Solar Power: Part 3-Inverter

Inverters convert your battery voltage (for example, 12 volts) to 120 volts, the typical voltage needed for appliances, computers, tools and many other household items. Lights, fans and water pumps are all available for 12 volt systems. Larger items, such as refrigerators are available as 12 volt and propane but these tend to be expensive. If you plan to be off-grid, it is best to wire the house for both 12 volt and 120 volt. The 12 volt wiring will go to a basic 12V circuit breaker panel then to the batteries. The 120 volt wiring will go to a standard household circuit breaker panel, then to the inverter and then to the batteries. It is possible to wire the circuit breaker panel so that you can use shore power (regular grid power), a generator and an inverter to power your needs. I will cover this in the next installment of this blog when I discuss transfer switches.

(image from amazon.com website)

In part one of this series, I stated that these blog articles assumed you were designing and building a basic solar power setup costing roughly $3500-5000. Therefore, I will only cover inverters for this setup. I will also assume that your battery bank is setup for 12 volt, not 24 volt or higher. Your first step in choosing an inverter is determining your needs. Inverters are rated in watts; you will need to convert all your appliances and other electrical needs into watts. Lights and other items are easy, they are rated in watts (for example, a 60 watt light bulb is 60 watts). Larger appliances might be rated in watts or amps. If amps, just convert to watts ( Amps X 12 volt = watts). Total up all your electrical needs, do not worry about amount of time used each day, just the total number of items that will run at any one time. If you do not know the energy needs or you worry that the manufacturer has been conservative in their reporting, you can determine the energy usage with a kill-a-watt meter.



Let us assume you have a refrigerator rated at 40 watts, six lights rated at 10 watts each (60 watts total), a vent fan rated at 2 amps (2 x 12 = 24 watts) and a toaster oven rated at 1200 watts. Assuming we use all these items at the same time, the total is (40+60+24+1200=1324) 1324 watts. We would need an inverter of at least 1324 watts to power our system. However, we also need a 10% margin of error (for electrical losses, voltage spikes, etc) so best to get an inverter rated at 1500 watts.

There are two basic types of inverters, modified sine-wave and pure sine-wave inverters. Without getting to technical here, know that some items will not operate or will fail if used with modified sine-wave inverters. Pure-sine waver inverters have the same waveform as traditional grid electrical current. Because the costs have fallen on pure-sine waver inverters, I see little reason to risk failure of your computer, refrigerator or other expensive items. Therefore, I recommend a pure-sine waver inverter.

There is a host of inverters sold from unknown brands to well know brands. I tend to purchase well know brands with the psychology that "you get what you pay for" (within reason). I recommend reading the reviews of others that have used the same inverter, amazon is an excellent site to read numerous reviews.

If you feel that you electrical needs will grow, I recommend purchase a larger inverter now as the cost to change will be at least double your original cost. I wish you luck and good fortune with you developing off-grid system.

This shows my inverter and my other electrical items:

Below are links to a few of the inverters I have tried and found to be quality equipment.

Solar Power: Part 1-Introduction

Entire books are written the subject of solar setups so I will try to digest it down to the basics.  The book I would recommend for learning about setting up a solar power system is the Solar Electric Handbook. (Purchase of any of these items through our links will give us a few pennies to cover internet costs and allow us to continue providing additional content, thank you).

 Designing a solar power system can be fraught with tension and stress. There are so many terms and it seems each device uses a different nomenclature. There are watts, amps, amp hours, volts, etc. It is enough to make you think you are at the United Nations and no one has a translator.

In a series of post, I will show you how I designed my solar power system and I will detail the reasons for each item I selected. I am assuming you want a basic system that cost $5,000 or less and will provide for basic needs such as a refrigerator, LED lights, tv, fans, laptop and mobile phone charger, and other basic needs. Appliances requiring high electrical needs (heaters, large air conditioners, clothes dryers, etc) can be operated with solar but require a larger system and most likely you will need a qualified professional for the install. What I will detail is a basic system I use in my tiny house.

Let us first list the required components: solar panels, solar controller, inverter, batteries, fuses, maybe a battery charger, transfer switch and monitors, and wires to connect all together. I installed the solar controller, inverter, transfer switch and my main electrical panel in a box on the tongue of my tiny house trailer. These items are outside my home but protected from the elements. The attached photograph shows the basic components. I will detail my reasons for each item in a series of blog posts but many other items work just as well if not better.

Batteries can not be stored outside in my region because they will loose amperage in cold weather. I have four deep cycle AGM batteries installed into a cabinet that is also my lamp stand adjacent to my chair.

Your first duty is to determine: Can you afford to go solar. If all you need is one or two LED lights and charging your mobile phone, you can setup a system for $100 or so. However, operating a tiny house with more comfortable needs will cost a bit more and will depend on your needs. A basic system will cost approximately $3-4,000 dollars (assuming new components). I define a basic system as one that can power an apartment size refrigerator, tv and dvd player, laptop computer, LED lights, fans, and other basic needs.  Therefore, moving forward, we are designing a basic system as I defined above.

Wow, $4,000 dollars, that is a bit steep for a basic system-some will say. However, the cost to get electrical service in the bonnies can top well over $30,000 or more. Solar is also an investment, being off-grid frees you from the invoices of the power grid. If you are a prepper, solar will be the only power available when the grid is shutdown by unrest or other problems.

Most books and professionals will tell you first need to add up all your electrical needs to design your system. I prefer to work backwards designing my system (figure out the system I could afford and then see what it would power) because I am on a limited income. I have no choice but to do solar because the electrical grid is not available to me.

So, this is how I started. I planned for a $3500 system with all new quality components. This would be able to generate 400 watts of power from four 100 watts solar panels. This is where it get confusing; it is not complicated but can be tedious because not all items speak the same language. Your friend is the following formulas:

Watts = Amps X Voltage

or the same formula rewritten as

Amps=Watts/Voltage

I may have lost a few of you, not to worry, this will not be a math class. I will give you instructions to figure your needs. Let us assume you live up north where there is less sunshine in the winter. If you live in Texas, Florida or other areas with abundant sunshine, you will have much more power available 12 months of the year. Living up north, we get about 7 hours of usable sunshine per day in the winter (assuming blue skies or light overcast).  Remember that figure from above, 400 watts from the solar panels. Take the hours of usable sunshine per day (7) and multiply it by the 400 watts to give you the total energy generated per day in the winter from your solar panels; in this example that is 2800 watts. You will get some loss of power because of resistance of the wires and such so let us assume you are getting 2500 watts of power added to your batteries each day. Of course, in the summer you will have more sunshine but you need to design you system for the times of the year with limited sunshine. Unless you have a summer cabin that is not used in winter or some other twist; I am assuming you are designing this system for year around use.

WooHoo, now we are making progress. But wait, batteries are measured in amps or amp hours.  No worries, just convert it. 2500 watts on a 12V system is 208 amps (2500 watts/12 volts = 208 amps). So, on this one day of sunshine you have added 208 amps to your batteries (assuming the batteries needed to be charged). Wait, you can not use all that energy because your batteries should not be discharged below 50% (assuming you have lead acid batteries, not salt water batteries). Therefore, divide the 208 amps by half to get roughly 104 amps for your daily use.

Ooops, here we are again at the United Nations; most electrical items are not rated in amps, many are rated in watts. For example, a 60 watt bulb or a 37 watt refrigerator. No worries, just convert it again: 104 amps X 12 volts = 1248 watts. You have 1248 watts available for your 24 hour day; the next day more energy will be generated. Some days, you might have excess and other day, you might draw more than what is generated from the batteries.

In the next blog post in this series, I will explain batteries and how to calculate your needs for battery storage and use.