How to determine your home's annual average energy use while designing a PV system.

How to determine your home’s annual average energy use while designing a PV system. 

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What is Electrical load?

Any electrical device people desire to utilize in their homes or offices is referred to as a load. You must decide precisely what loads you want to run and how long you intend to run them before you size a PV system. Throughout the design process, all of your subsequent calculations will be based on this data.

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In order to start the process of sizing all the necessary components, you must first determine how much energy each load (both AC and DC) consumes. Even while going through the load analysis may seem like a hassle, if you don’t spend the time estimating each load’s energy consumption, the installed system will either be significantly undersized or oversized for your requirements. Both scenarios are a waste of time and resources.

You need to know the wattage of each AC load, how long it runs for each day, and how many days a week it is in use in order to calculate the energy usage of each AC load in kilowatt-hours (kWh). Some loads might only run a few times each week, while others might run every day.

A regular pattern of energy use (average daily energy consumption) can be established by averaging out the loads over the course of a week. Use the equation shown below:

Energy (in watt-hours) = (Watts × Hours per day × Days per week) ÷ 7 days per week

Include all of the watts drawn when evaluating your weekly energy needs. For instance, when estimating energy use for lighting, consider all of the lights that will be on at once rather than just one.

Here’s another example: imagine your washing machine isn’t used every day. You would get at a result that is larger than usual if you calculated the washing machine’s energy consumption based on the days it operates. Instead, by averaging the washing machine’s energy usage over the course of a week, you arrive at a daily energy consumption that is marginally higher than the actual amount on days when the machine isn’t in use and marginally lower than the actual amount on days when it is. This yields a week-long estimate that is fairly accurate.

Take a 175 W washing machine and run it for 45 minutes. If it runs four days a week, multiply the power draw by the number of hours to get the average daily energy value:

175 W × 0.75 hrs = 131 Wh, or 0.131 kWh

The washing machine operates four days a week and consumes 0.131 kWh every day. Therefore, the average daily energy consumption is:

131 Wh × 4 days ÷ 7 days = 75 Wh per day.

Tracing the specific energy consumption levels for all the loads your PV systems need to supply might be challenging. To make it easier to keep track of all the calculations, I advise utilizing a spreadsheet. Additionally, it is simpler to make significant modifications once you have a spreadsheet. As in Figure, keep your load-analysis spreadsheet straightforward. A few loads that will be powered by a PV system are shown in this load chart.

The itemized loads are shown in the first column, and the number of each item is shown in the second column. The following two columns provide the estimated number of hours per day and days per week that each load is expected to run for. The third column shows the power demand (in watts) of a certain load. The final column calculates the average daily energy consumption of each load by multiplying the total run watts by the number of hours per day multiplied by the number of days per week and then dividing by seven. The second-to-last column shows the number of watts each load draws multiplied by the number of items.

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To understand the load chart well, take a look at the television row. Your family watches TV on a nice new big-screen TV that uses 200 W while it is on and is left on for at least 4 hours. The TV requires 200 W for 4 hours or 800 Wh. assuming that everyone in your family watches TV 6 days a week. In order to calculate the average daily energy usage for the week, multiply the 800 Wh by the 6 days per week that your family actually watches TV and divide the result by the 7 days per week. Doing so puts the average daily energy consumption for the TV at 686 Wh, or 0.686kWh.

You must include in the energy requirements of any DC appliances you want to utilize, such as lighting or refrigerator. You must account for the efficiency losses caused by converting the DC in the PV modules to AC for the AC loads; therefore, you calculate this consumption in the same manner that you do for AC loads, but separate the values in your tables. The overall energy consumption of all the loads can be calculated by adding the two figures after accounting for efficiency losses.

Unless sophisticated energy management techniques are applied while configuring the inverter, the inverter itself is an ongoing load. The inverter’s idle draw can have a considerable impact on the rest of your system sizing and the system’s overall performance, even while this load isn’t particularly huge or continuous. By consulting the specification (spec) sheet offered by the manufacturer, you can determine the precise amount of energy an inverter consumes while it is not in use. Simply take a look at the specifications of the inverters you plan to use most frequently and calculate each one’s power requirements.

Strategies for designing PV systems step by step are presented solely on a single page.

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