Description
Final Project
The goal of the final project is to analyze and design a PV system to meet a customer goal or answer a customer question. You are strongly encouraged to come up with your own project. To give you some ideas for project topics we are listing some of them below.
Project Topics: Pick one topic among all of those listed.
Residential/Commercial Grid Connected
Assumptions for grid-connected systems unless otherwise noted:
- You may vary any of the assumptions for the particulars of your system, as long as you justify where the numbers you use are coming from.
- You may assume a typical efficiency of 20% for the PV panels.
- In Arizona, the commercial electricity rate is ¢9.5/kWh and the residential electricity rate is about ¢11/kWh (you can look these up readily for other states). Unless noted, you may assume that the utility will buy solar back at wholesale rates, which is ¢4/kWh for Arizona.
- For simplicity, we have given you a representative load, which has similar yearly energy use to the US average.
- Other parameters you may assume for residential loads: Roof tilt = 30 °, facing south. Roof area = 2,000 ft²
- Calculate the economics of a solar parking lot shade structure. The cost for the parking structure is $60/m². You may assume that the installation cost for the PV panels is reduced by 50% from what it normally is (you should justify this ballpark number or another number). In calculating the LCOE, there will be an optimum for the solar to load ratio; you may assume either a load and then calculate the PV size, or just optimize on array-to-load ratio.
- Group project choices:
- Examine the effect of efficiency on the LCOE of the parking structure solar and how efficiency changes the optimum solar-to-load.
- Use a different economic scheme than net metering (e.g., time of day pricing).
- Group project choices:
Please make the code explainable so that I can write about it but don’t concern yourself too much with this part.
Overview of Design Procedure
A review of general design procedures is given below:
- Specify the system you will be analyzing. Where is it located? Is it grid-connected or stand alone? Does it have storage? What is the load? If you are analyzing an existing site, is there shading? Specify anything you think would impact system design.
- Define the problem or question to be answered. In most of the project topics given below, I have defined the general question to be answered, but I have also given you latitude to change the topic or question to suit your interests.
- Identify the system parameters you need to calculate in order to determine the answer to your questions. For example, if the question is to minimize the LCOE with availability > 97%, you need to calculate availability (the fraction of the load that is supplied by the system) and LCOE. What parameters or information do you need in order to calculate the system parameters?
- Determine how you are going to analyze the system. Determine what are the variables you can change, and what are the fixed inputs?
- Determine how you are going to do the calculations and analysis. Draw a flowchart or other guide to determine how you are going to do the calculations. For each section that you need to calculate, give the relevant equations. What data sources to you need? You should reference them. In general, the goal of report is to enable someone else to be able to replicate what you did.
- Do the calculations and get an initial answer.
- Check that your solution makes sense and that you are able to defend it as the best solution. The degree to which you are expected to do this depends on the degree to which your solution or analysis differs from previously done or other available examples or solutions.
- Determine if your problem specification dramatically impacts your design. For example, in designing the stand-alone system, you may have specified an electric stove, which requires large amounts of battery power to be used at night and dominates the size of the PV array needed. In this case, replacing the electric stove with a gas stove may significantly change your answer, so you might want to more carefully examine the problem specification.
- Determine if how sensitive your solution is to input parameters (or other parameters). For our project, it is acceptable to check this by manually varying inputs and checking to what you expect, but for a more rigorous analysis, particularly for costing analyses, you should do a sensitivity analysis as shown below. You do this by varying your inputs by a certain percentage and examining the effect on your output parameter (which in the case below is Net Present Value).
- How does your solution match with solutions to similar problems?
- Present your final solution and an example of why your solution was chosen.
Do not worry about the presentation part, just worry about the code.
Project report and presentation
The project presentation should have the following structure.
- Introduction:
- Technical goal/ problem; describe the goal of your analysis and problem.
- Critical technical problems or tradeoffs are clearly identified
- Context of problem or trade-offs are clearly identified – why is the problem important
- Background information
- Suitable to the audience and address the goals of the project
- Include necessary background equations, etc
- Previous work relevant to the project.
- If relevant, how is that what you are doing is different from other work.
- Technical approach/ Results
- What did you do, including equations, including program structure?
- Results and analysis; what you varied and what the analysis shows.
- The results must be relevant to what your stated technical problem was.
- Conclusion:
- Conclusion gives not only the technical solution to the problem laid out in the introduction, but also how this solution impacts a broader context.
- Why is your solution the best one?
Appendix A: Summary of Residential Rate Plans for Solar Customers
The types of rate plans for residential customers can vary substantially from one region to another, and often within a utility there are multiple plans. Despite these differences, the rates generally consist of several similar components. These are outlined in the table below and described in more detail after the table.
| Charge | ||
| Monthly Service Charge | Fixed charge, regardless of electricity usage. | |
| Electricity Usage Rates | · Based on the rate for each hour (or some other time unit) and the electricity used in that hour. The simplest is the same rate for every hour of the year, but it is becoming more typical to have 6 different prices depending on the time of year and hour of the day.
· Depending on the type of metering, the electricity used may be the net (electricity used – electricity generated) or the electricity generate. Price plans that use the net are more beneficial to photovoltaic systems and are called net metered. |
|
| Utility buy-back | · This is not used in net metering billing.
· The rate at which the utility buys back may vary throughout the year but is commonly constant and set to a value below the wholesale rate. For SRP it is $.028/kWh. · If you can’t find a utility buy-back price, the utility is generally net metering (i.e., the electricity used is the difference between what you buy and sell. |
|
| Demand Charge | See more detailed description below | This is a monthly charge based on the peak hourly usage in that particular month. |
| Access charge | Fixed number | Charge, typically a monthly fee, for solar customers. This is becoming less common, and SRP does not have one. |
1. Monthly Service Charge
The monthly service charge is charged to all customers, regardless of if they have solar or not. Generally, one charge appears on the bill, although in the detailed utility rate plans the breakdown of these charges in terms of administrative and distribution costs is typically given.
For SRP for a typical residential customer, the monthly service charge is $32.44
2. Electricity usage rate
The electricity usage rate is the electricity used in a particular hour (or other time period) multiplied by the electricity rate for that hour. If the electricity rate is constant (the old billing model, but not that common now), then finding the cost of the electricity is simple; multiply the electricity used in a year (in kWh) by the rate charge (in $/kWh). However, this is not used for solar residential customers.
- The first step is to determine the model used by the utility for calculating the costs of the electricity used by the customer. There are two major models:
- Net Metering: the net electricity usage = electricity bought from utility – electricity generated from the house and sent to the electrical grid;
In net metering models, the electricity company only charges you for the net amount of electricity you use. Mathematically, this is identical to having a buy-back of the utility equal to the electricity rate they charge the customer, which helps simplify the programing.
It is called net metering because in earlier residential systems, utility companies could not differentiate between electricity going to the customer from the grid and coming from the customer going to the grid. In many cases, the meter literally ran backwards when the customer was feeding the grid, so the meter reading from the utilities was the NET electricity used.
- Net billing, feed-in-tariff (FIT), export, solar buy-back models
In the net-billing or feed-in-tariff models or similar models, the utility buys back electricity at a different rate than they sell to the customer. Typically, net billing models buy back at a substantially lower rate than they sell to the customer. Historically, some Feed-in-Tariffs bought back at higher rates than they sold to customers to account for the higher societal value of renewable energy. Because of this, FITs are sometimes used to refer to cases when the buy-back rate is higher than the selling rate, but this is not true in all cases, and the terms net billing and FIT may be interchangeably used. There are multiple other terms for this model, including solar export or solar buy-back.
Sometimes it can be hard to find if the utility is net metering or net billing – in general, if they give you a buy-back rate, they are net billing, and defining the electricity used as the electricity coming from the grid. If no buy-back rate is given, the electricity you pay is the net electricity – i.e., the electricity you get from the grid – the electricity you send to the grid.
If there is a buy-back rate, the revenue from the utility buy-back is calculated separately from the cost of the electricity you use (item 3 below).
- The second step in determining the electricity usage charges is to find the electricity rate that the company charger you for every hour of the year. There are essentially no examples for solar customers where the electricity rate is the same throughout the year, and less and less common even for non-solar customers.
- A common model for residential solar is to have 6 different rates depending on the time of year and time of day. There are usually three different “seasons” and an on-peak and off-peak rate for each day in the different seasons. These rates are graphically depicted by Figure 1, which is taken from an older SRP price plan.
Figure 1: Seasonal definition and pricing of the six different cost categories for on and off peak.
Figure 1 gives an overview but doesn’t show what time of day is on-peak and off-peak, More detailed plots are shown below. The “TOU export” notation on plots indicates this is a net billing model, not a net metering model. The number given is electricity bought from the grid. The buy-back rate isn’t listed on the plots and is $0.0281/kWh.
Figure 2:Definition of peak time periods during winter, summer and summer peak. The prices are NOT those for the customer generation, just the timing.
3. Electricity Buy-Back Rates
The utility company typically buys electricity back from the customer at a particular electricity rate.
- In Net Metering models, the buy back and selling rate are the same. In calculations for net metering, you can either ignore the electricity buy back and use the NET electricity to calculate electricity charges, or you can calculate the electricity buy back using the same rate as the utility company sell to the customer. Either gives the same answer, and the choice depends on which is more convenient for you.
- In Net Billing, Feed-in-Tariffs, or export models, the electricity is bought by the utility from the customer at a different rate than they sell to the customer. This rate can vary continuously (this is uncommon for residential systems), can be constant, or can changes depending on the time of day and year. SRP and APS (two Arizona utilities) use constant buy-back rates.
4. Demand Charges
A demand charge is an additional monthly charge that is calculated based on the PEAK electricity usage (in kW) in a given month. The peak electricity use is found by examining the electricity use in each ½ hour increment for the given month. The monthly charge is based on the value of the peak electricity usage, with the value depending on what month of the year it is. Note that the tine frame of the peak charges are calculated by the utility on a shorter interval (½ hour is commonly used), but this data is not provided by the utility to the customer.
Figure 3: Demand charges for Customer Generation Plan.
The demand charge works in that your program should find the peak kW requested from utility in each month. As an example, say it is 11 kW in July. Then the additional charge in July is $9.59 for the first 3kW, then plus $17.82 for the next 7kW (for a total of 10 kW) and then $34.19 (for the next 1 kW to get to a total of 11 kW). Let’s say it is 3 kW in February. Then the charge for February is $3.55. And so on for all the months.
