EEVblog #724 – Home Solar Power System Analysis & Update

Dave looks at his 3kW home solar power system after being in operation for 18 months and analyses the results.
How much energy was produced?
How does net and gross metering work?
What is the payback period?
What is solar insolation?
The 3kW system uses 12 x 250W LG MonoX panels
and an SMA Sunnyboy 3000TL inverter.
Uploading data to using PVbeancounter and bluetooth from the Sunnyboy inverter. data HERE

Forum HERE

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  1. I don’t get all the rumbling about how poorly you are paid – 6 cent/kwh it probably still a subsidized price (nice word for: stealing from your neighbours) for energy that you deliver more or less at random.

    You are still using the grid – and hence you pay for it. Energy producers with control over delivery (e.g. power plants) do not get paid more.

    • I know, he must have said it 50 times. Why would the retailer pay him anything more than the wholesale cost of energy, which is about 8c/kWh? If you grow potatoes in your garden, you can’t sell them to the supermarket for the retail price. The best they’ll give you is the wholesale price. I’m a bit shocked that Dave doesn’t understand this. The higher feed in tariffs were just designed to kick start the solar industry by reducing the payback time for what was a pretty expensive and unproven technology 10 years ago. The fact that some Oz state governments didn’t reduce the FiT before was because they didn’t want to be seen to spoil the party. As for Dave hoping that the FiT will go back up; dream on. I wouldn’t mind, but he’s just made a video entitled “Free energy BULLSHIT”. Maybe he should watch the video “Free money BULLSHIT”.
      But, back to the issue in hand; how can Dave get more value from the energy he harvests? Well, he could swap out his gas boiler for an electric one and use his excess PV to make hot water. In this case he’ll be using the boiler as an energy battery, which will still stay warm overnight.

      • He should get paid less then an conventional power plant – his energy is of lower value, since it is not controllable. Depending on the market, the power plants usually have contracts to deliver base load, peak load or grid stabilization.

        With a solar installation you can deliver neither of these with any level of reliability.

        Using it for hot water would like not work out – I don’t know the price of gas there – but it should be around 5 cents/kwh.

        If someone would use a power source with the economical and physical properties of solar panel in a circuit he probably would rightfully get the giant rant from Daves – but solar seemingly being a personal hobby of him, obviously clouds his judgement.

        At least AFTER figuring in the revenue of the videos he makes of about the installation, it should be economical investment for him. 😉

        • It’s true that he’s in a fortuitous position of being able to dump as much excess power into the grid as he wants; maybe there should be a consideration for the retailer for this. But getting the average wholesale price would seem about fair. Getting the retail price would be stupendously generous, yet that seems to be what he expects.
          Using the excess for hot water is viable. We don’t know if he’s on mains gas or bottled. And since he pays a “green premium” on his bill and is considering buying an electric car, he’s clearly thinking of the planet. So using electric rather than gas might appeal to him due to reduced CO2 emission.

          • Average wholesale price is a hard concept – energy is either traded on an exchange on a e.g. quarter hour basis or bound to specific contracts (baseload, peak, network stabilization, etc.). Getting the exchange rate would be a worse deal, especially if there are many solar installations in a country, since prices will be low whether the sun comes out. May be a better deal, if there aren’t and there is much need to A/C.

            It is viable as a calling or as a hobby, but not economically. I don’t know the price he pays, but it shouldn’t be more then 4-6 cents per kwh- so selling the energy for 6 is more economical.

            Paying the green premium is just stupid – this will work out to one of the following scenarios:

            -If there is not much competition, the seller will simply partition up the existing generating capacity among it’s customers along it’s preferences – and assign the green sources to customers paying a preemium he will pocket as additional profits

            -If competition is tight, the seller will also partition the existing supply – but now use the additional revenue he pockets from Dave to lower the average price (and hence cut out the competition) – now Dave will subsidize the users on the non-green tarifs

            There would have to be a very large number of users on green tarifs to make a difference – this is unlikely to happen (especially amoung large scale industrial users). As long as this doesn’t happen, this is just a ripoff.

  2. Hey, i also don’t get why you should get the same price for buying/selling yor energy. But actualy i want to ask you, why you don’t use some sort of battery-pack? if it would cost you another 5000$ but it would enable you to use all the power you generate, woulndn’t that make sense?

  3. You know, you should turn on the A/C and use up some of that power while it’s the hottest time of the day (perfect use of solar) then turn it off at night when you’re using the grid.

    And many governments are struggling with how to handle distributed solar – Germany and California now require “smart inverters” that can be commanded to help stabilize the grid more than supply power to it. So the grid will NOT purchase all the electricity you generate – it will throttle the amount so to stabilize it. Should a sudden load come online (causing a frequency dip), the inverters will be commanded to supply more power to the grid to bring the voltage and frequency back up. Likewise, if there’s too much supply, the inverters will be commanded to reduce their output to keep the grid stable.

    Grid stability is actually the major challenge with distributed generation – which is why many utilities are looking into storage batteries or other mechanisms (e.g., flywheels) that can be brought online and taken offline very quickly.

    • They sure have to buy all power in Germany, especially from smaller supplieres. This has totally destroyed the energy market to the point that the former deregulated market is now a very regulated mess, since now everybody -the renewable, the old plants and the grid – need to be subsidized to be viable. And since Germany is connected to the grids of other european contries, their markets get disturbed too – when heavily subsidized german green energy is dumped there for free.

  4. I’d been thinking about setting up a solar system, but I’d want to have the batteries and use them for most of the power. Export power only when the batteries are completely charged, and hopefully configure it to drain down to 50-60% capacity before going back on the grid again. (So there’s a bit of buffer always for power outages.)

    More interesting would be a smart meter that communicated with the power company and knew how much money it could get for selling to the grid on quickly updated basis, so that it could sell power when the value per kwh exceeded a certain amount, and charge the batteries otherwise. If the meter also sold you energy at a quickly updating price, you could configure it to switch to batteries when the price goes too high.

    • First of all, you would have to have high electricity prices and a high self-consumption, since the biggest savings come from the difference from the price you pay in comparision to the wholesale price. Since a big part of the prices is taxes and the fixed costs of the energy grid – this would primarily be an arbitrage deal to the disadvantage to all other users/tax payers.

      You would need big batteries (expensive) batteries for that and they wouldn’t last too long if you charge/discharge them daily – so it is very questionable whether this would ever be economical.

      Even in Daves case it is not clear, that the whole enterprise is economical. Since he is not factoring in inflation (a dollar on the day you but the system is not of the same value you are getting e.g. after 5 or 10 years), capital costs, maintenance (yes – there was none until today, but on average there sure will be) and insuring against the additional risks (system catching fire, tree destroing 3 panels, that have to be replaced, fireman getting electrocuted when extingushing fire, etc.).

      • That’s why I was saying not to do a full discharge, as that’s the biggest thing that kills the batteries. If you’re not fully discharging them, they can last for years.

        It’s really not that economical to even do solar where I live, with the price ranging from 10 to 15 cents per kwh. I just want to do it so that I have a whole-house UPS, and so I could go off the grid if I really wanted to. (If Xcel Energy annoyed me enough.) It’s more of a fun experiment/toy than a real cost savings. (Pretty much just like that CNG car I wanted to buy.)

        Luckily, I have no trees within range of my roof.

        • Sure, you can’t say anything negative about it if you drop the assumption it is an economic enterprise and doing it just for the fun of it. 🙂

      • Tyler, you seem to keep emphasizing taxes. From what I can quickly access, my electric utility seems to be paying something like 300-400 million in taxes on almost 14 billion in revenues. That doesn’t sound like “a big part of the prices”. Are you basing your opposition to solar on real numeric analysis or political beliefs?

        There’s a good point that supporting peak capacity incurs infrastructure costs. Currently that cost is amortized over (average or cumulative, not peak) usage. A case could be made to assess each residential or commercial electricity user some monthly fee based on their peak usage, in addition to a now lowered set of usage rates. Note however that we haven’t mentioned solar in this paragraph – the question of how best to allocate peak capacity costs long predates solar buildout, and extends beyond it. If solar becomes a major portion of generating capacity, some of this might need to be rethought. But it’s really not impacting the bottom line enough to worry about yet – and may be more than offset by the differential between incoming and outgoing rates for solar homes.

        But utility company taxes appear to be a very small part of this picture. Sure, if a power company has to have 10 substations rather than 9, it may pay more property taxes – which is folded into the rates along with other fixed costs, being a small thing compared to the cost of building and operating that infrastructure.

        (And of course any taxes that are proportioned to usage would go DOWN as people conserve electricity and/or generate some of their own.)

        So here’s the thought experiment. Suppose household A reduces their average electrical usage by 30% (tho perhaps not their peak). Notice that we are not saying HOW they do so. Perhaps they install more efficient appliances and lights; perhaps they reduce how often they use the air conditioner or get rid of a backyard pool; perhaps they install solar to cover some of their usage; perhaps they turn off unused equipment better; perhaps their kids went off to college; perhaps some combination. The Question: are they inherently harming their neighbors by using an average 30% less electricity than they used to? Are they “beggaring their neighbors” by reducing their usage and thereby pushing more of the fixed costs onto neighbors? Is this morally suspect?

        If the answer is “they are beggaring their neighbors ONLY if their method of reducing usage include using solar”, then we have a political or ideological issue only masquerading as as a technical or fairness problem.

        • I wasn’t primarily revering to corporate taxes (but the would also be a factor) but usage based ones. 30-40% of my electricity bill are usages based taxes and fees. Since Dave is paying 24 cent/kwh (which is quite high) I assume that this contains some direct taxes. I also mentioned that this depends upon local circumstances and I said that they should simply pay the same amount for self generated power.

          Reducing your usage it in the long/medium term not a “beggar thy neighouhr” tactic – since it is indeed reducing peak demand and diminishes needed capital investment for generation and grid – replacing equipment with more efficient one brings a net benefit to the national economy. You are getting the same output with less input – this generates economic wealth. It does generate a equity problem regarding taxation, but only if the saving can or will only be realized by a subset of society. This will most likely not hold true for LEDs, efficient ACs or more efficient fridges. For solar this will still hold true – at least because you have to own a house and not be a renter and have to be able to provide the needed capital (there are more reasons).

          Savings everybody gets from lower consumptions resulting in lower direct taxes are not real savings – taxes will simply be raised.

  5. The “problem” with the lousy charge for the extra kWh is also common here in Switzerland. In the past when home installed solar power systems was rare, the power companies paid a lot more than today, so they made some calculus and at the bottom of the line….we get it right up in the….how do you say, “posteriors”?

    There are some interesting concepts to store the extra generated energy. Not only with batteries. Fuel cells produces some hydrogen out of electricity, the hydrogen is then stored in some gas bottles. To produce electricity go the way back.
    It`s a question of the efficiency and price as usual.

    • It is (or was) sure nice if your neighbor is mandated by law to pay for your hobby. 😉
      But is hard to see private solar installations ever becoming viable without subsidies in one form or another. Most calculations -including Daves- because they are shifting costs that still have to be paid, like taxes, grid and backup power onto other parties. They are a “Beggar thy neighbour” models and not not work for the country as a whole. The grid costs and taxes that Dave does not pay by substituting grid power for solar power – will no be borne by someone poorer who has to rent an apartment an thereby can not install a solar panel, because these costs are mostly fixed costs.

      • It`s obvious that if something develops in certain way there are changes to make. And at the end it makes sense that the change is like it is. I`m sure if I`m an electrical power company I will go that way too, finally we want to earn some money in a more or less fair way. The question is: How fair?

        So energy storage systems to get complete independent from the grid, where possible of course, is fascinating me for a long time and I think it`s not a bad option.

        • Sure, being energy independent is fair in regards of the grid costs, if you are really not connected at all (you can supply yourself even if there are two months without sunshine and do not add to the needed peak capacity for grid and generation). It is still not fair in regards to taxes (except if there are not or only minimal taxes).

          So fair would be:
          -To be really not connected or pay a fair share for grid & peak generation capacity
          -To pay the same tax rate for bought and self produced power

          This of course would in almost all cases make private PV installations uneconomical – the same way it is uneconomical as growing your own food in the garden – you can not reap the benefits of scale.

          Even if it is fair and economical as a single project, it may still not be beneficial in regards to the economy as a whole – because there must likely still be a grid after all (street lighting, larger consumers, etc.).

      • Tyler – for every KWh that the utility does not have to supply, it saves at least the cost of the fuel. If power usage is growing, it may also save on the cost of new power plants and distribution infrastructure due to slower growth. I’m not aware of taxes that still have to be paid on unused fuel, postponed infrastructure, or uncollected revenues; for the most part, corporate taxes are very low anyway in the country in which I live.

        Of course, the generating and distribution capacity have to be sized for peak need, so there is some fixed cost to be allocated. There’s rarely any single “correct” way to distribute fixed costs – raise the rates, have a base charge per home, whatever. Solar is not unique in this regard. Every time you turn off a light, use an LED light, or get a more efficient refrigerator that means that you are paying for less of the fixed charges in your usage rate – and yet we feel no obligation to waste more electricity just so as to avoid pushing more fixed charges onto higher usage neighbors. So that seems (on first glance) like a conceptually suspect framing, more like a political talking point against solar than an analysis.

        If conservation and solar wind up eventually becoming a high percentage of total power generation, it would not be surprising if the rates wind up needing some adjusting to cover some “shared infrastructure”. In particular, the utility winds up serving a function not entirely unlike an external battery – takes in your excess, supplies your deficits. That function requires financial support – currently handled by feed-in rates which subsidise the utilities. That might not be the best way in the long run. But for not, feeding power back at the bargain rate of 6c/KWH – at the usage end of the transmission lines (ie: less transmission loss from a remote power station), is SUBSIDING either the power company, or the neighbors.

        So on first pass I don’t really see the “beggar thy neighbor” argument as very strong. However, perhaps you can present some solid analysis with real measured numbers (power, energy and costs) which would be more convincing. I’m an engineer not a politician, and I’m open to the facts leading either way. But for now, the “beggar thy neighbor” point seems murky and possibly more political than objective.

        • The fuel logic it problematic and whether it holds true depends upon the make up of generating capacity. It is definitely not true that at least the fuels cost is always saved. Not all generating capacity can be shut down quickly and it may be that you have to sell your power below the cost of the fuel alone.

          Yes the power is inserted near the point of possible use, but this may not translate into savings. The distribution network is almost 100% fixed cost – the needed investment determined by the expected peak load.So the grid needs to be sized and financed for the case that solar is not available (exception: Very high A/C needs in warm climates where solar production always is coupled to high A/C usage).

          I don’t know numbers for Australia but electricity use in Europe is stagnating and only growing slowly in the US. Also: The above argument still holds true.

          I can of course not do a full analysis for this discussion – but to get a rough handle: You can compare energy prices in Germany with an expansive green energy program and France with a centralized nuclear program. In Germany you pay more than double the end user price compared in France.

          To get a rough overview for market prices, you can take a look at:

          The main underlying problem is an engineering problem: Solar is simply a power source that has very disadvantageous properties (at least for most climates):

          -It does not produce energy during the whole day
          -even during the day is may be intermittent or not produce at all
          -there is limited control over output
          -you can only forecast output over a short period of time

          These are properties you don’t want to have in a power source – and these have to be made up with considerable cost savings to be really viable – and these are simply not there.

          • @tyler – It’s true that solar has many systematic disadvantages as a power source, as does wind. They can potentially reduce conventional fuel cost, but you have to duplicate 100% of their capacity with conventional sources, if your society requires near 100% availability without brownouts and blackouts (unless we found a feasible massive storage solution).

            But I don’t see this as a “beggar they neighbor” situation any more than other forms of use reduction (through behavior or efficiency). If Dave reduces his usage with solar, that’s no different than reducing his usage by other means, from the system viewpoint.

            I’ve reluctantly come to see 4th generation nuclear, like IFR, as the only potential white knight in the energy puzzle – unless LENR really does pan out after all. Fukushima unfortunately poisoned that well, in terms of public support – people tend to paint all nuclear with the same brush, so the worst examples of very old technology will likely torpedo the newer tech we need (to retire some of the older nuclear reactors among other things!). Unfortunately, despite the attractions of solar, we still need a low carbon power source with long term supplies which can also be powered up and down on demand, unlike solar and wind (hydro and geothermal have the right dynamics, but are not scale-able enough for our needs).

            • It’s strange that something that ended up not really causing that much of a problem directly ended up “poisoning the well” because of the government and media overreaction to it.

              • Alas, I don’t think Fukushima was “not that much of a problem”. That would seem to overly minimize the many real impacts. And one of the casualties is trust – many people trusted that TEPCO was competent in protecting the public interest, and/or that the government was maintaining adequate supervision and setting and enforcing appropriate standards. Those proved not to be the case. That erosion of trust has greatly harmed public acceptance, and not entirely unreasonably so. To blame “government and media” overreaction is to seriously mis-allocate responsibility. Government and corporate under-reaction was more the root of the problem (the after-study says the disaster was entirely predictable and preventable) – don’t shoot the messenger instead.

                And that’s unfortunate. It’s hard to sell people on new generation nuclear already – they don’t understand the technology or the implications of new designs. And thus there’s some need to “trust the experts in industry and government” – exactly what people are even less willing to do now. TEPCO (and the lap-dog Japanese regulators) really blew it, and thus poisoned the well for other nuclear technologies (and other corporations and governments). Unfortunately, rather than a response of “move to newer and safer nuclear with solid government oversight”, too may just say “avoid nuclear entirely, period”.

  6. Hey Dave, you could use more of your solar energy if you go back to making videos in the garage like the good old days 🙂

    I’m from Manchester UK, and our rainy weather give insolation figures way below sunny Oz.. our 3Kw system has taken 3 years to generate about the same as yours.. Wouldn’t be without the free electric though 🙂

  7. It doesn’t matter where you are or when you bought solar, it is all about pay back period. I am in UK, bought in 2010 and a bit more in 2012 and my pay back will be about 10yrs. That includes a generous government feed in tariff. To get the tariff, you had to have a qualified installer so no DIY. The installations were double the price when I had mine installed, but so was the feed in tariff. The tariff shot down but so did the costs. A few people installed at just the right time and managed to get a really good deal. Oh, as an aside, I used to have an old meter that went backwards when exporting (my system has no individual export meter) – but my electricity company replaced that pretty sharpish.

  8. Do you have problems with hail there? I’m in Colorado, (USA). We’ve had two roofs (one wood shake and one asphalt shingle) at least partly destroyed by hail in five years, and I’m wondering if your panels have had to stand up to that.

  9. So how do you REALLY feel about getting only $0.06/KWh for the feedin tariff? 🙂

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