Curious neighbors looking at my solar system

solarvic

Guess I started something in my area. since I got my solar system online DEC 24. I am getting lots of visitors dropping by that are asking all kind of questions about my solar systems. I did most of it myself even though I am not an electrician. Hired one at the end to do the wireing from solar panels ect. A neighbor about 3 miles from me stopped in today asking me all kind of questions. He bought 4 Suntech 270 watt panels and told me he is going to connect them to a 40 gal. waterheater and preheat the water before it goes into his 82 gal. waterheater. Said he was going to use 2 dc heating elementsin the 40 gal and maybe put 1 in the 80 gal water heater. I don,t know for sure but I am thinking with all them solar panels he might overheat the water heater. I told him my personal opinion that he better make sure the pressure releaf valve is working and he has a place for the water to go. I told him also that I thougt it might be better to get an inverter and make use of the electric in his house. Anyone that knows a lot more than me have any opinions?
S:cool:larvic:D

dwaller

Re: Curious neighbors looking at my solar system

Sounds like a perfect scenario to be using evacuated tubes. Much more efficient and cost effective vs. using solar electric to heat water.

I am no expert though....

BB.

Re: Curious neighbors looking at my solar system

It sort of will heat his hot water... He can go through the normal thermostat/over temperature limit switches...

However, there is the issue that DC voltage/current arcs much better than the equivalent AC voltage/current. I am not sure the switches would survive (it is possible that they will almost never cycle during normal use). Also, he could look at placing a high voltage capacitor across the contacts to allow them to open more before they arc (remember condensers on car ignition points in the old days) (may or may not help--I am not sure--should not be any inductive kick--so the condenser/cap may not help).

-Bill

Windsun

Re: Curious neighbors looking at my solar system

It is something that sort of works, but probably not the best way to do things. He could possibly overheat the water with no temperature control, but the main thing is that it is a pretty expensive way to do it. I have seen a few similar systems where the incoming water was very cold so was used just to preheat.

On the other hand, with only ~1000 watts or so of panels probably not worth setting up a grid tie system.

n3qik

Re: Curious neighbors looking at my solar system

Windsun wrote: »

pretty expensive way to do it.

I see this stated many times. Has any one done a cost comparative of each system?? Going this way eliminates any freeze/pump problems. Plus I like K.I.S.S.

icarus

Re: Curious neighbors looking at my solar system

Just the solar conversion rate make using PV for hot water crazy. Dollar for dollar, using thermal directly is way cheaper,,, and way simpler net/net IMHO.

Tony

solarvic

Re: Curious neighbors looking at my solar system

I was over to see what neighbor is doing. First of all he didn,t get any permits and the township supervisors and secretary are preety close neighbors. He had to go under the road to get a good location without shadeing. Township supervisor already complained when he went under road without permit. Without measuring I think he is at least 150 ft, probably more from the house. Going to run wireing for each solar panel so he can control each solar panel on its own. Says he has an electrician friend that is going to help him wire it. Already boughtt 3 24/48 volt dc water heating elements. Didn,t want to buy an inverter and batterys. Couldn,t talk him out of it. So after he gets iy set up will post here if it works. Answers to 2 other postings. He has too much shade to use solar water and we can get temp down to -30 f here. And the kiss might work if he can find a way not to overheat the water. panels rated 270 watt 7.71 IMP 35 VMP. I was wondering if he could at least make 2 arrays of 2 and If this doesn,t work at least he has the wireing where he could get 4 more panels and use the wireing he already has for 2 arrays of 4 and do an inverter system. Are those triplite UPS any good? S8)larvic

niel

Re: Curious neighbors looking at my solar system

maybe this is going all over the place for me to properly follow here, but if there's not enough sun for solar thermal then there certainly isn't enough sun for pv. he should use solar thermal for water.
you've got mighty picky officials up there for them to get in an uproar over an off grid arrangement to heat water. i guess he'd want a permit for you to charge your car battery too with pv.
what about tripplite ups? in what aspect are you asking about them?
they are basically modsine inverters with a small battery that kicks in during utility power losses and aren't usually meant to last long for those with a supplied battery. they initially came to be due to the computers unexpectedly shutting off during brownouts or outages and most are sized for the pc to be shut down within so many minutes and aren't meant for continuous duty.

edit to add-
i've had people stop and ask about my solar pvs, but none had their own.;)

BB.

Re: Curious neighbors looking at my solar system

If I understand the issue correctly... "The Neighbor" has two pieces of property with a city/county road between them (or one property that got a road splitting it in times past).

Property A is home and has poor sun. Property B is across the road and 150' away from home to get good sun.

Running "hot water pipes" under road was not a great option (water pipe, insulation, heat losses?). So option B was to put solar panels on Property B and put the wires under the road (C--ticked off township as no permits where pulled).

To answer the question--Many of the 24 and 48 volt elements I have seen are simply 208/240 VAC elements derated by P=V^2/R ... Simply less current going through element at lower voltage.

I think the "optimum answer" is to figure out the optimum load point on the solar array. As the array voltage goes up, current goes up, and more power into the elements.

Figure out the crossing point between (for example) 4x panels in parallel (and high current available) vs up to 4x panels in series (and low current)... The point at which P=Imax*Vmax through the water heater element for the series/parallel combination of the solar array will get the most power.

• 4x parallel panels--> low voltage, low current through element
• 4x series panels --> high voltage makes high current... Does load point of electric element pull solar panel operating point off of the Peak Power curve (i.e., Vmp pulled way low because of low resistance of electric heater).
• 2x series/parallel --> just right (high enough voltage to force Imp current into element (but probably as mythical as Goldilocks and the Three Bears story).

Guessing:

Suntech STP210-18/Ub-1

Pmax @ STC 210 W
Pmax @ PTC 190 W
Vmp at Pmax 26.4 V
Imp at Pmax 7.95 A
Voc @ STC 33.6 V
Voltage change -114 mV/C

Lets guess that 4,500 watt element at 240 VAC (or VDC--does not matter):

• P = V^2 / R
• R = V^2 / P = 240v^2 / 4,500 watts = 12.9 ohms
• I=V/R= 240v/12.9 ohms = 18.6 amps

So--we have three ways to connect the panels, 4x parallel, 4x series/parallel, or 4x series:

• Vmp=26.4 volts ; Imp=7.95amps ; P=I^2 * R; V=I*R;
• X) 4x parallel: I=Vmp/R=26.4v/12.9ohms=2.05 amps; Imp=4x 7.95=31.9 amps
  • P=V^2/R=26.4^2 / 12.9 ohms = 54 watts
  • Voltage limited--cannot drive much current into element
• Y) 4 panels in series/parallel: 2x26.4=52.8 volts; Imp=2x 7.95a=15.9 amps
  • I=52.8v/12.9 ohms = 4.09 amp draw
  • P=V^2/R=52.8^2 / 12.9 ohms = 216 watts
  • Voltage limited--cannot drive full Imp into elements
  • Perhaps, wire three 4,500 watt elements in parallel for load
  • three elements = 648 watts @ 12.27 amps -- not a bad match for 15.9 Imp
• Z) 4 panels in series: 4x26.4=105.6 volts; Imp= 7.95a
  • I=105.6v/12.9 ohms = 8.2 amp draw limited to 7.95 amps of panel
  • P=I^2*R=7.95^2 * 12.9 ohms = 815 watts
  • Voperating = I*R = 7.95a * 12.9v = 102.6 volts

Z) has the optimum operating point (voltage and current). But given that not everything is operating at full sun all day long.

Y) would work well with 1-3 elements. Can see which setup would gather most power during day... Or step to have 3 elements near noon, and drop back to 2, or 1 early/late in day.

X) is probably not practical--would require a dozen or more 4,500 watt 240 Volt elements in parallel to sink sufficient current to make sense.

At least--that is how I would "fit the panels to the elements"... Not sure it would ever make sense.

Off hand--I cannot think of any off-the-shelf controller that would work a Pmp array to Pmp solar heater MPPT matching without involving a battery or Grid Tied power...

Adding a battery bank and inverter would cause more losses (controller, inverter, battery), more costs, and more maintenance.

3kW or more Grid Tied system would make most sense--if allowed by utility...

-Bill

RCinFLA

Re: Curious neighbors looking at my solar system

Good example why getting permit/inspections is probably a good idea. PV arrays are hard to hide. All it takes sometimes is one neighbor that has a 'bone to pick' with you because your dog once pooped in their yard.

solarvic

Re: Curious neighbors looking at my solar system

Back in my thread about chargeing 24 v batterys with a 48 vdc generator lots of people were thinking charge controlers. This trip lite inverter I ran accross sounded like it might work. model aps 2448. it says it has pulsewidth modulated sinewave. Is that a way of camoflogeing modified sinewave or is it the real thing (sinewave)? It is 2400 watt 115vac output from 48vdc imput to inverter. Niel that is why I ask about triplite. Solarvic

niel

Re: Curious neighbors looking at my solar system

ok i answered it in the other thread where you asked and i believe it probably is modsine.
i don't see the need for a permit to have an offgrid array heating water, but if they are going to have an attitude about it and insist upon it then i don't see the alternative. the only way to fight that is to insist upon seeing what regulation they are citing that requires it and the other is to run against them in the future.

solarvic

Re: Curious neighbors looking at my solar system

niel wrote: »

ok i answered it in the other thread where you asked and i believe it probably is modsine.
i don't see the need for a permit to have an offgrid array heating water, but if they are going to have an attitude about it and insist upon it then i don't see the alternative. the only way to fight that is to insist upon seeing what regulation they are citing that requires it and the other is to run against them in the future.

I think him going under the road might have been the problem(edited by niel to keep it clean for all). He put 2 1/2 inch conduit under the road. This is a rural area and some of the townshups come up with a new way to get more income. The natural gas drilling has been going on in this part of Pa. Sporadicly since the early 80,s. So most of the townships passed ordinances that the gas company,s have to buy a permit for about $250.00 everytime they go under the road. They bury them about 6 ft or more and it don,t hurt the road any. Now they are burying broadband cable so probably another one time windfall for the townships. S:Dlarvic

niel

Re: Curious neighbors looking at my solar system

i guess that could be a problem as the township probably owns the road and not your neighbor. maybe he should ask them the best way they would approve of his doing this and just plead ignorant when he went ahead and did that. he is not putting flammable liquids or big time power there, but i can understand them needing to know what is going on under the roadway even though what he's doing hurts nothing. if they are really mad at him for bypassing them, they could refuse and disapprove of any efforts he makes.
he may need a plan b like cutting down trees.

russ

Re: Curious neighbors looking at my solar system

İs there a right of way on both sides of the road? He is probably crossing an area where there may be a future use so it would be required to be done correctly.

solarvic

Re: Curious neighbors looking at my solar system

russ wrote: »

İs there a right of way on both sides of the road? He is probably crossing an area where there may be a future use so it would be required to be done correctly.

He owns the land on both sides of the road. The road goes east and west. He lives on north side of road where all the shade trees are. He owns field on south side of road and it is an open field. Really a good place to put some solar arrays. He also bought non ul solar panels too. We had the werner ladder plant here that employed a lot of people. Now if you get a werner ladder it comes from Mexico or China. More jobs lost. He got some fiberglass ladder sides to make a solar rack with. I thought it looks ok. S:cool:larvic

Photowhit

Re: Curious neighbors looking at my solar system

In PA, I'd a thunk you could place the panels on the north side of the road and get max sun most of the year, I'm in Missouri and am on the north side of the road and my top most panel is with in 15 feet or so of a black oak(I think) and another coniferous(?) tree, and I get just a tiny bit of shading during the summer solstis(?) and already below for the 'heat' of the summer.

Telco

Re: Curious neighbors looking at my solar system

I support the use of permits to go under roads. About 10 years back the main 4 lane highway between the town I was living in and Tulsa was paved. They did a beautiful job, and the road is still more or less smooth. About 6 months after the roadwork was completed, some j@(#@$$ natural gas company came in and did a line bore under the road, about a foot or so down. They buckled the 4 lane on both northbound and southbound lanes bad enough that when you hit it, it was like hitting a curb at 75MPH. The county made them "fix" the problem, and the fix was to cut the asphalt out and repave that one small section. They paved it with cheap asphalt patch. After the "repair" was made hitting that section made a loud noise for a split second, and now it's a small rough patch in an otherwise smooth road.

On your farmer friend, might point him to this site. I love trotting this page out when hot water is being discussed. I want this system for myself, bad! He'd be able to make better use of the solar panels by using them to offset electrical feed rather than to offset a heat load. If he really wants it, cutting a couple of shade trees should be no issue. He can even plant 5-6 times the number of trees he cuts down, and make them the same type tree, in the field across the road, on the far border to make up for any pollution reduction from the trees he cuts.

solarvic

Re: Curious neighbors looking at my solar system

He put the conduit in last summer and it doesn,t seem to have hurt anything at all. So that settled township hasn,t given him any more problems. The trees near his house is too close to the road so he can,t put solar panels on the north side of road where his house id. So South side of road from his house is a great location for panels. All open and he won,t get any shade on his panels there. I think he has either 2 1/2 conduit or 3 inch under the road so should be able to put lots of wireing thru that 1 conduit. I tryed to explain to him that he would probably be more efficient if he used the power to offset his electric bill. He thinks connecting directly to a water heater will preheat the water before it goes in 80 gal waterheater thus saving his electric on the ac powered 80 gal tank. One thing is it isn,t going to cost him that much to try his experiment to see for himself. If that works it bypasses inverter, batterys, charge controlers ect. The main cost he will have is the 3 dc waterheating elements and the 40 gal. tank he bought. If he finds that that won,t work for him then he can go for an electric system and buy all them other parts of the system he is bypassing for now. What he told me. Said he has been thinking of this for a couple years and he has an electrician friend that will help him. Telco, I really like that building . I bought a new tractor last fall and my garage isn,t high enough for me to get it in without folding down the rollbar which is a pain. Looks like if I got it high enough for the tractor it would be a good place to mount solar electric panels. Wish I would have known or thought about this sooner before I bought all the poletop racks and pipes. I probably spent enough on them to pay a large amount on this building. S:Dolarvic