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Sun Volt Solar

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We are at a cross roads in human history, we can choose to continue on as we have been, or we can make a change to improve our future and quite possibly the future for several generations to come. We are here to promote energy independence, a better environment, a secure future and a higher return on investment for your hard earned dollar. It is what I believe in, it is why I am in the solar business.

Photovoltaics or Gas Generators, what is the best backup power?

16 Dec 08 | Solar Electric, Training

Based on my experience during the Northeast Ice Storm of 2008, I thought I would do a comparison of a Photovoltaic system with battery back up vs. gas powered generators.  To be sure, a portable gas powered generator is the fastest least expensive way to get the power back on in an emergency.  They can also be dangerous, as several people have died of Carbon Monoxide poisoning over the last couple of days.

An installed system that automatically restores power can save time and money in the long run.  For that there are two basic options, a gas or diesel powered generator or a PV system with battery backup.

Here is a chart for comparison:

System category Photovoltaic system w/battery backup Portable gasoline generator Installed generator with auto transfer switch
Design Design intensive No Design Design moderate
Installation cost Initial cost high, approximately $20-27K Initial cost low, about $1-2K Initial cost moderate to high, about $10-20K depending on generator type/size
Installation labor Installation intensive No installation Installation intensive
Running cost Negative cost to run Cost to run high Cost to run moderate
Maintenance cost No maintenance High Maintenance High Maintenance
Environmental Non-polluting High polluting Moderate polluting
Fuel Non-fuel dependent Fuel availability dependent Fuel availability dependent
Load size Partial load sizing Partial load sizing Full load sizing
Operation Silent running Loud running Moderate noise running
Hazards Some batteries can produce Hydrogen if improperly charged Carbon monoxide hazard, fueling hazard, fire hazard No carbon monoxide hazard if properly installed
Other In use full time, can be configured to sell power back to grid when batteries are charged, reduces electric bill Standby use only, must be moved into position and use extension cords, does not reduce electric bill Standby use only, does not reduce electric bill

Notes:
1. PV design includes identifying critical electrical loads and doing a load analysis. Also includes local weather considerations, solar resources, sub panels, battery placement, etc.
2. Cost to run includes fuel and maintenance costs. Since PV systems can be configured to sell excess power to the utility grid thus reducing utility bills, it can make money, therefore have a negative cost to run.
3. Maintenance refers to mechanical maintenance, e.g. oil changes, belts hoses, etc. PV systems usually require no maintenance, properly charged batteries require no maintenance and will easily last 10 years if not discharge too deeply.
4. Load sizing refers to the house electrical load.  A PV system will usually be sizing to run critical systems, a generator can run the entire house.  This is a consideration for those that have electric houses (e.g. electric stoves, electric hot water, electric heat, etc)

To that end, I have put together a standard PV with battery backup package that will run most critical household loads during a prolonged power outage.  These include:

  1. Non-electric furnace or boiler and circulator pumps
  2. 1 HP well pump
  3. 1/2 HP sump pump
  4. Standard 20-23 CF refrigerator/freezer
  5. 1200 watt microwave oven (10 minutes per day)
  6. 20 inch TV and DVD player (5 hours per day)
  7. Table top or clock radio
  8. DSL or cable modem and network switch
  9. Battery charger for laptop computer
  10. 5 13 watt CFL lights (6 hours per day)

This system will have 3-4 days autonomy (no sunshine to recharge batteries).  A small wind generator can be added to create a hybrid solar/wind system.  These work well because usually when the sun is not shining, the wind is blowing and vice-versa.

Contact us to learn more about these systems.

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16 Dec 08 | Solar Electric, Training | Comments (2)

Solar power backup for Critical Household Systems

06 Apr 08 | Solar Electric, wind power

Almost everyone has experienced a black out. Thankfully, they are often for short periods and the line men work hard to get the power back on to everyone as quickly as possible. However, if major damage is inflicted upon the power grid, it can take quite a while to repair. Are you prepared to live without electricity for days, weeks or even months?

Many people have installed gas or diesel generators to power their houses. These units can run reliably for days or even weeks at a time, but they also require refueling. After Hurricanes Ivan in Pensacola and Katrina in New Orleans, it was discovered that motor fuel can often be in short supply after major disasters as the electric transfer pumps required to move the fuel from storage to use are inoperative. It can also be difficult to deliver fuel due to blocked or flooded road ways.

Additionally, generators require maintenance, the engine oil needs to be changed, they need to be  exercised periodically.  Solar panels need almost no maintenance, perhaps in a prolonged dry spell, the dust could be washed off once in a while.  Even that is optional.

As solar powered backup system requires no fuel and if properly sized can run your critical household electric load indefinitely. These systems can be individually sized according to the load calculations. Additionally, they can be configured as a normally solar powered system that is backed up by the electrical grid. If a location has a good wind resource, a small wind turbine and be used to augment the solar system during inclement weather.

Instead of using the PV panels to merely to keep a battery bank charged, the PV panels and battery bank can be the primary source of power. The electrical grid can be used as a standby in case the batteries get too low. A reserve charge can be built in to the battery bank to run the critical loads in absence of both sun and grid power.

This is best of both worlds.

Critical loads

Indentifying critical loads is the first step. At my house we have a well pump to supply water, an oil fired boiler for heat, an electric refrigerator, two sump pumps to keep the basement dry, and two circulator pumps on the solar hot water system. I would also like to power the computer network and one or two outlets for lighting. All of these appliances have name plate information which give the power consumed. If the loads are given in watts, they need to be converted to amps. To do this, use Ohm’s law, which states:

P=I x E

where P is the power in watts, I is the current in Amps and E is the Voltage.

Thus if something if something draws 300 watts, you would divide that by 120 volts and get 2.5 amps.

Load Name
 Manufacture/Model
 Load Current @ 120 VAC (Amps)
 Load Power (Watts or VA)
 Duty Cycle (percent/hr)
 Amp/day (Amps x duty cycle x 24)
Well Pump
 Goulds 10GS10422
 7.9*
 948
 2
 3.8
Boiler, heating
 Dunkirk/Grundfos
 4.3
 516
 10
 10.32
Refrigerator
 Kenmore
 2.1
 252
 10
 5.1
Solar Hot Water Pumps
 Taco 009B and 006B
 1.8
 216
 20
 8.64
Computer Network
 Various
 0.3
 36
 100
 7.2
Water Filters
 Kenmore
 0.3
 36
 100
 7.2
Misc loads, lights, etc
3.0
 360
 40
 28.8

Total power required is 2364 watts, if all loads are one at the same time, which is unlikely. Additionally, the well pump requires a large starting load, something in the range of 5,000 watts. This will have to be figured into the sizing of the inverters.

Total storage is 71.06 Ah per day at 120 VAC. Some of these loads are seasonal, e.g. the boiler will not run in the summer, but the refrigerator will likely run more. Over all, I think this represents a good picture of my critical household loads.

I plan to have a 24 VDC battery bank running two inverters tied together to derive 240 VAC for the well pump. I estimate a 355.3 Ah battery bank will give me 24 hours, but there are other considerations:

I would like to run for several days without recharging because sometimes stormy weather lasts for quite a while. Therefore 355.3 x 3 = 1065 Ah.

A battery bank should never be discharged by more than 40 percent. Doing so leads to shorter battery life and increased operating expense. 1065 Ah x 1.4 = 1493 Ah.

Finally, the inverter has some losses. A good inverter usually operates at about 95 percent efficiency. 1493 Ah x 1.05 = 1567 Ah.

That is a pretty big battery bank

The inverter chosen is a Xantrex SW2524 Plus, which as an internal battery charger and an optional controller for starting a generator. I plan to use the generator starting contact to close a power contactor from our house panel, which will be used to recharge the batteries when they reach 55 percent discharge and grid power is available. If the grid is not available, we have a 15 percent reserve, which means I will load shed until the batteries can be recharged.

Next consideration is the size of the solar array charging this battery bank. The total daily storage from above is 71.06 Ah. All solar panels are sized in Watts, therefore, using Ohm’s law, we have P=71.06Ah x 120 Volts = 8,527.2 watts or 8.5 kW rounded total charging per day.  We have about 5 sun hours per day average, so 8.5 kW / 5 = 1.7 kW of charging power.

I will be using a MMPT charge controller to charge the battery bank, as well as tracking mounts for the panels, both of which will increase the efficiency of the system.

Finally, I will be using a 400 Watt Southwest Windpower wind generator to keep the batteries topped off during story conditions. Without the wind turbine, I would have to double the size of the Battery bank.

Here is a list of parts:

  • Batteries; Surrette 4-KS-21PS 4V 1557 Ah, 6 each
  • Inverters; Xantrex SW 2524 plus, 2 each
  • Inverters, Xantrex SWI stacking kit, connects two inverters to generate electric for 230 VAC loads
  • Inverters, Xantrex GSM generator starting module
  • Charge controller, Blue Sky Energy Solar Boost 3024i MMPT controller
  • Photovoltaic panels, Sharp NE-170U1 170 watt panel, 10 each
  • Tracking Mounts, Zomeworks URTF90, 2 each
  • WInd Turbine, Southwest Windpower Air X 24 VDC
  • Wind Turbine Tower Kit, Southwest Windpower 45 ft

Total cost, retail $26,000.00

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06 Apr 08 | Solar Electric, wind power | Comments (3)