Solar Motor Home

In 2016 I designed a solar powered motor home that offers:

  • A 300 HP electric motor so you can pass all the gas stations.
  • A bank of batteries that can be charged by an AC source or by solar panels
  • An array of solar panels mounted on the roof.
  • A total price of $150,000

This invention requires some unique components:

  1. Accelerator with electronics needed to send the speed signal to the motor drive.
  2. Coupler to connect AC motor output shaft to the motor home drive shaft.
  3. Bus bars rated at 500 amps to connect the battery o the motor drive.
  4. Motor mounting brackets for the AC motor to use the gas engine motor mounts.

For details on any parts, email solarrv@invisco.com

Here is an article I published in 2016

Make Your Own Solar Powered Motor Home

By Kurt Shafer written in May of 2016

This article is about a design for a completely independent motor home that uses solar power or grid power to charge batteries to provide engine power, a dehydration system for water and hydroponics for food. Dehydration systems and hydroponics are well known so they are not discussed in this article. The purpose of this article is to describe how you can build your own solar powered motor home.

Tesla and other electric vehicle sources are showing us how good the latest technology is in battery powered vehicles. As you will see later in this article, Tesla’s latest powerhouse vehicle, the P90, offers over 762 horsepower and a range of nearly 253 miles using a battery that is small enough to hide in their car.

DESIGN GOALS

  1. Range – this is determined by the battery pack. Goal is to maximize it.
  2. Power – it is expected that the gas engine will be about 300 horsepower and it will be replaced by an electric motor with about the same horsepower.
  3. Recharge time – this is a challenge due to the limited space for solar panels.

RANGE

To understand the possibilities that exist one needs only to look at the latest Tesla P90. It has 762 HP and a range of 253 miles. So, in theory, if we just want 300 HP then using the same battery we should get a range of 642 miles, and at 60 MPH that should be over 10 hours! We know that this Tesla battery is small enough to hide in their luxury sedan body so with the amount of volume in a motor home our range is only limited by our pocketbook.

POWER

Research shows that many motor homes have gas engines that are rated at or about 300 horsepower.  It turns out that a 3 phase 460 volt AC motor  is readily available from many suppliers. An example is a simple search on EBay. RPM varies but 1800 RPM is quite common and, as you know, is nearly the same as the RPM of a gas engine at cruising speed. A valuable property of electric motors is that it is likely that the electric motor will have so much torque that the use of the motor home transmission might not be needed.

Here is an ad dated January 21, 2018 offering a used motor for under $4000 with shipping included!

300 HP JAN 2018

The next challenge is to cope with the power in amps needed to produce 300 horse power. Electric motors draw 750 watts per HP so the number of watts needed is 750 times 300 or 225,000 watts. At 460 volts that will result in a current of almost exactly 490 amps.

It is valuable to note that the huge current is only when the motor is asked to run at full power. It is likely that just a fraction of the power will be needed, especially when cruising. It is only at startup acceleration will more power be needed. I suggest that we use 100 HP as the optimum power. In that case, the power will be about 1/3 of 225,000 watts or about 75,000. Now we can calculate the total storage we want in the battery bank.

The Tesla PowerWall storage is a good example. The PowerWall is rated at 14 KWH total energy with a “Real Power” rating of 5KW. The battery is 50 volts and the output is 120 VAC at a maximum of 30 amps. If it supplies 5KW output and if we need 75,000 watts to run the motor we will need 15 of the PowerWalls. Since the PowerWall has 14 KWH capacity then 15 of them will put out 75,000 watts for just under 3 hours. And it is interesting to see that if we want to be able to run the motor at full power of 225,000 watts we will need 45 PowerWalls to do that. At a retail price of $5000 each, this is not likely the best path to take.

As you can see, the battery is the largest cost of all the components in this system. PowerWalls cost $5000 each in 2018. But we don’t need to pay that much if we eliminate the PowerWall packaging and put raw batteries in a larger container.

That current must be connected between the battery bank and the speed controlling variable frequency drive (VFD) by heavy copper bus bars.  Bus bar tables on line show that if one wants to limit the increase in the temperature of the bar to 30 degrees C (86 F) then a bar of copper that is 3/8 thick and 1 inch wide is recommended.

When replacing a gas engine with an electric motor it is necessary to replace the mounting hardware and the connection to the transmission shaft and the gas pedal. The frame used for 300 HP motors is technically termed a 449T and it is almost exactly 2 feet high and 2 feet long. The gas engine is larger than that and likely has 2 mounting points at the front of the engine and none at the rear because most vehicles depend on the transmission for the rear mount. It will be necessary to add a mounting brace to the front of  the transmission and then add a platform for the motor.

Control of the speed is accomplished by a 3 phase speed controller. They are known as a VFD or variable frequency drive and they are available from many sources. One source is vfds.com and another is EBay. VFDs take 0-10 VDC input to control the motor speed.  If you look for a VFD for battery input you need to specify a DC voltage input.

RECHARGE TIME

There are two ways to charge the battery bank, using solar power or using land based AC power from the grid. The goal of this design is to be independent of the grid so charge time will be very long on solar alone.

Here is what we can expect if we have grid power. Tesla offers a glimpse into the recent advances in low recharge time . Tesla gets a full charge in the P90 in just 1 hour and 15 minutes using 440 VAC! That makes a transcontinental motor home realizable. With New York about 2500 miles from Los Angeles, one could imagine traveling 642 miles at a time, stopping for a meal and a charge, then another 642 miles, etcetera.

Now, the reality of purely solar recharge is that a motor home is about 8 feet wide and 40 feet long and about 8 feet high. If we use just one side and the top for solar panels we get 640 square feet of panels. HOWEVER if we use the new articulating motors and arms now around, we can put more panels on TOP and eliminate the side solar panels. The articulating arms can put at least 3 panels in a pile that can fit on top and fold up and out so all 3 are facing the sun. That way we get 960 square feet of panels and they should all get maximum power by facing the sun all the time.

At 18 square feet per panel that is 53 panels. At 300 watts per panel that is 15,000 watts. We need 225,000 watthours to recharge the batteries from total discharge. That will take about 15 hours. That means we might recharge in just 2 days. Put another way, it is likely that we can drive each day and get enough recharge to drive the next day.

Now a rough cut at the cost of this solar powered motor home. First, a look at an average motor home on the market today. A quick search for 40 foot motor homes shows there are many listed for sale at under $100,000 and some under $50,000. This is, of course, the major expense. The second largest expense is the energy storage. If we compromise and limit the power to 100 HP and the drive time to 3 hours we can live with 15 PowerWalls at $5000 each or $75,000. I am going to estimate that we can get the same power for half that price or $37,500.

The solar panels are the third highest cost at about $300 each times 53 panels orabout  $16,000.  The AC motor is advertised on EBay for around $4000. VFDs are priced from $8000 up. Other miscellaneous parts might add up to $5000.

In summary, here are the costs if we start with a $50,000 motor home

$50,000 for motor home
$37,500 for batteries
$16,000 for solar panels
$4,000 for the motor
$8,000 variable frequency drive
$5,000 misc parts
$10,000 for labor for the parts and modifications.
$92,400 Total

The single most important advance in technology that makes this all viable is the advance in battery design. Without the latest batteries made by Tesla and others we would be forced to install huge lead acid batteries and the whole design might be undesirable. For more information and to follow the progress on this project email kurt@invisco.com

Energy storage prices forecast to tumble

Reprinted from https://www.chemistryworld.com

This comparison shows cost evolution among technologies including lithium-ion and flow batteries

Energy storage is needed to avoid wasting excess electricity from solar and wind – and a new analysis finds many options are surprisingly affordable. Oliver Schmidt and colleagues at Imperial College London see technology costs falling similarly rapidly as deployment expands. ‘There is no fundamental advantage of a certain technology in terms of capital costs,’ Schmidt tells Chemistry World.

While cost projections exist for individual technologies, the Imperial team noted that there was no evidence-based comparison between them. The researchers therefore applied an ‘experience rate’ approach to eleven vehicle, electricity grid and home energy storage technologies. The method looks at how costs have fallen as manufacturers have deployed systems and learned how to make them more cheaply. Projecting that these trends will continue can then be used as an indicator of future costs.

Schmidt’s team found capital costs of home and grid-scale systems generally heading towards $340/kWh (£263/kWh) once 1TWh of capacity is installed for each technology. For comparison, the UK consumed 337.6TWh of electricity in 2016. This was true for hydrogen fuel cells and lead acid batteries for homes, lithium-ion batteries on home and grid-scale and grid-scale vanadium redox flow batteries.

Energy storage cost fig3

Source: Springer Nature

Costs are projected to fall rapidly for many energy storage technologies

This figure is close to the cost of pumped hydroelectric storage, where water is driven uphill by excess electricity and allowed to flow and drive a turbine when needed. With over 1TWh already installed, pumped hydro costs less than $300/kWh.

Costs of lithium-ion and nickel metal hydride batteries for electric vehicles converged around $175/kWh after 1TWh deployment. The scientists forecast that vehicle lithium-ion batteries will be the first of any technology studied to pass the 1TWh milestone in 2027. Home fuel cells, lead acid and lithium-ion batteries would be the next technologies to reach 1TWh in 2038.

Similarly, the scientists forecast that the cumulative costs of installing 1TWh would be generally higher for home and grid-scale storage than for vehicles. Home lithium-ion batteries could be most expensive at $510 billion. However, by comparison with the $349 billion spent on renewable energy in 2015 these figures are ‘reasonable’ Schmidt says.

Schmidt highlights that such capital costs are only part of figuring out how economical energy storage is. ‘If you want to compare how competitive they are, you need to consider additional parameters like lifetime and efficiency,’ he says. ‘We do that with electric vehicles. We can say with good certainty that they will be competitive with conventional cars within five to 15 years.’

Peter Taylor from the University of Leeds calls the study rigorous and salient, and says the forecast that technologies could reach a similar price after 1TWh of capacity is installed is ‘good news’. ‘These results point to the fact that, while significant future price reductions can be reasonably expected in energy storage, greater policy intervention may be needed to accelerate early deployment in key applications in order that the technologies reach price-parity sooner rather than later,’ he adds.