Solar Power: Part 5-Generators and shore power

When I did my tiny house build, I did not have access to shore power. I guess I could have built my home with a manual hand saw but I wanted to get the job complete. I purchased a generator to power my tools and make my life a little better. When I moved into my home, it became my power source to charge my batteries till I setup my solar panels. Now, I use it to charge my batteries when there is insufficient sunshine in the winter and when I need to use my big tools.

The first step in choosing a generator is to selected generating capacity. Generating capacity is rated in watts. For example, this portable Honda generator is 2000 watts. That is sufficient for charging batteries and most power tools. Because I was building my house, I knew I wanted to plug in my table saw and my air compressor at the same time. This would exceed the capacity of a small generator. 

I was also on a very tight budget; the Honda unit is almost a grand and I wanted to spend my money on the tiny home, not the tools. The Champion 3500/4000 unit was only a bit over $300 and provided 3500 watts of power. The disadvantage of a larger generator is gas usage. My friend Ariel in Fy Nyth has a Champion 1500 generator. Her generator uses about 60% of the fuel that I use during the same time period.

I love the portability of the Honda generator. You can toss it in the truck or on  your four-wheeler-head into the bush and do work off-site. The Champion generator can be moved but it is not a fun task for a smaller person.

The next task is getting the power from the generator to the tiny house. An extension cord works best for this task. The smaller generators will just need a regular cord, such as a 12 or 14 gauge extension cord. Larger generators are able to provide higher current, you could also use a 30 amp cord set to provide greater power to your home.

After selecting your cord set, you need a way to plug the cord into your tiny home. Of course, you could just run the extension cord into the home and plug directly but I prefer to have a formal inlet. Inlets come in 15 amp, 30 amp, 50 amp, etc; match your cord set to the inlet. 

If you wire the inlet to your transfer switch (see this article), you will not need to change from the inverter to generator manually.  I also like protecting my generator from the elements. I live in an area with extreme snow so the generator box is necessary. This is the box I tossed together one afternoon.

There are many options for generators, most operate on gas but some use propane and larger ones use diesel.  The next installment of this solar power series will cover solar controllers.

Solar Power: Part 4-Transfer switches

A transfer switch is optional but a big convenience. The transfer switch automatically switches between the inverter and shore power. Shore power is any outside source of electric such as the tradional electrical grid (extension cord) or a generator.

Living off-grid, we get most of our energy from the sun but sometimes, we do not get sufficient energy from the solar panels to completely charge our batteries (such as during long winter snow storms). I use my generator as a backup to charge my batteries. Or we may want to use more current that our inverter will permit (such as a big tablesaw). On these occasions, I also use the generator.

The transfer switch has three wires. You may need to provide your own wiring for some transfer switches but the same wires will connect to your sources. One wire will plug directly into the outlet of the inverter. The other two wires connect to AC input (shore power or generator) and AC output (house electrical panel). The transfer switch automatically switches the energy to the inverter. Normally, my inverter converts my 12V battery to 120V AC power. When I use shore power, the transfer disconnects the inverter and automatically connects the shore power to provide energy to my home. There is a very short time lag for the switch over so it is best to turn off any computer and such unless they operate on an internal battery or APS battery backup.

A transfer switch is not mandatory, it is possible to do this task manually with either an electrical switch or series of electrical plugs. However, I like the lazy approach, just power up the genny and poof, I have power. My primary use of my genny is to charge my batteries or work on construction projects that require my air compressor or other tools.

Transfer switches are rated for a maximum amperage. My needs are minimal so I have the Xantrex 15A unit but most will want a 30 amp unit or even a 60 amp unit. Transfer switches are available at electrical supply stores and amazon. I have linked the Xantrex and Go Power transfer switches at the bottom. The Xantrex is limited to 15 amps and the Go Power to 30 amp.

In part 5 I will cover connecting to shore power including generators. Thanks for being a part of this on going discussion.

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.