Topic: Solar Hot Water Report

Solar Hot Water Report 

Here's a link to a report, just out, by the Parliamentary Commissioner for the Environment, Jan Wright, examining the benefits of Solar Hot Water in terms of climate change etc. and whether governments and councils should promote it.

http://www.pce.parliament.nz/assets/Uploads/Hot-Waterweb.pdf

Interesting, well put together, very readable report and, regardless of your opinions on the conclusions it makes, is a good overview on the state of the NZ electricity sector in terms of the challenges in moving towards an essentially carbon neutral electricity sector.

It argues that the primary concern for such a goal is the reduction in peak loading of the grid by use of such tools as ripple control and smart meters(ones that can actually talk to the devices such as the HWC.).

Re: Solar Hot Water Report 

No doubt that solar hot water is not the most economic way to heat water at the moment but it is a bit of independance from the power companies.
If we make ourselves totally depending on them, they can do whatever they like.
Being self sufficiant and independant as much as possible is the best asset for times to come.

Re: Solar Hot Water Report 

Just read the report - and the appendix comparing solar to heat pumps.

For many households it's clear a heat pump is a better option - and a better option for the environment as well. In real life they also invariably save more energy than solar.

The only downside with a heat pump could be the life expectancy versus a good solar system.

JK

Re: Solar Hot Water Report 

And dependency on the power companies!!
The pump of a solar system can be run by a very small gen or whatever if there is a power cut, but the heat pump stays cold. Or even gravity but lesser efficient.
We are rural and power is not the most reliable and the corporate rip off mentality of the power companies becomes most obvious in the rural areas.
The more we make ourselves dependant the more they can control us. A passive house is one way towards self sufficiency.

Re: Solar Hot Water Report 

I have a few criticisms of the report. It says our hydro peaking capability is quite limited but doesn't really quantify that and doesn't take into account that as peaking capacity effectively becomes more valuable that more investment will be drawn to it and innovation used in this area e.g Holding more hydro capacity for peaking, using storage like pumped hydro, perhaps having some limited battery storage in houses to cover peaking (and power cuts), using electric cars for storage.

As a study of how the government might get best value for money in meeting renewable/ carbon goals in the present day, it is quite useful.

Perhaps the cheapest method would be to have timers put on our HWCs to run only at night.

Re: Solar Hot Water Report 

Ripple control was mentioned in the report as being an effective means of reducing overall environmental impact of water heating.

Re: Solar Hot Water Report 

Yes that's right, unfortunately ripple control coverage is quite patchy these days and only effective in some parts of the country.

As to smart meters, it suggests that the current crop can't do the job of switching off the HWC when required and calls for standards to be established to ensure smart meters can communicate with appliances for grid management purposes.

Re: Solar Hot Water Report 

I saw the article about the report in the papers and it gave me a completely wrong impression... it was written really bad (the article - not the report)... anyway, I would say that solar HW with 50-70% savings is certainly a good option. Compare this with the heatpumps that on averave (though the year) might achieve COP of maybe just over 2.0 and it comes very close... when you say the heatpump is clearly a better option, I am curious why...
Nice think about the heatpump for me is when they are in the basement... dehumidifiers at the same time and can be used to cool you house too...

Re: Solar Hot Water Report 

My quick read of the report noted a photo of an evacuated tube system but there didn't seem to be any data about such collectors or the relative efficiencies of these compared to the more basic solar panels.

Re: Solar Hot Water Report 

Flat plate are more efficient.
see http://www.heliodyne.com/industry_professionals/downloads/Evacuated%20Tube%20Comp.pdf

Bottom Line:
Performance:• Flat plate gives better year round performance
Efficiency:• Flat plate is best at delivering temperatures needed for the most common hot water applications
Cost & Value:• Flat plate is generally less expensive and gives more energy per dollar spent than vacuum tube
Cold Weather Performance:• Vacuum tube does not carry an advantage over flat plate because snow build up hampers its performance
Installation:• Vacuum tube collectors take more time to assemble while flat plate collectors take more effort to hoist onto the roof
Durability:• Vacuum tube collectors are fragile and prone to more maintenance

Cheers
Mike

Re: Solar Hot Water Report 

That's interesting... I was under assumption that tubes will deliver more as their performance is not as dependent from the orientation and will deliver more in colder periods...
I have gone for the german Wolf TopSon F3-1 because they were half the price of their vacuum tubes.
Aren't most manufacturers in NZ selling vacuum tubes?

Cheers,
Dejan.

Re: Solar Hot Water Report 

Hi Solar Mike

The evac tubes I sell come ready assembled - so it's just a matter of lugging them onto the roof.

Been giving the whole concept of SHW some more thought - the evac tubes' efficiencies don't fall off so much at higher water temperatures as flat plates, so if you manage to have a tank with a high temperature rating (say stainless steel or copper, NOT enamel/glass-lined etc), then using evac tubes when the cylinder is already hot would give better performance than flat-plate.

I'm actually not fussed whether flat plate collectors or evac tubes are installed, as long as the system delivers hot water to my customer at a reasonable price. I am however concerned about the life of hot water heat pumps as well as the refrigerants used - so I think I would lean towards solar because of these reasons alone.

I would say that the power system would probably prefer hot water heat pumps since not only the summer/winter power demand variation is less for this technology than SHW, but when a HWHP is heating, it uses much less kW than SHW, which means the amount of transmission infrastructure can be less over time.

To address this possible disadvantage, SHW systems need to increase their storage capacity (double or more) so that you heat the water when the sun is shining and get the tank very very hot, then the need to top up when it is cloudy for a couple of days would be less.

Re: Solar Hot Water Report 

Hi Seeker

I agree with you, In reality provided the heat absorption areas of evac tube array or flat plate is sufficient, then it doesn't matter what technology is used. That article I posted (pdf) was in response to the previous question on differences in efficiency.
Obviously in extremely cold locations tubes will perform better, provided they don't regularly get covered in snow. For a given surface area though flat plate will transfer more heat into the transfer fluid in low sun or cloudy conditions, as the heat pipes don't start working efficiently until their internal temp exceeds 50 degrees.

I think the reason why tubes are now more common in NZ is, in the past the quality of flat plate collectors available in NZ has been very suspect, they were failing within a few years, where they should last 25. Also the installation methods were not up to standard, hopefully this is now not the case.

One has to remember all these systems are not maintenance free, it is not a case of install and forget, this issue will be the early demise of many installed solar installations.

Fully agree with you on sizing of HWC tanks, tanks installed in expensive NZ are just too small, family of 4 should have 500-1000 liters for best efficiency, with any heating element sitting in the top 1/3rd of the tank.

A new subdivision of 1000 or so homes is being developed short distance from where we live in Wellington, drive past it every day, to date I can only count 7 houses with solar hot water panels installed. People still don't get it, this is sad.

Re: Solar Hot Water Report 

Hi Solar Mike

With evac tube "U" tube systems as opposed to evac tube "heat pipe" systems, I don't think you have to wait until the temps exceed 50 deg. I have heard someone characterize the "U" tube systems as no different to flat panels except for the vacuum insulation on evac tubes.

The thing with SHW as a mass market product is that there are a lot of systems out there that simply do nothing. I have recently come across two people, each with a SHW system (pumped) but no controllers. So the system was pumping the whole time! How on earth could a seller get away with doing this to their customer!

Re: Solar Hot Water Report 

We have a Kloben KT12 (evacuated tube) based system as described here: http://www.energywise.govt.nz/product/kt12280
and have been extremely impressed with its performance. As a comparison in performance check out this flat panel system that returns similar zone 5 kWhs but with twice the panel area: http://www.energywise.govt.nz/product/greenglo-180d-two-greenglo
(Incidentally does anybody know how EECA's "zones" are defined?)

Our system uses a glycol carrier for heat transfer to the cylinder circulated by an 80W pump that is programmed to start once the collector header temperature reaches 8 degrees above the (bottom of) storage cylinder temperature. Once a 4 degrees differential is attained the pump stops but on a clear to light cloud day the 4 degrees differential is not reached until day's end. The 280L in-house cylinder has an electric element which heats the top 1/3rd of the storaged water.

We have had one alarming situation where a scheduled power outage (to reconnect a neighbour's pump shed) resulted in a 1 hour period at 9:30am where the pump was inoperative. The collector temperature reached 145 degrees during this time and as the system will not pump beyond 120 degrees, to safeguard the collector, circulation did not restart. As the temperature rose to 165+ our installer checked with his supplier to be informed that temperatures above 190 had been observed in other such installations with no damage occurring. The situation solved itself late afternoon as the sun dipped and we now have a UPS in place to prevent a reoccurrence. Incidentally the panel is two stories up on a 45 degree pitch so accessing it to cover it wasn't an option.

The low light conditions that our evacuated tube system 'cut in at' are impressive to say the least and probably betters the 'start up' light levels of our PV set-up. Obviously with any SHW system you will get what you pay for but we feel that any flat panel system would struggle to even come close to the performance of a system such as ours. We enjoy better than 6 months of electricity free (other than the pump) hot water per year with respectable solar contribution outside that period.

Re: Solar Hot Water Report 

Hi Harm Less Solutions

Evac tubes can withstand high temperatures - the "stagnation" temperature of the evac tube collector I sell was tested to 200deg C with no deterioration in the insulation around the manifold (everything else on the collector panel can handle those temperatures. I have one installed on my house and it has reached that temperature a few times without any issues - just got to make sure no-one decides to bypass the controller and pump cooler fluid through it in that condition.

Indeed, Paradigma (not my supplier) has teamed up with some Chinese govt body I think, to develop ultra high temperature evac tubes (which will operate above 150deg C) in order to get the heat required for solar cooling applications! (using absorption chillers).

The system you have would probably be higher cost than an equivalent flat-plate system - so the comparison of "better performance" is not telling the whole story. What I would like to get some data on is $/kWh delivered so that we can compare systems on a fairer basis.

Seeker

Re: Solar Hot Water Report 

Hi Seeker, you would be right with U tubes, they have exchange fluid flowing through them, so these would perform better than lesser insulated flat panels.

Harmless Solutions: You seem to have a quality setup which is great, any well built and designed system installed correctly will perform well, regardless of panel type. My own DIY built flat panels use a 12volt DC magnetic drive pump to avoid any issues with AC power outages, AC power to the cylinder element is only used approx 50 days per year, rest of the time its turned off. It is a great feeling to have a 20 minute shower, knowing its costs nothing except for the water.

We have a heat exchanger under the floor that extracts heat from the waste shower water and transfers it into the shower mixers cold water feed supply, this has an immediate effect of using 30% less hot water for that shower, good for winter when the HWC doesn't get as much heat input.

Re: Solar Hot Water Report 

Hi Harm Less Solutions

Solar Mike is right - your system does sound like a quality set up. And one that should last a long time. I did not mean to knock it.

I've stood next to an evac tube collector on a cloudy/rainy day at Field Days a couple of years ago - and the outlet piping was warm even in those low light conditions which you mentioned.

Seeker

Re: Solar Hot Water Report 

"The system you have would probably be higher cost than an equivalent flat-plate system - so the comparison of "better performance" is not telling the whole story. What I would like to get some data on is $/kWh delivered so that we can compare systems on a fairer basis."

@Seeker,
Our system combo was recommended by a plumber who is a close friend who also gave us 'mates rates' on what was a far from straightforward retro fit install so our costs will be too distorted for a meaningful comparison.

Re: Solar Hot Water Report 

I agree - every house is different as well, and how people use hot water is different too.