Is now a good time to invest in solar?

[Artman]

Plus, since solar's peak output corresponds well with the peak grid load, the types of power plants used for for meeting the peak demand are the ones being displaced: and those are almost exclusively fossil fuel plants. So it dovetails nicely with the type of energy we most need to displace.

This is very true. I did an HVAC project for a coal fired generating station that was used specifically for peak demand loads only.

blimkie.k and mheslep, more than likely, I won't be using the new sticker technology unless they pass legislation allowing me to sell back the excess energy at retail rates. There is some question as to longevity effects of the product (collection of dirt, scratching, discoloration, etc). However, I may consider it if switching to a heat-pump for heat makes my usage rise significantly, but it shouldn't, we hope, since we are also switching to a heat-pump water heater from a resistance electric type, increasing insulation, and the cooling efficiency is higher in the new heat-pump than in my old AC unit. Right now my solar array meets my house usage and a little over.

 

[mheslep]

blimkie.k and mheslep, more than likely, I won't be using the new sticker technology unless they pass legislation allowing me to sell back the excess energy at retail rates. There is some question as to longevity effects of the product (collection of dirt, scratching, discoloration, etc).

Yes, though there may be another side to the deterioration of the the sticky film, in that in protects the underlying surface panel. As an uncoated panel surface degrades from the elements you are stuck with it. With the film, maybe you replace it every ~7 years and return to a higher power output, cost basis permitting.

 

[Artman]

Yes, though there may be another side to the deterioration of the the sticky film, in that in protects the underlying surface panel. As an uncoated panel surface degrades from the elements you are stuck with it. With the film, maybe you replace it every ~7 years and return to a higher power output, cost basis permitting.

Yeah, I thought that too. As a further layer of protection they may have some value, however, my panels are pretty tough. They are supposed to be able to withstand a 1" diameter projectile (like hail) at 40 mph. My main point is that I don't currently need it to meet my load, so the the extra cost isn't warranted. Should switching to a heat-pump push us over our electric production, it might be worth the investment.

 

[mheslep]

Yeah, I thought that too. As a further layer of protection they may have some value, however, my panels are pretty tough. They are supposed to be able to withstand a 1" diameter projectile (like hail) at 40 mph.

I'm not referring to breakage. We know that panel output degrades at something like 0.5-2% per year. Part of that may be due to a degradation of the panel surface from simple abrasion over time, I don't know, and maybe a simple polishing would remove that effect. But if not, in 15 years, if your system is down 30% from today (extreme worst case), will that still be sufficient?

 

[Artman]

I'm not referring to breakage. We know that panel output degrades at something like 0.5-2% per year. Part of that may be due to a degradation of the panel surface from simple abrasion over time, I don't know, and maybe a simple polishing would remove that effect. But if not, in 15 years, if your system is down 30% from today (extreme worst case), will that still be sufficient?

I hadn't thought about that as a possibility. I'll ask my installer what he thinks about the film.

 

[OmCheeto]

I hadn't thought about that as a possibility. I'll ask my installer what he thinks about the film.

I'd also contact the manufacturer to see if it would void your warranty. It strikes me that a film on glass would restrict heat flow. And you know how hot they get already.

And I doubt the reduction in panel efficiency over time has anything to do with the glass.

 

[mheslep]

I'd also contact the manufacturer to see if it would void your warranty. It strikes me that a film on glass would restrict heat flow. And you know how hot they get already.

Yes, if the film increases the infrared trap then maybe so. I doubt conductive heat flow is changed on the surface.

And I doubt the reduction in panel efficiency over time has anything to do with the glass.

Well we know this much:

A dust layer of 4 grams per square meter can decrease solar power conversion by 40 percent, [...] To put this in perspective, dust deposition in Arizona is about 17 grams per square meter per month[...]

I don't know how much transmission might be typically lost in the surface glass (or polymer?) over time, but obviously surface impairment matters.

http://www.scientificamerican.com/blog/post.cfm?id=self-cleaning-solar-panels-could-fi-2010-08-22

 

[mugaliens]

Its interesting reading through this, as I designed a simple 4'x8' solar water heating system for my parent's place to be connected to a radiator in the basement. It's just supplemental, tied into the central air thermostat for activation. I tilted it to our latitude less 23 degrees for maximum influx during the winter.

Total cost is less than $400, not including labor. I estimate it'll take me about 20 hours for the install, but Dad's a little hesitant. I calculate it'll save him $400 a year, and the system should last 5 to 10 years with little or no maintenance.

One question I have is whether or not it needs a pump. Obviously, an appropriately-sized pump would increase its efficiency and heat output signficantly. My question is whether there's enough thermal expansion of heated water alone to power at least basic movement of the water. It sports about 100' of black hose in the collector, which is turned sideways, so only 4' tall. Entry is at the bottom and exit at the top, the reverse of the radiator. Line runs between the collector and the radiator are approximately 50', total, with standard 1/2" PVC piping. It's insulated only on the outside, as the purpose once inside is to heat, so if it heats, it heats.

Back to the question? Do I need a pump?

 

[Mech_Engineer]

One question I have is whether or not it needs a pump. Obviously, an appropriately-sized pump would increase its efficiency and heat output signficantly. My question is whether there's enough thermal expansion of heated water alone to power at least basic movement of the water.

The only method of natural flow of the water would be through natural convection, and for that to work the heat source has to be below the radiator. Convection flow also wouldn't work very well in a piped system. Just get a small pump, they aren't THAT expensive...

 

[Artman]

If it's a closed loop you may need a few things. It should have a small expansion tank for expansion compensation, over-pressure/temperature relief valve, and freeze protection (propylene glycol or some other antifreeze), depending on possible temperatures at nights and cloudy days. These may not be required with a plastic pipe loop like you described, but you should consider them.

It may work without a pump by placing the return connection at the top of the panel and the inlet supply at the bottom, but in a closed loop I'm not sure it will help. You could try that first.

Since you describe this as supplemental, you could put in a solar powered DC pump to circulate the system only when the sun is out heating the water. That will add to the cost of the system, however it might make back enough in electric savings over non solar pump over time to pay it back, should you find a pump is necessary.

 

[OmCheeto]

Back to the question? Do I need a pump?

Yes.

I did an experiment last summer using 1/2 inch 100' long black irrigation hose and a $22 http://www.cabelas.com/link-12/product/0001519012155a.shtml?cmCat=perf&rid=0987654321&cm_mmc=Performics-_-CSE-_-GoogleBaseUSA-_-0001519012155a&mr:trackingCode=DB6184C8-958E-DF11-A0C8-002219318F67&mr:referralID=NA". The system collected ~2.3 kwh of thermal energy in about 3.5 hours.

With no pump, you are just going to heat the water in the hose.

Some numbers:
flow: 1.6 gpm (~ 24 watts pump)
area of hose: 0.27 m^2
system fluid capacity: 32 gallons
max delta T / hr: 11 'F
To = 61.7'F
Tf = 90.9'F

Eek! Late for work. BBL.

 

[OmCheeto]

...to be connected to a radiator in the basement. ...

It sports about 100' of black hose in the collector...

You also have to remember that if the system is unpressurized, the weight of the water will draw a vacuum on your black hose. It had better be a robust hose, otherwise it will collapse.

(been there, done that. Black garden hose on the roof to the rubbermaid at ground level experiment. FAIL! Hose collapsed.)

 

[mugaliens]

I'm thinking MHD is the only solution

The only method of natural flow of the water would be through natural convection, and for that to work the heat source has to be below the radiator.

(slaps forhead) For some reason I was forgetting the fact the collector is about 4' above the radiator. You're right, of course. A pump is definitely required. This brings to mind some sort of passive system, though, much like a hammer pump... heh-heh... Perhaps a waterfall pump?

Just get a small pump, they aren't THAT expensive...

I've checked with Home Depot and Lowes, but aside from sump (bilge) pumps, all I get from them are blank stares, so I went to two pool places, but their pumps are way too big and designed to be used in pump houses (they leak). I need a small, non-leaking pump.

Does anyone have any links to pumps between 0.1 gpm to 5 gpm with which they've worked, are cheap, and are long-term reliable?

Eek! Late for work. BBL.

Lol - thanks for the numbers! Between your factors on kW-hr, time, and area, I can calculate some better estimates for here, but I'd need to know some measure of your area's solar influx on a median basis, either annual, seasonal, or monthly basis (I don't need to know your area).

You also have to remember that if the system is unpressurized, the weight of the water will draw a vacuum on your black hose. It had better be a robust hose, otherwise it will collapse.

(been there, done that. Black garden hose on the roof to the rubbermaid at ground level experiment. FAIL! Hose collapsed.)

Only about 4' to 6' of head. Shouldn't collapse a heavy-duty rubber garden hose (which I'm using for the collector). Besides, most of these systems are pressurized. I won't need much. The gas/water/radiator system in my home in Germany was pressurized at about 35 psi, but the green range was something like 20 to 45 psi. The landlord said "keep it around 30." I'd increase system pressure by means of the attached faucet to 35 psi, then check it once a month. About once every eight months I'd use the faucet, and walla!

Question is - where'd missing water go?? ! I never saw any leaks... Perhaps several micro-leaks which simply evaporated before they became puddles?

Anyway, this very modern and very efficient system did have its pump in the closet, along with a drain. I never saw a drop of water which might go down the drain, but that re-raises the question of microleaks. Who's a plumbing expert, here? Are microleaks (those which leak, but evaporate before they drip or puddle) common? I know such leaks can be avoided altogether in plumbing via well-executed materials and construction techniques. I also know of certain leak-sump systems which are effectively closed, but they're not cheap. Other, more exotic systems involving ferrofluids make effective zero-breach seals, but only up to http://en.wikipedia.org/wiki/Ferrofluidic_seals" .

Is there any way I can seal this system in toto, without resorting to such exotic measures? Perhaps by enclosing the pump in a pressurized environment equaling that of the fluid pressure? Symbiotic stacks* would do, but may lead to the encroachment of fluid on the pump body, and pose serious cooling issues with most pumps, which are air-cooled.

Pump supply system pressure itself is used to provide fluid to a a simple pipe column (or same-head air pressure vessel) which maintains pump housing pressure, thereby equaling the exit pressure at the bearings. Still - how does one continue to air-cool the pump? I'm thinking one might need a second system, a cooling system for the pump housing, but then... How does one seal that?

 

[OmCheeto]

(slaps forhead) For some reason I was forgetting the fact the collector is about 4' above the radiator. You're right, of course. A pump is definitely required. This brings to mind some sort of passive system, though, much like a hammer pump... heh-heh... Perhaps a waterfall pump?



I've checked with Home Depot and Lowes, but aside from sump (bilge) pumps, all I get from them are blank stares, so I went to two pool places, but their pumps are way too big and designed to be used in pump houses (they leak). I need a small, non-leaking pump.

Does anyone have any links to pumps between 0.1 gpm to 5 gpm with which they've worked, are cheap, and are long-term reliable?



Lol - thanks for the numbers! Between your factors on kW-hr, time, and area, I can calculate some better estimates for here, but I'd need to know some measure of your area's solar influx on a median basis, either annual, seasonal, or monthly basis (I don't need to know your area).

Insolation, kWh/m²/day 1.15 1.99 3.01 4.05 4.89 5.27 5.59 5.08 3.92 2.34 1.34 1.01
January through December

Only about 4' to 6' of head. Shouldn't collapse a heavy-duty rubber garden hose (which I'm using for the collector). Besides, most of these systems are pressurized.

I've changed my mind about your hose collapsing.
My prototype had the pump at ground level.
If your system is open to atmosphere above the level of the collector hose, then it shouldn't collapse. And I can think of no good reason why your system should be pressurized, other than by the head provided by your expansion tank. And that's where I'd put my pump.

I would answer your other questions, but I'm late for work again. :grumpy:

 

[mheslep]

Insolation, kWh/m²/day 1.15 1.99 3.01 4.05 4.89 5.27 5.59 5.08 3.92 2.34 1.34 1.01
January through December

In NJ? Tilted to latitude or flat? There's a difference in result.

 

[OmCheeto]

In NJ? Tilted to latitude or flat? There's a difference in result.

Jersey? I'm an Orygoonian. You've obviously mixed me up with Artman.

And what the hell is MHD?

 

[Astronuc]

Solar Power Projects Face Potential Hurdles
http://www.nytimes.com/2010/10/29/business/energy-environment/29solar.html

BrightSource Energy has a $2 billion project in the Mojave desert in S. California. The project, Ivanpah, is the first large-scale solar thermal power plant to be built in the United States in two decades. Apparently this is one of nine projects planned for California and Arizona. However, they seem to need substantial financial support from the federal government in the form of loan guarantees, tax credits and/or subsidies.

And even then the economics is still questionable.

The competitiveness of large-scale solar thermal plants in California also depends on the cost of natural gas, the state’s dominant source of electricity. According to Mr. Bullard, gas-fueled plants can produce electricity for about 10 cents a kilowatt-hour. After including the government subsidies, solar thermal plants are expected to generate power at 13 to 17 cents a kilowatt-hour, which the industry says is close enough in price to be competitive.

. . . .
Tessera Solar, based in Houston, has received federal approval to build two solar power plants that together would generate nearly 1,400 megawatts from 54,900 large solar dishes installed on 10,000 acres of government land. The company is seeking loan guarantees to help finance more than $4.6 billion in construction costs.

. . . .

 

[mheslep]

Solar Power Projects Face Potential Hurdles
http://www.nytimes.com/2010/10/29/business/energy-environment/29solar.html

BrightSource Energy has a $2 billion project in the Mojave desert in S. California. The project, Ivanpah, is the first large-scale solar thermal power plant to be built in the United States in two decades. Apparently this is one of nine projects planned for California and Arizona. However, they seem to need substantial financial support from the federal government in the form of loan guarantees, tax credits and/or subsidies.

And even then the economics is still questionable.

I find it difficult to ever cut the government involvement away from energy projects, so that one can see at last the thing just for what it is. Yes the solar projects get subsidies, but then a major recurring cost for solar plants is property taxes - the government giveth and the government taketh away. Property taxes are less out the middle of nowhere, but that then requires expensive transmission, once again requiring negotiation with every town, country, and state government the lines pass through.

 

[knickick]

Hi Artman. I think this will help you in your question http://www.sunpowerport.com.

 

[Artman]

Time for another report. With Winter fast approaching and the days getting shorter, I've noticed a definite decline in energy production from the system. On what we would call a "Screaming Sunny Day" which is a cloudless, haze-less day our production is only about 30 (down almost 20 from Spring and Summer). It still peaks at a decent level during the height of the day about 7.5 kW to 8.0 kW out of 8.8 kW design.

The system has produced overall 10.582 MWh for around 11 months of operation (Started mid Jan) and the design was for 11.000 MWh per year. So, with 1 month still to go, I think we will finish above design levels.

SREC sales have been good at around $600 as well.

One of the big benefits that I have noticed is that we could live more comfortably without it costing us more money for energy. We ran our AC on days that were a bit too humid for comfort in the Summer where we would have maybe just used fans before, and we've been using electric space heaters now to supplement the fossil fuel heat. Our meter is still about 750 kWh below 0.

 

[mheslep]

Small digression: I wonder if the EV/PHEV makers will eventually accommodate direct DC battery charging given the proliferation of residential solar panels. Avoiding the DC/AC inversion improves efficiency, and certainly reduces capital cost if the the panels were dedicated to only DC loads so that no inverted is required.

 

[Fish4Fun]

Small digression: I wonder if the EV/PHEV makers will eventually accommodate direct DC battery charging given the proliferation of residential solar panels. Avoiding the DC/AC inversion improves efficiency, and certainly reduces capital cost if the the panels were dedicated to only DC loads so that no inverted is required.

Really it has more to do with the Solar installation & the car. If there were a "standard" battery voltage (12V, 24V, 36V, ... , 275V, 375V) then the task might be simply a matter of matching your grid tied inverter input voltage to your car's charging voltage, but you would still require a "charge controller" to regulate the current into your car's batteries, and really, an AC to DC charger is not much more or less efficient than a DC to DC charge controller.

Artman,

I find your story and this thread fascinating. I have been researching Renewable Energy for quite some time, but have never been able to make Solar PV work on paper. The Federal Tax Credit of 30% combined with my State's (NC) $10,500 Tax Credit Maximum are not quite as attractive as NJ's SRECs. NC has started a 10% Renewable Energy Tax paid by all consumers of Grid Power, and created mandates for the percentage of grid power that has to come from renewable sources, but there are as of yet, no real incentives to consumers other than what local POCOs might offer. Net Metering is available only if the POCO decides to offer it, and the State treats renewable energy savings as income! By law, only 20% of any Renewable Energy Improvements are added to the property tax assessment; however, the property tax assessment process is so subjective in my area that the State law is meaningless.

The POCO in my immediate area will grudgingly allow you to sell excess power back to the grid only @ wholesale. Wholesale prices are to be determined by them, but the excess cannot exceed your monthly bill. You of course have to pay for all of the equipment/inspections/permits etc, and there is a monthly maintenance fee for having the equipment you purchased connected to their lines.

So, for ME the "Time is Not right" for solar PV. Essentially left to stand on it's own merits, as it is here in NC, the "break even point" is ridiculous. Assuming I installed a 20kW PV array, and could average 60kW a day, and assuming I could actually use 20kW's of that power rather than sell it back to the grid, I would "save" ~$60/month (our current rate is $0.09675/kWh) off my power bill. I would also receive "credit" for the surplus ~1200kWh/month @ ~$0.04/kWh = $48, for a total "savings" of $108/month.

If I could install the 20kW array for $5/W (I don't think this can currently be done), I would have an investment of $100,000. Assuming I could get 0% 15 year money, and received $30,000 in Federal Tax Credits and Managed to get ALL of the $10,500 State Tax Credits (virtually impossible), I would have $330.56 a month loan service on the $59,500 minus my $108 "savings", for a net loss of $222.56/month, or $40,600 over the course of 15 years. 31 years after the initial 15 year period (46 years total), the system would have "paid for itself". Obviously this bleak outlook would improve if electricity prices doubled or tripled over the term.

Current pricing on solar arrays is largely a function of "sub prime" silicone wafers purchased from the semiconductor industry. With modern IC makers' emphasis on higher and higher quality wafers, the price of "sub prime" keeps falling, and with it the price of solar cells. I think this trend will continue for some time into the future unless the growing of silicone crystals makes a giant leap forward, or the demand for sub prime wafers outstrips the secondary market. If the retail price /kWh reaches ~$0.25, and the cost of solar arrays drops to ~$2/Installed Watt, Solar becomes viable w/o subsidies.

Solar PV that is economically viable w/o subsidies is what I would truly like to see, sadly it pretty much requires electricity prices to double or triple. Right now, the only Home Owner Renewable Energy that has the potential to stand on its own is Solar Heat. I can make a good case for solar collectors & storage paying for itself in 10 years or less. When we built our house we oriented it with a 72ft x 25ft roof pointing due South. I had a heat exchanger installed in the HVAC system, and I have plans to install a solar collector array and a 2000 gallon Hot Water storage tank as soon as I have an extra $10,000. The system should supply 100% of DHW (Domestic Hot Water), 100% of the heat energy for my Hot Tub and >50% of our Winter Household Heat demand.

Our baseline consumption is 2200kWh/month, an estimated 1200kWh of which goes to generating heat. @ $0.10/kWh this is $120/month. (Obviously most of the savings is in the Winter). $10,000 @ 4% for 10 years ~ $100/month, leaving me +$20/month before any tax credits. Obviously a hot tub is a "luxury item" that makes the collection of heat a bit more viable (~$50/month average) in my case, but home heating alone in many areas may well make such a system worthwhile.

You mentioned looking into a heat pump, perhaps you should consider the addition of a solar heat collection system to go along with your solar PV array. If you augmented your heat pump with the solar hot water you could save as much as 1kW/M^2 of collector area (actual savings more likely ~500W/M^2). Evacuated Tube arrays cost ~$500/M^2 + Storage Tanks + Plumbing. Assuming 500W usable heat/M^2, this places the cost of solar heat @ ~$2/Installed Watt. That's a bargain!

If you went with a "Water Source" heat pump that used the solar heated water for its source in the Winter, and a well for its source in the summer, you could really save on heat/AC. Using 65F water for AC and 80F+ water for heat would make your heat pump SUPER efficient!

Sorry for the rambling, I just really enjoyed reading through this thread, and I obviously had a lot to say... Again, congrats on your amazing story; I only wish my State were willing to pay me to put in a solar array! With the Tax Credits and other incentives available to you in NJ, I think you made a great investment! I look forward to reading your updates in the future.

Fish

 

[mheslep]

Really it has more to do with the Solar installation & the car. If there were a "standard" battery voltage (12V, 24V, 36V, ... , 275V, 375V) then the task might be simply a matter of matching your grid tied inverter input voltage to your car's charging voltage, but you would still require a "charge controller" to regulate the current into your car's batteries, and really, an AC to DC charger is not much more or less efficient than a DC to DC charge controller.

Yes I suppose the scheme I suggest only works with panels dedicated solely to vehicle charging, as there always has to be a converter in the loop somewhere, whether DC/AC or DC/DC. In the case of dedicate panels, there need be only one converter, the one that will always come with the EV. Still that would be less expensive than charging a EV from a traditional solar system like Artman's here, which would be: panels -> DC/AC inverter -> house circuit -> car AC/DC converter -> car battery.

 

[Fish4Fun]

mheslep,

At the risk of hi-jacking this thread, AND arguing with someone who has invested over 2k posts on this forum, I would like to suggest that one of the "features" of EV's like the "Tesla" is the ability to charge "anywhere there is power". I cannot think of any way designing the car to be charged directly by a solar array would improve marketability of the vehicle.

The single largest problem I see with directly charging an EV from a solar array is the loss of any energy credits associate with the array (these are typically garnered from the inverter meter). The second major problem is that unless you primarily drive at night and sleep during the day, charging your car all day is not really practical. Ignoring these points, for the sake of argument, here is some data associate with the charging of the Tesla EV:Figures for the Tesla taken from their website:

Battery Pack Specifications:

Nominal Pack Voltage: 375V
Storage Capacity: 53kWh (141 1/3 AH)
Maximum Discharge Rate: 200kW (533 1/3A)

(Taken from http://webarchive.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf )

The High Power Wall Charger Specifications are as follows:

Maximum Current: 70A
Voltage: 208-240V, Single phase
Maximum Power: 16.8 kW

(Taken from: http://www.teslamotors.com/goelectric/charging/high-power-wall-connector )

A full charge is the energy equivalent of ~ 8 liters of gasoline, in today's market we will call that about $8. The charging time of the charger @ 16.8kW input is 4 hours (67.2kWh). We must assume the charging efficiency is 53kWh/67.2kWh = 78.9% and this efficiency likely represents a 88.8% converter efficiency and a 88.8% charging efficiency. At $0.10/kWh 67.2kWh = $6.72. I do understand your desire to cut the inverter out of the charging loop, but a grid tie inverter should be pretty close to 90% efficient, this would make the overall charging efficiency 78.9% * 90% = 71%.

Assuming 20k miles per year driving and the stated 245 miles/charge ~82 "full charges" would be required (obviously most charges would be "partial", and charging would occur daily) 82 * 67.2kWh = 5.5MWh/year. @ $0.10/kWh this = ~$550. The difference between 78.9% efficiency (a theoretical DC charge Controller + Battery Losses) and 71% efficient (Grid Inverter + Charger + battery Losses) would only amount to ($550/.71) - ($550/.789) = $77.56/Year. (Actually this number is a bit high, I should have used 53kWh, but the difference is trivial).

Compared to battery life (pessimistically 6 months, optimistically 3-5 years), any energy savings associate with charging would appear completely moot. @ ~$36,000, even a 36 year life span would place the cost of the batteries at almost twice the cost of charging.

Anyway, if you would like to continue this discussion, let's open a new thread to fully explore it rather than hijacking this very excellent thread on a Solar Installation. I certainly mean no disrespect to the thread starter, nor you.

Fish

 

[mheslep]

mheslep,

At the risk of hi-jacking this thread, AND arguing with someone who has invested over 2k posts on this forum, I would like to suggest that one of the "features" of EV's like the "Tesla" is the ability to charge "anywhere there is power". I cannot think of any way designing the car to be charged directly by a solar array would improve marketability of the vehicle.

The single largest problem I see with directly charging an EV from a solar array is the loss of any energy credits associate with the array (these are typically garnered from the inverter meter).

Yes, maybe so, but that's bookkeeping of subsidies problem, not a technical problem.

The second major problem is that unless you primarily drive at night and sleep during the day, charging your car all day is not really practical. Ignoring these points, for the sake of argument, here is some data associate with the charging of the Tesla EV:Figures for the Tesla taken from their website:

Battery Pack Specifications:

Nominal Pack Voltage: 375V
Storage Capacity: 53kWh (141 1/3 AH)
Maximum Discharge Rate: 200kW (533 1/3A)

(Taken from http://webarchive.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf )

The High Power Wall Charger Specifications are as follows:

Maximum Current: 70A
Voltage: 208-240V, Single phase
Maximum Power: 16.8 kW

(Taken from: http://www.teslamotors.com/goelectric/charging/high-power-wall-connector )

A full charge is the energy equivalent of ~ 8 liters of gasoline, in today's market we will call that about $8. The charging time of the charger @ 16.8kW input is 4 hours (67.2kWh). We must assume the charging efficiency is 53kWh/67.2kWh = 78.9% and this efficiency likely represents a 88.8% converter efficiency and a 88.8% charging efficiency. At $0.10/kWh 67.2kWh = $6.72. I do understand your desire to cut the inverter out of the charging loop, but a grid tie inverter should be pretty close to 90% efficient, this would make the overall charging efficiency 78.9% * 90% = 71%.

Assuming 20k miles per year driving and the stated 245 miles/charge ~82 "full charges" would be required (obviously most charges would be "partial", and charging would occur daily) 82 * 67.2kWh = 5.5MWh/year. @ $0.10/kWh this = ~$550. The difference between 78.9% efficiency (a theoretical DC charge Controller + Battery Losses) and 71% efficient (Grid Inverter + Charger + battery Losses) would only amount to ($550/.71) - ($550/.789) = $77.56/Year. (Actually this number is a bit high, I should have used 53kWh, but the difference is trivial).

Compared to battery life (pessimistically 6 months, optimistically 3-5 years), any energy savings associate with charging would appear completely moot. @ ~$36,000, even a 36 year life span would place the cost of the batteries at almost twice the cost of charging.

Yes I grant that the efficiency savings is small. As above, my point is that the solar array to charge a DC charged EV can completely do without the capital cost of an inverter at all. There are already pilot solar arrays so dedicated - Google has solar arrays to charge pilot EVs in its parking lot. Given all EVs charge off AC power right now, that means Google must have expensed an inverter - uselessly if the EV's could also handle a DC charge.

 

[Naty1]

Artman: Great project analysis and reports...

Time for another report. With Winter fast approaching and the days getting shorter, I've noticed a definite decline in energy production from the system. On what we would call a "Screaming Sunny Day" which is a cloudless, haze-less day our production is only about 30 (down almost 20 from Spring and Summer). It still peaks at a decent level during the height of the day about 7.5 kW to 8.0 kW out of 8.8 kW design.

Is this to be expected...or does it suggest a slightly different orientation of the panels might have been better...or neither?

 

[Artman]

Artman: Great project analysis and reports...

Thanks. I'm trying to keep you guys up to date.

Is this to be expected...or does it suggest a slightly different orientation of the panels might have been better...or neither?

Yes, it was expected. Our panel angle was around 40 deg, which is close to our Latitude, making it optimized for Spring and Fall. We had a cloudy fall so we've been using our reserve kW from the meter (We've dropped from around negative 1000 to around negative 500 in two months).

I went out and checked our sunlight at off-peak hours and I noticed that the panels are getting a lot of shade from tree branches early and late in the day with the shallow angle of the sun right now. So I imagine until we get past the Solstice our ratings will just continue to drop a bit. Still, overall the system built up a nice reserve prior to heading into winter and we're hanging in there enough on production to allow us to use electric unit heaters to supplement for comfort heating.

Fish4Fun, too bad about NC programs. They don't sound very conducive to putting in a system.

The single largest problem I see with directly charging an EV from a solar array is the loss of any energy credits associate with the array (these are typically garnered from the inverter meter).

This is not the case with us. We are under 10 kW at which point our production is estimated. We also have a commercial meter as part of the system in addition to the inverter so a reading can be taken of that if the Authorities change their method of accounting.

 

[Naty1]

Fish4:

(our current rate is $0.09675/kWh)

You sure that's the total cost about 10 cents per KWH, not just "distribution" or "supply" ?

When I looked at homes in New Bern, almost 2 yrs ago, I found the local electric rates were like NJ...about 18 cents per KWH...

 

[gmax137]

Oddly, just as I was reading the previous post, my wife handed me our current electric bill. Here in Connecticut, it's 13 cents for generation and 7 cents for distribution.

 

[mheslep]

Oddly, just as I was reading the previous post, my wife handed me our current electric bill. Here in Connecticut, it's 13 cents for generation and 7 cents for distribution.

Yep. What is going on up there? Virginia rates in cents/kwh are residential:10.6, commercial:7.5. and industrial:6.6. Connecticut's industrial rate is 2.15X higher than Va. How can Connecticut expect to have any kind of job base with power that expensive? I suppose having that new http://www.elp.com/index/display/article-display/3421342111/articles/electric-light-power/generation/natural-gas/2010/02/Deadly_explosion_hits_Connecticut_gas_fired_power_plant_.html" back in Feb. didn't help.

http://www.eia.doe.gov/electricity/epm/table5_6_a.html

Edit: more curious. Since 2000 Virginia's power company Dominion Power http://www.eia.doe.gov/cneaf/nuclear/state_profiles/connecticut/ct.html"

 

[gmax137]

...I suppose having that new http://www.elp.com/index/display/article-display/3421342111/articles/electric-light-power/generation/natural-gas/2010/02/Deadly_explosion_hits_Connecticut_gas_fired_power_plant_.html" back in Feb. didn't help.

Well, the rates were high before that, I'm pretty sure they've been high for years.

http://www.eia.doe.gov/electricity/epm/table5_6_a.html

Thanks, that's an interesting table. I'd like to know more about the reasons behind the variation from state to state, but that should be another thread.

 

[mheslep]

Interesting: this source shows New Jersey as the top ranked state for residential solar investment.
http://solarpowerrocks.com/reports/spr-report-card-2010-part-2-state-by-state-summary-grades/

 

[mheslep]

Price of solar continues to fall sharply. PV silicon panels per Watt, not corrected for inflation.
http://www.solarbuzz.com/Photos/moduleprices11-1.jpg

Year: $price, (% from prior yr)
Jan 2011: 3.38 (-13.7%)
Jan 2010: 3.92 (-15.6%)
Jan 2009: 4.65 (-2.3%)
Jan 2008: 4.76

 

[russ_watters]

"Continues to fall sharply" seems a little misleading to me. It looks to me like from that graph it went up for about 3 years in the mid-2000s. While I'm sure there is a general downward trend, it probably also reflects economic conditions, so I'd be shocked if the last two to three years of sharp downward trend continued.

 

[mheslep]

"Continues to fall sharply" seems a little misleading to me. It looks to me like from that graph it went up for about 3 years in the mid-2000s. While I'm sure there is a general downward trend, it probably also reflects economic conditions, so I'd be shocked if the last two to three years of sharp downward trend continued.

Maybe. But then looking at the full ten year period I'd be surprised if the -37% per decade declining trend didn't continue (5.4-3.4)/5.4. Also those prices are not corrected for inflation. So the 2001 price in http://data.bls.gov/cgi-bin/cpicalc.pl?cost1=5.4&year1=2000&year2=2010", giving a 50% per decade trend in real terms.