Starting from scratch...Hooray!!!

SystemSystem Posts: 2,511 admin
Hello all! This will be an interesting change from speaking with my usual crowd at the mountain biking forum- Dirt Rag...!
Here goes.. With our recent tax return and, ah, "gift" from G. W. and Co. I've decided to invest in a hybrid system.
Living here in Las Vegas, the sun and temps are pretty good for solar, and with the wind factor of this year..musta have had an average 20 mph-er blowin in my face everyday on the commute home!!! what the heck...we totally commute to work so are avid bicyclers, and conserve as much as possible- fans instead of ac cooling, laundry by hand etc. etc. so we are looking to outfit our home with a hybrid system to hopefully offset or possibly resale back to the grid.

We are on a couple of acres, all electric, with about a 2100' home, a 1000' guest house/shop that see's wintertime snowbirds visiting. I do a lot of metal fabricating and tool usage that involves grinders and welders and such...we are on a well, 230v pump, we also run a pool and associated pumps about 6 hrs a day..so the load is high for many start up apps...otherwise we keep everything we possibly can... off.

The shop has its own subpanel, which is about a 300' run from the main panel on the house... I'm concerned about V drop and efficiency, of course.
The shop roof is flat about 24x40', and I assume a good place for panels...
I have a nook that would hold batts and inverters and all that....
I intend to put the wind gen about 100' away from the shop .... I will be building everything that I can...

Is it possible to put together a system that will supply and return my investment of ....hopefully... about 10k $ or less? and where/how/why would you veterans start ? I'm anxious, but want to do it right and with as high of quality stuff possible....budget permitting...
Thanks for reading and your assistance! Jack.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!

    Welcome Jack! Hope we can help.

    Grid Tied solar would be worth investigating... But a $10,000 system would only be about 1-2kW of solar panels (depending if this a retail full turnkey install or a do-it-yourself project and your utility allows net metering). You can use this link to find out how much a 1kW grid tie array will generate for your area...

    A retail grid tied system installed $8,000-$10,000 for 1kW system would generate roughly 1,664 kWhrs per year (or ~138 kWhrs per month). Assuming your electric power is $0.097 per kWhr, that is $161.40 worth of electricity per year.

    $8,000/$161.40 per year=49.6 years to payback.

    Or, to look at the cost of Grid Tied solar power over 25 year life of the system:

    $8,000/(25yr*1,664kWhr per year)= $0.19 per kWhr (assuming no interest or taxes).

    Of course, there are economies of scale too... Installing a 1kW system will cost more per watt than a 3 kW system (which, from what I have seen, is a cost effective starting point--but you are still talking about a ~$28,000 turn-key installed system without state rebates and federal tax credits)

    You did not list how much power you currently use. And utility polices (net metering or not, special rate plans for solar power, etc.), permits, extra costs because of location (long wire runs, special mounting requirements) all will affect the end price.

    If you live in a consistently windy area (6 months or more per year), a wind turbine may make some sense--However, not very many of us here will recommend wind for anything as a money saving option--Wind turbines are "cheap" to purchase, can be expensive to install, very expensive to maintain as they have not been very reliable, and wind is highly variable seasonal resource. Solar is, for most areas, a more consistent and reliable/predictable resource.

    In the end, there are other options that usually end up being better places to first spend your money in the efforts to save money/energy overall...

    1. Conservation--between insulation, energy star appliances, double pane windows, heat gain/loss control through windows, attic ventilation, ground sourced HVAC heat pumps, and just turning off anything not needed. Look at your power bill... You probably have a newer home--so insulation and appliances upgrades may not make as much sense for you--but, just for the sake of discussion, under 300 kWhrs per month is probably a relatively energy efficient home, and around a 100 kWhrs per month is somebody who really stands out (typically 100 kWhrs per month maximum is a good aiming point for an off-grid system).

    2. Hot Water / Hot Air from solar thermal panels. Usually less to install, and if you have electric hot water / electric heat, almost always a better investment in renewable energy. There are issues with water leaks, freezing, and much more maintenance than a solar PV grid tie system would require.

    3. Look at moving your all electric loads (range, hot water, heating) to something else (propane or whatever is available in your area). Electric heat is typically better replaced by other fuel/energy sources (like solar thermal for domestic hot water).

    3. Grid Tied solar PV system--as discussed.

    ....

    199. Grid Tied Wind (based on currently available systems and their reliability)
    200. Off Grid system (battery bank, AC inverters, solar panels, diesel/propane/gas generator, water turbine, wind turbine, etc.) because of cost per kWhr (probably $1.00 per kWhr or higher)

    -Bill

    PS: Should add that Ground Sourced Heat Pumps may or may not make sense by the time you include drilling/burying the external heat exchanger into the earth. Solar Guppy (another poster here--IIRC) said that making a larger grid-tied solar system for a regular air sourced heat pump (a good Energy Star system) to support the HVAC may roughly be the same costs as installing the ground source HVAC system.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Starting from scratch...Hooray!!!

    BB - I see the Energy Information Administration lists the average retail price for NV as 9.63 cents/kwh, but if you look at the details it shows the retail electricity price for 2006 at 11.08 cents and it's been increasing about 5% per year since 2000.

    Also, there are federal incentives currently and they will most likely be renewed.

    Nevada Power Comanies and Sierra Pacific both seem to offer significant incentives in the Solar Generations program.

    I'm not saying you're wrong about anything, but even seeing the words "49.6 year payback" could be shocking. It might be a lot less when you take everything into account.
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!

    Newenergy,

    I agree that local rebates and federal tax credits help--plus multi-tiered electric utility rate plans can make grid tied solar systems a practical money saver (for example, in northern California, if you use more than 900kWhr per month, the top rate for "excessive residential usage" is currently $0.36 per kWhr--so that $0.19 per kWhr--without rebates/credits--is already a money maker if you have A/C or other needs)...

    My own system is probably somewhere around $0.25 per kWhr, but when California's old rebates (and FED tax credit) were taken into account, it is closer to $0.15 per kWhr (excluding any replacement inverter 10+ years from now).

    A difficulty for somebody like me who does not know poster's the power company, its Solar Grid Tie polices, or even which company is supplying power--it gets a bit more difficult to give a once size answer.

    For example, California has recently cut the rebates by 1/2 for homeowners, and changed to require a complex Time Of Use plan with Tiered pricing (E6). Even I with could not accurately predict my end bill for my own home using that plan.

    And for people that installed smaller grid tied systems, the E6 TOU plan actually increased their bills (small system could not offset very high TOU/Tiered charges vs the flat rate/tiered pricing they had before).

    Yes, one can come pretty close to breaking even with solar with good rebates and tax credits--but there are issues with the rebates/credits too (some almost require professional installation, others have limits like the FED tax credit).

    Also, some localities assess property tax on solar installations--I just don't know that detail of information.

    And if it is a business, other tax credits may be available--but then you may get into a whole 'nother can of worms with demand charges--where approximately 1/2 of your utility bill is metered power costs, and the other 1/2 is based on your peak kW demand for the billing period. All of a sudden, that heavy peak load (lights, A/C, night production, etc.) that occurs after the sun has set--1/2 your energy bill is set--even if your solar panels offset 100% of the power you use in one month (I posted an article here where a San Diego school district got nailed just because of this issue).

    That is why I try and give the formulas for figuring pay-back and cost per kWhr--it lets people plug-in their own numbers and see what the results are...

    And I mention things like (from my previous post just above):
    ...Of course, there are economies of scale too... Installing a 1kW system will cost more per watt than a 3 kW system (which, from what I have seen, is a cost effective starting point--but you are still talking about a ~$28,000 turn-key installed system without state rebates and federal tax credits)

    You did not list how much power you currently use. And utility polices (net metering or not, special rate plans for solar power, etc.), permits, extra costs because of location (long wire runs, special mounting requirements) all will affect the end price.

    You can also nail me on parts and installation costs... I try not to low-ball them because I hope people can get a feel for where their price point / comfort levels are (plus this is a commercial website owned by Wind-Sun / NWAS--I respect them too much to try and pull prices out of thin air that may look like I am trying to do their business for them). There is no way that I can give accurate quotes to people in 4 different continents.

    And don't worry... I am not taking anything personally here. I am too, am here to learn. If you have some suggestions as to how I can better present the information in an international forum--I am all "eyes". :cool:

    And Jack-of-All... I hope I did not scare you off--I was giving some basic starting points--as always, the devil is in the details.

    Questions (and answers) are always welcomed. :p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Starting from scratch...Hooray!!!

    It's always interesting to see peoples reactions when they learn the approximate, all in, final price on a solar or wind system, and how long the payback time will be.
    Cheers
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: Starting from scratch...Hooray!!!

    Well thanks Wayne!!! It's also always interesting to see who jumps outta the woodpile with uncalloused hands!;
    As was said, the devilsin thedetails.. So Yes ! we are a retail buyback Nev. Power. purchasesback at retail cost, also there is a 50% property tax reduction..but for commercial..and +10 kw produces.... stillllll I like to see some initiative.
    Is is wait? or do it now and upgrade? C''mon ! you are the guru''s... what is it?

    So why are you guys here, if not that one can "break even".. if your reeallllly good at this...'cause if its about stickin to the man, well, then count me in.....and start PM-me.... I've got some work to do-
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting from scratch...Hooray!!!
    Well thanks Wayne!!! It's also always interesting to see who jumps outta the woodpile with uncalloused hands!;
    As was said, the devilsin thedetails.. So Yes ! we are a retail buyback Nev. Power. purchasesback at retail cost, also there is a 50% property tax reduction..but for commercial..and +10 kw produces.... stillllll I like to see some initiative.
    Is is wait? or do it now and upgrade? C''mon ! you are the guru''s... what is it?

    So why are you guys here, if not that one can "break even".. if your reeallllly good at this...'cause if its about stickin to the man, well, then count me in.....and start PM-me.... I've got some work to do-

    i'm not sure if you are criticizing wayne or anybody else here because if you are know that they have solar and you don't and that's a big detail.
    the gurus here say do what you want if you think it's worth it for you to do. we aren't here just to convince you or anybody else to do this.
    we are here because we like the subject matter and try to help others who have the same interest. if you just desire to stick it to the man i caution you that the man is way bigger than all of us are and your pinpricks to him are only a slight annoyance.
  • System2System2 Posts: 6,290 admin
    Re: Starting from scratch...Hooray!!!

    Jack-of-all, did you bother to read the initial response to your thread? The one by "BB"?
    He was not handing you a line of BS. He was trying to help you see where to start.
    In general, folk living with alternate energy, producing their own power, live in a world which is often foreign to the way of mainstream thinking. A world of conservation and living WITH nature and what she will provide, when SHE decides to provide it, because that's the way it is. That's the reality of the situation.
    Mainstream North American society (I'm including Canada, because that's where I'm from) has been conditioned to live the way they want, when they want, use what they want when they want, take from nature what they want when they want, all with regard to nothing but their own personal whims, expecting nature to buckle down and serve their every desire.
    For some people, the move to alternate energy isn't all that hard, they've been gradually moving in that direction and learning along the way, while for others, it's a huge shock to one day find out that we are not the masters of nature after all.
    For the vast majority of folk with solar power, it's a way of life rather than a way to make money. The reason? There is no mint to be made with a $10,000 system, of for that matter with a $100,000 system.
    Them's the facts.
    Rethink the whole thing from the start and solar might work for you. Otherwise, if your main interest is money, forget it.
    That's my opinion, take it or leave it.
    Peace and all the best.
    Wayne
    And yes, like the others on this form, I live with solar energy. It's running my house right now, including the computer with which I make this post. AND, I did the complete installation myself, with my own two hands, with no help from anyone except the awesome folk on this form.
    As was said, them's the facts.
  • System2System2 Posts: 6,290 admin
    Re: Starting from scratch...Hooray!!!
    Jack-of-all, did you bother to read the initial response to your thread? The one by "BB"?
    He was not handing you a line of BS. He was trying to help you see where to start.
    In general, folk living with alternate energy, producing their own power, live in a world which is often foreign to the way of mainstream thinking. A world of conservation and living WITH nature and what she will provide, when SHE decides to provide it, because that's the way it is. That's the reality of the situation.

    Hey, Of course I did! If I hadn't been very interested in supplanting my electrical usage with an alternative source I don't think I'd have come along and made the post in the first place.... I live in a world of foreign thinking too boys.... I drive my bicycle. Everywhere. The fuel savings alone totals several solar panels a year- so-to-speak- EAsy there, Mr. uptight
    'm not sure if you are criticizing wayne or anybody else here because if you are know that they have solar and you don't and that's a big detail
    Moderator....
    I really DO understand where and why your motivated to live a specific lifestyle....."Stickin it to the man" is merely private icing on a cake baked by me.... Please don't assume I am so ignorant as to think even the thousand gallons of gasoline I DON'T use per year makes a lick of difference to anyone but me and my family who indeed see it as a lesson... My wife commutes by bike also... as do my 2 kids....
    I'm here to learn from the best in an open forum that [presumably] shares its knowledge with like minded folks!
    Thank you BB and Neil....Bill and Wayne! and those of you yet to proffer advice...

    Now on to what to do about it... AS mentioned, NV is a full retail buyback state...and yes, its net metering,
    Summary:
    Nevada's original net-metering law for renewable-energy systems was enacted in 1997 and amended in 2001, 2003, 2005 and 2007. Systems up to one megawatt (MW) in capacity that generate electricity using solar, wind, geothermal, biomass and certain types of hydropower are generally eligible, although systems greater than 100 kilowatts (kW) in capacity may be subject to certain costs at the utility's discretion. Systems must be designed to offset part or all of a customer-generator's electricity requirements. A system is not eligible for net metering if its generating capacity exceeds the greater of (1) the limit on demand that the class of customer of the customer-generator may place on the utility's system, or (2) 150% of the customer's peak demand. Each investor-owned utility operating in Nevada must offer net metering until the aggregate capacity of all net-metered systems in its service territory equals 1% of the utility’s peak capacity.
    thats the limit on what I have read...little bit confusing.... they also provide a 50% tax on real estate kickback, but I believe that is only for commercial facilities at the 10kw or larger point... real property owners are much lower, I believe- hence part of my desire to have a hybrid system...trying to get near that buy back level is no doubt daunting...Also, there are no restrictions in height for alternative E building...So as I continually strive to conserve and drop usage, last year it was 10,000 in windows, year before it was ceiling fans, year before it was awnings and shades;right now I am working on solar passive for hot water... eventually there will come a time when I can't do too much more on conservation ends, since I do use high consumption tools fairly regularly, I will always need - some
    connection until we leave this valley for alternative lifestyles...and until then I intend to research and implement at a rate that works...again, thats why I am here...and not off discussing the recent commuter trailer through-axel shortcommings....;) clearly this is more than an investment, its an attitude to be displayed- much like bikin in traffic, in a city who's sheeple don't know the meaning of bike lanes....and just who and what constitutes "traffic"!

    I see that it seems systems tend to be designed specifically for specific sizes... Does this always involve centering around the inversion system? or is there a better avenue of planning? How does one purchase for the now with the intent on the future? economically? when inverters seem to be efficiency limited by their intended use?
    can someone explain the abbreviations?
    Inverter
    Pnom 3300 Wac
    Idc max 17.5 Adc
    Vmptmax 550 Vdc
    Voc 600 Vdc
    Vmptmin 200 Vdc

    Efficiency 95.5 % AvgEfficiency

    Temperature Specifications


    Put it this way, if you were willing to commit 10k to an initial investment plus your own time and ability- which count for a lot in my book, is there no way to feasibly start out generating E- ?


    Does the axiom of 4-6,000$ per kilowatt generated by wind power hold true for solar at the 8-10,000$ level too?
    All that said, If 10 K can't get me started what else can? A second mortgage?-thats a joke, sarcasm and glibness comes later...thanks- Jack.

    Oh, someone mentioned wire runs... I would be using 1/0 secondary power [thats secondary residential service type c-i-c, aluminum] as my primary wire to and from panels and or windtower... which could be as little as 10-20' from panels, and say, 75' from tower to the shop....this would connect straight to battery bank and/or subpanel in shop for direct meter feed, you guys tell me which or both...?
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!

    Jack,

    It sounds like you are currently spending your money on the correct things (conservation and solar thermal)... In general, that would include converting as much of your all-electric home to alternate fuels (solar thermal for hot water, heating, a "solar powered clothes drier"--aka clothes line, and--if at all reasonable--look at your electric stove and decide if propane (or natural gas if an option) is reasonable or not.

    Once you have "tapped that out", then you can look beyond.

    How much electricity do you need per month/whatever. Normally, since systems are very expensive to install, and with net metering in most states, it does not make sense to over-size your system--matching to your typical loads is what you aim for.

    Nevada Power seems to have 1 year net metering (for residential systems and a 30 kW maximum size). At the end of the 1 year period, if you generate more than you use, they do not pay you the difference.

    Looks like there may be flat rate residential of $0.115 / kWhr and Time of Use too (~$0.085 / kWhr, execept summer peak at $0.24 / kWhr). No tiered pricing on any rate plans.

    The TOU rate plan is peak from 1pm to 7pm summer (June-September). This is a trial plan and only 12,000 customers may be signed up during the trial.

    If you can move your major power usage off of 1-7pm during summer, then TOU can be a big plus for solar systems... Any excess kWhrs you generate during this period, you get all most 3x the money back to buy off peak/winter power (say 20kWhrs per day, and 10 kWhrs per day are generated during 1-7pm--you "get" 10kWhr+$0.24/$0.08 * 10kWhr = 40 kWhrs effective power from your 20 kWhr system). Shifting loads to off-peak is a good way of making your system more cost efficient (assuming utility signs you up, and you can avoid heavy power use during summer peak). Of course, since this is only 6 months per year, you will not get a 2x in "power generation" because of the flat winter billing.

    If your shop is also a business--some of the rate plans may be more difficult for you to apply for.

    Jack, you also talked about:
    ...this would connect straight to battery bank...

    So, now, there is a question of what type of RE system do you want?

    1. Pure Grid Tied System (solar, wind, but if utility power is off, you have no power).

    2. Pure Off-Grid System (solar, wind, alternate power supply like Gen or utility power as battery charger).

    3. Hybrid Grid Tied / Off Grid capable system (typically for emergency power---many small outages or long term grid failure like tornado, ice storms, etc.).

    #1 is the cheapest, most efficient (power and co$t), and least maintenance costs over time. If you have reliable utility power--go with this system. Buy a some sort of backup generator if you need a few days (or week or two) of emergency backup power when the end of the world comes.

    #2 is the most expensive to install and maintain. Can work well, but power costs are going to be $1.00 per kWhr ore more (battery replacement costs, cannot shift power generated in full sun more than ~3 days--can't store summer sun for use in winter).

    #3 will cost about the same to install as #2, but because it is grid tied, it has the advantages of Grid Tie Net Metering, plus the batteries will last longer because they do not cycle nightly (only standby for emergency usage). Power still costs more than a simple grid tied system--but very nice for unreliable power or the risk of several weeks or longer of power outages. However, it must be sized for your maximum loads (well pump, electric stove, welding equipment, A/C, or whatever).

    For both #2 or #3, anytime you want to get over 100 kWhrs a month out of the system, you are talking about big bucks to install. #2 or #3 cost (very roughly) 50% to almost 100% more to install as an equivalent grid tie system (per solar panel watt).

    A grid tie system costs around $8-10 per solar collector watt installed (US pricing). A 1kW system around $10,000. A 3.5 kW system, around $29,000.

    If you want to "add a system"--typically, I would look at a ~3.5kW base system starting point (assuming you need this much electricity). The inverters are large enough that you get a better $$/watt vs the smaller systems. And you spread the, more or less fixed, labor/permit/etc. costs over a larger base system cost.

    In the end the difference between installing a grid tie system versus something with batteries/generator for emergency off-grid use is really based on your needs.

    I would have very much like to install a system like #3--but it does not make sense for me. My last 1 week power outage was 5+ decades ago--and the rest of the power outages have been an hour or two every few years (typically wind storms).

    So, I installed a Grid Tied solar system and bought a Honda eu2000i 1.6kW generator. This plus 20 gallons of gas, will give me a good 2 weeks of off-grid emergency power (just a fridge/freezer and a few lights/radio/tv).

    I even looked at a home standby generator--but they suck fuel like it is going out of style. We don't use propane here, and natural gas does not make sense as an emergency fuel for me--as I am preparing for an earthquake--so natural gas does not seem to be my fuel of choice. And even the smallest 8-10kW generator uses a few gallons a day--several times what I would use in my small portable generator.

    So--yes, I would tell you to put the $10,000 in the bank until you had more to "invest" in solar--and, for now, spend $1,000 or so for a eu1000i, eu2000i, or eu3000i, and something to store fuel for use as emergency power (if you need it). Plus a camp stove with back up fuel source, etc....

    You could also get a cheap 5kW generator just to run the well pump once in a while for water (the Honda's are probably too small for a good size well pump).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!
    I see that it seems systems tend to be designed specifically for specific sizes... Does this always involve centering around the inversion system? or is there a better avenue of planning? How does one purchase for the now with the intent on the future? economically? when inverters seem to be efficiency limited by their intended use?
    can someone explain the abbreviations?
    Inverter
    Pnom 3300 Wac
    Idc max 17.5 Adc
    Vmptmax 550 Vdc
    Voc 600 Vdc
    Vmptmin 200 Vdc

    Efficiency 95.5 % AvgEfficiency


    Pnom=Nominal Power?--inverter can supply 3.3kWatts steady state without overheating... Usually they can supply some extra power for surges (like starting a well pump) too.

    Idcmax=Maximum DC Current--Perhaps the short circuit current from a solar panel. Used when trying to size wiring per NEC / code requirements. Actual current from solar panels will be less during normal operation. There is also series fuse requirement to protect a solar panel/wiring from shorts when a bunch of panels are connected together in parallel for larger systems.

    Vmptmax=V maximum power point tracking voltage -- in this case, for an off grid inverter, MPPT generates the maximum power possible from a solar panel. If you run the voltage higher, the inverter's efficiency will fall a bit. Normally, you design the system to not exceed 550 VDC output from the solar panels under load. You also need to look at Voc max... The voltage which will fry your inverter if its input voltage is exceeded.

    Voc is the maximum open circuit voltage from an open solar panel (changes with temperature. Make sure that this voltage from a bunch of panels in series does not fry attached loads (inverters, charge controllers, etc.).

    Efficiency--typically used to describe inverters and solar charge controllers. Higher is better, and 95.5% is about as good as it gets, because the 4.5% is wasted power that you paid for. In terms of designing equipment, that wasted heat also makes the inverters run hot--so an inefficient system can back itself to death with low efficiencies (and poor heat sink/removal system).

    By the way, it is difficult to add Batteries to existing systems. Mixing old and new batteries together will generally cause the new batteries to fail at the same time as the old batteries (new batteries tend to carry the loads until the age down to match the old batteries in the bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Starting from scratch...Hooray!!!

    Wow...thanks Bill!

    Seems that the initial choice would be grid tied, our power is very reliable. I could dedicate an entire circuit in my shop for a sort of hybrid power... basic lighting- in and out, and beer cooler...;) or swamp cooler.

    What sort of battery power- [ as in number and size] would it take to run, say a 10 amp angle grinder for 1 hour?85% of its peak power- and/or intermittent other <20 amp tools....sporadically..
    Better yet, rather than you spend time answering- Is there a site to which I can apply various mock loads and usage run times and calculate my energy needs in any particular situation? J.
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!

    Jack,

    I would not even bother with the "Hybrid Power" version for your shop unless you have some reason that you need to run 24x7 even in storms and earthquakes. A better bet would be a generator (propane powered RV generator would be pretty sweet). Relatively cheap to install. And no operational costs except when you need power (replace the starting battery every couple years, exercise a few times a year, oil change).

    Battery/solar/inverter systems required to power large loads (motors, A/C, etc.) would have to be sized pretty large to power for any length of time (read--expensive to build and expensive to replace the batteries every 3-10 years). Plus, you have power losses just keeping the batteries charged (large battery banks--that is not an insubstantial amount of power--especially if flooded cell lead acid).

    Anyways, back to your other questions.

    You can just setup an Excel spread sheet with the equations. Just make some basic assumptions--and away you go...

    First, for measuring power on your 120 VAC 15 amp service... Get yourself a Kill-A-Watt meter--if you don't have one already.

    The basic readings you will need is the Watts (peak watts too), and kWhrs... You can plug your equipment into it and run it for an hour/day's worth of work, and read the kWhrs at the end--you will know exactly.

    Larger equipment (welders, A/C, etc., you might be better off just reading your meter and seeing how much they draw--IIRC, most home meters, every time the aluminum disk turns is 3WHrs of electricity).

    And the equations:

    Voltage = Current*Resistance (V=IR)
    Power = Voltage * Current (P=IV)
    P = I^2 * R = V^2 / R
    Work=Watts*Hours
    kWH=Watt*Hours/1,000 (units your power bill is in)

    Some assumptions...

    How much power will X kWatts of solar panel generate. Derating factor of 0.77 is from Solar Panel to your kWhr meter.

    Assume that Flooded Cell batteries are 80% efficient. AGM batteries are 90% efficient. Inverters (pure sine) are 85% efficient (some more efficient, running small loads, less efficient). Assume that motors run on Modified Square/Sine wave inverters will use 125% more power than a pure sine wave inverter / utility power.

    Assume, if you have lots of wiring runs, 5% wiring losses.

    Most lead acid batteries. Assume that you never draw more than 50% of capacity before recharging. Assume that any battery drawn down more than 25% (75% State Of Charge "SOC") should be recharged in the next 24 hours to prevent damage. Try to size loads to a maximum of Capacity/20 (20 hour rate) discharge rate. Size recharging at a 5-13% rate of charge.

    How much solar panel will I need for XX watt tool per day?

    From this site, For Las Vegas, a 1kW solar array for both Grid Tie and Off Grid (0.77=grid tie, 0.52=off grid).

    Grid Tie = 1,664 kWhrs per year or 4.5 kWhrs per day (1 year average)
    Off Grid = 77-105 kWhrs per month or 2.6 to 3.5 kWhrs per day (winter/summer average)

    Your 15 amp tool at 120 VAC? Assume that you don't pull 100% power--but 50% average power for 30 minutes an hour:

    Work=15 amps * 120 VAC * 1/50% load * 30min/60 min * 1 hour = 450 Watt*Hours = 0.45 kWH

    Available power from your 1kW of solar panel Grid Tie/Off Grid system:

    Hours of use (OG) = 4.5kWhr per day /0.45WH per hour = 10 hours per day (grid)
    Hours of use (GT) = 2.6kWhr per day /0.45WH per hour = 5.7 hours per day (winter)
    Hours of use (GT) = 3.5Whr per day /0.45WH per hour = 8 hours per day (summer)

    If this is done with a "cheap" modified sine wave inverter (MSW inverter) with a 1,000 watt of solar panel in Las Vegas--reduce the Off-Grid by 20%:

    GT Winter MSW = 5.7h/d * 80% = 4.5 h/d
    GT Summer MSW = 5.7h/d * 80% = 6.4 h/d

    Of course, with solar power, some times you will more power than average, and other times, less power than average (one winter I went several weeks with less than 1 kWhr per day generated from a 3kW grid tied system). The above numbers/calculations are "ideal" conditions--and actual conditions (weather, age of system, dirt on panels, tools, etc.) will always define how you can run the system...

    To size the batteries... Use this as a rule of thumb (takes into account many of the battery rules I mentioned at the beginning). Take the amount of work you want per day (WHrs or kWhrs per day) and multiply by 6 (3x for 3 days of no-sun standby power and 2x for 50% maximum discharge).

    So, 3.5 kWhrs per day (summer off-grid numbers for 1kW panels in Las Vegas):

    Battery Bank kWhrs = 3.5 kWhrs per day 3 days * 1/50% discharge = 21 kWhrs of battery storage...

    But since most batteries are rated in Amp*Hours, you will need to convert kWhrs. But to make the conversion, you need to know the voltage of your battery bank. 12v, 24v, and 48v are the most common. Use 12 volt for your cabin / RV with light loads (less than 1kW of peak load--ideally less than ~250 watts of load). For heavy loads, choose 48VDC...

    So, for a 12 volt bank:

    Battery AH = 21 kWhrs * 1,000 w/kw / 12 volt bank = 1,750 AH

    48 volt bank:

    Battery AH = 21 kWhrs * 1,000 w/kw / 48 volt bank = 438 AH

    Note that the actual battery cost is the same between both options... You will still need (rough visualization) 20 or more "car sized" storage batteries for this bank (to support 1kW of off-grid solar panels in Las Vegas)... It is just series vs parallel wiring to achieve the end A*H rating at XX volts.

    I will stop here for now... Questions?

    -Bill

    PS: I used 1kW of solar panels so that you can scale... Need twice as much work, double the panels. Need less, 1/2 them. Same with the battery.

    But you will still need to check some end conditions... Running a heavy load (say a 4.8 kW (~5 hp) well pump 30 minutes per day) for a few minuets a day will much larger inverter, cabling, and batteries versus just operating a 100 watt load for 24 hours per day. Both are the same amount of "work" (and solar panels) at the end of the day, but the wiring/panels/inverters must handle 4.8 kW vs 100 watts.

    PS: I had a brain freeze in the above post and started using 6.4 hours per day instead of 3.4 kWhr / day in the battery calculations...

    I have used BOLD to highlight the corrections.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Starting from scratch...Hooray!!!
    BB. wrote: »
    You can just setup an Excel spread sheet with the equations. Just make some basic assumptions--and away you go...


    And the equations:

    Voltage = Current*Resistance (V=IR)
    Power = Voltage * Current (P=IV)
    P = I^2 * R = V^2 / R
    Work=Watts*Hours
    kWH=Watt*Hours/1,000 (units your power bill is in)

    Some assumptions...

    If I had the time today, I'd upload a spread sheet (excel 97 format) and add a sticky.
    This would be a very useful "1st stop" to direct folks to.

    Thanks BB. Mike
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Starting from scratch...Hooray!!!

    You are very welcome Mike... I am not sure I would make up a spread sheet or not... There are so many assumptions and local requirements that I tend to suggest people "build their own" models in the spread sheet so that they can understand the pieces better...

    Perhaps, cleaning up a post like this, plus a few some information from others around here and posting as a starting point sticky would be helpful.

    I have (and others) have done this same thing multiple times here for new readers. A sticky may help save my typing fingers... but many times people skip over an all-inclusive post because it has to have so many exceptions and what-ifs for their particular needs, that it just causes their eyes to glaze over (been there, done than!).

    By the way, I made some mistakes in my post above--I have updated the changed numbers in bold where I made changes.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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