Creating a Renewable Energy System for My Home!

Welcome to my last post of 2020! I recently completed the course Exploring Renewable Energy Schemes taught by professor Jorge Santiago-Aviles of the University of Pennsylvania. The course provided a detailed look into how and why different renewable energy systems, especially photovoltaic (PV) solar systems, function. Mr. Santiago-Aviles discussed the different components of a PV system, including panels, batteries, charge controllers, and inverters, and how each of them contributes to the system's end goal of collecting sunlight and converting it into electricity to power a load. For the final assignment, I decided to plan out a PV solar system that would work efficiency for my home.


Energy Audit Summary


First, I needed to calculate roughly how much electrical power, in kilowatt hours (kWh), my home actually uses up each month. I found each value by finding the wattage (W) of the appliance, figuring out how many hours it is turned on and being used per month, and finally multiplying these two values together to find the kilowatt hours per month. For example, my microwave's wattage is 1000 W (1 kW) and it is used for about 10 minutes each day. This adds up to it being used for 300 minutes or 5 hours per month. Multiplying 1 kW and 5 hours together gives me that about 5 kWh is used by the microwave each month. Also, to double check, I looked through my household's electrical bills. By adding up all of the kilowatt hour values of each appliance in my home, I found my home's total monthly energy consumption, which came out to be 1220 kWh per month.


Key System Components

I needed to come up with a list of what components would be necessary in my system. My goal was to plan out the most efficient solar system, so I had to decide what type, of each part to use to maximize efficiency.

PV Panels and Solar Racking

Of course, most important part of any solar system, are PV panels, which absorb light energy from the sun, and convert it into electrical energy; electricity. For example, there are different types of PV panels on the market, monocrystalline, polycrystalline, and thin-film, which all have different prices and efficiencies. I went with monocrystalline panels, which are the most efficient due to their solar cells being made up of a single crystal, allowing more room for the flow of electrons (electricity). Mr. Santiago-Aviles used 400W panels in his example, and this high wattage indicates that a single panel can produce a lot of power, so I went with them.

Next, I needed to calculate how many panels I would need to power my load. For the area that I live in, I will need 28 panels in my array to be a bit above the approximate monthly energy consumption. My household's average energy consumption is 1220 kWh per month, which would be about 41 kWh per day. Where I live, we receive 4.23 hours of peak sunlight. The MPPT charge controller slightly reduces efficiency by about 6% and the AC inverter reduces it by another 4%, I need to divide 41 kWh amount by 0.94 and then divide that new amount by 0.9. This comes out to about 49 kWh, so in one day, the solar array will need to produce this amount. I will be using 400 W panels; with the equation, 4.23h * 400 W I can find how much energy is produced by a 400 W panel based on the peak sun hours in my area. This comes out to each panel producing about 1.7 kwh per day. To find how many panels I need, I divide how many kwh I need daily by how much each panel produces in a day, this would be 49 kWh/1.7 kWh, which equals about 28 panels. A meter would be installed to track how much power is being produced by the solar array. A disconnect button is also necessary to be able to turn off the system if need be.

To mount the solar panels onto my roof, I need solar racking components. These consist of flashings which prevent water from entering the home through drill holes on the roof, mounts which actually attach each panel and hold up rails that the panels sit directly atop of, and clamps which link solar modules to the rails. They also create a space between the panels and the roof so that the panels don't overheat.


Batteries and Charge Controllers

The PV panels need batteries that store excess energy produced by the panels, to be used when there is little or no sunlight available, such as at when it is night time or when it is cloudy. The batteries need to be able to store enough power for one full day, as a precaution. This means that for my system, they need to store about 49 kWh or 49,000 Wh. The equation, (49,000 Wh/48 V) finds how much power the battery needs to store for one full day of extra power according to the amount or power and voltage of the batteries; this comes out to about 1020 AH at 48V. I can achieve this battery bank with four 300 AH lithium batteries. Lithium batteries are more expensive, but are the most efficient.
The batteries being under or overcharged could be detrimental to the system, so a charge controller is necessary to keeps the battery from being under or overcharged, and maintain an appropriate voltage. I need the amperage of my system to select the proper sized charge controller that will maximize efficiency. For each of the four 300 AH batteries, I will need a charge controller of 60 amperes. To find this amount I multiplied the number of panels wired in series in each row by the wattage of each panel, and divided this amount by my battery voltage, the equation looks like (7*400W)/48V, which equals about 58 amps.


Inverter and Cables

The energy produced by the solar array is in the form of a direct current (DC), but regular home appliances need an alternating current to function. An inverter converts the DC current produced by PV panels into an AC current, that can actually be used by home appliances. To find the right sized inverter, I divided the daily power needed by 24 hours to find how much DC power the inverter will be converting to AC power per hour; this comes out to 2040 W. However, I need the surge value, which is how much the inverter can take at a given moment when many things are turned on at the same time inside of the home; to find this amount I need to divide the total wattage of all the panels which is 400W * 28, which is 11,200 W by the power efficiency factor, which I previously found to be about 0.9. This comes out to about 12,000 W; the inverter needs to be 12,000W.

Thick and short cables safely transport the electrical current into and from components. The cables in my system need to be able to have 58 amps of current flowing through them, so the best and safest type of cable to use is 4-gauge cables which can have up to 70 amps of current. Connectors will be attached to connect cables to each other. The cables will connect the solar panels with a battery and a charge controller together in series, and then to the inverter.

Overview

The 28 400 W monocrystalline panels, along with a disconnect button will be wired in series on the roof of my home, with a 4-gauge cable. There will be four rows of seven panels on the roof. Each row of panels will have a 300 AH 48V lithium battery and a 60 amp charge controller connected to it with a 4-gauge cable. These will all connect to a 12,000W inverter which will supply the AC current produced to the appliances. A meter will also be connected to the system. Connectors will be attached to connect cables to each other.

System Budget

One of the most affordable 400W monocrystalline panels are from the brand Trina Solar (these are the panels I used in my calculations) cost $210 per panel, which means that 28 panels would cost $5880. A set of all the components needed to mount one panel on the roof, from the brand Renogy costs $11; for 28 panels I would need 28 of these sets, which would come out to cost $308. A set of four batteries from the most affordable retailer I could find, costs $9475. One of these controllers from Renogy costs $400, so four of them would cost $1600. A 12,000 W inverter from the brand SunGold Power costs $2649. 4-gauge cable (and connectors): 4-gauge cables from the brand Windy Nation costs $22 per 10 feet, which will be used as needed. Adding up the cost of all of these components comes to the approximate total, not including necessary labor, being $20,000.

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