PV water heating

[russ]

Notice that I did not include the Heatpump water heater. That is because they have many controls & motors prone to failure, plus the sealed refrigeration system will leak. The projected maintainance is just to high to even consider these units.
The most reliable system is the simplest one, with the least amount of electronics and moving parts.

Come on - not different than a fridge really - maintenance free for all practical purposes. Or at least if one buys quality they are problem free.

Refrigerant leaks are due to lousy installation.

The scare tactics are a bit on the silly side.

[Sunking]

Solar thermal is indeed more efficient in terms of the energy it collects per unit area but there are maintenance problems with solar thermal that discourage me from using it.

I think electric water heating by solar PV has much promise - especially for off grid.

That is the worse possible idea I have seen here in the last 4 years. Resistance heating is the most inefficient process there is is without question.

[Sunking]

Solar thermal does require a bit more maintenance than PV.

Wrong, dead wrong. Your statement would be true if he was talking about Grid Tied, but he is talking about Off-Grid Battery which is a full time job.

[Sunking]

The input to the hot water heater will still be AC - not DC. There are no high voltages or currents on the DC side and the setup is very simple. The inverter output can connect direct to the existing water heater. Total cost for a 2.4kW

BS, What are you talking about? Watt = Watt. 2400 watts = 240 volts x 10 amps. 2400 watts = 24 volts x 100 amps every day of the week. The lower the voltage the more expensive and less efficient the system is. Something else that has escaped you is the conversion losses of going from DC to AC that is going to eat 20% or more of your power.

If you live in a Tropical environment you would be a fool to use resistance water heating with Off-Grid battery system. Two best solutions are solar thermal or a fuel like LPG or wood to also be used for cooking.

[Bintang]

Wrong, dead wrong. Your statement would be true if he was talking about Grid Tied, but he is talking about Off-Grid Battery which is a full time job.

Wrong. There are no batteries involved at all. See post #35:
" I’m considering an inverter with module level MPPT control that does not require batteries and is also not grid-tied. The input to the hot water heater will still be AC - not DC. There are no high voltages or currents on the DC side and the setup is very simple. The inverter output can connect direct to the existing water heater."

[Bintang]

BS, What are you talking about? Watt = Watt. 2400 watts = 240 volts x 10 amps. 2400 watts = 24 volts x 100 amps every day of the week. The lower the voltage the more expensive and less efficient the system is. Something else that has escaped you is the conversion losses of going from DC to AC that is going to eat 20% or more of your power.

If you live in a Tropical environment you would be a fool to use resistance water heating with Off-Grid battery system. Two best solutions are solar thermal or a fuel like LPG or wood to also be used for cooking.

There are no batteries involved - see post #35

[Bintang]

That is the worse possible idea I have seen here in the last 4 years. Resistance heating is the most inefficient process there is is without question.

Actually Sunking, “Electric resistance heating converts nearly 100% of the energy in the electricity to heat”.

By the way with over 12,000 posts in 4 years you must have seen it all. I'm therefore curious to know what is the second worst idea you have seen here in the last 4 years. Its always useful to know what the competition is.

Note to moderator: Thank you Mr Moderator for deleting the last sentence of Sunking's original post. I was beginning to feel unwelcome here but its good to see that this forum (which I have only recently joined) does not tolerate personal insults and derogatory statements.

[inetdog]

Actually Sunking, “Electric resistance heating converts nearly 100% of the energy in the electricity to heat”.

And you assume that you cannot do better than 100%?
A heat pump for domestic water heating can deliver energy into the water in the form of heat which is four times the amount of electrical energy used. So in this case 100% efficient is a very poor second to 400%.

[Bintang]

BS, What are you talking about? Watt = Watt. 2400 watts = 240 volts x 10 amps. 2400 watts = 24 volts x 100 amps every day of the week. The lower the voltage the more expensive and less efficient the system is. Something else that has escaped you is the conversion losses of going from DC to AC that is going to eat 20% or more of your power.

Sunking, I will elaborate for you:
The 2.4kW system will use 2 inverters each having maximum output of 1.15kW on the AC side.

Each inverter has 4 inputs to provide separate MPPT control of 4 x 300W PV modules. Therefore the max current in each input conductor will be less than 10 amps.

The outputs of the two inverters are daisy-chained and they have a wide operating AC voltage range.

For example, if the heating element in the hot water tank is 1.5 kW/230 V and the inverters are putting out maximum power the voltage on the AC side will be around 190V.

The cost of each inverter is US$880

[Bintang]

And you assume that you cannot do better than 100%?
A heat pump for domestic water heating can deliver energy into the water in the form of heat which is four times the amount of electrical energy used. So in this case 100% efficient is a very poor second to 400%.

COP of 4 looks a bit high. I’ve only seen a few spec sheets for these heat pumps and the max COP stated by the manufacturer was 3.5 but also ranging down to 2.4 because the COP is a function of ambient temperature.

But its not a matter of efficiency for efficiency’s sake. It’s a question of how much does it cost to achieve a particular energy output and that cost has to include, capital expenditure as well as operating and maintenance expenditure.
A PV system (batteryless) will have higher upfront cost than a heat pump but no running costs. The heat pump has lower upfront cost but has ongoing operating cost for the electricity it consumes.

Which system is better will ultimately depend on location and circumstances, such as:
- availability or absence of government incentives
- price of grid electricity

Just because one system appears to be best for a particular location doesn’t make it the best universal solution. I have openly provided my numbers and reasoning in this discussion and been rubbished for it . But when challenged the detractors have not offered anything to substantiate their own assertions.

I don’t mind being proved wrong and am more than happy to learn from those wiser and more experienced than me. But with a few exceptions all I’ve had so far is , “your analysis is useless” and “hasn’t been done properly” but “go figure it out for yourself”.

[Sunking]

Note to moderator: Thank you Mr Moderator for deleting the last sentence of Sunking's original post. I was beginning to feel unwelcome here but its good to see that this forum (which I have only recently joined) does not tolerate personal insults and derogatory statements.

The Moderators DID NOT EDIT ANYTHING. They do not do that much.

[Sunking]

Actually Sunking, “Electric resistance heating converts nearly 100% of the energy in the electricity to heat”.

Who cares, it is the most inefficient means there is. What counts is COP and resistance heating COP = less than 1. A heat pump type water heater has a COP is roughly 3 or 3 times more efficient than resistance. For every 1 BTU you get out of resistance heat, you could have produced 3 BTU's with the same amount of energy. That means 1/3 the initial input. Instead of 3000 watt panel, use a 1000 watt panel silly. Watts is Watts. Don't forget that as you seem to be doing.

But even using any form of electric water heating is just plain silly in a warm tropical climate. All you need is a black barrel and/or black tubing. You are only taking the water up at most 20 to 25 degrees from ambient 75 to 80 degree water to 105 degrees. Solar thermal is the most efficient and cost effective. That is what you are trying to determine but are using the wrong parameters. The mistake I keep see you making over and over again is looking is $/BTU cost. That is where the most bang for the buck lies. Solar thermal is the most efficient energy transformer when it comes to solar. That alone means much smaller space requirements which mean huge installation material/installation cost involved. Compare BTU dollars, not watts.

Please tell me which DC Battery Inverter you can use power directly from solar panels panels without batteries to run at rated power for any length of time?

[LucMan]

Come on - not different than a fridge really - maintenance free for all practical purposes. Or at least if one buys quality they are problem free.

Refrigerant leaks are due to lousy installation.

The scare tactics are a bit on the silly side.

Really, and what business are you in may I ask.
I have been in the HVAC & refrigeration business since 1973 and in the last 4-5 years the equipement being produced has been the worst junk ever, across the board few manufacturers have been immune. The problem in my opinion has been the use of recycled copper used in the refrigeration coils instead of virgin copper. Do some research before you spout off.

[Bintang]

Please tell me which DC Battery Inverter you can use power directly from solar panels panels without batteries to run at rated power for any length of time?

Sunking, there are some fantastic innovations happening in PV which are going to be ‘game changers’ but they are passing you by.

Its clear that despite spending 4 years contributing more than 12,000 posts to this forum you have not learnt very much – though if your other posts are of the same quality as your recent ones in this thread I can understand why.

So I will offer you the same helpful advice that Russ offered me:

Go figure it out for yourself.

[Bintang]

[QUOTE=Sunking;117954]
The mistake I keep see you making over and over again is looking is $/BTU cost …. Compare BTU dollars, not watts. QUOTE]

Sunking, I'm not sure what "is looking is $/BTU cost" means (grammar?). Are you trying to refer to LCOE and do you even understand the concept of LCOE (levelized-cost-of-energy)?

I have already provided the comparison in $/kWh. And here is a little hint for you: 1 kWh = 3412 BTU

Now go figure it out for yourself.