Solar / Hybrid system??

[cjc_td5]

I am looking at trying to reduce electricity and gas bills on our two year old house.

Our annual average usage is approx 20 units (kWh) per day, split as approx 10kWh daytime and 10kWh at night. Summer usage is lower (13-15kWh/day) and winter a bit higher (up to 25kWh/day). Daytime is easy and can be offset with PV panels. I would like to build a system that uses batteries to supplement the night-time demand and offset that electricity usage also. I am not worried about getting 100% night-time coverage, if the batteries run down, then I am happy to revert to the grid supply for the remainder of the night.

Assuming that a solar system consists of : panels > regulator > inverter > meter box > house/grid
is it as simple as using? : panels > regulator > battery bank > inverter > meter box > house/grid

From my initial research, there appear to be a few "control box" systems that distribute power between panels, batteries, house & grid based on demand etc. These boxes are about $5K?? Have they got really got $5K of electronics in them??

I am thinking about 3kW of panels are about the capacity I would need.

What are my options here?????

Also, hot water is provided by two instantaneous gas hot water systems which are supplied by bottled gas. These chew through gas at an alarming rate, about a bottle every 6 weeks, so cost about a $1K per year in gas. I want to change these onto electric storage systems that heat during the day using solar power. I need to research my best options here, bearing in mind that I need two systems to avoid excessive loss of water waiting for hot water to come through pipes etc (we are on tank water).


Any thoughts???

Cheers,

[muddymech]

I would say go 5kw, im in nsw and seem to average ( at a non caculated rate) 10kw a day. With a 3kw system. Some days I can make 20kw on cloudy days I make 0.5kw. On my bill I match what I use over the year. If I could I think a 5kw system would put me well ahead. In terms of what I make to use.

[Vern]

The last battery back up job I did was around $20k, 4.5 kW of panels, 5 kW inverter, 3kw inverter charger, can't remember battery size. All gear (except panels etc.)was from selectronics, really good gear, I would install it on my own place but am thinking of selling so no use.
Have a look at the selectronic my grid systems.

[Vern]

As for your hot water, look at apricus evacuated tube system, you will be able to retain your instantaneous hot water services which will only be required to boost the solar heated storage tank if required.

[DiscoMick]

Our 1.5 kw grid connect system cost about $2k from Origin two years ago and halved our electricity bills, but since then the rebate has been slashed so the numbers have changed. I agree about 3kw should generate enough power for a small family.
Battery bank systems seem to add a huge amount to the cost. Friends installed 3kw battery only with no grid connection and it met the needs of two people fine, but cost nearly $20k, which seems excessive.
I don't know the subsidy numbers for your area. Suggest you do a LOT of research.
In your situation I would either factor in solar hot water or get electric instant on heaters, if they could be powered fully from your solar system. Electric instant units are very popular in Asian countries because of the low cost, but not so common in this country, where we seem to prefer to have a big tank sitting there bubbling away unused much of the time. Seems a bit strange to me.

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[Vern]

Your 1.5kw system will be on a higher feed in tariff, 1.5kw just isn't worth doing these days.
As for your friends with their stand alone system, it may have cost $20k, but it may also have cost $40k to get power on to the property. My next house will be fully off the grid (with a big generator for back up), its not viable where I am now due to loading.
Never really dealt with electric instant hot water other than boiling water units, can't really see this being cheaper than solar storage to run. Those big tanks are thermostatically controlled therefore only heating water if they need to, if they get enough solar gain during the day, they won't need to heat via the electric element or gas boosting.

[cjc_td5]

Thanks for the replies so far guys.

Re batteries, if I aimed at 7kWh of capacity, I would require 700Ah of 12v batteries, so say 4 batteries? Even at $400 each, that is $1.6K. Add a controller at $5K, so $6.5K additional all up.

Remember that this is not a stand-alone "off the grid" system where I would have to allow for potentially several days of no sun. When there is a cloudy day and the batteries do not charge fully and run down, then I just revert back to grid supply.

I suppose add $5.5K for the panels and inverter, then the total cost would be approx $12K.

Cheers,

[Vern]

Inverter and 'controller' need to be able to talk to each other, therefore must be compatible with each other. The system will either be 24v or 48v, this will determine the number of batteries you will need (we have been using 8x6v (3x2v cells) wired in series parallel) You may also find there are only a select few brands that are ESV approved for battery back up.

If you can do this for $12k, you will be using very mediocre gear, to be honest, I highly doubt this can be done. You will be looking at around $4k just for install only, I can't see much , if at all any change from $20k for a decent system

[bee utey]

I doubt that if you factor in the lifespan of batteries being cycled that hard, the inefficiencies of charging/discharging etc that you'd be in any way ahead. I think you'd be best off looking at your appliances and throwing out the big users. A ginormous set of solar panels might cost more than an energy efficient fridge for example.

I live in a modest house with 3 adults, no plasma TV, 2kW of solar panels, LED lighting, wood heating and evap air conditioning. The hot water comes from an electric heat pump system with separate solar collector panels with a sunshine activated pump. Basically my consumption including hot water is around 10 kWh/day in winter and 5 kWh/day in summer. We're quite comfortable and the solar covers 80 to 95% of the eleccy bills due to getting the good feed in tariff. LPG instant hot water is waay too expensive these days IMO.

[JDNSW]

I find it difficult to visualise batteries as cost effective in any grid connected system. As beeutey comments, there are some aspects of battery use you may not be taking into account.

1. Charge/discharge efficiency. While the batteries used mostly give back the same current as used to charge them, they do not give back the same power. To use the numbers for a lead acid system (other batteries will be similar or worse), a twelve volt battery charges at about 14v, but discharges at about 12.5v. This gives a charge/discharge power efficiency of about 89%. There are likely to be further losses from other mechanisms, so this is about the best case.

2. As a general rule, depending on the battery type, the nominal battery capacity needs to twice (or more) the capacity you plan to use. And the deeper you discharge the batteries, the shorter their life. And battery replacement needs to be factored in as a running cost.

John