> Because it takes really big wire to move DC at any useable current.

Really? How big a wire does one need for six of these panels wired in series? How many gallons/day of water would they heat up by 50F?

Posted By NRT.Rob on 14 Apr 2015 11:06 AM
Sure, there are plenty of pragmatic arguments, no dissention there. I just don't like greenwashing. Natural gas is better than coal or oil, but that's not a very high bar to beat.
It might be the 'greenEST' option someone can afford. But that doesn't make it green.

Be aware in New York and a few other states, many people can get solar on their roof for free (F-R-E-E), with a power purchase agreement locking in your electrical rate lower than grid cost right now. Combine that with a heat pump and you're doing about the best we can do these days from the green perspective at a price that should be affordable to most.

No argument there, but you still have to find 50 grand to heat your home and DHW. The capital investment is one item and the resources invested is another. A fact rarely mentioned or factored in to these conversations. Is sustainability a matter of time or infinite? Will the panel pay for itself? The heat pump-- less government subsidies--just a transfer of cost from the collective to the individual? In residential applications, more especially low-load structures, I am a skeptic. How green is green? Unless you're living in a Tipi or a cave, you aren't really GREEN.

I don't think you caught that in NY you can cover your roof in panels for free, that's a zero capital investment to the homeowner. The solar company owns the panels and you just agree to buy power from them at a fixed rate for 20 or 30 years. It works because yes, the panels more than pay for themselves. Person gets solar with no capital investment, locks in a savings on their power bill, everyone wins. The time for skepticism there is over.

That's partly because in some states the state investment in solar makes the power purchase agreements economically feasible. But given the cost of solar's trajectory over the last few years, I'd say it's definitely headed in the right direction. They are starting to deploy some systems like that here in maine where the state subsidies are not very good at all...

That power is still pricier than buying natural gas, but then again, a heat pump is cheaper than a gas boiler (in most cases) or comparable in some other cases. And a heat pump running solar credited KWH will have about the same operating cost as a natural gas boiler, and it can cool to boot.

Exciting times!

Can't argue with free PV panels but they won' t heat space or DHW, the vast majority of domestic energy. I own as mini-split and it would beat NG even if I didn't get a discount or off-peak. Still can't beat the savings and performance of NG boiler and indirect or a combi, unless you can get a discount for electricity and heat pump your way to COP 3 or 4.

I will buy in when my co-gen will heat my floors, DHW and cool the place off for less than a buck a therm. The rest is a stretch.

http://www.cogenmicro.com/

I am sorry Jon, I was making assumptions, and they wern't about a 200VDC system. I didn't say it couldn't be done Jon, but there are way more efficient ways to make hot water from sunshine. 220V of DC is nothing for the feint of heart to play with IMO. To answer your question in direct sun, you start with 1800W add in line loss for say 100 FT to get to the load and you come away with 1700W at the load. Assuming the resistor element is rated to maintain that voltage from the panel, that should net you around 1700W at the heater. That equates to 5700 BTU per hour of operation at that level. 1 BTU will raise 1 pound of water 1 degree Farenheit. So a 50 gallon water heater tank would raise approximately 7 degrees per hour of operation best case. Or to more closely answer your question, it would heat 14.45 gallons of water 50F per hour in direct sun perpendicular to the panel. It goes downhill from there unless you pop for tracking panels which will net you about 40% increase in output over the day. How much per day is anyones guess as it depends on your cloudcover latitude, season ect. To contrast a 30 tube evacuatd system would deliver about 6000 BTU/HR typically. But that number was averaged from 7 hour days of spring time service, so peak in direct sun is probably substantially higher if we are attempting to compare under similar circumstances(peak output direct perpendicular sun)... The advantage of the tubes is that they are always better orientated to the sun if elevated at the correct angle. Output can be enhanced with reflector troughs behind the tubes. Trackers make it even better... The same area in evac solar on your roof as these panels would occupy would produce a lot more HW...

Here is a question or two back for you: How do you shut off your 200V DC system when the tank reaches set temp? DC dosn't like to stop flowing when the contacts break(that's why it works well for welding. The HW tank's controller will pretty quickly cook itself if you feed DC to it. This next question is for your insurer I guess. Are they going to pay when you cook something off with your home engineered 200V DC heating system?

Sounds like we agree that at $4k (or even less) the costs (purchase and operation) of an Ecocute don't compare well to PV solar + resistance heat at the rate many households use hot water.

Switching 220VDC at < 10 amps is trivial, but this isn't the place for an electronics design discussion.

Wait. What happens when it snows on you evac tubes?

morgan I'm not sure what you're saying about the PV not being able to heat a house. with net metering or buy backs, and a modest home, it's certainly possible to meet the yearly heating/cooling/DHW loads with PV. direct cost of such an array is around $50k for a typical modest home, but if you are doing the power purchase agreement, that's not your issue. THAT'S as green as it gets these days in any form that is accessible to a wider array of customers. Payback without credit if you bought it outright is under 20 years and with credit it's faster, and the panels are expected to last 30+. Even bloomberg is noting the trend.

Natural gas is the least worst fossil fuel option, but its time is ticking down every year to a "why are we doing this again?" level. NG cogen will be dead in the water before it even takes off within 5 years. You heard it here first

Where grew up $50 grand would buy a modest house. Is being GREEN only for the rich and those who live in mild climates? We are installing a condensing water heater in an 800 sq.ft. next week for people of modest means and reasonable expectations. GREEN enough for me and them.

Every market and environment demands, and deserves, it's own solution.


http://green.blogs.nytimes.com/2013/03/01/q-and-a-the-angry-economist/?_r=0

$50k is also what you'd spend on the electricity that particular array would generate over 20 years, at least in areas like the northeast were electricity is not cheap despite relying heavily on natural gas electrical generation. Which means roughly $25k is what you'd save over the next ten years of free electricity you get after that, and that doesn't count the immediate lock-in savings compared to grid electricity, or any savings for grid electricity price appreciation over time. and again, you can often in many states get it put up for free. It's not extravagance, it's long term planning.

Capital is an issue, which is why purchase power agreements are becoming popular, as it puts the capital problem in front of people with capital (investors), the solar equipment in the hands of solar professionals, and the energy benefit to the end user. that's all pretty good stuff. people of modest means are doing this in long island right now, every day. Very few all the way to netzero.. you need a lot of roof for that for most people. But it gets better every year. I'm not seeing a lot of investors lining up to put NG cogen in anyone's basement.

It's not for everyone everywhere today. but it's for a lot of people in a lot of places, today, and growing every year. Big green hugs, sir

OK. Pass the Cool Aide.

The levelized lifecycle cost of PV at the current~ $3.50/watt installed cost is still about 20 cents in an 20-25 lifecycle analysis, assuming a 4% discount rate. (SolarCity is offering 30 year guarantees & 30 year 4% financing in a few states beginning this year, that includes performance monitoring and inverter updates as-needed.)

But 20 cent electricity burned in resistance heaters at a COP of 1, that about $57/MMBTU, WAY over the cost of heating with oil, even if you include a boiler replacement every 25 years.  

With all of the tax credits and other subsidy money (and cheaper financing than you're likely to get)  the big solar companies can still make money selling you power from their array on your rooftop at 15 cents/kwh though.  But even at 15 cents/kwh that's still $44/MMBTU.

That's comparable to the marginal cost of burning oil at 85% efficiency at $5/gallon or a bit higher, which is considerably higher than this year's oil prices.

However, 20 cent electricity leveraged with a best-in-class ductless mini-split at a COP of 3.5-4 ( the new Fujistu 9RLS3H has an HSPF of 14, and can deliver 14,000 BTU/hr @ -5F), that's $11-13/MMBTU,  which is comparable to natural gas heating for marginal cost in most US markets.  At 15 cents/kwh heating with mini-splits is $8-10/MMBTU, which is cheaper than heating with natural gas in many US markets.  You still have the upfront cost of the mini-split, but it "pays back" on the the far lower marginal heating cost WELL within it's lifecycle.

By 2025 many banking sector analysts believe rooftop solar will be cheaper than the wholesale cost of any other grid sources, but that's not to say it pays to wait. (That call varies with your local retail grid rates and the type of subsidy and interconnect fees you run into.)  But by 2025 PV + local battery will become cheaper than grid-retail in much of New England.  We're still at the thin-edge of the rising PV tsunami, but it WILL crush utilities that are unable to adjust their business models.  (It already has in Germany, and arguably has in Hawaii, although the Hawaiian utility is under negotiation for a buyout by NextEra, a large US independent power generation company with a lot of distributed renewables experience.) In fact, not even the oil companies are immune from this rapidly rising tide.





(edited for grammar)

Dam double posts:(