Batteries and Renewable energy

"Would it make any sense to use a forklift battery charger"

milk999 - If it did it would make even more sense to use 5 or 10 of those in a row. (the surplus could be sold to a neighbour)

Remember : The watts out (voltage out x Amp out) must be more than watts in (voltage in x Amp in) to be of any value.

Unfortunately you would need some extra standard (non renewable) power somewhere to just cancel out the the additional losses added by all the power "creating" equipment.

My grumpy contribution for this month.

As a rough guide.......

For 220V 30A (6600W) average over 24 hours, 2 days capacity down to 40%. 24V inverter, 90% inverter efficiency ~= 24V 302A (7248W).

Roughly 36,000 Ah at 24V = 3000 x 2V 800Ah batteries (in a series parallel arrangement).

If using wind, as a rough guide with a wind utilisation factor of 10% of the day, 90% conversion efficiency, then you would need an alternator that can produce at least 332A at 24V (79kW)

If using solar, as a rough guide you would need over 2600 x 12V 125W solar panels.

As a rough guess you will need to shed some of your load.

Suggestion at this point is "Go back and check your measurement and the maths."

Even assuming US supply of 110 volts (ac), an average demand of 30 Amps gives 28,512 kWh per year (not 14,000 per your initial statement.) and that is a relatively large demand for a single residence.

You are talking about a significant capital cost for the hardware and these numbers really need to be checked again. Also, have a look at the size of the array of solar panels that you would need.

If you are really drawing that much power, then there may be alternatives to eliminate usage (like insulation, double glazing and so on) rather than build a big enough system to feed the monster.

I agree with 'Just an Engineer'. Your numbers don't make sense. 30 Amps @120V 24 hrs a day would give you something on the order of $350 a month electric bill. That's over twice mine in the hottest months (when most of my energy runs the Air Conditioning to keep my house cool so the wife can sleep days and work nights). Its about seven times my winter electric bill.

In addition to the usage, a couple of basic concepts:

1. Power is voltage x current. 120 V * 30 Amps is 3600 Watts, or 3.6kW. To get 3600 W at 24V without conversion losses would require 3600/24= 150 Amps.

2. Every energy conversion has significant losses. Although they keep improving inverters, they still waste a significant part of the incoming DC energy, so you are going to need between 200 and 300 continuous Amps out of those batteries! To charge the batteries and run the house at the same time, double that. You'll need a 10kW wind machine to run this system with steady winds, and bigger if the winds are intermittent.

As 'Just an Engineer' said, your first task should be to work on cutting that energy usage!

OK, that voltage roughly doubles all my power and cost calculations. On the other hand, it looks like your 30 Amps is more like a peak than an average, so perhaps not.

If you are using a compressor type refrigeration unit, you might be able to reduce your power consumption considerably by adding an evaporative pre-cooler.

For that size of operation, you definitely want MUCH higher than 24V in your battery array, to keep the current levels down and reduce or remove the need for a major step-up transformer. Remember that the peak voltage of 220V AC is around 350V.

Of course there are some major safety issues with this size of system, regardless of which voltage is used - You definitely want a professional to do, or at least supervise, this installation.

Batteries are not the way to go for anything longer than 15 minutes. You will need a diesel or natural gas generator. You may be able to feed it with the methane produced on the farm. It has been done before. It might not be financially viable simply for the energy savings but if might be if you take into account the ability to ride through a utility network failure and keep the production running.

You certainly do not want to have to maintain hundreds of batteries. This could be dangerous and could turn into a disaster if a fire ever happened. Batteries rooms follow very specific rules that you would need to comply to.

Marcot's suggestion of using available methane is excellent. I would however question your use of 24V as the battery system voltage.

Most off grid or even grid-tie systems now use 48V since losses are less. All the big names and quality equipment suppliers now offer 48V equipment. Battery voltage is simply a question of more cells in series and less in parallel. The reason for going to higher voltages is that losses are less at 48V than 24V and way better than 12V.

Apart from the obvious saving in large diameter DC cables due to the much reduced current for the same wattage, efficiencies are usually calculated as a percentage of total voltage current or wattage as the case may be. Most sine wave inverters run at 89 - 90% efficiency when running close to their rated loading. But there is a curve involved and once you drop below 60% this curve makes big inverters look very inefficient when lightly loaded. This is equally applicable to MSW inverters, but for your milking parlour - do no teven contemplate going that route.

My suggestion would be to to have a system that permits you to use two or more inverters running in tandem for your milking parlor and huge loadd; then back of to one or two or a smaller inverter when only driving lighter loads for the domecile. In Europe and Ireland my recommendation is Victron brand from Holland. They have extensive experience with of grid or grid tie systems. see www.victronenergy.com

Don't go with Mastervolt. By comparison they have junk. Their products are outsourced and mostly made by third parties.

If you go with an internal combustion driven genrator to drive the charger use a generator of only slightly more capacity as the output of the charger for the battery bank. You may not need a wind turbine as large as you expect. If your winds are fairly steady the wind turnbine runs 24/7 while your loads are intermittent and very low during the night.

Any house using 14000 KWH pa is one heck of a large house.

You don't say how many cows you have, but I've seen dairy farms run entirely from methane produced from cow manure. Basically, you have a pond that the manure is washed into. A cover over the pond collects the methane as it's released. It can fire heaters directly or run a generator to provide electricity.

You appear to have forgotten that Lead Acid batteries are only about 70% efficient (from memory), this means that you will need aproximately 30% more energy to actually recharge them.

Even battery chargers are nowhere near 100% efficient, so reckon with further losses there....somewhere between 70-90% efficient at a guess......

Your house/farm uses a huge amount of electricity per year.....

Therefore it would appear to me that you would be losing around 50% of your inputted roughly speaking, so unless you are going to install a fairly big windmill (or other free source of power), driving a large alternator to charge the batteries, I do see some problems, especially when the wind drops....

Sorry to be so negative, but you should factor this in most carefully to the whole experiment.....

Running a house off grid is more than feasible, it's being done everyday, all over the world.

I run two houses from one 12V 1100Ah bank. Charging is from a solar panel array of 750W. I would prefer to run at 24V but my system has grown this way and short of a disaster causing me to start from scratch, it isn't worthwhile to change.

We run a 7kW diesel generator for major loads, washing machines, dishwasher and well pump (to header tank). This needs about one hour summer and two hours winter runtime/ day. Generator reject heat is recuperated into central heating / hot water system.

It doesn't make sense to me to spec the solar/ inverter system to peak loads; it requires too much investment for a small gain.

Refrigeration is butane…no electric! ALL lights are low energy compact fluorescent. I may start changing to LEDs in the near future.

I don't share "ELNAVS" Taste for Victron products. I work with both brands, and those from the US/Canada (Xantrax). And I know where I would put my money.

All three brands produce equipment ("combi" or combination charger/inverters) that will look at the system load when running a generator and reduce the charging so as not to overload the generator output. Current units go one better in that they will revert to inverter mode in sync with the generator boost the generator output. This has a massive boost to the generator output efficiency as a smaller generator can be used which is then running at a higher % load without needing so much over-capacity to allow for peak loads.

If Milk999 is serious about doing this he should get several quoted projects from specialist suppliers who can show some examples of their systems. At the capital cost he will need for a commercial installation he could make some very expensive mistakes if he relies on just one supplier, as alternative energy people are notorious for whacky ideas! A neighbour, also of grid, has been sold a 37kW generator for a single-family house! His naivety and wallet size were self-evident!

Best of luck with the project.

Chas

Of course one can power any home without the grid. One should realize though that creating electricity without burning anything is expensive and difficult; it takes essential skills and determined consistency to install and maintain. Few are qualified. Understand this before hanging photovoltaic or erecting a wind turbine tower and the like. The battery bank is the biggest pain in the butt

And I agree with Just an Engineer that we consume enormous and excessive amounts of power unnecessarily . . . unwittingly. So, consider first the many ways to eliminate your power and consumption needs. The most power consuming is heating or cooling anything. So first figure how you can eliminate having to use electricity to heat or cool the home.

I believe the most natural and efficient ways to do this to tap the temperature of subsoil earth. It's always within 15 degrees F of the human comfort zone. Building partially underground or berming the residence into the side of a hill is one way; another is to use a slab to act both as a thermal mass and to store heat (or absorb heat) stabilizing the building temp. Thermal masses like fireplaces (heat providers) or stone walls, cisterns and trombe walls absorb and retain heat. Use flat plate collectors for hot water and run it through the slab with PEX tubing for radiant heating if needed.

Google "Passive solar." Orient the building toward the solar south to capture heat, or orient away from solar south in hotter climates. Deciduous landscaping provides shade in the summertime. South facing windows should be shaded overhead considering solar inclination bringing in more sun as it declines in winter. Solar facing window area must be limited by established conventions of passive solar. Glazing should be doubled and of the highest (affordable) technology to limit heat exchange. Natural light should be maximized to limit the use of power for artificial lighting even when provided by LED or compact fluorescent.

Insulate and seal the house well and measure transpiration with a vacuum door test. Make sure ventilation is adequate with heat exchanged recirculation. Consider natural convection; empower circulation of air with a solar chimney, or cupolas and assist the process with thermal mass. Consider prevailing wind currents in the placement of windows and doors. Use air locks (mudrooms, breezeways, enclosed porches).

If motors are employed such as for well pumps, consider the most efficient load or process for the motor design as well as the efficiency if the motor. Consider Energy Star appliances which squeeze the most efficiency out of any process.

Compare energy efficiency as well as prices in appliance or electronics value. Compare the time that an appliance is used as well as the current when comparing power consumption.

If all these measures were to become convention, pollution and the use of fossil fuels could be cut in half immediately. They can drastically reduce the use of power and a small energy source could easily achieve the Net Zero home.

Oh, and by the way, did I say Inflate your tires?

cornelius

First count your money, this will take a lot to get set up and quite a while to reach a break-even point so you will actually be profiting. First do the insulation and while you are in the walls do some rewiring. I would suggest an underground house or earth-sheltered house with geothermal cooling and heat pump. That would be seldom used due to the tendency of the house to stay between 55 and 65 degrees unless heated. It is likely that LEDs will be the way to go for lights at night and Solotubes during the day. That could reduce the number of windows.

The problem with wind power is that it doesn't always blow. Solar power is better, but there are times when the sun doesn't shine. By using a small efficient steam engine to power a generator you could use methane, natural gas or propane which will burn as a clean open flame. It would only need to be used occasionally when you needed 220V electricity or to recharge the batteries because the other methods failed. A 20 hp steam engine, 2 cyl. or 4 cyl. double-acting compound condensing type is best and the waste heat can be used to heat water or the house.

Look at all that and count your money again. Will it be cheaper to do the insulation and other energy saving things or to stay on the grid? Some things are interesting to do, are things you want to do, but they are not cost-effective over the period of time. If you took all the money your wind, solar and batteries would cost and invested it at about the 10% return on mutual funds, when would you have total return on investment and be making a profit, then compare to how long it would take to save enough money to repay the investment and begin getting a profit. I'll bet the mutual funds will win, even figuring in taxes. I hope you are right though, because I would like to do it myself, just no money to do it with.