Grid-tied solar

[deezler]

Dutch, you would need an awful lot of batteries to supply electric furnace and water heaters on demand. Unless, of course, you only want to run them during sunny days. Sounds like a cold winter in upstate NY to me!

Dave, this is a great thread. My wife and I are trying to start our home build within the next few years, and an earth sheltered, passive solar, PV array, woodstove design is at the top of the wish list.

 

[Dutch445]

i wasn't looking for an off grid system, thinking of converting appliances over to electric
then using a solar system with net meter,

 

[deezler]

Oh, duh, my bad. Hence the thread title "grid-tie". haha.

 

[dave1949]

i wasn't looking for an off grid system, thinking of converting appliances over to electric
then using a solar system with net meter,

You are sure welcome to use this thread, but I think if anyone has good info on electric furnaces, you would get their attention with a thread name asking about them.

I am not familiar with elec. furnaces, but I picture something that uses a goodly amount of elec. That would take a big/huge solar system to make a dent in your overall usage unless you are planning a super efficient home that barely needs any heat.

The top-down method is to make an "energy budget" that lists all of your btu uses and attempt to put numbers with them. This can be difficult for heating because you don't have enough information, and it can be hard to supply the info using the canned programs that predict the heat load for a home unless you are an architect or engineer of the right flavor.

If you look around you can find such programs free online, but for them to be accurate you have fill in thermal coefficients of walls, roofs, windows, doors, etc., etc. There are some tables for those values using standard construction. I tried one briefly and decided it was (1) above my pay grade , and (2) I was putting in so many guesses that the result would be a guess.

A useful measure is overall energy usage based on annual btu's per sq ft of conditioned space. For your current home, you can calculate that easily from your energy bills by converting everything to btu's. Here is an idea of that: How to Calculate BTU Per Square Foot: 11 steps - wikiHow

About five years ago, I read the US average for homes is ~100,000 btu/sq ft/year. Mine, excluding sunshine, was 43,187 btu/sq ft/year before the solar system. I think some of the better building techniques may be able to beat that. The need for AC will make a difference, and long winters do too. Anyways, it is some way to get a relative measure of where you are in energy use. And a useful method of comparing building/heating techniques if you have the numbers.

 

[Dutch445]

I agree, i don't have enough information seeing we moved into the house
in feb/march. I did pay to heat it during the winter after the purchase offer
was accepted, to help seal the deal with the prior owner who was out of state
and going further in debt. But, dec/feb was only minimal heat, 60 or so, to keep
pipes ok etc, and we had an unusually mild winter. so i have no track record.
Once i can find a reasonable guestimate of the home heating requirement, then
i guess i can answer more of my own questions. what it would come down to is:what are
the up front costs of the extra capacity of the system to heat with, compared to
using fossil or other type fuels for heat. right??


i did find some references that help put things in perspective. here's an excerpt from
another forum: Heating Help

fuel costs
1 kW-hr of electricity is 3413 BTU so you'll need 29.3 kW-hr for 100,000 BTU of heat, that's $3.22/100,000 BTU at $0.11 kW-hr. LP (propane) has 92,000 BTU/Gallon so you'll need 1.09 gallons for 100,000 BTU of heat that's $3.28/100,000 BTU at $3.00/gal or using the DOE's EIA weekly price survey results for PA for week of 10/15/2007 of $2.54/gal it's $2.77/100,000 BTU. (KY & OH are cheaper, NJ, NY, DE & MD are more for LP so it seems the further west your are in PA the better, so check local pricing. see: Weekly Petroleum Status Report - Energy Information Administration Again, using DOE EIA price data residential retail NG is $20.79/ million BTU in PA or ~$2.08/100,000 BTU but again check your utility's rate schedule. see: U.S. Energy Information Administration (EIA) Heating oil may be another option (not sure how common it is down there though) #2 oil has 140,000 BTU/gallon and DOE EIA shows a 10/15/2007 PA price of $2.28/gallon (residential retail) or $1.63/100,000 BTU One time installation costs will vary (e.g. nat. gas line installation cost, vs. LP tank install), so you've got to factor the payback for cheaper long term operating costs in, also you will have to adjust the costs for the efficiencies of the equipment, again higher efficiency equipment will cost more up front. Get local fuel cost and plug in to get costs per 100,000 BTU and go from there. Also, do you have an interest/desire in replacing the electric stove and/or dryer w/ gas (NG or LP)? Additionally, with a hot water (or steam) system you could also use the eboiler to provide hot water via an external "indirect" hot water tank, vs the electric HW heater

and here's another entire page with more of that info, including building specs etc:
Energy Engineering

 

[meburdick]

You *MAY* be able to gain some insight into the costs that the previous owner of the house incurred if you contact their fuel supplier. Explain that you've recently purchased the house and are trying to budget for the upcoming winter which should be much more 'typical' than last. Ask if they have any information on average amount of fuel used by that customer over the last few winters.

 

[meburdick]

Oh.. And if they make a statement about not being able to tell you that based on privacy or something, say this...

"Let me ask it another way, then. Based on your knowledge of the home, how would you set me up on a budget plan based on the estimated heating costs over the upcoming winter?"

You may have to do a little math at the end, but you'll get some information.

 

[dave1949]

-snip-

what it would come down to is:what are
the up front costs of the extra capacity of the system to heat with, compared to
using fossil or other type fuels for heat. right??
-snip-

That sounds right. My impression is it will be very expensive to install enough solar pv to offset electric heat unless you can reduce your heating requirements to something very low.

I just remembered the town up the way from us has their own elec. utility. They offer reduced rates on off-peak hours (night time) for electric space heaters that have a brick pile the elements heat up. http://www.madelec.net/ets Is that the type you are referring to?

 

[Redneck in training]

You might use geothermal heat pump to heat the house. It will use about 25% of the power required by direct electric heater. The upfront cost even though still high will be less than solar panels required to supply power for direct heat.
FYI. We have floor heating with geo in our house. We heat about 3800 sq ft for about $100 at coldest month. Our heating rate is 4.2 cent/kWh. Geo does AC also. It ises about 4.8 kW when it runs while it generates about 19 kW of heat.

 

[dave1949]

You might use geothermal heat pump to heat the house. It will use about 25% of the power required by direct electric heater. The upfront cost even though still high will be less than solar panels required to supply power for direct heat.
FYI. We have floor heating with geo in our house. We heat about 3800 sq ft for about $100 at coldest month. Our heating rate is 4.2 cent/kWh. Geo does AC also. It ises about 4.8 kW when it runs while it generates about 19 kW of heat.

If pairing solar pv (assuming an area with sufficient sunshine) with geothermal were affordable in upfront costs, that would provide some very green heating. Or, if the utility power came from green sources, same result but with transmission losses.

Any idea what your payback period is? For example, comparing your costs to other available fuels in your location. You probably have a pretty good idea of your annual kWh's for heating and cooling which can be converted to gallons of oil, propane, direct electric, etc.