Where to start?

Re: Where to start?

It does matter to a degree if the power is used during day time (when the sun is up and shining) vs night time. Also, surge current is a variable that may need to be taken into account (well pump would be an example).

Anyway, as a start of a "rule of thumb" system design assuming AC loads, flooded cell battery bank, fixed solar array, around Seatle Washington, assuming typical charge during the day and use power at night (at least for the 1,000 watt * 4 hour system), 1-3 days of storage with 2 days as a "ballanced design", 50% maximum battery discharge for long life, 9 months of year on solar, 3 months of year with help from backup genset, 5-13% rate of charge for battery bank--choosing 10%-13% as "balanced" the numbers would look something like this:

• 1,000 Watts * 4 hours * 1/0.85 inverter efficiency * 2 days of storage * 1/0.50 maximum discharge * 1/48 volt battery bank = 392 AH @ 48 volt battery bank

To charge such a battery bank, 5-13% rate of charge for solar is typically recommended. Use 10% (or larger) as "ideal" for most systems (less maintenance/management for battery bank capacity, some extra power for charging if loads are on during day, etc.):
392 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,004 Watt array "nominal" based on battery bank capacity

Then there is how much power you actually need to supply the loads from the solar array. Using PV Watts for "sunny" Seattle Washington, using defaults (tilted to latitude, fixed array):

Month    Solar Radiation (kWh/m 2/day)
1      1.54     
2      2.50     
3      3.71     
4      4.37     
5      5.31     
6      5.52     
7      5.88     
8      5.17     
9      4.98     
10      3.00     
11      1.76     
12      1.26     
Year      3.76      

Toss out the bottom three months, that would give us February at 2.50 hours of sun per day (that is not a lot of sun--much of the country that number would be around 4.0 hours of "noon time equivalent sun" per day minimum for 9 months of the year).

1,000 Watts * 4 hours * 1/0.52 end to end AC system efficiency * 1/2.50 hours of sun = 3,077 Watt solar array based on loads in February "break even" month.

So, very quick math would suggest a "cost effective" system with fuel powered genset at ~3,077 Watt array minimum.

For a 1,000 watt load * 24 hours per day, those would be 4x the numbers above. Plus maybe another ~1.5kW array wattage to account for the array charging the battery bank at 10% rated power but you have a 1 kW continuous load (0.85 inverter efficiency * 0.77 solar panel+charge controller efficiency):

• 392 AH * 6x larger load = 2,352 AH @ 48 volt battery bank

Solar array based on 10% battery rate of charge:

• (2,352 AH * 59 volt charging * 1/0.77 panel+charger derate * 0.10 rate of charge(7 + (1,000 Watt load * 1/0.85 inverter eff * 1/0.77 pane+controller eff) = 19,550 array based on minimum 10% battery charging

Note that this load offset for charging should also be calculated for the first example if your 1kW load was right in the middle of the day vs loads at night. Assumptions about loads/weather patterns make make a difference. If loads were daylight pumping (such as irrigation, then there are options such as no-battery/no-inverter systems which usually are much better solutions).

Solar array based on power usage:
6x 3,077 Watt array = 18,462 Watt array

So, minimum of 19,550 watt array using rules of thumb for a 1kW * 24 hour per day system.

You can change the numbers based on your needs/location/etc... The above system should work well and not need a lot of attention. But it is not "optimized" for loads/location/etc. Which could change/reduce/increase battery bank size. Different location with more sun in "winter" will make a big difference, etc.

Is this what you where looking for?

Nobody was trying to be difficult about your question. It is just loads (conservation, time of use, surge, seasonal, backup power, etc.) can play a major element in an overall "cost effective/reliable" system design.

-Bill

Re: Where to start?

Just to give you some round numbers...

~1kWH (1,000 WH) per day--Enough for some lights, recharge a laptop, radio, charge cell phone, etc.
~3.3 kWH per day--About the minimum requirement to support a full sized energy star refrigerator, washing machine, well pump, lights, etc..
~10 kWH per day--A pretty efficient home using ~300 kWH per month (natural gas/propane for heating/cooking/etc.).
~33 kWH per day ( 1,000 kWH per month)--North America average power usage for a the "average home"

Running cabin one season and random weekends the rest of the year... Propane fridge, a small solar power system (maybe 1kWH per day) for 24x7 lights/laptop/cell phone/pressurize water for cabin from cistern, etc.). Run a genset (like a Honda eu2000i) for "more power". Get a cheap 3.5 - 5 kW to run larger electric tools/shop/fire pump/emergency backup to smaller genset).

Power usage is a highly personal set of choices--We do not "go green" to be green. We help people plan their power needs to fit their requirements--what ever those may be. For example, there are some folks running A/C, heat pump heating/hot water on fairly small off grid systems--Very insulated homes, a choice to not be dependent on fossil fuels (and the chargers/issues with those fuels).

Just do not buy any major gear until you have done a couple "paper designs" first. Off grid solar power is not easy (or cheap) to scale up or down by more than a factor of 2 without major changes/different equipment.

-Bill