Sunday, July 17, 2016

A Trip Around Our Solar System

Our first solar panels, set up the day we moved onto
our property for charging our phones and laptops.
The Geek's Quad's first power station.
Our solar system has evolved and expanded over the past few years. We have added several panels to our solar system and have not downgraded any of them to non-panel status, although now I have the strong urge to name one 'Pluto'. While many readers know our alternative power source here at the Geeks' Quad is solar power, what many probably do not know is that, as with many projects we approach, we do not have your 'typical' solar system. The main differences are (1) we built it ourselves, component-by-component, at a fraction of the cost that solar companies sell installed systems for and (2) rather than convert the generated/stored power  to the standard 120 voltage used in houses, we set up our house to use 12 volts for almost everything. More on that later, let's start at the center of the solar system - the sun.

Our Harbor Freight array
As long as we have sunlight shining on our panels we are generating electricity. Solar electric panels are made up of numerous solar cells. A solar cell converts photons into electrical power through a chemical reaction. All light consists of particles called photons. When the material used to build a solar cell is hit with the photons that make up sunlight, the photons are absorbed and through a chemical reaction they release electricity. Each cell produces 0.5 volts of direct current (DC). Since each cell can convert 0.5 volts, a 36 cell panel can output 18 volts, and a 60 cell panel can output 30 volts.
Our first Grape Solar

We started out, 4 years ago, buying solar panel kits from Harbor Freight. At the time, these were the most cost effective. Each kit contains three 15 watt panels (45 watt total) for about $130. All solar panels are rated at how many watts they will produce. This rating number is based on a perfect test condition scenario, and you will not see your panels reach this perfect world production, but it is a good number to use when comparing panels. Divide the cost of  a panel by its wattage rating and you will have a cost-per-watt comparison to use when comparing panels. Back when we were buying the Harbor Freight panels they were $2.88/watt. Then, about 18 months later, another option became available from Grape Solar. The Grape Solar Panels are 265 watt panels that can be ordered at Home Depot for $370 ($1.39 per watt). We still use our Harbor Freight panels, but to compare them to our newer panels - all 18 of our Harbor Freight panels produce just slightly more power than just 1 of our Grape Solar.
Another Grape panel is added

With multiple panels (called an array), you need to decide if you are going to connect them in parallel, series or a combination of both. The deciding factor, especially in our case, is if the panels have any shadowing throughout the day. If all the panels are connected in series (one long chain) and a shadow falls on one of them the entire array stops producing power. If, on the other hand, the panels are connected in parallel and a shadow falls on one, the others will continue to produce power. At this point, you may be asking 'Why not always connect them in parallel?' I am not going to go into all the science, but in parallel, the current from each panel gets added together - more parallel panels means higher currents which means heavier wiring is required. Each parallel set also needs a pair of wires going from the array to where your system is being set up in your house.
When the array grew to four, we rotated the panels
so we could fit two vertically for a 2x2 grid.

Back to our specific situation. Our original Harbor Freight panels span the entire length of our south facing deck, about 30 feet. The length of this array and the fact that we sit low in a valley caused us to connect these panels in parallel. As the sun comes up in the morning the panels on the west side of the array can be lit for an hour or more before the panels on the east side of the array, and in the afternoon as the sun dips behind the mountain to the west the opposite shadowing occurs. If these panels were wired in series we would lose about 3 hours of power production from them each day as either end was still in shadows.

Our Grape Solars, which sit in our south garden (connected to the south deck) are arranged in a more compact block. We started out with just a single Grape panel, when we added a second we wired it in series because of the smaller footprint east-to-west, we did not need to worry about shadowing. When we expanded by adding two more Grape Solars we mounted the new ones below the two existing ones so the east-west footprint remained the same. We then had the opportunity to purchase two panels similar to the Grape's at a great price and those two made a third column of two which we added to the east side of the existing block of four (2 panels wide by 2 panels high became 3 wide by 2 high). 

With this third column, we started to notice a bit of shading on the newest column when the original four were fully lit as the sun topped the tree tops in the morning. I broached the question with Alan that we should experiment to see if there would be less shading if we moved the new panels to the west side of the original panels and thus it would catch shade in the afternoon rather than the morning. We mounted a panel sized piece of cardboard to the west of the panel array so we could compare the time we had shadowing on the new panels to time there would be shadowing on them if we moved them to where the cardboard was located.

While running the experiment, Alan came up with a completely different solution, since we had room for both the new panels as they were currently positioned on the east side of the array and the cardboard as a placeholder for panels on the west side of the array, we should just buy one more set of panels! (He had already done the calculations to determine what we would need to do to expand our system to handle the additional panels). At our next meeting of our self-reliance group, I was sharing this story and I just got to the part about how we were running the experiment to determine which side to place the panels on and two other guys, both with solar set-ups, said 'just add two more panels'. to which my reply was - it must be a guy thing. My experiment was to determine the optimal arrangement of our existing 6 panels, but somehow all three men, with no collusion, decided we needed to instead add two more panels.
Now there's a bunch of Grapes!

So, our most recent expansion, which was a few weeks ago was the addition of two more of the Grape panels. At this point, the east-west span of this array has expanded to the point that we decided to re-wire the panels in a combination of parallel and series connections. The eight panels are in a grid - 4 across by 2 down. Each vertical pair is connected in series and then each of these pairs is connected in parallel (from left to right) since we can have shadowing on either of the end pairs just as we do the Harbor Fright panels. In this way, as shadowing disables one pair of the 'Grape' panels at the beginning or end of our day the other 6 are still producing power. I can now run two dehydrators on sunny days and still have a fully charged battery bank by sunset. We still have a bit of tweaking to do with balancing some power draws, but we have been experimenting and we can even run an air conditioner on sunny days!
The beautiful MidNite Classic
with the amazing Whizbang Jr.!

Enough about solar panels, now that they are wired together, where does the wire go? The wiring is connected to a device called a charge controller. In our case, it is a thing of beauty called the MidNite Solar Classic 200.The charge controller is responsible for protecting your batteries from damage during charging. The batteries must not be charged with too much current, too much voltage, or over charged. The charge controller is also responsible for charging the batteries in the most efficient manner, wasting as little power as possible. And some charge controllers also protect the batteries from being too deeply discharged by automatically disconnecting the loads (lights, fans, radios etc.) when the voltage gets too low. The MidNite Solar charge controller has an optional accessory called the Whizbang Jr. (yep, that's its real name). Every amp of power that flows in or out of the battery bank goes through the Wbjr. The Wbjr measures all the current going into the battery bank during charging, and out of the battery bank when it's used, and it acts like the gas gauge in your car. Put gas into the tank at the gas station and the gauge goes up. Drive around and it goes down. That way you know how much gas is left in the gas tank. The Wbjr does the same for your battery bank, letting you know how much capacity is left at any given time. It has tons of features and Alan has access to all the data from his smartphone so we can check in on it when we are gone. 

The battery bank
From the charge controller the power can go directly to power devices we are using or into the battery bank to be stored for future use. Our battery bank consists of eight 6 volt 208 amp/hour golf cart batteries.Golf cart batteries are designed for slow power draws over long periods of time, which is what we are looking for in household use. If you connect batteries in series you increase the voltage (two 6 volt in series produce 12 volt). If you connect batteries in parallel you increase the amperage (those same two batteries connected in parallel would still produce 6 volts but for 416 amp/hours). With eight batteries to connect together in our battery bank we had a lot of options. However, the best choice is to not exceed two parallel strings of batteries.  Two will have a good balance when charging and discharging. Batteries have slight internal differences, called internal resistance. As you add additional parallel strings, these differences cause problems with equal charging and discharging. Therefore, we have two parallel strings of batteries - each string is 4 batteries in series. This means we have a 24 volt / 416 amp/hour battery bank. (6 volt x 4 batteries in series = 24 volts and 208 amp/hour x 2 parallel strings = 416 amp/hours).
Where it all comes together!

Enough of the math, actually there is never enough math, but that's my personal opinion. Here is a quick review: sunlight hits the solar panels and is converted to electricity, that electricity flows through wiring to the charge controller, from there power can be used directly throughout the house and all excess power is stored in the battery bank. If you have been following the numbers, you may have realized that something isn't right. In the beginning I said our house was wired for 12 volts,  but our battery bank is 24 volts. This is where the buck-boost converter comes in to play. The buck-boost can be set to a specified voltage to provide a more regulated service, or in our case it it can be use to step down the voltage from 24 to 12 volts. 

There is one other major device in our solar system - the inverter. This takes 12 volt DC from our batteries and outputs 120 volt AC. We only use this for one appliance in our house, the refrigerator which is a converted chest freezer but I will leave that story for another blog post. You may be thinking 'Wouldn't it be easier to run everything off the inverter, then the house would have normal 120 volt wiring?' We chose not to do this because of the amount of loss during the inversion process. You may recall that I stated we do not take the typical approach, the typical approach is to build a larger system, purchase a larger inverter and connect the inverter into you house's 120 electrical system. We wanted to change our lifestyle, design a system to meet our needs and realize one of our goals of self-reliance without breaking the bank.

So, how much did it cost? Ours has been a learning experience with several upgrades along the way. Below is an itemized list of the main components of our current day system. I have not included the Harbor Freight solar panels as they are such a small portion of our production capability now.

6 Grape Solar panels @ $370 ea. - $2200
2 Canadian Solar panels @ $232 ea. - $464
MidNite Solar Classic 200 Charge Controller - $695
MidNite Solar Whizbang Jr.- $45
Energizer GC2 232 amp hour 6 volt battery, four batteries at $85 ea  - $680
Samlex PST-1000-12 Pure Sine 1000 watt 12 volt inverter - $380 
Misc wiring, connectors - $500
Total= $4964

Our original system was under $2000 and was very adequate for meeting our needs, but as we have found with other areas of self-sufficiency, like water consumption, if more is available you tend to use it. One of our goals in setting up our own solar system was to provide an alternative energy source that did not require the sales pitch that every solar company out there seems to include include, which is 'and we'll provide the financing'. We proved we could set up a system for under $2000 and then over a few years expanded it to a more robust system for under $5000, not the typical cost of an installed system ($25,000-$35,000). 

And, in writing this post I have determined who Pluto is in our solar system. It is the Harbor Freight array. Now that we have eight of the Grape Solar style panels, and all of the Harbor Freights together equal about one more Grape Solar that would make them the 9th!

1 comment:

  1. As always, interesting and inspiring. I so want solar.... also wind turbines here on our breezy acres.