System for my daily usage - am i correct in doing it this way?

[Roly SA]

Hi All

I am looking at the possibilities of changing my grid-tied household to self sustaining alternative energy. Our local energy provider is currently unable to sufficiently supply the whole country, and we have are experiencing quite a few black outs. As a result i had to replace a few appliances and ramp up my surge protection in the home.

Now i have used a calculation table which i found online, and i saw that at peak times, my average electricity usage is around the 8kWh range. This is after work when we are all at home, watching tv, doing laundry and cooking. This 8kWh value includes the fridge, about 800watts worth of lighting, 1 tv, 2 computer/laptop, kettle, washing machine, microwave/stove, as well as our hot water heater (or geyser as we call them here in SA). I have added extra usage to cover for the "start-up" draw of the fridge and the water heater.

At night and during the day when we are all off to work, the only appliances using electricity is the fridge and water heater, as well as the tv thats on standby mode, and the microwaves digital clock. The last 2 devices usage is nearly negligable. The off peak usage is around the 3kWh mark, still with the extra added "start-up" usage in place.

If we have a peak usage for about 5 hours a day, and off peak for the remaining 19 hours, we can calculate the average as :

8. kWh x 5h = 40kWh peak
   
3. kWh x 19h = 57kWh off peak
   
   

average for the day = (40 + 57) / 24 = 4.042kWh

This is for a normal week day, in summer, when we are not using any electric heating.

So what system of battery/inverter will be sufficient to provide for my household with the estimated peak and average daily usage? Bear in mind that we can change the lightbulbs to more energy efficient ones,and the laundry can be started in the morning before we leave for work, in order to bring down the maximum peak usage.

Also what charge is needed to sustain the batteries in order to provide for the days usage?

As i am still new to the whole alternative energy way of life, any help with batteries, inverters and generation will be much appreciated?

Thanks

Roly SA

[fungus]

First, before you do anything else;

Conserve.

The 800w of lighting stands out at me, this is a pretty huge amount and I'm not sure (?) if its needed at all. If they are downlights you can get CFL's that fit into them or with normal lights of course there is the normal CFL's.

Another thing, the water heater being left on all day while you're gone, obviously it isnt needed at that time, there might be a timer switch built into it you can activate or get one installed?

Normal vertically oriented fridges can take a lot of energy as every time you open the door the cold air flows out, a chest fridge or freezer with added thermostat can be much better.

A nice thing to have around is a plug-in energy meter, commonly sold under the 'Watts-up' brand, this will tell you what the appliances actually use not just relying on the nameplate.

You might want to look into direct solar water heating, it doesnt need to be a hot day just some sun for them to work, even preheating the water before it goes into the water  heater can make a big difference.

It would be pretty hard to sustain that 4kW constantly with purely RE , you'd need a considerable investment, best to cut down as much as you can and then reconsider.

[DamonHD]

Hi,

At first glance you should not have divided by 24 and your final number should be kW not kWh and your energy use is HUGE.

However, I think that you are mixing kW (instantaneous power) and kWh (cumulative energy usage).

On your electricity meter see how many kWh (units) you rack up per day, and work to minimise that figure.  Little else matters (unless you have time of day metering).

Only when you can't make much further reduction in your daily usage (by converting all lights to CFL or LED, turning off things when leaving the room and not using standby, etc, etc), then consider sizing your RE system, and the units-per-day figure will guide you well for your electricity component.  If you have grid then you'll find RE to be relatively very expensive, so it's only realistic having eliminated waste first.  And a nice big unobstructed south-facing area such as roof or wall is handy.

My family home and home office uses about 7kWh (7 units) per day of electricity, which is quite good for the UK and would be exceptionally low for the average US homr for example.  But because I don't have south-facing roof I'm unlikely to be able to sensibly generate that from solar PV (more below).

Where possible avoid heating by electricity which is expensive in CO2 terms, and usually in money terms (about 2 to 3 times more per kWh than mains natural gas here in the UK).  Consider solar domestic hot water (SDHW) to use the heat from the sun more directly without inefficiently converting to and from electricity.

Have a look at a few of my pages for what I have done and hope to do:

http://www.earth.org.uk/saving-electricity.html

http://www.earth.org.uk/milk-tanker-thermal-store.html

http://www.earth.org.uk/towards-a-LZC-home.html

Rgds

Damon

[Roly SA]

Thanks for the replies so far.

Firstly i am aware that i will have to make changes to bring down my consumption of electricity. The water heater can be switched on about 2 hours before bath time and switched off straight after.

Most of the lighting can be changed to low energy ones. We are already in the habit of not leaving any unused lights on, and will switch the stand-by devices off as well. By also doing things like cooking, or laundry at different times, the maximum consumption value will also drop. Also, the startup consumption for the fridge is only for a few seconds until the compressor is running, so will only draw more power for that time, then return to normal operating consumption. The 8 kWh i calculated is absolute worst case scenario. By conserving in above ways, plus extra ways, i guess it can be brought down to about 4 to 5 kWh.

I assumed that if all the appliances use about 8kW at any given time at peak, then after 1 hour they would have used 8kWh. I multiplied the amount of hours i view as peak consumption by the maximum value, and the off peak hours with the minimum consumption value, then added them to give me the total kWh for the day, then devided by 24 hours to give me the average kWh.

What should i base the system on, the average kWh per day, or on maximum usage? I think that it should be able to supply my home sufficiently during peak hours, then get recharged to full capacity during off peak times. So the charging should be able to exceed the off peak electricity usage, and sufficiently supplement the battery supply during peak hours.

What battery voltages will i be looking at with the above electricity usage? As mentioned before, the appliances use 240V.

I know it will be expensive to setup the system, but im sure that in the long run, the saving on energy costs, and not replacing any appliances due to dodgy supply surges, will outweigh the costs.

thanks again

[TomW]

Roly;

The water heater can be switched on about 2 hours before bath time and switched off straight after.

A nitpicking point:

You can switch it off just when you start the shower / bath then it will not be trying to heat the incoming cold water as you use the hot. It all adds up and once you get that figured out you might be surprised where you can conserve energy use.

Cheers.

TomW

[zeusmorg]

 First step in going to RE electricity is to save as much energy usage as possible, then determine your needs from that, Second analyze your resources to see what you have available to convert to electricity/useable energy.

Then it's time to design your system. 48v dc systems make the most sense, since wiring costs are held lower.

So what resources do you have? Good wind? Good running streams? Lots of trees? A good site to locate solar heating? The most efficient RE is Solar Domestic Hot Water and especially if you have an electric DHW system now. The most expensive is probably Solar electric panels.

 A mixture of systems make it easier to "get over the hump" when one resource runs low.

[kurt]

i think you are still confusing KW - kilowatt /instantaneous power usage, and KWH - kilowatt hour /energy used over time.  the total of all your loads draw is measured in KW the amount of electricity your loads use in a hour/day/week/month is measured in KWH

[thirteen]

It doesn;t work for everyone but maybe an ondemand water heater might help. To install one you might even get a tax break.  Also if you have different sources to charge an off grid system that could help you get off grid or possibly even use a split system. A wind, solar or hydro while you are gone during the day might work. It depends on the usable power source available to you.

[Roly SA]

OK, so what should i be looking at in order to select a battery and inverter setup? Instantanious power usage in kW, or energy used over time in kWh?

I think that the instantanious kW value will give the maximum power required from the inverter/battery system, is that correct?

Can anyone give me some info on how to size the battery/inverter setup? I cant find anything in the boards to enlighten me with regards to this.

Thanks

Roly SA

[Roly SA]

Looking at the area i am in, solar will be the best bet, since we have loads of sunshine. A solar water heater system is also a good idea, as my house's roof has quite a large area thats facing to the sun.

As there are quite a few trees around, wind power will be a mission to get right, and my region is not a very good wind area.

But for now i am more concerned with what battery/inverter setup i can use. Can someone maybe give me an explanation on how the whole battery to inverter setup works? Guess this is asking a lot, but anything will help, even links to a post that might explain.

I have had a look at the board, as well as on the web, however i cant find an explanation on how exactly this works.

Any help will be appreciated.

Cheers

Roly SA

[DamonHD]

Daily units (kWh) used and number of days you want to be able to coast without sunshine will give you necessary numbers to compute required battery capacity (also remembering that you can only use ~50% of the nominal capacity of lead-acid without risking damage).

Yes, max instantaneous power will help you size the inverter.

Rgds

Damon

[zeusmorg]

 There are several options you could choose with installing a PV RE system. you could have a separate system with PV panels, using a charge controller to charge your batteries. Then an inverter to power separate systems in your house.

 Or you could choose a grid tied system with a battery backup, which may be your best option. Grid tied matches the frequency of your inverter to grid power, and supplements it when the grid is up. When the grid goes down, you have your battery backups to rely on.

When you're collecting energy, and the grid is up, it feeds excess to the grid, allowing you to recoup some of your costs of power (basically the utility is buying your excess) This option is not available to everyone, it would depend on whether or not your local laws/power company does this. Some power companies will give you a credit on power sent back, some won't. Some even will even give you money to help build the system.

There are also grid tied systems that do not use battery backups, but these go down when the grid looses power, also so that one wouldn't be a good option for you.

Other components to know about:

 AC/ DC disconnects: Located between various components of the system, should also be fused for protection.

 Battery types: Use deep discharge lead acid for the best reliability, if you attempt to use standard auto(aka starting batteries) they will not last long.

 System Meters: to help see state of charge and to help indicate efficiency of your system.

 Backup generator: This is when all else fails, your battery bank has become depleted, there's no sun and no grid.

 Kill-a-watt meter: for analyzing individual electrical component energy usage.

 Solar PV is probably the most expensive of all the RE systems available, so on a bang for buck philosophy, it's better to reduce usage, and use non PV systems whee you can.

Solar water/space heating, gas/propane cooking and water heating.

INSULATE and Conserve wherever you can first. Replace your incandescent bulbs with compact fluorescents big savings...Turn off everything not in use especially during a power outage, run only what is necessary! This will keep your system costs down.

[HomegrownPower]

Hey man just the timer thing you mention on the hot water will cut his use a lot not mentioning turning off a few lights . We cut our monthly bill by 25 to 30 bucks doing just that one thing . And surprizenly after learning the practice of doing it this way ( get the kinks out )  you get perty good at conserving hot water through the day and have it throughout the day anyway just as if it was on .

We have a timer on ours a very inexpensive fix thats less than 50 bucks with added insulation to boot . We kick ours on for an hour in the morning and an hour in the evening . Kids are grown so that helps we just set it to kick on about 30 minutes or so  before we expect to be using it .

And if something comes up and you need extra hot water you can always manualy kick it on or reset it to your needs .

More to conderving than one might think possable .

[elvin1949]

Roly SA

 No one here can size your system for you,because

we don't know everything you are using.

 You are the only one who can do that.I don't think there is an inverter big enough to start all of your loads at the same time.By the way what are your

heating and cooling systems running off of.

 What loads can you get rid of.What loads can you

make more effeicent [besides lighting] IE.TV_ microwave_coffee maker,put them on a power strip.

 I know i have missed a lot,but if it has a clock or a remote put it on a power strip.

 Things you can't run on RE electric stove,hot water heater,central air conditioner.WELL you can but it will cost a lot more money than i will ever see.

later

Elvin

[spinningmagnets]

I am still learning, and studying for a retirement RE home.

Rather than spend a lot of money now, when your design needs may change soon, perhaps for the next year or so you might install a simple backup power system, just big enough for a TV and some lights when the power goes out.

A small 48-volt battery pack (four 12-volt deep-cycle) that uses the municipal 120 VAC to keep topped off with a smart charger.

When the power goes out, an inverter will convert the 48 VDC to 120 VAC to power the lights and TV. Get a propane barbeque for cooking.

If you later install a comprehensive RE system, the small back-up system will still be useful, or even easy to sell, if you need to.

[ghurd]

I have to question the logic in that.  Simply by the cost.

"simple backup power system, just big enough for a TV and some lights when the power goes out" sounds like 12V to me.  Easy to do the whole system for $500 with RE (solar).

What is the cheapest, reasonably efficient, 48V inverter suited to a TV and some lights (250W?) load?

What is the cheapest 48V smart charger?

Then there are the issues with batteries, etc.

Compare the 48V cost to the 12V cost.

G-

[spinningmagnets]

Thanks, Ghurd. I must confess I have not looked up any numbers yet. I'm trying to figure out how I can "get my feet wet" (probably not a good electrical metaphor, meybe "get my fingernails dirty"?) without buying a whole system in one lump.

I don't have any hydro, and although it's windy here, I can't have a windgen in the city. There ARE homes here with solar water pre-heater panels and solar PV on the roof. Subject to the various city building codes. (easier to understand Chinese calculus, or a womans mind)

Since power went out in a lightning-started brushfire recently (common here) there is now interest in back-up systems (which can be looked at as the first half of an RE starter system).

Based on your experience, would you please post some links, prices, and part #'s of well-made inverters/smart-chargers if you were putting together a 12-volt or a 48-volt starter back-up system?

[Roly SA]

Thanks for all the responses guys. Let me ask more direct questions for now:

1. - If i have an appliance that uses 240V AC, do i need a 240V battery bank connected to the inverter?
   
2. - How would you calculate the total Amps of your battery bank?
   
3. - I understand the fact that your input charge must exceed the total voltage of the battery bank, otherwise no charging will take place. What current/amps is needed for charging the battery, more or less than the battery's rating?
   
   

Once i have a better understanding of the above questions, i will formulate more and post them again.

Cheers

Roly SA

[vantravlers7]

No, you dont need 240 DC "in" to get 240 AC "out".  BUT getting 240 AC volts out of a DC system (any dc system) is asking alot of it.. generally 240 volt appliances are very very heavy users.. well pumps, dryers, water heaters, etc.  

   The inverter itself controls the "out voltage".  You buy the inverter that you need.  

   What you are hoping for is a system that can run your house the way things are for less than what you pay for electric now.  That nothing has to be changed, except for bolting some sheets on your roof and some batteries in somewhere and away you go.  Unfortunately, this is far fetched.  Alot of the responses here were about conservation FIRST.  Before you even CONSIDER and RE system, you need to conserve.

   Why?  Because: you will require a MUCH smaller cheaper system if you can get your usaege lower.  It will determine "if" you even want to conserve- you HAVE to conserve with a RE system.  Because wasting energy at your current rate is just silly- its SO easy to conserve.  Because its flat out money not spent on a non renewable resource.

    Wrap the water heater in insulation, insulate the lines, too.  This ALONE can mean a 33% reduction in your useage.  (wow is right... ten bucks worth of insulation can save you hundreds of bucks a year).  Cut the water heater from "scald you" to just barely warm enough to shower with at full hot position.  STOP using the dryer.  Sell it.  Put in 11- 13 watt CFLs.  Unplug things that are "warm" when they are off (digital cable box comes to mind).  There things will bring your overall usage down by something like 50%, maybe a little more.  When I did these things, my electric usegae went form 10 kwh per day to less than 1.

   Do these things, then recompute your needs!  You'll be MUCH happier with the cost of the system.  As it stands now, the system you need would run at minimum 20,000.  Probaly more like 30k.  

[Roly SA]

I do want to conserve. I have already implemented a few methods, such as switching the water heater on 2 hours before its needed, as well as dropping the water temp from 65 to 50degrees celcius. I used a few rolls of tin foil to wrap around the heater as well, and covered that with a thick wool blanket to conserver the heat.

I have changed about a 3rd of all the lights in my house to low wattage flourescent ones. They take a while to get to full brightness, but thats no biggy. They are quite a bit more expensive then normal globes, so im doing the swap out in phases.

The reason i keep talking about 240V is that its the voltage that our energy supplier generates. Currently they cant support our countries power needs, due to poor planning on their part, so all of us are trying to cut back on power consumption to alleviate the situation a bit.

As all our appliances are set to work on 240V AC, it wont be easy to replace them with lower voltage ones, so i dont list that as an option.

This posting originally started with me asking (not necasarily in the most direct way) how to calculate the battery bank and inverter requirements to sustain my house over the 24 hour period.

As their are times of peak usage, and times of low usage, i thought that the system only had to cope with the maximum usage for a minimum of the hours required, then get recharged to full levels during the off peak times.

I will mull this issue over in my head untill i can formulate it better.

Thanks for all of your input so far.

Roly SA

[ghurd]

For a starter back-up system?

I don't know of any 48V stuff.  It's all big and/or expensive.  Not ideal for a starter back-up system, IMHO.

For 12V inverters and smart-chargers, starter and back-up stuff, I like Vector. Cheap, pretty efficient, more than reasonably reliable (but I would have 2 inverters with exposed fuses until you realize what CAN'T be done), good selection, and the market is flooded with them.

G-

[spinningmagnets]

Thank you Ghurd, Your posts from the archives have been very useful to me, and I trust your opinion.

[ghurd]

Oh, and make that the RED Vectors.  (or the marine colors)

NOT the silver Sam's Club or Target versions, or "Power On Board" or a part number starting with POB.

I have not yet decided about the orange plastic type that sometimes carry the Black and Decker name, or both names, but I don't have a good feeling about them.