Wanting to get into solar? Think HOT WATER
Wanting to get into solar? Think HOT WATER
(OP)
Some may be feeling that they are missing the solar power bandwagon and wondering how they can do something actually useful without spending a lot of money. Batteries and grid tie make a system expensive with a long payback. Creating hot water is the most effective way to use a couple of PV solar panels since close to 100% of the power generated will be used. This assumes you are currently using a resistive hot water tank and not on demand as the rest of the civilized world. Never could get used to climbing into a shower with a 240V line.I have been heating hot water for years with excess PV for years at my camp. With as little as 800WH, we can both get a long hot shower at the end of the day. Just a couple panels totaling 400W can make a significant dent in electric use for heating. Under powering the heater assures 100% of the panels output is used. That is much greater than any battery application and much lower in cost than grid tie which isn't even allowed in some locations. Typical heat loss during the daylight hours of a well insulated tank is more than 1KWH. Solar makes up for that loss.
Most tanks have two heating elements. The top is the primary and only one operates at a time. That allows the lower resistive element to be used for solar and still have grid power backup. At 240V even a 5500W element is 10 ohms, a replacement 120V 2000W is about 7 ohms. That requires at least a 36V panel string toget any useful power. One positive is that may keep the system classified as "low Voltage". Connecting a panel directly to a resistance will result in power losses of more than half. A simple PWM circuit keeps the panel voltage at the the power point. A small capacitor bank stores the panels power in the off cycle. A panels power point voltage is the same regardless of light level. It only varies with temperature. Attaching a couple of flat pack diode bridges to the back of the panel is an easy way to get a reference voltage tracks panel temperature. I use a $5 UNO to control everything and the 490Hz PWM makes driving a FET easy. Almost any switchmode chip would work just as well.
I'm not going to argue the economics of it. Watching solar work is just plain fun and panel prices are so cheap now. Everyone has some space they can stick a few panels on. It won't freeze and none of the plumbing issues of direct solar heating. I've built several versions with just junk box parts. I have more real world details if anyone is interested.
Most tanks have two heating elements. The top is the primary and only one operates at a time. That allows the lower resistive element to be used for solar and still have grid power backup. At 240V even a 5500W element is 10 ohms, a replacement 120V 2000W is about 7 ohms. That requires at least a 36V panel string toget any useful power. One positive is that may keep the system classified as "low Voltage". Connecting a panel directly to a resistance will result in power losses of more than half. A simple PWM circuit keeps the panel voltage at the the power point. A small capacitor bank stores the panels power in the off cycle. A panels power point voltage is the same regardless of light level. It only varies with temperature. Attaching a couple of flat pack diode bridges to the back of the panel is an easy way to get a reference voltage tracks panel temperature. I use a $5 UNO to control everything and the 490Hz PWM makes driving a FET easy. Almost any switchmode chip would work just as well.
I'm not going to argue the economics of it. Watching solar work is just plain fun and panel prices are so cheap now. Everyone has some space they can stick a few panels on. It won't freeze and none of the plumbing issues of direct solar heating. I've built several versions with just junk box parts. I have more real world details if anyone is interested.





RE: Wanting to get into solar? Think HOT WATER
Here in Ontario, Canada we are on time-of-use electricity charges Monday to Friday, and since our residential hot water demand is not great we've wrapped our tank in an insulating blanket for the extra R value, piped in a thermal loop in the outlet line, and wired the power supply through a timer such that the water heater is powered up only from 1915 local time until 0645 the following morning. For the most part this has worked out reasonably well.
The idea of hooking solar panels to the "back" contacts of the timer so they would be in service from 0645 to 1915 daily while off grid would dovetail in very neatly with this scheme...I'll definitely look into this.
Thanks, OperaHouse!
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
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RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
My buddy just put in 6.5kW of panels on his roof. Since Pacific Graft & Extortion doesn't pay for any energy over your annual total consumption he was looking for a way to not throw that excess away. He got a 30gal electric water heater and for starters has put it on a timeclock to avoid time-of-use energy draw. So, between 7pm and 10am he allows his water to be electrically heated. His gas usage has dropped a tier.
I'm not convinced a timeclock is going to be the best moderator for this scheme. I suspect some longer averaging will be needed to account for "dim" months or sporadic heavy electrical use when relatives have been by etc., etc. It could be something like a plc that watches the past days of a month and towards the end of the month starts piling on the pv waterheating to try to zero balance the energy consumption might work better.
I'm waiting for an energy mishandling that has him wailing and scratching at my door. LOL
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wanting to get into solar? Think HOT WATER
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RE: Wanting to get into solar? Think HOT WATER
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wanting to get into solar? Think HOT WATER
Now that summer is here (with the occasional cool day worthy of heat), I can barely see the meter move (cook and heat water with gas, too).
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Wanting to get into solar? Think HOT WATER
Obviously if you have already paid for a solar PV installation and are generating more electricity than you can sell, using it for any beneficial purpose is better than wasting it or disconnecting the panels, and hot water heating is an easy way to do that. That said, electric hot water heating, at our average cost of $0.20/kWh once all taxes and fees are in (that's the average of peak and off-peak rates), is an idiotic source for either comfort or hot water heating on an economic basis when compared to natural gas- unless you're running a groundsource heat pump with the electricity. An air-source heat pump might make economic sense in the shoulder seasons for comfort heating, but that just means you have even fewer days of sensible use per year to pay back its capital cost.
Here in Ontario, Canada, if you can install enough unshaded PV panels to pay back the (substantial) cost of permits, inspections and 2nd meter installation, you can obtain a microFIT contract which will pay you a premium for ALL your PV electrical generation- not just for generation in excess of what your own home uses. That's a spectacularly bad piece of public policy in my opinion- but if you can fit the maximum 10 kW of panels on your roof without cutting down all your mature trees, it can be quite lucrative- if you don't mind stealing from other rate-payers!
I'm contemplating a not-quite-legal small "behind the meter" solar PV installation for peak-shedding, which will pay back over the long term because our peak kWh rates are so high. To do it without "detection", I need a cheap, safe and reliable means to disconnect the panels or to add loads (such as a small hot water heater tank) to make sure I never, ever run the meter backwards- and I'm open to suggestions on the best way to do that. The microinverters I would use would already completely disconnect the panels in the event of a power outage (to avoid injuring service workers).
RE: Wanting to get into solar? Think HOT WATER
Smart meters are going to make a major change in energy usage. The utilities finally have a way to slice and dice billing costs into minute segments. Peak energy costs the utilities dearly and now they have a way to pass that on to the actual users. Energy management will be a major growth area. Those in renewable energy are actually bigger energy wasters that than that housewife in Sheboygan.
RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
I wonder what is its lifespan in charge cycles?
If it's not at least 3500 cycles, then it's fiscal nonsense.
(* YMMV with power rates.)
RE: Wanting to get into solar? Think HOT WATER
But, that means I only need 1129 cycles
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RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
I've seen commercial panels that used this concept. But I didn't see where the $4000 each price tag came from, being made with about $400 worth or materials. Must be some sort of 'Green Tax', LOL.
RE: Wanting to get into solar? Think HOT WATER
http://solar-trap.com/
He asked some questions in here:
thread240-368902: Relay EMI is triggering sensors on custom Arduino PCB
thread240-374737: How to properly measure currents with hall sensors
It actually makes some sense for peak shaving without the meter getting involved.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wanting to get into solar? Think HOT WATER
The HOT SHOT program I talked about was paid for by the utilities to study the effectiveness of heat heat pumps. Not only total energy savings and can a customer live with slow response, but the effect of reducing peak electrical demand for heating in the morning and evening.
On another site a poster had a concession stand with multiple food devices with heaters. He was only allowed a single 20A outlet by the festivals he went to. His total possible demand was a little more than double that. I thought it was an interesting problem that could be solved with a micro scheduling priorities and not interrupt his normal business. This will be the future of our smart appliances. Wife wants a dishwasher this year (I got a look when I told her I thought I married one) and it is possible with as generated solar. The dishwasher will cycle on and off as sun is available or other priority bumps up.
Just thought I'd throw that hot water heating idea out there and see if it stuck. About the only expense is the panels themselves.
RE: Wanting to get into solar? Think HOT WATER
One fridge isn't going to do much for me, and I only have one. My household draw can drop as low as 600 W mid-day and I'd be putting perhaps 1.5 kW of panel capacity on my back wall- can't put more, so a microFIT contract doesn't make sense for me. Didn't see any details about Solar Trap's means of power monitoring at first glance- will have to do some digging. My idea was much simpler: a couple turns of wire around each AC phase where it comes into the house, with a diode and a cap, running to the input of a couple comparators. Sensed current drops below a threshold and I turn on an auxiliary load (i.e. a hot water tank etc.). Current drops below a 2nd threshold and I open a contactor, disconnecting half the panels. The challenge would be to make it work fast enough- regrettably my scheme won't tell the difference between current coming into the house and current going back out to the grid (what I want to avoid).
As to the question about EV batteries- they can last about 3,000 cycles to something around 70% depth of discharge or less. They do suffer from capacity loss with respect to time at high voltage (sitting fully charged, ready to run) to some extent irrespective of charge/discharge cycles. The primary degradation mechanism, aside from cell reversal which occurs if you don't have a proper battery management system, seems to be electrolyte chemical damage leading to deposition of insoluble coatings inside the cell. Time at high voltage, particularly at high temperature, are both bad news.
RE: Wanting to get into solar? Think HOT WATER
RE: Wanting to get into solar? Think HOT WATER
You mean: ...1.5 kW-hour per day ?
It's about correct, as some of the really energy efficient ones are down to "$43 a year" (assuming something like $0.10 per kW-hour).
RE: Wanting to get into solar? Think HOT WATER
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RE: Wanting to get into solar? Think HOT WATER
With our low energy rates and fair climate, we are seeing loads of server farm interests.
RE: Wanting to get into solar? Think HOT WATER
Here is my chart. Energy star appliances, heat pump water heating, CFL and LED even use a wall switch to to turn off TV. Still I am double my neighbors. The energy sucker is the hot tub. At least I do good in the summer!
RE: Wanting to get into solar? Think HOT WATER
Worse than that, the Tier 1 allowance would only be sufficient for running the PVRs.
I'm not sure exactly what rate tariff is assumed for the Canadian EnerGuide labels when they provide dollar estimates for annual energy consumption, but it's a bit lower than ours. The $0.10 was a guesstimate.
My house uses simple electric baseboard heaters, but it also has about 24 sq m (!) of south facing glass (passive solar, very well insulated). My annual space heating cost is about the same as my Internet + telephone cost for a year. Not insignificant, but certainly affordable.
RE: Wanting to get into solar? Think HOT WATER
Seriously? We're in SOUTHERN CALIFORNIA; beaches, sun, bikinis, did I mention sun? Only slightly cheaper than northern Calif. While large scale manufacturing is mostly gone, it's not because of the utility rates, per se, but because of labor rates. Back in the 80s and 90s Northrop moved its manufacturing to places like Georgia for the cheap labor and tax breaks the state offered to lure Northrop there. Nevertheless, housing still goes up, and there are boatloads of startups 1069 startups according to that link. Obviously, 90% of them are probably going to flame out in time, but still...
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RE: Wanting to get into solar? Think HOT WATER
Here's a breakdown of my Toronto Hydro fees:
Basic rates: this is what everyone THINKS they're paying for power:
On-peak: $0.161/kWh
Mid peak: $0.121/kWh
Off peak: $0.08/kWh
Fairly high, but not so bad compared to California!
...but then there are the fees:
transmission losses: multiply kWh used x 1.0376
transmission charges: $0.014/kWh
distribution: $0.015/kWh
regulatory: $0.005/kWh
debt retirement: $0.007/kWh
customer charge: fixed fee, works out to $0.014/kWh for me over a typical month.
That's $0.055/kWh in fees, plus the 3.76% multiplier for distribution losses
Then there's 13% HST on the whole works- yes, that's a real cost, even though it isn't hidden in the price like it is in gasoline at the pump.
That works out to roughly $0.20/kWh all in, average of on peak and off peak. That's the figure I use for comparing cost savings from efficiency or offsetting with rooftop generation etc. Lots of options pay back at $0.20/kWh. What depresses me is that the microFIT contracts for solar PV pay people $0.50 or so (it was previously $0.80) per kWh for all the power they generate from their rooftops, even if not a single electron in fact leaves their houses and enters the grid...those FIT programs should only be for net excess power generated.
Contrary to popular belief, there hasn't been a mass exodus of manufacturing in Ontario due to increased power pricing. Manufacturing has been in decline locally, but it's resulted almost entirely from industry consolidation and offshoring- and that has helped us avoid installing another CANDU reactor plant which would cost tens of billions of dollars that we could otherwise invest in transit etc. As a society we prefer (now) to import cheap goods of all kinds and let others obtain all the benefits of manufacturing them. Trade protectionism is out of vogue in the developed world for manufactured goods. Agricultural goods produced by the very poorest workers in the world (in sub-Saharan Africa) are still subject to crushing duties here though- I guess farmers still have quite a bit of lobbying power, and unlike China or Korea etc., the sub Saharan countries lack the clout to fight back.
RE: Wanting to get into solar? Think HOT WATER
$10.83 / month fee 'base charge'
$0.14947 / kWh
Only 5% GST (the provincial HST is rebated for some reason)
That's it.
I've never bothered with ToD since my heating fraction is low, it would work against me.
RE: Wanting to get into solar? Think HOT WATER
Time of day metering is mandatory here. The great thing is that if you sign up for their Peaksaver program (giving them the power to turn your air conditioner off for short periods during the peak, actually saving me money in the process- we only really NEED it for sleeping in July and August), they give you a digital power monitor which interfaces with the smart meter. Easy way to understand what's drawing power in your home, and when.