Solar Scams

A dear friend of mine, knowing of my interest in solar power generation, asked me about an emergency power backup system being sold by Solutions From Science [sic]. She was quite interested in this offering because it was a seemingly reasonable alternative to a gas generator. In particular, she was attracted by the elimination of the storage of gas and the fumes from a running generator.

I took a look at the system which was being offered and sent her the following in an email:

Hi Friend,

I'm glad your forwarded this link to me as I was quite curious.

Executive Summary

It would be a waste of money and you would not be happy with this system's performance.

Analysis

This is basically a very low power solar panel (90 watts, barely enough to power a light bulb when in full sunlight). This panel is going to charge a battery capable of providing 1,800 watts.

They don't say how long that battery can provide those 1,800 watts which is one concern. Normally, a company will specify a battery's capacity in terms of watt-hours, or how many watts it can provide for how many hours. If we guess that the battery can provide 1,800 watts for an hour before it is completely depleted then we can estimate how long it can power certain appliances:

• A 22 cu. ft. Energy Star refrigerator typically uses 500 kWh per year, or 1.37 kWh per day. With 1,800 watt-hours available that refrigerator would run for about 31 hours.
• A washing machine uses anywhere from 1.9 kWh to 4.5 kWh per load. So the battery wouldn't even be able to do one load.

Actually, though, it's very bad to completely deplete a battery. Usually, a battery should never be discharged below 20%. I doubt that they're being honest about the battery capacity.

One other interesting question is: How long would it take to recharge the battery? Let's guess that we experience a power outage in the winter (since they seem to inject fear of power loss in a winter storm) but that there's no storm or even a single cloud in the sky. The normal 'peak' sun hours in winter is usually given as 4 hours. Let's say that we've used the maximum recommended capacity of the battery (80%) which means we need to put back into the battery a fresh 1,440 watt-hours. The efficiency of a charge controller is usually about 85%. So let's calculate how many hours it would take to recharge the battery:

• total hours to recharge = watt-hours required to charge the battery / (output of the solar panel x efficiency)
• total hours to recharge = 1440 / (90 x 0.85)
• total hours to recharge = 18.8 hours

• total days to recharge = 18.8 / 4
• total days to recharge = 4.7 days

So this says that at best you would have to charge that battery for five days just to do one load of wash.

This is also saying that the best power you could possibly get out of this system in the winter would be a measly 306 watts per day! This is barely enough to provide light.

This system is clearly a scam. You would probably be better off picking up a small diesel generator and barrel of fuel.

I hope these words are helpful.

Mike

It's disgusting how some people prey on other's fears.

$30!

Just got our September electricity bill -- $30.54!

Energy Production Report

The electric bill for April arrived last week and I'm pleased to announce that the bottom line was...

$37

This was about a third of what it was a year ago!

While I'm excited about the latest energy usage I'd like to say a few words about Tigo Energy. If you've read my earlier posts you will recall that Tigo provides small, individual micro-controllers which optimize the voltage output of each panel. In essence, this prevents a poorly performing panel from pulling down an entire series.

I cannot recommend Tigo highly enough. The product works as advertised and the company worked hard to insure that my 'bleeding edge' system had tender-loving care. Tigo has even automatically uploaded firmware updates to the LMUs increasing optimizer efficiency. The monitoring website gives high-level graphical information giving an instant view of system production. One can also download incredibly detailed information, by the second and down to the individual panel, suitable for low-level analysis using your favorite spreadsheet.

The weather has been too inconsistent to perform a thorough analysis of how the overall system works with and without the optimizers enabled. Later this year, when we have a forecast of several cloudless days, I will alternate days with the optimizers enabled and disabled to see if the boost in efficiency can be better established.

Gateway Placement & Analysis Tools

As with any antenna, the placement of the Tigo gateway is important. Things like aluminum soffit (commonly used for the ceiling of outdoor patios) and facia, metal conduits, and electrical wiring can make effective RF shields or introduce enough RF noise as to interfere with proper gateway operation.

Initially, I had hoped to place the Tigo gateway inside a portion of the roof facing towards the solar module array, above the plane of the array (understanding that the LMUs are below the plane of the array). Unfortunately, the combination of facia, conduit, electrical wiring and the relationship of the gateway to the plane of the array resulted in poor gateway communication with each LMU.

Tigo's website is a perfect tool for diagnosing such communication problems. On the right is an example of the Tigo 'Summary' page for my installation. Note the two panels showing in gray. Gray indicates a some kind of module failure; a communication failure in this case. At the bottom left of the page is a tool for scrolling through a day's worth of solar production data. If when dragging that scroller one sees frequent gray panels a communications problem is the likely culprit.

Tigo's website also provides extremely detailed information on an 'Advanced' page. This data is downloadable in CSV format, suitable for importing into your favorite spreadsheet, and can be as fine as one sample per second. Evaluating the downloaded data by looking for gaps in reported data can assist in the diagnosis of panel problems. If a single panel's LMU never reports data then there may be a panel problem. One can then report this to their installer so that the search for the problem is simplified.

What one wants, of course, is a presentation showing all green panels with relatively similar wattage amounts, as shown to the right. Data for past dates can be brought up by clicking on the calendar control at the bottom left and choosing the desired data. The day's recorded data can be 'played' by pressing the 'play' button. And the total day's accumulated production can be seen at the bottom right.

In my case, gateway placement was causing communications issues so I tried different placements over a few days. In consultation with Tigo's Stuart Davis, we identified a number of candidate placements. The optimum location would be within the attic just below the top row of panels and generally facing towards all panels. Unfortunately, that would be a difficult location to get to. Ultimately, I settled on a location about 25 feet in front of and two feet up from the bottom of the array. The gateway will be mounted on a short pole from the side of the house and face directly towards the array.

With this setup, things are working extremely well, and, on sunny days, I am seeing about 35kWh of production. I expect this number to rise as the days get longer.

Our March Rocky Mountain Power bill was, once again, one half of what it had been a year ago.

Production Analysis

The Tigo web site has several other important tools for analyzing power production. The 'Energy' page can show the performance of the entire array or individual solar modules. On the right is a daily snapshot hour-by-hour of my system for April 7th.

On the left is a weekly snapshot showing day-by-day production from April 3rd for seven days. Clearly, the 5th and 6th were cloudy days with low production, but the 8th was a terrific day for production.

It's Alive!

Monday, March 22nd

I received a call from Stuart Davis, one of my heroes at Tigo, telling me that yes, they had indeed modified the connectors on the LMU based on installer feedback. He said he would overnight a crimper and some new connectors.

While I was talking with Stuart, he mentioned that their system was seeing power from all of the modules! I was surprised, though I shouldn't have been — it isn't necessary for the panels to actually be feeding power to an inverter in order for the LMUs to be reporting panel performance.

Tuesday, March 23rd

The crimper and connectors arrived from Tigo in the early afternoon. Anxiously, I ran the scissor lift back to the panels, gathered some tools and cable ties, and proceeded to:

1. replace the connectors on the home-run cables,
2. connect the home-run cables to the series feeds,
3. re-energize the DC disconnect,
4. re-energize the AC disconnect, and
5. watch the inverter expectantly.

SUCCESS!

Power to the inverter!

SUCCESS!

Power being reported by the Tigo website!

Being on a roll, I then proceeded to cable tie everything nicely so there were no more loose, dangling cables.

The Big Day™: LMU Swap-out

March 20th, 2010

Finally, the forces of the universe converge (i.e. a Saturday with excellent (i.e. non-freezing) weather when my co-installer (i.e. my son) is available) and a swap out of the LMUs can proceed.

My very kind neighbor has once again loaned me his scissor lift. My son and I evaluate the situation and decide that it would be best to remove all solar modules from the roof rather than try to perform the LMU swap on the roof. So that's what we did: started with the bottom row, loosened the restraining bolts, and lowered panels to the patio three to five at a time. This took about three hours and we broke for lunch.

In order to prevent theft while off to lunch at Astro Burger, I pulled my Smart car into the space between the house and the garage so no one could get through the gate and to the panels. There's little theft in our neighborhood, but I wasn't willing to take any chances.

Once all panels were at ground level, and before we swapped the LMUs, we discussed how best to replace the panels on the roof. The idea was that we could sort the panels so that the desired panels would be front-most in each stack ready for the swap and then lifting to the roof.

We went round-and-round: Should we replace the panels one row at a time from the top down? Should we place the panels starting at the bottom in a diagonal pattern giving a base to hold the higher panels during mounting? Or should we place panels in series order?

We made our choice, sorted the panels, and it didn't matter anyway since we changed our approach. So the panels were all out of order! It would have been better to have left them in the order we removed them from the roof. No matter. We bravely motored on.

Three panels were pulled out of the stacks at a time, I disconnected and removed the old LMUs (with my brilliant clutch drill and hex wrench), my son clipped on the new LMUs, and I connected the LMU wiring to the panels. Then Jackie (my sweetheart) helped test each panel for proper voltage output (~50VDC), I strategically placed some UV-resistant cable tie mounts on the module framing, and back up to the roof we'd go.

Once we got an entire series of 8 panels re-installed we'd once again check voltages, this time looking for something in the range of 384VDC.

It was about 5 PM when we placed the last panel and sent my son back to his family. I then prepared to reconnect each series to the home-run cables to the inverter:

• DC disconnect disconnected: check!
• AC disconnect disconnected: check!
• Cable ends not laying in water in gutters: check!
• Visual inspection: check!

"It's ready to connect!" I say to myself.

A quick trip up on the scissor lift and I grab a feed from the last LMU in the first series and the matching cable from the home-run and... Huh? They don't match!

The two cables in the middle should look the same, as should the two cables on the outsides. Clearly, the connector types have changed with the new LMUs. Previously they used Tyco connectors and now they are using MC4 connectors. Well, no power to the inverter for a day or two I guess.

I dash off an email to Tigo hoping they will, once again, be able to help.

In Search of a 3mm Allen Key

In preparation for the Big Day™ (when the MMU/LMU swap-out would take place), I ran down to the local Home Depot to see if I could find a 3mm allen key (hex wrench).

The original LMUs are fastened to the frame of the solar modules with hex head bolts. Recalling how much time it took to perform the original, manual installation with an L-shaped hex wrench, I came up with a brilliant idea (if I say so myself): "I'll get a new 3mm hex wrench and cut off the end of the 'L' so that I can put it into my clutched drill and let a little electricity remove the old bolts."

I already had a very nice metric hex wrench set (a gift from my oldest son) but I didn't want to ruin the set by destroying one of its members. So it was off to the old Home Depot. Unfortunately, I could only find hex wrenches in sets (I miss the old hardware store where one could get just what one needed!) — and it wasn't worth running all over town in the vain hope of finding a single hex wrench of the desired size — so now I have two sets of metric hex wrenches.

But at least I have my drill all ready to go and I can look forward to a rapid disassembly of the modules.

There was no reason to delay enabling the new Tigo MMU and gateway so I temporarily placed the new MMU in our laundry room (which has a convenient ethernet connection), temporarily installed the gateway looking out the laundry room window towards the module array, connected the MMU to the ethernet, powered things up, and insured that there was an Internet connection.

Of course, I didn't not expect the panels to report anything yet because the LMUs had not yet been replaced.