There are several reasons why people consider installing an off grid solar system. Most often, it is because it is in a remote location that would either costs tens of thousands of dollars to install the grid, or connecting to the grid isn’t even an option; it’s too remote to get the grid there. Another reason is that the cost for electricity may be prohibitively high. Some islands have the grid available, but electricity may cost over $1 per kWh – five or six times the average US grid cost. Or you may be in a mobile situation, in a boat or RV, and cruising for long stretches without the grid nearby.
If you are considering an off-grid solar system, here are a few things to consider before starting.
It may be stating the obvious, but solar systems need sun. Any shade on the solar panels at all will dramatically reduce the electric output. It’s not a linear decline, shading half the panel doesn’t result in losing half the power. Shading a small corner of a panel can effectively shut off that panel, and possibly all of the other ones connected to it. Despite advances in technology, solar panels need full sun. Those that claim better performance in partial sun are talking about minimal improvements. Solar panels need full sun.
Double check the location to determine if the trees or surrounding buildings will shade the site during different seasons or times of day. Keep in mind a deciduous tree will loose its leaves in the winter, so there is a chance a tree that looks like it will shade your solar array in the winter may not be too bad. But watch out for evergreens, they’ll be a problem year round. Also take into account future tree growth, a poplar sapling today could be a 40’ tree blocking your system in five years. A device such as a Solar PathFinder can be used to determine the amount and times of shading at your location. You can see the white lines drawn in this picture indicate the edges of shade. Much of the roof was shady, so they installed the solar in the clearing in the yard. Based on the Solar PathFinder, this location will get full sun from 9:30AM to 3PM.
Amount of Power Needed
The most important step is determining how much power you need. Also think about future needs, to decide if you need to design it with growth in the future. Don’t design yourself into a corner with a system that you may outgrow in a couple of years. But unless you are already incredibly energy conscious, don’t think that you can just cut the cord and take your existing house off the grid without making some pretty dramatic changes. The “average” American grid tied household uses 900kWh of electricity a month. To take that house off grid, it would cost at least $50,000. You need to set a realistic goal of how much power you need to live off grid.
The best bang for your buck is to use the most energy efficient electrical devices you can get in your off grid solar system. Although energy efficient appliances often cost much more than energy hogs, you will save money buying the more expensive devices. For example, let’s compare using 60W incandescent bulbs with 10W LEDs. Granted, LED bulbs cost at least 20x more than an incandescent bulb, but stick with me. I’m going to show you how it makes sense to swap to an LED bulb next time your incandescent goes out.
Both bulbs put out the same amount of light, both are dimmable, immediately on, and work in the cold. If you replace 5 incandescent bulbs with LED bulbs, it would cost you about $50. But if you used those bulbs for 4 hours a day, that would save 1,000Wh a day.
60W incandescent bulb x 5 bulbs x 4 hours = 1200Wh
– 10W LED bulb x 5 bulbs x 4 hours = 200Wh
Electricity saved 1000Wh
To make and store that much wasted power, you’d have to buy at least $1,500 more solar panels and batteries. Paying $50 to save $1,500 seems like a good investment to me.
The same applies to replacing an old refrigerator with an ultra energy efficient one, replacing a CRT TV or monitor with an LCD or LED one, and many others. A quick way to tell how much power your existing devices use is to plug them into a device like a Kill A Watt meter, and monitor the use for a few days. Then, compare that usage with the ENERGY STAR rating of a new appliance. You can use this information to determine if it is cost effective to replace the old with the new. Also, keep an eye on vampire loads like a cable or set top box. Why? They use a small amount of power and having them on 24×7 adds up to a tremendous amount of power.
Once you’ve figured out what energy efficient devices you will be providing power for, you need to create a Loads List that spells out exactly how much power each device uses in Watts, how many hours a day it will be on, and if it has a start-up surge like a fridge or well pump.
A loads list is the most important step in planning an off grid solar system. It will help determine how many solar panels you need, how many batteries, and what size inverter is required.
Once you determine your loads, you can use our off-grid calculator to help size your system.
If you are living off grid, chances are you won’t have access to city water. A typical well pump is 240VAC, with a very high start-up surge. Consider using a PV-direct solar pump to pump water from the well or stream during the day to store it in a cistern, which then can be used as needed. They use much less power than an AC pump, and allow you to use a smaller inverter than what you may have needed with an AC pump. Battery powered pumps that can run off your battery bank are available to provide city pressure to your house from the cistern.
Let’s face it, there are very few places where the sun shines brightly every day all day long. You need to be prepared for stretches without sun and short days. An off grid solar system needs to be designed for worst case weather.
Most off grid systems will be designed with a generator to help with occasional large loads and stretches of bad weather. If you are living year round in your off grid house and have seasons that can see a stretch of bad weather, a generator can be used to power your house and charge your battery bank. An automatic generator start can be used to automatically turn the generator on and off as needed.
Likewise, if you plan on using a welder a few times a year, it doesn’t make sense to design the solar system to provide the high power for it, it is more cost effective to plan on a generator kicking in to provide the extra power.
We’ve been talking about an off grid house as solar powered. You may have a good location for a microhydro or wind turbine. A turbine is a great way to supplement your solar power, as they are often producing power when the sun is not shining.
Regardless of if you are generating power by solar, turbine, generator, or a combination of all three, you are going to need a battery bank to store the power to be used. There are several factors to consider when selecting a battery bank. A deep cycle battery is needed, as opposed to a car battery. Car batteries are designed with thin plates to provide a high burst of power for a short time. Deep cycle batteries are designed with thick plates to provide a small amount of power over a long time, and to be recharged and discharged over and over. While a car battery will work for a very short time, it will quickly lose its ability to hold a charge and need to be replaced.
Lead acid batteries have long been the staple of off grid living. There are two major categories for lead acid batteries, flooded and sealed. Flooded batteries require regular maintenance, such as adding water and checking the specific gravity (sg) levels. Sealed batteries require very little maintenance. A well maintained flooded battery will cost less and last longer than a sealed battery, but a poorly maintained flooded battery will quickly be destroyed if neglected. Flooded batteries need to be vented to the outside to prevent a buildup of hazardous gases. Sealed batteries off-gas very little, and can be stored in an unvented room, just not an airtight one.
Salt Water batteries are a new non-toxic technology available from Aquion Battery. They are able to be discharged down to 100% empty without harming the battery. This allows you to use more of the power in the battery, requiring a smaller battery bank. While the price per kWh for the battery may be higher than lead acid, the overall cost of the battery bank for the life of the system is lower.
Lithium batteries are able to be deeply discharged and have a long lifespan. However, they are very sensitive to being 100% discharged, and will have to be replaced after just one incident. Therefore they do need to have a battery management system (BMS) to ensure proper charging and discharging. Their initial price is higher than other technologies, but with changes in the industry, are expected to drop soon. Lithium batteries do not require venting to the outside.
Most off grid solar systems are either 12V, 24V, or 48V. The size of the system often dictates the voltage of the battery bank. The larger the system, the higher the battery bank voltage generally is. Don’t get stuck in a 12V system if you may be expanding in the future. Batteries can be wired in series to increase their voltage, so four 12V batteries can be wired in series to form a 48V battery bank.
An off grid inverter/charger does not have the option to be field selectable, so you need to decide the battery voltage before you buy the inverter.
Heating with electricity is very inefficient, so when going off grid, do not plan on heating with electric. Gas or wood heating are usually the best options for off grid life. The same goes for water heating. Solar Water Heating, using the sun to directly pre-heat your water, or a heat pump water heater, that takes the heat from the surrounding air to heat the water, are great options for you to look into.
Going off grid with solar can be an exciting change. Just be sure to do plenty of homework before you pull the plug so you are prepared for the life ahead. Give us a call so we can help you plan your off grid solar system.
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