I will be building a home on the very northern coast of Calif, and am want to eventually install a PV array.

I will also be installing a hydronic floor heating system.

What types of questions will I encounter for someone to help with designing a system of me?

Goals?
Size of roof and direction it faces? (22' by 52' garage roof with gable ends. Pitch is flexible, which will determine that available square footage, but I'm guessing appx 750 sq' available)

I'll try to answer some of them ahead of time.

I'd like to install this system myself, but willing to pay for some pro design
But from what I'm reading, I won't be eligible for federal, power company or state tax credits if I install myself? (perhaps I can find a local certified installer that woudl humour m e in installing much of the equipment myself, mop up after me and certify the installation)

This house is coastal property, 41 degrees latitude and the garage roof faces the SW (233 degrees on a compass).

I've Googled compass degrees of direction and there seems to be a lot of conflict on what degrees mean when indicating which direction a roof faces.  Can someone help to explain, so I can get an empirical figure that any professionals will need to know for design? 

Thanks. -John

Anything within 20 deg of S is just fine for a roof and in your latitude, a 20-30 deg slope is just right, unless you are off grid, which is a whole other ballgame. There is some lea way as you won't find a lot of difference in outputs within that range. As far as your rebates are concerned, someone else to chime in on that. Don't forget to consider solar hot water.

Posted By MikeSolar on 29 Apr 2013 08:35 PM
Anything within 20 deg of S is just fine for a roof and in your latitude, a 20-30 deg slope is just right, unless you are off grid, which is a whole other ballgame. There is some lea way as you won't find a lot of difference in outputs within that range. As far as your rebates are concerned, someone else to chime in on that. Don't forget to consider solar hot water.

No plan to go off grid. The hip end of the south (faces the same direction as the garage) roof might be a good enough size to accommodate a passive solar DWH and I am considering that. I don't yet know the size of that roof hip but I'd guess appx 100 square' or maybe a bit less. I will eventually be able to provide that figure

My math tells me that (at 223) I'm 43 degrees from due south (180 degrees). And I didn't even have to take my shoes off for that

If so, I fall a little out of the range of 20-30 degrees, but at least I'm facing S-W instead of S-E.

I would recommend PVWatts Version 2.0, which you can use for free at http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html. It will allow you to adjust the azimuthal angle (your 223 deg.) as well as the tilt angle and see the impact on total energy collected per month and per year. The collection efficiency is a function of collection angles, but not as strongly as I would have guessed. PVWatts includes the effect of cloud cover and average monthly temperature profiles for your zip code. You can start out assuming a due south orientation with a tilt equal to your latitude as pretty good. At my location, optimum azimuthal angle is 11 deg. east of south due to cooler temps in the morning (increasing PV collector efficiency), and the fact that it tends to cloud up on summer afternoons here, both of which PVWatts accounts for.

About a 10:12 or 11:12 pitch would be optimum for tilt angle for your latitude, but that is very steep for trying to work on. Optimum in my area is a 9:12 pitch, but I lost less than 2% in collected energy by going to a more practical looking (for my garage/workshop application) 6:12 pitch. Also the 6:12 pitch is much easier to walk on than the 9:12 pitch on my house.

If the solar energy was not bankable, in other words, you did not have the grid as an infinite battery, the pitch of the roof would be much more important but if you are not relying on batteries for all your power, you will get more annually by having the panels at a shallower angle. This assumes that the OP can net meter on an annual basis. If it is only monthly, then I agree that a 45deg pitch is better at his latitude. 

I ran some numbers through PVWatts for Arcata, CA, which is on the coast and about 41 deg. north latitude. Optimum tilt for a due south azimuthal orientation based on year-around total energy collected is 33 deg., with a predicted total collected A.C. energy of 4828 kWh for a 4 kW DC rated system. At the 223 deg. azimuthal angle, the optimum tilt is 31 deg., which produces a predicted yearly energy collected of 4693 kWh. Note that although the 223 deg. azimuthal angle is 43 deg. off of due south, the penalty for not-due-south orientation is only 2.8%. Therefore, Mike Solar's rule of thumb of "within 20 deg. of S" looks much too conservative. Solar PV can be very efficient (>95% of optimum) over a fairly large range of azimuthal angles.

According the PVWatts, the optimum azimuthal angle appears to be about 190 deg., or 10 deg. W of due south, probably due to more clear weather in the afternoon than the morning along the northern California coast.

Lee,

Thanks for that link. I spent a great deal of time on that site, and learned a few things and of course that spawned a few questions. But I'll read a little more there to see if I can glean my answers.

I ran the calculator for my specific property (223 degrees SW) and received similar numbers to what you just posted but slightly less annual KWH (appx 4400).

Those calcs are based on a 375 sf PV array correct? If so, one could double that by installing double the array (in theory)?

That is a cool tool they have there.

Posted By JohnRLee on 04 May 2013 10:41 AM
Lee,

Thanks for that link. I spent a great deal of time on that site, and learned a few things and of course that spawned a few questions. But I'll read a little more there to see if I can glean my answers.

I ran the calculator for my specific property (223 degrees SW) and received similar numbers to what you just posted but slightly less annual KWH (appx 4400).

Those calcs are based on a 375 sf PV array correct? If so, one could double that by installing double the array (in theory)?

That is a cool tool they have there.

John-

PVWatts starts out defaulting to an array rated at 4 kW DC power, but that is just a variable that you can set to any value.  The output power predicted by PVWatts is linear with the rated input power, so doubling the input rating doubles the output power.  The array size depends on the efficiency rating for the panel.  For example, for Sunpower X21-345 panels, which have a relatively high efficiency rating of 21.5%, the 4 kW DC rated array would cover about 18.9 sq. meters or 203 sq. ft.  Lower efficiency panels would require a larger array size.  There is no particular advantage to the higher efficiency panels other than the fact that they require less space for a given power rating. 

For whatever reason, PVWatts underestimates the energy that is actually produced by panels in my geographic area by roughly 20% (http://www.residentialenergylaborat...stems.html).  That is for panels that are completely unshaded, and performance degrades very quickly, and non-linearly, with shading.  Also, system output should decrease something like 0.65% per year due to aging. 

Some parts of California have complicated electric rate structures, including time-of-use (TOU) rates.  These rate structures charge the most for electricity used during the day, and this is the same time that PV systems produce electricity, so these rate structures can make solar PV systems very attractive financially.  It also depends on the details for how they credit net metering for power produced by PV systems, and what rebates are available locally.  The federal rebate of 30% of the initial cost is still in place. 

In your climate, I would skip the solar DHW and just put in a heat pump water heater and use the extra roof space for more PV. The HPWH will prob use less elec on a yearly basis than the backup resistive element in the solar tank (unless the solar is way over sized and very carefully designed), and the extra PV will be a small incremental cost that will net you more energy.

http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead

Posted By woodgeek68 on 07 May 2013 06:27 AM
In your climate, I would skip the solar DHW and just put in a heat pump water heater and use the extra roof space for more PV. The HPWH will prob use less elec on a yearly basis than the backup resistive element in the solar tank (unless the solar is way over sized and very carefully designed), and the extra PV will be a small incremental cost that will net you more energy.

http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead

I cannot agree with the above at all. Without incentives, SDHW puts out way more energy than PV does at a better cost. With incentives, who knows. If you only have so much room on the roof, look for a PV-Thermal panel. They are a bit more rare but available. HPWHs have their place but it is an energy conservation device and not a renewables device and while both are good, I think the PV and thermal are the best options (if you have the roof and money). Use the HPWH as a backup to the solar if you wish.

Posted By woodgeek68 on 07 May 2013 06:27 AM
In your climate, I would skip the solar DHW and just put in a heat pump water heater and use the extra roof space for more PV. ...snip...

Where does the heat come from with a heat pump water heater?

Given that Trinidad CA has effectively no sensible cooling load and a NEGATIVE latent cooling load, the benefits to heat pump water heaters drawing heat from the conditioned space air are extremely limited- it's just another load on the heating system.

A heat pump water heater that uses OUTDOOR air such as the EcoCute would make sense in that climate, but they are not available in the US.

The tank-top heat pump water heaters really rock in the southeastern US climates where they do double-duty as dehumidifiers/air-conditioners, but less so in N.CA.  About half the heat going into the water is from he compressor motor, and th rest is heat that needs to be made-up by the heating system. Trinidad may have only ~4400 heating degree days, but with the mean July & August temperature of about 57F, the heating SEASON is 12 months of the year- even a low heating load is still a heating load, and the HPWH just adds to that load.  But if the heating system is a high efficiency heat pump (air source or ground source), the HPWH is still more efficient than resistance electric heating, just not the ~2x implied by it's EF rating.

FWIW: Trinidad's climate is fairly ideal for running your radiant floor heat with a Daikin Altherma, which may beat ground source heat pumps on average efficiency.  But mini-splits would be as-efficient, and probably cheaper to install, if less cushy under foot on design day, the few mornings every year that you might actually get frost. (The 99% outside design temp in that area is about 32F.)

Looking at the climate data it looks like average temps in July are 48°F, and in January 38°F? Not what I expected at all. My bad.

If your weather is <50°F most of the year, a HPWH in unconditioned or semi-conditioned space is a no go. If you were heating the main space with a mini, you would prob get a COP of 3.5-4. In that case, I would still crunch the numbers for a HPWH in the conditioned space (figuring that 60% of the DHW BTUs are robbed from the mini delivered BTUs), and compare the result to the backup needs for a solar DHW system that may be struggling with fog during some seasons.

I'll take a stab....in a conditioned space a HPWH should get an COP/EF of 2.5, requiring 40% of kWh of a well insulated resistance unit.  The remaining 60% of the BTUs are stolen from a (hypothetical) mini.  If those come in at COP=3.5, then each BTU stolen costs you 28% of that for a resistance heater.  The sum is 40% + 0.28*60% = 56%, or a net EF of about 1.8.

IMO, the SDHW vs HPWH comes down to seasonal storage of solar energy. If your solar resource is 'even' through the year (e.g. Rockies), then SDHW is more appealing, if its concentrated in 6-8 mos of the year (as in midatlantic/new england) then your backup needs become a lot greater.  In your case, according to PVWATTS, it appears you have a nice 1200 hr/yr resource, running maybe 60% of summer output in the winter months.  Seems pretty favorable for a SDHW (esp given the mild climate).

Of course, the decision will prob come down to installed cost, incentives, and NPV calculations. Around here, the pre-rebate cost of solar DHW is ~$15k for a system to deliver ~50% of DHW.  Didn't pencil out even with a 75% rebate.

I will also be installing a hydronic floor heating system.

Altherma makes sense to me. Add a zone for water heating. Possibly add a large water tank if there are significant time of use discounts or you don't have grid-tie to use the utility grid as a battery.