Gunner Quinn
(Continued from Part 2.)
When it came to setting angles, my installer wanted to install at the U.S. default angle of 20 degrees. That angle serves the most people across the country in most situations. Now, I’m a taller-than average, bigger-than-average guy and wear extra-large gloves, so I know one-size does not fit all. You must consider what is best for you and your goals and not just what may be the rule of thumb. I happened to hear the guys talking about the angle after they had already set the poles in the ground. Like I said, I hadn’t even thought to consider this aspect of the install so I hadn’t thought to address it.
For me, I would have preferred that the panels be set at 28.1 degrees since that is my best year-round angle. However, the poles the guys set were not long enough to accommodate that angle, but I was able to get 25 degrees. That’s pretty much a happy middle between the rule of thumb and where I wanted to be, so I’m satisfied enough with it. In all actuality, if I hadn’t been out there when they were talking about it, I probably never would have known the difference. That’s why I’m giving you the heads-up.
To summarize, there are two completely valid schools of thought here.
Optimize credit generation by producing as much extra power as possible during the most productive time of year.
Pros: Optimizing power production, optimizing credits, least cost
Cons: Generate even less power during the weakest solar periods; increases reliance on grid during wet seasons and winter.
Optimize year-round generation by setting panels at annual optimum angle.
Pros: More productive year-round; reduces reliance on the grid
Cons: Generates fewer credits; may still provide less-than-ideal production during sub-optimal times
Question: At what angle are the panels being set?
Questions: What is the trade-off between that angle and other optimization solutions? Does your installer have any metrics to help you make a decision?
The key to these questions is to ask before they buy materials. It may also be less of an issue for roof-mount systems, but there is always the option to see if the angle can be changed even with a roof-mount. Various systems are in use which can change the angle of even roof-mounted systems to better align with the sun. Be prepared to pay more for any non-standard request.
Storage
I started to name this section ‘Batteries’, but I want to discuss inverters and the various systems which support the storage of electricity as well. These systems include the batteries themselves, the inverters, and transfer switches. There are other components, but these three will require most of your decisions.
Let’s start with the easy one: batteries.
This is what most people think about when considering storage. They are, after all, where the electricity is stored and basically what is used to properly size a system. First off, if you want to go totally off-grid in a house that wasn’t built for it, it won’t be cheap. Batteries and the hardware that power them are expensive. They are getting less expensive, but you’ll get a bit of sticker shock.
As a rule of thumb, consider that a battery will be about $10k, installed and after financing. This is for an outdoor battery that stores somewhere around 10-15kWh. If you remember back to the earlier example, we had about 129 kWh per day usage, which comes out to 5.3 hours of usage per hour. You can see that 10-15 kWh of storage will cover only about 2-3 hours of battery backup during the heat of a Texas summer. Of course you can add batteries until you have your consumption covered, but since I am using the cost-offsetting strategy, I could only cover a couple of batteries while still staying within the historical cost of my electric bill.
Here is where it gets a little tricky again. Most assume that overnight consumption will go down. The family goes to sleep, electronics and lights are turned off, and all is quiet. This leaves the air conditioner, electric clocks, all those 1-watt-consuming status lights, security cameras, internet equipment, and a host of other items still going. You aren’t going down to zero usage at night. You may drop significantly, but it is hard to determine exactly where you will be. My research shows that most estimate that daytime usage is about 60-70% of daily consumption while nighttime use is 30-40%.
Question: What is my overnight consumption? How do I size my batteries to accommodate this?
For my house, we have a tenant who works second-shift. This means that once the tenant gets home around 10:30 at night, there are still several hours of ‘awake time’ level consumption during our overnight hours. Thus my overnight consumption is in the higher end of the estimates, probably around 40-45%. Everyone is going to be a bit different in consumption. Just be aware of where you are so that you can size your system appropriately. Again, the company you work with may be able to help a bit, but you will need to let them know the various factors which influence your system size.
I found a few whole-home energy monitors that you could use to determine your energy consumption. Most led to Amazon links and pretty much all of them relied on your phone as the interface and required you setting up an account to view your information. I am someone who highly values my privacy – and yours – as such, I cannot confidently recommend any of them. Therefore, I recommend finding an option that works for you, even if that option is to use your best judgment rather than a piece of technology.
Inverters
An inverter is a device that takes in direct current (DC), like from solar panels or batteries, and converts that into alternating current (AC) like you get from your wall outlet. These devices are not 100% efficient, so there is some loss associated with this conversion. This means that 48 volts of DC at 10 amps (which equals 480 watts) will not equal 120 volts of AC at 4 amps (which is also 480 watts). It will be somewhat less. How much less depends on the efficiency of your equipment. Usually commercial-grade equipment is pretty close to the same these days, in the mid-to-high 90 percent range.
There are a few different types of inverters. We’ll discuss string inverters, microinverters and hybrid inverters.
In the most simplistic terms, string inverters combine all the solar panels in your array into one inverter (for the purists out there yes, you can have multiple string inverters but if you know this, you probably aren’t learning a lot from this article). String inverters, at the time of this writing, are the most efficient, at around 96-98% efficient. There are two main issues with string inverters – first, is shading. Since a string inverter is taking in all the power from all panels and solar panels tend to perform at the level of their weakest element (again, a huge over simplification, but serves the purpose of this article) then if you get shade on one panel, the whole system suffers. Also, if one panel gets damaged you suffer the same fate. The second issue is being a single-point of failure. If your string inverter goes out, your whole system is down.
A mircoinverter usually has one, smaller, inverter per panel and then combines the power output. Microinverters are a little less efficient at around 95-97%. As compared to a string inverter, this lesser efficiency is more than compensated for if you have any shading or sub-optimal placement – such as trees or even if your roof is not facing due south. The down side is primarily in cost. At the time of this writing, microinverters cost about double when compared to a comperable string inverter. As far as the single-point-of-failure concern, many sales people (and Internet experts) will tell you that microinverters eliminate this as you have one microinverter per panel. This is true as far as the argument goes. However, all those microinverters feed into a ‘combiner box’ – which then becomes a single point of failure. Yes, string inverters (if there is more than one string of panels) do this as well, but just be aware that microinverters are not as failure proof as some would like to advertise.
Hybrid inverters are used to combine your panels with a storage system. They are more complex, more expensive and more difficult to maintain. However, if you want to be as self-reliant as possible, this will likely need to be in your system. They cost about the same as microinverters, but provide some addition services, such as the inclusion (in most offerings) of a transfer switch.
Transfer Switch
In my opinion, the transfer switch is the most essential yet overlooked piece of equipment in a solar power generation system. It is also never talked about, and could have major implications in how your system works – especially during times of outage.
In very simple terms, if you have a solar setup without batteries, your system produces electricity while the sun is shining. That energy is sent to the grid and then your house draws back what it needs to operate and you get credits (as long as you have a net metering agreement). The catch is that during an outage, the electric company does not want your electricity endangering the folks out there working the lines and trying to restore power. So, your system gets disconnected from the grid. Thus, during an outage you don’t have power even if your system is working fine and you have plenty of sunlight. You’re just as down as your neighbors.
Enter the transfer switch. This is a piece of technology that serves as ‘traffic cop’ for your electricity. When it sees that there is an outage, it shuts off the trunk to the grid and waits to sense power restoration before allowing power to flow again. With this in place, your system will be capable of using the solar and battery power without endangering electrical workers, so you still have access to the power you generate and store. For those seeking any modicum of self-reliance this makes a storage system with a hybrid inverter almost a must-have.
Why not just get a transfer switch for the solar-only system, you might ask. Good question. For me, it wasn’t feasible, so I didn’t look into it too much. This is another consideration for you though. See, for me, my grid provider does not allow solar-only systems for net metering. You have to have storage for them to entertain the agreement. Perhaps this is so that your production is more balanced, perhaps it is a shortcut in their evaluation process to ensure you have a transfer switch. I don’t know. All I know is that storage is required and since I wanted storage anyway, it wasn’t worth researching much more.
(To be concluded tomorrow, in Part 4.)
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