Subject: Re: Search for solar-energy-storing

From: Francis Council <[email-masked]>
Date: 14 Apr 1996 21:05:43 GMT

Are you interested in disucssions where a photovoltaic panel is connected 
to a hot water heater and the hot water heater is used to store the solar 
energy?  The design is matter of using common sense.

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From: Frank Spiegel <[email-masked]>
Date: Mon, 15 Apr 1996 18:44:53 +0200

Hi,
 
> Are you interested in disucssions where a photovoltaic panel is 	> connected
> to a hot water heater and the hot water heater is used to store the >	> solar energy?  

No, not quite. I am more looking for solutions in the field of thermal
storage in a small oder medium scale (one house or at maximum a small
housing area). But I am also interested in new developments in related
fields (high-temperature-storage etc.) 

Bye,
	Frank

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From: "Duane C. Johnson" <[email-masked]>
Date: 15 Apr 1996 18:46:05 GMT

I am a sckeptic Francis;

>energy?  The design is matter of using common sense.

Well if common sense is used it is neither cost effective nor efficient.

1. The solar cell in a system is at best 15% efficient where a thermal
system can be over 50% efficient. Probably more.
2. The solar cell is much more expensive per square foot than the
thermal system. Probably like 4 times more expensive.

The concept of energy value needs to be discused.
Electric energy is much more valuable per BTU than just thermal energy.
Don't just waste this extra value by converting the valuable energy into
cheaper energy.

-- 
CUL8ER
Duane Johnson
Red Rock Energy
1825 Florence St.
White Bear Lake, MN 55110-3364
USA
[email-masked]
http://www.geocities.com/SiliconValley/3027/
(612)426-4766 home (615)635-5065 day

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From: Francis Council <[email-masked]>
Date: 18 Apr 1996 00:12:54 GMT

Can you tell me where you got the figure that a thermal system is 50% 
efficient?  My approach has been to eliminate some of the losses that are 
present in systems used today.  A typical arrangement involving 
photo-voltaic cells is to use the electrical power from the solar panels
to charge storage batteries and then when there is a power demand, take 
this stored chemical energy and convert it back to electricity. Not only 
is there is a loss of energy for these various changes of state but there 
would be some power loses  for the inverters.  As you can see, I am not 
proposing anything radical, I am only trying to eliminate some places 
where there are power loses.

                                       Frank

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From: [email-masked] (Jonathan sawyer)
Date: Thu, 18 Apr 96 22:34:07 GMT

>thermal system. Probably like 4 times more expensive.

What about PV's running a heat pump?   In my house I have a geothermal
heatpump heating a 3000 gal water tank which, in turn, heats the house
through slab heating.  COP of the heat pump is over 5.0 (50 deg to 90 deg).
Powering this with a 15% efficient photovoltaic panels will produce over
75% "heat" efficiency AND the colder it gets the more heat you produce!.

Of course you also get free electricity in the summer.

I am in the process of installing PV panels for such an operation.  I priced
the system cost of PVs and thermal panels and found the PV's to be only
50% higher on a square foot basis.

Jonathan Sawyer

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From: [email-masked] (Nick Pine)
Date: 19 Apr 1996 07:25:36 -0400

>>Well if common sense is used it is neither cost effective nor efficient.
 
Economies of scale and past subsidies may influence prices more than common
sense at the moment. These prices depend on biased advertising and ignorant
consumers. Perhaps a lot more $4/watt PVs are being produced than rooftop
water heating solar panels now, and maybe that's a good thing. There are more
efficient and cheaper ways to heat water, eg some commonsensical $4/ft^2 bare
swimming pool tube mat heaters or a $2/ft^2 site built EPDM rubber collector
or low-priced Big Fins in a sunspace. 

>What about PV's running a heat pump?

Dumb idea. But smarter than running electric resistance heaters or
electric clothes dryers with PVs...

>In my house I have a geothermal heatpump heating a 3000 gal water tank which,
>in turn, heats the house through slab heating.

How about heating the house via a low-thermal-mass plastic-glazed sunspace
with a low-power fan or motorized damper in series with two thermostats
on a day with some sun?

>COP of the heat pump is over 5.0 (50 deg to 90 deg).

The COP of John Christoper's 1981 CSI HQ building in New Hampshire is about
50 ("2% fan power, 98% sun power.") Improve that with a sealed containers of
water in the "rock bed" and motorized dampers vs fans or blowers and it might
have a COP of 500:1 at a lower initial cost. A motorized damper costs about
$100 and uses 2 watts when moving, 0 watts when not moving (most of the time.)

>75% "heat" efficiency AND the colder it gets the more heat you produce!.

Do I have this right? 1 joule of sun falls on the PVs, 0.15 emerge from
the PVs, 0.15 go into the battery, 0.15 come out of the battery, 0.15 come
out of the inverter, 0.75 come out of the heat pump, 0.75 go into the water
tank, and 0.75 come out of the water tank, all with no additional input
of energy, at a system cost of $10/delivered watt of house heat? 

Now suppose we put the PVs in a sunspace and the 85% of the sun's heat that
is normally wasted with PVs ends up heating the sunspace air which flows
into the house and heats the house. This would raise the system efficiency
considerably, no? And you and your friends could sit in the sunspace and
play cards and admire your PVs on a winter day with some sun, and revel
in how independent and creative you are.

Now omit the PVs, and the cost drops dramatically, while the system efficiency
remains about the same, on a day with some sun.

Now add a little insulated room containing enough sealed containers of water
to store heat for a week without sun, with 10' of fin-tube pipe near the
ceiling of the little room and a water heater in a warm-water convection loop
on the floor above, and the system efficency rises again.

Add a little more floorspace to the room, and you have a sauna with free heat
and a place to dry clothes.

Now omit the 3000 gallon tank, plumbing, slab plumbing, pumps, heat pump,
etc, and the cost nosedives again. Before long, you may end up with a simple,
practical heating system, unless you are in love with PVs and heat pumps. 

>Of course you also get free electricity in the summer.

"Free," after that little matter of buying the PVs, batteries, inverters,
etc, etc..

>50% higher on a square foot basis.

Water heating solar panels are no bargain at $30/ft^2. Polycarbonate plastic
"solar siding" or a roof or a sunspace that lasts 20 years at $1/ft^2 is.
Polyethylene film that costs 4 cents/ft^2 and lasts 3 years before it needs
recycling, while producing $3/ft^2 worth of heat is definitely a bargain.

PVs are not a bargain, altho putting them in a sunspace or adding an
extra layer of glazing and trickling some water over their faces before
the water goes back to your 3000 gallon tank might be a good idea.

Stanford Ovshinsky's amorphous PVs produce 50 peak Watt/m^2 at 20 C and
45 pW/m^2 at 60 C, at a cost of about $4/pW.

Nick

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From: "Duane C. Johnson" <[email-masked]>
Date: 19 Apr 1996 21:13:07 GMT

I am still a skeptic;
>>I am a skeptic Francis;
>>
>>>Are you interested in discussions where a photovoltaic panel is connected

>75% "heat" efficiency

I am aware of COP (Coefficient Of Performance) as used in heat pumps.
Solar systems can supply the heat energy input to the evaporator side
of these systems. I think NASA had a demonstration setup for one of
these systems.

>AND the colder it gets the more heat you produce!.

This is misleading. I think that you mean that as the input water
to be heated is colder the COP improves.

What you didn't say (to be fair) is that a solar collector can supply
the energy for the evaporator. Usually this temperature is higher than
can be obtained from geothermal sources. This also increases the COP.
I think the NASA demo had a COP of around 20 or so.

>Of course you also get free electricity in the summer.

Well nothing is free. The real cost of the electricity is the
amortized cost over the life of the panels and batteries. If you
already have an electric power utility near this amortized cost 
will never pay for itself .

In Minnesota there is a law that requires "Solar Equipment" have a 
today's dollar payback period of less than 40 years. There was a famous
case where the manufacturer of those small parabolic tracking trough
waters were prevented from being sold as solar equipment in Minnesota.
The cost was about $3000 and produced $50 worth of hot water per year.
At this rate there will never be a payback.

>I am in the process of installing PV panels for such an operation.

Do you have a power utility connected to your house?

>I priced the system cost of PVs and thermal panels and found the
>PV's to be only 50% higher on a square foot basis.

Now for the real comparison. What is the cost of the solar thermal
collector compared to the PVs and the geothermal system combined.
What are the costs of the heatpump service? 
This is the true comparison.

This seems to violate the KISS principal!
Keep it simple.

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From: [email-masked] (gcp)
Date: Sun, 21 Apr 1996 12:48:24 GMT

>thermal system. Probably like 4 times more expensive.

This idea is actually being seriously considered.  
The National Institute of Standards and Technology in Maryland has
patented a houshold solar-powered water heater - it is a photovoltaic
and resistive element(s) system.
Quote:  'At the Department of Energy's long-term goal of $0.50 per
peak watt, the NIST system would cost less than half of today's cost
for a solar thermal unit'
It is also worth considering that if photovoltaics are designed into
roof tiles or windows (there is now a process that makes this
possible, and although the efficiency is lower it may be cheaper) then
it is possible to write off part of the cost.  Also, though they may
not appear to compete with utility prices, if you eliminate the
middleman and the transmission costs they are near competative.
At present an idea worth considering might be to connect a solar
thermal unit to a well insulated low-grade thermal store, and heat
pump out of that with a photovoltaic or wind generator?
No substitute for designing a house to make best use of the available
energy in the first place.

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From: [email-masked] (David)
Date: Mon, 22 Apr 1996 09:41:27 GMT

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From: [email-masked](Will Stewart )
Date: 22 Apr 1996 10:37:44 GMT

In <[email-masked]> [email-masked] (Jonathan sawyer)
>through slab heating.  COP of the heat pump is over 5.0 (50 deg to 90

Are you in an area that generally demands A/C?  I've considered the
slab approach, though have shied away due to the condensation problem.

How much do you spend to heat with the geothermal heat pump?  Would you
recommend it to others?  Any lessons learned?

>Powering this with a 15% efficient photovoltaic panels will produce
>over 75% "heat" efficiency AND the colder it gets the more heat you
>produce!.

How did you size your panels; can we assume you are on the grid?

>Of course you also get free electricity in the summer.

And other times of the year too!

Cheers,

Will Stewart

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From: Dave Austin <[email-masked]>
Date: 23 Apr 1996 16:15:14 GMT

Hi Will:
   I saw your posting about a solar assisted heat pump system you have in 
your home. I thought I was the only one who did this. We have had one in 
our house since 1982. The solar tank in ours is 1500 gallons with 620 sq. 
ft. of solaroll collector. The tank is the source for the heat pump. We 
use ground loops for backup. We also have radiant floors. I had thought 
about PVs to run it but I figure it would take about 30 to 40 panels to 
run it, about a $25,000 investment , so we just use the power line. But I 
am reconsidering now that our electric rate is $.15 per kwh. Even so we 
heat a 2500 sf old farm house in upstate NY 7300 deg days for about $600 
per year. Our system also has AC for summer.
I have a business installing these systems. You might want to check out 
my web page: 
http://ourworld.compuserve.com/homepages/davenrgman/savngnrg.htm

Dave Austin