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My green solution


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Hi everyone,

 

My solution to Eskom and the global warming issue goes like this; for hot water; a Geyserwise 900W/2200W AC/DC element powered through a Microcare 40A MPPT from 4, 305W black series Sunpower solar panels and then for electrics a 3kW plus Infini powered from 14, 305W black series solar panels with 8 100Ah Lead Crystal batteries as backup.

 

The system works great, the geyser has been up & running for just over a month and in this time I've only had to add AC power for half an hour on two occasions, otherwise we see 75 degrees almost every day.

 

The inverter is a peach. The Infini has been operational for 3 weeks now and has surprised me with it's output, and although the plan was not to run it grid-tied I tested it for a few days. The veld fire smoke here on the highveld really dampens the power generation, however I've still seen 21 to 24.4 kWh on normal sunny days and 13.1 kWh on a cloudy day.

 

Here are some pics

 

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It may make sense if you have excess PV capacity on your existing system. 

 

I would go for it if my system was intelligent enough to use the excess PV capacity only and dump that into a variable load, such as a DC element to heat my domestic hot water. 

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Hi guys,

 

thanks for the compliments. I also started out looking at vacuum tube systems and heat pumps, however I found that they just had too many issues.

To answer the question as to why I went with PV geyser heating:

  • evacuated tube systems are sensitive to cold and can freeze, have problems with lime scale build-up and temps running away in summer and then there's the matter of the plumbing. To size the number of tubes so as to have perfect heating in the winter the system will be over spec in summer and the heating action of the tubes can not be turned off. If left unattended the only thing that can control temp is the TP valve. Should the pump be turned off, without the waters heat dissipation, the vacuum tubes can go to their stall temp of 255 - 270 degrees damaging the internals of the vacuum tubes and shortening their lifespan. In my opinion one should fit a roller shutter over the tube assembly to close off the sun once thermostat temp has been reached, however this is an additional expense!
  • Heat pumps work better when the heat gain required is small like in summer. These systems use the heat generated by the compression of the gas to heat your water. The more heat that is gained from ambient air temp via the heat ex-changer or geothermal loop the better the compression temps thus the better the water temp. Generally heat pumps have a coefficient of performance (cop) of about 4, meaning that the input power of the pump is multiplied by 4, thus a 1 kW pump should have a heating output close to 4 kW. However in the winter when incoming water temps are lower and air temps are also low this cop can drop to 1, leaving one with cold water when it is needed most!  A heat pump that is geothermally linked through an underground heat ex-changer tubing loop has a higher cop, 7 or more and is more consistent all year round, but is very expensive.

I hope this helps to explain my choice in rather going with the PV AC/DC setup. So far this winter it has performed well giving me gains of between 28 and 36 degrees on a 200 L geyser necessitating AC boosting of no more than 30 minutes only a few times.

 

For those who are interested, check out the Thermo Max system on www.kingspan.co.za.

 

Clint, I used Deltek power in Alberton for my batteries and they gave me good service. 

 

Good power generating.

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  • 2 weeks later...
  • 4 years later...

Very neat but why the fuse on both positive and negative lead?

Correct me if I'm wrong but fuses do have a power loss across them, which although very low can be more significant in high current applications.

Either way fusing both legs seems unorthodox for an electrical installation.

EDIT: Interesting: https://www.linkedin.com/pulse/case-dc-system-design-why-fuses-mandatory-both-poles-only-upadhyay/

Looks like it is important :) 

Edited by Gnome
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1 hour ago, Gnome said:

Looks like it is important :) 

As you discovered through that link (that is a brilliant article by the way), it has to do with whether the system is floating. In such cases the first earth fault goes unnoticed and things only go bad once the second fault completes the loop.

If you think in terms of a car: It is normally negative grounded, and you will have a fusible link on the positive side at the battery. Imagine that you duplicated this setup for your camping battery in the back of your bakkie (only one fuse), but you left it floating. If the positive side somehow chafes through, that system is now positively grounded and a short on the negative side will cause a fire unless you fuse that side too.

If however the odds of such an earth fault is low, such as not having any exposed metal around the positive pole of the battery, then one could possibly argue that a single fuse is sufficient.

Edited by plonkster
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Yeah I've taken for granted that AC supply ties one leg to ground potential to avoid exactly this situation of a floating supply.  Something I've studied but totally forgotten about until that article forced me to think about it.

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