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solarusmc

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Posts: 180
Reply with quote  #1 
I bumped into this website today goofing around on the web looking up electrical ways of heating things including water.

This gentleman has one pretty nice little gagit that allows you to take juice from your PV Panels and send it directly to your hot water tank heating element without using batteries, charge controllers or any of that other costly stuff..

If you are using PV panels right now at your place or plan to get some soon ya might want to check this gagit out.

I currently do not have any PV panels at my house but really thought this was a cool solution to help heat your hot water.

The website is called Tech Luck   --  http://www.techluck.com

Anyone into electric PV I think will really enjoy reading there.

I wrote to the owner of the site asking him to come to the forums here and post about his gagit because everyone here is into solar and alll DIYourselfer's looking for cool ways to accomplish home built systems.

I hope he registers and does post so everyone can ask him your questions rather then me.
I know ZERO about electricity issues.. sorry. [confused]


__________________
Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'

netttech

Registered:
Posts: 720
Reply with quote  #2 
Hmmm, watched the video, website. First it claims no inverter, but the diagram shows DC voltage, then ac after the cut-switch. Inverters changes DC to ac.....regardless what title is uses...it still inverts the power.

Everyone confuses Wattage as power. Wattage is a measurement....not power. Amperage is true power. The higher the amperage, the more 'power'. I've always known heating elements (all types) to use a lot of amperage to produce heat.

A quick check on Lowes website a 4500 watt WH uses 18+ amps.

Having 2 24V panels connected in series, ups the voltsge, but not the amps. Two panels may be producing 5-6 amps at best.

I'm not doubting some benefit from it....but not sure I would dedicate solar panels for hot water.

Jeff
Central IL
Ray D Benham

Registered:
Posts: 7
Reply with quote  #3 
No it is NOT economical to use solar panels directly to heat water.  They are only about 16% efficient.

Its more efficient to heat water directly from the sun.  A solar panel will produce about 330 KwH per year.  That equates to raising the temperature of 50 gal of water per day by about 7 deg F.

Ray D (Monte) Benham
Professional Chemical Engineer
solarusmc

Registered:
Posts: 180
Reply with quote  #4 
Quote:
A solar panel will produce about 330 KwH per year.


Hi Ray,

Could you elaborate a little more on your statement.

What size solar pv panel produces the 330 KwH? annually.. and if it were hooked to the top heating element on say a 40 gallon electric hot water heater would that help to keep the water temps up in the tank during sunny days?

__________________
Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'
Ray D Benham

Registered:
Posts: 7
Reply with quote  #5 
240 Watt panels hooked to enphase M215 inverters.

Solar panels do not put out max output until about mid day.   And it is almost always less than the 215 watts of the inverter.  The solar panels are sized greater than the inverter to account for a 10% loss in output afer 10 years and a 20% loss after 20 years.  My solar panels will produce about 1.2 KwH per day in the summer.  In the winter time about 15 to 20% of that.  On average my system produces 900 watts per day  or  66.6KwH per day for the entire year.

The web site promoting hooking panels up directly to the top existing heating element sends the wrong message.  The heating element must be sized to the voltage and amperage of the DC supply for the most efficiency.  On the average you can expect an average water heat gain with solar panels hooked directly to your water heater of heating 50 gal/ per day by 7 deg F.

The bottom line is that it is most effective to heat water directly from the sun rather than going through the efficiency loss of solar panels.

I have found that heating directly from the sun is equivalent to about 5 to 7 solar panels.

For more information go to my web site.  If you select "local power production" you can view the output of my solar panels by the hour, by the day, and by the day from the time I installed them in early March of 2012.

http://www.solarkitsllc.com


Ray D (Monte) Benham

PS  My electrical bill is $11.05 per month because I must pay for a meter read and the state of Washington paid me $3,633 last year for a years production.  That equates to about $5500 per year on an out of pocket investment of $41,000 and an actual cost of $28,700 with the 30% federal tax credit.  My system pays for itself in 5.2 years.  Less time if power rates go up.  Then if I sell my house Ill get my money back twice.
solarusmc

Registered:
Posts: 180
Reply with quote  #6 
Ray,

Thanks for that explanation Sir,

appreciate it for sure.

__________________
Pat B. Warwick, Rhode Island Rest Assured! Comments and/or suggestions I make here at the forums on 'your' projects as well as my own have all been carefully and scientifically calculated by the 'seat of my pants'
netttech

Registered:
Posts: 720
Reply with quote  #7 
Ray, that's how I felt too...waste of a good solar PV for a dab of heat. Solar hot water panel is way more effective & cheaper than a solar PV panel.

You obviously live in a state that's generous for solar pv users. Here (Illinois) the regulations vary even to individual utility companies.

You are lucky to get anything back & then...maybe pennies. You mostly get credit against your account, for the most part. According to our regs...IF you get paid anything, it's the price of the fuel the utility company would need to generate that much power.

If you're utility company is a coop, you get 'credit' against your monthly bill only. Even then, the credit can only accumulate over a period of a few months...then wiped clean. 

Pay back can take longer here.

Jeff
Central IL
sunwest

Registered:
Posts: 4
Reply with quote  #8 
Quote:
Originally Posted by netttech
Wattage is a measurement....not power. Amperage is true power. The higher the amperage, the more 'power'.

100A x 1V = 100W not much "power" there, but a lot of amps.

Wikipedia: Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent 'energy per unit time'.

Quote:
Originally Posted by netttech

A quick check on Lowes website a 4500 watt WH uses 18+ amps.

Generally on a water heater they use a big heating element for fast recovery, so the 18A runs for something like only 10 minutes.

With any solar, it's a all day long thing. Thermal or PV it doesn't matter because to be economical you don't size the system for fast recovery, the system would be too big and expensive to only run for 10 minutes and then not be used for the rest of the day.

That same 10 minute run could be done with 750W in a hour, same energy spent.

Quote:
Originally Posted by Ray D Benham
Its more efficient to heat water directly from the sun.

If you can get it directly to your tank. But you forget about the long pipe losses, leaks, freeze problems or systems to prevent it, pumps and other expensive equipment that needs maintenance. Installation costs and time for all that also need to be considered. Glycol needs to be changed for risk of it becoming acid that eats little holes in the copper pipe. Losses in transfer tanks and night time losses from a second transfer tank if used.

So for the simplicity, cost and versatility of PV (can be used for other things, re-wired for SHTF) you lose a little efficiency. And it's easy for the starting out DIY guy to install PV with just wires.

As for the element has to be sized, that's what MPPT does electronically, efficiency is constantly adjusted for the maximum power to the element and tank.

There was a government NIST study done years ago that concluded that HW using PV will be OK when the prices come down to about what we have now, less than $1/W.
http://fire.nist.gov/bfrlpubs/build02/PDF/b02012.pdf

stmbtwle

Avatar / Picture

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Posts: 2,859
Reply with quote  #9 
The advantage of PV is it's versatility. My solar thermal water heater can only heat water and once the tank is up to temp it just sits and cooks. The PV array can run everything in the house.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
GaryBIS

Registered:
Posts: 243
Reply with quote  #10 

Hi,
Solar thermal is about 3 times more efficient than PV (about 50% vs 15%).  

So, to produce a given amount of heat, you have to have 3 times the area of panels on the roof for PV.

PV has gotten down to about $1 per peak watt for the PV panels.

DIY solar thermal collectors cost about 17 cents per peak watt -- 6 times less expensive.
(the 17 cents for 50% efficiency and $8 per sqft of collector)


Drain back solar water heating systems are very simple and low maintenance.  

Gary











 

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