Hi,
We are building a small one bedroom granny flat and would love to include PV array , solar hot water and other green features however budget and available space may limit some options. I would like others opinions about installing PV panels and connecting directly to a standard 250 litre electric tank on the ground .At a later date, we would like to add a battery bank if possible to upsize the PV system .
I read in a recent RENEW magazine that Lance Turner thought it a practical option with several advantages over a traditional solar thermal HWS .
Has anybody done it who would like to desrcibe the methodology and parts required ?
Are there commercial systems available as yet ?
What would the boosting options be ?
Thanks in advance for all your thoughts ...
advice on pv connected directly to hot water system
(8 posts) (6 voices)-
Posted Thursday 15 Sep 2016 @ 8:05:04 pm from IP #
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Bushwalker
MemberThere was an article in ReNew a couple of years back. I think it was in NZ and the PV panel was connected directly to the electric hot water tank (resistance element) It worked.
Maybe someone has access to that copy?
Posted Thursday 15 Sep 2016 @ 10:53:10 pm from IP # -
It is a bit tricky to use a standard element designed for 240VAC- DC is dangerous in that arcs tend not to extinguish as easily as with AC, and switchgear, circuit breakers etc must be rated for DC, which means they are a lot more expensive. Also, it would be illegal to set up yourself. You would need a reasonablly sized array to produce enough heat, and be careful about matching up your panel string lengths.
As long as you stay below 120VDC you are allowed to work on it yourself, but must still follow the regulations. Putting 120V into a 240V 2.4kW element will only deliver about 600W (see ohms law). There are 48V elements available though, so no doubt it could be done.
Whether or not it is a good idea is the question
Why use ~15% efficient PV panels to heat water, when you could be using 80% efficient evacuated tubes? Feeding PV generated 240VAC into an electric HWS in the middle of the day when you have excess energy available is a good idea, and especially so if you are on a NET FiT, which everyone will be soon when the Gross schemes end. Using your own essentially free energy instead of peak or off-peak dirty grid power is a good money saving practice, plus much more environmentally sound.
New generation inverters have built-in smarts that can divert excess energy to loads such as solar hot water, rather than exporting the energy to the grid.Posted Friday 16 Sep 2016 @ 1:38:21 am from IP # -
thanks for your thoughts .. i should have been clearer.. I had envisaged also installing an inverter ,not simply using DC power.
Posted Friday 16 Sep 2016 @ 2:00:53 am from IP # -
Greg
MemberSome info in these ATA threads that might help (or hinder)
http://www.ata.org.au/forums/topic/12294
http://www.ata.org.au/forums/topic/1752
DC devices like these http://commodoreaustralia.com.au/product/solar-hot-water-booster/
are avaiable as well.Posted Monday 19 Sep 2016 @ 2:34:18 am from IP # -
David
Memberdave lawrence said:
I had envisaged also installing an inverter ,not simply using DC power.That's fine, all STD Grid Solar installs are only NET now so all power from the system will always be used locally for everything first before excess is exported. If you wish to specifically use power from the system to heat water then some electronics is required so that only power from solar is used to heat water, I'm assuming that it is an element (resistive)hot water unit in this case, If a heat pump system is used then it more difficult to do due to inductance from motors being involved and the electronics that will work for a resistor will not work for a heat pump.
Posted Monday 19 Sep 2016 @ 3:48:04 am from IP # -
David
Memberaxess said:http://www.easywarm.co.nz/
I am sure they distribute in OZ.
Interesting, I'm not sure there approved here, I could find anything for AUS in quick 5 min hunt, does not mean there not but be aware they may not be.
If you're specifically wanting produce HW then retrofit solar-tubes are vastly more efficient than installing PV to the job and still have the fallback of grid if there is not enough HW or not enough Solar to heat the water.
Solar PV system, using an electronic energy diverter connected in such a way as to monitor gross PV output specifically a STD Solar system can do exactly the same thing even though though it is connected to the grid. Once the Hot Water is heated it will supply energy to the rest of the house and if there is still too much then it exports excess to the grid. Personally if HW is your first target and your going to use STD PV this would be the way I would do it, it makes the most of the power all the time, rather than just for HW.
Posted Tuesday 20 Sep 2016 @ 1:28:19 am from IP #
