Grid-tied solar

[dmccarty]

...
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

 

[dave1949]

.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.

 

[Redneck in training]

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.

 

[farmeratheart]

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

 

[dave1949]

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.

 

[buckeyefarmer]

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.

 

[JCByrd24]

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.

 

[dave1949]

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.

 

[dave1949]

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.

 

[dave1949]

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 :laughing:

Revision Energy impressed me from start to finish. Friendly, smart, hard working folks.

 

[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.