Write By: administratorPublished In: Created Date: 2019-08-05Hits:502Comment:0
Lighting and charging devices is a huge win for most people. But you might still be wanting some power for other appliances like refrigerators and fans. This part of the guide will cover buying and building a solar panel and battery system for your home. These DIY off-grid solar panel systems have gotten dramatically cheaper and easier to assemble in the last couple of years. Homesteaders, survivalists, vanlifers, and homeowners of all types are meeting their electricity needs without hassle, noise, fuel costs, or great expense.
Powering Appliances: Calculating Power Needs
The first step toward building a basic solar + battery panel system is figuring out your bare minimum power needs. What do you need to power exactly (e.g. lights, fridge) and how much power do those each need? There are a number of calculators and resources to help with this. We’re going to use the kWh/hour and kWh/month numbers given by the City of Santa Clara’s Appliance Energy Use Chart. This guide will focus on powering lighting, refrigeration, fans, and electronics.
Flashlights are the first thing most people reach for in a power outage. Being able to see, work, cook and read at night makes life a whole lot easier. As you probably noticed in the previous section, lighting is quite an easy thing to power with solar panels and batteries. Many LED bulbs use under 10 watts and most fluorescent bulbs use under 20 watts (this is not much). It’s possible to light a home with minimal power draw on a battery.
Air conditioning is downright amazing but it uses a lot of energy. It cannot be used in a minimal solar panel system. Portable fans are the next best option for staying cool and most are relatively efficient. Most portable fans use around 0.03 kWh per hour.
Electronics (TV, Phones, Laptops)
TVs, phones, and laptops are arguably necessities in modern times. You can live without them but most of us don’t want to. These electronics vary greatly in their electricity consumption. TVs use between .1 and .4 kWh per hour while laptops tend to use 0.02 – 0.05 kWh per hour. Charging an iPhone 6 completely uses about .105 kWh while a Samsung Galaxy S8 take about .115 kWh to charge.
Now that we know what we’re going to power, we need to calculate the energy this system must be able to generate and store.
Refrigerator: Approximately 75 kWh per month. Older fridges will use more energy and newer fridges will generally use less. We went with a number in the middle but you should check the date and energy consumption of your fridge (it’s almost always written inside).
Fans: 0.03 kWh per hour * 12 Hours * 30 days * 2 fans = 21.6 kWh per month
TV: .12 kWh per hour * 2 hours * 30 days = 10.8 kWh per month
Laptop: .03kWh per hour * 3 Hours * 30 days = 2.7 kWh per month
Lighting: 0.015 kWh per hour * 4 Hours * 30 days * 5 bulbs = 9 kWh per month
75 + 22 + 11 + 3 + 9 = ~120 kWh needed from solar panels + batteries
Note: These items can make life a lot better. That said, they can be cut out or severely minimized to limit the amount of electricity consumption. Skipping refrigeration would allow you to have a much smaller/cheaper system size.
Sizing and Building a Solar Panel System
How big of system do you need to sustain 120 kWh of use over a month? Sunny Puerto Rico gets around 5.5 hours of peak sunlight per day. Using the PVWatts System Size Calculator, we calculate a system size of 1000 Watts. The PVwatts calculator says that with a 1kw system we can generate around 1500 kWh per year (or around 125 kWh per month).
What exactly do you need for a 1kw solar panel and batteries system? To generate 1kw of electricity, you need to get a set of panels that adds up to 1kW (e.g. 4x250W panels). For the batteries, the calculation is a bit more complicated. Here’s the math:
120 kWh per month / 30 days in average month = 4kWh / day
4kWh per day * 2 days (for backup storage) = 8kWh or 8000 Watt-hours
The system will need solar panels, batteries for storage, a charge controller to monitor charging and prevent overcharging, and an inverter. Both Amazon, Walmart, eBay, Home Depot, and numerous other online retailers offer solar panels and solar panel kits. We’ll review both the options for buying these parts separately or in a kit.
Panels are, no surprise, the engine of any solar energy system. Here are some well-reviewed solar panel options.
For 8kWh with a 12V system, you’ll need roughly 660 Ah (It is hard to find 1 battery of this Ah; it is easier to connect 3 to 4 batteries in series to make up 600 to 700 Ah).
Batteries are used to store the power generated by the panels so it can used later. Batteries come in many types but sealed lead acid (SLA) batteries are going to offer the right balance of maintenance, price, and storage capacity for most setups. Here are some well-reviewed battery options.