Grid-tied solar

[dmccarty]

...

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.

I know how many KWH's we use each month over a period of years. So one could easily assume that I get at least eight hours of sunlight year round and if I put 5,000 watts on the roof I would get 40KWH a day. That would be wrong. VERY wrong. In fact I will only get 19KWH or so. If I want 40KWH a day, we would need over 10,000 watts on the roof. The difference in dollars between a 5K and 10K system is a bit huge.

I really only get five hours of usable light per day and those 5,000 watts are really 3850 watts at the outlet. With a bit of digging one will find out about the usable number of hours issues, the amount of the loss of power from roof to outlet was a big surprise to me. That loss is expensive because you have to add 30% more panels to get what is really needed. That 30% is big dollars.

My point in asking what you are seeing is because I am shocked at the power loss and the cost implication. When I first read of 30-40% power loss I was really surprised at how high it is and I was wondering if your system was seeing the same performance.

Later,
Dan

 

[dmccarty]

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.

NC is the same. Not sure about the Feds.

Later,
Dan

 

[Redneck in training]

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.

Does anyone know how hard it is to get the certification? I searched Internet and found several providers of 5 day course for about $2000. Is that enough education to be considered certified installer?

 

[dave1949]

I know how many KWH's we use each month over a period of years. So one could easily assume that I get at least eight hours of sunlight year round and if I put 5,000 watts on the roof I would get 40KWH a day. That would be wrong. VERY wrong. In fact I will only get 19KWH or so. If I want 40KWH a day, we would need over 10,000 watts on the roof. The difference in dollars between a 5K and 10K system is a bit huge.

I really only get five hours of usable light per day and those 5,000 watts are really 3850 watts at the outlet. With a bit of digging one will find out about the usable number of hours issues, the amount of the loss of power from roof to outlet was a big surprise to me. That loss is expensive because you have to add 30% more panels to get what is really needed. That 30% is big dollars.

My point in asking what you are seeing is because I am shocked at the power loss and the cost implication. When I first read of 30-40% power loss I was really surprised at how high it is and I was wondering if your system was seeing the same performance.

Later,
Dan

Sure it is. My system has a perfect conditions, zero loss output of 18 X 240 watts = 4,320 watts. So far, the highest sampled reading I've seen is 2,900 watts on a very clear sunny day.

But, I think you are looking at it from the wrong perspective. You don't lose sleep over the 70% of the heat energy contained in a gallon of gasoline your car engine wastes, do you? At $3/gal, that is $2.10 per gallon burned that just disappears, but what you are concerned with is getting from point A to point B at what you consider a reasonable cost.

Use the same logic on a solar system. Size and price out a system that delivers the annual kilowatts you need, and compare the cost to alternatives over the expected 20-year life of the solar system. That's not an easy calculation because it includes a lot changing and unknown values over a 20 year period. With a solar pv system, you are "buying" electricity at a 20-year fixed rate.

The calculation would include the cost of money (your gain if it was invested/earning interest instead of used to purchase a solar system), the predicted price of utility electricity or other energy source (elec. and propane in my case) over the next 20 years, the chance of having to make an expensive repair to the solar system, the positive or negative impact on the market value of your home should you sell it during that time, and whatever else matters to you such as putting a value on environmental benefits.

If you do all that calculating and prognosticating, you will probably find that after X number of years, you break even if you ignore the cost of money. You will likely have some number of years of useful life after the system has paid for itself to recoup some of the cost of money. That's my best guess. Consider that $20K @ 3% compounded annually for 20 years earns over $16K.

Breaking even or foregoing gain is not the normal goal of an investment - of course. You will need incentives that go beyond purely financial ones or you probably will not be satisfied. In that case, opt for the Harley

 

[dmccarty]

Sure it is. My system has a perfect conditions, zero loss output of 18 X 240 watts = 4,320 watts. So far, the highest sampled reading I've seen is 2,900 watts on a very clear sunny day.

But, I think you are looking at it from the wrong perspective. You don't lose sleep over the 70% of the heat energy contained in a gallon of gasoline your car engine wastes, do you? At $3/gal, that is $2.10 per gallon burned that just disappears, but what you are concerned with is getting from point A to point B at what you consider a reasonable cost.

Your comparison is flawed. When I buy a gallon of fuel I know it will bet me from point A to B. With solar power, buying 5,000 watts is buying roughly 30% less. If buying a gallon of gas was the same as solar I would be loosing 30% of my mileage. The solar energy loss is not obvious, and the percentage of loss, I think would surprise most people. I know it shocked me. I expected some loss but not 40%.

Use the same logic on a solar system. Size and price out a system that delivers the annual kilowatts you need, and compare the cost to alternatives over the expected 20-year life of the solar system. That's not an easy calculation because it includes a lot changing and unknown values over a 20 year period. With a solar pv system, you are "buying" electricity at a 20-year fixed rate.

The calculation would include the cost of money (your gain if it was invested/earning interest instead of used to purchase a solar system), the predicted price of utility electricity or other energy source (elec. and propane in my case) over the next 20 years, the chance of having to make an expensive repair to the solar system, the positive or negative impact on the market value of your home should you sell it during that time, and whatever else matters to you such as putting a value on environmental benefits.

If you do all that calculating and prognosticating, you will probably find that after X number of years, you break even if you ignore the cost of money. You will likely have some number of years of useful life after the system has paid for itself to recoup some of the cost of money. That's my best guess. Consider that $20K @ 3% compounded annually for 20 years earns over $16K.

Breaking even or foregoing gain is not the normal goal of an investment - of course. You will need incentives that go beyond purely financial ones or you probably will not be satisfied. In that case, opt for the Harley

I won't opt for a Harley. That truly would be a waste of my money.

I have run the calculations KNOWING the hidden loss of power and that I only have five hours a day to produce power. A 5,000 watt system on our house is only going to produce, at best 17.5 KWH at the outlets. We need 41 KWH on average per day so a 5,000 watt system is not even half of what we use. We pay 10 cents a KHW hour so that 17.5 KWH hour "saves" me $1.75 per day. To save $1.75 I would have to spend at least $25,000. The only way that is possible for me to install solar is with subsidies but we can't afford solar even with subsidies. I don't have the cash to install a system nor can I afford YEARS to get the subsidies back from the state. If the installed price ever gets to $1-2 a watt then things will be interesting.

The other solar surprise is that people think solar will provide power during an outage. It will, but only if you have batteries which are danged expensive and will be a continuing expense over the years.

Later,
Dan

 

[farmeratheart]

Interesting thread for me ...

DMCCARTY- "The solar energy loss is not obvious, and the percentage of loss, I think would surprise most people. I know it shocked me. I expected some loss but not 40%." I can tell you that in my experience the loss is not 40%, but more like 10%. We have 20 panels at 200 watts each- a 4kW system. During the middle of the day on a very sunny day the output of our system as measured at the inverter is around 3600 watts. On the cool clear days of early March or early April I have seen the output as high as 3800 watts. During the heat of this year's July the panels produced around 3400 at their peak (while air temperature at ground level was approaching 100F). If I am not consuming the elctricity being produced, every watt made "flows" back to the utility and I get credit for it against my upcoming bills. A 40% loss would imply that I would never see a number higher than 2400. I'm not trying to argue with over what you have read or been told- I'm just sharing my personal experience over the last 2+ years.

Thanks.

Frank

 

[dave1949]

Dan,

The PVWatts v2 calculator using the airport between Raleigh and Durham as a location, says a 12 KW system would produce 15,556 AC kwh annually. ~50 panels, that's a big residential system. If I plug 12 kw in for my location, the output is 14,517 AC kwh annually, in Colorado Springs, CO the output is 17,931 AC kwh annually.

I suppose your usage, almost four times mine, is driven by AC needs and having kids at home (as I recall) Up north we tend to forget about the cost of AC and focus on heating.

I still think you are hung up on "hidden" costs. Unexpected and hidden are two different things. But I can see your point, it would be roughly a $25K system producing $1,550 worth of power each year. That is 16 years to break even ignoring the cost of money and without any credits/rebates. If you can use the federal 30% credit, your eventual net cost is $17,500, or 11.3 years to break even, ignoring the cost of money. You would have 8.7 years after that worth $10K - $11K at current elec. rates and assuming a 10% drop in system output due to age. It's possible elec. rates would climb at about the same rate output would decline, offsetting each other.

Ten to twelve years is in the ballpark for residential systems after credits that I have looked at. That doesn't seem to change much across residential system sizes because they have very similar costs per watt. The upfront costs are a high hurdle, that seems to be true of most alt. energy even though the lifetime net costs are very low.

 

[zonta223]

I think what may be being missed is the cost of electrical energy. To continue to think the power can be supplied at 5cents or 11 cents a kw for the next 20 years is I think a little short sited. Already in your country in some states power costs 30kw the same price we pay here.
My electricity bill used to be about $450 before we installed solar. Present bill is about $35 to $50. Do we think its a great idea YES. Also means the pressure is off building more power stations and conserving scarce resources (no I am not a greenie fanatic but would like the lpg/natural gas to be used in my car not a power station) . The payback time on the system we have is about 4years. Plus the value of my house went up by about 150% of the price of the solar installation.
So could I suggest that people stop working out payback times on unrealistically low energy costs. The push is on world wide to cut carbon emissions. Makes no difference if you agree with global warming or not carbon taxing is coming and the biggest payers of these taxes will be power companies/cement plants/aluminum plants etc and they will certainly pass on the taxes in the way of price rises.

just my 2c worth

 

[Kyle_in_Tex]

Thanks for posting! Keep us updated on your electric bills.

 

[Travelover]

You don't need to justify your solar system. If you enjoy it, that is enough, regardless of payback time.

My toys will never achieve payback but that is my business.