View Full Version : Solar experts

July 17th, 2006, 11:53 AM
Anyone install anything like this on their houses:




I was thinking this would be good in emergency situations if there is no power or if you don't have a generator.

Glen Miyashiro
July 17th, 2006, 01:05 PM
It's interesting to see how many photovoltaic panels you'd need to cover all your electricity needs. My household uses about 1000 kWh per month. Assuming PV could generate power for 8 hours every day, I'd need 4167 kW of PV capacity to give me 1000 kWh/month.

Costco's biggest PV panel is $1,600 for 240 W. I'd need about 17,363 of them to give me 4167 kW of juice. Clearly, an all-PV home is not in my immediate future. :p

Da Rolling Eye
July 17th, 2006, 07:13 PM
I've been waiting, but it doesn't look like the prices will be coming down anytime in the near future. I'd love to set up a rig big enough to handle one refrigerator and a couple of small appliances for emergency use and make my meter run backwards other times, but that ain't going to happen in my lifetime. :(

Gonna go back and keep shopping for a decent generator.<sigh>

Oh yeah, I do have a small panel on the roof to power the solar water heater pump, but it's way to small for anything else.

July 17th, 2006, 07:43 PM
Saw this article in The Garden Island a couple weeks back. Interesting read.


July 17th, 2006, 07:53 PM
It's interesting to see how many photovoltaic panels you'd need to cover all your electricity needs. My household uses about 1000 kWh per month. Assuming PV could generate power for 8 hours every day, I'd need 4167 kW of PV capacity to give me 1000 kWh/month.

Costco's biggest PV panel is $1,600 for 240 W. I'd need about 17,363 of them to give me 4167 kW of juice. Clearly, an all-PV home is not in my immediate future. :p

Let me help you with the math......

Your house uses 1000 kWh per month or 33 kWh per day.

Honolulu Hawaii, on average, receives 6 equivalent sun hours(ESH) per day. Depending on what time of year you want to use your system, the value changes but I will use 6 ESH since it is a round number.

Sun hours times system size equals kWh per day

Pluggin in what we know.........

6 ESH times system size(kW) equals 33 kWh per day

or......system size is 5.5KW.

5.5kW divided by 240W equals roughly 23 panels.

This is rough.....cuz you have to factor in system losses.

Need to factor in batteries and an inverter as well as wiring and labor.

Rough cost for entire package using $10 per watt installed is $55,000

Here is a neat site, plenty of them to chose from.


Hope it helps.

July 17th, 2006, 08:16 PM
Pretty good feedback! Mahalo!

I was just wondering cause I only realized a while back I have no idea how to power my son's nebulizer if there is no electricity. I think the solar panels would do the trick. But I also wonder what else could be powered by the solar panels.

Glen Miyashiro
July 17th, 2006, 08:47 PM
Let me help you with the math......Sounds like you know your stuff. Thanks.

Edit: Aha. I guess I was off by a factor of 1,000. If you take that into account, then my original estimate was that I'd need 17 panels. That's in the general ballpark. :rolleyes:

July 17th, 2006, 10:04 PM
Phyiscally how big is one of these panels?

July 17th, 2006, 10:09 PM
But I also wonder what else could be powered by the solar panels.

At 240 Watts per panel, that's basically two 100 watt light blubs and little bit left over for something. Three way light blubs hit 150 watts on the brightest setting.

July 17th, 2006, 10:59 PM
I am in the process of buying a home so I was looking into buying both Solar water and Electric systems. I found you could buy off the internet a Electric kit for about $16k (plus $400 shipping) That included 4 Sanyo panels/inverter/batteries to power a household of 4 people. This is the same parts I got quoted by a local shop with labor for $26k. My electrician friend said he would install it for $2k. Right now I am paying HECO about $240 a month! So the only killer is the life of the batteries. by the time It starts paying for itself I will have to replace 2 sets of Batteries. but then again on the next power outage I will be the only person on the block with electricity.

For the solar heating I was thinking of buying a kit and also a heat pump. My mom used a heat pump in our old house and we had the heat pump venting into the house. The byproduct of the heat pump is cool air. so basically A/C!
the only problem is we had to control it manually through vents.
So basically I will be spending $5k plus installation on the water heater.

July 18th, 2006, 06:17 AM
Anyone use solar devices to cool their home? Crawl space?

Should we talk about wind now that the Maui wind farm is running. ;)

Composite 2992
July 18th, 2006, 08:24 PM
Rather than install a battery reserve system, look into the possibility of taking advantage of Net Metering.

During the day you sell excess power back to the utility. At night you draw what you sold back. It's possible to get away with a zero bill if things work out just right.

The disadvantage is that if the grid goes out at night, so do you. But you can probably run an AC during the day.

I'm considering solar power options. With the clamor about neighborhoods not wanting high tension lines crossing their areas, and all the attention being given to global warming, you'd think there would be more support for options like solar energy -- such as bigger tax credits.

The state just raised the tax credit out of the "pointless" range. But it's still not high enough to push a lot of people off the fence.

Here's what I discovered so far regarding how practical this might be:

Current home power usage between 19 to 29 kilowatt-hours/day. Sept 2001.
Average is 990 KWH/month.

"Insolation" value, average: 6.02 hours of full sunlight per day, minimum (winter).
Translates into 4 kilowatts of panel. Add 30% for inefficiency: 5.2 kilowatts of panel required.

72 72-watt panels would be required to generate this much power.
72-watt GE panel measures 21"x48" Panels would cover 8' x 63' or 1008 sq. ft.

18 300-watt SCHOTT Solar panels. 75" x 51". Panels would cover 12.5' x 38.25' or 478 sq. ft.

July 23rd, 2006, 05:51 AM
Article in the Honolulu Advertiser on Solar Water Heating and Tax Credits.

July 23rd, 2006, 06:38 AM
So that particular model is just for emergencies? Not for day to day that you can use to make your monthly bills cheaper?

July 23rd, 2006, 06:32 PM
My system is 22 x 110 watt panels and a SunnyBoy gridtie inverter. It works very reliably. Currently we producing about half of what we use. It is strictly grid-tie so when the utility goes down the inverter shuts down also. It is a minor inconvenience, but saves me the hassle of battery maintenance chores and expense. 3 years ago, we spent about $24K for equipment and a couple thousand to our electrician. Today I produced 12.5 kilowatthours. Year around average is about 9. We have not been able to use any of the tax credits yet. We didn't have any state taxes for last two years and our accountant is not sure how many years forward you can carry them.

Solar water heating is the best bang for your buck! Except for maybe a couple days in winter, we almost never pay to heat water. We got an extra big tank and also a recirculating system so extra hot water is continously being stored in the pipes (insulated, of course).

We are building a new house right now. Even though I like my current photovoltaic system the next one is way better. This one will be a hybrid gridtie and battery system. It works like a regular gridtie system, but when the utility goes off, it automatically shunts the outside world, and switches over to a very small battery system . 4 batteries are sold with the inverter as a single UL approved unit (this allows the batteries to be kept in the house rather than in a special shed or enclosure). Since the batteries are rarely used and are kept up with a trickle charge, they should last a very long time. The batteries will feed a special circuit that will have just fridge and freezer and a few lights. With a little care, we could survive a long term outage. After Iniki, this area didn't have power for about a month. Assuming I still had panels on the roof, I could get by, hopefully. A sunny day would allow me to run power tools to repair the house too. The system my solar contractor is getting me is from Outback.

For the new house, we could not use the rebate that our utility offers for solar water heating. Our plumber is not on the very short list of approved installers that you must use to qualify for the rebate. That's another gotcha to look out for.

I am glad I am doing these things even if I do not get the incentives. It just makes me feel better.

July 23rd, 2006, 10:08 PM

Are you a solar consultant? It sounds like you know a lot.
Can I ask where your old house and your new house is?

July 30th, 2006, 05:40 AM
I am on Kauai--in Princeville. The new house is also in Princeville. I used Hanalei Solar for consultation. I also bought a few issues of Home Power magazine and borrowed some books from the library. The Real Goods Resource Book is also an excellent reference.