Photovoltaic systems - Oahu

[alex7777]

[quote=hotzcatz;20316386]The solar water heater also cuts way down on propane costs, so it's good even if your water heater is gas. We had been using about ten gallons of propane each month at our old house which had a tankless water heater QUOTE]


How effective/efficient did you find the tankless heater? I guess the main issue is the initial cost (2-3 grand?) but if it saves a lot of propane, it might be worthwhile.

[hotzcatz]

Originally Posted by alex7777

<SNIP>
P.S.: Do any Hawaiian homes have basements? I know it's a big rock and all, I'm just wondering if it's feasible to tunnel into it. B/c I definitely know it's much cooler in a midwestern basement in the summer -- ridiculously cooler, actually. If I had a basement in Hawaii, I doubt I'd ever even need A.C..

It doesn't get hot enough to need to tunnel into the rock. We have tradewinds which are usually light breezes - five to ten miles per hour - that almost always blowing. We also have a huge amount of fairly stable temperature water surrounding the islands so the wind blows in off the ocean and cools things down or warms them up as necessary. It rarely gets above ninety here during the summer, let alone over one hundred. I think the record ever recorded temperature lows and highs Waikiki are somewhere around fifty five for the lows and ninety nine for the high. Waikiki is at sea level on the leeward side of an island. If you go up in elevation, it gets cooler. During the winter on the Island of Hawaii (the Big Island) when there is snow on the mountain, then it can get colder since the cold comes down from the snow.

Pick a spot to build your house where you will get the tradewinds. Build the house with really wide eaves - three feet is common - to shade the sides of the house and keep the sun off. Use white roofing. Have the windows situated so there is cross ventilation. Put your house up on post and pier foundation and make some vents in the floors of the closets with louvered closet doors. Put some ventilation louvers in the roof peak - a "Dutch hip" roof is common for that reason. A few ceiling fans if you like. Your house will be lovely and cool without the need for A/C at all.

A/C uses a lot of power and if you don't have to size the photovoltaic system to run an A/C system it will be a lot more economical.

[hotzcatz]

[quote=alex7777;20319769]

Originally Posted by hotzcatz

The solar water heater also cuts way down on propane costs, so it's good even if your water heater is gas. We had been using about ten gallons of propane each month at our old house which had a tankless water heater QUOTE]


How effective/efficient did you find the tankless heater? I guess the main issue is the initial cost (2-3 grand?) but if it saves a lot of propane, it might be worthwhile.

I think it was about $650 - $750 or so and we bought it about two years ago. Bosch Aquastar is what we got. We had County water so we didn't need a water pump or pressure tank. The Aquastar is a good water heater, it makes unending hot water however you have to demand hot water to get it. It was more sensitive and would produce hot water in smaller demand amounts than the Paloma, though. If you want just a trickle of hot water, on demand water heaters occasionally have trouble knowing when to turn on. Other than that, they work great. We were filling up a huge float around sized tub each day so there was a lot of hot water used.

The Bosch can also be installed on the exterior of the building without needing a vent through the roof. That saved a lot of installation bother as well as cost. It was easy to hook up, too.

[KauaiHiker]

I replaced an ancient 40 gal propane hot water tank with a 120 gal solar system, which the contractor got used from an army base on Oahu. He guaranteed it for a year, and installed it for 3000, all included (including the solar PV pump I wanted extra). With the state and Fed tax credits it paid for itself in 18 months. Except for those few days a year we need to turn on the electrical backup, we've had totally free hot water ever since.

[MsHell]

Thank you all for the replies.

[alex7777]

Great posts, Hotz and Kaui. I have relatives in Mexico, their kitchen is about 50 yards from their boiler (Very long house), so they really never have hot water in their kitchen, which is an obvious problem. Sounds like a tankless will be a great solution for them.

I was also thinking of putting the house on stilts, to get more breeze. (Got the idea from House Hunters International in the Carribean.) I'll also try to incorporate the other tips mentioned. It sounds like Hawaii overall will be a great place for making a home that is inexpensive to maintain/operate, without central heat, a.c., etc. That should hopefully help offset the high cost of goods once I get the solar systems in.

It sounds like the tradewinds might also power a small windmill or two? These might be useful for powering the house/batteries on cloudy days. It also seems that if you're in a rainy area, you could design some sort of turbine that gets powered by concentrated rainfall. (Rain that overflows the catchment system, or rain collected elsewhere, could be focused through a large funnel to turn a turbine similar to a windmill, charging batteries in the process.)

Love the idea of letting nature do all the work, and getting free juice in return. (Obviously, you have to pay for the systems up-front, and maintain them, but long-term, seems like you'd save a lof of money, and have a much easier budget to work with.)

[mokeanne]

i would do more research about windmills if you're seriously thinking about it. on oahu, you probably wouldn't be able to do it, but maybe on the big island there would be less resistance.

[MickeyE]

Check out the Yahoo groups 12VDC_Power : 12 VDC Power , axialflux : Axial Flux Alternators , simplyoffgrid : preparedness for daily living , SimplySolar : SimplySolar , simplesolarhomesteading : Simple Solar Homesteading .

Also Green Trust Renewable Energy & Self Sufficiency . Rummage around Green-Trust for lots of great info on off-grid living and how-to-do-its.

Mickey

[hotzcatz]

Some areas of the Big Island are better for windmills than others. There are several wind maps you can refer to which will give you an indication if an area you are looking at would be suitable. Adding in a small wind generator to a photovoltaic solar array might be nice since the wind generator would be working when the wind blows at night as well as during the day. They do make a bit of noise, though, and would vibrate so most folks seem to mount them on a post separate from their house. You also have to arrange it so if it falls over it won't fall outside of your property lines.

They now have inverters which are real efficient so you can wire up a house just as if it was going to be attached to the grid and then put an inverter where the electric meter would go. Power the inverter with the 12/24/48 DC current you get from your wind/solar and you're good to go. We used a battery bank to store the power since we were completely off grid. Once we shift the panels to the new house we will keep one or two outlets in the carport connected to the grid and those will be used for heavy loads as well as for running a battery charger for when the solar panels don't carry the load. It's cheaper to use the grid as a backup generator than to maintain and run a gas/diesel generator.