Water, water everywhere....and a power update.
by, 2013-09-13 at 01:19 PM (106371 Views)
Continuing the story of our journey to go off-grid that started over here.
Solar Hot Water
Our local utility provider is pretty adamant that water heating contributes to approximately 28% of household power usage; that seems a little high to me but I'm guessing that they don't take into account households with electric vehicles. In any case, we got the option to apply for, and were granted, a $1,000 rebate for an additional solar water heater. We already have a solar heater for the master bathroom and with our move to full solar it seemed to make sense to add an extra heater for the kitchen and laundry and my daughters bathroom.
Somehow it was kinda ironic seeing that big panel being hoisted up over our back-up generator:
I was surprised to learn that the panel only holds 1.6 gallons of water with another ~1.5 gallons in the pipes going from the garage to the roof. The collector is so efficient that the water is being heated by the sun to ~170F so it cycles quickly down into the insulated holding tank. We installed a thermal valve on water going to the kitchen to mix back in cold water and reduce the temperature to 140F, which should prevent any scalding accidents. The install went well and within 24hrs we were all connected and signed off by the code inspector:
We'll recycle the old tank, which was in good condition but too small, back into the new stables so that we can have occasional hot water there.
The total install cost for the new system was $5,500 minus the PoCo rebate. We are paying an average of $400 monthly for electricity right now and I estimate that hot water (directly and from the dishwasher/washing machines) accounts for 20-25% of our total bills. Given our elevation, popular wisdom here is that we should save at least 80% of the current electricity usage and that seems to have been borne out by watching our meter usage during the last two weeks. The worst case finances look like this:
Install Cost = $5,500 - rebate $1,000 = Total cost $4,500
Power costs $400 x water heating @ 20% = $80 x savings @ 80% = $64 monthly = Annual Savings of $768
Amortization in 5.8 years.
When an average solar water heater replaces a conventional electric water heater, the electricity saved over 20 years represents a reduction of more than 50 tons of greenhouse gases. That significantly reduces the environmental impact of our hot water activities.
We broke ground this week and withing minutes were greeted by a torrential rainstorm that came out of nowhere:
This has been one of the wettest Florida summers in living memory and we are now the proud owners of a perfectly square 40' wading pool. Further work was suspended for 3 days to allow it to drain out naturally...
However, the building hiatus did allow us to hold a site meeting at which we discovered that the building contractor is married to the niece of the solar engineer; it's really amazing how smooth and easy it was for these guys to work together and come up with ways to incorporate everything we want to do.
My research work continued and following up on a comment on my previous post from Slackjaw I emailed Mike Stritzki in New Jersey who did the very same thing several years ago. Mike was kind enough to call me that same night and we had a great chat about all things green and what the true potential was. Mike was a real ground breaker and spent a fortune developing ideas to make them work. From that discussion I took away two key points:
- What I had in mind was absolutely possible to achieve today.
- Although the costs have been coming down, it could still push up to $200,000.
Now the question is how fast do I expect costs to continue falling? We're definitely not looking at a Moore's Law situation but there's no sign of an amortization that makes financial sense. We have discussed that money shouldn't be the only determining factor so it makes sense to continue investigating what I expected would be a two year project as well as looking at battery development as an alternative.
I had initially battery backup as an off-grid alternative due to the ongoing environmental recycling costs and the problems involved with power draw spikes caused by a house with 3 HVAC systems (welcome to Florida!). When I wrote the first blog I had put out questions with various folks and was also interested in dpeilow's previous comment link that he found in the UK. Getting the guys together for a site visit today for a brainstorming turned up some new alternatives...
Firstly, Mike Stitzki had told me that he avoids the power spikes by using a series of intuitive timers that prevent certain items items operating at the same time; turns out our electrician has a simple way of connecting our AC systems via contact switches to prevent them starting up simultaneously. One problem solved!
Secondly, we have some new options on different types of batteries which have much longer expected life, better recycling opportunities and are deep cycle so that we could reduce the quantity of batteries needed. There are still two physical issues but both are manageable:
- Air-conditioned storage space. I have a 12' x 12' area in my existing barn that I can wall in and add a small AC unit to house the batteries and the inverters.
- Weight. Batteries at up to 100lb apiece means we'll need some custom racking and check the floor load capacity.
Thirdly, there is a company here in Florida that builds custom batteries and where we might find Li-Ion alternatives. Conversations have started.
Lastly, we got creative with evening out our loads between the various meters and came up with a plan to incorporate our existing generator as a final back stop for any unlikely apocalyptic battery failure. It'll be a manual switch that would still provide power for lighting, AC, refrigerators and water pump.
More news to come on batteries in the next installment but there's no doubt it would be much more affordable and definitely short term attainable. There is a small level of added urgency as a battery back-up system would affect our choice of inverters versus those we would use for a longer-term hydrogen plan. The rebate program that takes place in October requires us to detail what we want to do and that's only 4 weeks away....
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