Functional and Useful 100W Solar Array

Once the Monoprice PowerCache 220 was connected to the Harbor Freight 100W Solar Kit (Item #63585), we have everything we need to gather a little bit of sun power and make use of it every day. Given the non-optimal solar panel position and the fact we’re close to the winter solstice, this is just about the worst case scenario for solar power. Nevertheless this system has been gathering enough power to keep all the battery-powered electronics in the house charged up. This includes daily use & charge items like cell phones, tablets, and laptop computers. Plus the occasional items like a digital camera.

There is much more we can do to improve performance of this system, but it has met a minimum level of satisfactory performance so we can leave it running as-is for a while and switch gears to other projects. The focus will eventually return to this solar power system and here are two candidate projects for later:

Physical tracking: the panels are currently just sitting indoors vertically set against a south-facing window. It was done as an easy nondestructive way to experiment. When it comes time to improve upon this configuration, we can build a more permanent outdoor installation that angles into the sun. Maybe even motorized sun tracking throughout the day!

Electrical tracking: at the moment, the solar panel output voltage is dictated by the battery being charged. This is convenient and simple to implement but not the most efficient. We can buy (or design and build our own) a “maximum power point tracking” (MPPT) charger that keeps the solar panel voltage at its most efficient level and transform that to the correct battery charging voltage. It costs some power to do this tracking & voltage conversion, but if implemented correctly, the additional power will more than offset the cost.

We’ll add these projects to the bottom of the “to-do” list. For now, behold the glory of electronics being charged by sun power.

PowerCache 220 At Work cropped

Solar Charging Plug for Monoprice PowerCache 220

The product description page for Monoprice PowerCache 220 (Item #15278) had pictures showing its solar charging input as two round ports, but there were no connector specifications. Since it was advertised as a solar power cache, it would make sense for them to be MC4 connectors. This turned out not to be the case – they were actually two identical sockets that are electrically wired in parallel.

The device comes with an AC adapter for the charging port, but using household power would miss the point of the exercise. Neither do we want to lose the option to charge from grid power, so we don’t want to just cut off the charging plug. We should find an identical plug for solar charging.

The calipers indicate this connector has an outside diameter of 7.9mm and an inside diameter of 5.5mm. There is a small pin in the center roughly 0.5 mm in diameter. Putting those dimensions into search returned a few candidates and a large number of Lenovo laptop power adapters. A fortunate association, as there is a Kensington “Universal Laptop Power Supply” already on hand. It came with a set of interchangeable plugs to fit different laptop brands. This one was purchased to power a Dell, so the Lenovo plug has sat unused. But not for long!

Kensington Laptop Power

The Lenovo laptop plug matches all the diameters, and is slightly longer. It appeared to fit in the socket nicely. Since the two charging ports are electrically parallel, we could plug the AC adapter into the other charging port. This allowed us to read the voltage on the pins of the Lenovo plug so we know where to solder the positive and negative wire.

The plastic housing of the Lenovo plug was damaged in the soldering process so this plug will probably never fit on the Kensington laptop adapter again, but that’s fine. It now has a new purpose as solar charging plug for Monoprice PowerCache 220.

Lenovo now Solar plug

Hunt for AC Inverter Finds Monoprice PowerCache 220

Now that we have a 20 amp-hour 12 volt battery, charged by a solar array delivering up to 125 watt-hours daily. To put that power to use, we’ll need an inverter to convert battery power into household 120 volt AC power. This way the collected solar power can be used for more than just charging USB devices.

An old inverter was dug out of the old equipment collection, but it could only sustain about a minute of work before it would stop, reset, and restart. This isn’t great for the electronics, but what made it intolerable to humans were the cascade of noises that devices emit when charging began. Hearing the symphony roughly once a minute was unacceptable so the search begins for a replacement AC inverter.

The Harbor Freight lineup of AC inverters were obvious candidates. Starting from a basic model just under $20 and going up from there. While investigating options outside of Harbor Freight, one stood out: Monoprice #15278  “PowerCache 220”

It is designed exactly for the task we’re building for. It can accept power from a solar array to charge its 18 amp-hour 12 volt battery. That power can be consumed directly as 12 volts DC, as 5 volt USB power, or as 120 volt AC power.

The PowerCache mostly duplicates the components already in the current solar experiment setup. Buying one might be called wasteful, but for the sake of exploration we’ll call it redundancy. This nearly doubles the battery capacity and allows more ways to put solar power to use. It is also more user-friendly than the current maze of wires and connectors. It is an enclosed unit therefore easily portable. This might come in handy if we ever have a reason to take a little portable power source on the go.

So the search that began as a search for a simple AC inverter ended up with purchase of an integrated unit that included the AC inverter and basically everything else short of the solar panels themselves.

PowerCache 220

Initial Results of Solar Generation by 100 Watt Kit

Once the replacement battery arrived, it was possible to use the power captured by the Harbor Freight 100 watt solar kit. (Item #63585) The E-Flite Power Meter tracks the cumulative solar energy pumped back into the battery every day. Over several sunny days with minimal cloud cover, the daily tally ranged from 8 amp-hours to nearly 10 amp-hours. On an overcast day, the daily tally struggled to reach 4 amp-hours. (Reminder: the solar panels are not optimally placed to face the sun in these experiments.)

At the battery voltage range of 12 to 13 volts, this means a sunny day gives us about 125 watt-hours of electricity. (12.5 volt * 10 amp-hour) An overcast day’s output drops to about 50 watt-hours. (12.5 * 4) Since the sunniest and most productive times for solar largely overlaps with the most expensive times of the time-of-use electricity rates, we can try our best to make this solar array look good, by comparing against the highest rate of 35 cents per kilowatt-hour.

Even when using that expensive rate, a sunny day’s generation only works out to a tiny bit over 4 cents of grid electricity. A cloudy day couldn’t quite make up to 2 cents worth. Rough estimates point to a meager 10 dollars a year of savings on the electric bill.

Fortunately, we’re not doing this for money, and there is room for improvement as well. The solar array can be better aligned with the sun which, from earlier experiments, we know will make a huge difference. But a more immediate concern is the fact only a few items around the house can directly use DC power. There aren’t enough cell phones and tablets to consume 125 watt-hours a day.

In order to make solar power more useful, we’ll need an inverter to take the battery’s 12 volt DC power and turn it into household 120 volt AC.

20Ah Battery.jpg

Initial Use of 100 Watt Solar Kit Hampered By Battery

For the initial round of testing, the solar panels of the Harbor Freight kit (item #63585) was set up in a very temporary way: they were leaned against the south-facing windows of the house. To measure the output, we’re enlisting another member of the parts pile, unearthed when we were digging for the lead-acid battery: an E-Flite Power Meter designed to measure electric consumption of remote-controlled aircraft motors. It can handle the expected range of voltage and amperage and as a bonus it also tracks the total power in milliamp-hours.

E Flite Power Meter

Based on experiments with the small 1.5 watt panel, we knew not to expect the advertised 100 watt output with this sub-optimal, non sun-tracking orientation. The power meter gave confirmation: over the sunlight hours of a winter day, the panel generated power ranging from 20 to 30 watts. This is roughly in line with the small 1.5 watt panel experiment indicating sub-optimal placement returned as little as 25% of the power compared to directly facing the sun.

The solar charge controller allowed the battery voltage to rise to 14.4 to top it off, then disconnected the battery from the panel to avoid over-charging. Once the voltage dropped to 13.8 volts the controller kept the battery at this sustained charge level for as long as the solar panel could keep it there. All this fits expectation of a charge controller doing its job properly.

But something was wrong when withdrawing power from this assembly after the sun went down. Trying to charge a cell phone at night, battery voltage quickly dropped below cutoff threshold of 12 volts and the controller halted operations. There seems to be usable battery capacity remaining but the battery should have been able to hold roughly 12.5 to 13 volts for the majority of the power delivery period.

Looks like this battery did suffer some damage when it dropped down to 6 volts while sitting neglected in storage. Time to head over to Amazon and buy a replacement lead-acid battery with a good amp-hour per dollar ratio. The best ratio varies from day to day pricing fluctuation but at the moment meant this 20 Ah unit.

Harbor Freight #63585 100 Watt Solar Kit

Seeking more power than what a 1.5 watt solar panel could provide, it’s time to step up to the 100 watt solar kit, Harbor Freight item #63585. The manual, posted online as a PDF, fails to describe a few useful details which we’ll cover here.

Every product picture showed the four panels lined up in a row. But in fact the four panels are capable of standing separately as each panel is in their own frame and has their own folding stand. Bolting them together is optional. If the panels are to be deployed and stowed frequently, leaving them separate might make sense as the panels are much easier to handle individually.

The package content lists wires but not their length. Each panel has a 3 meter long wire permanently attached. This wire terminates in a connector common to Harbor Freight solar products but its exact type specification is unknown. It is definitely not the MC4 connector common in rooftop solar installations.

(UPDATE: Thanks to a tip in the comments, we now know this is a connector commonly used in the automotive world and can be purchased from auto parts stores. For example it is commonly used to make electric connections to trailers. While this connector follows the pattern of SAE J928 and J1239, it is not explicitly covered by either specification.)

The four panels connect into a 4-to-1 module. The four wire side are half a meter long, and the unified side has a 3 meter long wire towards the controller. A final half-meter long adapter has the unknown HF solar automotive connector on one end and a barrel connector on the other. (~5.5mm OD, ~1.5mm ID, 12mm length) The barrel connector fits into a corresponding jack on the controller.

HF 63585 100W power adapter

Adding it all up: Each of the panels can be up to 3.5 meters from the central 4-to-1 hub, and that hub can be up to 3.5 meters from the controller. The package includes a 1 meter cable to connect controller to battery.

The kit included two LED light bulbs, each of which have a 5 meter long wire. Curiously, the long wire ends in a standard light bulb socket. But instead of the 120V AC household voltage we would expect from such a socket, it carries the battery DC voltage. This is a decidedly nonstandard and confusing way to do things. (UPDATE: An earlier version of this paragraph incorrectly stated 120V AC conversion took place, a bad assumption based on the standard light bulb socket. Voltage meter told the truth and paragraph has been rewritten.)

HF 63585 100W LED bulbs

The simple charge controller covers the basics, guarding against battery overcharging and over-discharging at adjustable voltage thresholds. The manual claims there is over-current protection as well, but there appears to be no way to adjust the current limit, either for charging or for discharging.

Hunt For Larger Solar Panels

Now that the project ambitions have grown beyond a little 1.5 W solar panel from Harbor Freight (Item #62449) the hunt is on for something larger. The 1.5 watt panel is intended to trickle-charge automotive batteries and is sized well for the job. We’re aware of much larger multi-kilowatt installations for household rooftop solar. What kind of market would support solar equipment in between that range?

One answer is the outdoor activities market, where some people desire a bit of electric power while away from civilization. Cell phones won’t work in the wilderness but there are still other reasons to have a power source: LED lanterns, GPS equipment, and cameras to document the adventure. The products designed for this market place focus on size and weight, important for carrying in a backpack. But since those values aren’t important for the current experiments, there’s no reason to pay the corresponding price premium.

Another answer is the market of people who want a less rugged experience away from home: boats and RVs. While these leisure vessels have power generators, supplementing them with solar panels reduce fuel consumption and associated noise and fumes. For this market there isn’t much desire to make trade-offs for size or weight, and so we can get more watts for the dollar.

Which brings us back to Harbor Freight who offers two products for this market. A small single 15 watt panel (item #96418) or a larger package featuring an array of four 25 watt panels plus a controller module (item #63585). The constantly varying world of Harbor Freight coupons means the exact dollar-per-watt changes for any given day. But the general trend is clear: between the 15 watt kit and the 100 watt kit, we pay roughly double the money for over six times the power plus a control module to treat the battery properly. The choice was easy to make.

HF 63585 100W

Old SLA Battery for a 1.5 Watt Solar Panel

The little solar panel (Harbor Freight #62449) has proven itself to be capable of sending out 1.2 W, within reasonable reach of the 1.5 W announced on the box. However, we’ve also learned its actual power output varies tremendously depending on its orientation relative to the sun and the weather. As a result it’s not terribly useful on its own. We’ll need to add a battery in to the mix.

Enercell SLA

An old sealed lead-acid (SLA) battery from the parts pile is thereby enlisted in the project. We can start the experiment by hooking up our solar panel directly to the battery terminals. It’s not ideal, but a big lead acid can tolerate this abuse, at least in the short-term. (Never do this with lithium-ion batteries of any size.)

The volt meter indicated this battery was overly neglected in storage, because its voltage had self-discharged down to 6 volts. This is far below the recommended range for lead-acid batteries and may have caused some damage. Fortunately it was able to handle a charging cycle and held an open-circuit voltage of 12.5 volt. Good enough to continue the experiments.

Once the battery is in place to cache power delivered by the little solar panel, we can now power a 12 volt USB charger and charge a cell phone on solar power. But the small panel does not track the sun throughout the day, so it could deliver only a fraction of its maximum power. As a practical matter this means the panel need to charge the lead-acid battery over several days before enough power is collected to charge a cell phone for a single day of use.

Based on the latest findings, we can take the solar investigation in one of two directions:

  1. Wring more power from the little panel: build a sun tracker so it can face the sun throughout the day.
  2. Throw money at the problem: buy bigger solar panels.

The sun tracker can be a fun project, but it’ll have to wait. The vote was decided by the arrival of a Harbor Freight coupon for their solar kit. So: option #2 it is!

Observing Behavior of 1.5 Watt Solar Panel

Now that we have a power meter for the small solar panel (Harbor Freight #62449) it’s time to take it into the sun and see what it does. The first lesson learned is that a solar panel’s voltage range is far wider than a battery. A charged and rested “12 volt” lead-acid battery’s open-circuit voltage is around 12.5 volts, and the charging voltage should never exceed 14.4 volts. In contrast, the open-circuit voltage of this “12 volt” solar panel sitting in the sun is more than double that nominal rating. Yikes!

Open 27V

While we expect the voltage to drop as soon as a load is put on the circuit, there’s still that momentary spike of voltage which might cause problems until we better understand how to handle it. Digging through the parts pile for a test load found a 24V cooling fan that was retired due to a bad bearing. Since it was designed for 24V operation, a quick spike of 27V (or possibly higher) should not be immediately fatal. The maximum amperage listed on the label is 0.1A, which translates to a maximum power ceiling of 2.4W so it should be able to handle the power of a 1.5W solar panel.

Upon connection to the voltage output, the fan twitched but did not start turning. A tap of the fan started it turning and we can see the solar panel delivering 9.3V * 0.0328A = 0.3W. This is only 20% of the advertised power while the panel is sitting flat on the ground.

Flat 0.3W

This was in the mid winter afternoon, when the sun is already at a fairly shallow angle relative to the ground the panel was sitting on. Now we have this baseline, the next experiment is to prop up the panel so it faces the sun directly. We expect the power output to increase, and the meter will tell us by how much.

Facing 1.2W

The answer: 19.3V * 0.0625A = 1.2W, or roughly quadruple the output, just by finding a better angle into the sun. This reinforces why solar installations prefer to face into the sun and some photo-voltaic solar systems even track the sun’s movement across the sky. Since this is not a rigorous test, there may be other factors involved that may overstate (or understate) the effects. But after this experiment it should be fair to state:

  • The advertised power rating of 1.5W probably represents the most optimistic value under ideal conditions, but we can get reasonably close.
  • Orienting solar panels to face directly into the sun makes a huge difference.

Measure Output of 1.5 Watt Solar Panel for “Free”

Now that we have a small cheap solar panel (Harbor Freight #62449) to play with, we can start exploring solar panel behavior. The initial quick and dirty test was to connect it to a car USB charger and while we were able to light a little power LED, the panel didn’t do much beyond that.

Before we repeat the experiment (and tackle new ones) we’ll need a way to monitor the voltage and amperage output. The multi-meter in the standard tinkerer toolkit can perform these measurements, but not both at the same time. Aside from the obvious problem of having only a single numeric display, there’s also the fact voltage measurement has the meter wired in parallel with the circuit while the amperage measurement requires it to be in series. Constantly changing wires around would get old very quickly.

We can buy instruments that are designed to monitor power output and simultaneously track voltage and amperage. But for the sake of a small side project, we’re going back to the Harbor Freight catalog. They sell some basic digital multi meter as item numbers #69096, #90899, and #92020. These multi-meters are frequently part of the Harbor Freight “free with purchase” coupon offering, so their prices are “free” subsidized by other sales.

Two of these were wired together so one monitors voltage and the other amperage, displaying their readings side-by-side. A few zip-ties to hold the contraption together and now we have a cheap clunky power meter. Here it is, showing that the solar panel has almost 18 volts of open-circuit voltage just sitting under the light of the photo booth.

Solar power monitor

The upside of a super cheap power meter is that we would shed no tears if an experiment accidentally destroys it. The downside is that we have to be realistic about the (in)accuracy of cheap Harbor Freight instruments. For one data point, we can connect a good Fluke multi-meter to compare readings. This difference is not great but acceptable for exploration.

HB and Fluke

 

 

 

Solar Experiments Begin with Small Panel

Solar power can be a part of everyday life in many different ways, from tiny solar-powered calculators to a home rooftop solar power system. There is great potential for interesting solar power projects. But before that: some investigation to get orientated.

The low-power capability of the 8-bit PIC micro controller might make an interesting pairing with calculator-sized solar panels, but let’s not overly constrain ourselves on power budget until we are comfortable dealing with it. Similarly, a home rooftop solar system is well into the realm of power that can kill, and thus a bad idea for beginner experimentation.

Let’s learn with cheap things first by starting with a small solar panel from Harbor Freight. Item #62449 is designed to be placed in a parked car to keep its battery topped off with solar power. With the coupons typical of Harbor Freight, it should be obtainable for less than $10.

The panel is advertised to supply power to a car battery. So our first quick-and-easy experiment is to wire it up to an accessory meant for car power: an USB charger designed to plug into the lighter socket.

Small solar

This particular USB charger has a blue LED to indicate power. When the solar panel is placed in direct sunlight, the blue LED illuminates. Unfortunately it doesn’t do much beyond that – if a USB peripheral is plugged in to charge, the LED goes dark and there is no sign of charging taking place.

Well, we’ve tried the easy thing first. Now we start poking around to better understand what we’re dealing with.