Wednesday, July 10, 2013

Simplifying Solar Power

One of the big problems that I have with solar power is that installation is typically half or more of the cost of a photovoltaic system -- turning what might be a temptation into a "this doesn't make sense" situation.  Worse, if you want to just experiment, by putting in a couple of 200 watt panels to see how much you are getting, those installation costs make it absurdly expensive.

There are several companies that are producing what are intended to be DIY (do-it-yourself, or disaster-is-yours, depending on your competence) solar systems.  Westinghouse, for example, has this panel with an integrated mounting system and inverter, as well as simplified connectors.

What is pretty interesting, however, is how some companies are producing plug-and-play products, like this Goal Zero 1250 watt-hour solar generator over at Lowe's.  It is a combination of two 30 watt solar panels with inverter and deep discharge battery.  This isn't intended as a primary solar power system, but as an alternative to a backup generator.  The two 30 watt panels are supposed to fully charge the battery in 20-22 hours, or you can recharge from the grid in 16-20 hours.  When fully charged, it gives you 1250 watt-hours -- which for short-term emergencies is probably sufficient.  They also claim that you can add more panels to reduce charge time, or add more deep discharge batteries to increase capacity.  And it is all portable.  For $1799, this doesn't seem like a bad product idea.

The Westinghouse Instant Connect 235W panel is available for about $860 on eBay (including tax and shipping).  That's not a particularly impressive price if you are only looking at the dollars per watt, but it does include the inverter, and I guess that you could just plug it into a wall socket.  I believe that our backup generator already has a grid disconnect built-in, so something like this would be a plug-and-play device.  This wouldn't run our power meter backward without net metering equipment installed, but in the heights of summer, when our electric utility bills are high to pay for air conditioning, this would make a lot of sense.

UPDATE: Reading the DIY installer instructions for the Westinghouse give me pause.  They are still written for an electrician.

A reader points out that he suspects air conditioning costs are a big chunk of the average household's electricity use.  I suspect that he is right, at least in summer.

There is an amusing synergy here: air conditioning is a big cost in areas where solar energy is most available and reliable.  When solar energy is not so available, air conditioning costs drop nearly to zero.  In addition, electric utilities charge higher electricity costs above some threshold level, so even in places where solar power as a source for all your electric power might not make economic sense, solar power might make sense for getting your electric consumption down below that threshold.

UPDATE 2: An email from Westinghouse Solar indicates that the pricing will be back on the website shortly, and at about $600 per 250 watt panel.  This isn't really a bad price, considering the panel has its own AC inverter.  This is cheap enough that it should call my electrician and find out what he would charge to do the connection to the breaker panel.

UPDATE 3: I was just paying my electric bill this evening.  My consumption last month was 680 KwH, or about 22 KwH per day.  At the peak of last summer, we were consuming 41 KwH per day; in the depths of winter, about 29 KwH per day (with spring and fall generally less).  A nominal 4 Kw system operating 12 hours a day (pretty typical around here at the height of summer) would produce enough power to satisfy all of our needs.  In winter, we might average 4 hours a day, or a bit less than half of our needs.  Spring and fall would produce about 25-28 KwH per day, a bit more than we need.  Of course, that would mean 16 $600 panels, or $9600.  With the 30% federal tax credit, and the fairly minor state tax deduction, that means a net cost of about $6500.  I would expect to see our annual electricity bill fall from about $700 a year to perhaps $150 a year.  That would mean about an 11 year payoff at current electricity rates -- and a bit less with the likely rise in electricity prices.

Time to call my electrician, and find out what he will charge me to hook this up.  I could start with two panels, and perhaps add two panels a month once the fall semester starts.


  1. I'm assuming that A/C is one of the biggest current draws in many households. Evidence:
    1) The summer power bill,
    2) If you have A/C for your RV, you need a big fat electrical cord with a special plug, to plug in at the RV park.

    I wouldn't know from personal experience. 10 years or so ago I installed an evaporative "swamp cooler" on the roof of our abode. The only electrical cost is the blower motor and a tiny water pump. (A solar array might actually run that - I'm thinkin' it wouldn't even come close to running your central air.) From what I understand, it's MUCH cheaper to operate, and quite effective in our hot but arid climate. We've been quite happy with it. Yeah, we're not enjoying 68 degrees inside... but it keeps the indoor temperature 20+ degrees cooler than outside.

  2. Clayton,
    The only way solar power for a home makes any sense is IF the tax incentives make it so, it will not pay off all by itself.

    We use a solar power system on our travel trailer, and it covers our needs almost entirely IF we don't use the computer. Anyone who is considering solar power for an RV or home should educate himself a bit. Here's a good start that I wrote several years ago:

    Do the arithmetic (not rocket surgery math) and you'll see exactly what I mean.

  3. There's no question that the tax incentives encourage solar power where a free market might not, and it is a good argument against those incentives.

    However: there are some advantages to solar power, such as having an energy source that is not dependent on the rest of our civilization continuing to operate -- and I have decreasing confidence that it will do so.

    While the tax incentives are bad policy, if it reduces the costs to the point where you individually benefit from it, even if the society as a whole is injured by it, it is difficult to resist.

    Everytime I do the math, I find that the payoff on solar as a complete replacement takes 11 to 20 years (even with the tax incentives). But including the intangible benefit of greater independence from a society that is dying is attractive.

  4. Here in Austin Texas, we certainly have high demand for summer A/C, and a recently passed power rate bump in the summer just hit.

    But, all the locals say that it's a matter of when, not if, your roof will be damaged by hail. For example, all the houses on our street have roofs replaced after a 2009 hailstorm. That's what gives me a big pause on considering solar for now. If I could be reasonably confident that a solar panel would survive a roof-shredding hailstorm, it might make a bit more sense.

  5. I have used this company for both parts and support with good results.

  6. Seems like an integrated approach would produce the greatest benefit: more insulation in walls and ceiling to reduce the heating/cooling load; smaller, higher efficiency heating/cooling equipment; roof construction to make PV and solar hot water installations easier; pre-wiring and pre-plumbing for PV and SHW systems. While there's no such thing as an inexpensive PV or SHW system, all these benefit from inclusion at the pre-construction planning stage; one of the cost adders to PV and SHW is the hassles associated with retrofit.

  7. When I had the house built in 2005, I went well beyond code on insulation in walls, ceiling, and under the floor.

    Fortunately, I won't need to mount the PV panels on the roof; I have 11 acres, and the hillside behind the house is completely unobstructed (unless my neighbor builds a seven story building!)

  8. If you just want to play around and see what you can do at the low end (which the interest in the GoalZero product suggests, with its low wattage), Harbor Freight has some very decently priced stuff.

    $150 or so for 3x15W panels with a charge controller makes for a very low cost barrier.

    I've thought real hard about making something go from that for camping purposes - I already have one of the little 7W GoalZero folding units, but wouldn't mind a more powerful setup.

  9. I'd say your payoff time is about the same or slightly longer than your crude estimate.

    First, solar panels lose 1% efficiency per year even if properly maintained, and the typical household value is higher than that since they usually aren't well maintained. That's probably faster than your electric rates are going up, although the War on Coal might change that.

    Secondly, those power estimates are peak power and only valid for a short time during the day unless you install tracking devices and the like. In a typical fixed installation you're lucky to get a daylight-averaged 70% of that number. You can do about 75% of that number if you're willing to go out and adjust the tilt angle of the array quarterly.

    And thirdly, you've got the made-in-China aspect of the majority of these panels. There have been a series of scandals where the deterioration of the panels has exceeded 5%/year, where the wattage levels haven't been as high as claimed, durability is terrible, fires, etc. Even if your warranty covers replacement of the panel, it won't typically cover installation and that's a big part of the expense of the system.

    I'm not trying to dissuade you from trying solar, just noting some concerns you should take into account when you're selecting suppliers and calculating rates of return. I'm in a reasonably good area for solar but I'm still not convinced that the probability of an acceptable ROI is high enough to justify the investment -- and being an electrical engineer my installation cost is probably much lower than yours (although why they think that a guy who views "high voltage" as 1.5V should be legally allowed to wire a house is beyond me).

  10. Oh, and I should mention that when doing your calculations you're in the 4.9 hours of full sun equivalent per day (3.3 in winter, 5.8 in summer) area of the country and should plan accordingly.

  11. My plan was to adjust angles quarterly. The full sun equivalent is a concern, but I have spent some time experimenting with aluminum reflectors to increase input during the morning and late afternoon hours. I spent a bit of time experimenting with trackers as well a couple of years ago, and I might use one or two panels for experiments. My small scale experiments with tracking and reflectors allowed me to get full output from a small PV panel from five minutes after sunrise to sunset. I am pretty confident that I can get quite a bit more than the passive hours of full sun just with passive reflectors alone.

  12. One of the attractions of the Westinghouse Solar product is that Westinghouse won't be going out of business in the next several years. Many of the smaller companies in this business... hard to say.

    What sort of maintenance do you need to do to a PV panel? Clean the dirt off of it?

  13. I should mention that at least part of what makes these integrated units attractive is that I should be able to start with a small investment of perhaps two panels, and see what sort of power I actually get.

  14. Maintenance is "just cleaning the dirt off it". The panels are covered with tempered glass and are extremely resistant to hail damage. Degradation over time is minimal; our 2 panels still seem to put out the same current as initially, and they're now 12 years old. And, they were "seconds" in the first place.

    I always figured on 4 hours of full, rated output and another 4 hours of about half output, assuming that they're aimed correctly. This seems pretty valid, after watching the meters for a while. My first installation included an analog meter in the panels' feed and it was very interesting to watch. The slightest cloud caused a dramatic drop in output.

  15. The clouds are pretty amazing. My experiments a couple of years ago very much impressed me. Remember that full overcast is about 1% of the light of a clear day. You don't notice it because your irises dilate to get more light, but the reduction is very substantial. I did find that with an adjustable reflector, I could keep a PV panel running at full output even when a very dense cloud went across the Sun.

    It was unfortunate that I could not find a way to raise any money; I have a method for getting effectively full power from sunrise to sunset, and full power until you get dark clouds, or close to it, across the Sun. Unfortunately, much of the green energy business model is built on dishonesty and political corruption.