I have decided to go off grid on a new house design in Rhode Island (where a new service would cost $20K and power is $.55/kwh) and have a couple questions. I'm contemplating an array of about 4 KW but have the roof space (45 degrees at due south) to go as high as 6kW. House is four bedrooms, hyper insulated. Loads will include the normal stuff - refridgerator, laundry (gas dryer), occaisional toasters, hair dryers etc. There will also be a well pump (well is about 180'). Septic is gravity so no load there. House will be rented to vacationers during summer and doubtful they will want to change their lifestyle so there will be a propane generator (about 8 to 10 kW) to maintain the batteries as required. I'll probably backcharge tenants for gen time to encourage thifty energy use. First question is what well system is best with an off grid system. Conventional pressure tank with a soft start pump or a VFD constant pressure? Second question is how difficult would it be to add a small wind turbine (like an Air X) to the system in the future? Does that need to be considered now in selecting the charge controller? All input welcome!!

First question is what well system is best with an off grid system

I like solar slow pumps with a tank or cistern sized for 2-3 days use. That allows a submersible pump to bring up water slowly during daylight hours to fill the cistern. An on-demand pump with an accumulator tank actually supplies the pressure water for the home from the cistern.
1) I like having some water storage.
2) You can set the well pump to operate during hours in which your other loads are low.
3) I like having the pressure pump up top where it is serviceable.
4) Two small draws are better than one large draw.

Does that need to be considered now in selecting the charge controller?

It is nearly impossible to get an electrician to set up for future needs unless you can tell the sparkie EXACTLY what unit will be there. Best plan is to situate your panels so that it is easy to add panels and transfer switches. Lay underground conduit from the wind location to the panels. That makes things a lot easier when it is time to add the wind generator.

I live in RI, you must be talking about Block I.

I read on solarpaneltalk, what the pros say often is that off grid systems could cost more then the 20K for service hook up. Batteries will need replacing every 5-6 years.

I thought something was said in the news about a wind farm being near B. I. With all the wire needed to connect the wind farm couldn't they connect the island to the grid?

ChrisJ RI

A 6kw array is enough to deliver ~7000-7500kwh of electricity per year in your location, with output weighted toward the summer months. A 4kw system would deliver ~5000kwh/annum.

If you have only high-efficiency lighting (and a limited number of overall wattage), all EnergyStar or better appliances, with a smaller than average refrigerator (over/under configuration, not side-by-side), and don't have big-screen TVs on game systems the summer rentals might very well do OK without burning propane given sufficient battery.

One key factor to estimate would be the amount of power used by the well pump- folks who leaving the water running or families who take multiple endless showers would be capable of bringing the system to it's knees. The instantaneous power requirement of a high-flow well pump on startup could end up oversizing the inverter making it less efficient for other loads too- ICFHybrid's low-flow pump + cistern concept has merit on a couple of levels from the power systems point of view, and water-abusers would quickly find out the value of water if they run the cistern dry.

Off grid living takes some mental adjustment, and some tenants will have a tougher time of it than others. Having a posted list of tips handy at the house may ease the adjustment though.

Grid-tied PV is running ~$5/watt for systems in CT, and there would be the cost adder of the storage, so even a 4kw off-grid system is going to run more than $20K, but it's not going to be 2x more.

Small wind turbines tend to be little more than ornamental unless you have sufficient height. At current PV prices you get more kwh/annum for your money with PV, unless you have an exceptionally good location (like the top of a hill), and can mount it on a tall tower.

The Block Island offshore wind project is only 30mW peak (~9mW average, assuming a 30% capacity factor) and it will be hooking up to Block Island, as well as the mainland. See:

http://dwwind.com/block-island/block-island-project-overview

IIRC the contracted-for wholesale price to the utility for it's output is 24cents/kwh, which is still cheaper than Block Island's oil-fired power generation. Once it's up and running it would tend to lower the local retail power rates. I suspect the average grid load of B.I. may be equal to the peak output of that relatively small off-shore wind resource, and well above it's capacity-factor output. If they oversize the peak output relative to the very-local B.I. load they would have to either upsize the power link to the mainland or lose out on being able to use the available power during peak wind periods, which would lower their return on investment. But with the planned power links the rates is already going to fall, since with both the very-local wind and the link to the mainland's power grid the on-island diesel power would then be relegated to peak-power only, if not eventually abandoned altogether.

Is there a net metering grid-tie option? If net metered, with conservative annual use you'd never really pay much of the 55 cents/kwh power, and you get payback of the $20K hookup-charge by avoiding the costs of the batteries & generator systems, etc. I suspect you'd be eligible to reap SREC production credits for the next decade or so to the tune of 20+ cents/kwh, which could be enough to pay for the whole shebang (hookup charge included) before the SREC expires, or at least be much lower cost in the long term and lower maintenance than a true off-grid solution.

I would probably go with the VFD well pump and a tank. It would be interesting to see a computerized load shedding system that could prioritize and combine circuits to always stay within the inverter's range. And detect loads that require starting the generator.

As always thanks for the replies!! Yes, this is Block Island - where else has 55 cent power (and lousy power at that) . The Wind Farm, I think, will happen. Some are still dedicated to preventing that so it could be in the 5 to 8 year range till it's totally on line. In the meantime my financial model demands this house be rented during the summer as I can't pass up the $35,000/season rental. That means that whatever I do I need to provide a house that folks don't have to "think about" (much as I would love to try to educate them). The proposed wind farm will include a cable to the mainland via a substation on the island. The peak farm output will be 30mW and the island demand is 5mW in summer and < 1mW in winter so we will be a net exporter of power, taking off the island demand on its way to the mainland and drawing from the mainland on calm days. Our island power is expected to drop to about the upper twenty cent range (better but still quite high). No one knows what the net metering potential will be but we will become Nat'lGrid customers so I assume it will be available. Currently there is no net metering as the "grid" on the island is so small it disrupts the generators. The wind turbine idea is primarily to provide a charge to the batteries in off solar days during winter as there is a nice off-set (peak wind in winter and lowest solar in winter). Right now I'm planning to initially do all PV but would like the potential to add small wind. My site is on a hill and the wind resource is very good. ICF- the cistern sounds good from an operational point but 2 -3 days for four bedrooms could be 2000 to 4000 gallons. That sounds like a big cost for a potable water tank. Plus two pump systems vs one. Not sure the budget will stand that. I like the idea of water hog tenants running out of water but I'm not sure they would. We're dealing with folks who complain to the broker if the flatware is mis-matched. One thing that is intriguing would be to drop a coil of PEX in that cistern and run the coil through a coiling coil followed by a reheat coil with solar HW to act as a dehumifier - is that nuts? If the cistern is seeing 100 gal per person per day and I can get a delta T of say 10 degrees that could be about 60,000 Btu of cooling. Last few weeks the RH has been in the high 90's there with temps in high 70's (dewpoint about 2 below dry bulb). having the option to close the house up and dry it a bit would be nice. Sorry for the tangent.... The recommendation I have now is a conventional submersible pump with a soft start or to use an oversized pressure tank to prevent short cycling. I'm not savvy enough to understand the electrical ramifications of VFD constant pressure system although I'm told it eliminates "inrush" which I gather is hard on the batteries. In short I think my options are down to those two. JonR - my understanding is that the VFD system either doesn't need a tank or if it does only one in the 2 to 4 gallon range as a cushion - is that what you mean? That system would be great - but for now I think it's manual (like looking at the forecast and deciding to vacum tomorrow instead of today).

Correct, a VFD eliminates the need to oversize the inverter to handle the very large start-up current. A larger tank (pressurized or non-pressurized) can allow you to downsize the well pump to well below the peak GPM needed (I can take an entire shower on my pressure tank). The best thing you can do for humidity is seal the house well - of course renters will probably turn the dehumidifier on and then leave the windows open.

I'd be interested in knowing if you can get a 10K generator quiet enough that they don't complain. Maybe some of the Onan RV models and a concrete enclosure.

Jon R - thanks.
Does a "soft start" submersible protect the inverter in the same way?

I am just beginning to shop for a generator. Most are "standby" and will not warrantee the unit if it is used as back up in an off grid situation. This would be a propane unit so inherently a bit quieter than diesel. Most come with a weather proof enclosure assuming a pad mount and there are various levels of acoustic "fluff" to try to dampen sound. I plan to locate this unit in a separate shed about 40' from the house with the cooling intake and outlet aimed away from the house and I've asked about (but have no answer yet) as to whether there is an additional muffler that can be installed without creating too much back pressure. Part of me says it should annoy the tenants as it's an audible message that the "lived beyond the panels". But then that's mean....

One thought is whether to use the new genset during construction or rather get a "beater" for that and start occupancy with a brand new unit.

The tales of what renters will do here are amazing. One batch of tenants I heard about showed up with four window AC's in their car when they arrived - my friend had $700 electric bill for the month and they were only there 2 weeks!

One other thing. When tenants were in the house the genset would be on an "auto on" control that would read battery charge level and come on at a set point of discharge. This may not be the optimal time as, for example, it may trip on just before dawn of a sunny day. While we were there we would go to a manual mode and operate the house by usage, weather forecast, etc. So if we needed to vacuum on a dark day we might run the genset proactively - or wait for a bright day - an informed choice. Frankly, I think it would put us more in touch with the weather which is nice.

I'm not familiar with how soft start works or how much reduction it gives. My guess is not nearly as much as a VFD.

A quick read - normal motor 6x, soft start, 3x, VFD, 1.5x.

The capacity factor of offshore wind tends to run about 30%, so the average output will be ~9mw, which is still well above the quoted 5MW summertime average load, so the link to the mainland grid is necessary to use the excess of the offshore array rather than having to throttle back on it.

To get efficient dehumidification out of a coil it has to be at least 10F below the dew point temp of the air flowing through it. Average summertime dew points in that area are in the mid-60F, and your deep-well water temps are in the low 50s, so best case you'd only be able to bring the dew point down to the high-60s during the most-tropical of conditions. Even room dehumidifiers are ~500W loads, which will suck a lot of juice out of your batteries if you need to run it very long. A 3/4 ton mini-split might dehumidify as-efficiently, but would be an invitation for the tenants to air condition the place.

If you're planning on being off-grid, mechanical dehumidification is pretty much off the table, and you'll just have to suffer through the sticky days when the dew points are in the 70s.

Unless you do a real wind survey it will be difficult to predict the output of a tiny turbine. But in all but the best-case scenarios you'd be better off spending the turbine installation money on more PV + storage to cover dark-and-stormy-winter-week shortfalls.

Given the island's grid development plans it might be worth thinking about being sure the PV array is readily adaptable to and compliant with a grid-tied application at some point down the road.

To mitigate issues with the renters bringing window-AC, if it's not already baked in to the cake, you could use only casement & awning windows (which are inherently tighter than double-hungs anyway).

Dana,
The thought with the dehumidification was just to take the curse off those really bad days - as you said. I realize getting down to purely "comfortable" range is unreachable. For the last few days the dew point hasn't dropped below 72. As I try to get paper through my printer it's like using cooked lasagna..... The hope is that we could close up the house and wring a little moisture out of the air once in a while just to interupt the mold growth cycle for a couple days till the sun came out. If nothing else it could be a cheap experiment (two small pumps, a couple coils and some pex.

Just got the power bill for July - 220 kWh with a total bill of $148.17 (including a $12.38 flat fee for being connected) so that works out to $0.617 per kWh!!

Being able to tie to the grid in the future is a good idea. It's unlikely the rates here will come down to the mainland rates but $.28 or so is a lot better than $.61. That rate will probably hold for the foreseeable future as the cost of the substation and marine cable needs to be amortized over the next 20 to 25 years. On the island power company side, the distribution system is horrible. The still push primaries at 2,000 volts and have huge line losses that they pass on to the 1,800 or so rate payers. The quality of the power is bad too - brownouts, voltage drops and surges are the norm and motors often have a short life here. Improvements in the local distribution will be totally separate from the wind farm which will only involve the substation interface with the island system and the marine cable. I'm thinking that with power rates staying in the $.28 range for the next 20 years I'm probably ahead of the game being off grid. Even if it's break even there's the psychic benefit of being able to be "holier-than-thou" - priceless!

I like the "casement deterant to window a/c's! Perhaps I should install wind bars to prevent the "theft" of my juice!

Since the net output of the wind farm will far exceed the local load for Block Island the ratepayers on the mainland should rightly absorb a significant chunk of the capitalization cost. Most southern New England states have signed up for significant Renewable Portfolio standards, which is usually achieved by buying production credits from regional renewable generators. eg:

http://www.ucsusa.org/assets/documents/clean_energy/rhode-island.pdf

By the time it's been up for 10 years I'd expect the rates to be more in line with the rest of the region, since the levelized cost of energy out of an offshore wind array is comparable to that of thermal gas-fired production.

This is an interesting discussion but as a landlord whose family has operated rental properties since the 1950s I'm struck by one common theme...

...That a tenant paying $35k is somehow in the wrong for wanting to be comfortable during hot humid weather!!! WTF?

I live in Florida, and our house is well shaded, multi-story and otherwise configured for maximum use of ventilation by opening windows. Nearly all rooms have windows on two or more walls.

That said, I'm uncomfortable and don't work efficiently or sleep well whenever dewpoint exceeds low 60s, so all those windows are shut tight mid May through September.

While 60 cent power is quite pricey, the ability to get a good night sleep while paying big bucks for a vacation rental is priceless.

Strive to find a way to economically provide tenant comfort rather than obstructing / sabotaging their desire to be comfortable, day and night. My guess is the best solution will turn out to be small, very high SEER minisplit heat pumps.

Curt,
There's a slight misunderstanding - I'm building this house primarily for myself and family however what makes it work in my unusual location is the fact that for about 8 to 10 weeks of summer I can rent it to vacationers for big bucks. I don't think they're "wrong" for not wanting to deal with the vagarities of an off grid solar house - they're paying big bucks and expect all the bells and whistles. Bear in mind there are about 800 rental homes on this island - of those I would guess perhaps 20 have AC - only two are off grid - it just isn't the life support system in offshore Rhode Island than it is in Florida. Nights in particular are quite cool here - rarely above mid 70's. If I did not have to rent this house I would perhaps enlarge the solar array and battery bank and forgo the genset. My plan is to provide a genset/solar array combination sized so it will provide all the "grid tie" conveniences if desired, but I will also provide detailed "operating instructions" so if the tenants want to test drive living on solar they can. To make it fair I plan to read the hour meter on the generator at the beginning and end of each let and charge them a flat rate per hour (disclosed in advance of course). I suspect some tenants may enjoy taking on the energy challenge but most will just party hardy and pay the bill.