2.07.2009

sustainable energy project: providing Kyle O'Keefe with a working solar system

In order to complete the Ridge to Reef program, we must each complete a final project and present it to the class. Patrick and I will be designing and installing a solar energy system for a home currently under construction. After one week of work, we have consulted with Kyle twice and come up with a good estimation of his energy needs and a quote for the price of a sufficient system. Most of the supplies are already on the farm, but we are working through this process from start to finish in order to gain experience.

On Thursday, we had a second consultation with our client, Kyle. Before the meeting, Patrick and I had to prepare by sizing and pricing a system based on the things he had told us in our earlier consultation.

We knew that he needed an AC (alternating current as opposed to DC, direct current) system that would provide power for:
  • a ceiling fan during hot summer nights
  • a laptop computer
  • a CD player
  • compact fluorescent lighting (with future expansion for front porch and compost toilet)
  • halogen lighting
  • cell phone charger
  • possible electric single-burner stove
We used a sizing worksheet copied out of the Solar Living Sourcebook to calculate his energy needs. Based on average wattage for the above appliances and electronics, we guesstimated that he would use 936 daily watt-hours. This amount of energy would demand (based on St. Croix's solar climate) three solar panels providing 19.5 amps of energy to a battery pack of six batteries providing 36 volts. He would also need a sufficient charge controller that could convert the 36 volts into 12, and an inverter that could handle the amperage. All together, this would cost Kyle approximately $4,187 (not including a few hundred dollars worth of extra supplies and accessories).

A diagram of a solar system using both AC and DC:

We met with Kyle and ran through our findings. We gave him the initial quote, but made sure to note that if his energy consumption could be decreased, we could knock dollars off of the price. We were generous in the amount of daily watt-hours he would need when we sized his system because we figured it was better to be safe than sorry. But after our second meeting with Kyle, he let us know that his usage would be less than we had planned for, so we went back to our sizing worksheet - this time with these numbers in mind:
  • ceiling fan for 8 hours a day, 7 days a week (only during summer, but must be considered year-long) - 320 watt-hours/day
  • laptop computer for 4 hours a day, 7 days a week (a generous amount, but he scratched the CD player in lieu of Pandora or Itunes) - 140 watt-hours/day
  • 13-watt yellow compact fluorescent for 2 hours a day, 7 days a week (for inside mood lighting - the porch light was not considered as it will be a future addition) - 26 watt-hours/day
  • 2, 20-watt halogen lights for 3 hours a day, 7 days a week (as task lighting) - 120 watt-hours/day
  • cell phone charger for one hour a day, 7 days a week - requiring little to no wattage
  • (The electric stove was nixed after research showed the energy requirement to be very inefficient. Running one of these for two hours a week used more energy than running the ceiling fan for 56 hours a week - Kyle settled with his trusty propane stove instead)
These numbers, while still generous enough to give Kyle and ourselves room to work with, allowed Patrick and I to cut back his system considerably. After our second time through the sizing worksheet, Patrick and I found that Kyle would only use 680 daily watt-hours instead of the previous 936. This meant we could knock off one of the three solar panels and two of the six batteries. We could also get a much cheaper charge controller now that we didn't need one to convert the system voltage (the new battery pack could be wired at 12 volts, the usual amount needed to power appliances and other electronics).

These three changes alone dropped the price from $4,187 to $3,028. A difference of $1,159. Any client would be thrilled to hear that!

Our next task will be to decide on a reasonable inverter for his system. We need to shop online and find one that will fit his needs (a pure sine wave inverter with a sufficient amp rating). We also need to finish talking with Kyle and decide on our final location for the panels - because his home is surrounded by trees, the panels will have to be located on a stand in the field in front of his home. There are at least two possible locations. We must work through the pros and cons of each location in order to decide.

More on that next time...

4 comments:

Audrey said...

so proud of you,....awesome!

Mom said...

I'm impressed!

max. said...

i don't know if this helps, but i did some research because i've used pure sine wave inverters to power lighting equipment...

http://www.powerbright.com/puresine_inverters.html

http://www.xantrex.com/products.asp

it could be way off and not what you need. i have no idea if you can use the same inverter on solar and lighting equipment. whatevs.

benjamin said...

thanks adam - that's exactly what I'm looking for, but those might be too expensive (I didn't see prices on those sites) for the budget we are working with.

we have been looking on ebay and solarelec.com - and backwoods solar (a quarterly) carries xantrex, so I have actually looked at one of theirs as a possibility. $850 for a 1000 continuous watts, 12 volt.

we'll see....