My down and dirty math... Is it even close?

SteppapajonSteppapajon Registered Users Posts: 11
Hello everyone,
I have been a member for about six months and this is my first post.
I just wanted to say thanks to everyone that contributes to the forum. I have read everything I can to better understand the dos and don't of off grid PV power.
My question is this...
I have been using some simple math to ball park my loads verses equipment needs for a future off grid cabin ( 3+ years if all goes well.)
Will some of the more experienced off gridders tell me if I am even close.
It goes like this.
Assuming a 12 volt system
for every 1000 watts of panel multiply by .06 to get amps out. (1000 x .06 = 60A)
Multiply amps out times 10 to get battery bank size in ah. (60 x 10 = 600 AH)
I am also using 1000 x .06 =60 watts to get the number of watts I can leave on 24hours a day (60 watts x 24 hours = 1440 watthours.)
Is this even close?
Thanks to everyone that takes the time to respond,
Jonathan

Comments

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: My down and dirty math... Is it even close?

    A couple of real simple rules of thumb that seem to work quite well in the real world.

    First, all design considerations come from the loads. Figure your average and max loads and work back words to the batteries, and the charge regime. Average daily loads in watt hours or kwhs, plus what is the max short term peak load.

    Once you have our basic load calcs, then you can size a battery system, sized for an ideal draw of no more than 25% daily if you want your battery to last. Then figure how much autonomy you wish (number of days without sun before you need to run a genny to top up the batteries). 25% daily draw would give you 2 days before you draw to the recommended max of 50% SoC. I personally like a 20% daily draw, which in the real world give 3 days of autonomy.

    Then, figure charge current of ~10% of ah capacity. I have found that Wattage rating of the PV * .7 give a pretty good average of output, so a 100 watt rate panel will likely put out ~ 70 watts under ideal sun on average.

    The simplest rule that I have is this,, Rating/2*4=useable wh.

    So for example 100 watts of panel,, 100/2=50*4=200 wh/day.

    The /2 takes into account all variable system loses, from PV conversion, wiring loses, battery ef, cc ef, inverter loses etc. The 4 represents the average hours of GOOD sun one can reasonably expect to see on a daily basis, on average per day over the course of the year. You can adjust that number according to local circumstance, but avoid being too opptomistic. For example, if this is summer only you may have longer days,, but you may also have more cloud events.


    So in my case,, for example,we have 400 watts of PV, 400/2200*4=800wh.

    We happen to use between 500-800 wh on a average day for all loads, and most days we stay even, on good days we get ahead, poorer days behind, but over the course of the year it averages out. On an ideal day we can push 2 kwh out of the PV, but I can't count on that. Those days, I take advantage, and run optional loads like charging tool batteries etc.

    That 400 watts of PV pushes ~ 20 amps, (12 vdc) which is ~5% of battery capacity, which is a bit light, but is within the 5-13% recommended rate of charge,, and we usually run no loads of consequence during the day. Under ideal circumstances, cold days, reflection off of snow and or the water, edge of cloud events etc, we can bump 30 amps

    Two more simple rules of off grid. People tend to, at the same time, over estimate their solar potential, and under estimate their loads, leading to deficit charging. The second is that loads, WILL grow with time, so a fudge factor should be built in at the outset, both on the PV and the battery.

    I hope that helps, Welcome to the forum, and keep in touch with any questions,

    Tony
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: My down and dirty math... Is it even close?

    As a PS to the previous:

    All load calcs should be done in watt HOURS (or KWHs) Watts mean little, whs is what you actually consume, and need to recharge. Also realize, that in simple terms, for every watt hour you consume, you are going to have to put 1.2 wh (or more) back into the battery because batteries are not one for one so to speak. FLA batteries take at least 20% more power to charge than they can deliver.

    Also keep in mind that there are loses everywhere, most of which cannot be overcome, and indeed need to be included in the calcs.

    For example, in addition to the 20% for the battery, you need to include inverter loses that, depending on the invert ef and loading can be 5-50%. Charge controller loses, wiring loses also should be figured in. (which is why my /2 rule works pretty well as a simple, yet not 100% accurate calc).

    Also, as loading gets bigger say over 1 kwh/day or peak loads over say 500 watts ~40 amps 12vdc, going to a 24 or even a 48 vdc system has big advantages. Bottom line, in the design stage, do everything you can to estimate the loads, but at the same time, do everything to limit them. CFLs, gas cooking, water heat etc, limited appliances etc.
    I use the genny for all the really big loads, since they are rare, it is much cheaper to build a solar system for average peak loads (and daily loads) instead of building it to run the skill saw or vacuum once in a while).

    Since you will need a genny any way, plan on using it for the big, occasional loads, and wire the house accordingly. Also, consider your water pumping requirement carefully. A large, fast (high powered) well pump, might well be suited to run on the genny into a big tank run once a day ( or once a week) instead of trying to run it off the PV system. You could also consider a small (slower) less powerful pump that might run more, but in the net, consume about the same amount of power, but not require a big, inefficient inverter for example. DC water pumping may be an advantage.

    Once again, hope this helps,

    T
  • SteppapajonSteppapajon Registered Users Posts: 11
    Re: My down and dirty math... Is it even close?

    Thanks for the comment Tony. I meant watthours and have edited the original post to reflect it.
    I understand about the losses involved and was looking to simplify the formula to include those. It just makes it easier for me to do it in my head.
    So in my case,, for example,we have 400 watts of PV, 400/2200*4=800wh.

    We happen to use between 500-800 wh on a average day for all loads, and most days we stay even, on good days we get ahead, poorer days behind, but over the course of the year it averages out. On an ideal day we can push 2 kwh out of the PV, but I can't count on that. Those days, I take advantage, and run optional loads like charging tool batteries etc.

    That 400 watts of PV pushes ~ 20 amps, (12 vdc) which is ~5% of battery capacity, which is a bit light, but is within the 5-13% recommended rate of charge,, and we usually run no loads of consequence during the day. Under ideal circumstances, cold days, reflection off of snow and or the water, edge of cloud events etc, we can bump 30 amps

    My math would be 400x.06=24 amps
    24 amps x 10 = 240AH of batteries.
    24x24= 576 WH per day

    So short of your bigger battery bank my math came pretty close. If I bump to your 5% charge rate instead of my proposed 10% I would have a 480AH battery bank and be right in the ball park.

    Thanks for posting your numbers and allowing me to confirm I am on the right track.
    I must say I applaud your talent of living on .5KWH a day. I have much to learn
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: My down and dirty math... Is it even close?

    For the sake of anyone else who might be reading this, the usual method of system design goes like this:

    Loads in kW hours / system Voltage = Amp hours used.
    Amp hours used / DOD % = size of battery bank.
    Battery bank size * desired percentage peak charge rate = expected maximum Amps.
    Maximum Amps * system Voltage (low point) = derated array size.
    Derated array size / efficiency (usually 77%) = total array size.

    So to use the OP's 576 Watt hours per day on a 12 Volt system we get:
    576 / 12 = 48 Amp hours used.
    48 Amp hours / 25% DOD = 192 Amp hour battery bank.
    192 Amp hours * 10% peak charge rate = 19.2 Amps.
    19.2 Amps * 12 Volts = 230.4 Watts.
    230.4 Watts / 77% efficiency = 299 Watt array.

    Again, this does not include system losses. Also along the way it is necessary to "size up" to meet commercially available equipment. This means the 192 Amp hour battery might be increased to a 200 Amp hour 12 Volt AGM and the subsequent calculations affected, resulting in a 311 Watt array which would be "sized up" to a pair of 180 Watt panels for 360 Watts total.

    The 299 Watt (or whatever size) array can be checked for "harvest" by using the simple formula:
    Array size * hours of equivalent good sun / 2 (for 50% over-all system efficiency) = AC Watt hours.
    Plugging the numbers in we get:
    299 Watts * 4 hours / 2 = 598 Watt hours which exceeds the OP's original 576 Watt hour figure, so all is good.

    Note to my fellow moderators: I know! I said I write a bunch of these formuli up and post them and I've almost started on the project! :p
  • solar_davesolar_dave Solar Expert Posts: 2,362 ✭✭✭✭
    Re: My down and dirty math... Is it even close?

    Note to my fellow moderators: I know! I said I write a bunch of these formuli up and post them and I've almost started on the project! :p

    Looks like a good start to me. Add appropriate disclaimers and you are good.

    And I am not even a moderator! :D
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: My down and dirty math... Is it even close?

    My living with 5-800 wh is not really a trick. It should be noted that we use a propane fridge. If I was to start over, I would consider a conventional fridge, effectively doubling the PV and batteries. The point is the new fridges are very efficient, and reasonably priced. That said, propane is the better choice the less a cabin is used. For week ends or the occasional week, a lp fridge wins, but for full time the conventional wins nowdays. When I started, a conventional might use 2 kwh/day, and propane was $.30/gallon. and PV cost $10/watt. Nowdays, a new fridge might use .5 kwh, propane is close to $5 and Pv is $$1.50/watt.

    As for the other ways is really pretty simple. We have a very small house, we pump water directly out of the lake, and we have no TV. That said, we are well lit, enjoy radio through a good 12 vdc car stereo and good speakers. We have Sat radio, listen to internet radio using a Ipod touch system. Our ISP Sat modem draws 15 watts, that plus the router are on for most of the day. We use lap tops (and now Ipads) and we time shift the loads so that we generally charge them during the day, run them on the batteries at night. I am excited to discover that at long last, we will be able to access the net via a HSPA cell system with a monster Yagi antenna. That system will involve a mobil hotspot that will only draw 15 watts max, and eliminate the need for the router, making the total internet power draw,, 15 watts, down from over 30, plus the inverter loss,, which isn't much. So we will increase our speed 5 fold, and reduce our load by half,,, gotta love it!

    We also heat with wood, we have a couple of paddle fans, and we cook with propane. We also don't use any electrically heated devices, no toasters, hair dryers, no micro etc. (I do use a soldering iron, but also use a butane one instead) I have also built a propane toaster that uses little bottles that I refill.

    We also run the shop tools with the gennies. A few gallons of fuel per year,, maybe 30-50 total is much cheaper than trying to build a system to power saws, routers, planers etc.

    As I noted before, you have the advantage of starting with a clean slate, making your choices rational. Please do remember my rules however,, don't over estimate your solar potential, don't underestimate your loads, and realize that those loads WILL grow with time. Just to give you an example, we started with a simple car battery, and a couple of window mounted battery tenders, all to run the radio. Then we realized that having a 12 vdc light over the bed made a great reading light instead of the Kerosene lamp, then we added another over the cookstove. Then we realized we needed a real panel, and ran with a 53 watt Solarex for a number of years. That was followed by a couple of computer fans to get the heat moving, then by a Sat phone,, an inverter to power the lap top in the old days (no ISP in those days). Somewhere alone the line we bought a couple of T-105s and a real 120 vac charger, followed by a better SW inverter, followed by a few more lights, a paddle fan, then another, a fridge light!, water pump, Sat internet, cell phone, laptops, Ipads sat radio, internet radio etc.

    Like I suggested before, do your load calcs, and build the system around those calcs, building in a good size buffer.

    Tony
  • SolaRACSolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: My down and dirty math... Is it even close?
    So to use the OP's 576 Watt hours per day on a 12 Volt system we get:
    576 / 12 = 48 Amp hours used.
    48 Amp hours / 25% DOD = 192 Amp hour battery bank.
    192 Amp hours * 10% peak charge rate = 19.2 Amps.
    19.2 Amps * 12 Volts = 230.4 Watts.
    230.4 Watts / 77% efficiency = 299 Watt array.

    Wow.. I learn so much from this forum every day! :D
  • nnshardannsharda Registered Users Posts: 10
    Re: My down and dirty math... Is it even close?

    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage, as I only have one refrigerator (LG high efficiency side by side) and only do two loads of laundry a week....

    Am I missing something? I wish there was a way to do actual calculation of house power consumption rather than blindly accepting the power company calculation.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: My down and dirty math... Is it even close?

    For plug-in appliances, a Kill-a-Watt meter or similar is a great start.

    Run each appliance on the meter for at least 24 hours and get an average kWH/Day estimate.

    A whole house monitor or even some of the newer ones that have several inputs so you can measure specific branch circuits as well.

    52 kWH per day is the equivalent of running a load (or electric heater) at:
    • 52,000 Watt*Hours per day / 24 hours per day = 2,167 Watts @ 24 hours per day
    So, your average refrigerator will only use around 1-2 kWH per day, a desktop computer may use:
    • 200 Watts * 24 hours = 4,800 WH per day or 4.8 kWH per day
    So, you can see a simple computer on 24x7 can be responsible for 10% of your daily power.

    Add the heat from the computer (plus lights, fridge, cooking, etc.) and the A/C has to work even harder to move it outside.

    A clothes washer and gas drier may use ~1/4 to 1/2 kWH per day per load...

    My home, all natural gas, and cheap family of 4, will use around 250-350 kWH per month (or around 8-11 kWH per day)... Early on (no second fridge/freezers), I could get down to ~175 kWH per month. But kids are growing, they now have computers (laptops), etc...

    Changed most lights to CFL's (yea, ugly lights, but cheap to run and much less heat in an un-air-conditioned home in summer), energy efficient appliances. Use laptop computers most of the time (20-30 watts instead of 200-300 watts for a desktop), lots of insulation, double pane windows (original late 1930's home with zero insulation and drafty windows when I moved in 7 years ago).

    Power usage is a highly personal set of choices... And most of the guys (and gals) here are pretty cheap... So we look closely at the demand side before we throw solar panels at a solution.

    If you have never worked on reducing energy usage before with an older home, it is possible to reduce your energy usage by ~1/2 without altering your life too much (don't have to go Amish).

    If A/C is a major portion of your electric bill... You should look at attic insulation (R39 or better, weather stripping, double pain windows) and review your AC system and see if it would be worth installing a new Energy Star rated unit (high SEER).

    -Bill "not an expert" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,362 ✭✭✭✭
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage, as I only have one refrigerator (LG high efficiency side by side) and only do two loads of laundry a week....

    Am I missing something? I wish there was a way to do actual calculation of house power consumption rather than blindly accepting the power company calculation.

    I am with BB on the measure routine. Know your loads and you can start to make decisions on where to attack the problem. We attacked the problem backwards and added a large solar system first.

    One item that might be a concern is the pool pump. How big is it? How long does it run? A 2 hp pump can draw lots of power, I replaced mine with a VFD pump with a controller that is much more efficient and can be programed to run full speed for a short time to in floor clean and a reduced speed to stir and filter.

    Summer loads from AC can be huge. My 2500 sq ft house was built in 1997 and had the required 10 seer units on it. After adding the TED it was obvious that this was a major load, over the last 2 years both my 3 ton ground mount units were replaced with Trane high efficiency 2 speed units and added attic insulation to R50. That cut my consumption by at least 1/3, maybe more.

    Our system on a good day in May can generate 70+ kWh a day. With our utility net metering system we bank kWh early in the year to use in the major portion of the cooling season. That being said this summer our peak day was over 120 kWh yet we paid nothing to the utility until our Aug bill and then it was only $85.

    The key to all that is to understand your TOU rates and your net metering tariffs at your utility. Our utility will buy back our excess generation at year end for a credit on the account for the following year. This covered all our off peak usage, fees and taxes until Aug this year and our solar covered all our on peak usage. We study our usage often and look for ways to minimize usage and load shift as needed to control our costs.

    That being said we determine that we need a bit more solar as we added some new loads this year, a pair of Chevy Volt EREV cars. They can use up to 13kWh per charge. I found a lease deal for $1 a watt up front for 5 year term with a $99 residual payment at lease end. Lots cheaper than buying gasoline.
  • dBeaudBeau Registered Users Posts: 24
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I'd take a look at the pool pumps too (pumps?). When I bought my house it had a very noisy and over-sized pump that ran about 800w. Mostly because of the noise, I replaced it with a fancy new Intelliflow variable speed model. Most of the time it runs it's moving 20gph and drawing only 200w. If I turn on the spa and want the jets doing their thing (spa pump is shared with the pool) it will draw 800w or more depending on the flow setting.... and at 20gph, you can barely hear it run.

    One pump at 800w for 12 hours/day is nearly 1/5 your bill, and you have more than one?
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: My down and dirty math... Is it even close?

    NN,

    you must realize that my situation is atypical. First, my house is ~350 sq ft., about 1/10 the size of yours. In addition, we use a genny for some occasional loads that are not included in that calc, as well as propane for the fridge. We have no pool pump, which is a big deal, and no A/C which is a much bigger deal.

    As has been suggested, look at your line item numbers and I would posit that with a modicum of effort, and some investment you could save a bunch of KWH/day. For example, I would guess in your climate solar hot water is a no brainer. Perhaps more important would be a ground source or hot water (for pool or DHW heat) recapture heat pump system. Such a system gives two benefits. The first is it allows your A/C to work less hard, and it gives you hot water. Next, as has been suggested, look at the pool pump. Size, run time etc will have a huge effect on KWH load. Then one could look at insulation, especially on the roof, roof colour, shade trees, retractable awnings etc, all might have an effect on your A/C load.

    Wash in cold water, use a clothes line. (Why for example, would anyone in a desert climate use power to dry clothes when they dry on a line very fast?) Lighting, motion/heat sensors to turn off unused lights, CFLS (which are now very good light sources both in light quality as well as design shapes, unlike the ice cream cone lights of old!) High efficiency appliances, lap tops vs desk tops, turing off phantom loads etc. (a cable box or sat box might draw 25-100 watts even when "off", (600-1200wh/day!) power bricks at ~5 watts each, and many houses might have a dozen or more, another ~1kwh.

    Bottom line is all the little things add up, and making the small changes can have a small but significant effect on the whole, but generally cost little or nothing. Making the bigger changes have a bigger effect, but come at a greater up front cost.

    Good luck, and search out the ways to save.

    Tony

    PS, as Dave suggests, if you have Time of day metering (TOU) solar can work wonders in your costs. If you are paying top tier rates at the height of sun, then you can sell back at a premium and buy back cheaper. With some time shifting/load shifting you can game the system to your advantage, for example over cooling when the power is cheap, turning it warmer during the day when the power is expensive.
  • jagecjagec Solar Expert Posts: 157 ✭✭
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage....

    Except for heating and cooling loads, which are often the largest portion of a power bill.

    52 kWh/day IS pretty low for a large air-conditioned house in the desert with a pool (is the pool heated?), but all those things--"large", "air-conditioned", and "pool"--suck down tons of power. During the hottest month of this summer, AC alone accounted for 2/3 of my power usage...good thing my house is small!

    A swamp cooler, and solar hot water for both domestic and pool usage, would probably go a long way toward reducing your bills.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: My down and dirty math... Is it even close?

    Look at your pool pump... Frequently they are over-sized.

    Look at a new, efficient, smaller pump. A two speed pump or a VFD (variable frequency drive) controlled pump. Plus timer.

    -Bill "no pool I" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage, as I only have one refrigerator (LG high efficiency side by side) and only do two loads of laundry a week....

    Am I missing something? I wish there was a way to do actual calculation of house power consumption rather than blindly accepting the power company calculation.

    I'd say that it's all very subjective, what you might consider minimal most people on this planet would find extravagant. AC is a luxury that most don't have, same with a pool...etc. I'm not meaning any disrespect here, but let's be honest that we all have our own "luxuries" that we tend to view as minimum standards for enjoyable living (I have my own vices here as well).

    One of the beautiful things about going "off the grid" or even going grid tied, providing all or most of your energy needs by PV electricity, is the perspective change that occurs. When you have to start adding it all up and when you see the $$$ signs that each of those "little" things actually cost in the long run, it usually makes you look a lot harder at how to conserve when and where possible... possibly even going without certain items that suddenly don't seem quite as valuable.

    My wife and I have what we consider to be a VERY comfortable home, and enjoyable lifestyle in our off the grid home (about 800sq'). Our wants and needs slowly grow, and we are now consuming between 2KWH-4KWH a day (a lot more than we did in the early days on our system). All in all there isn't much more that we really need, although there are a few additions that are in our likely future (such as a chest freezer). I don't see our overall daily loads ever going more than 100KWH-150KWH/month.

    We made some sacrifices here and there, and allowed/budgeted for others here and there. Mostly we are really careful about double checking the energy consumption of every single item we consider purchasing, and almost always end up buying the most efficient version that we can find (or afford). It's not that hard really, but it is all a case of priorities... ours were greatly influenced by our small budget and where we most wanted to spend it.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: My down and dirty math... Is it even close?

    For a "same place" comparison:
    We have a cabin at the lake which is off-grid and a house in town that is on-grid. They are roughly the same size abodes with the same two people living the same kind of lifestyle in each one. The only significant energy consumption difference is that the town house has electric hot water and electric clothes dryer, two freezers, and a TV with satellite receiver.

    The cabin uses 2.4 - 3 kW hours per day. The town house uses 14 - 16 kW hours per day. Roughly 5X difference.

    The electric hot water and and dryer are going to go. Possibly one of the freezers if I can convince herself that we do not need two. That could be more difficult than anything else. :p
  • SevenSeven Solar Expert Posts: 292 ✭✭
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage, as I only have one refrigerator (LG high efficiency side by side) and only do two loads of laundry a week....

    Am I missing something? I wish there was a way to do actual calculation of house power consumption rather than blindly accepting the power company calculation.
    Dont feel bad, just four years ago we used 160+kwh a day. Almost 5000kwh in one summer month. That house was only 2800sqft, but there were 4 adults in it(2 of them all day) and two teenagers. We had a huge pool, an attic converted to living space, welders and compressors running for hours a day, half a dozen desktop computers and a server, a monster home theater( just turning on the amp dimmed the lights and had to have a seperate circuit ran for it),and rooms with fifteen foot ceilings.

    Last month the total was just over 1100 for the month. We downsized people and size, went crazy with efficient equipment, and no pool. We run Ipads instead of desktops. We are adding two feet of insulation to the attic this winter and are putting in new windows next year. We are planning on being in this house for a long time so most of the money will be recouped eventually. You just really have to look at the big, long term, picture.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: My down and dirty math... Is it even close?
    nnsharda wrote: »
    I don't understand how people run their houses on solar.

    I looked at my Nevada Power bill for September. I used 52 KW per day! That is 100 times what Icarus is using, and I am NOT wasteful of power. Heck, air conditioning at 83 degrees, gas stove, high efficiency lights and I am out of house all day working! Only pool pumps going during day. I don't even watch television, mostly work on computer at night like tonight....

    I live in a 3340 square foot house so I guess it's a little bigger than average, but that should not really change total power usage, as I only have one refrigerator (LG high efficiency side by side) and only do two loads of laundry a week....

    Am I missing something? I wish there was a way to do actual calculation of house power consumption rather than blindly accepting the power company calculation.

    actually, i can understand as your home is large compared to the average and you are in a hot climate. when you see 103 degrees i might see 93 degrees. given the exact same house in my area would mean it could be put down to 73 degrees to get the same kwh used. i'll be more comfortable than you though. most homes are 2000sq ft or less, at least around here and 2000sq ft is not small so your area is 50% to 100% larger than that of others so you are cooling like a house and a half to 2 houses with your home comparatively. maybe limit cooling to only occupied rooms would help or getting a swamp cooler.

    side by side refrigs also generally consume far more energy than other refrigs of the same size even if they say it is energy star. why this is i'm not sure, but i suspect the newer french door style is even worse as every new style can't be compared to other styles and are not applied to all refrigs on a cubic ft basis. this allows manufacturers to set standards in a strange sense.

    now in general i can say 52kwh in a day is high, but maybe not for your area and home size. other efforts seem to be in order like going with windows that have multi-panes. if you have 2 panes now then start going to 3 and put awnings or shutters into use to block solar collection. add insulation wherever possible, including the walls. it's possible your air conditioner is poor on its eer or has become defective by a coolant leak. there are so many things and factors that come into this that it would be difficult for me to pin it on just a few things. even all of you taking long hot showers rather than the preferred cooler short ones can greatly impact your cooling bill in a bad way. you also have a year round clothes dryer in solar that people in more colder climates can't do in the winter months and i hope you are taking advantage of it.
  • nnshardannsharda Registered Users Posts: 10
    Re: My down and dirty math... Is it even close?

    Thanks all. I guess we need to think of solar as an adjunct and look to reducing our overall energy consumption as a first step. Solar heating, window caulking, awnings and planting a shade tree seem economical and do-able, with solar panels etc when the price gets down a tad....

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