Off-Grid Solar Setups

[Raspy]

We purchased 32 acres 2 years ago & would *like* to start building. While I'm still figuring out the house logistics (could that be another thread?) as to whether or not to build with SIPs or another method, I've run into an issue with getting electricity to the house. Our utility company in NY is National Grid and they've tentatively given me a $25k number for running electrical from the road, 1300 feet to where we'll put the house. They won't give me a FIRM number until I have some sort of structure built on the property (which seems kinda ***-backwards to me).

With Federal, State & Local rebates I was wondering about going off grid completely with a battery system. My initial findings was that the batteries weren't even lasting 10 years, which made the setup very cost-prohibitive if I had to replace the batteries every 7 years or so. The Tesla Power Wall came out & they guarantee nothing more than 8% loss at 10 years, which would *seem* to me to mean that it should last longer.

Our current temporary house is 120 years old and we use 13,000 kwh per year or 1083 kwh per month. But that's on an OLD home with very little insulation, etc. We're hoping to build with SIPs or closed cell spray foam at the very least, so figuring that along with LED lights energy efficient appliances, a propane stove and dryer, it should all add up to considerably less usage. I'm also looking at hydronic radiant floor heating. Cooling is my biggest concern, though in CNY, we're talking all of 3-4 months and it's not run constantly.

Thoughts, issues, concerns? Anyone already doing this or looking into this?

Here's our land in case anyone is curious...the black outline is ours. I don't have a current areal picture of the driveway we put in last year, sorry!
View attachment 436789

Seems like you should get yourself a good tractor and backhoe and dig the ditch yourself, put the conduit and pull boxes in to their specs and just have them pull the wire. I did this on my house, but it was only 220' from the pole. You'll save enough to pay for the tractor. I also bought an off-road forklift for the project and it too has paid for itself over and over. Then it will move on to another project somewhere, but my tractor stays!

By all means add hydronic radiant in your slab!!! But drive it with thermal solar. Very low cost of operation, also does domestic hot water and there is no heating system more comfortable. Last winter we used three 70 watt circulators, running during the day, to heat our 2,800 sq ft house through the winter. No energy source other than solar. But I also have a wood stove in case we want an evening fire or to take the chill off a surprise cool morning. Now, in the spring, summer and fall months, we have 650 gallons of domestic hot water on tap for occasional bathroom floor heat and unlimited showers. I can't imagine a cheaper or more comfortable heating system! Then, if you need to, you could add a simple air conditioning system that is entirely separate from your heating system. I added a simple duct system and wired the house for air conditioning, but I doubt I'll ever install it.

My priorities in the house design included a steel frame, but most of the structure is 2/6 and 2/8 walls with blown in insulation and blown in attic insulation. Not the absolute lowest heat loss, but totally practical and a structure that is incredibly strong.

I don't like propane, so I only put it in for cooking with the rangetop. I installed a cast iron boiler that runs on oil for backup if needed. Then I modified it to be more efficient than originally designed. We also have an electric water heater that remains permanently switched off unless the solar is shut down for more than about three days or in the event of severe winter conditions for an extended period. In the end, the cost of heating is insignificant

Be sure to include practicality in your design considerations. For instance, you might sacrifice a bit of theoretical R value for much simpler construction or lower cost or stronger structure. R value is only one of many considerations

 

[Redneck in training]

We have 100% electric house but because our PV can't be "islanded" when power grid goes down we have two propane fireplaces for heat backup.

Do you have any battery or just use the grid for backup electicity now?[/QUOTE]

We are Grid Tie.
We installed Enphase inverters that are grid commutated. In other words when grid goes down they disconnect. When grid comes back ON they wait 5 minutes before they reconnect.
The reason for selecting microinverters was DIY solar installation without previous experience. When the panels are illuminated they are ON and more or less impossible to switch off. I didn't want take risk of shorting something and burn the cables or got killed by high voltage. Then I learned during actual installation that it was irrational fear. Installation of PV is pretty straightforward. If you are able to install an outlet or change a breaker you should be able to install PV. 95% if installation is plug in and the rest is simple wiring. If I would do it again I would use "island-able" inverter.
I am thinking about energy storage but so far can't find a controller that would manage it the way I want to. My idea is to manage it such a way that my system will supply energy to the grid only when all energy storage is full and prevent charging of energy storage from grid when sun is not shining. Then allow import of energy from grid only after energy storage system(s) are depleted.
As I already said elsewhere in this and "Grid-Tie" thread our utility doesn't offer net metering at all. In addition the utility cancelled our heating rate after installation of PV essentially increasing our electric bill by 500-600 USD a year. The result is that we generate about 30% more energy that we use and we still have, though low, electric bill. When I initially talked to them about the PV installation they sent me pamphlet describing net metering. But after we installed the PV they backpedaled saying that, because of the size of the system, we are industrial generators and net metering will not apply.
Therefore it is very important to have connection agreement detailed and signed before you spend money for the hardware and installation.
Still I don't want it to look like I am complaining (though I am rather disappointed how I was treated by the utility). We used the tax rebate as down payment for few duplexes bought for distressed price that we sold year later with very good profit making our system paid for itself. You can get lucky sometimes I suppose. I was asked by many people if the system is profitable. I respond with a question if their 50K truck or Porsche is profitable or how much their CD in a bank brinks in. There are many ways to look at investment in alternative energy systems.
If you can include solar in the mortgage it is no brainer. If you get net metering on top of it it is an investment that is hard to beat. That is MHO.
Ladia

 

[Redneck in training]

I'm interested in reducing the draw so a battery system could get through the night. Example; Say I take a shower at night, I'd like the hot water heater to delay recovery until PV system is working to cover recovery rather that tax battery all night while it's running AC or heat? Same with a well pump, no need to fill cistron at night under battery. How can all that be managed. HS

That is very easy to accomplish with a timer with battery backup and contactor . If you want to get fancy then buy a PLC for about 100 USD on ebay. You need to (preferably) select one that has real time clock with battery backup or have external timer that will reset the PLC timer once a day sync it in the case power goes down.
https://www.google.com/webhp?source...n=1&espv=2&ie=UTF-8#q=30a contactor 120v coil
Amazon.com: Hydrofarm TM01715D 7-Day Digital Program Timer: Patio, Lawn & Garden

 

[Redneck in training]

For heating, we're LOOKING at going strictly with hydroponic radiant floor (no HVAC) - it's a solar based system and would be really efficient.

....but that leaves me with how we cool the house for the relative little we need to in the summer.

Instead installing passive solar invest the money in more PV and heat/chill liquid for heating and forced air AC. I just read an article while ago about PV versus passive solar and the numbers showed PV was cheaper than passive collectors and associated heat storage. Since you are in TX you have, presumably, many more AC days than heating days. Here is a link to a heat pump that would do both: Small Heat Pump Chillers | Chiller Air Conditioner For Home or Office | Residential Ductless Mini Split Chillers If you have only small number of heating days I wouldn't spend money on floor heating but rather increase size of PV. If you would be grid tie with net metering then I would use mini split units. They are cheap, easy to install and replace, quiet, very efficient and every room has its own independent temperature control.

We have geothermal HP with floor heating/ forced air AC in our current house but if I would do it again I would do mini splits. We have one unit with two indoor handlers in my shop office and guest room and I like them better than geo. Not speaking about the cost of the geo plus floor heating and forced air. Geo costs at least three time as much as mini splits even though we did a kot of the work DIY.

 

[Got2BTru]

What's the difference between passive solar and PV?

 

[BitChin1]

We have geothermal HP with floor heating/ forced air AC in our current house but if I would do it again I would do mini splits. We have one unit with two indoor handlers in my shop office and guest room and I like them better than geo. Not speaking about the cost of the geo plus floor heating and forced air. Geo costs at least three time as much as mini splits even though we did a kot of the work DIY.[/QUOTE

I agree with you on this point - We have a very low cost for our GSHP and it works well but I also have 2 mini-split units (for ares that duct work was difficult to get to) and would much rather have $18,000 of PV on my roof along with a couple more mini-split units: Put out warmer air in heating mode and worked this winter at -5' F, able to control each area independently, have back up if a unit breaks down, lower peak load than my GSHP along with well to pump water.

DIY PV is very quick pay back (our electricty is ~ $0.13/kwh) - looking into adding it to current house but most likely will wait and install during the build of next house.

How large of a system do you have that triggered the "industrial generator" interpretation? around here I think it is 15KW

 

[dave1949]

What's the difference between passive solar and PV?

This is how I would define solar categories. The distinctions are a bit fuzzy.

I wouldn't consider either of these to be "passive."
solar thermal: collect sunshine heat and transfer it to a medium such as water or glycol. This can be quite "passive" in a thermo-siphon or batch heater tank system but there are usually some active controls involved.
solar electric (pv): generate electricity from sunshine.

direct gain passive solar space heating: heating interior space with sunshine coming through windows. The gained heat is generally absorbed by a thermal mass such as concrete. It works based on thermodynamics: heat moves from a warm object to a cooler object. Warm air to cooler concrete on sunny days, and warmer concrete to cooler air overnight.

indirect gain passive solar space heating: heating a storage medium (salt, glycol, rock, Trombe wall, etc.) that then radiates that heat into the interior space.

active solar space heating: a good example would be a radiant floor heat system using solar thermal collectors as the heat source.

 

[Raspy]

What's the difference between passive solar and PV?

The term passive solar was misused in one of the previous posts. Passive is just building orientation, overhang design and window sizing to "passively" catch the sun seasonally and store some of that in exposed concrete or other mass in the house. No moving parts. PV is electric solar generating that stands for photovoltaic. Active solar is water heating where a liquid is pumped through the collectors. It gets warm and is stored for later use in radiant heating or domestic hot water systems. Geothermal gathers heat from warm earth below ground level and uses a heat pump to deliver useful energy to the house. It's kind of a backwards refrigerator that sends it's "waste" heat to the house for heating.

Comparing mini split systems to in-slab radiant and discussing only the cost is misleading. Radiant heat is the most comfortable and quietest delivery system there is and it can easily be zoned with as many thermostats as wanted. Whereas a mini split does nothing for warming floors, makes more noise and takes up space in each of it's zones. It is better suited to homes with carpeting, ones being retro-fitted or when adding air conditioning. Geothermal is OK, but scares me with its enormous requirement for ground collecting and it's complicated and expensive equipment. My neighbors put it in their house and I did the radiant. Then the Geo contractor connected the two. They have an extremely efficient home with some passive solar and domestic hot water solar too. But they still pay about $350./month, in the winter for electricity and they have had to replace the heat pump once in only about 5 years. Overall it would have been cheaper to just heat with propane, and much simpler and less expensive to install.

As I mentioned earlier, I think the benefits of active solar for radiant heating, and a simple air conditioning system, if really needed, is the way to go for heating and cooling. If someone wants to build their own system, it's an excellent match because it's somewhat labor intensive, but simple in it's application. And it has all low tech equipment that is easily serviced if needed.

 

[Garandman]

The term passive solar was misused in one of the previous posts. Passive is just building orientation, overhang design and window sizing to "passively" catch the sun seasonally and store some of that in exposed concrete or other mass in the house. No moving parts.

This was designed as a passive solar house. There is a central atrium and stairwell to circulate air. There is a tile floor over slab. Orientation is south. On a sunny day the house will stay at 70 until temps are below freezing.

In lower temps the house is heated by baseboards, a Rinnai wall heater, or a Hearthstone wood stove.

 

[Tororider]

Another approach to cutting a house's energy footprint is earth berming. A house with thick brick walls, earth berms, or one that is sealed to Passive Haus standards has virtually no air infiltration through the walls. That is as important as the R-value of the wall. Besides cutting air infiltration to zero, earth berms replace ambient outdoor air temperatures with ground temperatures. Ground temps in winter can be 50-60 degrees warmer than air temps in northern climates. Preventing frost penetration into the ground near the foundation is accomplished with 2-4 inches of Styrofoam sheets laid out as a apron surrounding the exterior walls--very much like a shallow frost-protected foundation is done. That can be combined with ICF walls or by using foam on the exterior of a poured concrete wall. The end result is no air infiltration, reasonable R-values for exterior walls, and a very low delta between the exterior and interior temperatures which means the rate of heat exchange between them will be very low.

Dave speaks truth. Like he said, plan to use passive solar. Build your house with an overhang that shades from the sun in the summer but allows sun in in the winter.