Help with planning solar system (long)

labradoodleladySeptember 11, 2005

I'm finishing up the design stages for a house I'm building, and have questions. I'm looking at putting in a solar electric system, trying to decide batteries or no batteries, and when I try to use any of the online calculators, they tell me that there's no solar system under $100k that will meet my needs. That's a bit distressing, to say the least.

So at the risk of some of my questions seeming too primitive to be believed, here goes.

I live in Hawaii. The house will be facing due south, with no obstructions to cause shade until 4 pm at the earliest. The sun will be going pretty much right over the roof from 8:00 am until 5 Pm, depending on time of the year and which wing of the roof. The house is located in a rainy place, but that's pretty seasonal as well. I've lived on that part of the island before and had solar water. THere were probably no more than half a dozen times that I had to turn on the electric, and that was solely due to my use of the whirlpool tub.

Here's the bad news. Cost per kwh where I live is 29 cents per, and according to my past 11 months of bills, I'm averaging 1400 kwh per month. THe hot water is solar. There really aren't a LOT of ways I can cut that down, although I'm trying to think creatively for the new house.

First, I need to explain that my 6 year old daughter is classified as "medically fragile", and a lot of that electric usage is generated caring for her. She requires constant nursing care. That means there's a lot of laundry done, and the dryer in this house is electric. The rest of the house has to be cleaned with hospital strength stuff once a week as well, more laundry. The nurses like a lot of intense overhead lights, so all the ceiling fans have four regular bulbs, and the cans have the biggest spotlights that fit. Dishwasher is run with less than full loads. This particular house also has two full kitchens, so it's supporting two refrigerators and one tall freezer, none of which are likely very energy efficient. Ceiling fans constantly operating in all rooms, no ac (until the middle of last month, when my daughter's health required it - only needed 2 window units, and likely may not need those at the new house because it's a higher elevation).

The other major use of electricity now is the whirlpool tub. It's used just about every day, to alleviate pain from a nerve injury. In the past, I've found that the tubs seem to use about $100 per month here in electricity.

First, can I set up an overhead lighting system based on low-voltage, actually a 12V line? Something that would keep the nurses happy, but hopefully no lights hanging off the ceiling fans. I see LED spotlight bulbs listed on ebay, would this be the type of thing I should do? What else could be run on a 12v line?

I'm obviously planning on solar hot water, and wondering if I should do two separate ones: a small system to cover the tub and master bath, and a larger one for the rest of the house. Is there some kind of solar panel that can be tied just to the tub to power the motor? Motor runs out of power, it's time to get out of the tub....

I'm going to switch to a gas dryer and oven -- right now the oven is electric too. Outdoor path and driveway lighting will be solar. I've got to put an extensive intercom system into the new house, but I can't imagine that will use a lot of power.

There will only be one big fridge, not 2.

On the other hand, I'm going to be needing to put in quite a bit of water filtration equipment, and I don't know what impact that will have on the electric needs. Right now we go through about $80 a month of bottled distilled water, and I'm thinking about putting a 16 gallon distiller in. It will go strictly to the icemaker, and the "prep" sink in the kitchen, which will actually be the sink for all of Hannah's meds, and making her formula (she feeds through a g-tube). I'm assuming that thing is going to burn a lot of electric all on its own, but I have to be sure as much trace elements of pesticides and heavy metals are removed as is possible.

Are there small wind generators that can provide any kind of input? The winds come straight across the mountains over a valley, and I think one wing of the house will have a straight shot with no obstructions (there's another house being built on that side of the house now). But this is going to vary a lot more than the sun will.

My contractor has already said this is something he's going to talk to me about, and the system would only add on $20k to the price. With the kind of price estimates I was seeing in the online calculators, I figure I need to understand enough about this stuff to ask what I'm getting for that, and hopefully understand what I need.

Any input, ideas and suggestions on this whole situation would be greatly welcomed.

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I've been on a PV / battery grid-tied system for a year now. My usage was ~ 300 kWh / month winter; 175 kWh / month summer. Basic initial cost before any incentives etc was ~ 32k. I have two 10 foot square arrays; a total of 2800 watts of PV. You've got some major electrical usage going; and you obviously must provide for your daughter.

I'll say that firstly; cutting your USAGE will be cheaper than supplying that energy via PV / wind / whatever. Electric stoves, water heaters are BIG users; actually anything with any kind of heating element in it is a hog. Next on the list is compressors . . . fridge / freezer / AC equipment. Buying newer ( more efficient ) fridge / freezer / AC could possibly save you a lot of usage; depending upon how old your existing stuff is. Buy by Energy rating; not doo-dads / frills . . . and buy the size you need . . no less; but no more. AC only room(s) that need it.

Lighting is another area you can likely save some usage in . . . the variety / styles / sizes of fluorescents is very good now; and they produce the same amount of light with ~ 20% of the energy. They can be had in "daylight" spectrums as well. Also produce FAR less heat; which in turn can help lower your cooling costs. They also last FAR longer; usually about 10 times longer.

I'm in central New York state; certainly NOT the sun capital of the world. You likely have FAR more sunshine hours . . my system has 2800 watts worth of panels . . . sized for sun here to basically provide all of my electricity in the period of a year. Get a good surplus during the summer; but run into deficit in the winter.

You don't have to, but might want to consider; doing battery back-up for your medical equipment for if / when the grid goes down . . usually there is a "critical load panel" that is powered when running on batteries; so you would keep necessities on this panel . . they are also powered when the grid is up. That way; you wouldn't have to scramble to find a generator etc. You can size a battery bank for practically any load / time. Again; your sun situation is likely far better than mine here.

You're not gonna end up with a cheap system by any means; but there may be some incentives for you . . . in my case they were substantial . . between NY state incentives, tax credits, and a federal tax credit; ended up paying ~ half the system cost. Your mileage may vary. You should also check with your local utility about net metering and waht the laws are there . .. some places they are not obligated to credit you ANYTHING for any power you may generate . . some places require that the utility buy it back, sometimes at above market costs; since it's "green" . . . those policies are local regional . . don't know your particulars.
Again; if you're planning a new place, NOW is the time to make some choices to save energy; which will MORE than pay for themselves in terms of lowered system cost if you do so.

Can't say much about wind power . . but your site can be evaluated relatively easily to see if it would be feasable and what power you would get from it. There may be some zoning / code questions with wind generation too . . or even the solar panels for that matter. Look into that before you get too well dug in . . .

Good luck . . .


    Bookmark   September 11, 2005 at 8:05PM
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Hi Bob, thanks for your input.

I'm really at a loss as to where the electric is going. All our hot water already is solar. Clothes are washed in cold water. I'm already planning on replacing the current 2 fridges and a freezer (all older models) with one side byside fridge in the new house. There are 7 ceiling fans operating almost constantly -- is that really using that much power?

The current usage figures also don't include the AC -- I only bought the two room units after the last bill came, and their use is limited to the three rooms where Hannah spends most of her days.

I wasn't sure if I could keep part of the house on a battery back-up but not all of the house -- thank you for that information. Our power goes out every couple of months as it is, so I like that idea.

As for incentives, bah humbug (for lack of a better way of putting it). With all the free power shining down on this state, Hawaii offers no incentives, my power company offers a whopping $800. State tax credits are limited to $1500 (although it's not clear if you can claim once for the solar hot water and a second $1500 for the PV). And yes, our power company allows net metering. Net metering credits can be carried forward up to 12 months, but from what I'm gathering, I'm not going to be generating enough to meet my needs, let alone get credits for higher usage months.

So what else can I do to make this work?

Tia, Summer

    Bookmark   September 12, 2005 at 2:16AM
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