Energy Products

Cost estimation for a 4 bedroom (40KWh per day) to install solar roof + powerwall please?

Could anyone give me a breakdown price of cost estimation for a 4 bedroom(40KWh per day) to install solar roof + powerwall please? What area size is required for the roof to provide enough solar power? ( Must I change all the roof?) Thanks!


  • edited September 2017
    There are many cost factors involved. Let me list but a few of them.
    The energy available from the sun varies with location so the amount of solar collectors (be it panels or a roof) will vary. On a more prosaic note, the country and state will have a considerable effect on the financial equation e.g. here in the UK there are no tax incentives and subsidies are very slim but it appears (from reading this forum) there are substantial incentives in some US states.
    What you intend to achieve
    If your intention is grid independence then your costs can be an order of magnitude greater that if your goals are the optimum financial outcome as you would have to cater to cover the dullest series of days. It is worth noting that in some latitudes the average solar gain can vary by more than 20x between summer and winter.
    What you want the PW to do
    If you simply want the battery to shift your daily solar gain to the night then sizing is primarily based on the amount of power used when the sun doesn't shine. Additional capacity may be required if you want the battery to cover power cuts. To cover this you would need to reserve some of the battery capacity.
    ...and then there are secondary capacity issues...
    A single PW can charge and discharge at 5kW (or only 3.6kW if you're in the UK and under G83 rules). This may mean that if you install a large solar array you may not benefit fully from your daily solar gain and conversely may not be able to supply your total loads if they exceed this at night.
    I cannot comment on the solar roof aspect but in the UK a rule of thumb would be about £1200 / kWp for a simple moderately sized installation. My last 6kWp addition cost me £7k. I'm adding another 6kWp ground mount next month to cover my wife's new BEV (sadly not a Tesla as her car will not last until the M3 hits our shores) and that will be slightly cheaper.
  • edited October 2017
    In the US it should be 30% tax credit until 2019 (?) not sure about the number...Will look for some more information.
  • edited October 2017
    So, I found this, if you want to have a look: It says, 30% tax credit as I mentioned yesterday. And apparently SRECs are also a possibility in some States. Check where you live.
  • edited August 2019
    I just had my solar roof installation completed with two powerwalls on a roughly 2000 squ. foot house at the end of July 2019. Everything was included in the price (permits, labor, materials, and all filing of paperwork as well as the site surveys) which came to just shy of (hope you are sitting down) $150,000.00 USD. One thing of note is in California the solar rebate programs ended 12/31/18 so we did not get any state rebate but Federal incentives will be received in the form of a 30% tax rebate on a good portion of the solar cost (only solar specific portions qualify). It was justified mainly because the house had to have the entire roof replaced anyway as it should have have been done one year ago. And it is spectacular looking and the install team from Tesla was beyond professional and extremely knowledgable. And you will not find a better warranty anywhere (tiles warranty is infinity, install is 30 years and PW is 10 years).
  • edited August 2019
    @millerberumen - Wow, very expensive. Thanks for the information!
  • edited August 2019
    Seattle area, nominal use 25 KWH/day. Installer recommended 9 KW solar (27x 335W LG panels) and 2 Powerwalls. Total ~$55K before rebates (30% federal tax credit). WA exempted solar installs from sales tax since July 1.

    Note that the number of Powerwalls recommended will depend on your peak expected usage. Each one can put out 5 KW, with 13.5 KWh usable capacity (or a little over 2.5 hours at peak load). If you have electric heat or air conditioning, you will need a lot of capacity to run it all night...
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