Badger, you don't even know what his oil cost is. the answer is not "clearly" as simple as you say. his electricity is more than 4x the typical cost here in the northeast. I see no reason to assume that his oil costs are typical.

Actually I just finished a radiant floor heating design for a client in R.I. and I do know the cost of fuel oil thereabouts: http://www.newenglandoil.com/rhodeisland/zone4.asp?x=0

I have deduced, from Mr. Birdman's previous posts, that his electricity is 58 cents/kW and further that propane is double the price of oil. If he won't put in a compressor, can't afford the propane, and we all agree that the ROI on a hybrid thermal solar system, for a modest load such as this, will be in the negative numbers...big ones. Then i stand firm.

We often use water heaters for such small loads, but Polaris is exclusively gas-fired, so I am quite confident that a Bock oil-fired water heater pressed to dual-duty is the obvious answer, to wit, Ockham's Razor.

Electricity is not 0.58/kwh in rhode island typically. so I'm beginning to think oil is also not regular pricing. IF oil is indeed typical pricing I agree with your analysis. But I suspect mr. birdman lives on an island. which adds at least $1/gallon to any fossil fuel and maybe more. that can change this analysis in a hurry.

You are correct Rob his house is on Block Island, electricity is diesel generated, no net metering. I would guess there is a premium to bringing oil out there just like propane.

There is a wind farm coming, just not sure how long it will take. That should get the island connected to the main land grid.

How much of a gamble would it be to set up the house electric and hope the future prices will fall to twice the main land, instead of 4x. Net metering will probably become available.

ChrisJ

I had a client on block island last year. he noted that electricity drops to about 0.40 in the winter season and his propane bill as of may 2011 was $5.15/gallon. wow! but still, if oil is half that I don't know if we are talking about per BTU or per gallon. Per gallon would seem unlikely... same price as the mainland. we'd be at about $4/gallon if it's half the cost per BTU which seems more likely.

assuming 4k degree day active on an 18k load I'd say we're talking about a couple hundred gallons of oil or about $800/year, less solar gain if the house is designed for it, at about 85% efficiency. or $2/year per penny that oil costs per gallon. so anything else would have to use that as the potential ROI cap.

PV would still have a ROI calc vs 0.40 and 0.53/KWH electricity that was damn good in most cases, probably including a battery bank, but even without it.... $800/year would make a heat pump install look pretty good if you can run it when you have PV and just use oil as a backup. even better with slab radiant as a way to timeshift your demands and do overcharging.

but it's not a slam dunk and it is a bigger up front investment. variance in my fuel costs change the conversation. I'd look at PV in any case, but in the end if the numbers get lengthy the safe bet is oil now on a low temp system, and convert to heat pump when electricity is more accessible.

Posted By BadgerBoilerMN on 14 Dec 2012 09:50 PM
Few can seriously consider space heating with solar, especially if they live in R.I. But you knew that.

We design multi-fuel hydronic heating systems all over N.America and recognize that the local energy market must dictate the fuel source for all but the wealthiest of our clients. Oil is the obvious answer here. Pursue it without guilt. Economy is the essence of GREEN living, since waste is the antithesis of sustainable energy.

The worst use for oil is in heating DHW in the summer, no matter how it is done. Even in Rhode Island, a properly sized solar system will give almost all the hot water for 5 month. Every technology has its place and if the OP has the money or desire to use solar, more power to him. He will have a cleaner, healthier and cheaper to run system in the long run. At those prices, get the PV on the roof pronto.

a properly sized solar system will give almost all the hot water for 5 month.

Saving perhaps $65/month? We do solar, but around here $65 won't buy a solar water heating system. Not doing heat pumps, probably not doing solar. But hey, it pays to be positive.

We do solar, but around here $65 won't buy a solar water heating system

But $65 times 5+ months times 10 years might.

But generating your own electricity with a diesel generator running on oil gives you free heat.

in most cases an oil boiler doing DHW is throwing away a tank of oil a summer. around here that's more like $600, PLUS the actual usage. horribly inefficient. purge control can improve that significantly though.

With apologies I'm just getting back to this thread having been away from the internet access for a while. Thanks for the informative debate. I am indeed building on Block Island and it complicates everything..... Oil here, last I checked, was about $4.35/ gallon. I had been paying $5.35 for propane at another house for just DHW and cooking but in speaking with one of the two suppliers here he tells me if I have my own 500 gallon tank he can go as low as $4.00/gallon. That's a substantial drop but on a raw cost per therm basis still almost 50% more than oil. Oil and propane both come by boat, however, the difference is that Coast Guard regs will not let propane on the passenger boat so it comes on a dedicated hazmat charter. Oil and diesel come in tractor trailers on the passenger boat. Electricity here is diesel generated and bounces around in price following oil prices - perhaps around $0.53 now. There is no net metering now. There is an offshore windfarm planned for about 2015 but because of the cost of the cable to the mainland and the PPA for the wind power our rates would go down to about $0.28/kWh (still double mainland cost). We may also get net metering at that point. The house I designed has high insulation and airsealing levels and has a conductive heat loss (not including infiltration and ventilation) of about 18,000 on a design temp of +5. The design temp is rare here because of the tempering of the ocean water and the average January temp is 35. The house is designed for passive solar gain with south glass at about 8% of floor area and limited north glass. There is no cooling - all doors will have transoms to allow CV (some old technologies still work!). Basement (all below grade and unfinished) and first floor are concrete slabs with radiant heat and the second floor is wood frame with radiant in 1 1/2" gypcrete. I realize radiant in a highly insulated house isn't ideal for the "warm floor" effect but I had other reasons for it as well.

solar DHW will be a no brainer for you. PV would probably be a great investment. however with good passive solar and such a high average temp, it would be a tricky modelling situation to tell you for real whether upgrading your heating system makes a lot of sense. are there any similar structures on the island? or is there any "bin data" available for block island?

As to solar PV and thermal - I had originally planned to take this house off the grid (as our "grid" kinda sucks) However, this house has to be a summer rental for some years to come to make the $$$ work and vacationing tenants and off grid systems don't mix well. I will definitely be installing PV to some extent as the payback at our electric rates is a no-brainer. AS to thermal I had thought of it as meeting the DHW needs and perhaps a bit more for space heating - but maybe that complicates it beyond reason. With the highest production in summer and demand in winter I'm afraid a system designed for space heating would have to dump heat all summer long. For the lots of reasons I'd prefer the propane heat but I can't get my head past the cost. Per my rough calcs for a typical January I'd use about 64 gallons of oil or about 88 gallons of propane - that is still about $80 more for the propane for one month (with the "bargain" $4.00 propane).

Rob - "bin data"? as in "bin there, done that"?

I'm afraid a system designed for space heating would have to dump heat all summer long

You can set the angle on the solar high to maximize winter output and help defeat some summer production. Or, you can put them on an adjustable mount and make the adjustments seasonally.

Posted By ICFHybrid on 17 Dec 2012 08:06 PM

I'm afraid a system designed for space heating would have to dump heat all summer long

You can set the angle on the solar high to maximize winter output and help defeat some summer production. Or, you can put them on an adjustable mount and make the adjustments seasonally.

Some people have that luxury but some cannot. If I were building this house myself and I had radiant floors, the floor temp would be so low that a wall mounted solar thermal system feeding an ASHP and have as much PV on the roof as practical. But that is just me......

Bin data is weather data that is broken up into "temperature bins" for yearly energy usage analysis. Birdman, how are you calculating your anticipated usage for winter heating without bin data?

In fact I don't have the bin data and haven't calced the energy usage for the entire year. I did find the average January temp from some weather data however I can't now remember where I got that - I don't have the other months. I have been focusing on the relative costs of oil and propane rather than the predicted seasonal cost for each. At this point I'm trying to make sure I am covering all the bases for both fuels (foundation sleeves for vents and exhausts as well as sleeves under the basement slab for oil lines etc. Having the season cost difference would be great if the data is available but I can make an informed decision simply knowing one fuel is x% higher in cost than the other. On a separate note I see Triangle Tube makes a mod/con boiler (CC 65) with a double heat exchanger that will produce both Space heating water and DHW. Perhaps this is the way to go and have a separate solar tank to preheat the DHW or temper the return side of the radiant?

How will you utilize PV solar without grid-tie? Automatic transfer switch (blips)? AC->DC->AC conversion (efficiency loss)?

Between PV and a future decrease in electric rates, I'd consider heat pumps (for heating, cooling and DHW).

Right now I pan to be tied to the grid - I seriously considered going off grid but have backed off of that plan. Hopefully in a few years we'll have net metering and that will certainly make PV worthwhile. PV panels are cheap right now and if I forgo the batteries I eliminate a big part of the cost. With our power costs here it seems pretty wild to heat pumps - even if it goes down to $.28 or so. The other factor here is the quality of the power - lots of surges and spikes which tend to eat up appliances and controls. How well to heat pumps tolerate bad quality power?

at 0.28, divided by three, you may be doing better with heat pumps. especially with PV offset.

for power you will want to use line conditioners and/or surge protection, or at the very least high quality uninterruptible power supplies. same for any electronics and/or mod/con boilers.