Our Solar Electric Panels: Done!

Thank you for those stats, it pretty much mirrors my 7.5 kW system. Yesterday was nice and sunny up here in the Crescenta Valley, and the system put out 16 kWh's. Due to the ridgeline of the Verdugo Hills, my solar cutoff is about 3 pm, and since Winter Solstice just happened, it will head uphill until it peaks on Summer Solstice at approx 45 - 50 kWh's per day. I really love this system!

 

:rockon:I am a little farther south and a little farther east. My 5.1 kW system will generate 25-26 during a sunny December day, and as low as 4 during a big storm (like today and tomorrow!).

I will peak out in May at around 37. The June heat will retard the system and lower the peak to 34-35.

 

My little 400 watt off grid system (which by nature suffers a huge efficiency hit because it is battery based) on a really nice winter day will yield ~ 1.5 kwh. This is pretty hard to quantify, since we are drawing power for loads while we charge, so the only way to "gauge" input is the net between solar in and power draw out. If I didn't draw any loads, it might push 2 kwh.

Interestingly, it puts out more in the short northern winter because the orientation is better suited for winter harvest, and the combination of cold PV and reflection off snow and ice increase the yield. In the summer, the sun is so high in the sky, my effective solar day is actually much shorter in the summer. The side bar to that is, that my draw is much less, as the days stay light until nearly 11 PM so the lighting load is nil.

Icarus

 

Life gets more interesting in the off grid world. I chuckle at those that come looking to stick it to the utility by wishing to go off grid, thinking somehow that is going to be "free power". The fundamental equation with off grid PV is that it comes at about twice the per watt price with about half the efficiency, leading to power that is about 4 times the price of grid tied PV. (Not to mention any battery bank needs replacing every 3-10 years at about 1/2 the total system cost depending on variables).

In an ideal solar calculation people use a 53% conversion rate for off grid. I personally prefer a maximum of ~ 50%. Between basic Pv efficiency, wiring loses, charge controller loses, basic battery charging loses (it takes 120 watt/hours put back into a battery to recapture 100 watt/hours drawn, a ~20% hit right out of the box!) basic inverter loses etc. I then take that number, and multiply it by 4 to represent the AVERAGE hours of GOOD sun one might expect per day over the course of a year. Remembering that a battery based system requires either a certain built in head room for cloudy periods, and then requires charging from some outside source (generator or grid power).

So, a typical 1000 watt system might yield this" 1000/2*4=2000 wh/day. But it actually gets worse! A battery based system also loses potential harvest as the battery (ies) come closer to fully charged. As the battery comes closer to fully charged, the charge controller will dial back the current available to the battery, leading to bigger, uncalculatable loses. Unless you can design a system that allows the battery to come 100% charged just as the sun goes off the PV, this loss is inevitable.

So in the above example, that same 1kw system might only yield 1500 wh net/net instead of the 2kwh one would expect. Some of these loses can be mitigated somewhat by time shifting loads. For example, when the house batteries are near fully charged, I then pump extra water, using Pv power that might otherwise be left on the table. Or I charge lap top batteries, or power tool batteries. It is more efficient to use the power directly than it is to power from the battery and then have to recharge that battery.

So, in my case, in our off grid house, we routinely use ~ 6-800 wh/day, and our 400 watt system replaces that on most days. As I said earlier, on an ideal day we might pump out 1.5-2kwh but that would only be with a deeply discharged battery to start.

So, to anyone who is considering an off grid system as a way to cut the cord to the utility, I say this. The grid is your best friend. It allows your solar dollar to go 4 times as far, as well as having reliable power 24/7 with out worry about battery health and net solar input. If you have the grid available,,, use it!

 

icarus, I think a lot of solar installers have stopped installing the battery setups because of the reasons you listed. I inquired, and the battery cost, reliability were the main reasons they said not to do it. Not to mention, I still use 50% of my power annually from the grid as it is.

I get roughly 5000 kwh production annually from my 5.2 kw system. I have spreadsheets from a monitoring program I use with my setup of production almost since 30 days after installation. I don't keep a computer running 24/7 to monitor it anymore, just do an update of the numbers whenever I'm on my desktop computer. It's connected w/ an RS232 at the inverter using Cat5 cable to another RS232 connector to a USB adapter at my computer. I only needed 3 wires for the hookup, but all I had around was Cat5 so I figured I'd put it to use. The program was recording every 15 seconds and at one time, I had a screen capture of the image uploading to my website every 5 minutes. After a few months, I decided it was a waste of power to keep that up and running!

 

I've attached my December spreadsheet. Here are the highlights for those who do not have access to MS Excel:

- 686.5 kWh production in the month or 22.15 kWh daily average
- Highest daily production of 28.73 kWh on Dec. 1
- Lowest daily production of 3.55 kWh on Dec. 30
- Peak DC watt production of 5,007 W at the inverter (compared to rated panel output of 5.4 kW) on Dec. 15, during the 15 min window starting 11 AM

 

Only 6 months after I was promised my installation, I finally have my 3KW system up and running. Sorry, no photos available - need to climb onto the next door neighbours roof to take a photo of my roof, and that is a little too dangerous for me.

The system was fully installed a little over a month ago, and I have just got my first bill for electricity. The period for the billing was 44 days. As part of the installation, I also got time of day billing (this was going to happen this year regardless of anything I did, but for me the new meter installation forced the issue).

We have three time bands - 2pm to 8pm - peak power, 7am to 2pm and 8pm to 10pm - shoulder, and the rest off-peak. Weekends and public holidays are 7am to 10pm - shoulder, and the rest off-peak. Peak power is charged at 36.6c per kWh, dropping down to 13.6c for shoulder and 8c for off-peak.

The totals - my family used 525kWh in the 44 days, while we generated 398kWh. The really nice thing, for me, is that I got in under a state government program that was promoting solar power, and they pay me 66c per kWh, regardless of time. This will only last for 6 years, and then it all converts to a net supply agreement, but where I will be paid the rate applicable for the time of day. As my panels are on the western side of the house, most of my power is generated during the peak period, so I still will maximise on the return from the panels.

One thing I will be checking over the next year was the fact that I actually generated a whole 0.3kWh in the off-peak time zone. As the installation was done in autumn, and we are heading into winter, I am surprised that we generated anything in this period. The sun is only just up at 6:30am at present. Probably will not see any more off-peak generation until next summer.

 

Nice! $.66 is a nice fet. Ontario was offering $.8 for a while but I think they have stopped it. If you get $.66 for 6 year, beat peak time rates most of the time when you buy, you are going to win big time!

Icarus

 

Just finished adding another 3KWh of panels, video here: [ame=http://www.youtube.com/watch?v=t1mbvx-ODKY]YouTube - 100 0077[/ame] , along with this install, added an extra sub-panel in garage with 220V box for future EV, and increased my buss-bar size at meter to 225A. Now probably over 10KWh of panel power, plus the small contribution (<400KWh last year) of the wind turbine.

http://smilingdogsranch.com/priusblog/wp-content/uploads/2010/01/power31.jpg

So:

44 200W panels in ground array
16 235W panels on roof
SkyStream 3.7 wind turbine

Prius with 10KWh conversion (PlugInSupply)

Figure I will probably be gone before all this pays itself off, but hey, its about more than dollars.

 

Time to resurrect this thread and provide an update after one year of the PV panels being in service (photos of my system were provided earlier in this thread: posts 97, 99, 105.)

- Household kWh consumption from Oct 2010 to Sep 2011: 10,440.3 kWh
- PV system production: 10,723.3 kWh, which I value at $1,212 (Tucson Electric charges $0.113 per kWh, net of taxes.)
- Maximum daily production: May 2, 2011. 37.46 kWh
- Maximum peak production: February 3, 2011. 5,339.38 DC watts produced on average, during the 11:30 AM 15-minute window. Note that the run from the panels to the inverter is ~100 feet, so resistance losses play some role here.
- System: 24 225W Schott panels, 5.4 kW DC power rating. SMA inverter, Sunny WebBox for continuous monitoring.

BTW, Tucson Electric paid me at the rate of $0.03 per kWh when my kWh "bank" was cashed in. This is nothing to write home about. That low rate is why I wanted to install a system whose production would be consumed without difficulty. No point in producing excess kWh given that low price.

I project financial payback in 6.5 years assuming no change in electricity rates. Tax-free, this is better than most other investments I've made. Nice to benefit from "other peoples' money" (consisting of federal and AZ state income tax credits, and the Tucson Electric rebate.)

 

Patrick, you get roughly double the production I do over the course of a year. Mine have been up for 3 yrs and a couple weeks, and I'm between 17k-18k kwh lifetime.

That's roughly 50% of my usage annually, depending upon how much I use my heatpump in the colder months. I've never had a bank of excess production, of course. My electric usage did increase this past summer, probably from moving the A/C to 75 from 76 last year. Could also be the water heater as it's now almost 5.5 yrs old and probably lost some efficiency. I really need to do a drain on it to flush out any settled matter in it.

Do you get to sell RECs out there, too? If so, how have the prices for them held up? We've lost about 60% of the value out here, if not more, over the last year or two. Delmarva Power is buying large amounts from the big projects that have gone online, thus screwing over us small owners in the process.

 

Hill,

Have you received a refund check (like Patrick did) this year? We got our notice in March that we qualified, and a couple of notices (the last in August?) saying the rate hadn't been approved yet.

Congrats Patrick!

 

Wick,

If you can produce PV power as well as you do, heating hot water with PV is ,, how can I say this nicely,, silly. Solar hot water comes at less than 1/2 he cost and well over double the efficiency of PV solar on a per BTU basis. Solar hot water, either a simple loop system, or evacuated tubes perform way better in partly cloudy and or partially shaded locations. You might look seriously into adopting a solar hot water system. Also consider a demand gas (either natural or lp) for hot water. Tank type electric is just about the least efficient way to heat water,, especially if you are in a location where you need A/C, since the stand by loses net/net heat up the living space, and then add to the A/C load.

If you do have large A/C loads, consider also hot water heat recovery A/C units. There is a double benefit. The first is it gives you "free" hot water and the second is it allows your A/C to run more efficiently,, therefore using less energy.

Icarus

 

No, I believe that Tucson Electric benefits from that since they contributed substantially via rebate to the system acquisition.

Hi Hill:

$7,230 was the PV system net cost after rebate and tax credits. Each month I pay $7.65 to be connected to the grid. Hence, assuming my annual production experience can be extrapolated into the future:

$1,212 value of production - (12 mo. x $7.65 monthly fee) = $1,120 net annual value.

$7,230 net cost / $1,120 annual value = 6.45 years

If I didn't own the PV system then I would have to generate ~$1,700 of pre-tax income annually, to net $1,212 of after-tax income used to pay my electric utility bill. Although this may be of interest, it is not clear that this fact is relevant to the payback computation.

To the extent that electric rates rise, then of course the payback period will be correspondingly reduced. However, I am assuming flat rates for ease of computation.

My dad is currently driving a Nissan Leaf. He wants me to buy it after the three-year lease is up. If I should do that, then that would become another consumer of my kWh production. (My garage already has a 240 VAC outlet.)

 

I've seen so many people speak against electric water heaters in combination with PV Solar.

I have to assume they always mean pure resistant heating electric water heaters.

I'm using a unit like this Electric Water heaters, Electric Hot Water Heater | GE Appliances though I don't remember "geospring" in the name in 2009.

It uses 1/3 the energy of a resistant water heater and I get the side benefit of free air conditioning/dehumidifying in the garage which is below the bedrooms. So it reduces my AC bill to some small amount.

Maybe thermal solar is more efficient than my water heater with it's own indoor heat pump but enough to make it worthwhile to install the thermal solar?

I would like to add solar PV at some point but I live in a part of the country where electricity is cheap and the incentives are less for PV.

My thought was to work on reducing the load so I could do with a smaller PV setup and save money on the bills until I go that route.

Do you really think electric water heaters are that bad or are you just used to saying "electric" when you are thinking "resistant"?

Oh, and fwiw I ripped the natural gas heat system out of the house and went fully electric. I had them take the gas meter off my property. I'll never use gas here; not for home heating, water heating, nor cooking.

My annual consumption is around 12,000 kWhs a year but I expect to continue to cut into that with more efficient appliances, consumer electronics, additional changes to the house.

Since I wouldn't get much from my utility I'm dreaming about a system like this (don't know the angle of my roof but its closer to E or W choice than southern facing)

"PVWATTS v.2: AC Energy and Cost Savings"
"Cell ID:","0247384"
"State:","Tennessee"
"Lat (deg N):", 35.82
"Long (deg W):", -83.98
"DC Rating:"," 6.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.8"
"Year", 4.02 (kWh/m2/day), 6557 (kWh)

apparently my cell is 4.92 (kWh/m2/day) but my worst case assumption of a 270 degree array puts it a little worse than 15% less efficient.

 

I am only passingly familiar with the Geo-spring technology, and can't speak to it's relative efficiency. That said, resistance electric heating, of any sort be it a toaster, furnace or water heater is far and away the least efficient use of energy (for that purpose) that I know of.

The factor that I have heard of is tht it takes ~ 10 BTUs of genation and transmission energy to provide 1 BTU in the room (or toast or what or what ever). This comes with the environmental cost and carbon foot print of the generation and transmission. Now if all your electric comes from clean hydro, wind or solar that it not really an issue.

My point is tht it is much cheaper, and way more efficient to heat water directly from solar instead of using PV to do so. So in this example it would take 10 BTUs of solar to put 1 BTU into the water. At once and the same time, PV converts sunlight (under ideal test conditions) at a conversion of ~15%. Hot water on the other hand can convert upwards of 60-80% depending on technology.

So for example, one might need a 2-4 kw PV array simply to power a water heater reliably, costing $15-30,000 in today's market, while a solar hot water system, to provide the same amount of hot water weight cost $2000. It becomes a no brainier.

Personally I would not use resistance electric heat for anything if I could reasonably avoid it. I would use natural gas or propane. Especially for hot water simple pre heated hot water, demand gas is a perfect mate. Even without per heated solar, a gas demand water heater beats electric, both on the BTU conversion efficiency, but also there is no stand by lose.

I hope that is clear as mud.

Icarus

PS. I am not sure why you are so anti gas. Environmental issues aside ( and I think gas generally wins over electric, especially coal fired electricity) gas is a much more efficient fuel when it comes to heat, as stated above. Much of the fear of gas is IMHO misplaced. More people die by electrical fires than gas fires by far. Also modern safety systems from gas detectors coupled With shut off valves, seismic shut off valves, electronic controlled ignition etc makes gas very safe. Propane is marginally less safe, because of it's density, it settles, and can ( and does reliquify) and design considerations need to be made.