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  1. #21
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    Default Re: Grid-tied solar

    Quote Originally Posted by dave1949 View Post
    ...
    The "derate" factor (top area of chart I posted) of .77, is the efficiency loss within the system, beginning with the power actually produced by the pv panels. For every watt generated, .77 watts comes out the other end. I did not attempt to refine the default derate factor of .77 in my modeling--beyond my paygrade .
    ...
    .77 is better than .60 but but that is still a 33% loss of energy from panel to outlet. This is a hidden cost, at least it was hidden to me until I read of the power loss, since if one wants/needs 5,000 watts at the outlet they need almost 7,000 watts on the roof. That is a big price increase that is not readily apparent. If the installed cost is $5 per watt then one has to spend $35,000, not $25,000, to get the 5,000 watts at the outlets.

    At least the cost of PV is dropping. Finally.

    Later,
    Dan

  2. #22
    Super Member dave1949's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by dmccarty View Post
    .77 is better than .60 but but that is still a 33% loss of energy from panel to outlet. This is a hidden cost, at least it was hidden to me until I read of the power loss, since if one wants/needs 5,000 watts at the outlet they need almost 7,000 watts on the roof. That is a big price increase that is not readily apparent. If the installed cost is $5 per watt then one has to spend $35,000, not $25,000, to get the 5,000 watts at the outlets.

    At least the cost of PV is dropping. Finally.
    Later,
    Dan
    I don't know how accurate the default derating is, but there will be losses in the wiring and the inverter for sure. The derating may include array losses due to temperature deviation from some normal test condition, like 72 deg. As the array gets hotter, its efficiency drops. I also don't know if they include a factor in the derating that represents the ~1 percent per year drop in array output just because the silicon is aging.

    My panels are guaranteed to produce no less than 80 percent of their rated output after 20 years. It's a pro-rated thing like a car battery or tires. Interestingly, they claim to buy insurance for this from an underwriter to cover any losses. I guess that would be really important to someone putting in a commercial scale 1 megawatt system.

    But, in general, the residential systems are sized by working backwards. How many kwh's do you need/want in a year is used to determine the capacity of the system and it is what it is. The loss of efficiency is less important than the break-even price points. We don't reject buying a car because a gas engine has only a 30 percent thermal efficiency, for example.
    "Those were the days my friend, we thought they'd never end ..."

  3. #23
    Elite Member Redneck in training's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by deezler View Post
    Good stuff! Anything realistically projecting a break-even in under 20 years is fantastic, in my opinion. Shoot, once I can afford to build my home and add solar, I would be happy with a 40 year break-even. To some folks (me), it's worth a little money to save that much carbon emission.
    If you can install it by yourself the pay back time goes down dramatically. 4.3 kW system cost $4.20/W installed. The same system DIY would cost about $2/w.
    You can buy complete kit here: Grid-Tie Systems
    Then you add your own work and get 30% subsidy from the total.
    Ladia

  4. #24
    Silver Member farmeratheart's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by dave1949 View Post
    Thanks. So far, the inverter says the system has generated 30.6 KW in 40 operating hours. I plan on recording the accumulated output on the same day each month for a year or so until I see what's what. My electric bill will have some info too regarding credits and debits to the net usage.

    In a net-metering system, you never want to generate more power than you use since most state utility regs don't require the utility to pay you for any excess. Basically, the excess credits generated in summer's long days get used up during winter's short days. My utility banks any credits for up to 1 year, then they delete the oldest credits in a FIFO method. The credits will be worth different amounts as/if rates change.

    For those thinking about solar hot water or electric, geothermal heat pumps or small wind turbines, the 30% federal tax credits for consumer energy are scheduled out to the end of 2016: Federal Tax Credits for Energy Efficiency : ENERGY STAR. It applies to existing and new construction principal residences only, not to second homes or rentals.
    Dave- I think that you will find that your best power generation days will be in March or April. The panels are much more efficient when temps are cooler. I have recorded our best single power days on the 26th of March in both of the last 2 springs. We have had 20 panels @ 200W each on our roof for the last 2 years. Here in northern Maryland electricity runs about $0.15kWh delivered (generation + distribution + administrative costs). We have made over 11000 kWh hours in 2 years (which represents ~90% of our total power usage) so the electricity alone = $1650.00. We also sold Solar Renewable Energy Credits back to our utility last year to the tune of $1200 and expect to do the same this year. With the Federal and State tax credits I expect to reach the break even pont in about 5 or 6 more years. It is also hard to put a price on the satisfaction of knowing that most of the electricity we are using comes from the sun and not from the remains of some dinosaur or prehistoric plant.

    Good luck.

    Frank

  5. #25
    Super Member dave1949's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by farmeratheart View Post
    Dave- I think that you will find that your best power generation days will be in March or April. The panels are much more efficient when temps are cooler. I have recorded our best single power days on the 26th of March in both of the last 2 springs. We have had 20 panels @ 200W each on our roof for the last 2 years. Here in northern Maryland electricity runs about $0.15kWh delivered (generation + distribution + administrative costs). We have made over 11000 kWh hours in 2 years (which represents ~90% of our total power usage) so the electricity alone = $1650.00. We also sold Solar Renewable Energy Credits back to our utility last year to the tune of $1200 and expect to do the same this year. With the Federal and State tax credits I expect to reach the break even pont in about 5 or 6 more years. It is also hard to put a price on the satisfaction of knowing that most of the electricity we are using comes from the sun and not from the remains of some dinosaur or prehistoric plant.

    Good luck.

    Frank
    Thanks. Sounds like you have a great system there, if I do half that well, I'll be very happy. I've never checked on selling renewable energy credits or heard about doing that on residential systems here.

    I know RE credits are key to Maine wind farms and some our paper mills that self-generate from wood waste. I believe they are more less auctioned/sold within the ISO New England grid using day ahead pricing.

    I try to limit my personal fossil fuel use, so that is certainly part of my motivation. One perspective of solar system rebates and credits is it doesn't matter whose roof the panels are on, they clean the air equally for everybody. I hope to see the day when home/small business solar systems play a role in a distributed grid design. There is a lot of inertia to overcome though.
    "Those were the days my friend, we thought they'd never end ..."

  6. #26
    Veteran Member buckeyefarmer's Avatar
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    Default Re: Grid-tied solar

    My electric in northern MD is $.10 KWH. Thats total bill / total KHW. Has anyone on here bought a DMSOLAR system? I've been looking at them for awhile.

    The problem is as more and more people install grid tie system, there is less and less incentive for a utility company to be there just to be your battery.
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  7. #27
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    Default Re: Grid-tied solar

    Just to chime in on what Frank said and give Dave some encouragement. All indications from revision energy, and several of their customers that I spoke to independently who have been up and running a couple of years, is that the payback on systems in Maine is around 10 years. Dave you will see your production ramp up shortly due to the angle of your panels and the cost of your plumbing and heater don't count. I also see payback time as only part of the equation, the amount of good that you are doing is something to feel really good about.

  8. #28
    Super Member dave1949's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by buckeyefarmer View Post
    My electric in northern MD is $.10 KWH. Thats total bill / total KHW. Has anyone on here bought a DMSOLAR system? I've been looking at them for awhile.

    The problem is as more and more people install grid tie system, there is less and less incentive for a utility company to be there just to be your battery.
    Sorry, don't know anything about DM Solar, there web site looks like they offer good prices.

    Good point about the utility becoming everyone's battery. It might change their peak use patterns from day to night and from summer to winter too. Alternate energy does take some re-thinking.

    I've done some reading on commercial-scale wind and how grids might deal with "non-dispatchable" power as they call it. There is a lot of financial pressure for Maine to be the renewable energy credit supplier to New England, and lots of fights about turbines on hill tops, noise, etc.

    There is a recognized lack of accuracy in forecasting wind resources on an hourly basis, and grid operators think 20% of demand is about the reasonable percentage that is manageable and compatible with current traditional generation within the grid. I see it as an engineering challenge that will be improved upon and refined over time.

    Wide-spread solar faces some of the same challenges if it were to be counted on as a significant contributor to overall daytime grid demand. There would be a need for accurate insolation forecasting over a wide area, probably have to hire some math whizzes to model all that.

    Add in smart appliances that can schedule their usage intelligently based on time of day, current weather, what other uses are occurring and when will they end, prioritizing use, etc., and it becomes an interesting problem.

    The last time I did a rough calculation of it, an all electric car recharged from solar pv gets the dollar equivalent of about 50 mpg if gasoline costs $3.50/gal. assuming 1000 miles per month driving. If those cars could be usefully charged during daylight hours, their batteries make the perfect local solar pv storage place, converting excess electricity to transportation miles.

    I see a lot of energy changes and challenges in the next 20-30 years.
    "Those were the days my friend, we thought they'd never end ..."

  9. #29
    Super Member dave1949's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by Redneck in training View Post
    If you can install it by yourself the pay back time goes down dramatically. 4.3 kW system cost $4.20/W installed. The same system DIY would cost about $2/w.
    You can buy complete kit here: Grid-Tie Systems
    Then you add your own work and get 30% subsidy from the total.
    One caveat, Maine requires a certified solar installer/service provider to sign the state rebate claim form. Not sure what other states with rebates require.
    "Those were the days my friend, we thought they'd never end ..."

  10. #30
    Super Member dave1949's Avatar
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    Default Re: Grid-tied solar

    Quote Originally Posted by JCByrd24 View Post
    Just to chime in on what Frank said and give Dave some encouragement. All indications from revision energy, and several of their customers that I spoke to independently who have been up and running a couple of years, is that the payback on systems in Maine is around 10 years. Dave you will see your production ramp up shortly due to the angle of your panels and the cost of your plumbing and heater don't count. I also see payback time as only part of the equation, the amount of good that you are doing is something to feel really good about.
    Thanks. I understand the payback for electric is being inflated by my plumbing changes. I am looking at the payback period for my total project as the most meaningful number to my check book

    Revision Energy impressed me from start to finish. Friendly, smart, hard working folks.
    "Those were the days my friend, we thought they'd never end ..."

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