The simulation model diagram for a single 250W p solar PV module connected to the MI is shown in Fig. 12.8. This MI is based on the Enphase-M250 (Enphase IQ 6 and IQ 6+ Microinverters datasheet, 2018) data sheet. The basic circuit for MI is used with a DC–DC flyback converter and one-phase full bridge inverter. The comprehensive model is available in Pal et al. (2016), where the authors have used high-voltage gain and fly back arrangement with isolated HFT. The three-phase AC output of 5 kW for both the MI systems is represented with an AC cable equivalent resistor.
Figure 12.8. Simulation model of the grid PV module connected to the MI.
Synchronous dq reference plane system (Pal et al., 2016; Yazdani & Iravani, 2010) is used for three-phase SI and one-phase MI control models whose schematic representation is shown in Fig. 12.9. The sensed grid voltages and currents are transformed to the dq plane. The grid voltage vector is positioned along the d axis of the dq plane using the Phase Lock Loop. This method imparts independent control over active and reactive powers of the inverter by means of cascaded voltage and current control loops. The external voltage control loop is modeled using in Figs. 12.7 and 12.8. The PI controller in the outer voltage loop maintains DC-link voltage at its reference value, , and produces d-axis current reference for the inner current control loop. In the current control loop, d-axis current tracks the current reference set by the voltage control loop for the power transmission from the solar PV to the utility grid. The q-axis current reference is kept zero. In the current control loop, the grid voltage is applied with the voltage error produced by the PI controllers and the voltage feed forward loop to generate the inverter terminal voltages in the dq axis. In addition, the estimated inverter terminal voltage is divided by half of the measured DC-link voltage to produce modulation indices . The modulation index is then used in Sinusoidal Pulse Width Modulation for generating switching pulses for the inverters.
Figure 12.9. PWM pulse generating technique for SI and MI.
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Solar energy for electricity generation
Jorge Morales Pedraza , in Non-Conventional Energy in North America, 2022
Solar photovoltaic
Solar PV, also called "solar cells", are electronic devices that transform the sunlight into electricity using special materials with photovoltaic effects (see Fig. 3.1). In other words, a solar PV system converts the Sun's radiation, in the form of light, into usable electricity and heating. It comprises two main components: a) the solar array; and b) the balance of system components (BOS).
Fig. 3.1. Solar arrays at Desert Sunlight California, USA.
Source: US Department of the Interior First Solar Desert Sunlight Solar Farm, California, USA. https://commons.wikimedia.org/wiki/File:02-09 15_First_Solar_Desert_Sunlight_Solar_Farm_(15863210084).jpg.Various aspects can categorize a solar PV system. These aspects are the following:
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Grid-connected vs. stand-alone systems;
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Building-integrated vs. rack-mounted systems;
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Residential vs. utility systems;
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Distributed vs. centralized systems;
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Rooftop vs. ground-mounted systems;
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Tracking vs. fixed-tilt systems;
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New constructed vs. retrofitted systems.
Other distinctions may include the following aspects:
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Systems with microinverters vs. central inverter;
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Systems using crystalline silicon vs. thin-film technology;
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Systems with modules from Chinese vs. European and US manufacturers.
Undoubtedly, the most developed source of solar energy today is solar PV. According to reports from the environmental organization Greenpeace, solar PV could supply electricity to two-thirds of the world population by 2030 (Teske, 2008). Thanks to the technological advances achieved in this type of energy source, sophistication, and economy of scale, the cost of the electricity generated by solar PV parks has been reduced significantly in recent years and has increased its efficiency. a
For the above reason, today, the average cost of electricity generation from solar PV parks is competitive compared with other non-renewable energy sources in a growing number of countries located in different geographic regions. Other solar technologies, such as thermal solar energy, reduce their costs considerably. However, their use for electricity generation is still low in several regions of the world, particularly in the North American region. The prices of solar panels used in solar PV parks have dropped by a factor of ten during the last decade. This price reduction has made electricity generated by solar PV parks more competitive than other energy sources. With the help of wind energy, it opened the path to a global transition from the use of conventional energy sources for electricity generation and heating to increased use of all renewable energy sources. That transition is indispensable to mitigate global warming. However, it is important to know that the use of solar PV as one of the main sources for electricity generation, heating, and desalination requires energy storage systems or global distribution by high-voltage direct-current power lines causing additional cost.
A solar PV park (see Fig. 3.1) employs solar modules, each comprising several solar cells, which generate electrical power on a commercial scale or arranged in smaller installations to be used for mini-grids or personal use. A solar PV system for residential (see Fig. 3.2), commercial, or industrial energy supply, in addition to the solar array, has several components often summarized as the balance of system (BOS). That system balances the power-generating subsystem of the solar array with the power-using side of the AC-household devices and the utility grid (see Fig. 3.3). BOS-components include (see Fig. 3.4):
Fig. 3.2. Schematics of a typical residential PV system.
Source: S-kei – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=17181966. 
Fig. 3.3. Balance of a solar PV system.
Source: Rfassbind – Own work based on the Solar Energy Technologies Program. U.S. Department of Energy archived website. Public Domain, https://commons.wikimedia.org/w/index.php?curid=35283841. 
Fig. 3.4. Solar string inverter and other BOS components in Vermont, USA.
Source: Cheeeeeese – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=28631474.- •
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Power-conditioning equipment and structures for mounting;
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One or more DC to AC power converters, also known as inverters;
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An energy storage device;
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A racking system that supports the solar array;
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Electrical wiring and interconnections;
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Mounting for other components (Wikipedia Photovoltaic, 2020).
Optionally, the balance of a solar PV system may include one or more of the following components:
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Renewable energy credit revenue-grade meter;
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Maximum power point tracker (MPPT);
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Battery system and charger;
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GPS solar tracker;
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Energy management software;
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Solar irradiance sensors;
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Anemometer, or task-specific accessories designed to meet specialized requirements for a system owner;
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Optical lenses or mirrors and sometimes a cooling system (Wikipedia Photovoltaic System, 2020).
The use of solar PV to power mini-grids is an excellent way to bring electricity access to communities located in remote areas of a country far from the national power transmission lines. That is particularly true in developing countries located in the region of the world with excellent solar energy resources. Solar PV parks may be mounted in the following manner:
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Ground-mounted;
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Rooftop mounted;
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Wall-mounted;
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Floating.
"The mount may be fixed or use a solar tracker to follow the Sun across the sky. Solar PV has specific advantages as an energy source: once installed, its operation generates no pollution and no greenhouse gas emissions, it shows simple scalability in respect of power needs, and silicon has large availability in the Earth's crust" (Wikipedia Photovoltaic, 2020).
Solar PV has long been used as stand-alone installations and grid-connected PV systems since the 1990s (Bazilian et al., 2013). Solar PV modules were first mass-produced in 2000 when German environmentalists and the Eurosolar organization gained government funding to implement a program to install ten thousand solar PV panels in private houses and buildings. Advances in solar technology and increased manufacturing scale have significantly reduced solar PV panels' cost and increased solar PV parks' reliability and efficiency (Bazilian et al., 2013).
"The cost of manufacturing solar panels has plummeted dramatically in the last decade, making them not only affordable but often the cheapest form of electricity. Solar panels have a lifespan of roughly 30 years and come in a variety of shades depending on the type of material used in manufacturing" (IRENA Solar Energy, 2020).
It is projected that the total installations of solar PV cost projects will continue to decline in the next three decades. That decrease would make solar PV projects highly competitive in many energy markets. It is expected that solar PV project average costs will decrease between US$340 and US$834 per kW by 2030 and between US$165 and US$481 per kW by 2050. In 2018, the cost of solar PV parks was US$1210 per kW (IRENA, 2019) b .
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