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 2-Batteries

Without batteries, you will only be able to use solar power when the sun is shining. Honestly that is not so convenient so I would say batteries are a necessity with a solar panel system. Of all the battery choices (wet cell, maintenance free, lithium, Tesla, salt water, etc), I only have experience with wet cell and maintenance free batteries. Therefore, I will limit my discussion to these two types of batteries. These are also the most common types used for solar power.

Most of us own or have owned a car; a battery is used to start the car and power parts of the car during use. Typically this is a wet cell or maintenance free battery. These batteries work great because they are given a continuous charge during use. However, once you turn off the engine, it does not take long for these batteries to drain. Another type of battery, common in golf carts, sailboats and electric wheel chairs is deep cycle batteries. These batteries are designed to be charged and discharged repeatedly; however they are not designed to be discharged completely. It is best if deep cycle batteries are not discharged below 40-50%. Typical life of a car battery is 3-4 years. Typical life of a well cared for deep cycle battery is 7-10 years. Typical life for a poorly cared for deep cycle battery is 1-3 years; they are much to expensive not to care for properly. Batteries will be about 1/3 (or greater) of your solar budget.

When I lived aboard a sailboat, I had wet cell golf cart batteries. I used two 6 volt Trogan T105 wired together in series to make a 12V battery bank. These were strong reliable batteries but it was a pain because wet cell batteries give off small amounts of hydrogen gas in addition to the possibility of sulfuric acid spills. Wet cell batteries need to be vented and also maintained (water added). I prefer to have my batteries inside my home and I did not want to vent them to the outside as that opened up another hole in my structure. Maintenance free, for me, are a better choice.

 (Image from amazon.com)

Maintenance free batteries are available as automotive, deep cycle gel cells and deep cycle AGM (absorbed glass mat). Automotive batteries are a no-go for the reasons previously stated; gel cells (in my opinion) are temperamental but I like the AGM batteries. This is a sealed maintenance free battery, it can be mounted normally, sideways or even upside down. AGM were designed to use in military jets.

Deep cycle batteries are rated in amp hours; this is like the storage capacity of a water tank. Amp hours is the amount of energy the battery will store if fully-charged. For example, my AGM batteries are 125 amp hours each. As previously stated, you should only discharge a deep cycle battery approximately 50%; therefore an 125 amp hour battery is only really providing 62.5 amp hours of energy for use before needing to be completely recharged.

In part one of this series on solar power, I mentioned this series of blog articles would be for a basic solar setup costing in the neighborhood of $3500-5000. This size setup can easily accommodate 4-6 AGM batteries. I have experience with both the Vmax 125 amp hr and the 155 amp hr batteries. Both are excellent. When combined (wired in parallel so it remains 12V but the amp hours are additive) into a system, four 125 amp hr batteries will provide 500 amp hr (125 x 4 = 500) of storage or 250 amp hr (50% of 500) of usage before recharging.

Shown below is my battery storage, two batteries on each shelf and enclosed in a cabinet that becomes a lamp stand next to my chair. This is the advantage of AGM batteries, they do not need maintenance so can be stacked.

 I have room under the sofa for further battery storage if I decide to expand my system at a later date. This is important, always plan for expansion of your system so you are not locked into a set system.

In the next installment of this series on solar power, I will discuss the inverter. The inverter converts the battery power to AC electrical current for use in typical appliances and other needs in your home.

Below are affiliate links for the batteries discussed in this article. As always, questions are welcome.