Photovoltaic Power and Prepping – Part 1, by B.S.V.

Preparedness comes in many shapes and sizes. Where we get a little extra complexity is when we have to prepare to prepare. I encountered this in one of my recent large endeavors, and found myself somewhat lacking. It worked out, but it could have gone smoother. Hopefully this article will help you avoid a similar situation.

In a recent SurvivalBlog article, I discussed some strategies for using solar backup. Since then, my wife and I decided to move forward with setting ourselves up a bit better and entering the solar arena with a whole-house system.

Before you think that this isn’t for you, I must say that I kind of thought so, as well. But you may be able to make it work. What we did was essentially pay off our new electric system with our current electric bill. We live in an older house that could probably stand to be insulated better. We have an old air conditioner which should probably be updated to a more efficient system. We live in a portion of Texas where both temperatures and humidity percentages hover in the 90s for a large portion of the year. When we combined all of that, with a little price shopping and forethought, we found that we could pay for our solar package – panels and batteries – for less than we were paying for electricity from our utility company.

For us, March and April will be about $25 more expensive than if we were paying an electric company directly. However, June, July, August, and September will all come in around $250 less than our average electric bill. The other months are break-even to slightly lower for the solar as opposed to grid-only electric. So, while I am not a huge proponent of debt, if you have to go into debt, choose a type that will pay itself off. Also, consider that my payment for solar are locked in while electricity rates keep drifting up. In a few years, I’ll likely be operating in the black year-round.

With that out of the way, let’s talk about the real meat of the article. Throughout, I’ll explain my situation and provide some questions I asked as well as some that I didn’t know to ask. Hopefully, that will help you be better prepared if you choose this path.

I had spent about ten years looking at solar, the various options, and how I could do it myself. My first conclusion was that I couldn’t really do it myself. I’m fairly capable, and I know the basics of electricity and electronics. I’m familiar with alternating current (AC) and direct current (DC) as well as how to switch from one to the other (inverters and rectifiers). I have a passing knowledge of volts, amps, watts, and cable sizes to carry that current – more importantly, I have access to the Internet where I can reference pretty much every piece of information I would need to do the calculations and install. Sounds like I had it figured out, right?

Not so much. Think about it like knowing how an internal combustion engine works then going to your local auto parts store and trying to build a car based on what you could acquire there. You may be able to do it. Doing it as a one-off is possible, but you will lose all efficiencies – efficiencies of scale, efficiencies of cost, and efficiencies of expertise. You’ll probably end up spending more on parts, more on tools, and more on time spent than if you had simply bought a finished car. So I did what most of us do in a similar situation – I outsourced.

Location

Most solar companies will ask for the graph on your electric bill so they can measure your consumption. They then spec out a system. Depending on the company you work with, that system will either meet your needs or it will meet the needs of what they want to sell. My first piece of advice: check reviews and references. I spoke with four companies before moving forward. I got to the contract phase with one before I checked reviews and saw they had a pitiful 2.3-star average review online and couldn’t provide a reference within 100 miles. I was just too excited, so I slowed down and started doing the due diligence that I should have done originally. The next company wasn’t much better. The one I went with had 4.7 stars and gave me three references who I called and talked to.

The design (if three of my four interactions are indicative of most experiences) will be for a roof-mount system that does not include storage (batteries). That system will offset somewhere between 60-80% of your electrical usage.

I thought that was interesting, but it wasn’t what I was going for. I’m on some property, so I wanted a ground mount system. I have a friend who is a contractor and his advice is to not mount anything on the roof. No Internet connections, no satellite dishes, no solar panels. Roof damage leads to house damage and that isn’t always immediately obvious.

I also wanted to have battery backup power. I was hoping to get a lot more backup than I was finally able to afford, but I did get batteries to serve that purpose and get me through power outages (though not significant long-term disruptions).

I also discovered that since ground mounts can be more finely adjusted, as they don’t rely on the direction your house faces nor on the slope of your roof, ground mounts can be up to 20% more efficient than roof-mounts. Don’t let that efficiency be your deciding factor though. A skilled crew can set up a roof-mount in one day. Ground mounts usually have poles set in concrete – drying time is one day. They require building the structure – another day. They require trenching of electrical lines from the mount location to the house (and/or your meter), more time. More cost. So you may be able to reduce the number of panels or increase your production, but a ground mount system will cost more. Mine took a week to install.

Production Versus Usage

That little graph on your utility bill seems to be pretty helpful. After all, it tells you how much electricity you used and you’re trying to generate electricity, right? Right. Well, it is helpful. It is not all-guiding.

While the graph tells you how much you used, it does not tell you when you used it. This becomes particularly important when it comes to battery backup. Let’s see why this is the case.

First, a quick side trip. Electrical consumption is generally measured in kilowatt hours (kWh). What does this mean? Let’s take an old incandescent light bulb. The bright ones were usually 100 watts. A kilowatt (kW) is 1,000 watts. A kilowatt hour is the consumption of 1 kW for one hour. Thus, it would take a 100 watt light bulb burning for 10 hours to equal 1 kWh. By the same token, many of the little LEDs that serve as power indicators or status lights on your computer (like at the bottom of your monitor or to show your computer is on) use about 1 watt. In this case, it would take about 1,000 hours of use – almost a month and a half – to use 1 kWh.

Okay, given my southern climate, let’s say I have AC power usage similar to the following:

To size the system, you have to determine your daily consumption rate. What I found is that there is a service that does this for most of the solar sales folks (all four I worked with). With this being the case, the sales/install companies may not know exactly how the calculations are done. Here is the best I was able to figure out:

Take your highest consumption month and divide it by the number of days in that month. For me, that is August @4,000 (kilowatt hours) kWh consumption. (Crazy, huh?) That would be 4,000 / 31 = ~129 kW (kilowatt) day. As a side note, some people also say that they take an average of all the months. It seems to be the ‘secret sauce’ of the solar industry.

Now, take that figure and divide it by the number of expected hours of sunlight for your location. This site gives a good guesstimate. I think it is off a little bit, but we’ll use it so we have a common point of reference.

For my area, the site says I will have about 6.5 hours of production during August. We now take the 129 usage figure and divide it by 6.5 hours. That shows that we need about 19 kW system, assuming no losses.

(To be continued tomorrow, in Part 2.)