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Wow you did take it personally!!!!
Unfortunately I don't have time for a responsible reply - got fencing to do. However, due to the importance of the topic I will take the time this evening.
David
quote:
Originally posted by TheYogi
Hi David,
Thank you for your reply.
Just as you have a pet peeve, I do too. As a PV system designer, I absolutely cringe any time I hear someone say what you have. And I quote:
quote:
Wanna guess the almost universal lament we hear? "Our system was sized too small, we need more panels"...
quote:
Except for rainy season, we produce quite adequate power.
If I install a system and someone utters those words, that's like me selling someone a truck to pull their boat but not telling them it won't have the power to pull the boat uphill. And the thing is, those words are being uttered on GOOD insolation years. What happens when we have a bad one? The system I design will be fine. The system most installers design will be sucking tanker loads of gas to power the generator. I feel generators should only be used for surges, not as a tow truck for the truck that can't pull the boat over the hill.
As for the 3rd world off-grid living, most people don't have the budget necessary to maintain the lifestyle they're used to. As I don't want to hear them utter the words I quoted above, my job as a PV installer is to help them determine if there is a lifestyle change and PV budget that can they can accept.
As for battery banks, my post stated golf cart batteries. There's no way you'd want 48 of them. You'd definitely jump up to L16's (as stated in my post) which is what I'm guessing you have.
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One of the best thoughtful discussions about power generation in this 2.5 world I've read. Mahalo to all contributors.
Fifteen years ago, in April, I came from the Santa Cruz CA area to Fern Acres, my daughter had married a local boy and they were expecting a baby. They were also living with his mother, who powered her home with car batteries. She had given them 1-acre as a wedding present. My daughter had love and stars in her eyes, and shortly after, a 10-lb. son, delivered at a neighbor's house, because the neighbor had electricity in the house they were renting.
I bought them a very quiet, expensive, Honda Generator that I purchased in Santa Cruz and shipped to Hilo. It was less expensive for me to rent a pickup, purchase the generator, drive to Oakland to ship the generator than to purchase the same model generator in Hilo. That was a lesson.
That experience, numerous visits before I moved to HPP, prior experience as a technical editor for a consortium of electric generating utilities reminded me daily, to never take power for granted. Who/what is the major power generator? How are they regulated? What is the major source of the power being provided now? Does that make sense to me? How do I live? How do I want to live? How much passive solar can I incorporate in my house? What are necessities for ME? What do I plain not need in my life. Are the trade-offs worth it?
My single biggest mistake was expecting a responsive county/state government. Oh, and a relatively smart one, who advocated for their constituents.
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quote:
Originally posted by David M
Wow you did take it personally!!!!
Unfortunately I don't have time for a responsible reply - got fencing to do. However, due to the importance of the topic I will take the time this evening.
David
Hi David,
No I didn't  I can understand how tone might have been misinterpreted, however. I attempted to show that I appreciate this discourse by thanking you for your reply, but sometimes that isn't enough since voice inflection can't be heard. I'm enjoying this discussion and learning a lot. For example, I need to be clearer about the fact I am very conservative with my numbers, why that is, and that functional systems can be had for less if you're willing to run the generator.
Point being, thank you and I'm all smiles
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Glad to hear you didn't take it personally TY. As you state, sometimes easy to miss the right tone.
One could wonder why I'm about to make such extensive posting. Two basic reasons - 1: The OP, Chris, as well as others interested, deserves good answers to his question to help him make informed decisions; 2: I think TheYogi could become a good resource here on PW.
As for some expansion of earlier comments:
quote:
"Wanna guess the almost universal lament we hear? "Our system was sized too small, we need more panels"...
Two of the systems the comments were from the 2nd owners, newly moved mainlanders. The originals were happy with the systems, but I suspect the new owners had different requirements.
In a 3rd case, the original system may or may not have been adequate for the original owner, 2-3 kw, 12 volt PV and wind, but was woefully inadequate for the new owners with 3 school kids. As the original owner built and sold 2 properties with systems that were immediately upgraded - this case 11Kw 48 volt PV with multiple battery banks, I suspect a small system was budgeted to increase the profits which he used to buy an island in Panama.
In a 4th case, I suspect the owners may not have communicated their true usage to the installer - this is my guess when visiting the house shortly after they moved in and remarking to Sophie, "Wow, I can't believe they expect to power all this off there system.
In a 5th case, I suspect the installer may have undersized the system to get the sale based on price - I do know the owner has added panels, replaced his battery bank and is trying to ferret out other unresolved issues. Note that all these cases used different installers.
A 6th system, same installer as me, the owner is quite happy and knowingly traded off another array against the probability of running his generator 20 hours per year (yep, just 20) and has told me if he well had to, he could reduce his usage and not use a generator if forced.
Kinda like your boat towing analogy. Rephrased from my perspective:
You live in Florida and go to the truck dealer to buy your tow truck. Lots of HI-FL comparisons posted elsewhere.
Salesman, knows his vehicles and sells you one based on your requirements, but mindful of your budget, doesn't oversell either.
You mention your potential move to Hawaii and ask if vehicle is appropriate.
Salesman fondly recalls his honeymoon in Hawaii and assures you all is OK.
Of course, salesman did his honeymoon in Waikiki and you know you're moving to Big Island, just not exactly where.
Over the next year, you proudly haul your boat around FL, happier still with your tow vehicle.
You also find your piece of paradise, way up Mauka, you decide you prefer the cooler aspect of that elevation.
One day, you're chatting with your neighbor about your upcoming move. Of course, he's a PWebber.
You discover not only is his boat comparable to yours, but he has the same tow vehicle. As you smile at your good fortune, your PW neighbor asks if you also have the special towing/transmission gizmo and special braking whatamacallit. Of course, you don't - not needed in FL.
Sooooo. Did the salesman mess up? Nope, he sold you a vehicle based on your needs, needs as YOU and he saw them. Neither you nor he were aware of the local needs for living mauka on BI - but your PW neighbor did.
OK, need to get back to the nitty gritty. I'm going to break this up into several posts.
Enjoy
David
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Let me attempt to design my system based on the theory you (TY) presented for Chris.
Chris needs 7820 watts per day, I need 15000watts per day.
System 1 - Simple ratio:
7820 watts (7819.5 actual) is to 9.240kw as 15000watts is to X - X=17723.78 or 17.724 kw.
System #2 - Calculated using your format. I'll do mine in red:
Ok, let's take the 7819.5 watt hours and round it up to 7820. Let's say you go with a 48 volt nominal system rather than 24.
7820 / 48 = 162.9 amp hours per day
Ok, let's take the 15000 watt hours.
15000 / 48 = 312.5 amp hours per day
I'm going to multiply that by 1.2 to account for batter losses, wiring losses, and add a safety factor. These numbers can be calculated much more intricately, but I'm not going to do that and 1.2 is a safe number.
162.9 x 1.2 = 195.5 amp hours
312.5 x 1.2 = 375 amp hours
Here is Hilo, Hawaii the worst insolation (daily sun hours) if you're using the wrong inclination, etc according to nrel.gov ( http://rredc.nrel.gov/solar/old_data/nsr...state.html) is 2.9 hours per day. We'll use that number to build in additional safety.
We divide 195.5 by 2.9 which equals 67.4 which is your total PV array current in amps.
We divide 375 by 2.9 which equals 129.31 which is your total PV array current in amps.
Now we'd have to choose a solar panel. As an example, I'll use a Sharp NE-165U1 which is 165 watts and is rated at 4.77 amps.
That means we take our 67.4 amp PV array from above and divide it by 4.77 which equals 14.1 or 14 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 14 panels and we find out that we need 56 total panels. Not cheap.
That means we take our 129.31 amp PV array from above and divide it by 4.77 which equals 27.11 or 27 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 27 panels and we find out that we need 108 total panels.
If we multiply our 108 panels by the 165 watt output we get 17820 watts or essentially the same number we derived via ratio above.
I'm not sure the above array calculation is correct. Not familiar with these panels, but I wonder if they are perhaps 24 volt panels, not 12, meaning an array is 2 not 4, therefore cutting panel requirement in half to 54 versus 108.
Let's look at battery sizing. We determined our daily amp hours was 195.5. Standard reserve time (how many days of juice your battery bank has) is 3. You can go higher or lower but we'll use 3. So 195.5 x 3 = 586. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 586 by .5 and get 1173 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1173 divided by 225 = 5.2 which we round up to 6 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 8 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 48 golf cart batteries. That means we'd likely go up to L16's which are more expensive but live longer IF you take good care of them.
Daily amp hours was 312.5. Standard reserve time is 3. So 312.5 x 3 = 937.5. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 937.5 by .5 and get 1875 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1875 divided by 225 = 8.33 which we round up to 9 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 9 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 54 golf cart batteries. That means we'd be checking 54 times 3 or 162 cells every month.
THIS is why if you're going to be off grid, cutting down on your energy consumption is first and foremost. You need to ditch the guzzlers and get that 7820 watt hour number WAY DOWN.
How much is this going to cost you? I did a QUICK search and a 12kw (you're almost 8kw) system on ebay WITHOUT BATTERIES and a ton of other needed equipment is selling for $41,000: http://cgi.ebay.com/solar-panel-off-grid...RCH:US:101 and that includes 72 solar panels.
Based on the $/kw costs of my system, this theoretical system would cost only $182K. A show stopper for me.
As I questioned earlier "Why would someone build a 9.2 kw system to generate 7820 watts (7.82 kw) on a daily basis?" Now I ask, why would I build a 17.82kw system for my 15kw requirement?
Quote from TY: "As for battery banks, my post stated golf cart batteries. There's no way you'd want 48 of them. You'd definitely jump up to L16's (as stated in my post) which is what I'm guessing you have."
I have to ask - why even use them for an example? If you could get them at $75 each, that's $3600. And no, I do not have L16's
David
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OK, let's look at your response to my comment below:
quote:
Except for rainy season, we produce quite adequate power.
Quote from TY:"If I install a system and someone utters those words, that's like me selling someone a truck to pull their boat but not telling them it won't have the power to pull the boat uphill. And the thing is, those words are being uttered on GOOD insolation years. What happens when we have a bad one? The system I design will be fine. The system most installers design will be sucking tanker loads of gas to power the generator. I feel generators should only be used for surges, not as a tow truck for the truck that can't pull the boat over the hill."
OK, I honestly had hopes my system would NOT require a backup generator. In fact, I ran it most of the 1st year without one, but I was building and not living there - no lights, no water system, no power needs after dark at all - so not a fair test of the system. But I did come to realize I would need back up, especially once the pool was brought on line.
So let's examine so real data and build me a system that would would need a generator for surge only, not make up for rainy season lack of sun. No doubt, the system designed in previous post would be adequate.
Using my systems actual data, my worse 4 days this rainy season are:
3/5 - 5.2kw
3/6 - 8.3kw
3/7 - 2.3kw
3/8 - 3.8kw
That's an average of 4.9kw per day. Definitely bring my battery bank below 50%.
My requirement is still 15kw per day.
On these days, I only produced 32.7% of my requirement, averaging only 1.09 hours isolation.
So using my current 4.5 kw system as reference, I can figure that those days I produced 1.09 kw per kw of PV. Needing to produce 15kw would require 13.78 kw of panels. My panels are 125watt, therefore 13.78 divided by .125 = 110.2 panels. My arrays are 4 panels each, so 110.204 divided by 4 + 27.55, rounded to 28. 28 arrays of 4 = 112 panels @ 125watts each = 14kw system. 14Kw X 1.09 isolation = 15.26kw production.
Based on the $/kw cost of my current system, this upgraded system would cost me: $143K. Of course, this does NOT include the supporting roof structure I'd need to support it. Obviously, this is a solution only for the well heeled - not me.
So how did I survive with my theoretically inadequate system? My generator. As previously stated, I've run my diesel generator approx 250 hours the last 22 months. For ease of figuring, let's call it 125 hours per year. If it costs me $4 per hour to run my generator, that would be $500 per year - not exactly sucking tanker loads. So to balance this out, I can spend $90K immediately to avoid the genset. To be quite honest, at my present age of 62, even if my generator cost were to double to $1k per yr, I doubt I'll live long enough to break even. I also suspect my wife, son, and granddaughter would prefer we spend $500-$1000 per year rather than drain an immediate $90K out of our retirement and their inheritance.
Bottomline - I don't like the genset, but economically, it's a reasonable tradeoff.
Sidenote: I did another analysis - Windpower vs Genset. Only $20k for a viable wind generator with no guarantee of output. Again, that's 20 plus years of diesel and known output.
OK, break time
David
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Back again
Previously, we looked at designing a system based on meeting our stated requirement for daily power - 7820watts for Chris, 15kw for me.
The reality of the situation is the systems will produce more power than the requirement. For example, my current 4.5kw system produced an average of 21.11 kw per day the last week of May. That's 4.69 per kw of panel. That's 140% of my daily requirement.
So how would that translate to the above theoretical systems. 83.6kw produced on the 17.82 system - 557% of requirement.
The no-genset 14kw system would have produced 65.68 kw or 438% of requirement. Basically wasted - can't store it in my current battery bank and adding additional battery banks would add an expense without a benefit. Even if on Helco, couldn't sell them that much!!!!!!
Actually, I don't waste my overage - currently, it's free power to power the pool pump - but that's another story
Anyway. I just hope I've given some insight as to why it's important on this forum to temper theory with local experience.
Any questions? Enjoy [} ]
David
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Long post ahead. I haven't been following this thread too closely and get a bit lost in the many calculations. I'll try to contribute our experiences and some numbers. We are entirely off grid. Our original 24 volt system, installed in March, 2005, consisted of 12 165 watt panels (1980 watts total, 4.77 amp each), Morningstar pulse-width modulation charge controller, racked dual 2000w Outback inverters and 12 Deka L-16 batteries. After discovering that our insolation at the 1000' foot level (a cloud forming level) was not great (far too frequent low battery readings) we finally decided to invest in four more panels, 160w this time (total 2620 watts) and another charge controller to handle the amperage of the panels. Not that we knew what we were doing exactly, but that seemed like the right thing to do.
My data consists of the daily amp-hour throughput to the batteries and house as registered by the charge controllers recorded at 5-6AM in the morning along with a "low point" battery reading after the night's battery consumption (mostly by the refrigerator). The low point reading seemed to me to be a good indicator of the battery charge status. After fairly complete records for 2006 and some of 2007 I got tired of the daily recording and only did some occasional monitoring. Probably not the wisest course of action as it turned out.
Looking back at those records, our direct power consumption (measured on a used power company-style electric meter) mostly varied between 3.7 to 4.5 kw per day with a few dips and spikes, depending on whether we watered in the greenhouse (1 hp pump) that day, did laundry, how much TV, were in town all day, etc. We had a "legacy" 27 cu ft refrigerator from our on grid days that pulled about 1.6 kw per day. The amp-hour consumption range is a little hard to characterize but on any at least moderately sunny day it easily exceeded 250 a-h with many days over 300 a-h with one or two peaks of over 400 a-h. During the winter months we still pulled over 200 a-h most days, but there were also gray days of in the range of less than 50 to 90 a-h. A 3.7 to 4.5 kw consumption with a loss fudge factor of 1.2 gives about 4400 to 5400 watts required. At a nominal 24 volts that wattage will require about 185-225 a-h. The low point readings (after the extra panels were installed) were typically in the 24.3-24.8 v range in the winter months (say December through March) and 24.8-25.1 v rest of the time. While we worried about the refrigerator load things seemed to be pretty stable. We typically used the generator after one or two very gray days or if I saw that the batteries were consistently in the low 24 volt range in the morning.
Late last year I started noticing that the low point battery reading was staying low no matter how sunny the day before had been. We had been keeping the battery water level topped up so we were rather surprised and resumed taking daily readings. Finally the inverter's low battery monitor started shutting the system down in the middle of the night, probably around 22 volts. At less than four years old we were rather shocked at the early demise of the batteries. We are still not sure why this happened with speculation that, in spite of generally good power production by the panels, our load level simply caused too great a discharge level in the batteries overnight. Also, we noticed that even on great sunny days the charge controllers often did not reach the modulation point for the dozen batteries. With pulse-width modulation the controller maintains a certain voltage, around 30 volts for the L-16's, dialing back the amperage consumption (the pulse width) as the battery "fills" with more charge. We never saw a "float" condition which represents fully charged batteries, probably because we are nearly always consuming at least some current. We had to bite the financial bullet and purchased eight new L-16's (plug for the Pahoa battery store in the Pahoa Marketplace - they had the best L-16 prices we found) plus we also dug for a new refrigerator. Propane at $15 to fill a five gallon tank was not appealing with a large solar array in the yard and the propane refrigerators are quite on the small side. The new refrigerator (purchased at Sears with the maintenance agreement) consumes only 0.7 kw per day. Currently our power consumption is averaging about 3.2 kw/day with a range of 2.7 to 3.7 kw/day. A big improvement that is probably due almost entirely to the refrigerator replacement as we also are probably consuming a bit more with an upgraded satellite system and using the Mr. Coffee machine for the first time in years. The low point battery reading is consistent at 24.9 v with occasional ranging from 24.8 to 25.1 volts, very similar to the original system.
An interesting point is that now the amp-hour consumption has decreased significantly. From typical 250-300 a-h on sunny days we are only rarely seeing much over 230 a-h. In addition we reach a very high modulation point on a regular basis, meaning that the charge controller has dialed back the amperage to very little, indicating the smaller number of batteries are very well charged. This made me realize that a major day to day factor in amp hour consumption is feeding the batteries after their night time discharge as well as the day time load. So, in our view, in determining the number of batteries, night time consumption probably should be considered more than powering through gray days. Our experience is that most moderate to severely gray days are either marginal or will not meet our consumption needs or maintain battery charge. Rather than having a large array of batteries to power through the gray days (and which the panels may not fully charge on many days) judicious use of the generator (commonly 1-1.5 hours in the evening, don't let the batteries stay low overnight) we feel is a better bet to maintaining charge through the severe cloudy periods. Restoring the night time consumption and gaining a very high level of charge nearly every day, for us anyway, seems to be the critical parameters in avoiding another big bill for batteries. The rest of the system should be reasonably expected to live for 15-20 years. The batteries are the real weak point and must be coddled.
With our current variety of appliances and other electrical consumers, we are confident we can run our house and facilities nearly any day on sun power alone. This is another whole topic. Unless you can go for a really big system, forget resistance heating like electric water heaters, electric grills (Mr. Coffee is OK only if you turn it off as soon as the coffee is done!), air conditioners and leaving the computer on overnight. All electronics on power strips, low consumption refrigeration and laundry, laptop computer, low wattage lights and so on. Leaving a 23 watt CFL bulb on for 24 hours is half a kilowatt! We feel pretty good about our average 3.2 kw/day while maintaining quite a comfortable lifestyle and that our solar system is well sized for this consumption.
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Great post Pete
I often don't actively think about the cloud issue. We are at 1100 ft and pretty much accept that it comes and it goes, but it sure plays a role. I also think of any solar charge I might get after about 3PM as a bonus.
You are so right regarding battery sizing. I could write a long post on expensive lessons but won't. The reality is we look to have them last through the night as opposed to the theoretical 3 days. Even in rainy season, when I check my numbers, my evaluation as to start the generator or not is my anticipation of the next 24 hours.
I sincerely hope Chris has gleaned some useful stuff here.
BTW, you might not remember, but we bought your UV light a couple years back.
David
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quote:
BTW, you might not remember, but we bought your UV light a couple years back.
Sure do. The UV light with its requirement to be on all the time was one of the 'nice to haves' that we decided to do without.
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