Question about kw and kwh

• dm27

  For a class our group is working on ways to reduce the electric bill for our school and an idea is to invest in a wind turbine. A problem I'm having is trying to figure out how big of a wind turbine we would need to eliminate the need for electricity from another source. The school uses approximately 440,000 kWh in one month so what size turbine (KW or MW) would be sufficient?
  
  This seems like an easy question but for some reason I'm drawing a blank, any help would be appreciated.
• vball10set

  http://www.awea.org/faq/wwt_basics.html
• Tiernan

  440,000kWh / 30 / 24 = 611kW x 1.10 (contingency) = 672kW ~ 700kW. So you may want to consider a 1MW turbine.
• vball10set

  Google is awesome,isn't it??
• OneBuckeye

  

  You should get an anaerobic digestor and burn the gas in a generator. It is used on dairy farms around the country. I'm sure there is enough crap in your school to keep it powered.
  
  http://www.mrec.org/anaerobicdigestion.html
  

  Anaerobic Digestion and Bio-Gas Top
  
  Anaerobic digesters convert the energy stored in organic materials present in manure into biogas. Biogas can be fed directly into a gas-fired combustion turbine. The type of turbine most often used for small-scale electricity production is the microturbine. Combustion of biogas converts the energy stored in the bonds of the molecules of the methane contained in the biogas into mechanical energy as it spins a turbine. The mechanical energy produced by biogas combustion in an engine or microturbine spins a turbine that produces a stream of electrons, or, electricity. In addition, waste heat from these engines can provide heating or hot water for use on farm.
  
  As a fuel, biogas composed of 65% methane yields about 650 Btu per cubic foot. Often used when designing systems for the anaerobic digestion of manure, these energy estimates can predict the amount of power production per animal. General estimates predict one kilowatt of electricity production requires five to eight dairy cows.

• dm27

  vball10set wrote: Google is awesome,isn't it??

  it is, I was actually on that site before and must of skipped over that specific information. thanks though
  

  You should get an anaerobic digestor and burn the gas in a generator. It is used on dairy farms around the country. I'm sure there is enough crap in your school to keep it powered.

  there is plenty of liberal crap, to bad that can't be burned
• Thunder70

  

  OneBuckeye wrote: You should get an anaerobic digestor and burn the gas in a generator. It is used on dairy farms around the country. I'm sure there is enough crap in your school to keep it powered.
  
  http://www.mrec.org/anaerobicdigestion.html
  

  Anaerobic Digestion and Bio-Gas Top
  
  Anaerobic digesters convert the energy stored in organic materials present in manure into biogas. Biogas can be fed directly into a gas-fired combustion turbine. The type of turbine most often used for small-scale electricity production is the microturbine. Combustion of biogas converts the energy stored in the bonds of the molecules of the methane contained in the biogas into mechanical energy as it spins a turbine. The mechanical energy produced by biogas combustion in an engine or microturbine spins a turbine that produces a stream of electrons, or, electricity. In addition, waste heat from these engines can provide heating or hot water for use on farm.
  
  As a fuel, biogas composed of 65% methane yields about 650 Btu per cubic foot. Often used when designing systems for the anaerobic digestion of manure, these energy estimates can predict the amount of power production per animal. General estimates predict one kilowatt of electricity production requires five to eight dairy cows.

  Saw that on an episode of Dirty Job. Pretty interesting stuff..
• fan_from_texas

  Is the goal to save money or to be green? If it's saving money, a wind turbine may not put you ahead in the short-run. Depending on size and the timeline you're looking at, there can be a solid payoff in the long run if you're willing to partner with someone who has the expertise to make it work.
  
  A typical capacity factor for a wind turbine is 20-30%. You'll want to scale your turbine in such a way as to maximize the benefit at the retail rate without having excess. Are you doing this in Ohio? It might be worth looking into the Ohio net metering regulations, as that will allow you to offset your cost at the retail rate rather than the avoided cost rate. Off the top of my head, I believe net metering in Ohio doesn't permit net annual excess, and you'll want to check with the local utility to determine whether you can roll over monthly/annually. That's going to affect the size of turbine you want.
  
  A few additional thoughts:
  
  *How are you planning to finance this? There are tax-advantaged ways (30% ITC, PTC, etc.), but a government entity like a school won't have the tax appetite to swallow them. On the other hand, a tax-exempt entity may have bonding power and can issue tax-advantaged debt to cover this rather than covering it out of pocket.
  
  *My recollection is that Ohio is a community choice aggregation state. You may be able to get together with other schools to buy renewable electricity in bulk under the aggregation statutes.
  
  *It may be easiest to contract with a third party to install, own, and operate wind turbines or solar panels through a stnadard PPA. It may also be possible to pre-pay a portion of that to provide for the upfront cost, though you'll need to check with a lawyer to ensure.
• fan_from_texas

  Tiernan wrote: 440,000kWh / 30 / 24 = 611kW x 1.10 (contingency) = 672kW ~ 700kW. So you may want to consider a 1MW turbine.

  You want to be careful, though. Check the wind capacity ratings for your region. Also, a school's load isn't going to be consistent--it'll be higher during the week, lower on weekends, higher during the year, lower during the summer. If you simply divide the total load by the expected availability, you'll have excess in some periods an a shortfall in others. Depending on how electricity is priced in your area and whether it's net-metered, you can end up paying substantially more than you would anticipate.
• Tiernan

  That's the purpose of the .10 contingency, which is accepted design swag. You have to design for max. capacity and then be able to sell back surplus to the local distribution grid.
• OneBuckeye

  

  Another idea... purpose going to school during off peak hours... electricity will be cheaper!
• gorocks99

  

  Or, propose demolishing the school in favor of a park. Do the rules stipulate that the school must exist in this new reality?
• fan_from_texas

  Tiernan wrote: That's the purpose of the .10 contingency, which is accepted design swag. You have to design for max. capacity and then be able to sell back surplus to the local distribution grid.

  Right, but given a 20-30% capacity rating, is a .10 contingency going to cover it? Even if it would, there are some big issues with selling back surplus to the local grid. If you're selling it directly to entities to use (i.e. a retail sale), you may be a state regulated public utility and have to file for rate approval, facilities approvals, etc. That can cost untold thousands of dollars annually.
  
  Or if you're selling it back in wholesale, then you're regulated by the Federal Energy Regulatory Commission (FERC) as a wholesale generation facility under the Federal Power Act (FPA). Depending on the size and type you're dealing with, you can self-certify as a QF and avoid much of the regulation (MBR/PUHCA, etc.). But then you have to contract with the local utility under PURPA to figure out what the avoided-cost rate is, or whether you're selling directly into the wholesale markets (and I believe Ohio is part of the Midwest ISO, rather than PJM).
  
  In most states, you can't simply sell excess back to the grid without dealing with a huge mess of energy regulatory issues that can cost thousands of dollars to deal with. When you're dealing with a distributed generation system as small as this one (1 MW), the transaction/regulatory/legal costs can often outweigh the benefits for all but the most sophisticated of parties.
• fan_from_texas

  If your goal is simply to save money on electricity costs, energy efficiency and weatherization usually generates the biggest "bang for your buck." Check with the state public service commission or local public utility to see if they have incentive programs or can help out. There was a lot of stimulus money available for those type of programs, though I believe it may all be spent by this point.
• dm27

  This is definitely going to be a long term investment but I believe it is one that can really pay off. To save costs a lot has been done to make the buildings more energy efficient but because the school wants to be "green" I feel like they need to draw electricity from a renewable source. The school is in NW Ohio which according to the wind maps I found is a marginal to fair classification for wind power. From Sept 22 to Oct 22 of this year the school paid $32,000 in electric costs. 32000*8 months (school in session)= $256,000. I'll add $44,000 (guess) for the summer months for a $300,000 bill for the year.
  The AWEA says that it costs approximately $2M per MW so a 1.5 MW turbine would cost $3M. I haven't thought to much about financing yet but I roughly guessed it could be paid off in 10-12 years with current interest rates. It's not cost effective in the short term but for a school that claims to tout it's going green I think it's an investment they should do.
• fan_from_texas

  You need to consider the cost of the debt, as well as O&M and regulatory issues. Is the school itself going to service the project and perform the maintenance? Are they going to handle interconnection to the grid?
  
  AWEA's estimates are generally pretty good, but they're geared toward sophisticated parties who do this a lot. You absolutely need to structure it in a tax-advantaged way, as that's the largest driver of renewable investments right now.
  
  The interest rate will depend on the financing structure. How are you calculating a 10-12 year payback? It's doable, but if you're serious about going forward with this, you would be absolutely well served by talking to someone who has gone through it before. It's a massive investment with some great tax breaks/energy breaks, but you want to make sure you're doing it correctly.